Lubricants, greases and petrochemicals are most versatile on the Industrial Plateau now a day. The significance of Lubricants, Greases and specialty products in the day to day functioning of nearly every machine part, instrument, appliance & device cannot be over emphasized lubricants reduce friction & wear between rubbing parts, thereby enhancing their life. A lubricant is a substance introduced to reduce friction between moving surfaces. It may also have the function of transporting foreign particles. The property of reducing friction is known as lubricity.
The broad types of lubricating oils are as under; crankcase oils, gear oils, metal working oils, metal drawing oils, spindle and other textile oils, steam turbine oils. Synthetic lubricants have a higher viscosity index, but are less stable to oxidation. They are suitable for high temperature applications.
In the modern industrial year, greases have been increasingly employed to cope with a variety of difficult lubrication problems, particularly those where the liquid lubricant is not feasible. Greases are essentially solid or semi solid lubricants consisting of gelling or thickening agent in a liquid lubricant. Greases and lubricants are one of the important products derived from crude petroleum. Petroleum is formed by hydrocarbons (a hydrocarbon is a compound made up of carbon and hydrogen) with the addition of certain other substances, primarily sulphur. Petroleum in its natural form when first collected is usually named crude oil, and can be clear, green or black and may be either thin like gasoline or thick like tar. The principal product of petroleum refining are motor gasoline, aviation gasoline, kerosene, jet fuels, diesel fuels, lubricating oils and fuel oils. Considerable quantities of petroleum wax, bitumen, liquid petroleum gases (LPG), industrial naphtha and coke are also produced. Petrochemicals are chemicals made from petroleum (crude oil) and natural gas. Petroleum and natural gas are made up of hydrocarbon molecules, which are comprised of one or more carbon atoms, to which hydrogen atoms are attached. The Indian lubricants industry claims to be the sixth largest in the world. The petrochemical industry in India has been one of the fastest growing industries in the country. This industry also has immense importance in the growth of economy of the country and the growth and development of manufacturing industry as well.
Some of the fundamentals of the book are types of lubricating oils, crankcase oils, gear oils, metal working oils, metal drawing oils, spindle and other textile oils, steam turbine oils, synthetic lubricants, formulations and com pounding of lubricants, additives for straight mineral oil gear lubricants, raw materials for lubricants, equipments for lubricants manufacture, reclamation of used lubricating oil, nature of contaminants in used lubricating oil, gravity methods of purification, metal forming and deforming lubricant, cutting oils, heat treatment oils, greases, sodium soap greases, lithium soap greases, aluminium soap greases, mixed soap greases, complex soap greases etc.
The objective of this book is to furnish comprehensive information about nearly all prominent types of lubricants, greases and petrochemicals. This book covers formulae, processes of various petroleum items. This book is an invaluable resource for entrepreneurs, existing units, professionals, institutions etc.
1. TYPES OF LUBRICATING OILS Crankcase Oils Gear Oils Metal Working Oils Metal Drawing Oils Spindle and Other Textile Oils Steam Turbine Oils Synthetic Lubricants Miscellaneous Oils Fatty Oils Residual and Petrolatums as Lubricants Asphalt Residual as Lubricants Application of Asphalt Residual as Lubricants Petrolatums as Lubricants Paraffin Wax as Lubricant Resinous Materials as Lubricants Solid Lubricants Thickeners Carbohydrates and Proteins as Thickeners Polymers as Thickening Agents Acetylene Black as a Thickener Petroleum Lubricants Bolt Lubricants Cryogenic Bearing Lubricants Lubricants for Missile Systems Lubrication with Glass
2. FORMULATIONS AND COM-POUNDING OF LUBRICANTS Additives for straight Mineral Oil gear Lubricants Formulation of Open or Exposed Lubricants Formulation of mild type E.P. Lubricants Aircraft Lubricant Miscellaneous Formulation
3. RAW MATERIALS FOR LUBRICANTS Test for good fatty acid Preformed Soaps Advantages and the Use of Preformed Soaps Lubricating Oil Gravity of Lubricating Oil Pour Point of Oil Dyes for Colour Perfume Filler Synthetic Lubricants
4. EQUIPMENTS FOR LUBRICANTS MANUFACTURE Equipments Handling Packaged Raw Material Equipment for Saponification Equipment for Dispersion of Thickening Agents Manufacture of Lubricating Oils Milling Equipment
5. RECLAMATION OF USED LUBRICATING OIL Nature of Contaminants in Used Lubricating Oil Gravity Methods of Purification Filteration Regenerating Process of Used Lube Oil Contaminants present in Used Lube Oil Principles of Used Lube Oil Existing Process for Regeneration of Used Lubricating Oils Lubricant Recycling Reprocessing Reclamation
6. ADDITIVES FOR LUBRICANTS Antioxidants, Rust & Corrosion Inhibitors Extreme Pressure Additives Antiwear Agents Foam Inhibitors Viscosity Index Improvers Detergents and Dispersants Pour Point Depressants Antiknock Agents Antiscrackers Agents
7. CHARACTERISTICS OF LUBRICATNG OILS Viscosity Index of Lubricating Oils Vapour Pressure Gravity of Lab Oil Thermal Properties Electrical Properties Properties under High Pressure Surface Properties Carbon Residue Colour of Tube Oils Neutralisation No Saponification No of Petroleum Products Aniline Point of Petroleum Products Ash content of Petroleum Oils Precipitation No of Lube Oils
8. CUTTING OILS Metal Forming and Deforming Lubricant Cutting Oils Heat Treatment Oils Industrial Applications Types of Cutting Oils E.P. Additives or Anti Weld Future Trend of Cutting Oil Formulations of cutting oils Hydrogenation Process in Lube Oil Production Choice of Catalyst
9. GREASES Solid Lubricants Semi Solid Lubricants Solid Lubricants Greaves Lubricants Type of Greases Calcium Soap Sodium Soap Greases Lithium Soap Greases Aluminium Soap Greases Mixed Soap Greases Complex Soap Greases Non-Soap Greases Properties of Greases Grease Applications Market Position Fillers Carbon Black Asbestos Mica Vermiculite Talc Various clay or silicate Metal Powder Metal Oxide Manufacturing Process for Grease Industrial Grease Manufacturing Process of Greases in General Fire Hazards in the Manufacture Processing of aluminium base lubricants and greases Production of another Barium Base Lubricating Grease Preparation of Lead Soaps Preparation of Lead Base Lube Greases
10. FORMULATION OF GREASES Mixed Base Lubricating Greases Colouring Lubricating Oils Refining of Lube Oil Purification of Lube Oil Reclaiming Used Lube Oil Non-Bleeding Grease
11. LUBRICANTS AND THEIR MANUFACTURE Composition of Mineral Oil Refining Blending Synthetic Hydrocarbon Synthetic Non hydrocarbons Polyalkylene Glycols
12. VARIOUS FORMULATIONS OF LUBRICANTS AND GREASES Textile Lubricant for Spinning Jute, etc. Application of Lead Base Lubricating Greases Preparation of Lube Grease from Normal Strontium Soap Mixture Base Strontium Soap Lubricating Greases Complex Soap Lubricating Greases Importance of Soap Salt complexes and their characteristics
13. ANALYSIS OF QUALITY ASSESSMENT OF LUBRICATING GREASES AND PETROLEUM PRODUCTS Lubricating Greases Analysis Tests for Melting or Liquefaction
14. REFINING OF PETROLEUM PRODUCTS Chemical Refining Physical Refining Solvent Extraction Processes Dewaxing Propane Dewaxing Benzol-Acetone Dewaxing Benzol Sulphur Dioxide Dewaxing
15. MANUFACTURE OF ASPHALTIC BITUMEN Steam-Refined Asphaltic Bitumen Blown Asphaltic Bitumen Pitch-Type Asphaltic Bitumen
16. CHEMICALS FROM PETROLEUM Feedstocks Chemicalsfrom saturated hydrocarbons Chemicals from Olefins Oxidation of Olefins Chlorination of Ethylene Chlorination of Olefins Chlorination of Propylene Chlorination of Butenes Chlorhydrination of Olefins Hydrochlorination of Olefins Sulphonation of Olefins Oxo Process Ketones and their derivatives Aldehydes and their derivatives Acids and their derivatives Acetic Acid and Acetic Anhydride Olefin oxides and their derivatives Aromatics Naphthenes and Naphthenic Acids Carbon Monoxide-hydrogen system Inorganic Compounds
17. NATURAL AND CRACKED GASES General Properties Natural Gas Refinery gas Liquefied petroleum gas
18. PETROLEUM WAXES Nature of the petroleum waxes Composition of the petroleum waxes Production of waxes The properties of petroleum waxes Paraffin Waxes Microcrystalline waxes Solid state transitions in paraffin waxes The effect of crystallinely modifying agents of the properties of paraffin wax Utilization of petroleum waxes
19. BITUMEN Emulsions and cutbacks Rheological Properties Wetting and adhesive properties Application Industrial applications
20. PETROLEUM PRODUCTS L.P.G. (Liquefied Petroleum Gas) Synthesis Gas Motor Gasoline Aviation Gasoline Kerosene Jet Fuels Diesel Fuels Industrial Naphthas Heating Oils and Residual Fuel Oils Light, Medium and Heavy Fuel Oils Petroleum Waxes Micro Crystalline Wax from slack wax Petroleum Jelly Bitumen Petroleum Coke Carbon Black
21. ABS RESIN Uses and Applications Manufacturing Process
22. ACETALDEHYDE
23. ACETIC ACID
24. ACETONE
25. ACRYLAMIDE MONOMER
26. ACRYLONITRILE
27. BENZALDEHYDE
28. ADIPIC ACID
29. BENZENE HEXACHLORIDE (B.H.C.)
30. BENZOIC ACID
31. BENZYL CHLORIDE
32. BISPHENOL -A
33. BUTADIENE
34. DIETHYL TOLUAMIDE
35. DIMETHYL FORMAMIDE
36. ETHYL ACETATE
37. ETHYLENE OXIDE
38. FORMALDEHYDE
39. FORMIC ACID
40. FUMARIC ACID
41. ISO PROPYL ALCOHOL
42. METHYL AMINES
43. NITROBENZENE
44. PHTHALIC ANHYDRIDE
45. POLY CARBONATES
46. POLYOLS
47. POLYURETHANE FOAM
48. VINYL CHLORIDE
49. STRUCTURE OF PETROLEUM Molecular Species in Petroleum Volatile Fractions Nonvolatile Constituents Resin Constituents Composition Structure Molecular Weight
50. SCOPE AND LIMITS OF LUBRICANT TESTING Fresh oil testing of industrial oils Fresh oil testing of engine oils
51. LUBRICANT STORAGE Lubricant life
52. COLLOIDAL STABILITY OF LUBRICANTS Low-Temperature Stability Hot-Temperature Stability
53. REFINERY WASTES Process Wastes Desalting Distillation Thermal Cracking Coking Processes Fluid Catalytic Cracking Hydro cracking and Hydro treating Catalytic Reforming Alkylation Isomerization Polymerization Deasphalting Dewaxing Gas Processing 54. TYPES OF WASTE Gases and Lower Boiling Constituents Higher Boiling Constituents Waste Water Spent Caustic Solid Waste
55. WASTE TOXICITY
56. MANAGEMENT OF REFINERY WASTE
57. PLANT & MACHINERY PHOTOGRAPHS
The basic raw materials for the manufacture of lubricants are: (1) Saponifiable fats and oils, (2) Saponifying agents, and (3) the base lubricating oil. But to improve the quality and grade of the manufactured lubricants, the following are added to make standard: (1) Performed soaps, (2) densifiers, (3) stabilizers, (4) chemical additives, (5) fillers, (6) dyes, and (7) perfumes. Densifiers may be employed in the presence or in the absence of soaps.
Saponifiable fats and oils. Theoretically any fat or oil may be converted into a lubricant or grease, but generally animal fats are used, because they are cheap, next comes vegetable oils, and other synthetic or non-synthetic materials: rosin-oil, naphthenic acids, sulphonic acids, synthetic fatty acids, montan wax, and wool grease. Wool grease is a good substitute for fats. Other substitutes are: tallow; olein, corn oil, repessed oil, cotton seed oil, etc.
While purchasing raw materials, the following points should be kept in mind.
(1) For the manufacture of lubricating greases with good storage stability or long life in service, fatty materials of low iodine value or containing little or no polyunsaturates are recommended. This points to animal fats or chemically or physically modified fats of low iodine value, for this purpose.
(2) For the same type of product, fatty acids are preferable to glycerides, or if the latter are used, they should constitute not over 20% of the total fatty acids.
(3) More translucent calcium base lubricating greases can be made by employing fatty acids rather than fats.
(4) The length of fiber in sodium base lubricating greases can be varied by a change in titer to the fatty ingredients. Thus a very long fibre results if vegetable oils or fats containing a large proportion of unsaturated fatty acids are employed.
(5) Conversely, short fiber sodium base lubricating greases result from the use of predominertately saturated fatty acids such as hydrogenated tallow.
(6) Long chain fatty acids from soap with the greatest solubility. For this reason, if a sodium base lubricating grease of a smooth nature is desired, hydrogenated fish oil fatty acids should be used.
The following are the chief fats fatty acids used in this industry:
Fatty Acids: Lauric, Myristic, Myristoleic, Palmitic, Stearic, Oleic, Linoleic, Linolenic, Arachidic, Gadoleic, Arachidonic, Behenic, Clupanodonic.
Fats: Lard, Beef tallow, Hydrogenated grease, Herring oil, Menhden oil, Sardine Oil, Hydrogenated Herring, Hydrogenated Sardine.
Oils: Com, Castor, Coconut, Cotton seed, Linseed, Olive, Palm, Palm Kernal, Peanut, Repeseed, Soyabean, Tung, Hydrogenated, Castor. Fatty acids are preferable to fats, because they have the following advantages:
To 25 gms. Of liquid fatty acids in a clean beaker add 25 ml. Of alcohol, free, from indicator warming again if necessary to have the mixture liquid. To the above add, while stirring, 15 ml. Of a 50% solution of KOH in distilled water. A good fatty acid will show very slight colour change. A bad acid will be a dark raddish brown.
Nearly all manufacturers of lubricating greases Employ preformed soaps to some extent. Since such soaps have a variety of other uses they are manufactured by a number of suppliers and stocked by most chemists. Soaps of almost any metal are available, but the manufacturer of lubricating grease is normally interested only in aluminium, calcium, barium, lithium sodium, lead and zinc soaps.
Compounding of lubricating greases is simplified by employing preformed soaps rather than manufacturing soaps from raw materials. Fewer ingredients need be stocked and weighed or measured. Since the saponification step is eliminated, the time required for the preparation of a batch of lubricating grease should be less when preformed soaps are employed than when fat and alkali are used. Moreover, elimination of the saponification step and the time consumed result in a lower heat demand.
Lubricating oil constitutes the largest proportion of the total raw material required for the compounding of lubricating greases. Selection of the proper lubricating oil is important both from the standpoint of lubrication and of the structure and stability of the finished product.
The gravity of lubricating oil is a numerical value with an index of the weight of a measured volume of the product. Readings are made on a hydrometer. Tables are available for the conversion of such readings to specific gravity and weight per gallon.
The gravity of lubricating oils is interest to the manufacturer of lubricating greases because of its influence upon costs. Oils are purchased by the gallon and lubricating greases are sold by the pound. Therefore, if instead of purchasing an oil of 28 gravity, weighing 7.387 pounds per gallon; an oil of 20 gravity, weighing 7.778 pounds per gallon, is purchased, over 5% more weight would be secured for the same volume.
Since the pour point of an oil indicates the temperature below which it is not possible to pour the fluid (Liquid) from a container, it is also indicative to a degree, of the temperature at which lubricating greases, made from such oil, can be forced through pipes or fittings. However, too much dependence cannot be placed upon the correlation of pour point and apparent viscosity at low temperatures.
Most lubricating greases depend upon the natural colour of the mineral oils to provide colour to the finished product. But to make them attractive certain colouring is necessary and dyes are frequently employed for giving vivid colours, which otherwise (naturally) not possible.
Almost all the dyes used for colouring lubricating greases are oil soluble materials. Some colours are sold especially to provide fluorescent green or reds for mineral oils and such colours are also effective in lubricating greases. In selecting a dye, its stability towards light and heat as well as toward free alkali or fatty acids should be checked.
The predominating colours employed in lubricating geases are green, orange, red, and yellow. Less than a pound of dye should be required for 10,000 pounds of finished lubricant. It is well to dissolve the dye in warm oil before adding to the batch of lubricant.
A small percentage of lubricating greases have perfumes added particularly in the case where an oil is of low grade and smells badly. Perfumes should be added when the product is as cool as possible. Perhaps less than a quarter of a pound of perfume base is sufficient for over 10,000 pounds of finished lubricant.
A great variety of solids of various types are added to lubricating greases to give bulk, provide resistance to removal of the lubricants, and, according to some workers, to increase the lubricating value.
They are: Graphite, Asbestos, Mica, Talc, Vermiculite, Metal Oxides, Powdered metals, Metal Sulphides and similar Solids, Carbon Black, etc.
Include Silicones, Olefin Polymers, Polyakylene Glycols and Derivatives, Esters, Silicone Fluids, Chlorinated Compounds Halogeno-hydrocarbons, etc.
Silicones are organosilicon oxide polymers. Silicones are available as liquids, semi-liquids, and solids. One of their-outstanding properties is that their viscosity is much less ssensitive to temperature than that of mineral oils. For example, even a relatively insensitive mineral oil, when lowered in temperature from 120ºC to 25ºC., becomes about a thousand times more viscous, whereas the corresponding figure for a silicone fluid is only about seventeen times. Other properties are : good oxidation stability, very low pour point, and low volatility.[]
Fluorosilicone: By careful control of the polymerization conditions and the use of suitable end-blocking agents e.g. hexamethyl disiloxane, various degress of polymerization can be gained to yield any desired viscosity of fluorosilicone oil.
