Food and Technical Grade White Oils and Highly Refined Paraffins
WHITE OILS
Introduction
The term “while oil” refers lo highly refined distillate fractions
in the lubes boiling range whose water white color (and
therefore the “while” descriptor) is due to the almost complete
absence of aromatics as well as sulfur- and nitrogen-containing
compounds. While mineral oils, also known as “paraffin oil,”
“liquid paraffin,” and “while mineral oil,” are liquids at room temperature
and are predominantly mixtures of isoparaffins and
naphthenes with lesser amounts of n-paraffins. White oils are
manufactured for use in agriculture and the chemicals and
plastics, textiles, food, Pharmaceuticals, personal care and
cosmetics industries, and their purity is regulated in most
countries. The manufacturing objective is to produce oils of high
purity and low toxicity with the composition, being almost entirely
saturated hydrocarbons. Toxicity specifications require
polynuclear aromatic hydrocarbons (PAHs) to be at very low levels.
White mineral oils were first developed by a Russian
chemist, J.Markownikoff, and the first plant for their manufacture
was set up in Riga, Latvia, around 1885. When European supplies
to the United States were cut off during World War I, the L.
Sonneborn Company was the first US company to begin to
manufacture them and used Pennsylvanian crude. This was later
followed by the Pennsylvania Refining Company (Penreco) and
many others. The major North American manufacturers now are
Sonneborn, Lyondell-Citgo, Penreco and Petro-Canada.
White oils are of either “technical” or “food/medicinal”
grade, with the food/medicinal grade having tighter specifications
and therefore requiring more stringent processing. Technical grade
white oils are employed as components of nonfood articles
intended for use in contact with food (e.g., in food machinery
lubricants) and in the United States are governed by Food and
Drug Administration (FDA) regulations (21 CFR 178.3620(b)). For
technical grade white oils, color must be better than 20 on the
Saybolt scale (ASTM D156), however, most technical grade
material made today is +30, the same as food grade.
Food/medicinal grade specifications (21 CFR 172.878) are
designed such that products meeting these specifications can
be safely used in food and pharmaceuticals. The specifications
control PNA levels by the UV absorption limits given in Table 2
and by the carbonizable substances lest (ASTM D565).
Food/medicinal oils are frequently referred to as meeting
United Slates Pharmacopeia (USP) or National Formulary (NF)
specifications, usually written as “meets USP/NF specifications.
USP and NF specifications differ only in specific gravity and
viscosity. USP oils must have specific gravities between 0.845
and 0.905 at 25°C and have viscosities greater than 34.5c St at
40°C. NF oils must have viscosities less than 33.5 c St at 40°C
and must have densities between 0.818 and 0.80 at 25°C. Further
details on specifications are provided later. In addition, food grade
while oils must satisfy the following:
Second-Stage Operation
The second stage is said to operate “cold” (i.e., greater than
150°C but less than 340°C) and universally employs a very active
hydrogenating catalyst (e.g., a noble metal such as platinum or
lead or a Raney nickel-type catalyst) whose purpose is to
hydrogenate remaining aromatics, particularly polyaromatics. The
“cold” operation is to keep the aromatic saturation temperature
in the region of kinetic control, particularly for polyaromatics.
At higher temperatures, thermodynamic control can take over
and cause reversible formation of polyaromatics from three-ring
and higher naphthenes. This eventuality would cause the product
to fail specifications for polynuclear aromatics levels. If the
reactor temperature is too low, the product may also fail
specifications due to kinetic failure (i.e., insufficient removal of
PNAs).
Process operating conditions for the BASF second-stage unit
are given as a 120°C to 300°C reactor temperature, 10 to 20 MPa
hydrogen partial pressure and 0.1 weight hourly space velocity.
In the case of both stages, increased hydrogen partial pressures
will obviously assist in meeting product specifications more
easily.
Products
To address any concerns that there might be chemical
differences between white oils produced by the acid process and
hydrotreatment, the mass spectra of Lyon-dell Duotreat products
were compared with those from acid treatment. The authors
concluded that there was indeed little difference at the same
viscosity level. White oils made by acid treating can have higher
sulfur levels than those that are produced by hydrotreating.
Table 4, a comparison of the mass spectra of white oils
produced from lube hydrocracking and SK’s fuels hydrocracking
process for lubes, which entails severe hydrocracking followed
by hydroisomerization and hydrofinishing, shows higher paraffin
(presumably essentially all isoparaffins) in the SK product compared
with the hydrocracked material and lower polycyclic naphthene
content. The SK product will also obviously have higher
VIs (which is not among the white oil specifications).
