Lubricant Industry Terminology


Lubricant Industry Terminology

Lubricant Industry Terminology Reference

This is a ready reference of just some of the common terms and their meaning which can assist in a better understanding of lubricants and their applications.

Abrasion A general wearing away of a surface by the processes related to friction and or foreign matter like dirt, rust or metallic debris. Poor lubrication can be a contributing factor.

Absolute Viscosity Absolute viscosity is the ratio of shear stress to shear rate. The coefficient of absolute viscosity is a measure of the internal resistance of a fluid. The common unit of measure is the poise. Absolute viscosity divided by fluid density equals kinematic viscosity.

Acid Number The quantity of base required, expressed in milligrams of potassium hydroxide to neutralize the acidic constituents in one gram of sample.

Additive  Usually a chemical added to a base stock that imparts favourable properties to a lubricant. Common product additives are detergents, dispersants, anti-corrosion inhibitors, anti-oxidants, demulsifiers, viscosity index improvers, EP additives, etc.

Agglomeration  A favourable environment for the attraction and adhesion of particles within a system.

AGMA An acronym for the American Gear Manufacturers Association.

Ambient Temperature The prevailing temperature surrounding a process. This is different to the operating temperature of a process or operation.

Anti-Foam Agent  An additive that causes foaming to dissipate more readily.

Anti-Oxidant. A chemical added to lubricant who role is to increase the oxidation resistance of a lubricant to increase its service life.

Anti-Wear Agent An additive used to minimize the wear that is caused by metal to metal contact, usually in a boundary lubrication setting. ZDDP & TCP are common agents. They act by forming a sacrificial film. Activation is initiated by either heat or pressure.

API An acronym for the American Petroleum Institute. A trade association of producers, marketers and transporters who interests lie in the day to day operation, including the liaison between the industry and government.

Aromatic A weak hydrocarbon bond that can be highly reactive. These are usually identified by the presence of benzene rings.

Asperity A microscopic protrusion that usually occurs with finishes processes. The aim of lubricant is for such asperities to puncture the viscous layer of a lubricant but not through it thus performing the intended role.

ASME  American Society of Mechanical Engineers.

ASTM  American Society for Testing Materials. The society that develops standards and materials for testing.

Atomization A liquid that converts to a spray of micro-fine droplets.

Base Oil Base stock or blend inert in nature which is used for the production of automotive and industrial lubricants.

Base Stock A refined petroleum or synthetic compound product that can be blended with other base stock and supplements to produce lubricants.

Beta Rating The efficiency rating when comparing filter performance.

Beta Ratio The comparative ratio of particles greater than a target size in fluid to the number of the same size remaining in the sample under test. This is normally associated with a multi-pass test.

Biodegradable  The capacity of chemical breakdown by the action of microorganisms in the environment.

Boundary Lubrication  The environment that exists between surfaces where a full-fluid film does not exist. This can occur in varying degrees depending on the application. Anti-wear additives are commonly used in severe situations. Some occasions exist where compounded oils are utilized. Commonly, lubricants with EP additives are applied to address the issue in more severe cases.

By Pass Filtration A filtration system in which a portion of the fluid being filtered is passed through, usually a finer micron size filter in parallel to the main circulatory system.

CAFÉ  Corporate Average Fuel Economy.

Cavitation  The formation of a pocket of air in a liquid which usually forms after a solid body passes through the liquid. Wear of the metal is also associated with such an event caused by the sudden collapse of the pocket or bubble in the surrounding fluid. Hydraulic systems are prime situations where this process can occur.

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

Centistoke (c St)  A unit of kinematic viscosity. 1 centistoke = 0.01 stoke.

Channelling  A scenario, where gear lubricants and especially greases form a groove or track through which the part being lubricated actually passes through without fully making contact with the lubricant. Most usually observed due to the thickening of the lubricant due to cold conditions or other circumstances.