Fluorosilicones fluids are used mainly for defoaming of solvent based wash solutions or processes and lubrication.
The chemical stability and heat stability of fluorosilicone oils, coupled with their good lubricity, accounts for their use as lubricating oils in chemical compressors and in vacuum pumps exposed to chemical fumes. Fluorosilicone fluids are also formulated with various thickeners to make grease-like sealing compounds and lubricating greases.
Synthetic esters are now produced in considerable variety. Esters, which are compounds of acids and alcohols, occur widely in nature, for example in fatty oils, but other types of ester, with special properties are now synthesized. One type (of which di-2-etlhyl hexyl sebacate is an example) is characterized by good viscosity-temperature characteristics, together with better boundary properties and lower volatility than mineral oils of similar viscosity. Its chief advantage is the very low flammability.
Polyalkylene glycols are a group of non-hydrocarbon polymers produced in a wide range of viscosities, and in water-soluble and water-in-soluble qualities. They possess good temperature-viscosity characteristics and find application as hydraulic oils and in special greases.
Halogeno-hydrocarbons are hydrocarbons in which hydrogen atoms have been partly or wholly substituted by fluorine or chlorine atoms, or in some cases by a mixture of both. The outstanding merit of the liquid varieties is their high chemical and thermal stability-their demerits are poor viscosity-temperature characteristics and high volatility.
Synthetic lubricants also includes solids materials consisting of carbon and halogan, of which Teflon is the best known. Teflon and Fluon are commercial names for Polytetra fluoroethylene (PTEE), which gives remarkably low coefficients of friction as a metal lubricant, and is effective up to the usefully high temperature of about 320ºC. This is particularly valuable on a small scale when particularly low friction is desired, as for example instrument work. One method of use is as a surface coating in conjunction with a liquid, which may be oil or water.
There are two chief processing methods: (1) Batch method, (2) Continuous method. These both methods have a number of steps in common. Therefore, the equipments required will be the same in many cases. Steps in processing are as follows, and the equipments are required to fulfill these processing needs:
(1) Material storage and handling.
(2) Material measuring, either by weighing, or gauging.
(3) Saponification, which involves: (a) Mixing, (b) Heating. This step is eliminated if preformed soaps or bodying agents other than soaps are employed.
(4) Dispersion of bodying agent in the lubricating fluid. If this bodying agent is the soap formed in step 3, the dispersion may take place as the soap is formed. Normally, the dispersion will require additional heat, agitation, and perhaps shear.
(5) Dehydration, which may take place during saponification or at any other point in the processing. In some processes the final removal of water occurs by vacuum treatment of the finished or semi-finished product.
(6) Cooling of the soap dispersions. This may take place during agitation or in a static state. In the case of lubricants in which the bodying agent is dispersed by shear only, this step is not required.
(7) Milling.
(8) Removal of entrained air or of volatile materials. Only a portion of finished lubricant greases are subjected to such a step. Some dehydration may take place during the step.
(9) Handling finished product, which may include packaging and storage: No mention has been made of handling in connection with the equipment by which the various steps are carried on.
Most of this handling will be by means or pipelines and pumps, therefore, certain notices may be kept in mind:
(1) Pipelines should preferably be welded and equipped with long redius bends.
(2) Apparatus in which heating is carried out in which rot material is handled should be well insulated.
(3) Individual drives for each piece of equipment should be provided.
(4) Flow of material into finished product and in a package should be downward and toward shipping or storage.
(i) Material Storage and handling
In most plants manufacturing lubricants, oil account for probably 85 to 90% of the total tonnage of raw materials. Fats and Fatty acids are next in volume. Raw materials, other than those above are seldom received or stored in bulk; but rather in the original containers. Raw material storage, therefore, involves both tank storage and warehouse storage. The space for tanks is devoted to fluid lubricants and to some type of fatty products, while the warehouse stock consists of a variety of materials in bags, cartons, and barrels.
(ii) Oil Storage and Handling
Oil handling in a lubricating grease plant is little different from that in a refinery, except that lesser amounts are handled. Most plants prefer vertical storage only, since horizontal tanks require more space for an equal gallonage than vertical tanks. No set correlation between the capacity of a plant and the amount of oil storage is possible. This will depend upon the location of plant and the variety of the products manufactured. Thus a lubricant plants adjacent to or located on a refinery property will probably require less oil storage.
In some cases oils must be blended before use. When this is done in storage tanks, the mixing is generally done by the use of dry air. Proportioning pumps can also be employed for preblending ad delivering to storage. In humid climates condensation may occur inside storage tanks and as a prevantative, some tanks use calcium chloride drying units on breathers of oil storage tanks. Other plants simply provide a ½ to 1 inch drain, flush with the bottom of the tank, so that water which collects can be drawn off.
(iii) Fat Storage and Handling
Fats, unless of high titer, are handled in either drums or tanks, both such materials are of steel, as a rule.
It should also be kept in mind that fat held in storage and subjected to heat and moisture will tend to hydrolyze and if agitated, to oxidize or polymerize to some extent.
Pumps for handling melted fats may be either reciprocating or centrifugal types. Pipelines, valves, and pumps used to handle fatty acids, should be of stainless steel. Where a positive displacement pumps is required for such service, bronze end pumps are satisfactory. Duriron pumps will also serve, but of course consideration most be given to the fact the such metal is quite brittle.
(iv) Storage and Handling of Caustic Soda
Solution of solid caustic soda may be accomplished in an ordinary steel tank by placing the solid cakes on grids which will hold them off the bottom. The drum metal can either be stripped from the solid cake of caustic or number of slits can be made in the drum with an axe before placing in the tank. A centrifugal pump can be connected to the bottom of the tank, and after water has been added, circulation will aid solution.
Flake caustic soda may also be dissolved by suspending it in the upper part of a tank of water. Since the rate of solution of flake is much more rapid than that of solid caustic, a short period of mechanical agitation will suffice for complete solution. Large single additions of flake caustic may heat the water above the boiling point, and caustic solution may be thrown out of the tank by the sudden evolution of steam.
While handling caustic soda or its solutions workmen should be protected by gloves, goggles, and preferably cotton clothing. In case of accidental contact of caustic with any part of the body, the afflicted surface should be flushed with copious quantities of water.
50% liquid caustic soda may be unloaded by pumping, by gravity flow, or by air pressure, but pumping is the most commonly used method. Since the solidification point of this solution is 54% F it should be handled and stored at temperature above this. Ordinarily steel will serve for storage and handling of this grade of caustic soda. If the temperature of the caustic solution does not exceed 140ºF, welded tanks will be satisfactory. Above this temperature caustic embrittlement may set in at the welds. For higher temperature it is usually more economical to construct riveted storage tanks.
Since 74% liquid caustic soda freezes at 144ºF, special provision must be made for handling this grade. In view of this high solidification temperature, the general practice is to dilute the liquor to 50% strength or less before storing. The matter of dilution is not as simple as might appear, since the heat of dilution may raise the temperature of the solution to the point where caustic embrittlement of the steel storage tank occurs. With nickel-clad equipment such embrittlement does not occur. It is best to cool the diluted caustic solution to 150ºF or below before placing it in storage. An alternative is to have a stock of diluted caustic soda from a previous shipment which has cooled naturally, into which the freshly diluted liquid can be mixed. Addition of a calculated amount of water to a tank car of 74% caustic soda may be made by adjusting a steam through a meter or by proportioning equipment. After unloading either grade of liquid caustic the pipelines and pump should either be blown free or washed with dilute caustic.
For handling caustic soda solutions, standard black iron pipe is satisfactory preferably equipped with flanged joints, since coupling tends to leak in service. Asbestos gaskets will resist hot caustic solution. If the lines are to be exposed to temperatures below the freezing point of the solution they should be traced with a steam line inside a common insulation. All iron stopcocks are preferable to valves for such service and if high temperature are to be encountered, nickel-iron cocks are best. Brass or bronze valves or fittings should not be used for caustic soda solutions. If valves are desired, they should be of all-iron or of iron trimmed with nomel, nickel, or an alloy of this metal. All iron centrifugal pumps with extra deep stuffing glands and graphite-asbestos packings are satisfactory for handling caustic solutions. For high temperatures, nickel or monel shafts will give better service than iron.
Packaged raw material received by a plant manufacturer of lubricant and greases will include bags, barrels, or cartons in loads. How such packages are stored and handled will of course depend upon the storage facilities of the plant in question. A better plant is to provide a weighing hopper, carried by suspended scales, into which the bag and carton material for a single charged are dumped.
Fillers generally go into the finishing kettles and may be handled by one of the above methods. Since addition of fillers will cause considerable dust, some plants provide a closed room where an oil slurry of materials such as graphite are prepared preliminary to addition to kettles. One supplier of graphite now offers graphites which have been coated with oil so that the dust problem is entirely eliminated.
Preformed soaps, such as aluminium stearate, are also likely to cause considerable dust when handled into vessles. Dust is a source of contamination in other products and increases the work of housekeeping but soap dust is also a fire or explosive hazard. Every effort should therefore be made to reduce such dust. By having all open kettles covered and kept under a slight suction, dusting can be reduced materially.
The most satisfactory equipment for saponification is that which will permit complete reaction of the ingredients in as short a time as possible. The main factors which influence the time of this reaction are probably temperature, concentration, presence of catalysts, and intimate contact of reacting ingredients. Equipment for saponification therefore should be selected which will provide the best heat transfer possible and which will provide intimate contact of the ingredients.
Equipment for Batch Saponification at Atmospheric Pressure
Almost any kettle with an agitator and some heat will do some sort of job of saponification. The older kettles, some of which are still in use, were of riveted construction with agitators consisting of straight bars 21/2" or 3" wide, bolted to a shaft at about 18-inch intervals. These agitators were driven through bevel gears, by belts from a line shaft, tight and lose pulleys being provided. In some cases flat bottom vessles used, but modern kettles have either cone or dished bottoms. Fire-heated vessels are single walled.
The source of heat used to promote saponification varies. If direct fire is used, the fuel may be coke, fuel or gas. Steam is the most common source of heat, being used at the pressure available, which is normally 100 to 125 psi. An increasing number of saponification vessles are heated by circulation of hot oil through the jacket. Some installations have been made employing Dowthern as a heating medium. Where temperatures much above 300ºF are desired, something other team should be employed for heating.
Since practically all open type saponification vessles are vertical, a shaft will extend vertically from the driving gear with probably a step bearing in the bottom of the vessel and occasionally an intermediate bearing between this bottom bearing and the one at the top. The most simple agitators design consists of flat, bars bolted or welded to the shaft at intervals of 15 to 24 inches. Such "paddles" can be made of 3" by 1/3" steel bars twisted so that they will give a down thrust. Since better mixing is accomplished by double motion agitators, many installations stimulate such motion by having a set of stationary blades and another set rotating. Simpler still, breaker bars can be welded to the shell at intervals intermediate to the paddles. Of course such bars will be off-centre so that they miss the shaft. Actual double motion agitators complicate the design but are frequently worth the added expense.
Scrapers to clean the inner shell of saponification vessel not only insure better heat transfer and thus a shorter reaction time, but also improve mixing. When fat, mineral oil, and alkali are first charged to a kettle and warmed, the mass is quite fluid, and as long as agitation takes place, the fluid next to the vessel wall will be displaced by turbulence and reasonable heat transfer will result. However, as soon as part of the fat or fatty acids is converted to soap, the mass becomes more viscous, and heat transfer will be retarded if the portion next to the kettle wall is not removed mechanically.
If the same vessel is also used to finish lubricating grease, scrapers have an additional advantage. Without such equipment heavy material would stick to the sides of the kettle and in later stages of the process might become loosened and then break into particles which would remain as lumps and never disperse. Some scrapers consist of a flat bar carried by the ends of the paddles. In some cases the bar is changed to an angle which is so mounted that it is on a swivel and actuated by a spring to hold it against the kettle wall.
A saponification vessel can be used with a minimum of instrumentation, but a certain amount is desirable. Of course a gauge to indicate the pressure on the jacket should be installed. In addition a regulating valve is often provided on the steam inlet so that processing can be carried on at different pressures at various stages of manufacture. Most kettles used for saponification are provided with connections to a recording thermometer. The recorder may be used for one or several kettles, and an individual kettle may have thermocouples must be so placed that they will not interfere with the operation of the agitators or the scrapers and yet they should not become coated with lubricating grease or soap which would act as an insulator and thus prevent a true reading. If the bulb is inserted through the jacket of a vessel, clearance or air spacing should be provided so that the jacket temperature does not influence the reading. In some instances paddle blade near the bottom of the vessel will be slotted so that a bulb can be inserted in the space provided by the slot. In kettles which have a beaker bar attached to the inside of the shell, the bulb can be fastened to this bar so that a rigid location is provided. In still other cases the thermocouple is inserted through a bottom opening near to shaft. When a pump and circulating line are provided for a kettle, it is advantageous to have a thermocouple in such as line.
A ammeter for the operator to watch is desirable in connection with processing lubricating greases which pass through a very heavy stage. Ammeter readings can then be made of a part of the compounding instructions so that the operator will know when to shift to a different speed of agitation or to add oil.
Agents employed for thickening lubricating fluids to produce lubricating grease structure can be divided into two classes, those which undergo phase changes and which require heat or a chemical method of dispersion and those which require heat or a chemical method of dispersion and those which do not undergo phase changes with heat and which can be dispersed in lubricating fluids mechanically. The first class consists primarily or soaps and it remains to be demonstrated that they can successfully be mechanically dispersed in liquids to form lubrication greases. Perhaps if applied energy were sufficiently concentrated, so as to be converted to heat momentarily, soaps could be dispersed in lubricating fluids by such means.
Milling or shearing equipment is often used as an aid in soap dispersion. The simplest arrangement is to provide screens in the circulating line. One plant has such screens progressively smaller, starting with 10 mesh and finishing with 60 mesh. While this aids in soap dispersion, the screens must be screens is rather laborious procedure, modern practice is to use various types of mills for this purpose.
As shown in Fig. 2 the conventional steps in lubricating oil manufacture, are pretreatment of the crude oil charge, as required, followed by distillation of the crude in two steps, deresining or deasphalting, dewaxing, solvent extraction, finishing and blending, including mixing various additives with the final lubricating oil. The recovery and refining of asphalts, resins and waxes are important to the overall economy of lubricating oil manufacture.
The chemical composition of lubricating oils is exceedingly complex the number of carbon atoms varying from approx. 20 to 70. Well refined lubricating oils contain very little olefenic un aturation but do contain some aromatic un aturation. The compounds contained in lubricating oils include paraffins, cyclo paraffins the aromatics.
Waxes generally are paraffin compounds, both straight and branched and also contain 3-25% cycloparaffins, depending upon the source of crude oil.
Petroleum resins are hydrocarbons of very high molecular weight containing small amounts of oxygen, sulphur and nitrogen compounds, which can be found in bridge compounds or in ring compounds. The hydrocarbons include the paraffin, cycloparaffin and aromatic types in varying amounts and configurations.
Asphalt is physically made up of brown solids called asphalters, i.e. asphaltic resins of high molecular weight viscous compounds with a degree of unsaturation and oils. The asphalters are believed to contain condensed aromatic ring compounds with oxygen, sulphur and nitrogen in ring compounds with oxygen, sulphur and nitrogen in ring compounds or in bridge positions.
Where (1) Atmospheric tower
(2) Vacuum tower
(3) Deresining
Pretreatment of crude: In order to remove inorganic salts from the crude oil charge to the crude distillation unit, chemical or electrostatic desalting is used. Salts in the crude oil cause fouling of heat exchangers, corrosion in the distillation units and increased coking of the furnances.
Distillation: Crude oil after pretreatment, is charged to the atmospheric tower, where the crude oil is separated into light products. The bottoms of the atmospheric tower, to reduced crude, are charged to the vacuum tower.
The prime object in the manufacture of lubricating oil is the initial separation of the light products and the separation of wax distillate and cylinder stock without any decomposition or cracking of the lubricating fractions; thus a vacuum distillation unit is used to separate the wax distillate and cylinder stock at a lower temperature.
Deresining or Deasphalting: Asphalts, which contained in asphalter crudes can be constituted into different properties by further distillation or by air blowing. Resins occur in paraffin or low-asphaltic crudes.
Propane is used as a solvent and at different temperatures and ratios causes asphalts or resins to separate from the oil due to a difference in solubility. This process requires a tower for separation of the oil and the asphalt or resin.
Dewaxing: Wax is probably the most troublesome product in the manufacture of lubricating oil. Its presence in lubricating oils prevents free movement at lower temperatures.
Usually, methyl ethyl ketone (MEK) and an aromatic solvent, such as toluene are used for dewaxing purposes. The MEK causes the wax in the oil to crystallize, and the toluene is used to dissolve the oil. The solvent mixture, at a carefully controlled temperature, is added in measured amounts at points in the chilling to produce proper crystallization of the wax. Both the wax solution and the oil solution are distilled for removal of solvent (to be reused) and to provide solvent free wax and oil. Thus the two products are a wax-free oil and an oil-free wax.
Solvent Extraction: To upgrade or improve the quality of neutral or bright stock, solvent extraction is carried out. It can be performed before or after dewaxing, but most solvent extraction is performed after wax removal in order to prevent any interference from wax in the charge oil. Solvents such as chlorex, nitrobenzene, phenol, benzene, and sulphur dioxide are used. The improved oil (or raffinate) and solvent are taken overhead from the treating tower, and unsaturated material of extract and solvent are removed from the bottom. Solvent is removed from both the raffinate and extract in recovery equipment and reused.
Filtration: Bauxite is the common filtering medium or absorbent for the removal of asphaltic and resinous undesirables or simply for light filtration or finishing. The bauxite is placed in a vertical steel tank, and the oil is permitted to gravitate through the bauxite in the filter. A screen in the bottom head of the filter prevents the bauxite from being removed from the filter with oil.