REFINED WAXES
Solvent dewaxing produces an initial wax, known as slack wax,
that contains substantial quantities of oil up to 20% by volume. A
second treatment of the wax, essentially another “dewaxing” step
called deoiling, produces essentially oil-free wax and as a by-product,
“footes oil” consisting of low melting point paraffins and naphthenes.
Deoiled wax from hydrocrackates will contain only parts per million
quantities of nitrogen and sulfur compounds. From solvent refined
oils, the level of these impurities in deoiled wax will necessarily be
higher. In both deoiled wax cases, further treatment is necessary to
meet food grade standards.
Feedstocks to dewaxing units are generally waxy distillates
intended for lube base stock production but dewaxing to produce
wax may be performed on crude distillates if the wax content is
high enough.
Formulation of Automotive Lubricants
INTRODUCTION
This chapter discusses the main influences on current and
future light-duty (passenger) and heavy-duty (truck) vehicle
engine oils and also small engines for motor-cycles/light appliances
in terms of engine design, emissions and fuel economy. This
is followed by a detailed discussion of lubricant composition and
performance assessment.
2. PASSENGER CAR ENGINE OILS
Passenger Car Engine Types
Internal combustion engines, ICE, for light vehicles can be
divided into two main types, gasoline and diesel although other
types of engine are emerging. The gasoline engine still dominates
most light-vehicle markets today although diesel popularity in
Europe now accounts for more than 50% of new light-vehicle
sales.
Diesel and gasoline engines share many similarities in their
mode of operation and in their component parts. However, there
are some important differences that ultimately impact on their
lubricant requirements, namely the fuel used, mode of ignition,
temperature of combustion, exhaust gas composition and the
resulting combustion products. The soot produced during diesel
combustion is at the heart of the differences in the lubrication
requirements between gasoline and diesel vehicles and this soot
also affects exhaust emission handling.
Passenger Car Trends and Emission Legislation
The engine segment has classically been driven by targets
set by the Original Equipment Manufacturers, OEMs including
such targets as fuel economy, longer lubricant drain intervals,
engine durability and cost of ownership. These targets attempt
to simultaneously meet the needs of vehicle manufacturers,
vehicle owners and government legislators.
In recent decades, the OEM requirements have been
supplemented by the need to meet government vehicle emission
legislation. Future legislation will penalise the sale of vehicles
that do not meet the fuel economy and emission standards of
the time. As a general principle, this requirement applies globally
but there are regional variations in these aspirational targets.
Air quality has historically been the main driver in both North
America and Europe and all engine manufacturers are required
by legislation to meet targets for emissions of CO, NOx particulates
and hydrocarbons. Additionally in America, OEMs are
required to meet Corporate Average Fuel Economy (CAFE), targets
or face stiff financial penalties.
Legislative trends - air quality and carbon emissions: Existing
exhaust after-treatment technology has already enabled more
than a 90% reduction in emissions related to local air quality.
The future challenge is to improve fuel economy and reduce
carbon dioxide emission levels. The developed world has fuel
economy/C02 targets for the end of the decade and beyond and
OEMs will have to meet these targets as an average across their
fleets. However, when combined these improvements will require
further drivetrain friction reductions, aero-dynamic improvements,
reduction in tyre rolling resistance, etc. Engine hardware
will also evolve, for example engine downsizing, increased exhaust
gas recirculation, more turbo/supercharging and advanced
fuel injection systems. However, even when combined, these
improvements are not expected to achieve the new emissions
targets and consequently OEMs will have to develop new powerplant
technologies. Increasing emphasis on vehicles with significantly
reduced emissions will lead to a variety of new competing
technologies. Examples being considered include electric
vehicles, hydrogen internal combustion, homogenous charge
compression ignition (HCCI) and carbon-neutral biofuels.
Lubricant Formulation Trends
Before 2001, the components used for specific lubricant
functions had remained relatively consistent since the introduction
of ashless dispersant technology in the 1960s. However,
recently introduced emissions legislation mandates the use of
exhaust after-treatment for both gasoline and diesel light
vehicles in many parts of the developed world, and this requirement
affects component selection for modern formulations.
Three-way catalysts are used in gasoline cars to control the
emissions of hydro-carbons, carbon monoxide and nitrogen
oxides. Oxidation catalysts and diesel particulate filters. DPFs,
are used in diesel vehicles to control the emissions of soot
particles, hydrocarbons, carbon monoxide and nitrogen oxides.
