Lubricants Glossary

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Abrasion A general wearing away of a surface by constant scratching, usually due to the presence of foreign matter such as dirt, grit, or metallic particles in the lubricant. It may also cause a breakdown of the material (such as the tooth surfaces of gears). Lack of proper lubrication may result in abrasion.

Absorption process by which one substance draws into itself another substance.

Acid A member of an important and fundamental category of chemical substances characterized by having an available reactive hydrogen and requiring an alkali to neutralize them. Acid solutions have a pH less than 7.

Acid treating A refining process in which unfinished petroleum products, such as gasoline, kerosene, and lubricating oil stocks, are contacted with sulfuric acid to improve their color, odor, and other properties.

Additive An agent or chemical substance added to a product and used for imparting new, or for improving existing characteristics of lubricating oils or greases.
Common petroleum product additives are:

  • anti-foam agent
  • anti-icing additive
  • anti-oxidant
  • anti-wear additive
  • corrosion inhibitor
  • demulsifier
  • detergent
  • dispersant
  • emulsifier
  • EP additive
  • fluidizer
  • oiliness agent
  • oxidation inhibitor
  • pour point depressant
  • rust inhibitor
  • tackiness agent
  • viscosity index (V.I.) improver

Adhesion The force or forces causing two materials such as a lubricating grease and a metal, to stick together.

Aeration The state of air being suspended in a liquid such as a lubricant or hydraulic fluid.

AGMA An acronym for “American Gear Manufacturers Associations,” an organization serving the gear industry.

AGMA Lubricant Numbers AGMA specification covering gear lubricants. The viscosity ranges of the AGMA numbers (or grades) conform to the International Standards Organization (ISO) viscosity classification system.

Air entrainment The incorporation of air in the form of bubbles as a dispersed phase in the bulk liquid. Air may be entrained in a liquid through mechanical means and/or by release of dissolved air due to a sudden change in environment. The presence of entrained air is usually readily apparent from the appearance of the liquid (i.e., bubbly, opaque, etc.) while dissolved air can only be determined by analysts.

Alkali In chemistry, any substance having basic properties. The term is applied to hydroxides of ammonium, lithium, potassium, and sodium. They are soluble in water; have the power to neutralize acids and form salts. They turn red litmus blue. In a more general sense, the term is also applied to the hydroxides of the so-called alkaline earth metals: barium, calcium, and strontium.

Ambient temperature Temperature of the area or atmosphere around a process, (not the operating temperature of the process itself).

Aniline point The minimum temperature for complete miscibility of equal volumes of aniline and the sample under test ASTM Method D 611. A product of high aniline point will be low in aromatics and naphthenes and, therefore, high in paraffins. Aniline point is often specified for spray oils, cleaning solvents, and thinners, where effectiveness depends upon aromatic content.

In conjunction with API gravity, the aniline point may be used to calculate the net heat of combustion for aviation fuels.

Anti-foam agent An additive used to control foam.

Anti-friction bearing(s) A type of bearing using rollers, cones or balls. They are also known as rolling element bearings.

Antioxidant chemical added to lubricating oils to resist oxidation.

Anti-seize compound grease-like substance containing graphite, moly or metallic solids (Copper, Zinc, Silver or Lead), which is applied to threaded joints, particularly those subjected to high temperatures, to facilitate separation when required.

Anti-wear additive additive in a lubricant that reduces friction and excessive wear.

API The American Petroleum Institute (API) is a trade association that promotes U.S. petroleum interests, encourages development of petroleum technology, cooperates with the government in matters of national concern, and provides information on the petroleum industry to the government and the public.

API Engine Service Classification System Classifications and designations for lubricating oils for automotive engines developed by API in conjunction with SAE and ASTM. An recently also with ILSAC.

API Gear Lubricant Service Designation Classifications and designations for lubricating oils for automotive transmissions developed by API in conjunction with SAE and ASTM.

API gravity A nonscientific and arbitrary scale expressing the gravity or density of liquid petroleum products. The measuring scale is calibrated in terms of degrees API.

Aromatic Derived from, or characterized by, the presence of the benzene ring. Aromatics are used extensively as petrochemical building blocks in the manufacture of pharmaceuticals, dyes, plastics, and many other chemicals.

Ash Metallic deposits formed in the combustion chamber and other engine parts during high temperature operation.

Ash content The percent by weight of residue left after combustion of an oil or fuel sample. (ASTM Method D 482 or D 874 [sulfated ash]).

Lubricating oil detergent additives contain metallic derivatives, such as barium, calcium, and magnesium sulfonates, that are common sources of ash. Ash deposits can impair engine efficiency and power.

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.

Asphaltic Essentially composed of, or similar to, asphalt; frequently used to describe lubricating oils derived from crude oils which contain asphalt.

ASTM The American Society for Testing and Materials (ASTM) is a professional society that is responsible for the publication of test methods and the development of test evaluation techniques.


a. In realtion to Fuels & Combustion in Internal Combustion Engines it is the spontaneous ignition, and the resulting very rapid reaction, of a portion or all of the fuel-air mixture in an engine. The flame speed is many times greater than that which follows normal spark ignition. The noise associated with it is called knock.

b. In realtion to Lubricants it is the Temperature at which the lubricant will self ignite when exposed to air and continue to burn.


Bactericide  additive included in the formulations of water-mixed cutting fluids or coolants, to inhibit the growth of bacteria promoted by the presence of water, thus preventing the unpleasant odors that can result from bacterial action.

Barrel  Standard unit of liquid measurement in the petroleum industry. Used to measure quantities of crude oil, gasoline and fuel oils. Equivalent of 42 U.S. Gallons.

Base Oil  A base oil is a base stock or blend of base stocks used in an API-licensed engine oil.

Base Stock  A base stock is a mineral hydrocarbon or synthetic lubricant component that is produced by a single manufacturer (independent of crude source or manufacturing location), that meets the same manufacturer’s specification, and that is identified by a unique formula, product identification number, or both.

Bearing  basic machine component designed to reduce friction between moving parts and to support moving loads.

There are two main types of bearings:

  1. rolling contact bearings (also called anti-friction bearings) commonly ball or roller
  2. sliding (plain) bearings, either plain journal (a metal jacket fully or partially enclosing a rotating inner shaft) or pad-type bearings, for linear motion.

Rolling-contact bearings are more effective in reducing friction. With few exceptions, bearings require lubrication to reduce wear and extend bearing life.

Biocides  Additive designed to inhibit the growth of microorganisms in liquids

Biodegradation  The chemical breakdown of materials by living organisms in the environment. The process depends on certain microorganisms, such as bacteria, yeast, and fungi, which break down molecules for sustenance. Certain chemical structures are more susceptible to microbial breakdown than others; vegetable oils, for example, will biodegrade more rapidly than petroleum oils. Most petroleum products typically will completely biodegrade in the environment within two months to two years.

Blow-by  in an internal combustion engine, seepage of fuel and gases past the piston rings and cylinder wall into the crankcase, resulting in crankcase oil dilution and deposit formation.

Boiling point The temperature at which a substance boils, or is converted into vapor by bubbles forming within the liquid; it varies with pressure.

Bottoms  The liquid which collects in the bottom of a vessel (tower bottoms, tank bottoms), either during a fractionating process or while in storage.

Boundary lubrication  The state of lubrication when conditions exist that do not permit the formation of a lubricant film capable of completely separating the moving parts. As a result the asperities of the moving parts come in contact and a high wear rate results. Boundary lubrication can be made more effective by including additives in the lubricating oil that provide a stronger oil film, thus preventing excessive friction and possible scoring. There are varying degrees of boundary lubrication, depending on the severity of service. For mild conditions, oiliness agents may be used; by plating out on metal surfaces in a thin but durable film, oiliness agents prevent scoring under some conditions that are too severe for a straight mineral oil. Compounded oils, which are formulated with polar fatty oils, are sometimes used for this purpose. Anti-wear additives are commonly used in more severe boundary lubrication applications. The more severe cases of boundary lubrication are defined as extreme pressure conditions; they are met with lubricants containing EP additives that prevent sliding surfaces from fusing together at high local temperatures and pressures.

Bright stock  Refined, high viscosity base oils usually made from residual stocks by suitable treatment, such as a combination of solvent extraction, propane asphating or catalytic dewaxing.

British Thermal Unit (BTU)  The quantity of heat required to raise, by 1°F, the temperature of one pound of water at its maximum density (39.2°F).