Blending of additives: Additive blending is done after bauxite filtration, since filtering will remove the additives. Additives are used according to the severity of the operating conditions for which the lubricating oil is intended and the quality of the base lubricating oil. Naturally, a high quality lubricating oil base requires fewer additives than a lower quality base. Fully formulated lubricants contain additives to boost their properties. Wise choice of additives can increase the biodegradability of the full formation.
Lubricating oil deteriorates, and becomes contaminated with foreign materials, in service. In circulating systems, where a quantity of oil is involved, it is desirable to maintain the oil as clean as possible to provide maximum lubrication efficiency, and to keep wear and damage of lubricated parts to a minimum.
When the lubricating oil reaches the end of its life in the engine, what most probably happens is additive depletion. Because of the engine operation, these chemicals, slowly lose their effectiveness. This is the time to change the oil. This used oil can be re-refined for use. Technically speaking, re-refined oil can be used to replace some of the original base stocks. For some applications, in fact, they are better. But the usages depends heavily on the process used to manufacture the re-refined oil and so many other things like the chemical compatibility etc.
Reconditioning of a used oil may be accomplished by full flow, by pass, of batch methods or combination of these. In the full-flow system, the entire flow of oil form the main pressure line is continuously filtered. In the by-pass system, a fraction of the total of flow is continuously filtered and returned to the oil reservoir. In the bath system, as the name implies, all the oil is removed from the lubrication system and is reconditioned as a batch.
Contaminants in a used oil may be divided into two classes:
(1) Products resulting from chemical action within the system, including effects due to fuels; and
(2) Foreign material which enter the system.
Products resulting from chemical action within the system are as follows:
(a) Carbon, and other products of partial decomposition of oil or of incomplete combustion of fuel;
(b) Oxidation products (which may be either soluble or insoluble in the oil), due to chemical action at high temperatures;
(c) Gummy product, both soluble and insoluble, resulting from polymerization (combining) of unsaturated components in the oil; and
(d) Sulphur compounds, formed by sulphur in the oil or fuel.
Foreign materials may include some of the following:
(I) Dirt and dust from the air;
(II) Metal particles resulting from wear of operating parts of the machine, or left over from machining operation during an overhaul;
(III) Foundry core-sand from castings;
(IV) Water condensed from air moisture or products of fuel combustion; and
(V) Fuel dilution.
Purification of Oils
Three basic methods of treating contaminated oils are used, both singly and in combinations:
(1) Gravity purification,
(2) Filteration, and
(3) Reclamation
Gravity methods which are based on the relative weights of clean oil and the contaminants to be separated out, include the use of settling tanks and of centrifuges.
In a settling tank method, a batch of dirty oil is allowed to stand for ten or more days in a tank, and insoluble matter (including water), which is heavier than oil, settles to the bottom under the influence of gravity. The tank should be free from vibration and the oil is undisturbed. Small particles and dispersed oxidation products are not removed in this process. Best result are obtained when the oil is heated to the range of 120ºF to 160ºF reduce the oil viscosity, thus facilitating settling.
Drawbacks to the settling tank method of purification are : the time element, the space requirements for tanks, extra oil charge for the engine during settling process, and the fact that impurities are only removed periodically.
This method is adaptable to straight mineral oils, but is generally unsatisfactory with heavy duty additive-type oils.
A centrifuge works on the principle of separation by centrifugal force. This force, supplied by the high-speed rotation of the bowl containing the contaminated oil, is several thousand times the force of gravity. As a result, the centrifuge is much faster and more efficient than the settling tank. Substances having a higher density than the oil, such as water ad heavy particles, are thrown out against the walls of the centrifuge with greater force than the oil. As a result, a stable oil water leave by separate outlets, the oil discharge tube being nearer the center. The sediment is removed from the walls by cleaning at regular intervals. For some types of centrifuge; special arrangements are provided to prevent mixture of purified oil with incoming contaminated oil, in the vicinity of the oil water boundary.
"Through-put" capacity is the maximum number of gallons of contaminated oil which can be sent through the centrifuge each hour, with no regard for the degree of purification. The effective capacity of the centrifuge, which is much more meaningful, is the rate at which contaminated oil may be processed to give the desired degree of purification. This rate depends upon prevailing conditions and what is deemed to be a desirable degree of purification in each case.
In so-called wet centrifuging, water is intentionally added to the entering stream of contaminated oil. This added water may have a washing effect on the oil and a tendency to carry away more of the lighter solid, as well as some acids which are more soluble in water than in oil.
A centrifuge is especially well adapted to a by-pass system, in which part of the oil being circulated is by-passed through the centrifuge each cycle. Centrifuge is also suitable for the batch system of purification.
Filters may be applied on full-flow, by pass or batch systems where there is sufficient pressure to overcome the internal resistance of the filter. There are three principal types of filters:
(1) Mechanical, (2) Absorption, (3) Adsorption. Where a filter is installed in the lubrication system of machinery, such as an engine, a relief valve is provided to cut off flow to the filter at a predetermined pressure. This is for the protection of the engine against loss of oil supply. Filters may be integral units composed of a filter element in a sealed container, in which the entire unit must be replaced. When blocked with filtered material, or they may be replaceable element type, wherein the container can be opened for the replacement of the used element.
Lubricating oils are discarded after a specific period of use, to give engines longer life and better performance. These are either drained into rivers or burnt in air, causing pollution of air and water. Thus the re-refining of used lubricating oil is another way of tackling the disposal problem through reutilization. The 80-90% of used lubricating oils remain unchanged, these can be economically regenerated.
India depends mostly on the foreign market to meet her requirements of lubricants and greases. The deficit in indigenous availability of lube stock is fulfilled through import. As such, the import of base stock and lubricant technology is making the important product "Lubricant" costilier, with the passing of each day. The economic factor alone is the most critical factor for industry to recognize the conservation of lubricant as an important area.
Regeneration of lubricating oil, a practice in many oil rich countries, should be popularized as this will stop drainage of foreign exchange and conserve our existing stock.
Contaminants Present in Used Lubricating Oil
Contaminants present in used lubricating oils can be classified as :
(1) Volatile, (2) Oils soluble compounds, (3) Oil insoluble compounds. Unburnt fuel and water constitute volatile component while in use in the engines, lubricating oils from primary oxidation products which polymerize and finally converted to asphalts by pyrolysis. These constitute oil soluble compounds. The third category of compounds includes dust, metallic particles, soot, degraded additives; metal soaps, etc.
Re-refining and reclamation are the two procedures used in regeneration. Re-refining may involve the following steps:
(1) Settling and Dehydration.
(2) Acid treatment.
(3) Clay treatment of acid treated oil.
(4) Removal of clay by filteration.
(5) Distillation or fractionation.
(6) Blending with bright stock and incorporation of additives.
Re-refined oil compares well with the virgin oil. Reclamation, on the other hand, involves steps like settling, dehydration, removal of asphalts and other solid bodies. It does not remove diluents and certain oil degraded products.
Processes employed in United States:
1. In the process followed at Mohawk Refinery Co. Newark N.J. a 10,000 gall. Dish bottomed tank is charged with feed stock which is heated to 82ºC (dispersant filled oils require higher temp.) with 98% sulphuric acid and settled, leaving mainly saturated naphthenic and paraffinic molecules. After acid and settling treatment 82-84% of the feed remains. This is followed by heating to 316ºC in the clay contact step. In a flash chamber, clay and residue drop down while overheads are pulled down to reflux with a product steam joining the second tower. Here the lighter ends are gathered for process fueling, and the bottoms are recycled. Two lubricants products result a 350-SSU at 37.8ºC stream and 110/120 SSN at 37.8ºC light distillate.
2. S and R oil co. Houston Tex. re-refiner process (i) 300,000 gal./mo. Of crank case drainings. First the waste oil runs through a pipe still for dehydration. Next, acid treatment in air blown agitator is followed by clay containing at 204ºC. Then filteration takes place using sweetland filters, rotary vacuum filters or even plate and frame presses. The final step is blotter pressing to remove any remaining clay.
3. Diamond Head Oil Refining Co. Keramey N.J. does not use acid in its re-refining processes but employs more severe clay treatment, coupled with higher temperatures.
4. A new re-refining method for lubricating oils is said to offer favourable economies and eliminate refiner's own water pollutants acid sludge and filter cake. The process has been developed at Villanova University.
The new process has five basic steps:
1. After the moisture content is reduced to less than 0.1 percent by heating to 138ºC the acidic contaminants are neutralized by sodium hydroxide or other undisclosed agents.
2. Dilution with light naphtha as a coagulant followed by solids removal.
3. Atmospheric distillation to recover the light naphtha for recycle.
4. Vacuum fractionation to recover product and splilt out No. 1 heating oil.
5. Clay treatment. The oil is heated with clay to 338ºC for about an hour under a nitrogen blanket and with mechanical agitation. The mix is then colled to 149ºC and the clay is removed via a rotary vacuum filter.
By products of the process are a carbonaceous material similar to carbon black and a potential rubber extender oil. Out of total lubricating market in U.S. reclaimed oil accounts for about 6%.
In the field or re-refining of used lubricating oils, acids treatment is being replaced by light hydrocarbon treatment (propane and naphtha) resulting in better yields and obviating the problem of the disposal of acid sludge.
Research is being carried out in different countries of the world to evolve further cheaper methods of used oil regeneration.
Characterstics of a Used and Regenerated Heavy Duty Motor Oil.
A flow diagram for a process on regeneration of used lubricating oil is given in figure : below 7.1 which gives complete idea.
Plants are said to be running on this process.
Process developed at the Regional Research Laboratories, Jorhat Assam (Indian Patent No. 127751) consists of the following steps.
Used lubricating oil together with activated fuller's earth and water is heated to suitable temperature in a closed vessel with constant stirring.
Oil from (step 1) is cooled and then passed through a filter press.
Filtered oil (step 2) is then subjected to vacuum distillation. Some portion of the distillate collected is discarded as heating oil. Distillation is continued upto a still temperature ensuring more or less complete recovery of the oil. Distillation residue comprises most of the spent additive and is discarded.
Distilled lubricating oil (step 3) is blended with additives to improve viscosity index and other properties.
Novelty of the Process
Novelty of the process lies in the elimination of sulphuric acid treatment a severe clay treatment step thereby avoiding acid sludge handling and disposal problem and in turn making the whole process more enonomical.
Considerable effort is underway to improve and expand recycling of lubricating oils. Although typical processes result in 80-90% yield, questions remains regarding the initial collection and the separation of the used oil from water and other contaminants. Subsequent treatment varies from simple cleaning to essentially the complete refining process used with virgin oil. The following are typical steps involved in reprocessing used petroleum lubricating oils are indicated schematically in the figure.
It involves simple separation of contaminants by gravity setting of water and dirt, centrifuging, filtering and membrane techniques. Chemical emulsion brakers are first added and consist of sulphuric acid and then aluminium sulphate as a coagulant. Polymers sometimes are used to speed up the process. The separated oil is then decanted, skimmed or centrifuged and commonly is burned. 1-5% reprocessed waste oil generally may be added to fuel.
It involves flash distillation in an evaporator at about 100-200ºC in partial vacuum to remove water and low boiling contaminants e.g. gasoline and solvents.
1. Chemical Engineering, Vol. 75, Sept. 9, 1968.
2. Industry and Commerce, May 1, 1970, Vol. VII, Nov. 9.
3. Joshi T.C. and Goes P.K. Re-refining of Used Motor Oils, Seminar on Import Substitution in Petroleum Products, process and Other Know-how, Indian Institute of Petroleum, Dehradun, May 10, 1969.
4. Proceedings of a Seminar on Modern Trends in the Production and Utilization of Lubricants. Chemical Age of India, Jan. 1971.
5.Lubricants Production and Utilization in India in the Seventies, P. K. Goel and M.G. Krishna, Indian Institute of Petroleum, Dehradun, Chemical Age of India, Jan. 1971.
In the modern industrial year, greases have been increasingly employed to cope with a variety of difficult lubrication problems, particularly those where the liquid lubricant is not feasible. Over the last several decades, grease making technology throughout the world; has undergone rapid change to meet the growing demands of the sophisticated industrial rapid change to meet the growing demands of the sophisticated industrial environment. With automation and mechanization of industry, modern greases, like all other lubricants, are designed to last longer, work better under extremes of envirnment and generally expected to provide adequate protection against rust, water, humidity and dust. Industrial development and advances in the field of greases have been geared to satisfy all these diverse expectations.
Primary components of grease are mineral oils and soaps. The mineral oils consist of varying proportions of paraffining, napththenic and aromatic hydrocarbons. Soaps used in grease may be derived from animal or vegetable oils or fatty acids, wool grease, rosin or petroleum acids. Apart from this, variety of other compounds are added to lubricating greases to improve specific properties. Such components are - corrosion and rust inhibitors, film strength agents, antioxidants, passivators, colour stabilizers. V.I. improvers wear prevention agents. A grease thus produced is properly thickened in order that it remains in contact with the moving surfaces and does not leak out under gravity or by centrifugal action, or be squeezed out under pressure. Grease acts as real against dirt, dripping and spattering is eliminated, minimizes starting friction on journal bearing.
Greases are essentially solid or semi-solid lubricants consisting of a gelling or thickening agent in a liquid lubricant.
However, in general, greases are the substances whose basic components are soaps and mineral oils. Mineral oils comprise varying proportions of paraffining, naphthenic and aromatic hydrocarbons, whereas soaps used in greases may be derived from animal or vegetable oils or fatty acids, wool grease, rosin, etc. Besides, a number of other components are added to lubricating greases so as to improve specific properties, such components are antioxidants, corrosion and rust inhibitors, film strength agents, passivators colour stabilizers, wear prevention agents, etc. The grease thus produced is properly thickened in order that it remains in contact with the moving surfaces and does not leak out under gravity or by centrifugal action or be squeezed out under pressure.
However, one of the basic characteristics of most solid lubricants is that they reduce friction and remain in place longer than oils.
Most solid lubricants reduce friction because their molecules from very thin plates or sheets that slide over one another very easily.
The main advantage of solid lubricants is that they remain in place longer than oils or greases. Parts that are not easily reached are often lubricated with solid lubricants so that they will not have to be lubricated as often. The most important solid lubricant is graphite, a form of the element carbon. Graphite is the black material used to make the "lead" in lead pencils.
A semi-solid lubricant, or grease, consists of a thickening agent in a mineral oil or synthetic liquid base. Most industrial greases have mineral oil base. The most common thickening agents are metallic soaps made with aluminium, calcium, sodium, barium, or lithium. Animals and vegetable fats, saponified fats, gels, resins, waxes, fatty acids, and naphthenic acids can also be used as thickening agents. The metal soap-based greases have good water resistance and a high melting point. Greases are used as chassis and wheel-bearing lubricants. In many cases, oils are preferred to greases because they are better coolants and are easier to handle and apply. However, greases are preferred for applications where it is essential that the lubricant does not run out or drip and for higher temperature operations.
Greases for some special applications have a synthetic-liquid base. Fluorocarbon liquid bases greases offer good resistance to fire and oxidation and are used where acids, hydrogen peroxide, and other corrosive agents may be present. Silicone liquid-based greases are used at high temperatures and for show-moving machinery.
Solid lubricants are used when the operating conditions of pressure and temperature are too severe to be met by liquids.
There are many forms of solid lubricants. Among them are powders, which are used either alone or with binders. They are found as dispersions in non-volatile carriers as soaps, fats or waxes, and as soft metal films.
The most common powdered lubricants are inorganic materials, such as graphite, molybdenum disulfide, tungsten disulfide, boron nitride, and zinc oxide. They are able to function continuously at temperatures up tp 650ºC, and are used as lubricants in such metal working operations as wire drawing, extrusion, forging, and machining. These solids are often used as additives to mineral oils, synthetic liquid lubricants, and greases, where they increase the load carrying capacity of the material. Powdered solid lubricants and soft metals are used as additives to other solids and metals to improve frictional properties. For example, graphite and graphite metal mixtures are fabricated into bearings and brushes used in motors and generators.
Gases are used as lubricants where their circulation ability, high and low temperature properties, and resistance to reaction cannot be duplicated. They are used in ultracentrifuges, nuclear reactors, gyroscopes, gas turbines, and jet engines. The principal gas lubricant is air, but halogenated hydrocarbons, sulphur hexafluoride, and nitrogen are also sometimes used.
The metallic radical of the soap largely determines the characteristics of the grease, the fatty radical having a secondary effect. Greases are, therefore, classified in terms of the metal they contain. Normally a great proportion, nearly about 90 per cent of greases contain lithium, calcium or sodium soaps. "Other soaps" (such as potassium, barium or strontium) are of minor importance.
The conventional type of calcium soap grease has smooth buttery texture and are water resistant, with drop points acound 90-100ºC. They are water stabilized, i.e. the water is present in the soap crystals as water of crystallization. The optimum amount of water varies considerably with the type of formulation, fatty material, and mineral oil used, but is usually within the range of 0.4-1.0 per cent wt. At high temperatures, the water is gradually lost and the soap structure is weakened. Consequently, calcium soap greases are restricted to use at fairly low maximum temperatures (about 50-60ºC). Such greases turn fluid after exposure to high temperatures and many separate into the oil and soap phases. Only those which contain other stabilizers besides water (e.g. wool grease or fatty acid) will regain their structure on cooling.
There is also a type of calcium soap grease made with hydroxyl-fatty acids which is anhydrous and does not depend on water for stabilization. Such greases have drop points around 145ºC and do not suffer from the limitations of water stabilized greases.
These are usually more or less fibrous in texture depending mainly on the nature of the fatty material, high unsaturation yielding very fibrous greases. They have drop points usually not less than 150ºC and sometimes as high as 200ºC and are useful for relatively high temperature service. Owing to the solubility of the soaps in water, they are not water resistant.