All of these after-treatment devices are sensitive to additive
components of the lubricant.
‘Low SAPS’ engine oil technologies: Low SAPS technologies
are being intro-duced primarily in markets with both a highdiesel
population and high-quality diesel fuel. Legislators in
markets with high-diesel populations have driven diesel fuel
quality to higher levels. That same legislation is now driving
reduced tailpipe emissions via after-treatment devices such as
diesel particulate filters. These filters can be blocked by metallic
ash formed from oil burned during the combustion process. As
a consequence of the introduction of DPFs, modem formulations
are now using less of traditional ash-containing components.
Ash for oils is measured by a standard method known as
‘Sulphated Ash’ via the ASTM D874 procedure.
Passenger Car Lubricant Specifications and Evaluating
Lubricant Performance
Lubricant specifications: The required performance of a lubricant
in a specific application is defined by a specification. For
passenger car oils, the specifications are normally set by a
regional industry body such as API, ACEA, JASO or by a vehicle
manufacturer such as Ford, VW, Mercedes Benz. In some other
applications such as heavy-duty lubricants and transmissions,
specifications may also be set by a military organisation or by a
Tier l supplier to the vehicle manufacturer. Irrespective of the
organisation defining the specification there are common areas
against which the passenger car lubricant will be measured.
Passenger car lubricant performance evaluation: Specifications
usually contain a mixture of physical/chemical requirements and
performance properties. Physical/chemical limits include viscosity
at multiple temperatures, volatility, pour point and limits
on chemical components such as phosphorus and chlorine.
Heavy-Duty Trends and Emission Legislation
In general, emission legislation continues to drive hardware
development in the automotive industry. In future, global legislation
will mandate progressively tighter limits for NO2, particulates
and COx. This is forcing OEMs to make significant
advances in engine and exhaust after-treatment technology to
meet the legislated exhaust emission requirements. This is
further complicated since there is no harmonisation of current
global emissions standards: Figure 3 shows the state of the
heavy-duty legislated emissions requirements around the world.
Many countries in emerging markets are using the Euro
legislation to set their emissions limits, phasing them in a few
years after they are implemented in Europe. 'Off-highway' limits
are also being tightened and again these tend to lag behind the
'on-highway' limits.
MOTORCYCLES AND SMALL ENGINES
Introduction
The lubricant requirements for motorcycles and small engines
can be broadly split by their engine types: i.e. two-stroke or
four-stroke. Small engines cover lightweight portable equipment
such as chainsaws through to applications such as personal
watercraft or snowmobiles.
Overview of Two-Stroke Lubricants
Historically, the two-stroke engine has been a dominant
force in the world of motor-cycling and portable equipment due
to its high power-to-weight ratio, simplicity of construction and
low cost compared to equivalent sized four-stroke engines.
Aviation Lubricants
INTRODUCTION
Three factors dominate all aspects of aircraft design. First,
the need for the highest possible reliability due to the inherent
higher risk and potentially catastrophic consequences of in-flight
failure. Second, the need to minimise weight and volume of all
components, resulting in high specific loading in all mechanisms.
Therefore, there is high specific power dissipation so that operating
temperatures are high. Third, the extreme range of environmental
conditions encountered from –60°C on the ground, or –
80°C in the stratosphere, to over 200°C skin temperatures in
supersonic aircraft. Pressures can range from over 1 bar down
to less than 10 mbar. An example is aircraft wheel hearing
grease which can be subjected to a cold soak during long-haul
flights but then rapidly subjected to high temperatures generated
by the brakes on landing.
Because of these factors, the lubrication requirements of
aircraft are generally very critical. Only in a few cases can
lubricants developed for non-aircraft applications be used
satisfactorily in aircraft. This has not always been the case; the
mineral oil or castor oil lubricants used in the earliest aircraft
were all standard automotive or marine products.
World War I led to the recognition of the need for special
lubricants in aircraft engines. Previously, aircraft rarely climbed
to higher than a few thousand feet and engine mechanical reliability
was so poor that lubricant reliability was not a limiting
factor. But by 1918 aircraft were flying regularly as high as 18,000
feet and flights often lasted up to 5 h.
Castor oil lubricants in rotary engines gave no problems,
for reasons explained later but long-range bombers and flying
boats did not use rotary engines and their needs led to a steady
improvement in engine lubricant quality.