Chromatography The elution of a complex substance for the purpose of analysis, where the substance is adsorbed on a liquid or solid substrate which results in the make up or components within the substance under investigation are differentially soluble. In the case of oil analysis using this test method and the substrate is blotting paper, differing “coloured” bands develop as the chromatogram develops. The laminating phenomenon of the oil causes particles of the same size to deposit on the paper on the same concentric zones which permits accurate observations to be made. This test is particularly useful for engine oil, however it also has applications with gas chromatography.

Cleanliness Code A measure of the cleanliness of a fluid. ISO 4406. The table list 25 codes, each code, representing the number of particles of pre-determined size per ml of sample. ISO 4406 measures particles of 4 micron, 6 micron and 14 micron in size. In ascending order, each code has double the number of particles to the code proceeding it.

Cleanliness Level  A measure of the relative freedom from contaminants.

Cloud Point. The temperature at which an oil or fuel will form a cloudy appearance.

Coefficient of Friction An empirical number which is obtained by dividing the resisting motion between two bodies by the force pressing the bodies against each other.

Cold Cranking Simulator A viscometer that predicts the ability of an oil to permit an acceptable cranking speed to be developed in a cold engine.

Copper Strip Corrosion The gradual erosion of copper surfaces which results from the process of oxidation or particular chemical action. Most often caused by acids and other agents.

Corrosion The decay and loss of metal caused by a chemical reaction between metal and another substance, such as contaminants in a lubricant.

Corrosion Inhibitor An additive that protects lubricated metal surfaces against chemical attack by and or other contaminants.

Demulsibility  A lubricant’s ability to separate from water.

Density  The mass of a unit volume of a substance.

Detergent  Additives or a compounded agent, that, when added to finished product neutralizes acidic contaminants in the oil before they become insoluble and form sludge. These additives possess the capacity to hold contaminants in suspension and thus promote cleanliness.

Dispersant  A descriptive word used interchangeably with detergent. These additives, usually ashless in character, have the capacity to hold contaminant in suspension or depending on the quality of the filtration, some particles are carried along in the oil stream and are filtered out and thus not permitted to settle out and accumulate.

Dielectric Constant The dielectric constant of any substance refers to the relative permittivity of the dielectric substance. It is the proportion of the permittivity of the material to the permittivity of the free space.

Dielectric Strength A measure of the ability of an insulating material to withstand electric stress without failure.

Dropping Point The temperature at which grease passes from a semisolid state to a liquid state under specific conditions.

Dry Running The condition that develops when moving surfaces have no lubricant between them. Dry running can lead to blistering. Also known as the corona effect.

Elasto-hydrodynamic Lubrication The elastic deformation of metal, usually experienced with bearings, where a “ flattening” of material surfaces occurs when under load. The momentary flattening and reformation of the surface assists hydrodynamic lubrication properties of the lubricant.

Elastomer A rubber-like material used in the production of seals, hoses and other products associated with machinery manufacture. Lubricant selection depends in part on the compatibility of the lubricant and the elastomer.

Emulsifier Additives that promote the formation of water and oil to form a mixture or emulsion of oil and water. Emulsions usually have a cloudy appearance, with metallic soaps making up some of the additives.

Emulsion A mixture of water and oil. It can have two basic makeups. Oil in water or water in oil.

Ester A chemical compound typically formed through the reaction between an acid and an alcohol.

Extreme Pressure EP Agent Additives that prevent sliding metal surfaces from seizing under conditions of extreme pressure. Temperature inducement of the EP additives combines chemically with the metal to form a surface film that prevents the asperities of opposing metal surfaces from welding together. Compounds such as sulphur, chlorine and phosphorus are used to form these inorganic films.

Film Strength The capacity of a lubricant to prevent the scuffing or scoring of metal surfaces.

Filtration The process by which insoluble particulate matter in fluids are separated by mechanical or physical means.

Filtration Filter Efficiency Beta Ratios The ratio is defined as the particle count upstream divided by the particle count downstream at the rated particle size. The beta rating comes from the Multi-pass Method for Evaluating Filtration performance of a filter element. ISO 16889:1999.