These greases first appeared during World War II and were made from lithium stearate pre-formed soap. Now-a days, lithium hydroxystearate greases made by saponification in situ from hydrogenated castor oil predominate. Depending on the composition lithium greases are smooth or slightly grainy in appearance. They have the highest droppoints (about 190ºC) of the conventional greases and the highest service temperatures. They are water resistant, mechanically stable and can be made with a greater variety of types of oil than most other greases. Their versatility and wide operational scope (especially in high speed service) had led to their use as multi-purpose greases to the displacement or earlier types of more specialized greases.
They have an attractive translucent, smooth and polished appearance. The drop points are low (about 90ºC), the mechanical stability is poor and the greases tend to become rubbery at high temperature. They are almost invariably made from high viscosity oils and often incorporate polymers. Such products are water resistant, stringy and adhesive and find application as chassis and gear lubricants. They are not recommended for rolling bearings.
A variety of mixtures are used, the commonest being sodium/calcium, and the greases are generally manufactured by saponifying the fatty material with mixed alkalies derived from different metals. One of the soaps usually predominates and determines the general character of the grease, while the other modifies the structure in same way. This results, for example, in change in texture and improved mechanical stability.
The normal soaps can be complexed with various inorganic salts, usually salts of aliphatic acids with carbon chain lengths varying from C2 (acetate) to C14 (myristate) or mixtures thereof. Calcium complex greases (same including lead compounds) have been made for many years. More recently, aluminium complex greases have been introduced using benzoate as the complexing salt. Lithium complex greases have also made their appearance. The greases are water resistant and have very high drop points, in the range 200º-300ºC. Modern greases of these types are suitable for multi-purpose use.
There are two main types, those intended for general industrial use are those for specialized applications. The former include greases thickened with silica, clay or carbon black and organic derivatives such as terephthalates, diamino dicarbonyl and aryl-substituted areas. Published data (high service temperatures, mechanical stability, water-resistance, etc.), suggest that they are multi-purpose greases with a wider scope than soap greases. However, the rather far-reaching chains have not been supported by any notable impact on the market. The type used for specialized applications (mainly for very wide temperature ranges) includes greases made from the dyestuffs indanthrene and phthalocyanic, which are generally combined with synthetic fluids such as diesters, silicones, polyesters and polyethers and hence are very expensive.
The properties of greases depend upon the composition of grease and nature of its constituents. The gelling agents determine to a large extent the texture and mechanical stability of the system. The liquid phase on the other hand influences flow properties particularly at very low and high temperatures.
By virtue of being semi-solid or semi-fluid greases exhibit unique properties which are not shown by other fluid lubricants. Salient among these properties is the ability of greases to retain their position in a mechanism without significant leakages and yet release sufficient quantity of liquid lubricant for reducing friction and wear during usage. That greases can do so over a wide range of operating conditions over long durations of time, is an advantage which cannot be matched by lubricating oils. It is for this reason that for many industrial applications where oils have traditionally been used, greases are now emerging as superior and more effective alternative.
The ability of a grease to resist changes in consistency as a result of a severe mechanical working is important in relation to service in rolling bearings.
If the grease loses significant amount of oil on evaporation, its lubricating properties would be seriously affected and the life of grease curtailed.
Oxidation stability of greases is dependent on the oxidation stability of the oil. Oxidation of oil leads to acidity development, increase in viscosity, blackening caused by asphalt like bodies, and ultimately to the formation of bituminous mass.
Heat stability is the ability of the grease to hold the oil at elevated temperature (below the drop point) for extended period. This is measured in terms of the oil separated from grease in a standard test at a fixed temperature (usually 100ºC) after a fixed period (usually 30 hours). The grease which gives less oil due to separation is more stable.
Temperature Limits for Different Greases
Typical Properties of Lubricating Greases
Typical Properties of Synthetic Greases
Greases and lubricants are one of the important products derived from crude petroleum.
The particular virtues of grease that make it preferred to oil in many cases, and especially for rolling bearings, are ease of application and simplicity in use, while oil can carry away heat from the lubrication point and in general will lubricate rolling bearings more efficiently, it needs goods seals and relatively elaborate means of application such as circulation systems. Grease, on the other hand, can be used in simpler housing designs because it can be retained easily and therefore, seals against contamination, and requires much less attention and maintenance. Consequently, the majority of rolling bearings are now lubricated with grease. For similar reasons, plain journal bearings not operating under critical conditions are also commonly grease-lubricated.
However, in general, grease applications vary from high loaded ballbearings on small electric motors motors and fans to heavy duty plain and antifriction bearings on the largest of steel mill rolling equipment. Owing to their many advantages over oil, greases are now the first choice for the lubrication of ball and roll bearings in electric motors, household appliances, etc. They are also used for the lubrication by small gears drives and for many slow speed sliding applications.
Naturally enough the less critical conditions can be met by the cheaper products, i.e. the conventional calcium soap greases, which are mostly used for plain bearings and for low-speeds rolling bearings. For rolling bearings operating at high temperature and speed, the choice can be made from the remaining types of grease depending on service conditions, the more severe conditions requiring high quality inhibited greases. These latter have a multipurpose character and are increasingly used in many plants, with benefits in stock holding and freedom from misapplication, in place of the variety of cheaper greases that would otherwise be needed. Extreme temperatures, say from 150ºC upwards, call for greases made from the non-soap thickeners. They are also needed for critical mechanisms in nuclear power plants where soap greases cannot withstand conditions involving exposure to nuclear radiation.
It is important to use the right amount of grease in bearing, especially for high speeds too much can cause churning and over-heating, which may result in the grease breaking down and running out of the bearing. Too little can result is dry running and damage to the bearing. Best practice is to pack the bearing full and leave enough free space in the covers to accommodate excess grease working out from the bearing during the initial running. This can be achieved by packing the covers between about two-thirds and three-quarters of the total capacity.If external contamination is severe and the bearing speed is fairly low, effective sealing can be maintained by packing fully.
The mechanism whereby grease lubricates a rolling bearing is somewhat controversial. It is accepted that under settled conditions the bulk of grease within bearing and housing is stationary and that only a very small amount of grease is actually circulating on the moving parts, this being rapidly degraded by the mechanical action of the rolling elements. Some consider that this alone does the job of lubrication and that the soap itself plays a valuable part. Others consider that the lubrication and that the soap itself plays a valuable part. Others consider that the lubrication is done by slow oil release from the stationary bulk of grease. It seems probable that both mechanisms of lubrication may operate to a greater or lesser extent, depending on the nature of the grease and the applicational conditions, particularly temperature.
The consumption of lubricating oils and greases in India has been increasing steadily in the wake of economic and industrial development.
The change in their consumption pattern is governed by the supplies and partly by change in maintenance and lubrication practices (i.e. oil drain period, maintenance, conservation/re-refining, etc.) of industries in the wake of change in prices.
The consumption pattern of lubricating oils and greases show an increase. Also, the import figures show that there is a drastic demand for greases in India. As India is progressing towards self-sufficiency in the field of petroleum and allied products, the import of greases is diminishing but the demand for greases is increasing as the industrialization in our country is on full swing in general and automobile in particular.
Fillers may be considered as solid materials which add bulk, and if present in sufficient amount, decrease the penetration of a lubricating grease. Most fillers consist of inorganic compounds and normally such material are powders or flakes rather than granules.
These are:-
1. Carbons in various forms
Such as: Graphite, carbon black or lamp black.
2. Silicates
Such as: Asbestos, a magnesium silicate, bentonite, a form of clay, calcium silicate, mica, a potassium aluminium silicate, talc or soapstone.
3. Metal Powders or Flakes
Such as: Aluminium powder, copper powder or flakes, lead powder, zinc dust.
4. Metal Oxides
Such as: Alumina or aluminium oxide, hydrated alumina, magnesia, litharge or lead monoxide, zinc oxide, titanium dioxide.
5. Metal Carbonates
Calcium carbonate, lead carbonate, basic lead carbonate, white lead.
6. Metal Sulfides
Antimony trisulfide, antimony pentasulfide, lead sulfide.
7. Metal Sulfates
Barium sulfate, lead sulfate.
It is the most widely used filler. Natural graphite may have some impurities, and if 100% pure graphite is to be used, artificial graphite is generally employed. These may be in the form of powder or flake.
Graphite is presumably absorbed on metal surfaces. The utility of graphite, the small plates of graphite lying with their large surfaces parallel to the metal surfaces. Thus, the solid surface is much smoother and more uniform than before such adsorption. Also the layer of graphite has a tendency to absorb oil and to be wetted of it. This action, therefore favours the stability of a thin oriented layer of lubricant.
Graphite may be used in any lubricant, but it is particularly recommended in anti-seize compounds, spring lubricants, thread sealing compounds and valve lubricants.
Grades of Graphite Recommended
Preparation of Graphite Lubricating Greases
The addition of graphite to lubricating greases best made when the product is partially or almost completely finished, for if the addition is made before the soap structure forms, settling of the filler may result. If possible, one mixing kettle should be set aside for the manufacture of graphited products because it is difficult to entirely free a vessel of the filler once it has been used in equipment.
The addition of powdered graphite is accompanied by dust which settles on the sides of the mixing vessel, and if the mixer is not covered, escapes to soil the surroundings and perhaps to contaminate other products.
For general purpose lubricating greases, graphite is seldom added in concentrations greater than 5%, and 3% or less is more common. These products include graphite cup greases, graphite chassis lubricants, graphite fibre greases and graphite axle greases.
Because of the fineness or small particle size of carbon black or lamp black, it has been often used as a filler in lubricating greases. To obtain the full value of carbon blacks, when employed as a filler, through dispersion is essential. Simple mixing will not suffice, but should be followed by some type of milling. Greater trouble will likely be encountered from dusting with carbon black than with fine graphite. In addition to acting as fillers, carbon black are inert and resistant to the solvent action of fluids with which they may come in contact.
A formulation of such a lubricating grease in which this filler used is described in a U.S. Patent 2,486,674 in which 8.94% of carbon black, having an average particle size diameter of 250 A, is dispersed in a silicon polymer having a viscosity at 25ºC of 140 centistokes. Dispersion consists of stirring, heating to 115ºC, and finally passing through a three roll paint mill.
The type of asbestos normally used as a filler in lubricating greases is a grade known as "asbestos floats". Such a product should not have any particles held on a 20 mesh screen and not over 16% held on a 30 mesh screen. While this grade is presumably recovered by air separation from heavier particles, grit can generally be detected by rubbing a small amount of the asbestos between two glass plates.
Most of the asbestos fitted lubricating greases are made by simply mixing the asbestos with a suitable oil. The asbestos is fed through a shaker screen into the oil, which is agitated during the compounding. No heat is required unless a cylinder stock of high pour point is used. Most of the oils for such lubricants had viscosities within the range of 175 to 210 SUS at 210ºF. Such oil varied from bright stocks to black oils, but in most cases consisted of well refined cylinder stocks. Most producers of such lubricants give them a rough screening by passing them through a coarse screen or a perforated disc with 1/8 inch holes before packaging.
Mica in flake form is sometimes used a filler in lubricating greases, in horse drawn vehicles or such other vehicles, axle grease containing flake mica has such a reputation for service that the name "Mica Axle Grease" was copyrighted in America, from a fraction of percent to 5% of mica is employed for much the same purpose as flake graphite.
In bearing wear tests by experts, while mica did not show the abrasion which asbestos did, scratching and scoring of the bearing surface is evident, and the material is thus placed in a questionable class as far as lubrication of antifriction bearing is concerned.
Vermiculite has somewhat the same form and nature as mica and thus can be expected to serve much the same purpose as a filler. The flakes of this material have a yellow golden colour which make it evident when added to light coloured lubricating greases. Such a filler can be expected to be of doubtful value in lubricants for use in antifriction bearings.
Lubricants are being prepared for use on metallic moving parts by completely expanding vermiculite by heating to 300ºC, and grinding and mixing it with lubricating greases. Oxides of zinc or cadmium could also be included in such lubricating greases.
The slippery nature of talc (known also as soapstone) has made it attractive as a filter in some lubricants.
A hot neck lubricating grease for use after the rolls are warmed up in older steel mill equipment consists of petroleum pitch (125º C.M.P.) 47%, degras 7% talc 27% and cylinder stock, of 500 flash, 19%.
Both talc and asbestos used to be employed in Ford spring compounds as below:
A stainless, emulsifiable, grease-like composition, suitable for pipe bending and wire drawing opetrations, has been suggested. The base oil for this product contained 10 to 15% of alkali metal petroleum sulfonates. The proportions of ingredients used : 25 to 75% of the base oil, 0.5 to 2.0% of tall oil, 0.5 to 2.0% of diethylene glycol, 0.3 to 1.0% of cyclohexylamine, 0.05 to 0.2% of stearic acid and about 38% of either talc or mica.
It is well to keep in mind that talc or mica are often preferable to graphite in die or drawing lubricants because the latter material is difficult to clean off after drawing.
Bentonite, calcium silicate, magnesium silicate, magnesium aluminium silicate for their wear or abrasiveness when included in 10% concentrations in a soda base lubricating grease. The tests were on tapered roller bearings which were run for 200 hours at 1000 rpm under a load of 75% of thrust. Of above compounds only calcium silicate should be rated as non-abrasive.
Metals in powdered or flake form are employed as fillers in certain types of lubricating greases, the softer metals generally being used.
A lubricant for die-forming magnesium and its alloys may be prepared from the following combinations : 50 to 70 parts of comminuted aluminium of 120 to 400 mesh size, 20 to 30 parts of potassium or sodium palmitate or stearate, and 10 to 20 parts of either hydrogenated cottonseed, lard oil, or peanut oil.
Finely divided lead is employed as filler in lubricating greases for more than one purpose. Thus, US Patent 2,383,148 provides a formula described below:
Some powdered metals, particularly aluminium and zinc, are used in various lubricants. Thread lubricants are made with proportions of zinc powder varying from 10 to 60%. It is well to introduce the zinc dust when the cup grease is as cool as possible, since it hydrogen is to be generated, the reaction will be accelerated by heat.
The most promising compounds contained a mixture of 2 to 4% flake copper, 18% graphite, and 42 to 44% of mixture of powdered lead and zinc (consisting of 2.35 to 3.17 parts by weight of lead to 1 part of zinc) dispersed in 34 to 36% of vehicle.
The copper is said to function as an active thread lubricant. An increase in copper content, from 2 to 4% by weight, resulted in a 10% decrease in make up torque.
Oxides of a number of metals have been and are being employed as fillers in lubricating greases. In selecting oxides care should be observed that they are of a physical nature which will not be abrasive. As these oxides act as anti-acids, they are suitable in many machineries, such as canning machinery, etc. A lubricant which is to be used on canning machinery contained magnesium oxide in order to neutralize any acids derived from fruit or vegetables.
Zinc oxides is sometimes added as a colouring aid in calcium base greases. For this purpose 1 to 2½% of a lead free, fully zinc oxide is employed.
A suitable zinc oxide for use as a filler in lubricating greases has the following specifications:
Manufacturing Details-In industry lubricating grease is manufactured by two processes:
1. Batch Process
2. Continuous Process
Following steps are used in processing:
(a) The required materials are properly weighted.
(b) For saponification mixing and heating of ingredients is involved.
(c) Dispersion of bodying agent in the lubricating fluid.
(d) Dehydration by vacuum treatment of the finished or semi-finished product.
(e) Cooling of the soap.
The value of lubricating grease in service depends upon the following physical characteristics:
1. Stability to working or shear
2. Thermal stability
3. Body or consistency
4. Viscosity or low
5. Structure
6. Syneresis
7. Texture and appearnce.
Following types of greases are manufactured and used in industry:-
1. Sodium, calcium, aluminium, barium, lithium, strontium, and lead base lubricating greases.
2. Mixed base lubricating greases.
3. Miscellaneous metal soap as components of lubricating greases.
4. Complex soap lubricating greases.
5. Non-soap thickeners for lubricating fluids.
There are two main processes : (1) Batch Process, and (2) Continuous Process. Most lubricants are produced by the Batch process, which is still popular, particularly for a small scale manufacturer. In this process the amount of lubricants made in one lot may be from few hundred pounds to 60 or 100 barrels. Batch process may further be divided into two parts : (1) Open kettle, and (2) Closed kettle manufacture.
Simply, this process have the following successive steps in the production of lubricants:
(1) Open Kettle Manufacture:
(a) Saponification and finishing carried out in one vessel.
(b) Dispersion of preformed soap and finishing or product performed in the same kettle.
(c) Saponification and dispersion of soap carried out in one vessel, followed by cooling in auxiliary equipment.
(d) Dispersion of preformed soap in one vessel, followed by cooling auxiliary equipment.
(e) Saponification conclude in one kettle and finishing done in another.
(f) Preformed soap dispersed in one vessel and finishing carried out in second vessel.
(g) Fatty materials preferably fatty acids or rosin acids, mixed with a portion of the total oil in one vessel and the alkali mixed with the remainder of the oil in another vessel. The two mixtures are then brought together to the package where saponification takes place.
(2) Closed Kettle Manufacture:
(a) Saponification carried out under pressure and finishing done in a second vessel.
(b) Saponification carried out in a pressure vessel, soap dispersion in a second vessel and cooling in auxiliary equipment.
The simplest process for the manufacture of lubricants is that in which the soap is made in the same vessel in which the finished product is completed. This entails the use of only one vessel for complete greasemaking and requires no auxiliary equipment, either for transfer of partially completed lubricants, or for cooling or milling of the completely formed lubricants.
In this process, though the vessel used is only one, but the whole process is divided into several steps, they are:
(1) Weighing or measuring materials for the formation of soap.
(2) Mixing and heating such a mixture of ingredients to form soap.
(3) Dispersion of the resulting soap in portion of the total oil.
(4) Hydration of the soap oil mixture.
(5) Introduction of additional oil, which oil may act as a coolant or serve to reduce the mixture to the desired consistency. Additives or modifiers may also be introduced in this step.