Brookfield viscosity  apparent viscosity of an oil, as determined under test method ASTM D 2983. Since the apparent viscosity of a non-Newtonian fluid holds only for the shear rate (as well as temperature) at which it is determined, the Brookfield viscometer provides a known rate of shear by means of a spindle of specified configuration that rotates at a known constant speed in the fluid. The torque imposed by fluid friction can be converted to absolute viscosity units (centipoises) by a multiplication factor. See viscosity, shear stress. The viscosities of certain petroleum waxes and wax-polymer blends in the molten state can also be determined by the Brookfield test method ASTM D 2669.


CAFÉ  Corporate Average Fuel Economy Minimum Fuel Economy for Cars and Light Trucks established by U.S. Congress.


a. The amount of heat required to raise the temperature of 1 gram of water 1ºC, at or near the temperature of maximum density. This unit is called a “small calorie”, or “gram calorie”.
b. The amount of heat required to raise the temperature of 1 kg of water 1°C.
This unit is called a “large calorie” or “kilogram-calorie”.

Capillary viscometer  A viscometer in which the oil flows through a capillary tube.

Carrier Oil  Oil (Petroleum), usually solvent neutral (SN) or process oil, used to “carry” or dissolve and/or disperse additives, which would otherwise be too viscous or even solid, and therefore not easily mixed with the Base Stock Oil.

Catalyst  substance that causes or speeds up a chemical reaction without itself undergoing an associated change; catalysts are important in a number of refining processes.

Catalytic cracking  in refining, the breaking down at elevated temperatures of large, high-boiling hydrocarbon molecules into smaller molecules in the presence of a catalyst. The principal application of catalytic cracking is the production of high-octane gasoline, to supplement the gasoline produced by distillation and other processes. Catalytic cracking also produces heating oil components and hydrocarbon feedstocks, such as propylene and butylene, for polymerization, alkylation, and petrochemical operations.

Cavitation  formation of an air or vapor pocket (or bubble) due to lowering of pressure in a liquid, often as a result of a solid body, such as a propeller or piston, moving through the liquid; also, the pitting or wearing away of a solid surface as a result of the collapse of a vapor bubble. Cavitation can occur in a hydraulic system as a result of low fluid levels that draw air into the system, producing tiny bubbles that expand explosively at the pump outlet, causing metal erosion and eventual pump destruction. Cavitation can also result when reduced pressure in lubricating grease dispensing systems forms a void, or cavity, which impedes suction and prevents the flow of greases.

Centipoise (cp)  A unit of absolute viscosity. 1 centipoise = 0.01 poise. See Poise.

Centistoke (cSt)  The worldwide unit of kinematic viscosity. 1 cSt = 0.01 stoke. See Stoke.

Channeling  The phenomenon observed among gear lubricants and greases when they thicken due to cold weather or other causes, to such an extent that a groove is formed through which the part to be lubricated moves without actually coming in full contact with the lubricant.

Circulating Oil  A lubrication system wherein the oil pump runs continuously and circulates oil to the friction points on a continuous basis. The oil is drained back to tank, filtered, cooled as required and reused.

Circulating System  A lubricating system in which oil is recirculated from a central sump to the parts requiring lubrication and then returned to the sump.

Cloud point  The temperature at which paraffin wax or other solid substances begin to crystallize or separate from the solution, imparting a cloudy appearance to the oil when chilled (ASTM Method D 97).

Coking  The undesirable accumulation of carbon (coke) deposits in the internal combustion engine or in a refinery plant or tThe process of distilling a petroleum product to dryness.

Color  A factor in the identification, rather than in the quality rating of a petroleum products and lubricants, except where staining or appearance are considerations.

Complex grease  A lubricating grease thickened by a complex soap consisting of a normal soap and a complexing agent.

Compounding  The addition of fatty oils and similar materials to lubricants to impart special properties. Lubricating oils to which such materials have been added are known as compounded oils.

Compounded oil  mixture of a petroleum oil with animal or vegetable fat or oil. Compounded oils have a strong affinity for metal surfaces; they are particularly suitable for wet-steam conditions and for applications where lubricity and extra load-carrying ability are needed. They are not generally recommended where long-term oxidation stability is required.

Copper strip corrosion  The gradual eating away of copper surfaces as the result of oxidation or other chemical action. It is caused by acids or other corrosive agents.

Corrosion  The gradual eating away of metallic surfaces as the result of oxidation or other chemical action.
It is caused by acids or other corrosive agents or by electro-chemical reaction of the metal with its environment.

Corrosion Inhibitor  substance which protects a metal against corrosion by substances which originate from products of combustion, or from deterioration of the lubricant.

Cracking  petroleum refining process in which large-molecule liquid hydrocarbons are converted to small-molecule, lower-boiling liquids or gases; the liquids leave the reaction vessel as unfinished gasoline, kerosene, and gas oils. At the same time, certain unstable, more reactive molecules combine into larger molecules to form tar or coke . The cracking reaction may be carried out under heat and pressure alone (thermal cracking), or in the presence of a catalyst (catalytic cracking).

Crude oil  complex, naturally occurring fluid mixture of petroleum hydrocarbons, yellow to black in color, and also containing small amounts of oxygen, nitrogen and sulfur derivatives and other impurities. Crude oil was formed by the action of bacteria, heat, and pressure on ancient plant and animal remains, and is usually found in layers of porous rock such as limestone or sandstone capped by an impervious layer of shale or clay that traps the oil (reservoir). Crude oil varies in appearance and hydrocarbon composition depending on the locality where it occurs, some crudes being predominantly naphthenic, some paraffinic, and others asphaltic. Crude is refined to yield petroleum products.

Cutting Fluid  Any fluid applied to a cutting tool to assist in the cutting operation by cooling, lubricating or other means.

Cutting Oil  A lubricant used in machining operations for lubricating the tool in contact with the workpiece, and to remove heat. The fluid can be petroleum based, water based, or an emulsion of the two. The term “emulsifiable cutting oil” normally indicates a petroleum-based concentrate to which water is added to form an emulsion which is the actual cutting fluid.

Cylinder  A device which converts fluid power into linear mechanical force and motion. It usually consists of a moveable element such as a piston and piston rod, plunger rod, plunger or ram, operating with in a cylindrical bore.

Cylinder Oil  A lubricant for independently lubricated cylinders, such as those of steam engines and air compressors; also for lubrication of valves and other elements in the cylinder area. Steam cylinder oils are available in a range of grades with high viscosities to compensate for the thinning effect of high temperatures; of these, the heavier grades are formulated for super-heated and high-pressure steam, and the less heavy grades for wet, saturated, or low-pressure steam. Some grades are compounded for service in excessive moisture; see compounded oil. Cylinder oils lubricate on a once-through basis.


Demulsibility  ability of an oil to separate from water, as determined by test method ASTM D 1401 or D 2711. Demulsibility is an important consideration in lubricant maintenance in many circulating lubrication systems.

Demulsifier  additive that promotes oil-water separation in lubricants that are exposed to water or steam.

Density  The mass of a unit of volume of a substance as compared to Water which has a density of one.

Detergency  The ability of an oil to keep working surfaces of equipment clean (i.e. free from contaminants) by holding oil-insoluble material in suspension thus preventing deposition where it would be harmful.

Detergent  important additive component of engine oils and some industrial lubricants, such as paper machine oils and hydraulic fluids; helps control deposits by preventing contaminants of combustion from directly contacting metal surfaces and, in some cases, by neutralizing acids. A detergent is usually a metallic (commonly barium, calcium, or magnesium) compound, such as a sulfonate, phosphonate, thiophosphonate, phenate, or salicylate. Because of its metallic composition, a detergent leaves a slight ash when the oil is burned. A detergent is normally used in conjunction with a dispersant.

Detergent oil  Is a lubricating oil possessing special sludge-dispersing properties usually conferred on the oil by the incorporation of special additives. Detergent oils hold formed sludge particles in suspension and thus promote cleanliness especially in internal-combustion engines. However detergent oils do not contain “detergents” such as those used for cleaning of laundry or dishes. Also detergent oils do not clean already “dirty” engines, but rather keep in suspension the sludge that petroleum oil forms so that the engine remains cleaner for longer period. The formed sludge particles are either filtered out by Oil Filters or drained out when oil is changed.

Dielectric strength  A measure of the of insulating properties of electrical insulating oils for use in electrical cables, transformers, circuit breakers, and similar apparatus (Tested by ASTM Method D 877).