The divergence between ordinary automotive engine
lubricants and aircraft engine lubricants widened during the
1930s when there was a steady increase in the use of additives
in automotive lubricants. Additives were considered undesirable
for aircraft use and aircraft engine lubricants remained largely
additive free.
The introduction and development of gas turbine engines
led to the development of new lubricants. While the early gas
turbine engines ran successfully on mineral oil lubricants, and
in fact many Russian aircraft engines still operate on such lubricants,
the demand for higher specific thrust, with the concomitant
high operating temperatures, needed lubricants with better
thermal stability. Carboxylic esters were developed which, with
yet further improvements, are still used today. These lubricants
are also used in aeroderived industrial and marine gas turbines,
meaning that for the first time lubricants developed for aircraft
were used in other applications.
PISTON ENGINE LUBRICANTS
Lubrication of Rotary Engines
In the aviation context, the term ‘rotary engine’ refers to the
class of reciprocating piston engines where an assembly of radially
mounted cylinders rotates around a stationary crank-shaft.
Strictly, such engines should be referred to as ‘rotating-radial
engines’, but ‘rotary engines’ have become the accepted term, an
example is shown in Figure 1. Rotary engines were a major factor
in aircraft propulsion for only 10 years but during that short period
they made a vital contribution to World War I military aviation.
The first aircraft rotary engine was a seven-cylinder Gnome used
by Louis Paulhan in a Voisin in June 1909. By 1917 they were
used in thousands of many of the best British and French scout
(fighter) aircraft. By 1925 production had virtually ceased, although
some remained in service until about 1930.
Because of the difficulty in providing a controlled lubricant
supply to the rotating cylinder assembly, lubricant was supplied
in the fuel feed. High centrifugal forces caused rapid lubricant
loss from the piston/cylinder interface so that the technique of
dissolving a mineral oil in the fuel, as in modem small twostroke
engines would leave an inadequate oil film on the cylinder
walls.
Lubrication of Conventional Aircraft Piston Engines
Apart from the rotary engines described above, piston engines
can all be classified as radial or in-line. In-line engines may have
either one bank of cylinders, horizontal or vertical, or they may
have two or more banks in various arrangements, Figure 2.
Radial engines may have one, two or four rings of cylinders,
each containing between three to nine cylinders mounted radially
about an axis parallel to the direction of flight. Figure 3, with
always an odd number of cylinders in each ring.
Ashless additive development has reduced the risk of solid
deposit formation and ashless dispersants, anti-oxidants and
anti-foam agents are now permitted in most engines. Nondispersant
mineral oils are now used primarily for older aircraft
and as a running-in oil for new engines or after overhaul.
The viscosity characteristics of the oil are important High
viscosity is needed at high operating temperatures because of
high specific power and consequential high bearing loads. Good
low-temperature performance is also required because aircraft
are often stored outdoors und must be capable of stalling after
a long overnight soak at low ambient temperatures. The lubricant
must have a low pour point as well as good temperature-viscosity
characteristics, that is a high viscosity index. Good viscositytemperature
characteristics are obtained by using highly refined
paraffinic basestocks and ashless dispersants can give some
viscosity index improvement. In spite of this, oil viscosity at low
temperatures is usually too high to allow the engine to respond
satisfactorily when increased power is required. It may even be
too high for the engine to be started at all and leads to several
constraints on engine operation:
These problems can now be alleviated to some extent by
the use of a multi-grade engine lubricant. The use of multi-grade
oils, 15W/50 and 20W/50 has continued to grow since their
introduction in 1979 but single-grade products still have a strong
following in the industry. Single versus multi-grade discussions
are still hot topics among pilots and mechanics alike and are
frequently the subject of trade publication articles. Some multigrades
are marketed as ‘semi-synthetic’ and some are not - the
desirability of synthetic oils in aircraft piston engine oils is also
often debated. A separate ‘class’ of products has come to the
market that contain a pre-blended supplemental anti-wear
additive that meets the requirements of (Airworthiness Directive)
AD 80 04 03 R2, paragraph b.l. The AD applies to certain (mostly
0-360 family) Lycoming engines that require additional cam and
lifter wear protection provided by Lycoming additive part no. LW-
16702 (TCP). Anti-corrosion additives are also now included in
some formulations to help protect against corrosion during
extended idle periods.