Flash Point The lowest temperature at which vapour from a petroleum product or other combustible fluid will flash in the presence of the ignition source.

Foaming A mixture of air and petroleum in it’s various forms, that severely reduce the effective operation of machine operation. Causes can occur from agitation, air leaks, cavitation or even low fluid levels.

Foam Inhibitor An additive that has the capacity to prevent the formation of foam due to aeration of the a liquid.

Food Grade Designations Three food-grade designations have been established to meet the requirements laid down the USDA. H1 requirements are met by making a lubricant suitable for food processing where incidental contact is possible. The H2 category is for equipment and machine parts in locations where there is no possibility of food contact, While the H3 category focuses on edible oils used on equipment used in the production of various foods.

Friction The resisting force that is encountered on a surface of the boundary between two bodies when contact is encountered between them both. This is sliding friction while fluid friction is that which occurs between the molecules of a fluid motion. Both types expend energy. Sliding friction causes wear.

Fuel Dilution  The amount of unburned fuel that enters a crankcase of an engine by way of blow-by. Left unchecked, It has the potential to cause wear related issues in a motor.

FZG Wear Test  This test has been developed for industrial gear lubricants to specifications. Graduated loads are introduced on gear sets which are driven by an electric motor until a failure point, which is when a 10 milligram weight loss is recorded in the gear set.

Galling  Wear that involves the seizing or tearing of metal from a gear or bearing face.

Gear A machine component which transmits motion and force by means of successively engaging teeth which are part of the same mechanism. The smaller component of a pair is called the pinion, the larger of the two, the gear. When the pinion is on the driving shaft, the gear set acts as a speed reducer. Conversely, when the gear drives the pinion, the result is a speed multiplier. The basic gear type is a spur or straight cut tooth gear, with teeth cut parallel to the gear axis. Spur gears transmit power in applications using parallel shafts. In spur gear applications the teeth mesh along their entire length, creating sudden shifts in load from one tooth to the next, which can result in unacceptable noise and vibration.

Helical gears can overcome this problem as they have teeth which are cut at an angle to the centre of rotation, so the load is transferred progressively along the length of the tooth from one edge of the gear to the other. When shafts are not parallel and the drive is transmitted at a 90angle, the common gear type used is the bevel gear, with teeth cut on a sloping gear face, rather than parallel to the shaft. Spiral bevel gears have teeth cut at an angle to the plane of rotation which, like the helical gear, transmits power at an angle and reduces noise and vibration. The hypoid gear resembles a spiral bevel gear, except that the pinion is offset so that its axis dose not intersect the gear axis. This gear configuration is used widely in automobile differentials.

A worm gear consists of a spirally grooved screw moving against a toothed wheel. In this gear type, where the load is transmitted across sliding, rather than rolling surfaces, EP oils are necessary to provide effective lubrication. The herringbone gear has teeth cut at an angle on the gear face, but the teeth are cut at right angles to each other on both the pinion and gear faces. This provides gear drives which eliminate excessive shaft end play, while ensuring low noise and vibration of the gear set.

Gear Oil A lubricant specially designed, for use usually with highly loaded gear sets or where excessive sliding of gears is occurring. Such lubricant has good rust protection, resistance to foaming, load carrying properties and oxidation stability. Enclosed chain drives also use this type of product.

Graphite  A crystalline form of carbon which is used as a lubricant.

Grease A type of lubricant composed of fluid, typically lubricant oil which is thickened with a material that causes a plasticity. Just as viscosity is the basis property of lubricating oil, consistency is the basis property of grease. This aspect is measured by a cone penetrometer. Recordings, in tenths of a millimetre determine the consistency.

Hydrocarbon A compound of hydrogen and carbon of which petroleum products are examples. Petroleum based oils are grouped into three parts: Naphthenic possess a higher proportion of unsaturated cyclic molecules while paraffinic have a lower proportion of unsaturates.

