Unfamiliar with lubrication terminology? Problem solved…
A glossary of common terms used in the lubricants industry, we hope you all find it informative. Bookmark it, you’ll probably need it someday.
ABRASIVE WEAR: Wear between two surfaces in relative motion due to particles (three bodies) or surface roughness (two bodies).
ABSOLUTE VISCOSITY: Term used interchangeably with dynamic viscosity to distinguish it from kinematic viscosity. The SI unit of absolute viscosity is the poise, however, is generally reported as centipoises (cP).
ABSORPTION: The process by which one substance draws another substance into itself, i.e. sponge absorbing water.
ACCUMULATOR (HYDRAULICS): A device in which hydraulic fluid is stored under pressure in a system to be used as source of fluid power.
ACID: A compound containing Hydrogen, which can be replaced by a metal, forming a salt. In grease manufacture, Fatty Acids are used, which form a specific type of salt, known as soap. (See Definition of Soap).
ACID AND BASE NUMBER: An indication of the amount of free acidic or alkaline materials in a petroleum product. These materials may be either inorganic or organic. The acid number is the weight in milligrams of potassium hydroxide (KOH) required to neutralise the acidic constituents in one gram of the sample. Base number is the number of milligrams of potassium hydroxide (KOH) equivalent to the acid required to react with one gram of the sample. The unit usually expresses as mg KOH/g. Also known as Neutralisation Number.
ACIDITY: A valuable indicator of refining quality of a new oil, or the extent of oxidation of a used oil. Also, as pH, an indicator of the condition of a cutting fluid emulsion as affected by the excrement, etc..of water-borne bacteria.
ACTIVATED: The condition of a substance which has been treated in a special manner to increase its activity which may be physical, such as the behavior of catalysts. Organoclay and silica are materials which have received special treatment of this type, when they are used as inorganic grease thickeners.
ACTUATOR: A mechanic device, like a cylinder or hydraulic motor, used to convert hydraulic energy into mechanic energy.
ADDENDUM (GEARS): Distance between the pitch circle and tooth crest.
ADDITIVE: Name given to petroleum oils compounded with chemical addition agents to enhance certain properties such as detergency, antioxidant characteristics, etc. or any material added to a lubricating grease or lubricating oil to improve its suitability for service. It may improve a property already possessed by the lubricant, or give it properties not naturally possessed. Typical examples are antioxidants, EP agents or anti-wear additives.
ADHESION: The force which causes the unlike substances to to stick together, for example treacle to a spoon. The force or forces causing two materials, such as lubricating grease and a metal, to stick together.
ADHESIVE WEAR: Wear caused by metal-to-metal contact; characterised by local welding and tearing of the surface.
AFFINITY: The attraction between elements which, under favourable conditions, result in their union.
AGE HARDENING : An undesirable process during which a solid (a grease, an elastomeric seal or rubber hose) hardens with prolonged storage.
AGGLOMERATION : The potential of the system for particle attraction and adhesion.
AGMA : American Gear Manufacturers Association.
AGMA LUBRICANT NUMBERS : Arbitrary numbers assigned by the AGMA to designate various
viscosity grades of gear lubricants.
AIR ENTRAPMENT : The presence of air bubbles throughout an oil as a result of agitation and/or
the release of dissolved air because of a sudden change in environment. Air entrainment is visible,
as the oil becomes opaque and bubbly.
AIR LINE LUBRICATOR : An oil reservoir attached to an air line that provides automatic air-borne
lubrication to air operated power consuming equipment by means of venturi action.
AIR OIL SEPARATOR : A mechanical device that defoams oil, using a centrifugal oil trap, or any oil
condensing device in an air line.
ALKALI : Any substance having basic properties (as contrasted with acid properties). In a restricted
sense in grease manufacture, this term is applied to the hydroxides of the alkali metals, including
lithium, sodium, calcium and other metal ions.
ALKALINITY : Broadly, soluble mineral salts based on ammonia or alkali metals are alkalis. The
converse of acidity, insofar as it is indicated by numbers in excess of 7 on the pH scale.
ALUMINUM COMPLEX GREASE : A grease prepared from a lubricating fluid thickened with
aluminum complex soap.
AMORPHOUS (WITHOUT FORM) : A term applied to such materials as carbon black, as contrasted
with such crystalline materials as graphite or Molybdenum Disulfide.
ANGULAR CONTACT BEARING : This anti-friction bearing has an inner race that slopes at an angle
away from parallel with the shaft axis. In this way a greater axial load can be taken, in the appropriate
direction, in addition to normal radial loading.
ANHYDROUS : Being devoid of water.
ANILINE POINT : The lowest temperature at which equal volumes of aniline and hydrocarbon fuel or
lubricant base stock are completely miscible. A measure of the aromatic content of a hydrocarbon
blend, used to predict the solvency of a base stock or the cetane number of a distillate fuel.
ANNULAR GEARS : Gears which are internal in nature having parallel teeth similar to the spur gear
but cut on the inside rim or inner surface of a cylinder or ring. The companion pinion of an annular
gear, however, must be a standard gear.
ANTI-CORROSION ADDITIVE : Helps prevent oxidation of metal by displacing water from metal
surfaces. It plates to metal with a polarized effect to give an internal ?umbrella?, helping to resist ironoxide
ANTI-FOAM AGENT : An additive used to suppress the foaming tendency of petroleum products in
service. May be a silicone oil to break up surface bubbles or a polymer to decrease the number of
small entrained bubbles.
ANTI-FRICTION BEARING : A bearing that makes use of the benefits of rolling friction over sliding
friction. Hence, the common term roller bearing as a differentiation from plain bearing.
ANTI-MICROBIAL AGENT : A substance that kills or inhibits the growth of microbes, such as
bacteria, yeast and mould in the finished products, such as lubricants.
ANTI-SEIZE COMPOUND : Grease-like substance with significant amount of dispersed solid
lubricants, such as graphite, molybdenum disulfide and metallic powders, primarily to prevent seizure
on threaded joints. Sometimes, it is also called a tool joint compound.
ANTI-WEAR AGENT : Additive or its reaction product, which forms a thin, tenacious film on highly
loaded parts to prevent metal-to-metal contact.
ANTIOXIDANT : Reagents used to prevent the oxidation by air or free
oxygen of a variety of substances including greases and gear lubricants.
API : American Petroleum Institute; an organisation composed of producers, refiners, etc. of
petroleum and allied products. It is devoted to the study and promotion of all branches of the
API ENGINE SERVICE CATEGORIES : Gasoline and diesel engine oil quality levels established
jointly by API, SAE and ASTM; formerly called API Engine Service Classifications.
API GRAVITY : (See Gravity).
APPARENT VISCOSITY : The ratio of shear stress to rate of shear of a non- Newtonian fluid,
calculated from Poiseuille’s equation and measured in poises or centipoises. The apparent viscosity
of most greases varies with changing rates of shear and temperature, and must therefore be reported
as the value at a given shear rate and temperature.
APPEARANCE : Those characteristics of a lubricating grease which are observable by visual
inspection only. This general term includes various characteristics described under BULK
APPEARANCE, TEXTURE, BLOOM, COLOR AND LUSTRE.
AROMATIC : Containing the benzene ring as in asphaltic residues of crude mineral oil distillation. An
undesirable component of crude oils that must be removed during the refining process to improve
oxidation resistance and viscosity index.
ASH : Metallic deposits formed in the combustion chamber and other engine parts during hightemperature
ASH CONTENT : A measure of the amount of inorganic material in lubricating oil. Determined by
burning oil and weighing the residue.
ASPERITIES : Microscopic projections on metal surfaces resulting from normal surface-finishing
processes. Interference between opposing asperities in sliding or rolling applications is a source of
friction, and can lead to metal welding and scoring. Ideally, the lubricating film between two moving
surfaces should be thicker than the combined height of the opposing asperities.
ASPHALT/BITUMEN : Also called asphalt or tar, bitumen is the brown or black viscous residue from
the vacuum distillation of crude petroleum. It also occurs in nature as asphalt “lakes” and “tar sands”.
It consists of high molecular weight hydrocarbons and minor amounts of sulphur and nitrogen
ASTM : American Society for Testing and Materials; an agency that standardises testing petroleum
AUTO IGNITION POINT : The point at which a material will spontaneously ignite without the presence
of a flame. (See Flash Point).
AXIAL : The line about which a body rotates, i.e. the centreline of a bearing/shaft. A bearing
supporting axial loads is called a thrust bearing.
AUTOMATIC TRANSMISSION FLUID (ATF) : Fluid for automatic, hydraulic transmissions in motor
BACTERIA : The smallest living units capable of carrying out, independently, all of the basic functions
BACTERIAL DEGRADATION : The effect of excessive bacterial action is to increase the acidity of a
cutting fluid emulsion and the depletion of emulsifiers to the point where corrosion protection is
affected. Ultimately, the emulsion can no longer be maintained and it ‘splits’ into layers of its
BACTERICIDE : Additive to inhibit bacterial growth in the aqueous component of fluids, preventing foul odors.
BARIUM/BARIUM COMPLEX GREASE : A grease prepared from a lubricating fluid, thickened with
barium soap or barium complex soap.
BASE OIL (Base Stock) : Commonly used to refer to the oil phase of a grease, these terms more
correctly apply to the refined oil before blending or before additions are made to enhance
BASE STOCK : The base fluid, usually a refined petroleum fraction or a selected synthetic material,
into which additives are blended to produce finished lubricants.
BASES : Compounds that react with acids to form salts plus water. Alkalis are water-soluble bases,
used in petroleum refining to remove acidic impurities. Oil soluble bases are included in lubricating oil
additives to neutralize acids formed during the combustion of fuel or oxidation of the lubricant.
BEARINGS : Contact surfaces between the frame of a machine and the moving parts whereby
support and guidance are given to sliding, revolving or semirotative members. They are not
necessarily stationary parts, however, as in the case of gudgeon pin and crank pin bearings, where
both bearing and pin are in motion. Another form of bearing is that in which rolling members such as
balls or rollers are used to control the relative movements of the connected parts, and which are
known as anti-friction bearings.
BENCH TEST : A modified service test in which the service conditions are approximated in the
BENTONITE THICKENED GREASES : A non-soap thickened grease that makes use of an inorganic
powdered clay to absorb the base oil without the need of chemical reactions or shear. They have a
wide operating temperature range and very good water resistance. They are said to have no drop
point. Bentone is a trade name.
BENZENE : An aromatic hydrocarbon used as an intermediate and as a solvent. Benzene is a toxic
BETA RATING : The method of comparing filter performance based on efficiency. This is done using
the Multi-Pass Test which counts the number of particles of a given size before and after fluid passes
through a filter.
BETA-RATIO (ß-RATIO) : The ratio of the number of particles greater than a given size in the influent
fluid to the number of particles greater than the same size in the effluent fluid, under specified test
BEVEL GEAR : Gear in which the teeth are cut on an angular surface, such as would be presented
by a truncated cone. They are used for the transmission of motion between shafts with intersecting
center lines which form an angle between each other, usually 90 degrees.
BIODEGRADABLE : Capable of decaying through the action of living organisms.
BIODEGRADABILTIY : A measure of the degree by which a lubricant can be converted to harmless
substances in waterways, forests, etc.. through the action of micro-organisms such as bacteria and
BIODEGRADATION : The process of chemical break-down or transformation of a substance caused
by living organisms and their enzymes.
BLACK OILS : Lubricants containing asphaltic materials, which impart extra adhesiveness, that are
used for open gears and steel cables.
BLEEDING/OIL SEPARATION (GREASE) : The separation of oil from a grease structure. A certain
amount of bleeding is considered desirable in greases, since this tends to provide continuous oil
lubrication to bearings.
BLENDING : Blending is regarded as the process of mixing lubricant components for the purpose of
obtaining desired physical and/or chemical properties. It is the intent to establish a difference between
blending and compounding. COMPOUNDING is regarded as the mixing or otherwise combining
lubricant components with other components for the purpose of securing chemical and/or physical
properties not usually obtainable by blending of fluid lubricant components alone.