Diester oil  A synthetic Iubricating fluid made from esters: also called ester oil or an organic ester, formed by reacting a dicarboxylic acid and an alcohol; properties include a high viscosity index (V.I.) and low volatility. With the addition of specific additives, it may be used as a lubricant in compressors, hydraulic systems, and internal combustion engines.

DIN  Deutsche Industrie Norm (German Industrial Standards).

Dispersant  A dispersing agent, which holds a very finely divided substance in a dispersed state in the carrier fluid. Such as sludge or a wear particles in a motor oil.

In engine oil dispersant is additive that helps prevent sludge, varnish, and other engine deposits by keeping particles suspended in a colloidal state (see colloid) within the bulk oil.

Dispersants are normally used in conjunction with detergents.

A dispersant can be distinguished from a detergent in that the former may be non-metallic and thus does not leave an ash when the oil is burned; hence the term ashless dispersant.

Distillate  Wide range of and any product produced by distillation.

Distillation  The process of condensing into liquid the vapours distilled from any liquid such as water, petroleum or alcohol.

In the petroleum oil industry it is the primary refining step, in which crude oil is separated into fractions, or components, in a distillation tower, or pipe still. Heat, usually applied at the bottom of the tower, causes the oil vapors to rise through progressively cooler levels of the tower, where they condense onto plates and are drawn off in order of their respective condensation temperatures, or boiling points — the lighter-weight, lower-boiling-point fractions, exiting higher in the tower. The primary fractions, from low to high boiling point, are: hydrocarbon gases (e.g., ethane, propane); naphtha (e.g., gasoline); kerosene, diesel fuel (heating oil); and heavy gas oil for cracking. Heavy materials remaining at the bottom are called the bottoms, or residuum, and include such components as heavy fuel oil (fuel oil) and asphaltic substances (see asphalt). Those fractions taken in liquid form from any level other than the very top or bottom are called sidestream products; a product, such as propane, removed in vapor form from the top of the distillation tower is called overhead product. Distillation may take place in two stages: first, the lighter fractions — gases, naphtha, and kerosene — are recovered at essentially atmospheric pressure; next, the remaining crude is distilled at reduced pressure in a vacuum tower, causing the heavy lube fractions to distill at much lower temperatures than possible at atmospheric pressure, thus permitting more lube oil to be distilled without the molecular cracking that can occur at excessively high temperatures.

Dropping point  In general, the dropping point is the temperature at which the grease passes from a semisolid to a liquid state. This change in state is typical of greases containing conventional soap thickeners. Greases containing thickeners other than conventional soaps may, without change in state, separate Oil.

Dry lubricant  Solid material left between two moving surfaces to prevent metal-to-metal contact, thus reducing friction and wear. Such materials are especially useful in the region of boundary lubrication, and for lubrication under special conditions of extremely high or low temperature where usual lubricants are inadequate. They may be applied in the form of a paste or solid stick, or by spraying, dipping, or brushing in an air-drying carrier which evaporates leaving a dry film. Or can be present in a “sol”, a colloidal suspension in Water, Alcohol or Oil.

Some examples of dry lubricants are:

  • graphite
  • molybdenum disulfide (moly)
  • boron nitride
  • plastics such as tetrafluorethylene resins (PTFE or Teflon).


Elastohydrodynamic lubrication  Lubrication model modified to take into consideration the elastic properties of the bearing material and the viscosity increase of the lubricant under concentrated load.

Emulsibility  The ability of a non-water soluble fluid (such as oil) to form an emulsion with water.

Emulsifier  A substance used to promote or aid the emulsification of two liquids and to enhance the stability of the emulsion.

Additive that promotes the formation of a stable mixture, or emulsion, of oil and water.

Common emulsifiers are: metallic soaps, certain animal and vegetable oils, and various polar compounds (having molecules that are water-soluble at one extremity of their structures and oil-soluble at the other).

Emulsion  A mechanical mixture of two insoluble liquids such as oil and water.

Engine deposits  hard or persistent accumulations of sludge, varnish, and carbonaceous residues due to blow-by of unburned and partially burned (partially oxidized) fuel, and/or from partial breakdown of the crankcase lubricant. Water from condensation of combustion products, carbon, residues from fuel or lubricating oil additives, dust, and metal particles also contribute. Engine deposits can impair engine performance and damage engine components by causing valve and ring sticking, clogging of the oil screen and oil passages, and excessive wear of pistons and cylinders. Engine deposits are increased by short trips in cold weather, high-temperature operation, heavy loads (such as pulling a trailer), and over-extended oil drain intervals.

Engine Oil  An engine oil is a lubricating agent that can be classified according to one or a combination of the viscosity grades identified in Table 1 of the most recent edition of SAE Standard J300. Engine OiIs are also called Motor Oils. Engine oils include diesel engine oils and passenger car motor oils (PCMOs).

Engler degree  A measure of viscosity. The ratio of the time of flow of 200 ml of the liquid tested, through the viscometer devised by Engler, to the time required for the flow of the same volume of water gives the number of degrees Engler.

EP additive  lubricant additive that prevents sliding metal surfaces from seizing under conditions of extreme pressure (EP). At the high local temperatures associated with metal-to-metal contact, an EP additive combines chemically with the metal to form a surface film that prevents the welding of opposing asperities, and the consequent scoring that is destructive to sliding surfaces under high loads. Reactive compounds of sulfur, chlorine, or phosphorus are used to form these inorganic films.

EP lubricant  Any of the lubricating oils or greases which contain an Extreme Pressure additive specifically introduced to prevent metal-to-metal contact in the operation of highly loaded gears. In some cases, this is accomplished by the additive reacting with the metal to form a protective film.

Exhaust gas recirculation (EGR)  system designed to reduce automotive exhaust emissions of nitrogen oxides (NOx). The system routes exhaust gases into the carburetor or intake manifold; the gases dilute the air-fuel mixture (see combustion) which lowers peak combustion temperatures, thus reducing the tendency for NOx to form.


Fat  An animal or vegetable oil which will combine with an alkali to saponify and form a soap.

Fiber grease  A grease with a distinctly fibrous structure, which is noticeable when portions of the grease are pulled apart.

Film strength  The property of an oil which enables it to maintain an unbroken film on lubricated surfaces under operatIng conditions, where other otherwise there would be scuffing or scoring of the surfaces.

Fire Point  The lowest temperature at which an oil or other product vaporizes sufficiently rapidly to form above its surface an air-vapor mixture which when subjected to a source of ignition or a flame, will ignite and continue to burn.

Typically for most Petroleum products the Fire Point is about 50°F above the Flash Point.

Fire-resistant Fluid  Lubricant used especially in high-temperature or hazardous hydraulic applications. Three common types of fire-resistant fluids are: (1) water-petroleum oil emulsions, in which the water prevents burning of the petroleum constituent; (2) water-glycol fluids; and (3) non-aqueous fluids of low volatility, such as phosphate esters, silicones, and halogenated hydrocarbon-type fluids.

Flash Point  The lowest temperature at which vapors arising from the oil will ignite momentarily, when subjected to a flame. (i.e., will flash or “poof”).

The vapors will ignite and then go out.

Floc point  The temperature at which wax or solids separate in an oil.

Foam  An agglomeration of gas bubbles separated from each other by a thin liquid film which is observed as a persistent phenomenon on the surface of a liquid.

Foaming  occurrence of frothy mixture of air and a petroleum product (e.g., lubricant, fuel oil) that can reduce the effectiveness of the product, and cause sluggish hydraulic operation, air binding of oil pumps, and overflow of tanks or sumps. Foaming can result from excessive agitation, improper fluid levels, air leaks, cavitation, or contamination with water or other foreign materials. Foaming can be inhibited with an anti-foam agent. The foaming characteristics of a lubricating oil can be determined by blowing air through a sample at a specified temperature and measuring the volume of foam, as described in test method ASTM D 892.

Foam inhibitor  A substance introduced in a very small proportion to a lubricant or a coolant to prevent the formation of foam due to aeration of the liquid, and to accelerate the dissipation of any foam that may form.

Food Grade Lubricants  Lubricants acceptable for use in meat, poultry and other food processing equipment, applications and plants. The lubricant types in food-grade applications are broken into categories based on the likelihood they will contact food. The USDA created the original food-grade designations H1, H2 and H3, which is the current terminology used. The approval and registration of a new lubricant into one of these categories depends on the ingredients used in the formulation.

H1 Lubricant  Food-grade lubricants used in food processing environments where there is some possibility of incidental food contact. Lubricant formulations may only be composed of one or more approved basestocks, additives and thickeners (if grease) listed in Guidelines of Security Code of Federal Regulations (CFR) Title 21, §178.3570.