(6) Cooling which may be accomplished in step 5 or following that step.
(7) Filling of containers or delivery to storage. This step will include screening of the finished product.
It is evident that all the steps outlined can be carried out in one vessel. Such a simple process is not applicable to al types of lubricating greases but this method will permit the manufacture of most calcium and sodium based lubricants and greases. Lubricants and greases will have the most satisfactory structure provided that the crystallization of soap takes place while the mass is still dormant.
Use of more than one vessel in manufacturing lubricants and greases is the very common practice, and probably the most economical method of production. The two vessles, as far as possible, should not be identical in construction, so that provision can be made for one vessel which will permit dispersion and hydration to the best advantage. Thus, the saponification vessel can have a much smaller capacity than the finishing kettle. Two stage manufacturing processes permit greater through put and flexibility than one stage procedure.
When preformed soap is employed, one of the most time consuming steps in open kettle processing is eliminated, namely saponification, so that processing of preformed soaps is normally confined to one vessel and any auxiliary equipment.
The process by which soap formation takes place in the container is employed to a limited extent. Axle grease is made by such a process and mention will be made of this when continuous processes are described. One disadvantage of such a process is that any moisture present in the reacting mixtures, or formed by reaction of acids and alkali, remains in the finished product.
1. Mineral oil (Turpentine Oil)
2. Rosin Oil
3. Hydrated lime [Ca(OH)2]
1. Mixing vessel made of mild steel or carbon steel jacketed for steam heating.
2. Baby Boiler Cap. 100 Kg/Hr.
3. Storage Tank (M.S.) capacity 1.5 cu. Mt.
4. Weighing Scale.
5. Instrumentation, process control & Lab. Testing equipment
6. Pipes, fitting, pumps, valves and other miscellaneous equipments.
Manufacturing Process
Modern plants are normally arranged for gravitational flow, with raw materials received at the top, saponification and finishing processes on intermediate flows and filling and packaging on the ground floor materials are usually metered in a fluid condition as far as possible rather than weighed for processing. For example, fatty materials in bulk are stored in heated tanks, calcium hydroxide is used in concentrated aqueous solution.
The first step in making soap greases is to specify the fatty material by heating with a chemically equivalent amount of alkali in the presence of a proportion of the oil. A small amount of water must also be present to ionize the alkali and so facilitate the reaction when saponification is complete, more oil is added and the soap/oil mixture is conditioned by a more or less critical adjustment of heating, cooling and stirring in order to control the crystallization of the soap fibers and hence the properties of the finished grease. The balance of oil and any additives are added at suitable stages depending on the type of grease, the process used and the nature of the additives. The grease is finally stirred or milled to obtain uniformity and correct consistency and then filled into packages.
Processing
Most greases are made by batch processes that involve stages of heating (saponfication) and cooling (finishing). Heating may be by steam, which allows the possibility of water cooling in the same vessel, by direct firing with oil, gas or solid fuel, by hot oil or Dowtherm circulation systems or by electric induction heating vessels heated by direct firing or hot-oil circulation cannot be water-cooled and are generally coupled wilth water-jacketed finishing vessels (kettles).
The kettles are fitted with stirrers which should give a good wall-scraping action to assist heat transfer and good circulation to avoid dead spots. Provided that the stirring is efficient (particularly during cooling), the product is normally satisfactorily uniform and does not require any further treatment to ensure satisfactory properties. In some circumstances a more vigorous shearing is needed during finishing and can be provided by pumping or circulating through mills or homogenizers. Such equipment is of two main types, with the grease pumped either between stationary and rotaing surfaces set close together or through special valves set to lift at high pressure.
Now-a-days closed pressure vessles (i.e. autoclaves) are almost universally used for saponification and frequently also for finishing, although open kettles are still common for this part of the process. Saponification is much easier and quicker at the higher temperatures obtainable in autoclaves, which are generally operated at 50-80 psig, corresponding to temperatures of about 148º - 162º C. With some greases, it is also necessary to provide for heating the autoclave contents to over 200ºC.
Modern practice is to prepare soap concentrates in an autoclave, this being coupled to one or two larger finishing kettles (typical capacities are 1-2 tons for autoclaves and 2-5 tons for kettles). The general layout of a typical modern grease plant is shown in the figure. On this system much of the oil can be added cold to the soap concentrate in the finishing kettle, thus shortening the time otherwise needed for cooling. After saponification, the soap mixture is generally "blown down" under its own pressure into the finishing kettle, during which time practically all of the water is lost as steam. Alternatively, the autoclave may be vented and heated to higher temperatures if required before discharge into the kettle at the higher temperatures obtainable in autoclaves, which are generally operated at 50-80 psig, corresponding to temperatures of about 148º-162ºC. With some greases it is also necessary to provide for heating the autoclave contents to over 200ºC.
The finishing process is designed to develop soap fibers of the desired properties by suitable thermal and mechanical treatment. This involves a proper choice of heating and cooling rates, process temperatures and stirring speeds at different stages. These factors vary so greatly according to the size and design of the kettle, and particularly the stirrer, that each plant must work out its own process for a given type of grease according to the equipment available.
Instead of kettles, other forms of equipment can be used that involve rapid circulation of grease through narrow channels between heated or cooled surfaces. Such equipment, popular in U.S.A., but not widely used elsewhere, can be applied to continuous or semi-continous manufacture.
Some pre-made soaps, particularly aluminium, require a different type of process. The soap is heated with the mineral oil to form an isotropic solution which is then cooled statically at controlled rates in thin layers, generally in shallow pans of convenient size. This results in the formation of a stiff gel, which is then broken down into the normal plastic state by suitable stirring or milling.
With non-soap thickeners the manufacturing process is fairly simple; the thickener is first dispersed in the oil (heated it necessary) and the mixture is then milled. Milling is an important part of the process since intensive shear is needed in order to obtain the best properties and maximum yield of grease.
Current trend in grease manufacture are towards better instrumentation of the operations. In principle, automatic control of heating, cooling and shearing together with the use of ingredients with uniform properties, would give complete control over product quality. Despite the considerable practical difficulties, satisfactory progress is being made towards this objective.
The metallic radical of the soap largely determines the characteristics of the greases, the fatty radical having a secondary effect. Greases are therefore classified in terms of the metal they contain.
(i) Aluminium
(ii) Calcium
(iii) Lithium
(iv) Sodium
(v) Sodium
(vi) Non-soap (organic-inorganic)
Nearly 90 per cent of greases contain lithium, calcium or sodium soaps. "Other soaps" (such as potassium, barium or strontium) are of minor importance and will not be discussed here.
The manufacturing processes for all types of greases is nearly the same. The mineral oil and other fatty materials are heated in fire heated kettle. When all the fatty materials melt, then mix them with the help of an agitator. Now to this melted fats add the required quantity of alkali with continous agitation. The complete saponification is around 400ºF. After complete saponification the batch is kept for cooling. After cooling the grease is filled in desired packings viz. 1 kg, 2 kg, 4 kg, etc.
Basis: 300 kg/day grease; 90000 kg/annum grease
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As saponification and soap dispersion, normally involve heating, it may be pointed out that enough care should be taken to avoid fire hazards in these processes. The material which is used in the manufacture of such items are almost entirely inflammable.
Since standard fire prevention practices, such as all steel or concrete construction in new plants, installation of sprinkler systems, division of the plant by fire-walls and doors, and cleanliness must always be retained in this regard, so fire hazards may be reduced at least to a certain point.
While the use of open obviously increases fire hazards they need not endanger a whole plant. If fire-heated vessels are employed in place of those heated by hot oil or "Dowthern" to obtain temperatures above 320ºF, such equipment should be segregated by fire walls going through the top of the building. It should also be possible to install barriers or diversions to keep overflow from a vessel away from a fire.
Saponification is actually an alkaline hydrolysis of esters, which in this case are mixed triglycerides of higher fatty acids. While water has been considered a pre-requisite for such a reaction, very likely this compound may simply provide for more intimate contact of the reacting ingredients, since soaps have been formed in anhydrous systems by the reaction of fats and fatty acids with finely divided dispersions of various alkali mineral oils. Since water alone, under proper conditions, will hydrolyze fats, it is possible that during saponification hydrolysis takes place preliminary to combination of the resulting fatty acids with the base.
Such a reaction may take place step-wise, so that the first product formed is a diglycerde, followed by a further reaction to produce a monoglycerine. Finally, the mono-glyceride reacts with still more alkali so that upon completion of saponification, glycerol and soap are the products.
Soap formation, by combination of a fatty acid and a basic compound, while actually a neutralization, is also considered as saponification by people in this industry, such a reaction results in the formation of water in addition to the soap. Since almost all inedible fats and fatty oils contain some free fatty acids, neutralization of such fatty acids no doubt precedes the hydrolysis of the fats, so that the remainder of the reaction proceeds in the presence of both additional water and some soap.
Certain metals will react with fatty acids to form soaps. In this case hydrogen is produced in addition to the soap. Since the soap thus formed may be deposited on the surface of metal particles, the reaction will be arrested.
This first step in the manufacture of aluminium base lubricating greases consists in weighing or measuring the primary ingredients, which consist of oil and soap. Since the soap will be in standard packages, generally holding 50 pounds or more per carton or bag, weighting is simple. As in all other types of lubricating greases, the oil may be either weighed, metered, or measured. In any event 20 to 25% of the total oil is added to the mixing kettle, followed by the aluminium soap. Some plants prefer to sieve the soap as added but in most cases this is not necessary. The oil should be below 150ºF when the soap is introduced, otherwise fusion of the outside of lumps of soap may take place and such lumps may be difficult to disperse later.
An intense mixing is desirable at this stage so that a good "Cream" results with no lumps of soap present. In some operations it is preferred to mix and heat at a temperature just below the gelling point, which is perhaps 150 to 160ºF, for one to two hours, in the belief that some of the moisture present may be removed before the soap is dispersed in the oil.
After the soap and the initial oil are thoroughly mixed, the soap is dispersed by the application heat. This dispersion can take place in the initial portion of oil but preferably more oil is added before gelling takes place. The temperature required for complete dispersion of the soap will vary with the specific oil and the type of aluminium soap employed, but it should fall within a range of 250 to 300ºF. If the hot mass is to be removed from the processing vessel, the top temperature may be required so that the mixture will be thin enough to handle. Modifiers and additives are to be mixed before the batch cools.
Cooling processes vary. In a few cases the hot grease is filled intocontainers and allowed to cool. In another case the mass is cooked in the kettle by means of water jacket. Another method is in shallow pans or trays to which the hot lubricating grease is delivered by pipes.
A flowsheet of a process for the production of aluminium base lubricants and grease, employing homogenizer, is shown previously. The first step in this process consists of preparations of soap oil slurry, in an open kettle, using half of the final mineral oil. This slurry is warmed to about 150ºF and passed through what is termed the hot grease homogenizer. This homogenizer consists of a rotating disc, housed in a vacuum chamber, with the inlet feed at the center of the disc and an outlet scoop out the circumference of the disc. Here, as the slurry travels continuously through the equipments, air and moisture are removed from the mixture and a thorough dispersion of the powdered soap is effected.
The next step consists of delivery to the heating kettle, where the batch is brought to 220 to 240ºF. After the heating step, the material is pan cooled and held until it gels.
The cool batch, plus an equal weight of oil, is then added to a mixing kettle where agitation breaks the cooled mass into small lumps. The final step consists of passing this slurry of soap gel lumps and oil through a cold homogenizer. As the mixture passes through this piece of equipment it is smoothed out, so that no lumps, graininess, or free oil remains.
Because the fact that moisture is removed before the soap and oil are heated to dispersion temperature, and also because the homogenizers are said to thoroughly disperse the soap, a smaller soap percent for a given consistency is claimed for this method than for other methods of manufacture aluminium base lubricating greases. A saving heat is also claimed because of the fact that the temperature required in the process is 240ºF.
This process has also been employed for the production of lithium base lubricants and greases, in which a higher temperature is used to disperse the soap. Likewise, instead of starting with preformed lithium soap, the lithium soap could be prepared in the initial kettle.
In employing the above process it is possible to have an oil-soap mixture exhibiting a brittle soap gel and free oil, which can subsequently be smoothed out by mechanical means to form a satisfactory lubricating grease. A recent procedure is applicable in processing preformed soaps of aluminium, barium, calcium, lithium, and sodium with mineral oil to form work-stable lubricants and greases.
The first step in this process consists of heating the soap-oil mixture, while agitating, until the entire mixture is liquefied and preferably until the oil and soap are miscible, which is said to be 365ºF, or above, for most mixtures. This step may be conducted in either open or closed vessels.
The next stage, cooling, is accomplished by discharging the hot soap oil dispersion into a cooling tank where cool oil is constantly supplied from an oil cooler. Here the soap separates as lumps of soap gel. The cooling time is usually 10 to 300 seconds. This cooled mixture is discharged to a separator consisting of either a centrifuge or a screen sieve where the lumps are retained for further processing and the oil returned to the coolers.
The final step consists of charging the gel lumps with desired amount of oil and subjecting the mixture to a severe working in a mill. The resultant finished product is smooth, plastic, and work stable.
The fat is employed in the mixer with oil equivalent to approx. 20 to 30% of the fat. This mixture is warmed so as to be fluid, after which the hydrated lime is added during agitation. The form in which the lime is added varies with different plants. In some cases it is added in the powder form and in other instances a slurry is made with oil and water. Such a slurry can be prepared in a small mixer.
Heating and mixing is started as seen as the open kettle is charged and continued until saponification is complete. Excessive water will result in foaming, and care must be must be taken to prevent boil-overs. No additional oil should be added until the soap is formed as such dilution will simply prolong the saponification.
After saponification is complete, most plants immediately add further oil to reduce the soap proportion to about one-third of the mixture and proceed with the hydration step. In some cases the soap concentrate is held in the cooking kettle overnight, reheated the next morning and then diluted and hydrated.
Lead soaps can be prepared in open vessels provided with heat and agitation. This is a one-step process since it simply involves mixing the fatty material or acids with mineral oil and adding litharge with efficient stirring. If any further processing is required it will be screening, settling, or centrifuging to insure that no free litharge remains.
Lead soap are produced at a low temperature by suspending litharge in mineral oil by means of a colloid mill and then mixing this suspension with a solution of fatty acids in oil.
Magnesium base lubricating greases are formed by the process of first suspending magnesium hydroxide in mineral oil by passing the mixture through a colloid mill and then mixing such a suspension with a solution of fat or fatty in further oil.
Grease manufacture in open kettles has always been basic to the grease manufacturing industry. A typical batch procedure using an open kettle consists of charging the kettle with a fatty material, an alkali and some mineral oil. These materials are then heated to about 200ºF to react the fat and alkali to form the soap. At this stage water is present form the saponification reaction. The batch is then heated to a higher temperature to remove the water from the soap oil mixture. Following dehydration, the batch may be held at an elevated temperature for one to four hours to "condition" the soap. After the soap has been properly conditioned, more mineral oil is added to the batch as it cools. Near the end of the cooling process, any additives required are added. The final consistency of the product is generally determined by the amount of oil added.
Although kettle manufacture is widely used, there has been considerable interest in the development of continuous, or at least semi-continuous processing. During recent years several semi-continuous processes for grease manufacturer have appeared. Basically, these processes fall into two types. One type consists of using a tabular reactor to form the soap base continuously and a kettle for preparing the finished grease. The second type consists of using a tabular reactor to form the soap base continuously and a kettle for preparing the finished grease. The second type consists of marking the soap in a bank of batch type reactors and blending the soap with mineral oil continuously to make the finished product. The process consists of reacting the fat and alkali in the presence of a mineral oil in a tabular type reactor. This portion of the process is continuous. The soap-oil mixture from the reactor is charged to a blending kettle where additional oil or additives are added to the batch. The grease is then packaged from the blend kettle.
In a similar semi-continuous process equipment consists of various weight tanks and metering pumps for charging the three pressure reactors. After one of the reactors is charged, the soap mix is brought up to temperature and recycled through a heat exchanger which serves as the reaction zone. Once the fat is saponified the soap base and mineral oil are charged in fixed portions to a high speed mixer where the finished product is continuously blended. While the first reactor of soap base is being used, a second is made, and subsequently a third; by sequential charging and saponification, soap base is always available for the blending operation. The apparent viscosity, or consistency of this finished product is monitored by a pressure viscometer. After passing through the mixer, the product goes directly into packages. This process through the mixer, the product goes directly into packages. This process can prepare calcium and sodium base greases at high production rates with relatively good yields.
Small Scale Process for Manufacture of Lithium base Lubricants
A U.S. Patent 2,478,917 describes the process for a small scale manufacturer. In this procedure a stream consisting of an intimate mixture of preformed soap in a lubricating fluid is (1) heated to effect complete solution of the soap in the fluid; (2) cooled suddenly to form a gel; and (3) subjected to mechanical working of the gel to obtain a product of a lubricating grease consistency.
The heating and cooling in this process are conducted as film heat transfer operations. This is apparently possible because of the small diameter of the pipes is the employed for heating and cooling. The diameter of the tubing for the equipment should be about 2 times the thickness of the free-flowing film of base fluid and that for most cases this would be less than 1/2 or 3/8 of an inch. If a large capacity unit were to be employed, a plurality of such small tubes would be required.
The method of heating employed is unique in that a pipe coil is electrically heated. This coil is electrically insulated from the rest of the system and enclosed in heat insulating material such as glass wool. Also, the heating coil is connected by electrical leads across the secondary terminals of a transformer and this transformer has a current regulating device inserted in series with its primary windings. The rate of flow of the mixture through the heating section is adjusted so that the total time does not exceed 15 seconds. The pressure at which the soap-fluid mixture is delivered to the heating system is 800 psi.
Cooling water is circulated around a coil of the same diameter as that used for heating, and thus cooling of the lubricant is said to be quite rapid.