BLOCK GREASE : A less common grease of very hard consistency (at least NLGI No.5). Often used
in the textile industry where shafts sit in cup bearings and the block of grease is held in contact with
the shaft; friction would then soften the grease to supply lubricant to the bearing.
BLOOM : The surface color (usually blue or green) of a lubricating oil or grease when viewed by
reflected daylight at an angle of about 45 degrees from the surface. BLOOM is associated with the
absorption of ultra violet light in the oil and may not be visible if the sample is viewed by artificial light.
Also called “Fluorescence” or sometimes “Outertone”.
BLOW-BY : Gases and unburned fuel which bypass the compression rings and go to the crankcase
each time the engine fires.
BODY : Refers to consistency or viscosity. Heavy or high body is synonymous to high viscosity.
‘BOMB’ OXIDATION STABILITY : A test method used for the measurement of the oxidation stability
of greases and lubricating oils.
BOUNDARY LAYER : The near motionless fluid layer found immediately adjacent to the surface of a
solid, past which the fluid flows with minimal effect. This description applies more to hydraulics and
aerodynamics than the common usage taken in lubrication – here it means ‘that area immediately
adjacent to a surface being lubricated where full-flow, or thick-film lubrication, does not adequately
separate the wearing surfaces’. (See Asperities, Friction, Thin-Film Lubrication, Solid Lubrication,
BOUNDARY LUBRICATION : Lubrication between two rubbing surfaces without the development of
a full fluid lubricating film. It occurs under high loads and requires the use of anti-wear or Extreme-
Pressure (EP) additives to prevent metal-to-metal contact.
BREATHER : An air filtering device placed on top of a reservoir to allow it to ?breath? as the oil level
rises and falls. All incoming air is thereby filtered to keep out airborne contaminants.
BRIGHT STOCK : A heavy residual lubricant stock with low pour point, used in finished blends to
provide good bearing film strength, prevent scuffing, and reduce oil consumption. Usually identified by
its viscosity, SUS at 210°F or cSt at 100°C.
BRINELLING : Denting caused by impact of one bearing component against another while stationary.
BROMINE NUMBER (VALUE) : The percentage of bromine that will be absorbed by a chemically
unsaturated substance (base oil, vegetable oil, rubber, etc.) in a given time under arbitrary conditions.
A measure of unsaturation.
BROOKFIELD VISCOSITY : Measure of apparent viscosity as determined by the Brookfield
viscometer at a controlled temperature and shear rate.
BULK APPEARANCE (GREASE) : Visual appearance of grease when the undisturbed surface is
viewed as an opaque container. BULK APPEARANCE should be described in the following terms:
- Smooth: A surface relatively free of irregularities.
- Rough: A surface composed of many small irregularities.
- Grainy: A surface composed of small granules or lumps of constituent soap particles.
- Cracked: Showing surface cracks of appreciable magnitude. In describing such a lubricating
grease, the number and size of the cracks should be included in the description.
- Bleeding: Showing free oil on the surface of the lubricating grease (or in the cracks of a
CALCIUM/CALCIUM COMPLEX GREASE : A grease made from a lubricating fluid thickened with
calcium soap or calcium complex soap.
CALCIUM (LIME) GREASES : Metallic soap greases which have particular resistance to water.
CALCIUM SULPHONATE COMPLEX GREASE : A calcium neutralized grease thickened with sulphonic
acid and other acids.
CAMS : Eccentric shafts used in most internal combustion engines to open and close valves.
CAPILLARITY : The tendency of certain liquids to ascend capillary tubes or fine orifices. This
property is of importance in wick feed lubricators, in kerosene lamps, etc.
CARBON DIOXIDE (CO2) : A colourless, odourless, gas produced by complete combustion of a
hydrocarbon fuel-air mixture. A harmless component of the exhaust from an internal combustion
CARBONISATION : Creation of undesirable, non-lubricating carbon debris and residues ranging from
gum and varnish through to abrasive coking. Caused by high temperature and subsequent oxidation
of the lubricant.
CARBON MONOXIDE (CO) : A colourless, highly poisonous gas produced by combustion of organic
compounds with limited amount of oxygen. A component of automotive exhaust emissions.
CARBON RESIDUE : Coked material remaining after an oil has been exposed to high temperatures
under controlled conditions. Laboratory test originally developed to compare the carbon-forming
properties of lubricating oils used in internal combustion engines, but now having more general
CATALYST : A material which promotes some chemical action without itself entering into the
CATALYTIC CONVERTER : An integral part of vehicle emission control systems since 1975.
Oxidizing converters remove hydrocarbons and carbon monoxide (GO) from exhaust gases, while
reducing converters control nitrogen oxide (NOx) emissions. Both use noble metal (platinum,
palladium or rhodium) catalysts that can be “poisoned” by lead or phosphorous compounds in the fuel
CATASTROPHIC FAILURE : Sudden, unexpected failure of a machine resulting in considerable cost
- The formation and subsequent collapse of vaporous cavities within a liquid; caused by movement
or vibration within the liquid film.
- In a lubricating grease dispensing system, failure for any reason of the material to flow to the
suction of the system pump (also see Feedability).
CAVITATION DAMAGE : An erosion process in which metal is removed by cavitation.
CENTIPOISE (cP) : A centipoise is 1/100th of the unit of absolute viscosity (the poise), e.g., the
viscosity of water at 20°C is approximately one centipoise. The centipoise is derived from one
kinematic unit of viscosity (the centistoke), by multiplying the latter by the density of the liquid, i.e. 1
centipoise = 1 centistoke x the density of the liquid.
CENTISTOKE (cSt) : Measurement unit of kinematic viscosity of a fluid. One centistoke equals 0.01
Stokes and is equivalent to one mm2/sec in SI units. (See definition of Stoke).
CENTRALISED LUBRICATION : A system of lubrication in which the lubricant for various parts of a
machine or a group of machines is supplied from a central location.
CETANE INDEX : A value calculated from the physical properties of a diesel fuel to predict its Cetane
CETANE NUMBER : A measure of the ignition quality of a diesel fuel, as determined in a standard
single cylinder test engine, which measures ignition delay compared to primary reference fuels. The
higher the Cetane Number, the easier a high-speed, direct-injection engine will start, and the less
“white smoking” and “diesel knock” after startup.
CETANE NUMBER IMPROVER : An additive (usually an organic nitrate) that boosts the Cetane
Number of a fuel.
CHAIN LUBRICATION : The links, leaves and pins in a chain suffer sliding friction requiring a
lubricant to minimise wear. Oils used for chain lubrication must have penetrative and adhesive
properties in addition to operation performance additives.
- A term used in connection with lubricating greases to describe the (usually desirable) tendency to
form a channel by the working down of lubricating grease in a bearing, leaving shoulders of unworked
grease which serve as a seal and reservoir.
- A term used in connection with liquid lubricants and flow type lubricating greases to describe the
tendency at low temperatures, for these materials to form a plastic structure sufficiently strong to
resist flow under gravitational forces only. (Similar to, but not identical, with the pour point of liquid
lubricants, it is measured by empirical tests such as Federal Test Method 791C 3456-2.)
CHLORINATED : In lubricants, this is the inclusion of chlorine compounds as extreme pressure (EP)
additives. The term also relates to any chemical combination of chlorine or its compounds with
another group, for example onto hydrocarbon chains.
CHURNING : Constant shearing (working) of a grease in a bearing will result in overheating leading
to severe loss of consistency, which is self-perpetuating, until the extremely fluid grease runs from the
bearing. The most likely causes include overfilling and selection of too soft a grease for the
application. (See Channelling, NLGI, Penetration, Slumping).
CIRCULATING OILING SYSTEM : In such lubricating systems, the oil may be pumped under
pressure directly to the parts requiring lubrication or, in a gravity circulating system, the oil is pumped
to a tank located above the parts to be lubricated and flows down by gravity. The used oil then drains
to a sump from where it is pumped through a filter or centrifuge then, usually through an oil cooler,
back to the initial reservoir. Term also sometimes used to describe pressure oiling system of
CLAY THICKENER : A term used in reference to bentonite.
CLEANLINESS RATING : A rating based on the number of particles of specified sizes in a measure
of fluid. The ISO 4406 standard specifies the code to be used for such rating.
CLOUD POINT : The temperature at which a cloud of wax crystals appears when a lubricant or
distillate fuel is cooled under standard conditions. Indicates the tendency of the material to plug filters
or small orifices under cold weather conditions.
COEFFICIENT OF FRICTION : The ratio of the friction between two surfaces to the pressure between
them. A low coefficient of friction means low friction losses, influenced by the viscosity and character
of the lubricant by materials, surface conditions and other factors.
COHESION : The molecular attraction causing particles of a given substance to attract each other
and stick together. Cohesion contributes to the resistance of a lubricating grease to flow.
COLD CRANKING SIMULATOR (CCS) : An intermediate shear rate viscometer that predicts the
ability of an oil to permit a satisfactory cranking speed to be developed in a cold engine.
COLLOID : Substances of particle size larger than molecules, but small enough to possess
reasonable dispersion stability in two phase systems. A lubricating grease is a colloidal system (See
also Thickening Agent).
COLOR (LUBRICANT) : The shade and intensity shown when lubricating grease is viewed under
conditions such as to eliminate BLOOM. Such conditions may be obtained by viewing the lubricating
grease in an opaque container such as a metal package, by reflected light, from a position
approximately perpendicular to the surface; or by viewing it with a transmitted light only, by placing
the sample on a transparent plate. When colors of lubricating grease are referred to, the method by
which colors are determined should be clearly indicated. Colors of lubricating greases are best
described in terms of the predominant hue such as amber, brown (or perhaps green, red, or blue for
dyed greases) with a qualifying adjective describing intensity in terms of light, medium or dark (of
lubricating oil). That shade shown when viewed under transmitted light only. Usually lubricating oil
colors are obtained by viewing the oil under specified conditions in test equipment. Several such
methods are available, the most widely used being ASTM D1500 which describes the colors in terms
COMPLEX SOAP (GREASE) : A soap to thicken grease wherein the soap crystal of fibre is formed
by a co-crystallization of two or more compounds:
- The normal soap (such as metallic stearate).
- The complexing agent. Examples of complexing agents are the metallic salts of short chain
organic acids, such as acetic or sebacic acid, or the inorganic salts such as carbonate or borate.
COMPOUNDING : Regarded as the mixture or otherwise combining of lubricant components with
other components for the purpose of securing chemical and/or physical properties not usually
obtainable by blending of fluid lubricant components alone.
COMPOUNDED OIL : Mineral oil to which has been added vegetable or animal oil or chemical
lubricating oil additives to enhance certain physical or chemical properties of the finished blend.
COMPRESSION RATIO : In an internal combustion engine, the ratio of the volume of combustion
space at bottom dead center to that at top dead center.
CONDITION MONITORING : The use of specialised techniques that monitor the condition of
equipment and detect the onset of failure in sufficient time to plan a maintenance intervention that
prevents failures; these techniques include lubricant analysis, vibration analysis, thermography, motor
current signature analysis, Non-destructive testing (NDT) surface inspections (such as ultrasonic,
acoustic emission, electromagnetic, radiography, magnetic particle and penetrant testing).
CONSISTENCY/HARDNESS (GREASE) : The degree to which a plastic material such as lubricating
grease resists deformation under the application of force. (It is therefore a characteristic of plasticity,
as viscosity is a characteristic of fluidity. Consistency is usually indicated by either apparent viscosity
or NLGI grade).
CONTAMINATION : Pollution of a lubricant by some external agent.
COPPER CORROSION TEST : To determine whether or not a lubricant contains corrosive or
tarnishing materials, a polished copper strip is submerged in the lubricant, which is maintained at an
elevated temperature for a period of some hours. If the lubricant contains any trace of a chemically
reactive substance under these conditions the copper strip becomes discolored with a characteristic
dark film. The test is particularly useful for detecting the presence of corrosive sulphur compounds.
CORROSION : Any chemical reaction which results in the conversion of useful materials, generally
metals or alloys, into substances of no value for the purpose fulfilled by the original material. Rusting
is the most common example of corrosion, chemical attack or reaction on metals by acid, alkali
oxygen, chlorine, sulphur, or other chemicals. This is distinct from metal destruction by wear and may
be evident by either discoloration or pitting.