Hydrodynamic Lubrication  Lubrication in which the shape and relative motion of the sliding surfaces results in the formation of a fluid film having sufficient pressure to separate the surfaces. Adhesion to the moving surfaces draws oil into the high-pressure area between the surfaces and viscosity retards the tendency to squeeze the film out. In cases where the pressure developed is sufficient to completely separate the two surfaces, full-fluid-film lubrication is active.

Hydrolysis A deleterious process that occurs in anhydrous hydraulic fluids which result from heat, water, and metal catalysts.

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

Hydrophilic Compounds that have an affinity for water.

Hydrophobic Compounds that repel water.

Hygroscopic Substances, including certain lubricants that absorb and retain moisture.

Hypoid Gear Lubricant A gear lubricant possessing extreme pressure properties for applications where hypoid dynamics require such attention. Hypoid gears resembles a spiral bevel gear, except that the pinion is offset so that its axis dose not intersect the gear axis.

ILSAC International Lubricant Standardization and Approval Committee, is a joint committee of AAMA and JAMA members that contribute to the development of new minimum lubricant performance standards.

Immiscible In capable of being mixed without a separation of phases.

Infrared Spectroscopy An analytical method using infrared absorption for detecting properties and variations of used lubricant and contamination suspended within.

Inhibitor One of many substances that slows or prevents chemical reactions such as corrosion or oxidation.

ISO A grading system approved by the International Standards Organisation (ISO) to evaluate the viscosity of a lubricant.

ISO Solid Contaminant Code ( ISO 4406 ) A code developed to determine the number of particles per unit volume greater than 4,6 and 14 micrometres in size. Range numbers identify each increment in particle population. There are 25 codes on the table with each code a doubling of the number particles within the respective code when compared to the code proceeding it.

Karl Fischer Reagent Method The laboratory test to ascertain the water content of mineral based fluids. Water reacts quantitatively with the Karl Fischer reagent. It is a mixture of sulphur dioxide, pyridine, iodine, and methanol. When excess iodine exists, electric current passes between two platinum electrodes. The water in the sample reacts with the iodine. Water that is no longer free to react with the iodine depolarizes the electrodes indicating the end of the test.

Kinematic Viscosity  Is defined as the ratio of absolute or dynamic viscosity to density. Kinematic Viscosity can be obtained by dividing the absolute viscosity of a fluid with its mass density.

Load-carrying Capacity  The property of a lubricant which enables it to form a film which resists rupture under load stress conditions. This measure is expressed as the maximum load the film can support without rupture.

Load Wear Index The measure of a lubricants ability to prevent wear under applied loads. The data is gained by subjecting the lubricant to the Four Ball EP test Method.  (See more about this in the Weld Point Index).

Lubrication  The control of friction and wear between two moving surfaces in relative motion by the introduction of a friction-reducing substance between the two.

Lubricity  Is the measure of the reduction in friction and /or wear by a lubricant. This is also related to film strength.

Material Safety Data Sheet  (MSDS) Is a document that lists information relating to the occupational safety and health for the use of various substances and products. These publications are widely used for cataloguing information on chemicals, chemical compounds and chemical mixtures. An MSDS must include the chemical and common names of ingredients that have been determined to be a health hazard if they constitute 1% or greater of a products composition.

Micron A unit of length. SI symbol μ or micrometre. One micron is equal to 39 millionths of an inch, (.000039”). In relative terms, a human hair is approximately 70 micron. Many common off the shelf spin-on filters capture contamination in a range between 10 and 40 micron. Filters designed to capture hydraulic fluid contamination are required to capture particles as low as 5 micron.

Molybdenum Disulphide  Is an inorganic compound composed of molybdenum and sulphur. Its chemical formula is MoS2. It is a black silvery powder. It is widely used because of the low-friction properties.

Miscible Capable of being mixed in any concentration without separation of phases.

Multigrade Oil  An oil that meets the meets the requirements of more than one SAE ( Society of Automotive Engineers ),viscosity grade classification and hence would have an application over a wider temperature range than a single-grade oil.