Base Oil Technology
Lubricants for the early gas turbine engines were essentially
highly refined mineral oils, a natural extension from the piston
engine lubricant technology available in the early 1940s. Such
an oil is still specified today in Defence Standard 91-99, UK MoD
Grade OM-11 and consists of ‘pure refined mineral oils with
0.05-0.10% stearic acid’ to enhance load-carrying/anti-wear and
anti-corrosion properties. It can also contain an anti-oxidant
which, in common with many mineral-based fluids, is the
‘hindered phenol’ type. Although not in widespread general use
as a gas turbine lubricant for many years it was still used by
the RAF in the Rolls-Royce Avon engines of the Canberra aircraft
until 2006.
However, rapid development of the gas turbine engine and
the quest for greater power resulted in higher operating
temperatures of the lubricated components and the mineral
based lubricants of the day could not withstand such temperatures
for sufficient lengths of time. The UK and the USA made
no real effort to develop mineral-based lubricants further. The
Soviet Block has continued development of mineral-based
lubricants, some of which are still in use today in Russian
aircraft. However, this chapter concentrates on those lubricants
developed and used in western aircraft engines.
In the UK and the USA the focus for lubricant development
turned to ester-based synthetic lubricants. In the 1930s and
1940s German scientists, led by Professor Zorn had conducted
research into using di-esters and polyol esters as lubricants
Compared with mineral lubricants, ester-based lubricants had
better thermal and oxidative stability in addition to good lowtemperature
properties without the need for pour-point depressant
additives. In the 1950s both the UK and the US militaries
produced specifications for turbine lubricants based on di-esters.
The UK initially concentrated development on lubricants for
turbo-props where the load-carrying requirements of the
reduction gears used in these turbo-props required a higher
viscosity lubricant. This led to the development of a polyglycol
ether-thickened 7.5 cSt at 100°C lubricant. The USA focused on
turbo-jets to develop a 3 cSt lubricant. Despite the differences
in viscosity both lubricants were based on di-ester technology.
Formulation and Structure of Lubricating Greases
INTRODUCTION
Lubricating greases attract little attention from their beneficiaries
because they are usually hidden away in inner joints,
gears and bearings and are expected to do their job for a long
time without fail. But their job is critical and when they do fail
even the most expensive and elaborate machinery fails with
them. When machines are designed to run colder, hotter, longer,
faster or farther away than before, they require lubricating
greases equal to the new stresses. The development of such new
lubricants requires a continued application of advanced tools of
organic chemistry, physical chemistry and engineering, sometimes
far out of proportion to the market potential for the
finished product.
2. APPLICATIONS
Some applications of lubricating greases are common to
several end uses and can be considered for their general
requirements.
Rolling (“antifriction”) bearings reduce starting friction
compared with sliding bearings but the rolling elements still slide
to some extent against retainers and raceways. As a result, they
need lubrication. The increasing demands made on rolling
bearings by higher speeds, miniaturization and extreme temperatures
in turn increase demands on their lubricants. These
lubricants are often greases. They must have enough solidity
despite working, heating and oxidation not to leak out but enough
fluidity when sheared by the rotating bearing to lubricate its contacting surfaces without fail.
The consistency of a grease is its most important property
in bearings, especially if we think of it broadly as the constancy
of the consistency over a wide range of time, speed and temperature.
A consistency or yield stress equivalent to the National
Lubricating Grease Institute (NLGI) No. 2 Grade (ASTM cone
penetration 265—295) is most generally useful in hand-packed
rolling bearings. NLGI No.1 Grade. greases (penetration 295–
325) are more often used in centrally lubricated bearings. Softer
greases churn and liquefy during bearing rotation; stiffer ones
are difficult to charge into bearings and to rotate in them.
Stiffened consistency achieved by milling of greases during
manufacture does not lengthen their life in ball bearings; high
concentration of gellant is more important. The most important
causes of loss of consistency in bearings are churning promoted
by heat softening of the grease or over-filling of bearing
housings, water contamination and mixing of incompatible
greases. Large losses in consistency and melting temperature
result from contamination by even small portions of foreign
greases. Figure 1 shows graphically the effect of mixing on the
melting temperature of soap-gelled greases.
Industrial Applications
The industrial grease market is feeling some antigrease
pressure like that in the automotive market. Here it takes the
form of increasing centralized lubrication, mist lubrication, plastic
bushings and bulk handling. But the concurrent increase in
industrialization and automation helps to keep net consumption
nearly constant at about 300 million pounds of grease per year.
Centralized grease lubrication systems are in all large,
modern factories that have many bearings to lubricate. For big
consumers, such as steel mills, the grease is now delivered in
4000-6000-lb. kettles and charged directly to the lubricant lines.