CORROSION INHIBITOR : Additive that protects lubricated metal surfaces from chemical attack by
water or other contaminants.
CORROSIVE WEAR : Wear caused by chemical reaction.
COUPLING : A frequently-used alternative term for ?fitting?: a straight connector for fluid lines; or a
large-diameter device that connects the ends of two shafts, between a motor shaft and a gear drive
unit, for example.
CROWN : The top of the piston in an internal combustion engine above the fire ring, exposed to direct
CUP GREASE : Common name for lime soap greases. Usually a calcium base grease having a
yellowish color and a buttery structure for use in grease cups.
CUTTING FLUID/OIL : Oil used in machining operations to lubricate the cutting tool, to act as a
coolant to dissipate the heat that is generated by friction and the stressing of the metal, and to prevent
rust and corrosion of the machine tool or machined part.
DEEP GROOVE BALL BEARING : Probably the simplest type of anti-friction bearing. Since the balls
roll in a deep track they are able to take a certain amount of axial loading in addition to the larger
radial vector. This type of bearing is capable of high speeds and is simple to lubricate.
DEMULSIBlLITY : A measure of a fluid’s ability to separate from water.
DENATURANTS : Toxic or noxious components used in fuel ethanol to make it unfit for use as a
DENSITY : Mass per unit volume. Usually, the unit expresses as g/ml, g/L or kg/m3.
DEPOSITS : Oil-insoluble materials that result from oxidation of the oil and contamination from
external sources (products of combustion in the internal combustion engine) and settle out on
machine or engine parts as sludge and varnish.
- Cleansing, purging.
- The property of an oil which prevents the deposition of gums or lacquers on engine parts and to
which carbon from the combustion chamber would otherwise adhere.
DETERGENT : A substance added to a fuel or lubricant to keep engine parts clean. In motor oil
formulations, the most commonly used detergents are metallic soaps with a reserve of basicity to
neutralize acids formed during combustion.
DETERGENT/DISPERSANT : An additive package that combines a detergent with a dispersant.
DETONATION : Uncontrolled burning of the last portion (end gas) of the air/fuel mixture in the
cylinder of a spark-ignition engine. Also known as “knock” or “ping.”
DIELECTRIC STRENGTH : Test designed to give a measure of the insulating properties of oils,
carried out by applying an increasing voltage to the oil under specified conditions until breakdown
occurs, denoted by the establishment of an arc.
DILUENT/CUTBACK SOLVENT : Instead of heating, a solvent added to viscous lubricants to permit
application in cold weather. The solvent evaporates after application, leaving the lubricant in place.
Diluent is widely used in open gear lubricant.
DILUTION OF ENGINE OIL : Contamination of crankcase oil by unburned fuel, leading to reduced
viscosity and flash point. May indicate component wear or fuel system maladjustment.
DILUTION RATIO : The relative proportions of concentrate to water in a cutting fluid emulsion.
DISPENSABILITY : The property of a grease which governs the ease with which it may be
transformed from its container to its point of application. Most used in discussions of dispensing in
grease systems, where it includes both the properties of pumpability and feedability.
DISPERSANT : An additive that helps keep solid contaminants in a crankcase oil in colloidal
suspension, preventing sludge and varnish deposits on engine parts. Usually nonmetallic (“ashless”),
and used in combination with detergents.
DISPERSANT ACTION : The property of an oil which prevents the coagulation or sticking together of
carbonaceous particles by keeping them in a finely divided state, and which thus prevents their
settling out and deposition on engine parts.
DISPERSION : A suspension of minute, discreet particles in a liquid, gas or solid. A dispersion differs
principally from a colloid in particle size – the dispersion is not homogenous and particles will
DISTILLATION : The basic test used to characterise the volatility of a gasoline or distillate fuel.
DN (DmN) FACTOR/SPEED FACTOR : Used as a guide to lubricant selection for rolling contact bearings.
DN value is determined by the mean bearing diameter in mm (D) multiplied by the speed of the
bearing at standard operating conditions in rpm (N).
DOUBLE-ROW BEARING : An anti-friction bearing having the capacity to support much higher loads
than a single row bearing. The ring of balls or rollers and cage is duplicated within a single bearing
DOWNTIME : Machine time lost due to mechanical failure. Also refers to shut down periods for
servicing or maintenance.
DROPPING POINT (GREASE) : The temperature at which a drop of material falls from the orifice of
the test apparatus under the conditions of ASTM D566 or D2265 tests. This test should be considered
as having very limited bearing upon service performance. It is not the melting point of the grease, this
being a term of little or no significance when applied to plastic materials such as lubricating grease.
These materials are characterised by a melting range during which the material becomes steadily
softer. Only through the establishment of an arbitrary and fully controlled test procedure such as the
ASTM Dropping Point, can any single temperature be established as a characteristic of the material.
Test carried out on grease which is, in general, an indication of the temperature of transition from the
solid or semi-solid, to the liquid state.
DRY FILM LUBRICANT : A solid material, such as graphite, molybdenum disulfide or PTFE, used
with loads in the boundary region of lubrication. These materials may be applied as pastes, by
spraying, dipping, brushing in an air-drying carrier, burnishing or resin bonding.
DYNAMIC VISCOSITY : A measure of resistance to flow in a fluid. Dynamic viscosity is also known
as absolute viscosity. (See Absolute Viscosity).
ELASTOHYDRODYNAMIC LUBRICATION (EHD) : A lubricant regime characterised by high unit
loads and high speeds in rolling elements where the mating parts deform elastically due to the
incompressibility of the lubricant film under very high pressure.
ELASTOMER : A rubber or rubber-like natural or synthetic material that can be stretched repeatedly
and that returns to its approximate original dimensions when the stress is released.
EMCOR : A test method used to evaluate corrosion resistance of a grease in a bearing.
EMULSIFICATION OF GREASE : The gross contamination of a grease with water leading to loss of
consistency and ‘dilution’ of all properties.
EMULSIFIER : Additive that promotes the formation of a stable mixture, or emulsion, of oil and water.
EMULSION : A mixture of water and oily material in which either very small drops of water are
suspended in oil, or similar drops of oil are suspended in water, the whole being stabilised by a third
component such as soap, called an emulsifying agent. Milk is an emulsion of fat in water.
A liquid in which is suspended another immiscible liquid. Water and oil can be emulsified under
certain conditions of oil type and severe agitation. Emulsifying agents are sometimes added to oils for
the production of cutting fluids, which are to be mixed with water.
END POINT : Highest vapor temperature recorded during a distillation test of a petroleum stock.
ENGINE DEPOSITS : Hard or persistent accumulation of sludge, varnish, lacquer and carbonaceous
residues due to blow-by of unburned and partially burned fuel, or the partial breakdown of the
crankcase lubricant. Water from the condensation of combustion products, carbon, residues from fuel
or lubricating oil additives, dust and metal particles also contribute.
EP AGENT (EXTREME PRESSURE ADDITIVE) : Lubricant additive that prevents sliding metal
surfaces from seizing under extreme pressure conditions.
EROSION : Wearing away of a surface by an impinging fluid or solid.
ESTERS : Compounds formed by the combination of an organic acid with an alcohol. Ester
compound, such as diester or polyol ester, is widely used as a type of synthetic oil.
EVAPORATION LOSS : That portion of a lubricant which volatilises under the effects of temperature
pressure and time. Such loss can occur in use or in storage. A widely used testing method is ASTM
FALEX TEST : Is used to determine the extreme-pressure (EP) or anti-wear properties of oils and
greases. ‘V’ blocks are placed on opposite sides of a rotating steel shaft, and the apparatus is
immersed in a bath of the test lubricant. Load is automatically increased until seizure occurs.
Measurable wear scars are formed on the blocks.
FALSE BRINELLING : Fretting of one bearing component against another; may appear as a dent,
but original surface finish is worn away.
FAT : An animal or vegetable oil which will combine with an alkali to saponify and form a soap (See
Definition of Soap).
FATIGUE : Cracking, flaking or spalling of a surface due to stresses beyond the endurance limit of
FATTY ACID : The acid-reactive part of a fat. Fatty acids are more uniform, since the refining of the
fat produces a more uniform raw material.
FATTY ESTERS : Used as greasy, boundary layer additives in lubricants and to promote good
surface finish. (See Esters).
FEEDABILITY : The ability of a lubricating grease to flow to the suction of a dispensing pump at a
rate of at least equal to pump delivers capacity. (Some lubricating greases do not feed satisfactorily
and cause cavitation at the inlet of a dispensing pump).
FERROGRAPHY : Magnetic particle analysis.
FIBRE : In lubricating grease, the form in which soap thickeners occur, the soaps crystallising in
threads, which are of the order of 20 or more times as long as they are thick. (Most soap fibres are
microscopic in size, so that the grease appears smooth to the eye. The greases having fibrous
appearance are those where the fibre bundles are large enough to be seen by the naked eye. The
most common fibrous bundles are large enough to be seen by the naked eye. The most common
fibrous lubricating grease is sodium based, although not all sodium based greases are fibrous).
FIBRIL : An extremely small fibre, usually barely visible, even at maximum magnification in an
electron microscope. Fibrils may collect in bundles to form larger fibres.
FIELD TRIALS : Following laboratory development and testing it is necessary to ensure practical
performance in a variety of applications as well as to evaluate market acceptance.
FILM STRENGTH : The ability of a film or lubricant to resist rupture due to load, speed and
FLASH POINT/FIRE POINT : Minimum temperature at which a fluid will support instantaneous combustion (a
flash) but before it will burn continuously (fire point). Flash point is an important indicator of the fire
and explosion hazards associated with a petroleum product.
FLUID FRICTION : The internal friction of the lubricating oil film when the solid surfaces between
which relative motion is taking place and separated completely by a fluid film. Under such conditions,
the oil flows in parallel layers like a pack of playing cards sliding over each other when the outside
cards are held adhering to the palms of the hands and the palms are moved relatively to each other,
thus causing the outside cards to move with the hands and the intervening cards to move in relation
to their position in the pack.
FLUID GREASE : A term used to describe grease of very soft consistency. NLGI penetration grade
below ‘I’. A grease used in centralised lubrication systems, where grease must flow, under pressure,
through long pipes to a bearing. In certain circumstances fluid greases can be used in gearboxes.
FLUIDITY : The property of flowing freely: the reciprocal of viscosity.
FOAMING : Oil foaming is generally caused from excessive agitation, moisture contamination or air
ingression in suction lines.
FOLLOWER PLATE : A piece of sheet metal used on top of grease in a pump type dispenser to
ensure the grease remains level as it is pumped. This avoids the formation of a cavity around the
grease pump pick-up tube and permits the dispensing of all the grease in the container without
manual leveling of the grease from time to time.
FOOD AND DRUG ADMINISTRATION (FDA) : Agency administered under the US Department of
Health and Human Services ‘to enforce the Federal Food, Drug and Cosmetic Act and thereby ensure
that foods are safe, pure and wholesome, and made under sanitary conditions; drugs and therapeutic
devices are safe and effective for their intended uses: cosmetics are safe and prepared from appropriate
ingredients; and that all of these products are honestly and informatively labelled and packaged’.
(Note: FDA do not approve products. See NSF).
FOOD QUALITY LUBRICANTS : Oils and greases which may come into contact with foodstuffs.
National governments, food manufacturers and consumers require such products to be assessed with
regard to their toxicity.
FOUR-BALL METHOD : In this popular test method, developed for the Shell Oil Co., three steel balls
are clamped together to form a cradle upon which a fourth ball rotates on a vertical axis. The 3
clamped balls are immersed in the lubricant under investigation and loaded against the rotating fourth
ball. The Four-Ball Wear Method is used to determine the anti-wear property of lubricants operating
under boundary lubrication conditions by measurement of wear scars developed on the balls during
the test. The Four-Ball EP Method is designed to evaluate performance under much higher loads
where there is increased potential for lubrication film breakdown resulting in scoring and welding.
(See Load-Wear Index).