Naphthenic A type of petroleum fluid derived from naphthenic or “sour’ crude oil. It has poor low-temperature fluidity while containing a high proportion of closed-ring methylene groups.

Neutralization Number  A measure of the total acidity or basicity (alkalinity) of an oil. ASTM D974-58T. The neutralization number is expressed in milligrams of potassium hydroxide or hydrochloric acid required to neutralize and acid or base in one gram of oil. The TAN – total acid number test uses potassium hydroxide as the neutralizing agent, while the (TBN ) total base number test uses hydrochloric acid as the neutralizing agent.

Newtonian Fluid  A fluid with a constant viscosity at a given temperature regardless of the shear rate. Single grade oils are Newtonian Fluids. Multigrade oils are non-Newtonian fluids because the viscosity varies with the temperature and the shear rate.

Nitration Is the chemical degradation of crankcase oil caused by the reaction of nitrogen oxides produced during the combustion process. Excess oxygen is the primary cause of such a process. These by-products are usually highly acidic, form deposits in combustion areas and accelerate the oxidation process.

NLGI National Lubricating Grease Institute. An association whose interests lie in grease and grease technology.

NLGI Grease Classifications or Grades A grading system established by the National Lubricating Grease Institute Several categories exist within Chassis and wheel bearing groups. Quality and performance levels within each category are determined by various ASTM tests.

Oil Filter A device, that removes various amounts of inherent or introduced contaminants from lubricating oil. Filters of various designs, modes of operation and effectiveness are utilized to maintain oil in a serviceable condition.

Oil Oxidation Put simply, oil oxidation is the chemical reaction of an oil molecule with oxygen, which is present from either ambient or entrained air. The process is accelerated by heat, light, acids, solid contaminants. It leads to permanent change to the base oil molecules.

Oxidation Inhibitor These take the form of substances added to petroleum products that increase the oils resistance to the process, thereby increasing the service life. They are also called anti-oxidants. Inhibitors perform their task in three ways; by combining with one main group of by-products, peroxides. Secondly, the oxidation catalyst  is rendered inactive and thirdly the chemical species is decomposed.

Oxidation Stability The resistance factor of petroleum products to the process of oxidation which is essentially the sequential addition of oxygen to base oil.

Paraffinic Waxy or “sweet” crude oil which is a common type base oil. It possesses a poor pour point due to the molecular chain. The base has good oxidation stability and a high viscosity index.

Phosphate Ester A base stock category with an alkyl subcategory which is typically used in aircraft fluids and an aryl subcategory which are found in compressor lubricants, metal production, mining, steam and gas turbine power generation. They have low volatility and good chemical stability and fire resistance. The groups are very sensitive to moisture and are considered toxic.

Polyalkylene Glycol PAG A category of base stocks commonly used in air and gas compressors, automotive air-conditioning compressors and marine oils. They are known for their oxidative and thermal stability and very high viscosity index, excellent film strength and high cleanliness standards. The category is known to burn clean and recognised for their low tendency to leave residue that form deposits. PAG’s are also recognised for their water absorbing capacities  while maintaining lubricity. The downside of PAG’s are their very costly.

Polyalphaolefin PAO  Polyalphaolefins are widely used in the industry today. The category are developed as opposed to be extracted or modified. They are very pure. The category has few negative attributes. The molecules are virtually all the same size and shape and are fully saturated, ( meaning they have fewer reactive tertiary hydrogen and carbon atoms are present). The potential benefits of PAO’s are improved oxidative and thermal stability, excellent demulsibility, a high VI and very low pour point. The properties lend themselves to both temperature extremes, i.e, high operating temperatures and low start-up temperatures. They are used extensively in engine oils, gear oils, and compressor oils. The negatives of PAO’s are the price and poor solubility. Low inherent solubility of PAO’s can create problems for formulators when dissolving additives. PAO’s are not compatible with glycols and other specialty chemicals.