Some working of the lubricating grease is accomplished by the shear as the product is rapidly forced through the small diameter tubing. However, the major portion of the working of the cooled lubricating grease is accomplished by forcing the product through a disc with a plurality of small perforations whose total area matches that of the cross section of the pipe or tubing used in the system. The major portion of the worked lubricating grease which passes the perforated disc is recycled to receive another working. Since only a minor portion of the stream, or worked lubricating grease, is taken off for delivery to packages, it is evident that the lubricant receives several working before it leaves the system.
With the use of tubing for the coils in this equipment, a throughout of about 120 pounds was secured in 8 hours, when processing a lithium soap-diester mixture into a lubricating grease.
Manufacturing of Barium Base Lubricating Greases
A barium base lubricant grease can be prepared from a normal soap if the proper oil is used and the processing procedure modified. This oil should have a viscosity gravity constant of atleast 0.870 in order to effect solvation of the barium soap.
As a first step in the preparation of such a product, stearic acid is to be melted with a little more than an equal amount of a napththenic oil having a viscosity of 312 SUS at 100ºF, and a solution of barium hydroxide was added. Agitation is to be carried on throughout the process. The mass is to be heated, first to about 210ºF until the major portion of the water is evaporated, after which the temperature is raised to 310º F where it is held for 15 minutes. The mixture at this point appears a stiff, tatty-like mass and slightly rubbery. Heating and stirring to be continued until the charge reaches a temperature of 200ºF. As soon as the material is cooled, the stringly product changes first to a dry, flaky mass at about 240ºF and then to a stiff, graying dough at about 230ºF. This becomes a smooth, pasty material as the temperature decreases further. When the temperature reaches at 200ºF, oil works into the mass to reduce it to the desired consistency and the lubricant is then drawn from the kettle.
In processing, it is essential that such a lubricating grease be continuously stirred, while the soap concentration is at least 40% of the whole, through a critical transition temperature, until a desired structure is obtained.
Barium Base Lubricating Grease
Manufacture of another kind:
The barium hydroxide-oil mixture consisting 331/3% oil, the oleic acid and the barium hydroxide-oil mixture, with about one-fourth of the additional oil, are added to the reaction vessel. The mixture is heated for a short time at 200ºF, with stirring, and remainder of the mineral oil is added. The product is then allowed to cool to about room temperature where it sets up to a smooth cup grease. It is then reheated to about 300ºF until all the water is driven off, after which it is poured into containers and allowed to cool.
The resulting lubricating grease is transparent and smooth, with a dropping point of 240ºF and a penetration of 320 to 340 at 77ºF. This product may be melted and cooled without change in structure. A similar lubricating grease made with 20% of hydrogenated fish oil fatty acids has penetration of 265 to 280 and dropping point of 250ºF.
15 pounds of hydrogenated castor oil and 15 pounds of Edeleanu extract are charged to a steam heated kettle and stirred while 8.1 pounds of barium hydroxide and 10 pounds of water were added. The temperature to be raised to 190ºF and maintained at this point for about 5 hours, after which the mixture is to be dehydrated, the temperature reaching 288ºF. Care must be taken to avoid heating above 300ºF because at that point the mass might melt and become lumpy. Now at this point, the charge is a smooth, dark brown, dough-like mass. After dehydrating, heating is discontinued and 12 pounds more of the extract is added and finally, 2 pounds more oil is also added. Agitation should be in continuation until the temperature of this mass drops at 130ºF.
The product, a dull, grayish, buttery grease has now the following qualitative characteristics:
Almost any calcium base lubricating grease may be obtained through Open Kattle Saponification process. The following ingredients are required:
The fat, 30 gallons of the lubricating oil, and 5 gallons of water are charged to the kettle. If variable speed is available, the agitators are started in the highest speed so that a through mixing takes place at once. The lime is then added, after which steam is turned into the kettle jacket and kept on until saponification is complete unless the charge foams and rises in the kettle. If this occurs and about 5 or 10 grams of antifoam will not check the rise, it may be necessary to shut off the steam and add some additional oil to cool the charge. It is not advisable because any dilution of the mixture will tend to prolong the time required for saponification.
If the fat contains some free fatty acids these will react immediately with a portion of the lime and the soap thus formed will aid in producing an emulsion. Such an emulsion will not only help to insure intimate contact of the reacting ingredients but will also help to retain moisture in the mass. Under such conditions saponification is accomplished in about 2½ hours. The steam pressure generally employed is around 125 psi.
When saponification is started, the mixture will have a thin consistency, and has the reaction proceeds, thickening will take place, until, near the end, a very viscous mass results. A sample of this mass taken from the kettle will be fatty-like when hot and brittle when cooled. The almost cool material should crumble between fingers much like flakes of oatmeal.
Grease makers have become quite skilled in determining when saponification is substantially complete. The manner in which the mixture flakes when rubbed between the fingers is one method of such determination.
When it is considered the saponification is complete, additional oil is added as rapidly as the mass will take it up. At this point the temperature of the mixture should be 300ºF or slightly higher. Heat and agitation are continued unless otherwise noted. The oil addition is continued until a total amount of oil approximately equal to twice the intial fat has been added. At this point the temperature of the mixture should be about 230ºF.
If the entire processing is to be completed in the one vessel, heating will have been discontinued so that the addition of cool oil lowers the temperature. However, in most instances the soap concentrate will be dropped or pumped into another kettle for finishing. In either instance, after the required amount of oil is present and the temperature about 230ºF, 10 gallons of water is added to the soap concentrate while it is agitated vigorously. If more than one speed of the agitators is available, the highest speed should be used during immediately after the addition of this water. It is important that a thorough mixing of the water with the soap mass should result, and no further oil should be added until the mass assumes a heavy, plastic nature. If water escapes at this point, further additions may have to be made at the rate of 2 to 3 gallons at a time. Some operators may prefer to add this water when the soap-oil mixture has a temperature of 215 or 220ºF.
As soon as the mass has the proper texture, further oil is added as fast as possible for thorough mixing. If the batch is grainy at this stage, it is an indication of water deficiency in the mass. If the mass is too soft for the percentage of soap present and is cloudy, no doubt the moisture content is too high. In either case correstive measures should be taken while the soap content is still high. Thus, the addition of oil is discontinued, and if water is required, this is added. If the moisture content is high further heating may be required.
It is presumed that a vessel with good agitation and scrapers is being used so that lumps will not result as further oil is added. If a pump and circulating line is available it is well to start circulation as soon as the final oil addition is started. It should be kept in mind that final batch temperature of 175 to 185ºF is desired in any calcium base lubricating grease. If a finishing kettle without any provision for heating is employed, it may be desirable to add hot oil to obtain the above temperature.
If dyes, perfumes, oxidation inhibitors, stringiness agents or other additives are to be used, these can be added at any time before the final oil is combined so that they have time for through blending.
Production Calcium Base Lubricating Greases. Some principles worth noting:
1. Use fatty material within the range of 37 to 42 titer which contains a minimum of polysaturates.
2. Use slightly more than the theoretical amount of hydrated lime for saponification and see that this lime is as free as possible from carbonates.
3. Irrespective of the method of saponification carry this reaction to the point where at least 97.5% of the fat or fatty acids is converted to calcium soap.
4. In order to secure the best yield and structure, work with lubricating oils and less than 50 V.I., if possible.
5. Unless the reaction provides the "tie" water as a result of neutralization, add the required amount of water at as high a temperature a possible, but not below 210ºF.
6. After the "tie" water is added, permit the grease structure to form before chilling the batch with additional oil.
7. In the case of calcium base lubricating greases of a good standard, package within a suitable temperature.
8. Pass all finished lubricants and greases through screens of not coarser than 40 mesh to insure the absence of material which may stop up pumping equipment or damage bearings.
Special Utility of Lead to Machineries
Since the introduction of thypoid gears in 1928, the importance of such lubricants has been noted in the industry, because it had been found that these lubricants prevent scuffing ands scoring of the gears.
1. Lead oleate, a mixture of lead acetate and sodium oleate in interaction, can still be used as high-pressure lubricant.
2. Lead naphthenate, is a good substitute, and mostly used for high-pressure lubricants, partly because it is a semi-transparent material and could easily be solved and suspended.
3. Lead soaps has all the qualities, which are lacking in other material, therefore, most manufactures use them. Lubricant made of them are hard at low temperatures, but can be fluid on heating by friction.
4. Lead stearate, derived by heating a solution lead acetate with sodium stearate, is another substitute. All the above materials are water-insoluble and oil-soluble. These all are used in the lubricant industry for various purpose.
Lead soaps of organic acids can be formed by reacting such acids with leads chips, flakes, or pellets. Circulation of the heated acids over the metal particles accelerates the reaction. In some cases oxidation inhibitors are present during the soap formation.
A U.S. Patent 2,308,599 describes the preparation of lead soap in the following manner:
100 grams of the fatty acids of hydrogenated castor oil are warmed with 50 grams of SUS at 100ºF coastal oil until the fatty acids are melted. To that is added a cold mixture of 35 grams of lead oxide in 50 grams of coastal oil. The lead oxide mixture should be added slowly while the temperature of the mass in maintained at about 300 to 325ºF. When all of the lead oxide is added, the temperature should be approximately an additional 35 grams of coastal oil is added. This 50% lead soap product can be cooled and used as it is or employed for the production of other lead base lubricating greases.
Another method which has been given in the same patent is:
100 grams of hydrogenated castor oils is melted in 200 ml. of water. To this is added 18 grams of sodium hydroxide dissolved in 36 grams of water. This mixture is heated until saponification is substantially complete after which 70 grams of lead acetate dissolved in 300 grams of water is added. After stirring for 5 to 10 minutes, just enough acetic acid is added to make the mixture react acid to phenolphthalein. A white precipitate is formed which is the lead soap of 12-hydroxy stearic acid. This soap is filtered from the solution and is then washed several times with hot water after which it is dried at about 105ºC. This soap should contain about 26.5 percent of lead.
Normal Soaps
After preparing the soap base, as described above, such preparation is to be dissolved in an oil of 2000 SUS at 100ºF, by heating to 310ºF, after which it is poured into a metal pan and cooled to room temperature in 12-12 hours.
Various modifying agents, added to the above type of lubricating grease just before it is poured, will tend to produce, a smoother texture and will also reduce the milling time after cooling. The additives used are : 0.1% of butyl carbitol; 0.3% of triethanolamine: 0.2% of cyclohexylamine: 0.2% of oleic acid: 0.5% of acetylated castor oil.
It should be noted that if the lead soap of polyhydroxy stearic acid are used, still other solubilizing agents may be required to keep the soap in suspension in lubricating oils. A suggested method is to include an organic soap of a mono or polyhydroxystearic acid, such as an ethanolamine soap of hydroxystearic acid.
Another US Patent 2,292,672 describes a semi-fluid neck grease from a normal lead soap. The ingredients consists of 1.17 pounds of litharge 2.94 pounds of hydrogenated fish oil fatty acids, 40 pounds of blown asphalt, 25 pounds of oil of 175 to 210 SUS at 210ºF and 31 pounds of oil of 70 to 150 SUS at 100ºF.
The litharge is added to a small amount of the mineral oil in a processing kettle and stirred into a smooth paste. The fatty acids are then added along with an equal amount of oil. During agitation, the temperature is maintained at about 200 to 200ºF while the water formed in the reaction is raised to 275 to 300ºF and maintained at this point until the reaction is complete. The remainder of the oil and all of the blown asphalt are then added and mixed thoroughly.
Lead based lubricating greases of this type, when completely dehydrated, are not as water-resistant as those containing a small amount of water. Therefore, when the batch has cooled to 210 to 220ºF, about 0.5% of water is added. Agitation is continued until the temperature drops to 100 to 120ºF before the lubricant is filled into packages.
Preparation of Lead Base Lubricating Greases:Mixed Soaps
A US Patent 2,295,189 describes the method as below:
To prepare a 50% lead fish oil soap base, 12 pounds of litharge and 5 pounds of oil of 95 to 100 SUS at 100ºF were added to a steam jacketed, positively scraped mixer and stirred until a smooth paste resulted. Twenty two additional pounds of the oil and 15 pounds of menhaden oil were then added. Agitation was continued and the mass was heated to 300 to 325ºF for four hours to complete the reaction. This concentrate is then ready to use for the formation of the final product.
In making the complex-lead-sodium fish oil soap, 31.8 pounds of the 50% concentrate, described above, is added with an equal weight of oil to a fire heated kettle. The mixture is heated to 160 to 200ºF and 3 pounds of sodium hydroxide, as a 48ºBe solution, is added. The temperature is then gradually raised to 400ºF. The resulting product is a highly heat resistant material which may be blended to form a variety of lubricants.
Grease are the important items for maintenance and smooth running of various machineries, automobiles, equipments, instruments and other mechanical items. The Greases and Lubricants are required in almost all Engineering Operations. Completed with the help of machineries. It adds the longitivity and durability of machineries by reducing the frictions between two parts. Several formulations applicable for different parts are mentioned here, with the use of indigenously available raw materials and plant & machineries. The quality products can be manufactured by the manufacturers in accordance with the norms of Bureau of Indian Standards specifications.
The grease manufactured by using above formulations are used for lubricating wheels of car and truck.
Take 20 kg. stearic acid and 20 kg. paraffin oil in a kettle. Heat these ingredients till complete melting takes place. Now add 4 kg. of lime water paraffin oil with continuous agitation where the grease reaches the temperature of 40ºC, pack it in desired packings.
This is stable when repeatedly heated above 212ºF consists of fatty acids, soaps and special low viscosity index oil.
This is used for the lubrication of water pumps. It essentially consists of an emulsion as well as a soap thickened oil.
A calcium base lubricating grease is loaded with finely dispersed metallic lead in order to increase density of the lubricant and make it non-floating.
A frost removing grease is a non-corrosive, paste-like composition for preventing tenacious adhesion of frost to chilled surfaces. It contains 60 to 80 percent of white mineral oil, 15% of calcium chloride, the remainder being a calcium soap to provide a grease-like consistency.
Composition for a wire rope lubricant which has improved internal friction and fatigue life with both anti-rust and low temperature qualities:-
The above ingredients are heated to a temperature of 500ºF.
To this is added 30 to 60 percent of an oxidised asphalt having a viscosity at 210ºF of 100 to 500 S.U.S. This mixture is cooled to 225ºF, after which 8 to 12 percent of lead oleate is added.
1 part of oil soluble in methyl cellulose and insoluble in water (having one methoxy group per glucose unit) is dissolved in 30 parts of water. To this solution is added a mixture of 16 parts of mineral oil and 11 parts of hydrogeneated fatty acids and the resulting emulsion is heated to 160ºF, 3.5 parts of 45% sodium hydroxide solution is added to this emulsion and agitation is carried on for 3 hours while the mixture is heated to 280ºF. The lubricating greases is finilly dehydrated at 330ºF. Polyvinyl alcohol or casein, or gelatin or natural gum may be used as thickeners.
260 pounds of tallow fatty acids, 50 pounds of tallow and the 70 gallons of low viscosity oil are warmed to 120ºF in an open kettle. 46.8 pounds of solid caustic soda (as 35 percent solution in water) is the added while the kettle contents are agitated. 70 gallons of 150 S.U.S. oil at 100ºF is added and then further 100 gallons at 210ºF is added. The mixture is agituted and then cooled.
13 parts of stearic acid is melted and then 1 part calcium hydroxide is added. Next 1.5 parts sodium hydroxides is introduced, after which heating is continued until the acids are neutralized. Finally, 3 parts aluminium sulphate and 2 parts magnesium chloride are added in the solution.
Lead Base Lubricant Grease
Procedure
Add tallow and the sodium mahogany soap in a mixer, together with about 5 lbs. of oil. Then, heat the mixture to a temperature of 160-180ºF. Add caustic soda lye (48ºBe). Maintain the temperature of this whole mixture at about 190ºF until the mixture thicknes. Now add litharge and slowly raised the temperature at about 500ºF. Hold this batch until the temperature becomes down. Now add oil and agitate continuously until the temperature is at 300ºF. At this stage fill it into containers.
(1) As per U.S. Patent No. 1,477,611 following lubricant grease to be used on heavy bearing surfaces:-
(2) Lubricant grease for extreme temperatures, used in Engines, etc. U.S. Patent 2,349,358.
(3) Mixed soap lubricating grease: Water insoluble, transparent, temperature stable and reversible:-
The fatty acid and one-third of the oil are to be heated to 150ºF and the barium hydroxide should be added. Stirring and heating to be continued until a temperature of 200ºF is reached, then another third of the oil should be added. After this the aluminium stearate is to be dispersed in the remaining oil and is added to the bulk. Temperature should be remained between 300 and 350ºF. It is to be filled into containers when the mass is thin and liquid.
In compounding the lubricating grease, the acid and about one fourth of the oil is charged to a free-heated kettle and mixed and heated to about 150ºF until the acids dissolves in the oil. The lithium hydroxide, dissolved in boiling water, is then added. Heating and agitation be continued and temperature should be raised to 200ºF. Then aluminium stearate is added. In the whole process agitation should be continued, adding lubricating oil. After the mixture becomes liquid, at about 370ºF, the phenyl alpha naphthylamine and zinc naphthenate, is to be dissolved in the remainder of the oil, is added. Heating is to be discontinued and the lubricating grease is stirred until the temperature drops below 100ºF. The bulk is ready for packaging.
Heat carefully with constant stirring until the solid material is dissolved and the solution begins to boil, then cool to room temperature with stirring. To increase fluidity add more glycerin; to increase greasiness add more manintol.
Lubricating oils are improved in colour by adding a solution in mineral oil or other blending agent of the product obtained by heating together until fluorescence develops, an acridine, rhodamine, cosine, or eurhodine dye with stearic, acid and a water insoluble soap. Soaps specified are aluminium stearate magnesium stearate, oleate, or resinate, and lb. Of aluminium stearate are heated to 120ºC until the fluorescence is a maximum; the mixture is cooled, pulverized, and dissolved to a 10% solution in a mineral oil, miscible with lubricating oil 0.25-0.5 gal. Of the solution is added to 100 gal. Of lubricating oil.