FRETTING : A form of wear resulting from oscillating or vibratory motion of limited amplitude,
resulting in the removal of very finely divided particles from rubbing surfaces. In the case of ferrous
metals in air, the wear particles oxidise to a reddish, abrasive iron oxide which has led to the name of
FRETTING CORROSION. This latter happening has also been called FALSE
FRICTION OXIDATION when it occurred in rolling contact bearings.
FRICTION : A resistance to motion between two surfaces in contact. When two surfaces are brought
into contact and made to slide, the one over the other, a force immediately comes into play resisting
this motion. This force is known as friction. Friction is not confined to solids; it plays an equally
important part with liquid and gaseous substances.
FROST : Field of micropits; form of micro-adhesive wear.
FUNGUS (plural,, fungi) : The simplest micro-organism having a true cell wall. They appear as
single cell yeasts (many times the size of bacteria) or as filamentous moulds. These filaments grow
and deposit spores that form new colonies in a ‘mat’ that eventually blocks coolant pipes, etc.. in
machine tools. (See Fungicide).
FUNGICIDE : A chemical that preferentially or selectively kills fungi.
FZG FOUR-SQUARE GEAR OIL TEST (Forschungsstelle fur Zahnrader und Getriebebau) : This
test is used in developing industrial gear lubricants to meet equipment manufacturer’s specifications.
The FZG test equipment consists of two gear sets, arranged in a four-square configuration, driven by
an electric motor. The test gear set is run in the lubricant at gradually increasing load stages until
failure, which is the point at which a 10 milligram weight loss by the gear set is recorded. Also called
Niemann four-square gear oil test.
GALLING : When loads are heavy and the film strength of the oil is insufficient to support the load,
momentary metallic contact occurs resulting in a ridge at the pitch line of the driven gear and a hollow
at the pitch line of driving gear. In severe cases, wear of the metal takes place along the faces and
flanks of the gear teeth, also known as “Galling”.
GAS : The vapour state of any substance that has neither independent shape or volume.
GASEOUS FUELS : Liquefied or compressed hydrocarbon gases (propane, butane or natural gas),
which are finding increasing use in motor vehicles as replacements for gasoline and diesel fuel.
GASOLINE : A volatile mixture of liquid hydrocarbons, containing small amounts of additives and
suitable for use as a fuel in spark-ignition, internal-combustion engines.
GASOLINE/ETHANOL BLEND : A spark-ignition automotive engine fuel containing denatured fuel
ethanol in a base gasoline. It may be leaded or unleaded.
GEAR LUBRICATION : Gears, whether enclosed or ‘open’, require lubricants that resist film
breakdown under high pressure and often severe sliding friction. Many gear lubricants contain
extreme pressure (EP) additives and tend to use higher viscosity mineral or synthetic oils. Open
gear lubricants will be extremely adhesive, containing tackiness additives.
GEAR RATIO : Ratio of the number of teeth on the gear to the number of teeth on the pinion, also the
number of teeth on the worm wheel to the number of teeth on the worm.
GEL : An elastic solid mixture of a colloid and liquid possessing a yield point and a jellylike texture.
GEL GREASES : Inorganic thickeners are used in gel greases to absorb the lubricating oil. (See
Bentonite, Silica, Thickener).
GENERAL PURPOSE GREASE : Also, incorrectly, called ‘multi-purpose grease’. While a multipurpose
grease purports to be successful in many applications and situations, a general purpose
grease makes no special claims, being suitable only for non-extreme conditions.
GLYCERIDES : An ester of glycerol and fatty acids.
GRAPHITE : A soft form of elemental carbon, grey to black in colour. It occurs naturally or is
synthesised from coal or other carbon sources. It is used in the manufacture of paints, lead pencils,
crucibles and electrodes and is also widely used as a lubricant either alone or when added to
conventional lubricants to impart anti-wear properties.
GRAVITY : Given in two forms, either degrees API or as specific gravity. The former is an arbitrary
standard adopted by the American Petroleum Institute (the higher the number, the lighter the oil).
Specific gravity is the ratio of the weight of oil to the weight of equal volumes of water.
GREASE : A solid to semi-fluid product of dispersion of a thickening agent in a liquid lubricant. Other
ingredients imparting special properties may be included.
GUM : (See Varnish).
HALOGENATED SOLVENT : Solvent formulated with one of the halogens, usually chlorine or
fluorine. Most of halogenated solvents are associated with the atmospheric depletion of ozone.
HEAT : Energy released during combustion.
HEATING VALUE : A measure of the amount of energy available in a fuel to produce work,
expressed as Btu/lb or Btu/gal.
HELICAL GEAR : Resembles the spur gear in that the teeth are cut on a cylindrical body, but differs
in that the teeth are spiraled around the body rather than formed parallel to the axis of the gear body.
Spiraling the teeth provides smoothness.
HERRINGBONE GEAR : Resembles two helical gears having reversed directions of spiral, placed
side by side, so that the teeth come together to form a chevron pattern. In the herringbone gear,
spiraling the teeth in both directions neutralizes end thrust.
HERTZIAN : In elasto-hydrodynamic (EHD) lubrication, the term used to describe the surface
deformations resulting from extreme pressures applied by load. The Hertz curve, used in the Four-
Ball Test as a part of the Load-Wear Index calculations, is developed on the basis of a formula that
determines the area of contact between two spherical surfaces caused solely by their deformation
HIGH TEMPERATURE HIGH SHEAR RATE VISCOSITY (HTHS) : A measure of a fluid’s resistance
to flow under conditions resembling highly-loaded journal bearings in fired internal combustion
engines, typically 1 million S-1 at 150°C.
HOMOGENISATION : The process of subjecting a lubricating grease to intimate mixing and intensive
shearing action, the end result of which is to obtain a more uniform and higher degree of dispersion.
HOMOGENISER : The machine used in grease manufacture to ensure effective homogenisation.
HYDRATED SOAP : A soap which has water associated with its structure. A typical example is water
stabilised calcium soaped grease which owes its stability to hydrated calcium soap.
HYDRAULIC FLUID : Hydraulic fluids are used to transmit force from one part of a system to another,
as in hydraulic brakes, to damp out suddenly applied forces to another, as in shock absorbers, or to
retard motion as in gun recoil mechanisms.
HYDROCARBONS : Compounds containing only carbon and hydrogen. Petroleum consists chiefly
HYDROCARBON POLYER : A repetitive chain of hydrocarbon molecules. (See Polymer).
HYDRODYNAMIC (FLUID FILM) LUBRICATION : That state of lubrication in which the shape and
relative motion of the sliding surfaces causes the formation of a continuous fluid film under sufficient
pressure to prevent any contact between the surfaces. It is also called Fluid Film Lubrication.
HYDROFINISHING : A process for treating raw extracted base stocks with hydrogen to saturate them
for improved stability.
HYDROLYSIS : Decomposition of a chemical compound as a result of reaction with water.
HYDROLYTIC STABILITY : Ability of additives and certain synthetic lubricants to resist chemical
decomposition (hydrolysis) in the presence of water.
HYDROMETER : An instrument for determining the gravity (either specific or API.) of liquids,
consisting of loaded bulk, surmounted by a narrow tube bearing a scale. The gravity is indicated by a
line on the scale which coincides with the meniscus of the liquid.
HYDROPHILIC : Having an affinity for water; capable of uniting with or dissolving in water.
HYDROPHOBIC : Having antagonism for water; not capable of uniting or mixing with water.
HYDROSTATIC LUBRICATION : That state of lubrication in which the lubricant is supplied to a plain
bearing under sufficient external pressure to separate the opposing surfaces by a continuous lubricant
HYDROXYSTEARATE : A term used to describe soap thickeners manufactured by reacting a metal
hydroxide (alkali) with 12-hydroxystearic acid (fatty acid).
HYGROMETRIC : Readily able to absorb water or moisture.
HYGROSCOPIC : Capable of absorbing water from the air readily.
HYPOID GEAR : Gear construction in which a line bisecting the pinion does not dissect the gear, i.e.
the pinion is offset to the center line of the gear.
HYPOID GEAR LUBRICANT : A gear lubricant having extreme pressure characteristics for use in
hypoid type gears, such as automotive differentials.
IP : The Institute of Petroleum (IP) is the British equivalent of the American Society for Testing and
Materials, ASTM and defines testing standards and methods as agreed by interested parties in the
ISO : International Standards Organisation. An all-embracing term used to indicate agreement
between contributing nations on methods and units of measurement.
IGNITION POINT : (See Auto-Ignition Point).
INCOMPATIBILITY : Two lubricating greases show incompatibility when a mixture of the products
show physical properties of service performance which markedly is inferior to those of either of the
greases before mixing. Performance or properties inferior to one of the products and superior to the
other may be due to simple mixing and would not be considered as evidence of incompatibility.
INDUCTION PERIOD : In an oxidation test, the time period during which oxidation proceeds at a
constant and relatively low rate. It ends at the point where oxidation rate increases sharply.
INERT : Exhibiting no chemical reactivity.
INHIBITOR : Additive that improves the performance of a petroleum product by controlling
undesirable chemical reactions, i.e. oxidation inhibitor, rust inhibitor, etc.
INORGANIC : Loosely, compounds containing no carbon. (See Organic).
INORGANIC THICKENER : (See Non-Soap Thickener).
- ASTM D893 – contaminants found in used oils due to dust, dirt, wear particles or oxidation
products. Often measured as pentane or toluene insolubles to reflect insoluble character.
- ASTM D128 – components of a grease that are insoluble in the prescribed reagents;
generally denotes fillers, additives and certain types of thickeners as well as impurities.
IODINE NUMBER/IODINE VALUE : The percentage of iodine that will be absorbed by a chemically
unsaturated substance (base oil, vegetable oil, rubber, etc.) in a given time under arbitrary conditions.
A measure of unsaturation.
JOURNAL : Male portion of a rotary bearing; part of shaft or axle that rests on bearings.
KEG PUMP : A grease pump fitted to the top of a ‘keg’ or ‘tub’ of grease and having a stack pipe that
extends to the bottom of the keg. Each pump stroke (by hand or air operated) lifts grease and pushes
displaced grease from a flexible pipe to the application. (See Slumping).
KETTLE GREASE : The manufacturing container in which a soap thickener is heated and stirred to
ensure complete reaction. Complexing agents additives and oil may also be added in the kettle.
KINEMATIC VISCOSITY : Kinematic viscosity is generally measured by taking the time of flow of a
certain volume of the product, at a fixed temperature (usually 40°C or 100°C), through a standardsized
orifice. The SI unit of kinematic viscosity is the stoke, however, is generally reported as
LACQUER : (See Varnish).
LEAD SCAVENGERS : Compounds of bromine and chlorine included in antiknock compounds to
help remove lead compounds from the engine after combustion of fuel.
LINEAR BEARING : A type of ball bearing where the balls are arranged to travel in tracks that extend
axially on a shaft or slide to reduce friction in a flat-plane, such as reciprocating, motion.
LITHIUM/LITHIUM COMPLEX GREASE : A grease prepared from a lubrication fluid thickened with
lithium soap or lithium complex soap.
LOAD-CARRYING CAPACITY : Property of a lubricant to form a film on the lubricated surface, that
resists rupture under given load conditions. Expressed as maximum load the lubricated system can
support without failure or excessive wear.
LOADING : The force to be supported by a body that decides its material and structure. For the
lubrication specifier, its size and direction may also determine the type of bearing and, with other
factors, will influence the choice of lubricant.
LOAD-WEAR INDEX (LWI) : This Shell Four-Ball ASTM Test is used to determine the relative ability
of a lubricant to prevent wear under applied loads. Referred to in the British IP test method as Mean
Hertz Load. (See Four-Ball Method).
LUBRICANT : A substance used to reduce friction or to make surfaces slippery. The lubricant prevents
adhesion between surfaces and introduces a material, either solid or fluid, of sufficient consistency to
maintain a film which can be easily sheared. Any substance interposed between two surfaces in relative
motion, which reduces the friction of wear of the surfaces.