H2 Lubricant  Lubricants used on equipment and machine parts in locations where there is no possibility that the lubricant or lubricated surface contacts food. Because there is not the risk of contacting food, these lubricants do not have a defined list of acceptable ingredients. They cannot, however, contain intentionally heavy metals such as antimony, arsenic, cadmium, lead, mercury or selenium. Also, the ingredients must not include substances that are carcinogens, mutagens, teratogens or mineral acids.

H3 Lubricant  Also known as soluble or edible oil. These are used to clean and prevent rust on hooks, trolleys and similar equipment.

Four-Ball Tester  This name is frequently used to describe either of two similar laboratory machines, the Four-Ball Wear Tester and the Four-Ball EP Tester. These machines are used to evaluate a lubricant’s anti-wear qualities, frictional characteristics or load carrying capabilities. It derives its name from the four 1/2 inch steel balls used as test specimens. Three of the balls are held together in a cup filled with lubricant while the fourth ball is rotated against them.


a. a rubbing, esp. of one object against another.

b. Mechanics: The resistance to motion of two moving objects or surfaces that touch.

c. Tribology: The resisting force encouraged at the common boundary between two bodies when, under the action of an external force, one body moves or tends to move relative to the other.

Friction is the resistance to the motion of one surface over another. The amount of friction is dependent on the smoothness of the contacting surfaces, as well as the force with which they are pressed together.

Friction between unlubricated solid bodies is independent of speed and area.

The coefficient of friction is obtained by dividing the force required to move one body over a horizontal surface at constant speed by the weight of the body.

Coefficients of rolling friction (e.g., the motion of a tire or ball bearing) are much less than coefficients of sliding friction (back and forth motion over two flat surfaces).

Sliding friction is thus more wasteful of energy and can cause more wear.

Fluid friction occurs between the molecules of a gas or liquid in motion, and is expressed as shear stress. Unlike solid friction, fluid friction varies with speed and area.

In general, lubrication is the substitution of low fluid friction in place of high solid-to-solid friction.

Fretting  form of wear resulting from small-amplitude oscillations or vibrations that cause the removal of very finely divided particles from rubbing surfaces (e.g., the vibrations imposed on the wheel bearings of an automobile when transported by rail car, or on the fifth wheel on tractor trailers). With ferrous metals the wear particles oxidize to a reddish, abrasive iron oxide, which has the appearance of rust or corrosion, and is therefore sometimes called fretting corrosion; other terms applied to this phenomenon are false Brinelling (localized fretting involving the rolling elements of a bearing) and friction oxidation. Fretting can be controlled with lubricants containing molybdenum disulfide.

Fuel Dilution  The amount of raw, unburned fuel that ends up in the crankcase of an engine. It lowers an oil’s viscosity and flash point, creating friction-related wear almost immediately by reducing film strength.

Full-fluid-film lubrication  presence of a continuous lubricating film sufficient to completely separate two surfaces, as distinct from boundary lubrication. Full-fluid-film lubrication is normally hydrodynamic lubrication, whereby the oil adheres to the moving part and is drawn into the area between the sliding surfaces, where it forms a pressure, or hydrodynamic, wedge. See ZN/P curve.

A less common form of full-fluid-lubrication is hydrostatic lubrication, wherein the oil is supplied to the bearing area under sufficient external pressure to separate the sliding surfaces.


Gear  machine part which transmits motion and force from one rotary shaft to another by means of successively engaging projections, called teeth. The smaller gear of a pair is called the pinion; the larger, the gear. When the pinion is on the driving shaft, the gear set acts as a speed reducer; when the gear drives, the set acts as a speed multiplier. The basic gear type is the spur gear, or straight-tooth gear, with teeth cut parallel to the gear axis. Spur gears transmit power in applications utilizing parallel shafts. In this type of gear, the teeth mesh along their full length, creating a sudden shift in load from one tooth to the next, with consequent noise and vibration. This problem is overcome by the helical gear, which has teeth cut at an angle to the center of rotation, so that the load is transferred progressively along the length of the tooth from one edge of the gear to the other. When the shafts are not parallel, the most common gear type used is the bevel gear, with teeth cut on a sloping gear face, rather than parallel to the shaft. The spiral bevel gear has teeth cut at an angle to the plane of rotation, which, like the helical gear, reduces vibration and noise. A hypoid gear resembles a spiral bevel gear, except that the pinion is offset so that its axis does not intersect the gear axis; it is widely used in automobiles between the engine driveshaft and the rear axle. Offset of the axes of hypoid gears introduces additional sliding between the teeth, which, when combined with high loads, requires a high-quality EP oil. A worm gear consists of a spirally grooved screw moving against a toothed wheel; in this type of gear, where the load is transmitted across sliding, rather than rolling, surfaces, compounded oils or EP oils are usually necessary to maintain effective lubrication.

Gear oil (automotive)  long-life oil of relatively high viscosity for the lubrication of rear axles and some manual transmissions. Most final drives and many accessories in agricultural and construction equipment also require gear oils. Straight (non-additive) mineral gear oils are suitable for most spiral-bevel rear axles (see gear) and for some manual transmissions. Use of such oils is declining, however, in favor of EP (extreme-pressure) gear oils (see EP oil) suitable both for hypoid gears (see gear) and for all straight mineral oil applications. An EP gear oil is also appropriate for off-highway and other automotive applications for which the lubricant must meet the requirements of Military Specification MIL-L-2105D.

Gravity (See API gravity)

Graphite  a soft form of elemental carbon, gray to black, in color. It occurs naturally or is synthesized 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 as a dry lubricant or added to conventional lubricants; both oils and greases.

Grease  A lubricant composed of a lubricating fluid, thickened with soap or other material to a solid or semisolid consistency.

A lubricating grease is a colloidal system, in which metallic soaps or other thickening agents are dispersed in, and give structure to, the liquid lubricant.


H1 Lubricant  Food-grade lubricants used in food processing environments where there is some possibility of incidental food contact. Lubricant formulations may only be composed of one or more approved basestocks, additives and thickeners (if grease) listed in Guidelines of Security Code of Federal Regulations (CFR) Title 21, §178.3570.

H2 Lubricant  Lubricants used on equipment and machine parts in locations where there is no possibility that the lubricant or lubricated surface contacts food. Because there is not the risk of contacting food, these lubricants do not have a defined list of acceptable ingredients. They cannot, however, contain intentionally heavy metals such as antimony, arsenic, cadmium, lead, mercury or selenium. Also, the ingredients must not include substances that are carcinogens, mutagens, teratogens or mineral acids.

H3 Lubricant  Also known as soluble or edible oil. These are used to clean and prevent rust on hooks, trolleys and similar equipment

Heat transfer fluid  Oil or other liquid medium used for the transfer of heat.

Hydraulic fluid  fluid serving as the power transmission medium in a hydraulic system. The most commonly used fluids are petroleum oils, synthetic lubricants, oil-water emulsions, and water-glycol mixtures. The principal requirements of a premium hydraulic fluid are proper viscosity, high viscosity index, anti-wear protection (if needed), good oxidation stability, adequate pour point, good demulsibility, rust inhibition (see rust inhibitor), resistance to foaming, and compatibility with seal materials. Anti-wear oils are frequently used in compact, high-pressure, and high-capacity pumps that require extra lubrication protection. Certain synthetic lubricants and water-containing fluids are used where fire resistance is needed. Synthetic lubricants also are used in extreme-temperature conditions.

Hydrocarbon  A compound containing only hydrogen and carbon. The simplest hydrocarbons are gases at ordinary temperatures; but with increasing molecular weight, they change to the liquid form and, finally, to the solid state. They form the principal constituents of petroleum.

Hydrocracking  refining process in which middle and heavy distillate fractions are cracked (broken into smaller molecules) in the presence of hydrogen at high pressure and moderate temperature to produce high-octane gasoline, turbo fuel components, and middle distillates with good flow characteristics and cetane ratings. The process is a combination of hydrogenation and cracking.

Hydrodynamic (fluid film) lubrication  An oil film which provides a pressure equal to the load. This pressure enables the moving parts to float on a layer of lubricant.

Hydrogenation  The chemical addition of hydrogen to a material. In non-destructive hydrogenation, hydrogen is added to a molecule only if, and where, unsaturation with respect to hydrogen exists.

In destructive hydrogenation, the operation is carried out under conditions which result in rupture of some of the hydrocarbon chains (cracking); hydrogen is added where the chain breaks have occurred.