Stock of about 68 viscosity index is subjected to the simultaneous action of 10% of aluuminium chloride and 10% of fullers earth at a temperature of about 350ºF to ½ hour.
If lubricating oil is shaken with phenol, the lower layer consists of oil and impurities in phenol; the upper layer consists of phenol dissolved in pure oil. The phenol is removed and recovered by distillation or by washing with sulphuric acid.
Fat and Oil Bleaching
In refining fats and oils the colour is improved by adding 8 to 10% soap stock to fat.
"Complex", is theoretically described as "A complex salt or absorption compound", but in manufacturing industry it is really meant "to refer to the soap modifications; i.e. hydrated soaps, basic soaps, and soaps associated or combined with various other compounds, as complex soaps"; Since many such soap combinations, and lubricating greases formed from them, has been accepted over a considerable period as normal products, they are important as well for a manufacturer like other grease products.
There are many kinds of complex soap lubricating greases, such as hydrated soaps, hydrated calcium soaps, hydrated aluminium soaps, barium soaps, lithium soaps, strontium soaps, acid soaps etc. only some of the important of these complex soap lubricants will be discussed here.
The particular characteristics which make soap-salt complexes valuable for the manufacturer of lubricating greases are:
(1) Their solubility characteristics : (2) their freedom from change in aggregation state over a wide temperature range; and (3) their stability as regards dissociation of soap and salt.
Most soap thickeners for lubricating fluids should be soluble or dispersible in the fluid at elevated temperatures, and, as the temperature decreases, crystallize in fibrous crystallites which serve to immobilize the fluid. Still, all complex soaps formed from metal soaps and salts will not exhibit this characteristic. Some will not exhibit this characterstic. Some will be so soluble that they will fail to crystallize and consequently no plastic body will form. Other complexes may be too insoluble and either not disperse, ever, by a proper choice of the metal, of the higher fatty acids and the low molecular weight acids, suitable complex soap can be found for the production of lubricating greases.
The most generalized claim for soap-slat complexes is to thicken the lubricating oils. It covers complexes at least two metals, one of which must be polyvalent. This polyvalent metal is preferably selected from the alkaline earth metals, such as : barium, calcium, magnesium, and strontium. But, aluminuim, beryllium, zinc, cadmium, boron, tin, zirconium, cerium, vanadium, antimony, bismuth, arsenic, copper molybdenum, germanium, columbium, chromium, selenium, tellurium, tungsten, manganese, iron, cobalt, nickel may be used as the polyvalent metal.
The second metal of the soap complexes must be different from the first and is preferably an alkali metal, name : lithium, sodium, potassium, or cesium, or an alkaline earth metal, such as : barium, calcium, magnesium or strontium. The other metals listed above may also be taken as substitutes. These soap complexes are not limited to the use of two metals, as three or even more metals can by provided at least one is polyvalent.
The saponifiable materials which contain high molecular weight fatty acids, either in a combined or a free state, include tallow, lard oil, hog fat, horse fat, stearic acid, oleric acid, higher molecular weight acids resulting from the oxidation of petroleum fractions, rosin and other related products, higher molecular weight naphthenic acids, sulfonic acids, and saponifiable waxes such as beeswax, sperm oil, degras, etc.
Suitable organic acids of low molecular weight whose salts may be employed for formation of complexes include monocarboxylic and polycarboxylic acids containing less than carbon atoms per molecule. Included in such groups are formic, acetic, propionic, valeric, oxalic, malonic, succinic, the low molecular weight alkyl and aryl sulfonic acids, and the low molecular weight carboxylic acids such as glyceric, glycolic, thioglycollic, etc., heterocyclic carboxylic acids, such as furoic, etc. and phenolic and thiophenolic compounds such as phenol, cresol, thiophenol, etc.
There are numerous methods for manufacture of metal soap-metal salt complexes. Some of them are:
1. The one method for the formation of the complex soaps, and the resulting lubricating greases, consists of starting with a normal soaps, which may be preformed or produced by reacting a saponificable material with a basically reacting compound. Such normal soap is dissolved in all or a portion of the mineral oil to be used, and subsequently a solvent is added. Agitation and heat are maintained on this mixture until all or a portion of the polar solvent is removed. Once the complex soap is formed, the production of the lubricating grease follows the usual pattern.
2. Another method for the manufacture of complex soaps and the resulting lubricating greases is to dissolve a normal metal soap in mineral oil, add to this solution a quantity of basically reacting compound, followed by sufficient low molecular weight carboxylic acid to neutralize a portion, only, of the base present. Finally, carbon dioxide is led into the mixture to neutralize the remaining base. A modification of this method is to mix mineral oil, normal metal soap, metal salt of a low molecular weight carboxylic acid, saponification reagent and water, and contact the mixture with carbon dioxide until the product is substantially neutral. The neutral product may then be dehydrated and finished in a normal manner.
3. Still another method is one in which a dry metal soap-metal salt complex is formed without any mineral oil being present. A suggested formula and procedure is given below:
The materials are added to a steam jacketed kettle, mixed and heated to 240ºF to effect saponification and partial dehydration. After cooling to room-temperature a brittle solid is obtained. This is removed from the kettle, powdered, and returned to the vessel. This powder is then heated in contact with air for 4 hours at a temperature of 300 to 350ºF. Under these conditions the free calcium hydroxide content deceases to a value of 0.1% and the water content to 0.1%. Under these conditions the free calcium hydroxide content decreases to a value of 0.1% and the water content to 0.1%. Then this product is being dispersed in a mineral oil.
The complex greases are produced from a mixture of low molecular weight aromatic carboxylic acids and higher molecular weight acids, are again a combination of co-precipitating water solutions of soaps of alkali meatls with an aluminium salt.
Examples of such soaps are aluminium benzoate stearate, aluminium toluate stearate, and aluminim didodecyl benzene sulfonate. These soaps are said to impart high melting point and resistance to emulsification with water to lubricating greases. For instance, 12 parts of aluminium benzoate stearate is dispersed in 108 parts of refined paraffin oil by heating to 450º F. The resulting product is a light brown, translucent lubricating grease with a dropping point of over 400ºF.
An aluminium-barium complex lubricating grease can be formed thus:
The aluminium stearate is dissolved in about one-half of the oil, the barium hydrate, urea, and acetic acid are then added during constant agitation. The reaction mixture is heated to a temperature of 300 to 350ºF for a period of two hours, after which the remainder of the lubricating oil is added while the batch cooled to about 200ºF. Finally 0.05% of water is added to improve the body and smoothness of the lubricant. This product contains 3.9% of metal soap complex.
A US Patent 2,595,556 gives the following ingredients to form such a grease:
The tallow, tallow fatty acids, 14 Kg. of oil, and the barium hydrate are charged to a steam jacketed grease kettle and heated about 235ºF with agitation. The urea and an additional 14.0 Kg. of oil are then added and the mixture is heated to 300ºF while agitation continues. After 1¼ hour at this temperature, the batch is cooled to 200ºF while mixing is continued for 1 hour. The remainder of the lubricating oil is then added while cooling the charge to 200ºF, after which 0.5 kg. of water is added. Dehydration is then accomplished by heating to 285ºF. The finished lubricating grease is slightly fibrous and had an un-worked penetration of 272.
For barium-sodium complex greases the following formula is found suitable:
The method of production is the usual compounding procedure followed by dehydration to the extent of giving the finished product increased temperature stability.
A calcium soap-calcium chloride complex formula is:
The hydrogenated fish oil, calcium hydroxide, calcium chloride and a trace of water are stirred and slowly heated to 450ºF. With the calcium chloride present, it is said to be necessary to heat the mixture to 450ºF in order to form a calcium soap. After all the water is removed at 450ºF the mineral oil is mixed in at such a rate that the temperature is maintained at 400 to 450ºF. Following the oil, to ethylene glycol monobutyl either is added and the batch is permitted to cool, without any agitation, to room temperature after which it is stirred until smooth. The melting point of the product is 375ºF.
There is a considerable choice of either mineral oils of soap stocks for the manufracture of these calcium soap-calcium chloride lubricating greases. The points which are emphasized about the manufacture of such lubricanting greases are that the soap be prepared before mineral oil is added and the reaction carried out at 400 to 500ºF.
A reversible high-temperature lubricating grease can be prepared by the following procedure:
A steam jacketed kettle is charged with 3000 grams of a 30% concentrate of calcium sulfonate of approx. 900 molecular weight, and 3000 grams of napththenic oil of 65 viscosity SUS at 210ºF. This mixture is agitated and heated to 180 to 200ºF, after which 180 grams of calcium acetate as an 18.4% aqueous solution is added. Five drops of an organic silicon polymer are added to control foaming and the temperature of the charge is readily increased to 250ºF. Cold water is then poured into the kettle jacket and agitation continues until the charge reaches a temperature of 100ºF, at which point the lubricating grease is packaged. The finished product has a melting point above 400ºF, and unworked penetration of 242 and a worked penetration of 278.
The recommended ingredients for producing a calcium sulfonate complex for thickening lubricating oils is as follows:
The procedure for compounding is to dissolve the calcium sulfonate concentrate in half the lubricating oil to be used and add the calcium stearate while agitating. When a paste is obtained with the above mixture, the calcium acetate is added as a 15% aqueous solution. This addition is gradual and when the mixture acquires the appearance of a homogeneous, milky emulsion, heating is started. When the charge is substabtially dehydrated, at about 280ºF, heating is discontinued and the remainder of the oil is added. Agitation is continued until the temperature drops about 280ºF, heating is discontinued and the remainder oil is added. Agitation is continued until the temperature drops to about 150ºF when the lubricating grease can be drawn. The lubricating grease thus formed is a stable, having worked penetration of 285, and dropping point of 425 to 450ºF.
Another Example is:
The tallow is mixed with 225 g. of the oil and the slaked calcium oxide is added. The batch is heated and mixed to effect saponification, after which the mass is cooled and another 225 g. portion of oil is added. The sodium hydroxide (as a solution) and the urea are then added to the mixture, which is re-heated to 300 to 350ºF for a period of 45 minutes. After cooling to 200ºF the acetic acid is added to neutralize the remaining sodium hydroxide. A substantial neutral lubricating grease resulted with a melting point of 275ºF.
A preparation of lithium soap complex lubricating grease is described in a US Patent 2,417,428 in which 980 grams of stearic acid, 3940 grams of sperm oil, and 5000 grams of waxy gas oil are mixed in a steam jacketed kettle before a slurry of 1130 grams of lithium monohydrate in 1060 grams of gas oil is added. While the temperature is increased to 300ºF the remaining gas oil, consisting of 10,000 grams, are added. The batch is then cooled to room temperature and worked through a 200 mesh screen.
The finished lubricating grease is smooth, buttery, and translucent. This product has an unusual character i.e. it bodied up when heated to 200 to 300ºF and yet when it is cooled to room temperature the lubricant grease returns to a soft consistency. A lubricating grease containing both the lithium soap of a fatty acid and lithium acetate has the following ingredients:
Complex Strontium Soap Lubricating Greases
One method of the preparation of lubricating grease from a strontium soap complex is as follows: 109 grams of cottonseed oil (approx. 0.38 equivalent), 16 grams of sperm oil (0.04 equivalent), 60 grams of a naphthenic type SAE 60 grade lubricating oil, and 102 grams of strontium hydrate (equal to 46.6 grams of strontium hydroxide or 0.76 equivalent), are heated at 200 to 300ºF until the vigour of the reaction subsided. Then an addition 250 grams of the some oil added, the mixture is heated for about 12 hours at about 500ºF at which time no substantial amount of free alkalinity remains. Finally 466 grams of the oils is stirred in, and the mass is cooled to room temperature.
An Extreme Pressure Lubricating Grease in which the preferred thickening agents for lubricating oil are strontium sulfonate, calcium acetate, and the calcium salt of ethane sulfonic acid:
The ethane sulfonic acid is the dissolved in twice its weight of water and neutralized with the hydrated lime. When the reaction appears to be complete, the neutralized solution is added to a blend of the strontium sulfonate and the oil. The batch is stirred at 180 to 200ºF until no solid particles remained. Then the calcium acetate is added as a 20% aqueous solution and the mixture is dehydrated slowly, with stirring, until a temperature of 300ºF is reached. The product is cooled to room temperature without stirring.
While the full name in the international dictionary complied by the "Permanent International Association of Road Congreses" is still gives as "Asphatic Bitumen", there has of recent years been a movement to recognize the single word "Bitumen". This was dealt with in a paper read before the Institute of Petroleum, and described as follows:
Bitumen: A non-crystalline solid or viscous material having adhesive properties, derived from petroleum either by natural or refinery processess and which is substantially soluble in carbon disulphide.
"Bitumens are black or brown in colour. Whilst they may occur naturally, they bare usually made as end products from the distillation of, or as extracts from, selected petroleum oils."
Bitumen is normall graded according to its softening Point R & B, its Penetration, or a combination of these two properties. Thus, hard grades having R & B softening points above 80º to 90ºC grade, 110º to 120ºC grade, and so on (frequently prefixed by the letter "H"). Softer grades up to 500 penetration at 25ºC are named according to their penetration only, such as 60-70 pen, 180-200 pen, and 400-500 pen, while in the case of blown or oxidized grades such as 85-25, 115-15, and 135-10 the first figure refers to the softening point and and the second to the penetration.
These two tests are now too well known to need description here, but it is important to consider how the temperature susceptibility of bitumen may be deduced by their aid. The penetration index method of Pfeiffer and van Doormaa is now a recognized way of establishing the extent of which the consistency of bitumen changes with changing temperature. If the logarithm of the penetration is plotted against the temperatute T, practically straight lines are obtained, is that
log pen = AT + K
where the slope A represents teh temperature sensitivity of the logarithm of the penetration. When these lines are extrapolated to the temperature of the R & B softening point, the corresponding penetration proves to be in the neighbourhood of 800. Therefore, A can be calculated from two penetrations at different temperatures or approximately from one penetration and the R & B softening point. An index figure PI is used fo indicate this temperature sensitivity according to the relation.
A = d log pen/d T = (20 - PI)/(10 + PI) Ã- (1/50)
If the temperature is expressed in degrees Centigrade, one point in teh penetration index corresponds to a difference of about 15 per cent in A.
Chemically, bitumens consist in the main of compounds composed predominantly of hydrogen and cabron. While many types of hydrocarbon may be present, bitumen is in general prepared from crude oils which are rich in arematics and naphthenes. Small quantities of sulphur, nitrogen, and oxygen are present in a combined state. Knowledge of the form in which these elements are attached is still very incomplete, but much of the sulphur is bound to the aromatic constituents, while the oxygen is present partly in the form of acids. Similarly, such metals as vanadium and nickel may be found, while salts of many other metals are frequently present in traces.
The nature of the organic constituents can be approached by the following methods:
Aromatic and unsaturated hydrocarbons may be sulphonated by means of 98 per cent sulphuric acid to give water soluble sulphonic acids and saturated hydrocarbons. The latter unsulphonated part amounts typically constituents will, however, remain attached to the sulphonic acids, and thus will not be accounted for. It will be seen that this method of separation does not lead very far.
Bitumen is by defination " substantilly soluble in carbon disulphide". The very small amount insoluble (typically one part per thousand or less) is mainly inorganic. When carbon tetrachloride is used as the solvent, rather more insoluble matter is found, although still very small, e.g. 0.2 per cent, except in the case of deeply cracked or highly oxidized varieties. These insoluble constituents, which are strongly aromatic, are known "carbenes".
When volatile saturated hydrocarbons, such as IP petroleum spirit (sulphonated 60º to 80ºC boiling range petroleum spirit) or n-pentane or n-heptane are used as the solvents, "asphalteness" are obtained as a precipitate, the remainder in solution being known as "malthenes." The quantity and nature of the asphaltenes will vary somewhat according to the solvent used, but broadly the asphaltenes and malthenes may be said to correspond with the micelles and the intermicellar liquid respectively of the colloidal bitumen system. By X-ray and combustion analysis asphaltences are shown to be typically very aromatic in nature, and can be considered as consisting of aromatic hydrocarbons having paraffinic side chains to varying extents, depending on the crude oil used and the manufacturing conditions. While the malthenes may be separated into so called "oils" and "resins" by adsorption on active earth and extraction with solvents such as the procedure developed by Strieter, this is only a very arbitrary separation. The latest approach to the chemical composition of the malthenes of bitumens of different origins is by means of combustion analysis and Waterman's ring analysis. From the former the C-H ratio may be deduced, while the latter may give approximate information regarding the total quantities of the three groups of basic forms of hydrocarbons, expressed in the percentage of carbon atoms occuring in paraffinic, naphthenic, and aromatic structure.
As indicated above, bitumens are typically collodial systems, so that generally speaking they do not behave as Newtonian liquids, except in the case of a very limited number of "petroleum resin" type bitumens substantially without asphaltenes. The disperse phase components of the malthenes, was referred top as "micelles" by Nellensteyn, who first considered bitumen as a colloidial system.
From the foregoing it will be appreciated that a relatively aromatic continuous phase will tend to peptize teh micelles and give a bitumen behaving as a sol, while a degree of flocculation will lead to a gel structure. In this way, depending upon the amount of asphaltenes present and the "aromaticity" of the malthenes, a wide variety of systems is possible from those showing purely viscous flow to the highly gelled type generally produced by oxidation or "blowing". In the oxidation process at elevated temperatures additional asphaltenes are formed largely at the expense of the more aromatic part of the malthenes. This results in an increase in the amount of disperse phase and a decrease in teh aromaticity of the continuous phase, which tends towards flocculation of the former, thus intensifying the gel structure. These bitumens exhibit elasticity and thixotropy, and when very highly gelled may actually sweat oil, thus exhibiting a form of syneresis.