LUBRICATING GREASE STRUCTURE : The physical arrangement of the component particles of a
lubricating grease thickener additive, if any, and liquid lubricant. It is the nature and stability of this
arrangement which determine the appearance, texture and physical properties of lubricating grease.
LUBRICATION : Control of friction and wear by the introduction of a friction-reducing film between
moving surfaces in contact. May be a fluid, solid or plastic substance.
LUBRICATION INTERVAL : The time between application of fresh lubricant. This can be calculated
from the volume of an anti-friction bearing in simple situations but the interval is significantly affected
by factors such as temperature and speed.
LUBRICITY : (See Oiliness).
LUSTRE : The intensity of light reflected by lubricating grease; its sheen or brilliance. Lustre should
be described as follows:
BRIGHT: Reflects light with a relatively strong intensity.
DULL: Reflects light with a relatively weak intensity. Some greases with a high water content
may have a dull lustre. Certain thickeners and fillers give a grease characteristic dull lustre.
MECHANICAL STABILITY (GREASE) : (See Shear Stability).
MELTING POINT : The temperature at which a product begins to melt or to change from the solid to
the liquid state.
METAL DEACTIVATORS : Additives used in gasoline, diesel fuels and lubricating oils to prevent the
catalytic action of metal surfaces to promote oil oxidation and gum formation in gasoline and diesel
METALLIC SOAP : (See Soap).
MICRON : 10-6 metre; one millionth of a metre.
MINERAL HYDROCARBON : (See White Oil).
MINERAL OIL : Term applied to a wide range of products with viscosities within the range of products
considered as petroleum-type oils.
MISCIBLE : Liquids capable of forming a liquid solution or uniform mixture of more than one type of
MIXED COMPLEX GREASE : A complex soap grease where the incorporation of 2 or more metal
alkalis will impart the properties of all in the final product.
MIXED FILM LUBRICATION : A condition of lubrication in which the lubricant film is so thin that the
friction between the surfaces is determined by the properties of the surfaces as well as the viscosity of
MOBILITY (GREASE) : Analogous to fluidity, the property of a lubricating grease that permits flow
under pressure, as in centralised grease dispensing systems.
MOLY, MOLYSULPHIDE : (See Molybdenum Disulphide).
MOLYBDENUM DISULPHIDE : A black, lustrous powder (MoS2) that serves as a dry-film lubricant, in
particular in high-temperature, high-load and high-vacuum applications. It is also used in the form of
pastes to prevent scoring when assembling press-fit parts, and as an additive to impart residual antiwear
lubrication properties to oils and greases. Molybdenum disulphide is often called ‘moly’ or
MOTOR OIL : Motor oil is a type of liquid oil used for lubrication by various kinds of internal
combustion engines. Other benefits from using motor oil include cooling by carrying heat away from
moving engine parts and often include cleaning and corrosion inhibition in internal combustion
engines. The major fraction of the majority of motor oils is derived from petroleum. Synthetic motor oil,
consisting of artificially-synthesised compounds, currently has a minority share in the motor oil market
place because it is more expensive, but offers enhanced performance.
MUCK POLE : A bucket operating device employed on some Ruston Bucyrus type quarrying faceshovels.
The ‘muck pole’ or ‘dipper pole’ is a 20’×18’ (approx.) steel tube which slides through a
brush, called a saddle block, fitted into the jib. Being a highly loaded sliding member constantly
exposed to the elements, lubrication is a common problem.
MULTI-GRADE OIL : Engine or gear oil that meets the requirements of more than one SAE viscosity
grade classification and that can be used over a wider temperature range than a single grade oil.
MULTI-PURPOSE GREASE : A high-quality grease that can be used in a variety of applications.
NLGI NUMBER/NLGI GRADE : A numerical scale for classifying the consistency range of lubricating
greases, and based on the ASTM D217 worked penetration (60 strokes) at 25°C (77°F). NLGI grades
are in order of increasing consistency (hardness) as follows:
NLGI CONSISTENCY NUMBER WORKED PENETRATION RANGE
25°C (77°F), mm/10 or dmm
000 445 – 475
00 400 – 430
0 355 – 385
1 310 – 340
2 265 – 295
3 220 – 250
4 175 – 205
5 130 – 160
6 85 – 115
Greases both softer and harder than this consistency range are well known in industry. Such greases
could bear an NLGI number such as 1.5 or 1½, but those grades are not official NLGI numbers.
NAPHTHA : Generic term describing a variety of light petroleum distillates such as mineral spirits and
other petroleum solvents.
NAPHTHENIC : A type of petroleum fluid derived from naphthenic crude oil, containing a high
proportion of closed-ring methylene groups.
NEAT CUTTING OILS : Oil used in machine tools as opposed to water-mix cutting fluid emulsions.
NEEDLE ROLLER BEARING : A bearing in which the rollers are several times longer than their
diameter. The rollers are tightly packed and no cage is used. These bearings are generally used in
low speed, or oscillating, high-load applications.
NEUTRAL OIL : The basis of most commonly used automotive and diesel lubricants, they are light
overhead cuts from vacuum distillation.
NEUTRALIZATION NUMBER : A measure of the acidity or alkalinity of an oil. The number is the
mass in milligrams of the amount of acid (HCl) or base (KOH) required to neutralise one gram of oil.
NEWTONIAN BEHAVIOR : The property of simple liquids by which the rate of shear is proportional to
the shearing stress. This constant proportion is the viscosity of the liquid.
NEWTONIAN FLOW : Rheological characteristic of a fluid where the rate of shear is directly
proportional to the shearing force, as with straight grade oils that do not contain a polymeric viscosity
modifier. When rate of shear is not directly proportional to the shearing force, flow is non-Newtonian,
as it is with oils containing viscosity modifiers engine oil.
NICKEL : A bright, hard, ductile ferromagnetic metal used as a plating, non-oxidising layer that
accepts rare metal coating. More recently described as a heavy metal whose powder is to be
handled as toxic by inhalation.
NITRATION : The process whereby nitrogen oxides attack petroleum fluids at low temperatures, often
resulting in viscosity increase and deposit formation.
NOISE : Tolerance and finish imperfections in an anti-friction bearing and/or variations in thickener
dispersion can lead to audible levels of vibration in a high speed bearing. This is not acceptable, for
example, in sound equipment motors. Grease must be carefully selected as to the purity and
complete homogeneity of the thickener.
NON-NEWTONIAN BEHAVIOR : The property possessed by some fluids and many plastic solids
including lubricating grease, of having variable relationship between shear stress and rate and shear.
(Non-Newtonian materials, therefore, do not possess a viscosity as defined by Newton, but rather an
apparent viscosity, the quantitative value of which may vary widely with varying shear rate.
Conventional types of viscometers with uncontrolled shear rates will not satisfactorily measure non-
NON-SOAP THICKENER : Any of several specially treated or synthetic materials, excepting the
metallic soaps of long chain fatty acids, which can be either thermally or mechanically dispersed in
liquid lubricants to form lubricating grease. Some of non-soap thickeners, such as polyurea, are also
called SYNTHETIC THICKENER. Certain types, such as silica, are called INORGANIC
NSF INTERNATIONAL : A US not-for-profit, public health & environmental organisation that sets
quality standards of, among other things, lubricants used in the proximity of foodstuffs. NSF (H1)
indicates suitability for use in incidental contact with foodstuffs under production. NSF (H2) shows
that a product has been assessed as unsuitable for lubrication of food production machinery where
there is a risk of food contamination. The NSF assesses complete product formulations and their packaging
statements rather than individual ingredients, which is the responsibility of the F.D.A.
OCTANE NUMBER : A measure of a fuel’s ability to prevent detonation in a spark ignition engine.
Measured in a standard single-cylinder, variable-compression-ratio engine by comparison with
primary reference fuels. Under mild conditions, the engine measures Research Octane Number
(RON); under severe conditions Motor Octane Number (MON). Where the law requires posting of
octane numbers on dispensing pumps, the Antiknock Index (AKI) is used. This is the arithmetic
average of RON and MON, (R M)/2. It approximates the Road Octane Number, which is a measure of
how an “average” car responds to the fuel.
OIL : A liquid of vegetable, mineral, animal or synthetic origin feeling slippery to the touch.
OIL BLEED : The rate of supply of oil from a grease to meet the demands of the surface being
lubricated as a function of pressure and/or temperature. Oil bleed therefore determines the quality
and thickness of lubrication as well as the lubrication interval. Correct oil bleed is therefore an
essential consideration in grease
OIL SLINGER : Device designed to prevent creepage of oil along a shaft.
OILINESS/LUBRICITY : A term used to describe the ability of a lubricant to reduce friction between
rubbing surface. There are no generally accepted test methods available to evaluate this property.
Oiliness is mostly important in conditions of boundary lubrication and probably represents some
relation to the ability of the oil to wet the bearing surfaces and to resist being rubbed off. Oiliness has
no known direct relation to oil viscosity.
OILLESS BEARING : Bearings made of porous metal impregnated with 10/20 percent of oil or
sometimes with graphite.
OIL WEDGE : In hydrodynamic lubrication, the build up of lubricant waiting to enter the reducing gap
created between two surfaces in relative motion, thereby creating a high pressure zone that tends to
seek equilibrium by lifting the surfaces apart.
ORGANIC : Of carbon compounds.
ORGANICALLY MODIFIED CLAY : Chemically activated bentonite clays.
ORGANOCLAY BASE GREASE : A grease prepared from a lubricating fluid thickened with an
organic modified naturally occurring earth or clay.
OUTBOARD MOTOR : Outboard motor for a boat is developed as a self-contained unit with engine,
subsidiary systems, and propeller, designed to be mounted at the stern (rear) of the craft. It is the
most common method of propelling small watercraft.
OXIDATION : Occurs when oxygen attacks petroleum fluids. The process is accelerated by heat,
light, metal catalysts and the presence of water, acids, or solid contaminants. It leads to increased
viscosity and deposit formation.
OXIDATION INHIBITOR : Substance added in small quantities to a petroleum product to increase its
oxidation resistance, thereby lengthening its service or storage life; also called antioxidant.
OXIDATION STABILITY : Resistance of a petroleum product to oxidation and, therefore, a measure
of its potential service or storage life.
OXYGENATE : An oxygen containing, ashless organic compound, such as alcohol or ether, that can
be used as a fuel or fuel supplement.
OXYGEN COMPATIBILITY : Where a substance, of synthetic or inorganic structure, resists oxidation,
particularly when exposed to strong oxidising agents.
OXYGENATED FUELS : Fuels for internal combustion engines that contain oxygen combined in the
molecule, e.g. alcohols, ethers and esters. Term also applies to blends of gasoline with oxygenates,
e.g. Gasohol, which contains 10% by volume anhydrous ethanol in unleaded gasoline.
P.F.P.E. : perfluorinated polyether. A synthetic oil of exceptional oxidation, chemical and thermal
P.T.F.E. : Teflon, Polytetrafluoroethylene. A synthetic, thermally stable thermoplastic. Resistant to
acids, alkalis and oxidising agents and showing an extremely low coefficient of friction. For the same
reasons, P.T.F.E. has excellent non-slip and release properties. (See Release Agent).
PARAFFINIC : A type of petroleum fluid derived from paraffinic crude oil and containing a high
proportion of straight chain saturated hydrocarbons. Often susceptible to cold flow problems.
PASTE : A soft, smooth, thick mixture.
PENETRATION (GREASE) : A measure of the hardness or consistency of a solid or semi-solid
material based on ASTM D217 Method (and similar methods standardiSed by other organizations). A
grease penetrometer consists of a specially designed cone which penetrates the grease under
prescribed conditions of temperature, force moving the cone, time and condition of the grease.
Penetration is the number of tenths of a millimeter that the cone penetrates into the product under
prescribed conditions. The ASTM definitions are given as follows:
- PENETRATION of lubricating grease is depth, in tenths of a millimeter, that a standard cone
penetrates the sample in a standard cup under prescribed conditions of weight, time and
temperature. The penetration depends on whether or not the consistency has been altered by
handling or agitation.
- UNDISTURBED PENETRATION is defined as the penetration at 25°C (77°F) of a sample of
lubricating grease in its container with no disturbance.