Two problems have arisen in centralized systems. One, the
difficulty of predicting pressure drops for greases in long lines,
is being aided with laboratory flow measurements and nomographs.
The second, separation of grease grease at small orifices
under high pressure, makes mandatory the use of smooth, lowbleeding
greases; filled greases and complex calcium greases
with excess calcium acetate are beneficial for their antiwear and
extreme-pressure qualities but may separate and plug up
distribution systems under some conditions.
Food canneries present a special challenge to industrial
grease formulators. The strong American desire for safety and
sanitation may lead to the requirement for edible greases in
food-processing machinery. Fortunately, some soaps used in
greases are normal products of fat digestion in the body and
some purified petroleum and vegetable oils are non toxic as well
as being good lubricants. Selection of additives will require care
but there should be enough nontoxic ones to round out good
safe lubricating greases.
Dyes and Pigments
Merker and Singleterry stimulated investigation in this
colorful field with their 1952 patent on phthalocyanines as
gellants. Most such pigments when ground or milled into oils
form microcrystalline pastes rather than fine gels; they must
be present at 20–30% instead of the 5-15% concentration of good
soap gels. Their principal application is in polysiloxane oils for
greases to be used at maximum temperatures of 300-500 °F.
Examples with typical bearing lives are in Table II. Versilube
F-50 is a poly (methylchlorophenylsiloxane) and DC 550 is a poly
(methylphenylsiloxane) oil; F-50 lubricates steel on steel better
but DC 550 resists heat better. The profroxidative effect of metal
ions seems evident even in this elaborate setting–the calcium
sulfonate pigment gave lower bearing life than the nonmetallic
pigments.
Polymers
Polymers should be a natural as oil gellants. But some of
them–polybutenes, polyacrylates used as viscosity index
improvers –are too soluble. Others –nylon polyamides, textile
polyesters –are not soluble enough. Attempts to find the balance
point of the seesaw often yield greases that are too rubbery to
feed well into bearings. As a group, linear hydrocarbon polymers
have been most successful. Melting temperatures of greases
made from them increase with increasing isotacticity and other
structural changes as shown in Table III. On aging, they tend
to separate oil more than soap greases do, especially when the
oil is highly paraffinic. Partial saponification raises the melting
temperature and sometimes the gelling power of saponifiable
polymers such as olefinmaleic anhydride copolymers, alkyl
acrylate-acrylamide copolymers and alkylphenol-fatty acidformaldehyde
condensates. ethyl hydroxyethyl cellulose, may act as gellants. Some polymeric
synthetic oils can be partly cannibalized to gel themselves: poly
(methylsiloxanes) cross-linked at 400-550°F. and milled into fresh
polysiloxanes do this; chlorofluorocarbons can also be selfgelled.
Even highly cross-linked or otherwise undispersible
Inorganic Gellants
Even the most oleophobic material can gel oil if it can be
divided finely enough and if it can be distributed as a loosely
coherent network. Hard particles lose their abrasiveness when
they are less than about 1 ì wide; they are then smaller
than normal irregularities in metal bearing surfaces. The
melting temperature of inorganics is higher than the decomposition
temperature of the oil and far above the 300°F. ceiling of
90% of the applications. But, as Peterson, Accinelli and Bondi
put it. “In a plant, the part most difficult to lubricate determines
the minimum quality expected of a multipurpose lubricant”. The
most used inorganics, silica and clay, also cost little as chemical
entities (but it’s sometimes expensive to make them behave
properly in lubricants) and promote oxidation less than most soaps
OILS
Lubricating greases generally make use of oils already
available as lubricants or plasticizers. But since greases are used
in small amounts and often under severe or neglectful conditions
they intensify weaknesses of oils.
Naturally, petroleum oils are used for the great majority of
lubricating greases. Their useful temperature range is about 0-
300°F. Naphthenic oils are cheapest and easiest to gel but are
vulnerable to evaporation and oxidation. Paraffinic oils require
more gellant but last longer at high temperatures.