Hydrolysis  Breakdown process that occurs in anhydrous hydraulic fluids as a result of heat, water, and metal catalysts (iron, steel, copper, etc.)

Hydrolytic Stability  Ability of additives and certain synthetic lubricants to resist chemical decomposition (hydrolysis) in the presence of water.

Hydrometer  An instrument for determining either the specific gravity of a liquid or the API gravity.

Hypoid gears  Gears in which the pinion axis intersects the plane of the ring gear at a point below the ring-gear axle and above the outer edge of the ring gear, or above the the ring-gear axle and below the outer edge of the ring gear.

Hypoid gear lubricant  A gear lubricant, having extreme pressure characteristics suitable for use with hypoid gears as found, for example, in the differentials of motor vehicles.


ILMA  The Independent Lubricant Manufacturers Association (lLMA) is a trade association of businesses engaged in compounding, blending, formulating, packaging, marketing, and distributing lubricants.

ILSAC  The International Lubricant Standardization and Approval Committee (ILSAC) is a joint committee of AAMA and JAMA members that assists in the development of new minimum oil performance standards.

Inhibitor  A substance in a petroleum product which prevents or retards undesirable chemical changes from taking place in the product, or in the condition of the equipment in which the product is used. Commonly used inhibitors are used to prevent or retard oxidation or corrosion.

ISO (International Standards Organization)

This organization which is worldwide in scope sets standards and classifications for lubricants. An example is the ISO viscosity grade system.

ISO viscosity classification system  international system, approved by the International Standards Organization (ISO), for classifying industrial lubricants according to viscosity.

Each ISO viscosity grade number designation corresponds to the mid-point of a viscosity range expressed in centistokes (cSt) at 40°C.

For example:

a lubricant with an ISO grade of 32 has a viscosity within the range of 28.8 — 35.2 cSt, the mid-point of which is 32. (see Table below)

ISO Viscosity Grade Number Table:

viscosity range expressed in centistokes (cSt) at 40°C






Kinematic viscosity  absolute viscosity of a fluid divided by its density at the same temperature of measurement. It is the measure of a fluid’s resistance to flow under gravity, as determined by test method ASTM D 445. To determine kinematic viscosity, a fixed volume of the test fluid is allowed to flow through a calibrated capillary tube (viscometer) that is held at a closely controlled temperature. The kinematic viscosity, in centistokes (cSt), is the product of the measured flow time in seconds and the calibration constant of the viscometer.


Lacquer  A deposit resulting from the oxidation and polymerization of fuels and lubricants when exposed to high temperatures. Similar to, but harder, than varnish.

Light Ends  Low-boiling volatile materials in a petroleum fraction. They are often unwanted and undesirable, but in gasoline the proportion of light ends deliberately included are used to assist low-temperature starting.

Lubricant  any substance reducing friction by providing a smooth film as a covering over parts that move against each other; lubricating a substance for reducing friction in this way, as oil or grease

Lubricity, Lubricities  slipperiness; smoothness; esp., effectiveness as a lubricant as indicated by this quality.


Mineral oil  Oil derived from mineral sources, notably petroleum.

Miscible  Capable of being mixed in any concentration without separation of phases; e.g., water and ethyl alcohol are miscible.

Molybdenum disulfide (moly)  a black, lustrous powder (MoS2) that serves as a dry-film lubricant in certain high-temperature 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 lubrication properties to oils and greases.

Molybdenum disulfide is often called moly or molysulfide.

Monograde  ‘Monograde’ (single grade) is a term used to describe an oil when its viscosity falls within the limits specified for a single SAE number.(SAE Standard J300)

Multigrade  ‘Multigrade’ is a term used to describe an oil for which the viscosity/ temperature characteristics are such that its low temperature and high temperature viscosities fall within the limits of two different SAE numbers. (SAE Standard J300)


Naphtha  generic, loosely defined term covering a range of light petroleum distillates (see distillation). Included in the naphtha classification are: gasoline blending stocks, mineral spirits, and a broad selection of petroleum solvents. In refining, the term light crude naphtha (LCN) usually refers to the first liquid distillation fraction, boiling range 32° to 100°C (90° to 175°F), while heavy crude naphtha is usually the second distillation fraction, boiling range 163° to 218°C (325° to 425°F).

Naphthene  One of a group of cyclic hydrocarbons, also termed cycloparaffins or cycloalkanes. The general formula for naphthenes is CnH2n

Naphthenic lubricating oils have low pour points, owing to their very low wax content, and good solvency properties.

Newtonian fluid  fluid, such as a straight mineral oil, whose viscosity does not change with rate of flow.

Non-Newtonian fluid  fluid, such as a grease or a polymer-containing oil (e.g., multi-grade oil), in which shear stress is not proportional to shear rate.

NLGI   National Lubricating Grease Institute

NLGI Number  One of a series of numbers classifying the consistency range of lubricating greases. The NLGI Numbers are based on the ASTM cone penetration number. The grades are in order of increasing consistency (hardness)

NLGI Grease Classifications  The following table shows the worked penetration values for the various NLGI grades of grease:

NLGI Number

ASTM Worked Penetration*

* ASTM Worked Penetration in millimeters at standard test temperature of 77°F ±1° (25°C ±0.5° )


Oiliness agent  polar compound used to increase the lubricity of a lubricating oil and aid in preventing wear and scoring under conditions of boundary lubrication.

Olefin  any of a series of unsaturated, relatively unstable hydrocarbons characterized by the presence of a double bond between two carbon atoms in its structure, which is commonly straight-chain or branched. The double bond is chemically active and provides a focal point for the addition of other reactive elements, such as oxygen. Due to their ease of oxidation, olefins are undesirable in petroleum solvents and lube oils. Examples of olefins are: ethylene and propylene.

Oxidation  the chemical combination of a substance with oxygen. All petroleum products are subject to oxidation, with resultant degradation of their composition and performance. The process is accelerated by heat, light, metal catalysts (e.g., copper, iron), and the presence of water, acids, or solid contaminants. The first reaction products of oxidation are organic peroxides. Continued oxidation catalyzed by peroxides, forms alcohols, aldehydes, ketones, and organic acids, which can be further oxidized to form high-molecular-weight, oil-insoluble polymers; these settle out as sludges, varnishes, and gums that can impair equipment operation. The organic acids formed from oxidation are corrosive to metals. Oxidation resistance of a product can be improved by careful selection of basestocks (paraffins have greater oxidation resistance than naphthenes), special refining methods, and addition of oxidation inhibitors. Also, oxidation can be minimized by good maintenance of oil and equipment to prevent contamination and excessive heat.

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 anti-oxidant.

An oxidation inhibitor may work in one of three ways:

1. by combining with and modifying peroxides (initial oxidation products) to render them harmless

2. by decomposing the peroxides

3. by rendering an oxidation catalyst (metal or metal ions) inert.

Oxidation stability  resistance of a petroleum product to oxidation; hence, a measure of its potential service or storage life. There are a number of ASTM tests to determine the oxidation stability of a lubricant or fuel, all of which are intended to simulate service conditions on an accelerated basis. In general, the test sample is exposed to oxygen or air at an elevated temperature, and sometimes to water or catalysts (usually iron or copper). Depending on the test, results are expressed in terms of the time required to produce a specified effect (such as a pressure drop), the amount of sludge or gum produced, or the amount of oxygen consumed during a specified period.


PAG Synthetic Fluid Polyalkaline glycol have excellent oxidative and thermal stability, very high VI, excellent film strength and an extremely low tendency to leave deposits on machine surfaces. The low deposit-forming tendency is really due to two properties – the oil’s ability to dissolve deposits and the fact that the oil burns clean. So when they are exposed to a very hot surface or subjected to micro-dieseling by entrained air, PAGs are less likely to leave residue that will form deposits. PAGs may also be the only type of base oil with significantly lower fluid friction, which may allow for energy savings. The other unique property of PAGs is the ability to absorb a great deal of water and maintain lubricity. There are actually two different types of PAGs – one demulisifies and the other absorbs water. The most common applications for PAGs are compressors and critical gearing applications. The negatives of PAGs are their very high cost and the potential to be somewhat hydrolytically unstable.