- UNWORKED PENETRATION is the penetration at 25°C (77°F) of a sample of lubricating
grease which has received only the minimum handling in transfer from sample can to test
apparatus and which has not been subjected to the action of a grease worker.
- WORKED PENETRATION is the penetration of a sample of lubricating grease which has
been brought to 25°C (77°F), subjected to 60 double strokes in a standard grease worker,
and penetration without delay.
- PROLONG WORKED PENETRATION is the penetration of a sample of lubricating grease
after it has been worked more than 60 double strokes a standard grease worker at a
temperature of 15 to 30°C (59 to 86°F). After the prescribed number of double strokes, the
worked and contents are brought to 25°C (77°F), worked an additional 60 double strokes, and
penetration without delay.
- BLOCK PENETRATION is the penetration at 25°C (77°F) of a sample of lubricating grease
that is sufficiently hard to hold its shape.
PENETROMETER : Instrument for measuring the penetration of semi-solid substances like greases.
PERCENTAGE PERMANENT VISCOSITY LOSS (PPVL) : Measure of the PVL related to the
viscosity of the fresh oil; equals PVL divided by fresh oil viscosity, multiplied by 100.
PERCENTAGE TEMPORARY VISCOSITY LOSS (PTVL) : Difference between the viscosity of an oil
measured at low and high shear rates, divided by viscosity measured at low shear rate, multiplied by
100. All viscosities must be measured at the same temperature and using the same units (cSt or cP).
PERFLUORINATED POLYETHER : (See P.F.P.E)..
PERMANENT VISCOSITY LOSS (PVL) : Irreversible reduction in lubricant viscosity due to
mechanical shear in engines or laboratory test rigs. PVL equals the difference between the fresh oil
viscosity and that of the degraded oil, both measured at the same temperature.
PETROLEUM JELLY (Petrolatum) : A gelatinous semi-solid, derived from petroleum, consisting of
various alkanes and alkenes. Used medicinally (i.e. as Vaseline) and as a carrier for lubricating solids
as well as a temporary anti-corrosion treatment.
PETROLEUM RESIDUE : That fraction of crude mineral oil that is removed to ensure the
performance quality of the useful fractions. Residue includes waxes, bitumen, acids, colourings etc..
pH : This measure indicates the acidity or alkalinity of an aqueous solution. The pH logarithmic scale
ranges from 0 (very acid) to 14 (very alkaline) with a pH of 7 indicating a neutral solution equivalent to
the pH of distilled water.
PICK-UP : Where sliding friction and surface quality allow one sliding surface to tear substantial
particles from another in relative motion, indicating failure of boundary lubrication.
PILLOW BLOCK : Denotes a block that encloses and supports a journal or shaft; a bearing. The
block is used for transferring energy at 90 degrees and supports a ?transfer shaft? with the use of
bearings. The shaft is secured via an ?off centre? ring that tightens itself onto the main bearing
manifold. Pillow block is also known as ?plummer block? outside of the US.
PITTING : Surface cavities; may be related to fatigue, overload or corrosion.
PLAIN BEARINGS : Bearings in which the motion is sliding as distinct from rolling, as anti-friction
bearings, vide “Bearings”.
PLASTIC FLOW : Surface deformation of metal as a result of yielding under heavy load. Plastic flow
differs from fluid flow in that the shearing stress must exceed a yield point before any flow occurs.
PLASTICITY : That property of apparently solid material which enables it to be permanently deformed
under the application of force, without rupture.
PLUMMER BLOCK: See pillow block
POISE (P) : Measurement unit of a fluid’s resistance to flow, i.e., viscosity, defined by the shear stress
(in dynes per square centimeter) required to move one layer of fluid along another over a total layer
thickness of one centimeter at a velocity of one centimeter per second. This viscosity is independent
of fluid density, and directly related to flow resistance.
POLAR COMPOUND : A chemical compound whose molecules exhibit electrically positive
characteristics at one extremity and negative characteristics at the other. Polar compounds are used
as additives in many petroleum products. Polarity gives certain molecules a strong affinity with solid
surfaces. As lubricant additives (oiliness agents) such molecules plate out to form a tenacious,
friction reducing film. Some polar molecules are oil-soluble at one end and water-soluble at the other.
In lubricants these act as emulsifiers, helping to form stable oil-in-water emulsions. Such lubricants
are said to have good metal-wetting properties. Polar compounds with a strong attraction for solid
contaminants act as detergents in engine oils by keeping contaminants finely dispersed.
POLISHING (BORE) : Excessive smoothing of the surface finish of the cylinder bore or cylinder liner
in an engine to a mirror-like appearance, resulting in depreciation of ring sealing and oil consumption
POLYAKYLENE GLYCOL (P.A.G.) : Synthetic oils with good viscosity index and very low tendency
POLYMER : A substance formed of repeated links of usually high molecular weight natural and
synthetic compounds, as in a plastic and elastomers.
POLYMERISATION : The creation of a polymer by chemical reaction. An unwanted reaction in oils
resulting in dramatic increase in viscosity. Sometimes loosely used to describe gum formation at
temperature or the effect of mixing two oils of different bases.
POLYTETRAFLUOROETHYLENE : (See P.T.F.E)..
POLYUREA GREASE : A grease made from a lubricating fluid thickened with polyurea or polyurea
complex thickener. Polyurea is created by the chemical reaction between an isocyanate and an
POSITIVE CRANKCASE VENTILATION (PCV) : System for removing blow-by gases from the
crankcase and returning them through the carburetor intake manifold to the combustion chamber
where the recirculated hydrocarbons are burned. A PCV valve controls the flow of gases from the
crankcase to reduce hydrocarbon emissions.
POUR POINT : An indicator of the ability of an oil or distillate fuel to flow at cold operating
temperatures. It is the lowest temperature at which the fluid will flow when cooled under prescribed
POUR POINT DEPRESSANT : Additive used to lower the pour point or low-temperature, low shearrate
fluidity of a petroleum product. Prevent insoluble wax molecules in oil from building a honeycomb
(lattice-like structure) at colder temperatures. Particularly useful for paraffinic oils. Gives useful ability
to pour at lower temperatures, An antifreeze for oil.
PRE-TREATMENT : Solid lubrication applied to give anti-wear protection under a fluid or grease
PROPELLANT : A volatile gas or liquid that, when permitted to escape from a pressurised container,
carriers with it particles or droplets of another material mixed or suspended in it as an aerosol.
Propane and butane are common petroleum-derived propellants, their having replaced CFCs.
Carbon dioxide, compressed air and nitrogen are also used as propellants – each with its own
benefits and drawbacks.
PUMPABILITY : The low temperature, low shear stress-shear rate viscosity characteristics of an oil
that permit satisfactory flow to and from the engine oil pump and subsequent lubrication of moving
components. This item also is used to indicate the “resistance to flow” of grease through grease pump
lines. Soft “buttery” grades are easy to pump. Hard, fibrous greases are difficult to pump. The ability of
a lubricating grease to flow under pressure through the line, nozzle and fitting of a grease dispensing
system. It is best indicated by the apparent viscosity at moderate rate of shear.
PYCNOMETER : A device for measuring densities of liquids.
PYROLYSIS : Chemical decomposition by the action of heat.
QUENCHING OILS : Oils used in dipping baths to control the rate of cooling of metals, especially
steel, in order to obtain desirable specific properties such as ductility, hardness, strength, etc.
R&O OIL : Oil compounded with chemical agents to inhibit rust formation in turbine lubricating
systems and to minimize oil oxidation.
RADIAL : Referring to loads and forces in a bearing that have vectors at 90 degrees to the rotating
RADIATION EFFECTS : Mineral oils, in particular, are affected by accumulated radioactivity in that
they show effects similar to high evaporation i.e. increased viscosity. There are oils that have
improved radiation stability and, in general, dry film lubricants that use solids such as molybdenum
disulphide or graphite are suitable.
RE-REFINING : A process of reclaiming used lubricant oils and restoring them to a condition similar
to that of virgin stocks by filtration, clay adsorption or more elaborate methods.
RECLAIMED OILS : This term should only be applied to used oils which have been treated by such
relatively simple processes as filtration or centrifuging, which aim mainly at removing foreign
REDWOOD SECONDS : A practical viscosity unit indicating the time taken for an oil to flow through
the tube in a Redwood viscometer. (See Brookfield, Engler, Saybolt).
REFINING : Series of processes to convert crude oil and its fractions into finished petroleum
products, including thermal cracking, catalytic cracking, polymerization, alkylation, reforming,
hydrocracking, hydroforming, hydrogenation, hydrogen treating, Hydrofining, solvent extraction,
dewaxing, de-oiling, acid treating, clay filtration and de-asphalting.
RELEASE AGENT : A film applied to a mould contour to enable removal of a newly moulded
component while protecting mould and component finish.
REPEATABILITY : The measure of the reliability of test results obtained using the same apparatus
on a number of occasions.
REPRODUCIBILITY : The measure of the reliability of tests carried out on different, but nominally
identical, apparatus by different operators and in different laboratories. To be of value a test must
produce the same results whoever performs it.
RESIDUAL FUEL : Fuel essentially composed of material remaining as un-evaporated liquid after a
distillation of crude oil. Usually high in sulphur but of relatively low cost. Widely used in high output,
slow speed, marine diesel engines.
RHEOLOGY : Study of the deformation and/or flow of matter in terms of stress, strain, temperature
and time. The rheological properties of lubricating greases are commonly measured by penetration
and apparent viscosity.
RHEOPECTIC GREASE : A grease which will heavy up in consistency on being worked or agitated
as little as would be caused pumping it through a grease distribution line.
RIDGING : In gear teeth, a form of plastic flow characterised by a rippled appearance on the surface.
RING OIL BEARING : Consists of a large diameter ring placed around the journal and dipping into an
oil reservoir. The rotation of the journal causes the ring also to rotate, although at a lower speed, due
to slippage, and to carry oil from the oil both to the bearing.
RING STICKING : Freezing of a piston ring in its groove in a piston engine or reciprocating
compressor due to heavy deposits in the piston ring zone.
RINGS : Circular metallic elements that ride in the grooves of a piston and provide compression
sealing during combustion. Also used to spread oil for lubrication.
ROLLER BEARING : An anti-friction bearing having cylindrical rolling elements in place of balls.
Usually used where high loads are to be carried, roller bearings are usually radial though roller thrust
bearings are used in more specialised applications.
ROLLING AND PEENING : In gear teeth, a form of plastic flow that gives the surface a hammered
appearance; metal may be rolled over the teeth tips.
ROLLING BEARING : (See Anti-Friction Bearing).
ROLL STABILITY : Resistance to grease disruption in an anti-friction bearing. Refer to Roll Stability
Test. (See Shear Stability, Consistency).
ROPE LUBRICATION : Wire rope strands fail as a result of bending and tension fatigue, sliding wear
and corrosion. A rope ‘dressing’ or grease, must have all the traditional lubrication properties but
particularly, the correct consistency to allow thorough penetration to the core as well as exceptional
anti-wear and corrosion protection.
RUNNING-IN : Newly machined surfaces have many asperities offering very highly loaded ‘peaks’ to
be welded and broken off into the lubricant, accelerating wear rates. Even in highly polished
elements, there will be a degree of polishing required to decrease the load per unit area. Running-in
is normal engineering practice, though it must be carefully controlled and monitored to ensure that the
final lubricating film is not contaminated with excessive wear debris.
RUST INHIBITOR : A type of corrosion inhibitor used in lubricants to protect the lubricated surfaces
RUST PREVENTATIVE : Compound for coating metal surfaces with a film that protects against rust.
Commonly used to preserve equipment in storage.
SAE : Society of Automotive Engineers; an organisation composed of persons interested in and allied
to the automotive and aircraft industries. Their many standards committees work for the
standardisation of parts, nomenclature and scientific investigations.
SAE NUMBER (Grade) : Numbers applied to crankcase, transmission and rear-axle lubricants to
indicate their viscosity range.
SAPONIFICATION : The process of forming soap (See Definition of Soap).