Industrial Lubricants
INTRODUCTION
General aspects of Industrial Lubricants
Industrial lubricants comprise a wide variety of products
which, depending on their application, differ widely in their
chemical and physical properties. With respect to the properties,
one can say that industrial lubricants involve all classes of
lubricants applied in practice. They include gases (mostly air),
various kinds of liquid products (mineral oils, animal and
vegetable oils, synthetic oils, water based fluids, etc.), greases
(simple soap greases, complex soap greases, greases with
pigments, minerals, polymers and other materials) and solid
lubricants. The latter comprise (i) inorganic compounds, e.g.
molybdenum disulphidc, boron nitride, tungsten disulphide and
many other chemicals and materials, (ii) solid organic compounds
and materials, e.g. phthalocyanine and tetrafluoroethylene, (iii)
chemical conversion coatings, and (iv) soft metals.
Furthermore, industrial lubricants make use of many additives
which comprise practically all the known additive classes
used in other types of lubricants and, additionally numerous
additives that have been developed specifically for industrial
lubricants, particularly for water based fluids. Thus, the importance
of additives in the formulation of industrial lubricants is
difficult to overestimate.
High speed and lightly loaded plain bearings need a low
viscosity plain mineral oil. The viscosity of the oil is essential
for ensuring hydrodynamic lubrication. Higher loadings and lower
speeds require higher viscosity oils. From the point of view of
the chemistry of lubricants, these oils are the simplest, being
composed of crude oil components. They mostly include isoparaffinic,
naphthenic, naphthenic-aromatic and to some extent,
aromatic hydrocarbons. All the ring structures are substituted
by alkyl chains. The viscosities of these hydro-carbons depend
on their molecular weights.
Apart from this simple lubrication of plain bearings, the
lubrication of tribological elements being rubbed under mixed
and/or boundary friction requires lubricants in the form of very
complex mixtures of appropriate mineral base oils and a number
of possible additives.
The selection of additives to formulaic industrial lubricants
involves consideration of the requirement of the equipment to
be lubricated or the metal process type of a metalworking operation.
Although hundreds of products have been used as industrial
lubricants and some other lubricants (e.g. engine oils) may be
applied in lubricating some industrial equipment, equipment
and lubricant manufacturers usually recommend lubricants for
particular applications.
In terms of quantities, industrial lubricants represent the
largest group (over 50%) among the lubricants. Lubricating oils
are the most important type of industrial lubricant.
BEARING LUBRICANTS
Bearings
Bearings are the most important machine elements used
in all branches of industrial machinery. They permit smooth, lowfriction
linear or rotary motion between two surfaces. Bearings
function by applying a sliding or roiling action. Bearings based
on sliding action are called plain bearings whereas those involving
rolling action are referred to as rolling-element bearings or
antifriction bearings.
Bearings can be lubricated by gases, liquid lubricants, greases,
or solid lubricants. The main function of the lubricant is to keep
the surfaces apart so that no interaction can occur thus reducing
friction and wear. Bearings lubricated by gases include aerodynamic
and aerostatic bearings (externally pressurised feed). Generally,
in externally pressurised bearings the solids are separated by a
fluid film supplied under pressure to the interface. The fluid may
be a liquid in which case the mode of lubrication is called
hydrostatic.
As the lubrication of plain bearings is more variable compared
to that of roiling-element bearings, the former are also
referred to by the lubricating principle involved. For example, a
specific class of plain bearings is the so-called full fluid-film
bearings, which include hydrodynamic (self-acting) and hydrostatic
(pressurised feed) bearings. In full fluid-film bearings the
load is supported by pressures within the separating fluid film
and there is no contact between the solids. In the hydro-dynamic
lubrication the pressure is developed by the relative motion and
the geometry of the system. The friction coefficient, f, in a plain
bearing is related to the lubricant dynamic viscosity, ç, the
bearing load, W and the sliding velocity, V, by the following
equation:
Refining of Petroleum
INTRODUCTION
Crude oil is the raw material for the manufacture of fuels
and lubricants. The combination of treatments performed on the
crude oil to obtain the desired products is called refining; the
treatments can be classified into separation operations, conversion
processes and chemical treating processes. The most
common separation operations employed are distillation, absorption,
adsorption, filtration and solvent extraction. Conversion
processes are those such as cracking, polymerization and
alkylation which change the chemical nature of the molecules
entering the process. Chemical treating processes either remove
undesirable constituents that are present in relatively small
amounts or convert them to other compounds whose presence
is not deleterious. How these methods are combined in a
particular refinery depends upon the characteristics and
composition of the crude oil and the relative amounts and specifications
of the desired products. Each refinery is individually
designed, with no two refineries exactly alike.
More than 7 million barrels of gasoline, fuel oil, lubricants
and other major products are manufactured every day in the
nation’s operating refineries.
Oil field emulsions are generally of the water-in-oil type.