Paper Chromatography A diagnostic method for testing engine oils, which involves placing a drop of fluid on a permeable piece of paper and observing the halos or concentric rings that can develop over time. The test does produce results which can be relied upon especially as experience is gained over time and used in conjunction with other diagnostic and laboratory results. Some major companies still use this test method today in determining whether an oil sample warrants further more exhaustive testing.

Pour Point A widely used low-temperature flow indicator. This is depicted as 5°F to which a normal liquid petroleum product maintains fluidity. Pour point is an important factor in cold-weather start-up.

Particle Count The number of particles present greater than a particular micron size per unit volume of fluid.

Patch Test A method by which a specified volume of fluid is filtered through a membrane filter known as pore structure. All particulate matter in excess of an average size which is determined by the membrane characteristics, is retained on its surface. The membrane discolouration by the amount proportional to the particulate level of the fluid sample is noted. Visually comparing the test result with standard test patches determines the acceptability of the test fluid.

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

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

Pitting A form of extremely localized attack characterized by minute holes on metal surfaces. Pitting is capable of one of the most destructive forms of corrosion. Pitting is dependant on many factors including the environment and may take lengthy periods of time to become visible.

Poise (absolute viscosity)  A measure of viscosity numerically equal to the force required to move a plane surface of one square centimetre per second when the surfaces are separated by a layer of fluid one centimetre 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 centimetre (Dyne Sec/CM2); 1 centipoise equals .01 poise.

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 for 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 end; in lubricants, they act as emulsifiers, helping to form stable oil-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/cylinder wall relationship and subsequent sealing and oil consumption performance.

Polyalkylene Glycol Mixtures of condensation polymers of ethylene oxide and water. They are any of a family of colourless 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.

Polymer A substance formed by the linkage (polymerization) of two or more simple, molecules, called monomers, to form a single larger molecule having the same elements in the same proportions as the original monomers; i.e. each monomer retains its structural identity. A polymer may be liquid or solid; solid polymers may consist of millions of repeated linked units. A polymer made from two or more similar monomers is called a copolymer; a copolymer composed of three different types of monomers is a terpolymer. Natural rubber and synthetic rubbers are examples of polymers. Polymers are commonly used as viscosity index improvers in multi-grade oils and tackifiers in lubricating greases.

Polymerization The chemical combination of similar-type molecules to form larger molecules.

Polyol Ester A 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 A polymer derived by polymerization of relatively simple olefins. Polyethylene and polyisoprene are important polyolefins.

Pour Point Lowest temperature at which an oil or distillate fuel is observed to flow, when cooled under conditions prescribed by test method ASTM D 97. The pour point is 3°C (5°F) above the temperature at which the oil in a test vessel shows no movement when the container is held horizontally for five seconds.

Pour Point Depressant An additive which retards the adverse effects of wax crystallization, and lowers the pour point.

PPM Parts per million (1/ppm = 0.000001). Generally by weight. 100 ppm = 0.01%; 10,000 ppm = 1%

Predictive Maintenance A type of condition-based maintenance emphasizing early prediction of failure using non-destructive techniques such as vibration analysis, thermography, and wear debris analysis.

Pressure Force per unit area, usually expressed in pounds per square inch.

Preventive Maintenance  Maintenance performed according to a fixed schedule involving the routine repair and replacement of machine parts and components.

Proactive Maintenance A maintenance strategy for stabilizing the reliability of machines or equipment. Its central theme involves directing corrective actions aimed at failure root causes, not active failure symptoms, faults, or machine wear conditions. A typical proactive maintenance regiment involves three steps: (1) setting a quantifiable target or standard relating to a root cause of concern (e.g., a target fluid cleanliness level for a lubricant), (2) implementing a maintenance program to control the root cause property to within the target level (e.g., routine exclusion or removal of contaminants), and (3) routine monitoring of the root cause property using a measurement technique (e.g., particle counting) to verify the current level is within the target.

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.

R & O (Rust and 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 A 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, dewaxing, de-oiling, acid treating, clay filtration, and de-asphalting. Refined lubricating oils may be blended with other lube stocks, and additives may be incorporated, to impart special properties.