PAO Synthetic Fluid  Polyalphaolefins, often called synthetic hydrocarbons, are probably the most common type of synthetic base oil used today. They are moderately priced, provide excellent performance and have few negative attributes. PAO base oil is similar to mineral oil. The advantage comes from the fact that it is built, rather than extracted and modified, making it more pure. Practically all of the oil molecules are the same shape and size and are completely saturated. The potential benefits of PAOs are improved oxidative and thermal stability, excellent demulsibility and hydrolytic stability, a high VI, and very low pour point. Most of the properties make PAOs a good selection for temperature extremes – both high operating temperatures and low start-up temperatures. Typical applications for PAOs are engine oils, gear oils and compressor oils. The negative attributes of PAOs are the price and poor solubility. The low inherent solubility of PAOs creates problems for formulators when it comes to dissolving additives. Likewise, PAOs cannot suspend potential varnish-forming degradation by-products, although they are less prone to create such material.

Paraffin  hydrocarbon identified by saturated straight (normal) or branched (iso) carbon chains; also called an alkane. The generalized paraffinic molecule can by symbolized by the formula CnH2n+2. Paraffins are relatively non-reactive and have excellent oxidation stability.

In contrast to naphthenic (see naphthene) oils, paraffinic lube oils have relatively high wax content and pour point, and generally have a high viscosity index (V.I.).

Paraffinic solvents are generally lower in solvency than naphthenic or aromatic solvents.

See normal paraffin, isoparaffin, saturated hydrocarbon.

PCMO  Passenger Car Motor Oils (PCMOs) refer to engine oils for passenger cars, light-duty trucks, and similar vehicles (see also engine oils).

Particulates  Particles made up of a wide range of natural materials (e.g., pollen, dust, resins), combined with man-made pollutant (e.g., smoke particles, metallic ash); in sufficient concentrations, particulates can be a respiratory irritant.

Pascal  Unit of pressure in the metric (SI) system.

Pascal’s Law  A pressure applied to a confined fluid at rest is transmitted with equal intensity throughout the liquid and that pressure is considered to act at right angles to each surface contacted by the fluid.

PCB  Polychlorinated biphenyl, a class of synthetic chemicals consisting of a homologous series of compounds beginning with monochlorobiphenyl and ending with decachlorobiphenyl. PCBs do not occur naturally in petroleum, but have been found as contaminants in used oil. PCBs have been legally designated as a health hazard, and any oil so contaminated bust be handled in strict accordance with state and federal regulations

Penetration  Consistency of a lubricating grease, expressed as the distance in millimeters that a standard needle or cone penetrates vertically into a sample of the material under known conditions of loading, time and temperature.

Petrochemical  any chemical derived from crude oil, crude products, or natural gas.

A petrochemical is basically a compound of carbon and hydrogen, but may incorporate many other elements. Petrochemicals are used in the manufacture of numerous products such as synthetic rubber, synthetic fibers (such as nylon and polyester), plastics, fertilizers, paints, detergents, and pesticides.

Petroleum  From Latin Petra (Rock) and Oleum (Oil) therefore meaning “Rock Oil ” the term is applied to crude oil and commonly used to describe products made from “Crude Oil”.

pH  Measure of alkalinity or acidity in water and water-containing fluids. pH can be used to determine the corrosion-inhibiting characteristic in water-based fluids. Typically, pH > 8.0 is required to inhibit corrosion of iron and ferrous alloys in water-based fluids.

Phosphate Ester  Any of a group of synthetic lubricants having superior fire resistance. A phosphate ester generally has poor hydrolytic stability, poor compatibility with mineral oil, and a relatively low viscosity index (VI). It is used as a fire-resistant hydraulic fluid in high-temperature applications.

Pinion  The smaller of two mating or meshing gears; can be either the driving or the driven gear.

Pitch Line  An imaginary line that divides the upper and lower halves of gear teeth while in the contact area.

Pitting  A form of extremely localized attack characterized by holes in the metal. Pitting is one of the most destructive and insidious forms of corrosion. Depending on the environment and the material, a pit may take months, or even years, to become visible.

Plain Bearing  A relatively simple and inexpensive bearing typically made of two parts. A rotary plain bearing can be just a shaft running through a hole. A simple linear bearing can be a pair of flat surfaces designed to allow motion.

Poise (absolute viscosity)  A measure of viscosity numerically equal to the force required to move a plane surface of one square centimeter per second when the surfaces are separated by a layer of fluid one centimeter in thickness. It is the ratio of the shearing stress to the shear rate of a fluid and is expressed in dyne seconds per square centimeter (DYNE SEC/CM2); 1 centipoise equals .01 poise.

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 performance.

Polyalkylene Glycol  Mixtures of condensation polymers of ethylene oxide and water. They are any of a family of colorless liquids with high molecular weight that are soluble in water and in many organic solvents. They are used in detergents and as emulsifiers and plasticizers. PAG-based lubricants are used in diverse applications where petroleum oil-based products do not provide the desired performance – and because they are fire-resistant and will not harm workers or the environment.

Polyglycols  Polymers of ethylene or propylene oxides used as a synthetic lubricant base. Properties include very good hydrolytic stability, high viscosity index (VI), and low volatility. Used particularly in water emulsion fluids.

Polyol ester  Synthetic lubricant base, formed by reacting fatty acids with a polyol (such as a glycol) derived from petroleum. Properties include good oxidation stability at high temperatures and low volatility. Used in formulating lubricants for turbines, compressors, jet engines, and automotive engines.

Polyolefin  polymer derived by polymerization of relatively simple olefins. Polyethylene and polyisoprene are important polyolefins.

Pour point  The lowest temperature at which oil will pour or flow when it is chilled without disturbance under definite conditions (ASTM Method D 97). It gives an indication of the lowest operating temperature for which particular oil is suitable.

Pour point depressant  A lubricating oil additive which lowers the pour point of an oil by reducing the tendency of the wax, suspended in the oil, to form crystals or a solid mass in the oil, thus preventing flow.
Also called pour depressor or pour point depressor.

Pour stability  The ability of a pour depressed oil to maintain its original ASTM pour point when subjected to long term storage at low temperature aproximating winter conditions.

Process oil  Oil not used for lubrication, but as a component of another material, or as a carrier of other products, such as additives.

Pumpability (lubricating grease)  The ability of a lubricating grease to flow under pressure through the line, nozzle and fitting of a grease dispensing system.


Rapeseed oil (blown rapeseed oil)  fatty oil used for compounding petroleum oil.

Redwood viscosity  method for determining the viscosity of petroleum products; it is widely used in Europe, but has limited use in the U.S. The method is similar to Saybolt Universal viscosity; viscosity values are reported as “Redwood seconds.”

R&O Rust & Oxidation inhibited   A term applied to highly refined industrial lubricating oils formulated for long service in circulating lubrication systems, compressors, hydraulic systems, bearing housing, gear boxes, etc.
The finest R&O oils are often referred to as turbine oils.

Refining  series of processes for converting crude oil and its fractions to finished petroleum products. Following distillation, a petroleum fraction may undergo one or more additional steps to purify or modify it.
These refining steps include:

  • thermal cracking
  • catalytic cracking
  • polymerization
  • alkylation
  • reforming
  • hydrocracking
  • hydroforming
  • hydrogenation
  • hydrogen treating
  • hydrofining
  • solvent extraction
  • de-waxing
  • de-oiling
  • acid treating
  • clay filtration
  • de-asphalting

Refined lube oils may be blended with other lube stocks, and additives may be incorporated, to impart special properties; refined naphthas may be blended with alkylates, cracked stock or reformates to improve octane number and other properties of gasolines.

Resins  solid or semi-solid materials, light yellow to dark brown, composed of carbon, hydrogen, and oxygen. Resins occur naturally in plants, and are common in pines and firs, often appearing as globules on the bark. Synthetic resins, such as polystyrene, polyesters, and acrylics, are derived primarily from petroleum. Resins are widely used in the manufacture of inks, lacquers, varnishes, plastics, adhesives, and rubber.

Ring Lubrication  A system of lubrication in which the lubricant is supplied to the bearing by an oil ring.

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 antifriction bearing comprising rolling elements in the form of rollers.

Rolling Element Bearing  A friction-reducing bearing that consists of a ring-shaped track that contains free-revolving metal balls. A rotating shaft or other part turns against such a bearing.

Rolling Oil  An oil used in hot- or cold-rolling of ferrous and non-ferrous metals to Facilitate feed of the metal between the work rolls, improve the plastic deformation of the metal, conduct heat from the metal, and extend the life of the work rolls. Because of the pressures involved, a rolling oil may be compounded or contain EP additives. In hot rolling, the oil may also be emulsifieable

Rust inhibitor  type of corrosion inhibitor used in lubricants to protect the lubricated surfaces against rusting. See R&O.