SAPONIFICATION NUMBER : The number of milligrams of potassium hydroxide required to react
with all fats and fatty acids in a one gram sample. This is a method of determining the quality of
compounding in a gear oil, steam cylinder oil, or other compounded lubricant.
SATURATED STEAM : Steam that is formed in a closed vessel to contact with water is called
saturated steam. Dry saturated steam is steam that carries no water in suspension.
SAYBOLT VISCOMETER : Industrial viscometer of the efflux type which is standard in USA. Now, it
is obsolete. There are two types – the Saybolt Universal for lube oils and the Saybolt Furol for more
viscous materials. The word “Furol” is a contraction of the phrase “Fuel and Road Oils.”
SCAR DIAMETER : A measurement taken after each ‘run’ of a Four-Ball test. Dimensions obtained
indicate resistance to wear of a lubricant. (See Load-Wear Index).
SCOURING : Is a washing process employed in the textile industry, where they generally utilise their
own formulas for manufacturing the scourable agent, which is usually an alkali and water solution
SCRAPER RING : A piston ring, the leading or upper edge of which is chamfered and which is
designed to return excessive oil on cylinder walls to the crank case. Mainly used in internal
SCRATCHING : Fine abrasive furrows in the direction of sliding.
SCUFFING : Abnormal engine wear due to localised welding and fracture. It can be prevented
through the use of anti-wear, Extreme-Pressure and friction modifier additives.
SCUFFING OF GEARS : When loads are heavy and the film strength of the oil is insufficient to
support the load, momentary metallic contact occurs resulting in a ridge at the pitch line of the driven
gear and a hallow at the pitch line of driving gear. In severe cases, wear of the metal takes place
along the faces and flanks of the gear teeth. Also known as “Galling”.
SEAL : A flexible component fitted outside the rotating elements of an anti-friction bearing and
rotating with the bearing against a stationary item to prevent ingress of contaminants.
SEIZE : To stick because of expansion caused by heat, friction or scoring.
SEIZING OF GEARS : An extreme case of scuffing where the lubricating film fails, and due to high
local temperatures, welding of the contacting surfaces occurs. Such damaged areas, cause of course,
scoring of succeeding tooth surfaces.
SEPARATION : The undesirable release of oil from the body of a grease in storage. (See Bleeding).
SET : In the manufacture of a lubricating grease is the change from a fluid to a semi-fluid or plastic
SETT GREASE : A lubricating grease made by mixing a mineral oil slurry of an alkali and a mineral oil
solution of fatty acid. Saponification is usually completed after the mixture is poured into the shipping
container. As the temperature of the mixture is generally less than 140°F, these products are
sometimes known as cold setts. Axle grease is usually a sett grease.
SHEAR : Stress resulting in portions of a body bending to slide one over the other. A grease is
sheared by stirring.
SHEAR RATE : The rate of slip within a substance engaging in flow. The average or mean shear rate
in a pipe or tube is the average velocity divided by the radius of the tube. It therefore has the
dimensions of the reciprocal of time and is usually expressed in the unit of reciprocal seconds (S-1).
The mean shear rate is reported in the determination of apparent viscosity in ASTM D1092.
SHEAR STABILITY (GREASE) : The ability of a lubricating grease to resist changes in consistency
(hardness) during mechanical working. Working may be in any of several types of laboratory
machines or may in actual service. This may also be called MECHANICAL STABILITY.
SHEAR STABILITY INDEX (SSI) : A measure of an oil’s irreversible viscosity loss attributable to the
viscosity modifier when the oil is subjected to engine operation or special test conditions. Also
sometimes called Permanent Shear Stability Index (PSSI), SSI is defined by the equation: SSI =
100(Vo-Vs)/(Vo-Vb), where Vo = viscosity of the unsheared oil, Vs = viscosity of the sheared oil, and
Vb = viscosity of the base oil.
SHEAR STRESS : The force required to cause shearing in a substance. In fluids the relation of the
shear stress to the shear rate is the viscosity of the substance.
SHEARING : Slipping or sliding of one part of a substance relative to an adjacent part in a solid, such
action involves cutting or breaking of the crystal structure but in a fluid of plastic, shearing does not
necessarily destroy the continuous nature of the substance.
SHIELD : A pressed ring positioned outside the rotating elements and between the races of an antifriction
bearing to give a measure of protection from radiated heat.
SILICA THICKENER : An inorganic relatively inert powder used, in particular, to thicken silicone oil
greases. (See Thickener).
SILICONES : Compounds which may be likened in many respects to hydrocarbons, except that the
molecular chain is made up of silicone atoms bound to a carbon. Because of their unique temperature
stability characteristics, silicones widely is used for specialty greases, etc.
SLIDING : The form of friction involved with rubbing of surfaces, as opposed to rolling. The resulting
wear is expensive in terms of parts, labour and downtime. The study of rubbing and wear is called
Tribology. It is the function of a lubricant to interpose itself between the sliding surfaces to reduce
friction and therefore wear.
SLUDGE : A thick, dark residue, normally of mayonnaise consistency, that accumulates on
nonmoving engine interior surfaces. Generally removable by wiping unless baked to a carbonaceous
consistency, its formation is associated with insolubles overloading of the lubricant.
SLUMPABILITY (GREASE) : A property of some greases which makes them partially self-leveling.
Greases possessing this property will be pumped from a container without the necessity of using a
follower plate. (See definition of Follower Plate). This property is often confused with PUMPABILITY
SOAP : A specific type of salt formed by the reaction of fatty acid with an alkali.
SODIUM COMPLEX GREASE : A grease prepared from a lubricating fluid thickened with special
sodium soaps and/or complex agents. Sodium complex grease usually has better properties, such as
water resistant property and high temperature property, than a regular sodium grease.
SODIUM SOAP GREASE : Also called Soda Grease, a grease prepared from a lubricating fluid
thickened with sodium soap.
SOL : A suspension of particles of colloidal dimensions in a liquid, which possesses the gross
properties of a liquid.
SOLID FILM LUBRICANT/SOLID BONDED LUBRICANT : Materials with inherent lubricating
properties which are firmly bonded to the surface of a substrate by some methods. Those methods
include a bonding agent, burnishing, mechanical impingement or vacuum deposition.
SOLID LUBRICANT : Any class of lubricants in which the reduction of friction and wear during sliding
is caused by making the shearing take place within the crystal structure of a material with low shear
strength in one particular plane. Examples include graphite, molybdenum disulphide and certain
soaps. Lubricating grease is not a solid lubricant, but may contain solid lubricants as additives.
SOLUBLE CUTTING OILS : Mineral oil compounded with suitable agents to permit the formation of
emulsions with water. Whilst all cutting oils act as a coolant as well as a lubricant, water is more
efficient as a cooling medium than oil, and for certain types of work it is necessary to provide a
combination of the two in order to secure the most satisfactory results.
SOLVENT : A compound with a strong capability to dissolve a given substance. The most common
petroleum solvents are white spirits, xylene, toluene, hexane, heptanes and naphthas. Aromatic-type
solvents have the highest solvency for organic chemical materials, followed by napthenes and
paraffins. In most applications the solvent disappears, usually by evaporation, after it has served its
purpose. The evaporation rate of a solvent is very important in manufacture: cement and delicate
plastic cleaners often require a fast-drying solvent, whereas adhesives that must remain tacky during
processing, require a slower-drying solvent. Solvents have a wide variety of industrial applications,
including the manufacture of pains, inks, cleaning products, adhesives, including the manufacture of
pains, inks, cleaning products, adhesives, and petrochemicals. Other types of solvents have
important applications in refining and in aerosols. (See Solvent Extraction, Solvent Refined).
SOLVENT EXTRACTION : Refining process used to separate reactive components (unsaturated
hydrocarbons) from lubricant distillates in order to improve the oil’s oxidation stability, viscosity index
and additive response.
SOLVENT REFINING : A process for extracting lubricant base stocks from stripped heavy gas oil or
other heavy, stripped crude stream using selective solvents such as furfural or phenol.
SPALLING : Severe damage characterised by large pits, cavities and related cracks; related to
overload and fatigue.
SPECIFICATIONS : Prescribed limits of control tests used to maintain uniformity of a specific product.
SPECIFIC GRAVITY : The ratio of the weight (in air) of a given volume of a material to the weight (in
air) of an equal volume of water at stated temperatures.
SPEED FACTOR : Centrifugal force and accelerations will throw oil from surfaces within a bearing,
resulting in inadequate lubricant supply and thin-film lubrication. Under these conditions oxidation will
be accelerated. For these reasons a grease is assessed as to its limiting speed with reference to
bearing size. This judgement is based on viscosity, thickener type and oil content. In the laboratory,
apparent viscosity is used to indicate high-speed performance. (See Dn). A dN resultant in excess of
1 million usually indicates the use of oil. For reasons of material stress the bearing is also given a
SPLASH LUBRICATION : Method of lubrication in which the oil in a bath is splashed by the moving
mechanism into those parts requiring a supply of lubricant.
SPUR GEAR : A cylinder, wheel or disc on the surface of which are cut parallel teeth, each in
common plane with the axis.
SQUEEZE FILM LUBRICATION : That state of lubrication in which surfaces thickly coated or flooded
with lubricant move toward each other at sufficient speed to develop fluid pressure sufficient to
support a load of short duration. Because of viscosity (or apparent viscosity), the lubricant cannot
immediately flow away from the area of contact. This action occurs for example between gear teeth
and between pins and their bushings.
STABILISER : A chemical additive that acts to reduce the effect of deterioration of a product as a
result of its required operating regime, i.e. oxidation at temperature would be counteracted by use of
an ‘anti-oxidant’. (See, for example, Oxidation Inhibitor).
STABILITY : Used to indicate resistance to failure under particular conditions, i.e. shear stability.
STEAM CYLINDER OILS : The steam engine is unique in that the lubricating oil is not applied directly
to cylinder walls or value surfaces, but is distributed by the steam after the latter has been charged or
impregnated with oil from a lubricator in the main steam line adjacent to the value chest. Steam
cylinder oils must be of comparatively heavy viscosity and possess high wettability in order to ensure
that the lubricating film will cling to the valve seats and cylinder walls, withstand washing off by the
steam, and resist the wearing or scraping effects of valves and piston rings. For operation under wet
steam conditions the oil is generally compounded.
STEARATE : A salt or ester of stearic acid. Used, very loosely, to refer to soap thickeners. (See
STEP-UP PUMP : A pump that increases delivery pressure in ever-increasing stages.
STICK-SLIP MOTION : The erratic motion of adjacent surfaces, usually at slow speeds, where
starting friction exceeds running friction leading to jerky initial movement, so making accurate
adjustments etc, very difficult. Stick-slip is overcome by introducing a low-friction film between the
STOKE (St) : A unit of measure of kinematic viscosity defined by the ratio of the fluid’s dynamic
viscosity to its density. Usually expressed as centistokes (cSt), where 1 Stoke = 100 cSt and 1 cSt = 1
STRAIGHT MINERAL OIL : A petroleum oil not containing compounds (animal or vegetable oils) or
SSU : Saybolt Seconds Universal. A unit of measure of lubricating oil viscosity commonly used in the
SULPHURISED CUTTING OILS : Cutting oils containing sulphur and used for difficult machining
operations, such as threading and tapping at high speed, broaching, and for alloy steels that machine
SUPER-HEATED STEAM : If more heat is added to steam after all the water it contains has been
transferred into steam, the temperature of the steam will be greater than that of ordinary saturated
steam having the same pressure.
SURFACE TENSION : The attractive force exerted by molecules below the surface upon molecules
at the surface/air interface. The strength of the surface tension various with the polarity of the liquid:
high-polar substances like water have higher surface tension than low-polar substances like oils.
SURFACTANT : An additive that reduces surface tension of a liquid. In a lubricating oil a surfactant
may increase its affinity with metals. A surface active agent.
SUSPENSION : In which relatively coarse solid particles are dispersed in a liquid. Usually poorly
suspended because of particle size or lack of polar additives, etc. and therefore requiring agitation to
maintain a satisfactory dispersion. Non-colloidal.