SAE Society of Automotive Engineers, an organization serving the automotive industry.

SAE Viscosity The viscosity classification of a motor oil according to the system developed by the Society of Automotive Engineers and now in general use. “Winter” grades are defined by viscosity measurements at low temperatures and have “W” as a suffix, while “Summer” grades are defined by viscosity at 100°C and have no suffix. Multigrade oils meet both a winter and a summer definition and have designations such as SAE 10W-30, etc.

Saturation Level The amount of water that can dissolve in a fluid.

Saybolt Universal Viscosity (SUV) or Saybolt Universal Seconds, (SUS) The time in seconds required for 60 cubic centimetres 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 anti-wear, extreme-pressure and friction modifier additives.

Shear Rate  The rate at which adjacent layers of fluid move with respect to each other, usually expressed as reciprocal seconds.

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 of a Newtonian fluid, the greater the shear stress as a function of rate of shear. In a non-Newtonian fluid.

Sludge The collective name for contamination in a lubricated system and on parts bathed by the lubricating oil. This includes decomposition products from the fuel, oil and particulates from sources external to the system.

Solvency The ability of a fluid to dissolve inorganic materials and polymers, which is a function of aromaticity. The degree of solvency varies along with the rate of dissolution which depends the amount of heat involved.

Solvent  A material with a strong capability to dissolve a given substance. The most common petroleum solvents are mineral spirits, xylene, toluene, hexane, heptane, and naphthas. Aromatic-type solvents have the highest solvency for organic chemical materials, followed by naphthenes 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.

Solvent Extraction.  A refining process used to separate components (unsaturated hydrocarbons) from lube distillates in order to improve the oil’s oxidation stability, viscosity index, and response to additives. The oil and the solvent extraction media are mixed in an extraction tower, resulting in the formation of two phases: a heavy phase consisting of the undesirable un-saturates dissolved in the solvent. And a lighter phase consisting of a high quality oil with some solvent dissolved in it. The phases are separated and the solvent recovered from each by distillation.

Specific Gravity. The ratio of the weight of a given volume of material to the weight of an equal volume of water.  Water has a density of 1 gram/cm3. The closer a lubricant’s specific gravity is to 1, the greater its tendency to absorb moisture and have poor demulsibility.

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

Spectrographic Oil Analysis Program (SOAP) Procedures for extracting fluid samples from operating systems and analysing them spectrographically for the presence of key elements.

Static Friction The force just sufficient to initiate relative motion between two bodies under load. The value of the static friction at the instant relative motion begins is termed break-away friction.

Stick-slip Motion Erratic, noisy motion, characteristic of some machine ways, due to the starting friction encountered by a machine part at each end of its back-and-form (reciprocating) movement. This undesirable effect can be overcome with a way lubricant, which reduces starting friction.

STLE  Society of Tribologist and Lubrication Engineers, formerly ASLE, American Society of Lubrication Engineers.

Stoke  Kinematic measurement of a fluid’s resistance to flow defined by the ratio of the fluid’s dynamic viscosity to its density. 1 St = 100 cSt   Water @ 20°C has a Kinematic Viscosity of about 1 cSt.

Sulphated Ash The ash content of fresh, compounded lubricating oil as determined by ASTM Method D 874. Indicates level of metallic additives in the oil.

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

Surface Tension. The cohesive force at the surface of a liquid that causes the surface to contract and assume a spherical form resembling a stretched elastic membrane. It is expressed in dynes/cm or ergs/cm2.

SUS 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 standard orifice is measured in Seconds. Fast flowing fluids (low viscosity) will have low value; Slow flowing fluids (high viscosity) will have high values.

Synthetic Hydrocarbon Oil molecule with superior oxidation quality tailored primarily out of paraffinic materials. They are commonly used in engine oils, and other automotive applications, hydraulic fluids, air compressors, and chain and gear fluids. They offer excellent thermal and oxidative stability, lubricity and water separation.

Synthetic Lubricant A lubricant produced by chemical synthesis rather than by extraction or refinement of petroleum to produce a compound with planned and predictable.