Rust preventive  compound for coating metal surfaces with a film that protects against rust; commonly used for the preservation of equipment in storage. The base material of a rust preventive may be a petroleum oil, solvent, wax, or asphalt, to which a rust inhibitor is added. A formulation consisting largely of a solvent and additives is commonly called a thin-film rust preventive because of the thin coating that remains after evaporation of the solvent. Rust preventives are formulated for a variety of conditions of exposure, e.g., short-time “in-process” protection, indoor storage, exposed outdoor storage, etc.


SAE  The Society of Automotive Engineers (SAE) is an engineering society founded to develop, collect, and disseminate knowledge of mobility technology.

Saybolt Furol viscosity  the efflux time in seconds required for 60 milliliters of a petroleum product to flow through the calibrated orifice of a Saybolt Furol viscometer, under carefully controlled temperature, as prescribed by test method ASTM D 88. The method differs from Saybolt Universal viscosity only in that the viscometer has a larger orifice to facilitate testing of very viscous oils, such as fuel oil (the word “Furol” is a contraction of “fuel and road oils”). The Saybolt Furol method has largely been supplanted by the kinematic viscosity method.

Saybolt Universal Viscosity (SUV) or Saybolt Universal Seconds, (SUS)  The time in seconds required for 60 cubic centimeters of a fluid to flow through the orifice of the Standard Saybolt Universal Viscometer at a given temperature under specified conditions. (ASTM Designation D 88.)

Scoring  Distress marks on sliding metallic surfaces in the form of long, distinct scratches in the direction of motion. Scoring is an advanced stage of scuffing.

Scuffing  Abnormal engine wear due to localized welding and fracture. It can be prevented through the use of antiwear, extreme-pressure and friction modifier additives.

Service Category  A Service Category is an alphanumeric code developed by API to specify a level of performance defined by ASTM D 4485 and SAE Standard J183. As new Service Categories are developed, new alphanumeric codes may be assigned.

Shear rate  rate at which adjacent layers of a fluid move with respect to each other, usually expressed as reciprocal seconds (also see shear stress).

Shear stress  frictional force overcome in sliding one “layer” of fluid along another, as in any fluid flow. The shear stress of a petroleum oil or other Newtonian fluid at a given temperature varies directly with shear rate (velocity).
The ratio between shear stress and shear rate is constant; this ratio is termed viscosity. The higher the viscosity of a Newtonian fluid, the greater the shear stress as a function of rate of shear. In a non-Newtonian fluid — such as a grease or a polymer-containing oil (e.g., multi-grade oil) — shear stress is not proportional to the rate of shear. A non-Newtonian fluid may be said to have an apparent viscosity, a viscosity that holds only for the shear rate (and temperature) at which the viscosity is determined.

Sludge  in gasoline engines, a black emulsion of water, other combustion by-products, and oil formed primarily during low-temperature engine operation. Sludge is typically soft, but can polymerize to very hard substance. It plugs oil lines and screens, and accelerates wear of engine parts. Sludge deposits can be controlled with a dispersant additive that keeps the sludge constituents finely suspended in the oil.

Solvent extraction  refining process used to separate reactive components (unsaturated hydrocarbons) from lube distillates in order to improve the oil’s oxidation stability, viscosity index (V.I.), and response to additives. Commonly used extraction media (solvents) are: phenol, N-methylpyrrolidone (NMP), furfural, liquid sulfur dioxide, and nitrobenzene. The oil and solvent are mixed in an extraction tower, resulting in the formation of two liquid phases: a heavy phase consisting of the undesirable unsaturates (see unsaturated hydrocarbon) dissolved in the solvent, and a light phase consisting of high quality oil with some solvent dissolved in it. The phases are separated and the solvent recovered from each by distillation. The unsaturates portion, or extract, while undesirable in lubricating oils, is useful in other applications, such as rubber extender oils (rubber oil) and plasticizer oils.

Sour crude crude oil containing appreciable quantities of hydrogen sulfide or other sulfur compounds, as contrasted to sweet crude.

Specific Gravity (liquid)  The ratio of the weight of a given volume of liquid to the weight of an equal volume of water.

Splash lubrication  A system of lubrication in which parts of a mechanism dip into and splash the lubricant onto themselves and/or other parts of the mechanism.

Spur Gear  This is the simplest variation of gear. It consists of a cylinder or disk, with the teeth projecting radially. Each tooth edge is straight and aligned parallel to the axis of rotation. Such gears can be meshed together correctly only if they are fitted to parallel axles.

Stoke (St)  Kinematic measurement of a fluid’s resistance to flow defined by the ratio of the fluid’s dynamic viscosity to its density.

Straight Mineral Oil  Petroleum oil containing no additives. Straight mineral oils include such diverse products as low-cost once-through lubricants and thoroughly refined white oils. Most high-quality lubricants, however, contain additives.

Sulfonate  hydrocarbon in which a hydrogen atom has been replaced with the highly polar (SO2OX) group, where X is a metallic ion or alkyl radical.
Petroleum sulfonates are refinery by-products of the sulfuric acid treatment of white oils. Sulfonates have important applications as emulsifiers and chemical intermediates in petrochemical manufacture. Synthetic sulfonates can be manufactured from special feedstocks rather than from white oil basestocks.

Sulfur  common natural constituent of petroleum and petroleum products. While certain sulfur compounds are commonly used to improve the EP, or load-carrying, properties of an oil (see EP oil), high sulfur content in a petroleum product may be undesirable as it can be corrosive and create an environmental hazard when burned (see sulfur oxide). For these reasons, sulfur limitations are specified in the quality control of fuels, solvents, etc. Sulfur content can be determined by ASTM tests.

Sulfur oxide  major atmospheric pollutant, predominantly sulfur dioxide (SO2) with some sulfur trioxide (SO3), primarily emitted from stationary combustion sources (furnaces and boilers). Sulfur oxides are formed whenever fuels containing sulfur are burned. SO2 is also present in the air from natural land and marine fermentation processes.

Surfactant  Surface-active agent that reduces interfacial tension of a liquid. A surfactant used in a petroleum oil may increase the oil’s affinity for metals and other materials.

SUS (SSU)  Saybolt Universal Seconds. A measure of lubricating oil viscosity in the oil industry.
The measuring apparatus is filled with specific quantity of oil or other fluid and its flow time through standatized offrice is measured in Seconds.
Fast flowing fluids (low viscosity) will have low value; Slow flowing fluids (high viscosity) will have high value.

Swarf  The cuttings and grinding fines that result from metal working operations.

Sweet crude  crude oil containing little or no sulfur.

Synthetic Hydrocarbon  Oil molecule with superior oxidation quality tailored primarily out of paraffinic materials.

Synthetic oils  Oils produced by synthesis (chemical reaction) rather than by extraction or refinement. Many (but not all) synthetic oils offer immense advantages in terms of high temperature stability and low temperature fluidity, but are more costly than mineral oils. Major advantage of all synthetic oils their chemical unformity.


Tackiness agent (tackifier)  additive used to increase the adhesive properties of a lubricant, improve retention, and prevent dripping and splattering.

Tacky  A descriptive term applied to lubricating oils and greases which appear particularly sticky or adhesive.

TAN (Total Acid Number)  The quantity of base, expressed in terms of the equivalent number of milligrams (mg) of Potassium Hydroxide, that is required to titrate the strong acid constituents present in 1 gram (g) of oil sample. (ASTM Method D 644 or D 974).

TBN Total Base Number)  The quantity of acid, expressed in terms of the equivalent number of milligrams (mg) of Potassium Hydroxide, that is required to titrate the strong base constituents present in 1 gram (g) of oil sample. (ASTM Method D 644 or D 974).

Thermal Stability  Ability of a fuel or lubricant to resist oxidation under high temperature operating conditions.

Thin Film Lubrication  A condition of lubrication in which the film thickness of the lubricant is such that the friction between the surfaces is determined by the properties of the surfaces as well as by the viscosity of the lubricant.

Thixotropy  The property of a grease or some gels to decrease in consistency when subjected to a shear stress and return to original consistency when the stress is removed.

Timken EP tester  One of many laboratory machines used in determining the load carrying ability and capacity of oils and greases; it measures the extreme-pressure properties of a lubricating oil (see EP oil).
In this tester (Timken Machine), an outer race of a roller bearing, which is lubricated by the product under test, is rotated against a steel block. The test continues under increasing load (pressure) until a measurable wear scar is formed on the block.
The Timken OK load is the highest load under which a lubricant prevents scoring of the steel block by the rotating cup. This load is the reported value.

Tribology  science devoted to the study of friction, wear and lubrication between interacting parts, in intimate contact during relative motion, such as gears and bearings.