Refinery emulsions are generally of the oil-in-water type.
Chemical treatment is more commonly applied to the oil field
emulsions and electrical treatment to the refinery emulsions.
Oil field emulsions are generally broken in the field.
POLYMERIZATION
The unsaturated refinery gases can be combined to form
larger molecules and increase further the yield of gasoline from
the crude oil. Commercially, the process is carried out catalytically
or thermally by a selective or nonselective process. In the
selective process the feed is a mixture of butenes (iso and
normal) and the product is a mixture of iso-octenes. In the nonselective
process the feed is a mixture of 2 to 4 carbon atom
olefins and the product is a mixture of isomeric 4 to 8 carbon
atom olefins.
Lubricating Oils
INTRODUCTION
A lubricant is used to reduce the coefficient of friction
between the rubbing surfaces in machinery, thereby reducing frictional
energy losses. The lubricant also prevents direct contact
of the rubbing surfaces since under proper conditions of lubrication
a film of the lubricant is maintained between these surfaces.
This prevents failure due to seizure and also reduces wear. The
frictional heat generated by the rubbing surfaces is removed by
the lubricant acting as a coolant or heat transfer medium. In
internal combustion engines the lubricant also seals the piston
and cylinder wall at the compression rings so that the high
pressure gases in the combustion chamber will not leak past
the rings and cause power losses. Briefly, the lubricant reduces
energy losses from friction, reduces wear, serves as a coolant
and may also seal. Most lubricating oils are derived from petroleum;
however, some synthetic lubricants are in use.
Essential properties of a lubricating oil are viscosity, viscosity-
temperature-pressure relations and oiliness. The changes
in these properties are minimized when the oil does not undergo
chemical change during use. Therefore, characteristics such as
the following are important: stability toward oxidation and other
chemical change, resistance to decomposition when exposed to
elevated temperatures and ability to resist emulsification. For
various applications special properties are important such as
detergency for severe operating conditions in internal combustion
engines or extreme pressure load-carrying properties for hypoid
gear lubrication.
SIGNIFICANCE OF VISCOSITY AND VISCOSITY INDEX
The most important property in selecting a lubricant for a
particular application is the viscosity. For a bearing operating
in the hydrodynamic region at given conditions of load and speed,
the viscosity of the oil at the film conditions determines the
point of operation on the ZN/P curve and the coefficient of friction.
This, in turn, determines the frictional power loss and heat
generation in the bearing and the oil flow rate through the
bearing. The viscosity of the oil at the film temperature should
be sufficient to maintain a fluid film, but not so high that frictional
losses and heat generation are excessive. A margin of safety
is desirable to insure that the fluid film is not squeezed out.
For oils exposed to oxidizing conditions and to high temperatures,
degradation of the oil is normally accompanied by an
increase in viscosity. Changes occurring in the oil under these
conditions can be followed by viscosity measurements.
Greases and Solid Lubricants
GREASES
1. Definition
For many years the ASTM defined grease as a “combination
of a petroleum product and a soap or mixture of soaps with or
without fillers, suitable for certain lubrication applications.”
Although this definition was generally accurate a few years ago,
it does not include many important products now being marketed
as greases. Among these are greases made from synthetic
lubricating oils and those made without soap by utilizing bentones
or silica gels as thickening agents. Recently the ASTM
revised its definition to include nonsoap thickeners. The current
definition is as follows: “Lubricating grease is a solid to semisolid
dispersion of a thickening agent in liquid lubricant. Other
ingredients imparting special properties may be included.”
2. Applications for Grease Lubrication
Greases are normally used under conditions of lubrication
for which oil is not as suitable or convenient. Greases perform
better than oils under conditions requiring:
Characteristics of Greases from Various Metallic Soaps
Metallic soaps are by far the most common thickening agents
used in manufacturing greases. The most widely used of these
are sodium, calcium, aluminum, barium and lithium soaps. These
metallic constituents have the greatest single influence upon the
properties of greases and characteristics of each are discussed
in the following paragraphs and summarized in Table 1.
Calcium soap greases. The waterproof nature of calcium
soap grease is its primary advantage. Because most of these
greases are stabilized with water, they cannot be used for any
length, of time above 160o F without separation of soap and oil.
The calcium soap fibers are very short and give the grease a
buttery texture. Calcium greases are widely used as cup and
pressure-gun greases for lubrication of plain bearings which
operate at normal temperatures and average loads, but they are
not suitable for use at very high pressures.