SYNERESIS : Loss of liquid lubricant from a lubricating grease due to shrinkage or rearrangement of
the structure. The shrinkage may be due to either physical or chemical changes in the thickener.
Syneresis is a form of BLEEDING.
SYNTHETIC HYDROCARBON : Artificial reproduction of naturally occurring mineral oil product but
without undesirable aromatics etc. (See Hydrocarbon).
SYNTHETIC LUBRICANT : Lubricating fluid made by chemically reacting materials of a specific
chemical composition to produce a compound with planned and predictable properties.
SYNTHETIC OIL : Man-made fluids possessing deliberately formulated properties such as high
temperature performance. (See Silicones, P.F.P.E.).
SYNTHETIC THICKENER : (See Non-Soap Thickener).
TACKINESS ADDITIVE : A highly viscous additive to enhance a products’ ability to adhere to
surfaces to be lubricated.
TACKY : A descriptive term applied to greases which appear particularly sticky or adhesive.
TAN (TOTAL BASE NUMBER) : A neutralising number intended for measuring all acidic and acid
acting materials in the lube, including strong and weak acids.
TANK FARM : Name given to collection of oil storage tanks.
TAPER ROLLER BEARING : An anti-friction bearing in which the rollers are inclined away from
parallel with the shaft axis, thereby offering a thrust reaction vector.
TBN (TOTAL BASE NUMBER) : A neutralising number intended for measuring all basic (alkaline)
materials in the lubricant, e.g. acid neutralising components in the lubricant’s additive package. High
TBN is desirable in a crankcase oil to control corrosive engine wear from acids of combustion.
TECHNICAL WHITE OILS : White oils which do not meet USP (United States Pharmacopeia)
requirements, but have many industrial applications.
TEMPORARY SHEAR STABILITY INDEX (TSSI) : The measure of the viscosity modifier’s
contribution to an oil’s percentage viscosity loss under high shear conditions. Temporary shear loss
results from the reversible lowering of viscosity in high shear areas of the engine, an effect that can
positively influence fuel economy and cold cranking speed.
TEMPORARY VISCOSITY LOSS (TVL) : Difference between dynamic viscosity measured at high
shear rate compared to that determined at low shear rate. Both viscosities are measured at the same
TENSILE STRENGTH : The force required to break a bar of unit cross section under tension. The
tensile strength depends not only on the cohesion of the material, but also upon the consistency, and
therefore, at least to some extent depends upon the rate of application of the load.
TEXTURE (GREASE) : That property of lubricating grease which is observed when a small separate
portion of it is pressed together and then slowly drawn apart. TEXTURE should be described in the
- BRITTLE: Has tendency to rupture of crumble when compressed.
- BUTTERY: Separates in short peaks with no visible fibres.
- LONG FIBRE: Shows tendency to stretch or string out into a single bundle of fibres.
- SHORT FIBRE: Shows short break-off with evidence of fibres.
- RESILIENT: Capable of withstanding moderate compression without permanent deformation
THERMAL STABILITY : Ability of a lubricant to resist oxidation under high temperature operating
THICKENING AGENT (THICKENER) : The solid particles which are relatively uniformly dispersed to
form the structure of lubricating grease in which the liquid is held by surface tension and other
THICK FILM LUBRICATION : (See Hydrodynamic Lubrication).
THIN FILM LUBRICATION : (See Boundary Lubrication).
THIXOTROPIC : Change of consistency as a result of stirring, shaking, vibration, etc and returning to
correct stiffness when allowed to stand.
THIXOTROPY (GREASE) : That property which is manifested by a decrease in consistency or
softening, as a result of shearing, followed by an increase in consistency or hardening, beginning after
shearing is stopped. (Thixotropic age hardening is a relatively prolonged process proportional to aging
time and is seldom, if ever, complete whereas the apparent viscosity increase which occurs in non-
Newtonian systems with decreasing shear rate, is instantaneous and fully reversible. Lubricating
grease is both thixotropic and non-Newtonian).
THRUST BEARINGS : These bearings support a load, acting in the direction of the axis of the
bearing. They may be plain, anti-friction, or involve special sliding elements.
TIMKEN EP TEST : A measure of the extreme-pressure (EP) properties of a lubricating oil. The test
utilises a Timken machine, which consists of a stationary block pushed upward, by means of a lever
arm system, against the rotating outer race of a roller bearing, which is lubricated by the product
under test. The test continues under increasing load (pressure) until a measurable wear scar is
formed on the block. Timken OK Load is the heaviest load that a lubricant can withstand before the
block is scored. (See Scoring, Timken Test Machine).
TIMKEN ‘OK’ LOAD : (See Timken Test Machine).
TORQUE : Force which produces or tends to produce rotation or torsion “twist”.
TOUGHNESS : The property of yielding to force without breaking.
TOXICITY : The degree to which a toxin (a poison) is toxic (poisonous).
TRACTION FLUID : Fluid displays high traction coefficients; under high stress it develops a glass-like
structure, simultaneously transmitting shear forces and protecting the contacting surfaces from wear.
TRIBOLOGY : Science of the interactions between surfaces moving relative to each other, including
the study of lubrication, friction and wear.
TURBULENCE : Rapid movement of the air/fuel mixture in an internal combustion engine which
affects the rate of combustion.
UNCOMPOUNDED OIL : Straight mineral oil.
UNSATURATED : A term applied to carbon compounds in which some of the carbon atoms are held
together by double bonds or triple bonds so that these compounds are capable of combining directly
with other elements or compounds. Lubricants containing unsaturated materials are usually
somewhat unstable and subject to oxidation.
VALVE LIFTER : Sometimes called a “cam follower,” a component in engine designs that use a
linkage system between a cam and the valve it operates. The lifter typically translates the rotational
motion of the cam to a reciprocating linear motion in the linkage system.
VAPOR PHASE CORROSION INHIBITOR : Corrosion inhibitor in the form of a vapor, which is made
from fine, volatile powders, after vaporizing, it is absorbed by metal surfaces.
VAPOR PRESSURE : Measure of the volatility of a liquid at specified temperatures and pressures (or
VARNISH : A thin, insoluble, non-wipeable film occurring on interior engine parts. Can cause sticking
and malfunction of close-clearance moving parts. Called lacquer in diesel engines.
VEGETABLE OIL : An oil produced from plant matter, such as linseed or rape. Though often not
having the load-carrying or temperature performance of mineral or synthetic oils, they are food-safe
and relatively inexpensive.
VELOCITY : Time rate of motion in a fixed direction.
VIBRATION : Oscillation or rapid reciprocating motion. Sudden reversals of motion in a system result
in breakdown of boundary lubrication without careful design. Vibration frequently produces thixotropic
reaction in grease gels, resulting in excessive loss of consistency.
VISCOMETER/VISCOSIMETER : An apparatus for determining the viscosity of a lubricant.
VISCOSITY : Viscosity may be regarded as a measure of the internal resistance to flow of a fluid,
semi-fluid or semi-solid substance. Its numerical value is based on the ratio of shear stress to the rate
of shear during flow. Viscosities are usually determined by absolute or dynamic viscosity and
VISCOSITY GRADE : Any of a number of systems which characterize lubricants according to
viscosity for particular applications, such as industrial oils, gear oils, automotive engine oils,
automotive gear oils, and aircraft piston engine oils. The commonly used systems are ISO and SAE.
V.I. IMPROVER : A material added to a fluid which alters the viscosity characteristic of the fluid and
increases its viscosity index: hence, the name V.I. Improver.
VISCOSITY INDEX (VI) : Relationship of viscosity to the temperature of a fluid. It is determined by
measuring the kinematic viscosities of the oil at 40 and 100°C and using the tables or formulas
included in ASTM D 2270. High viscosity index fluids tend to display less change in viscosity with
temperature than low viscosity index fluids.
VISCOSITY MODIFIER : Lubricant additive, usually a polymer, whose function is to provide beneficial
rheological properties to lubricating oils, such as reducing the tendency of an oil’s viscosity to change
VOLATILITY : The tendency of a product to change from the state of liquid to that of vapor. This
property is, of course, very important in gasoline.
WATER DISPLACING : The capacity of many oil-based products to ‘wet’ the metal surface with a
protective film to prevent corrosion. (See Wetting Agent).
WATER REGULATIONS ADVISORY SCHEME (WRAS) : Promotes knowledge of the water regulations
throughout the UK. WRAS assess testing of materials and publishes satisfactory materials in the scheme’s
‘Water Fittings and Materials Directory’.
WATER RESISTANCE : The ability of a lubricating grease to withstand the addition of water to the
lubricant system without adverse effects. Water resistabce is generally considered to be made up of
four components as listed below:
- WASHOUT RESISTANCE: The ability of a lubricating grease to resist being removed from a
bearing when operated fully or partially submerged in water. Generally measured by ASTM
- WATER ABSORPTION CHARACTERISTIC: The characteristics of a lubricating grease
when water is added to the lubricating system. Water absorption characteristic may be
measured by any of several suitable tests in which the lubricating grease may react in any of
these three ways – water soluble, water absorbent or water resistant.
- WATER CORROSION RESISTANCE: The ability of a lubricating grease to prevent corrosion
of surfaces when water is present in the lubricating system. May be measured either statically
by any of a number of standard tests, or dynamically by actual operation of bearings with
water added to the lubricant reservoir. (Refer ASTM D1743 and D6138).
- WATER SPRAY RESISTANCE: The ability of a grease to resist displacement from a surface
by the impact of water spray. The method of test used to evaluate this characteristic for
lubricating grease is given in ASTM D4049.
WAX : A viscous or solid, heat-sensitive, natural or synthetic substance that is characteristically
insoluble in water but readily dissolved in most organic solvents. Waxes are commonly used as
carriers of active ingredients in a wide range of products that are used industrially and domestically.
In lubrication, waxes are used to impart water resistance, among other things. Wax development at
low temperature in paraffinic oils is undesirable and its removal is an objective of solvent refining.
WEAR : The removal of materials from surfaces in relative motion. Three types of wear are described
- ABRASIVE WEAR: Removal of materials from surfaces in relative motion by a cutting or
abrasive action of a hard particle (usually a contaminant).
- ADHESIVE WEAR: Removal of materials from surfaces in relative motion as a result of
surface contact. Calling and scuffing are extreme forces.
- CORROSIVE WEAR: Removal of materials by chemical action.
WELD : To fuse together from heat and/or pressure.
WET STEAM : Steam containing minute globules of water in suspension.
WETTING AGENT : An additive that encourages an oil to spread and adhere more intimately with a
surface to give enhanced boundary layer lubrication and corrosion protection.
WHITE METAL : Bearing alloy made of lead, antimony and copper.
WHITE OIL or WHITE MINERAL OIL : Highly refined lubricant stock used for specialty applications
such as cosmetics and medicines. White oil usually must meet USP (United States Pharmacopeia) or
NF (National Formulary) requirements.
WICK FEED CUPS : Lubricators consisting of oil reservoirs or cups in which one end of a wick of
cotton, felt, wool, etc. dips into the oil and by capillary action drains the oil into the bearing to be
WORKED PENETRATION : The penetration of a grease sample immediately after it has been
brought to a temperature of 77°F and then subjected to 60 double strokes in a standard grease
WORKING : A term used to indicate the shearing and churning of a grease in an anti-friction bearing.
WORM GEAR : The two members of a worm gear set are known as the work and the worm wheel or
gear. The worm resembles a screw, although it is really a special form of helical gear, and its teeth
are referred to as threads.
WRAS : See Water Regulations Advisory Scheme
YIELD (OF LUBRICATING GREASE) : The amount of grease of a given consistency which may be
made with a definite amount of thickening agent. As the yield increases, percent thickener decreases.
YIELD POINT or YIELD STRESS : The minimum shear stress required to produce flow of a plastic
material. It is estimated by the intercept of the shear stress axis of the shear stress – shear rate curve,
by extrapolation of the straight portion of the curve.
ZERK FITTING : A common grease fitting, one of may types of fittings used in lubrication.
ZINC (ZDDP or ZDTP) : Commonly used name for zinc dialkyl dithiophosphate or zinc
dithiophosphate, an anti-wear/oxidation inhibitor chemical