In view of the solid or semi-solid nature of bitumens and the consequent relatively high temperature necessary to reduce their viscosity sufficiently in practical application, two main artifices have been employed to permit, where practicable, of working at prevailing atmospheric temperatures or at least at appreaciably reduced temperatures.
It is very fortunate and at the same time perhaps rather remarkable that such a complex material as bitumen can, as a rule be emulsified with water fairly easily and, moreover, that it can be re-deposited from the emulsified state in a controllable manner. Thus emulsions may be prepared of varying degrees of stability, being described as "labile", "semistable," "stable" etc. For read applications with bitumens of 100, 200, and 300 pen, soap solutions and protein type stabilizers are employed. The bitumen is dispersed in an aqueous continuous phase, the size of the bitumen particles being typically of the order of 1 to 3 m. Stable emulsions for industrial applications may be made with clay as the emulsifier. In this case quite hard bitumens can be employed, and the dispersed particles are ellipsoidal (cigar shaped) and typically of 10 to 20 m in length.
The other method of arriving at a workable viscosity at relatively low temperatures is that of dissolving the bitumen in volatile solvents which will subsequently evaporate at a suitable rate and leave a film of solid bitumen where it is wanted. Such a solution is known as a "cutback," and bitumen in this form has considerable advantages for several forms of road work. In addition to permitting of mixing at lower temperatures (and this applies to both the aggregate and the binder), another advantage in the case of precoated stone is ability to stockpile and lay at a later date, thus making the process more flexible. The basic bitumens used are generally in the range of 60 to 200 pen at 25º C for temperate climates, while the solvents employed are typically light kerosines and creosotes to the extent of some 10 to 15 per cent. Bitumen paints for industrial purposes are really another form of cutback. In this case the bitumens are generally harder and the solvents as volatile as practicable to permit of rapid drying, white spirit and solvent naphtha around 50 per cent in amount being normal practice.
It is not proposed to take up any of the space allotted to this chapter in describing the well established standard methods of testing bitumen. For details of these the reader is reffered to the current issue of "Standard Methods for Testing Petroleum and its Products", and for their interpretation significance to Part V. A few typical composite analyses of commercial bitumens is, however, appropriate according to standard methods and to special methods, some of which have already been referred to for elucidating constitution.
The 1946 edition of "Modern Petroleum Technology" described one or two special tests, such as the Fraass breaking point and the shatter test, which were then relative newcomers to bitumen testing technique. In the same way it is appropriate that reference should be made here to recently developed methods of test not hitherto described, which at the same time are something more than research tools only. In this category may be mentioned the following two methods, which have been published since the issue of the 1946 edition and which constitute major advances in testing technique.
As a result of considerable research towards arriving at a method which would get as near as possible to the true flash point of a cutback bitumen, a method was developed using a modified form of Abel apparatus. This now appears in "Standard Methods for Testing Petroleum and its Products" under the heading "Flash-Point (Closed) of Cutback Bitumen, IP 113. "It has been shown by experiment that the result obtained by this method do not differ appreciably from the minimum flash point of the material under equilibrium of temperature and vapour pressure.
Attention has rightly been drawn towards the development of more satisfactory methods of determining the amount of soluble bitumen present in mixtures with other materials, such as mineral aggregates, the need being particularly great in the case of asphalt road materials. Here there is a special call for greater speed while maintaining accuracy, and the use of methylene chloride, a new solvent for this purpose, has met with considerable success.
All bitumens are thermoplastic, but they do not all behave as Newtonian liquids, and the flow properties of the various types are of great importance in their practical behaviour. Thus it is axiomatic that bitumens of a certain rheological type will be chosen to meet particular practical requirements according to the mechanical stresses prevailing.
Saal divides bitumens into three groups:
(1) Those which behave entirely, almost entirely, as Newtonian liquids. Thus upon deformation the rate of shear is proportionate to the shearing stress applied. Elastic effects are either negligible or absent altogether.
(2) Those which, upon deformation at normal temperatures, show quite distinct elastic effects in addition to what may be termed Newtonian proportionality between rate of shear and shearing stress occurring the initial stage of the deformation.
(3) Those which at normal temperature show almost complete resilience after comparatively slight deformation. Greater deformations are permanent to a certain extent, but the rate at which the permanent deformations are effected is no longer proportionate to the shearing stress. The elastic effects are greater than in the second group.
Bitumens of the first group are either substantially without a disperse phase or else the asphaltenes are strongly peptized by virtue of the nature of the malthenes, as for example when the continuous phase is highly aromatic in nature. Those of the second group are elastic sols. The "steam-refined" bitumens of Mexican and Venezuelan origin, so well known and widely employed for road and other applications, come in this class. Alternatively, bitumens of this type may sometimes be manufactured from crude of low initial asphaltenes content, such as certain Middle East crudes, by means of a small degree of oxidation at high temperatures. These are becoming known as "semi-blown" bitumens. It will be realized from the fore going that "straight-run" bitumen, or one of any particular origin. In the interest equally of supplier and user, the specification should be concerned with tests based on rheological properties which have a known correlation with practical performance in the application for which the material is to be used.
Bitumens of the third group, which, as indicated above, are of a gel type, thus processing marked structure, generally result from appreciable "blowing" at high temperatures. Those bitumens known commercially as "blown grades" are typical of this group.
Early in this chapter the penetration index was briefly dealt with in connexion with the deduction of temperature susceptibility. An account of the relationship between this index and rheological type of bitumen follows. Bitumens of penetration index of less than minus 2 constitute the purely viscous type of group 1, and may be reffered to as the "Pitch" or "Z" type. Bitumens in the range minus 2 to plus 2 correspond with the intermediate or "Normal" type, while those of penetration index above 2 show increasingly the elastic and thixotropic characteristics resulting from the structure formation of the gel. These belong to the "Blown" type.
A great deal of attention has been paid of recent years of those physical properties of bitumens and cutbacks associated with the wetting of solids, such as stone, and the ability of the binder to remain adherent, particularly under adverse conditions, as for example in the presence of water. Surface tension value of bitumens of varying grade, type and origin have been found to be all of substantially the same order, and it has been concluded that is property alone is of but little help in assessing the adhesion of bitumens to solids.
In considering the interfacial tensions in the system bitumen-stone-water, one outstanding difficulty is the inability to measure the value bitumen-stone. Moreover, it takes considerable time to arrive at a state of equilibrium so that there is virtually no simple contact angles instead advancing and reading contact angles present themselves, the former when bitumen moves on to a surface previously wetted with water, and the latter when a surface coated with bitumen is displaced by one coated with water. The difference between two contact angles may be very great. The factors influencing adhesion are as yet by no means fully understood, and the present state of our knowledge in this respect cannot be adequately summarized in a short space.
It has been found, however, that the addition of small amounts of certain substances, possessing capillary activity can materially reduce the receding contact angle. Iron naphthenate and certain long chain amines, for example may have this effect, which can readily be demonstrated visually by the simple immersion of bitumen-coated stones in water. As yet, however, the value in actual practice on the road of including economically practicable quantities of these materials remains obscure.
Road and Airfield Surfacing
Although there has beenconsiderable development of the utilization of bitumen for a wide variety of purposes, the construction and maintenance of roads and airfields still constitutes the main outlet.
Various types of surfacing are employed, differing somewhat in composition and function, but all based upon the combination of mineral aggregates and bitumen, in which the latter acts as a durable waterproof binding medium. Most of the processes are well established and have attained a high standard of performance, so that there has been little necessity for the introduction of completely new techniques.
Modifications may be made to suit particular circumstances and to accommodate newer methods of manufacture and application, but the choice between the standardize main types of surfacing is primarily a matter of traffic requirements and local conditions.
Rolled asphalt, hot process, remains a popular choice for heavily trafficked areas, and is based upon a suitably chosen mixture of stone, sand, filler, and bitumen, which is mixed, laid, and rolled hot. Bitumens of penetration 30 to 80 are the normal grades for temperate climates, the precise grade being governed by traffic and site conditions.
Mastic asphalt consists of fine mineral aggregate intimately blended with bitumen (of 20 to 50 pen) during a long process of hot mixing, and is laid hot by hand floating. It is particularly suited for heavily trafficked roads in industrial areas, where hygienic considerations demand and impervious surface.
Bitumen Macadam differs from the so-called "Hot Asphalts" in consisting essentially of graded stone coated with bitumen, and characterized by having a relatively open texture. The binder used is frequently in the form of a cutback bitumen, and this permits manufacture at lower temperatures and allows the coated mixture to be laid, when desired, some considerable time after manufacture. One type of this material had been very widely adopted for proving "carpet coats", of ¾ of 11/2 inches thickness, for application to existing roads, which although sound have suffered surface deterioration, and the riding qualities can thus be restored for prolonged periods at reasonable cost.
Fine cold asphalt consists of fine graded stone dust coated lightly with soft bitumen or cutback. Although it is mixed warm, it can be laid cold after almost indefinite storage. The bitumen film facilitates compaction under rolling and traffic to give mechanic strength through interlocking of the stone particles, and imparts cohesion and water resistance to give a durable surfacing, which although of close texture is remarkably free from slipperiness.
Surface dressing is the process of applying a spray of hot bitumen (usually cutback), or of cold emulsion, to the existing road surface and covering with a stone chippings.
Grounding, or penetration method consists of pouring heated bitumen or outback, or cold emulsion, into the interstics of a layer of stone previously spread on the prepared road base.
Bitumen is also used for sealing wood block and stone sett paving and for the expension joints of concrete roads.
In addition to the foregoing conventional types of surfacing there has been some development of special precesses. Wet sand mix was introduced primarily as a wartime expedient for airfield surfacing on sandy sites, but offers interesting possibilities for certain road purposes. By the use of a special cutback bitumen, in conjuction with hydrated lime, cold wet sand, or other aggregate, can be effectively coated with binder to give a durable stable mix.
A process for using the existing the aggregate on a worn road by mixing in situ with bitumen has proed an economical method of reconstruction for lightly trafficked roads. "Mist-spraying" of emulsion provides a means of giving a slight enrichment of bitumen to surfaces deficient in binder.
To contend with the particular problem of the destructure effect on runways of the exhaust from jet aircraft, experiments have been made to cover existing flexible runaways with a jet-resistant mix based on a mixture of fine aggregate, Portland cement, and a suitable bitumen emulsion, conditioned by the inclusion of a small quantity of calcium chloride solution. The resultant asphalt possesses a structure which enables it to with stand the high temperature and blast without disintegation but is sufficiently flexible to avoid cracking under traffic loads.
During recent years there has been a notable development in the mechanization of road surfacing equipment, both for the laying of coated mixes and for surface dressing, with consequent improvement in the speed of execution, quality of finished work, and overall economy.
In road and airfield construction the use of bitumen is associated primarily with surfacing work, and foundations are conventionally of either broken stone on concrete ; there has, however, been some use of coated stone of a size permitting mechanical distribution, and this may well prove a time-saving and economical distribution, and this may well prove a time-saving and economical alternative. Sub-soil stabilization with cutback bitumens and asphaltic oils is another contribution towards foundation construction, but is recognized as being subject to certain climatic and soil conditions. The general process of soil stabilization with bitumen has been carefully explored, and its scope fairly well defined. The main purpose of the added bitumen or oil is to restrain the ingress of excess water to the soil formation, and thus avoid the loss in stability which would otherwise result. The soil itself needs to fulfil certain requirements in regard to inherent with a small quantity (3 to 5 per cent) of the stabilizing oil. The moist soil nodules are thereby enveloped in a water-repellent film and, on compaction, present a stable structure relatively immune from subsequent water absorption.
The use of bituminized fabric membranes for the temporary water-proofing of soil airfields and roads was a wartime device which extended the normal season of operation.
Hydraulic Engineering
The use of bitumen in the sphere of hydraulic engineering is of comparatively recent introduction, but it has already been employed in a variety of projects of extensive size, and its possibilities are becoming increasingly recognized. In canal lining the main object is to conserve water in permeable formations and to resist bank erosion. The treatment includes heavy sprays of blown bitumen or the application of a layer of a suitable bitumen-aggregate combination during the construction of the canal or, in cases where it has to be carried out during service, it has been found possible to apply large mattresses to a reinforced asphalt mixture.
Asphalt mixtures have also been applied in sea-wall construction, to resist wave action, and for the construction and maintenance of break-waters. For breakwaters and causeways of masonry, dilodgement has been effectively prevented, or corrected, by pouring large masses of hot asphalt between and over them to give a mechanical bond. This has proved surprisingly effective, even when applied through an appreciable depth of water. Erosion of bridge foundations and river beds has been similarly treated.
The grouting of stone or concrete block sea-wall facings with filled bitumen has been found to have advantages over more rigid grouts, in being more resistant to wave action, and in permitting deformation of the surfacing without fracture where subsidence has occurred.
Dam and reservoir construction are other projects where the application of an impermeable asphalt layer has proved beneficial.
The use of special bitumen emulsions, containing delayed-action coagulants, for soil injection permits the sealing of previous solids at predetermined depths and locations.
Bitumen enjoys an extensive and diversified use in a wide range of industrial applications. This is based upon its known inherent qualities-themoplasticity, durability, water and weather resistance, thermal and electrical insulation, binding properties, relative economy, etc., but the many processes may vary in the particular emphasis placed on one or more of these.
Bitumenized felts, fabrics, and papers
This group of products-comprising principally roofing felt, dampcoursing, felt base floor covering, and waterproof papers-constitutes the main industrial outlet for bitumen and has the common principle of impregnation and/or coating of a suitable membrane with an appropriate grade of bitumen.
Roofing felt consists typically of a rag felt impregnated with a soft grade of bitumen, and subsequently coated with a blown bitumen, usually admixed with a proportion of mineral filler. A diagrammatic lay-out of the type of plant used for the process is given in Fig 2.
The choice of blown bitumen as the coating illustrates the particular suitability of this material for conditions where the difficult compromise has to be made between flexibility, without cracking, at relatively low temperatures and resistance to flow (and stickiness) at elevated temperatures.
Roofing felts are manufactured in different weights, according to the thickness of the felt base and of the applied coatings, and may be finished with a dusting powder, such as talc, to prevent sticking in the roll, or given decorative finishes with coloured mineral particles. It is normally supplied in continuous sheet form, but may also be prepared in cut-out strip patterns or individual shapes to conform with conventional roofing designs. For "built up" roofing, multiple layers of roofing felt (often uncoated) are applied and bonded in situ with hot bitumen. For the underslating of roofs the roofing felt is frequently reinforced with fabric.
Felt base floor covering is made from a similar raw felt, impregnated with a harder grade of bitumen and printed with a decorative paint finish. Increasing use is being made of such impregnated felt as a base for cork linoleum and for plastic surface finishes.
Performed damp-coursings may consist of a heavy type of roofing felt or of heavily bitumenized fabric prepared in continuours rolls of standard widths.
Bitumenized fabrics are also used for mine ventilation (Bratiice cloth) and for waterproof covers. Mineral fabrics, of asbestos or glass, provide alternatives to the vegetable felts and fabrics for many of the above purposes.
Waterproof papers for packing and building purposes include several processes of bitumenization. Single-sided or double-sided coated papers are prepared by a surface application of hot bitumen to one or both faces of the paper. Duplex, or union, papers consist of two (or more) sheets united with a continuous layer of bitumen, sometimes reinforced with continuous fibers. The type of plant used for the manufacture of such papers is indicated in Fig 2. For special purposes one sheet of paper may be replaced by fabric or metal foil. Papers impregnated with soft bitumen are also manufactured, and are used, for instance, in the manufacture of electric cables.
Bitumen may alternatively be incorporated in the form of emulsion added to the fiber before the paper is formed, thus giving integral waterproofing, and a similar process is utilized for heavier boards.
Mastic Asphalt for Building Construction
Mastic asphalt, consisting of a mixture of fine limestone dust, or powdered rock asphalt, and bitumen, applied hot in situ by hand floating is an established practice for the flooring, roofing, and damp-coursing of buildings. Special compositions are prepared for industrial installations where elevated temperatures and chemical action may be encountered as, for instance, in tank lining.
Pipe Protection
Buried steel pipelines, for oil and water, need protection against soil corrosion, and this is normally effected by the application of heavy coating of blown bitumen, usually admixed with mineral filler and frequently reinforced with a fabric bandage. Water mains may be additionally lined with similar filled bitumen for internal protection and increased carrying capacity by reduction of friction.
Where such treatments are applied at the pipe works (a virtual necessity in the case of lined pipes) the prepared pipes are first dipped in a bath of molten bitumen to act as a primer. For lined pipes the hot bitumen is then poured into the warm pipe, rotating between chucks to give uniform distribution, and rotation continued until the lining has cooled. The coating is then applied hot, either by extrusion on to the revolving pipe or conveyed there to by a fabric or paper bandage passing through a bath of the molten bitumen. The grades of blown bitumen used are chosen to give a tough protective layer, resistant to flow at atmospheric temperatures and to soil pressures when buried, while being sufficiently resilient to avoid damage from shock during transit or subsequent pipe movements.
Where the coating is applied on the site of laying, a similar principle is followed, with suitable modifications according to the facilities available.
Electrical Purposes
The protective and insulating properties of bitumen are utilized in the electrical industry for the outer protection of heavy cables and for a variety of filling and sealing compounds of joint boxes and other electrical apparatus. Such compounds are normally prepared by specialist firms as proprietary products.
Other Uses
Among the other diverse uses of bitumen, mention may be made of thermoplastic moulding compounds, cold store insulation, cheap protective paints and waterproofing composition, marine glues, heavy lubricants, rubber plasticizers, and coal briquetting.
Considerable discrimination is obviously necessary in the choice of particular grades and types of bitumen for individual purposes, and extension collaboration between supplier and user has enabled the present wide scope to be developed and future trends to e explored.
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