Synthetic Oil Oil 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 is their chemical uniformity.

TAN (Total) acid number.

TBN (Total) base number.

Thermal Conductivity Measure of the ability of a solid or liquid to transfer heat.

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

Timken EP Test Measure of the extreme-pressure properties of a lubricating oil. The test utilizes 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 The heaviest load that a test lubricant will sustain without scoring the test block in the Timken Test procedures, ASTM Methods D 2509 (greases) and D 2782 (oils).

Total Acid Number (TAN) A test using potassium hydroxide as the neutralizing agent to measure the acidity of an oil. The result is expressed in milligrams of potassium hydroxide needed to neutralize one gram of oil. (ASTM Designation D974.)

Total Base Number (TBN) A test using hydrochloric acid as the neutralizing agent to measure the basicity (alkalinity) of an oil. The result is expressed in milligrams of hydrochloric acid needed to neutralize one gram of oil. (ASTM Designation D974.)

Tribology The science and technology of interacting surfaces in relative motion, including the study of lubrication, friction and wear. Tribological wear is wear that occurs as a result of relative motion at the surface.

Turbine Oil A top-quality rust and oxidation-inhibited (R&O) oil that meets the rigid requirements traditionally imposed on steam-turbine lubrication. Quality turbine oils are also distinguished by good demulsibility, a requisite of effective oil-water separation. Turbine oils are widely used in other exacting applications for which long service life and dependable lubrication are mandatory. Such compressors, hydraulic systems, gear drives, and other equipment. Turbine oils can also be used as heat transfer fluids in open systems, where oxidation stability is of primary importance.

Varnish When applied to lubrication, a thin, insoluble, film deposit occurring on interior parts, resulting from the oxidation and polymerization of fuels and lubricants. Can cause sticking and malfunction of close-clearance moving parts. Similar to, but softer, than lacquer.

Viscometer An apparatus for determining the viscosity of a fluid.

Viscosity Measurement of a fluid’s resistance to flow. 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 centimetre in area past a parallel surface at a speed of one centimetre per second, with the surfaces separated by a fluid film one centimetre thick. In addition to kinematic viscosity, there are other methods for determining viscosity, including Saybolt Universal Viscosity (SUV),  Engler viscosity, and Redwood viscosity. Since viscosity varies inversely with temperature, its value is meaningless until the temperature at which it is determined is reported.

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.

Viscosity Index The measure of the rate of change of viscosity with temperature. Heating tends to make lubricants thinner; cooling makes them thicker. The higher the viscosity index is on a particular fluid, the smaller the relative change in viscosity with temperature. In determining the viscosity index, two temperatures of viscosity are taken, one at 40°C and the other at 100°C.

Viscosity Index Improvers Additives that increase the viscosity of the fluid throughout its useful temperature range. Such additives are polymers that possess thickening power as a result of their high molecular weight and are necessary for formulation of multi-grade engine oils.

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 know 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.

Volatility The property of a liquid that defines its evaporation characteristics. Of two liquids, the more volatile will boil at a lower temperature and will evaporate faster when both liquids are at the same temperature. The volatility of petroleum products can be evaluated by tests for flash point, vapor pressure, distillation and evaporation rate.

Wear The attrition or rubbing away of the surface of a material as a result of mechanical 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 – ASTM D 4172 either seizes and welds to the three stationary balls, or at which extreme scoring of the three balls results. There also exists the Four Ball Extreme Pressure Test – ASTM D 2783. Both tests utilizes the same apparatus and set up.

Work Penetration The penetration of a sample of lubricating grease immediately after it has been brought to 77F 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. Penetration, ( in tenths of a millimetre ), that a standard cone penetrates  the worked sample. The NLGI National Lubricating Grease Institute Grading system contains 8 grades ranging from “00” to “6”.

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 An anti-wear additive found in many types of hydraulic and lubricating fluids. Zinc dialkyldithiophosphate.

Information courtesy Machinery Lubrication