Turbidity  The degree of opacity of a fluid.



1. hard, varnish-like coating formed from oil oxidation products, that bakes on to pistons during high-temperature operation of automotive engines and industrial machinery. Varnish can accelerate cylinder wear. Varnish formation can be reduced with the use of a detergent-dispersant and an oxidation inhibitor in the oil. See engine deposits

2. In ink formation, varnish — composed of resin, solvent, and additives —
is the vehicle to which pigment is added to make printing ink.

Vacuum Distillation  A distillation method which involved reducing the pressure above a liquid mixture to be distilled to less than its vapor pressure (usually less than atmospheric pressure). This causes evaporation of the most volatile liquid(s) – those with the lowest boiling points. This method works on the principle that boiling occurs when a liquid’s vapor pressure exceeds the ambient pressure. It can be used with or without heating the solution.

Vacuum Pump  A device that is used to extract gas or vapor from an enclosed space, leaving behind a partial vacuum in the container.

Vegetable oils  These are derived from a vegetable source. From pure lubrication considerations, they may be regarded as superior to mineral oils as their chemical nature provides excellent adhesion to metal surfaces due to their inherent polarity. However, they have relatively poor high temperature stability and are costly.

Examples: castor oil, jojoba oil, sunflower oil, rape seed oil, etc.

VI (Viscosity Index)  An arbitrary scale used to show the magnitude of viscosity changes in lubricating oils with changes in temperature. Oils with low VI number such as VI=0 (“zero”) have high dependence of viscosity change on temperature. They thicken quickly with decreasing temperature, and thin out quickly with increasing temperature. Oils with high VI number such as VI=200, will still thicken with decreasing temperature but not as rapidly, and also will thin out with increasing temperature, but again not as much as low VI oil.

VI number can also be “negative”

Tables found in ASTM Method D 2270 are widely used to determine VI number.
However, VI does not tell the whole story — it only reflects the viscosity/temperature relationship between temperatures of 40°C and 100°C. Two lubricants or base oils with the same VI number may perform dramatically different at low temperatures in the -5°C to – 50°C range.

Viscometer  device for measuring viscosity; commonly in the form of a calibrated capillary tube through which a liquid is allowed to pass at a controlled temperature in a specified time period.
See kinematic viscosity, Saybolt Universal Viscosity.

Viscosity  The measurement of a fluid’s resistance to flow. Low viscosity fluids flow easily (water); High viscosity fluids pour slowly (molasses). The common metric unit of absolute viscosity is the poise, which is defined as the force in dynes required to move a surface one square centimeter in area past a parallel surface at a speed of one centimeter per second, with the surfaces separated by a fluid film one centimeter thick. For convenience, the centipoise (cp) — one one-hundredth of a poise — is the unit customarily used. Laboratory measurements of viscosity normally use the force of gravity to produce flow through a capillary tube (viscometer) at a controlled temperature. This measurement is called kinematic viscosity. The unit of kinematic viscosity is the stoke, expressed in square centimeters per second. The more customary unit is the centistoke (cSt) — one one-hundredth of a stoke. See Saybolt Universal Viscosity.
Since viscosity varies inversely with temperature, its value is meaningless unless the temperature at which it is determined is reported.
See: viscosity index, viscosity-temperature relationship.

Viscosity Index Improver (VII)  Chemical additive that is added to finished lubricants to improve the viscosity index.  Usually a high-molecular-weight polymer, that reduces the tendency of an oil to change viscosity with temperature. Multi-grade oils, which provide effective lubrication over a broad temperature range, usually contain V.I. improvers.
While Viscosity Index Improvers can enhance viscosity index (VI), they can break down under shear or over time, resulting in diminished performance.

Viscosity-temperature relationship  the manner in which the viscosity of a given fluid varies inversely with temperature. Because of the mathematical relationship that exists between these two variables, it is possible to predict graphically the viscosity of a petroleum fluid at any temperature within a limited range if the viscosities at two other temperatures are known. The charts used for this purpose are the ASTM Standard Viscosity-Temperature Charts for Liquid Petroleum Products, available in 6 ranges. If two known viscosity-temperature points of a fluid are located on the chart and a straight line drawn through them, other viscosity-temperature values of the fluid will fall on this line; however, values near or below the cloud point of the oil may deviate from the straight-line relationship.

Viscous  Possessing viscosity. Frequently used to imply high viscosity.

Volatility  The degree to which a substance tends to vaporise or evaporate; expression of evaporation tendency. Liquids with high volatility will lose (by evaporation) high percentage of their weight or volume when heated to specific test temperature (Noack Volatility Test). The more volatile a petroleum liquid, the lower its boiling point and the greater its flammability. The volatility of a petroleum product can be precisely determined by tests for evaporation rate; also, it can be estimated by tests for flash point and vapor pressure, and by distillation tests.


Wax (petroleum)  any of a range of relatively high-molecular-weight hydrocarbons (approximately C16 to C50), solid at room temperature, derived from the higher-boiling petroleum fractions.

There are three basic categories of petroleum-derived wax:

1. paraffin (crystalline)
2. microcrystalline
3. petrolatum

Paraffin waxes are produced from the lighter lube oil distillates, generally by chilling the oil and filtering the crystallized wax; they have a distinctive crystalline structure, are pale yellow to white (or colorless), and have a melting point range between 48°C (118°F) and 71°C (160°F). Fully refined paraffin waxes are dry, hard, and capable of imparting good gloss.

Microcrystalline waxes are produced from heavier lube distillates and residua (see bottoms) usually by a combination of solvent dilution and chilling. They differ from paraffin waxes in having poorly defined crystalline structure, darker color, higher viscosity, and higher melting points — ranging from 63°C (145°F) to 93°C (200°F). The microcrystalline grades also vary much more widely than paraffins in their physical characteristics: some are ductile and others are brittle or crumble easily. Both paraffin and microcrystalline waxes have wide uses in food packaging, paper coating, textile moisture proofing, candle-making, and cosmetics.

Petrolatum is derived from heavy residual lube stock by propane dilution and filtering or centrifuging. It is microcrystalline in character and semi-solid at room temperature.

There are also heavier grades for industrial applications, such as corrosion preventives, carbon paper, and butcher’s wrap. Traditionally, the terms slack wax, scale wax, and refined wax were used to indicate limitations on oil content. Today, these classifications are less exact in their meanings, especially in the distinction between slack wax and scale wax.

Way  Longitudinal surface that guides the reciprocal movement of a machine part

Wear  The removal of materials from surfaces in relative motion.
abrasive wear: removal of materials from surfaces in relative motion by cutting or abrasive action of a hard particle (usually a contaminant).

adhesive wear (scuffing): removal of materials from surfaces in relative motion as a result of surface contact

corrosion wear: removal of materials by chemical action.

Wear inhibitor  An additive which protects the rubbing surfaces against wear, particularly from scuffing, if the hydrodynamic film is ruptured.

Weld Point  The lowest applied load in kilograms at which the rotating ball in the Four Ball EP test either seizes and welds to the three stationary balls, or at which extreme scoring of the three balls results

White oil  highly refined straight mineral oil, essentially colorless, odorless, and tasteless. White oils have a high degree of chemical stability. The highest purity white oils are free of unsaturated components (see unsaturated hydrocarbon) and meet the standards of the United States Pharmacopeia (USP) for food, medicinal, and cosmetic applications. White oils not intended for medicinal use are known as technical white oils and have many industrial applications — including textile, chemical, and plastics manufacture — where their good color, non-staining properties, and chemical inertness are highly desirable.

Work penetration  The penetration of a sample of lubricating grease immediately after it has been brought to 77ºF and then subjected to 60 stokes in a standard grease worker. This procedure and the standard grease worker are described in ASTM Method D 217.

Worm Gear  A gear that is in the form of a screw. The screw thread engages the teeth on a worm wheel. When rotated, the worm pulls or pushes the wheel, causing rotation.


ZDDP – ZnDTP  (zinc dialkyl dithiophosphate or zinc diaryl dithiophosphate)
widely used as an anti-wear additive in engine oils to protect heavily loaded parts, particularly the valve train mechanisms (such as the camshaft and cam followers) from excessive wear. It is also used as an anti-wear agent in hydraulic fluids and certain other products.

ZDDP is also an effective oxidation inhibitor.

Oils containing ZDDP should not be used in engines that employ silver alloy bearings. All car manufacturers now recommend the use of dialkyl ZDDP in engine oils for passenger car service (PCMO).

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