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Lubrication Glossary Of Terms

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Additive: A chemical added in small quantities to a base fluid in order to improve specific properties of the lubricant such as fluid life, lubricity, wear protection, rust protection, etc.
Alkylbenzene (AB): A category of base stocks often used in refrigeration compressors. Alkylbenzene base stocks are wax-free, offer good solubility with additives and have good miscibility with certain refrigerants in the HVAC/R industry. They also have very low viscosity indexes and a tendency to swell and soften seals.
Anti-Foam Agent: An additive that causes foam to dissipate more rapidly. It promotes the combination of small bubbles into large bubbles which burst more rapidly.
Antioxidant: A chemical added in small quantities to a petroleum product to increase its oxidative resistance in order to prolong its service life.
Anti-Wear Agent: An additive that minimizes wear caused by metal-on-metal contact by forming a film on the metal surfaces, typically activated by heat and pressure.
Aromatic: Weak hydrocarbon bond that is highly reactive. Aromatics generally are identified by the presence of one or more benzene rings, or by exhibiting chemical behavior similar to that of benzene.
Asperity: Microscopic protrusion on a metal surface that typically occurs with normal finishing processes. Ideally, lubrication should be sufficient to prevent asperities on each metal surface from protruding through the lubricant film and making contact with other metal surfaces.
Auto-Ignition Temperature: Minimum temperature at which a combustible fluid will burst into flame without the assistance of an extraneous ignition source. This temperature is typically several hundred degrees higher than the flash and fire point.
Base Oil: Base stock or blend used as an inert ingredient in the manufacturing of automotive and industrial lubricants.
Base Stock: Refined petroleum oil that can be blended with other base stocks and/or supplemented with additives to make lubricants.
Biodegradable: Capable of being broken down chemically, especially into innocuous products, by the action of living microorganisms in the environment.
Boundary Lubrication: A form of lubrication effective in the absence of a full fluid film. Made possible by the inclusion of certain additives in the lubricating oil that prevent excessive friction and scoring by forming a film whose strength is greater than that of oil alone. These additives include oiliness agents, compounded oils, anti-wear agents and extreme-pressure agents.
Blistering: The formation of blisters on the surface of a seal face, degrading it and increasing leak rates and friction, and increasing the potential for the seal shaft to fail.
Carbon Residue: Coked material formed after lubricating oil has been exposed to high temperatures. Many consider the type of carbon formed to be of greater significance that the quantity.
Cavitation: The formation of a pocket (bubble) of air or vapor in a liquid, typically resulting from the swift movement of a solid object (such as a propeller or piston) through the liquid. Also, the pitting and wearing away of metal or other solid surfaces caused by the collapse of air/vapor pockets in surrounding liquid.
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Corrosion: The decay and loss of metal caused by a chemical reaction between the metal and another substance, such as contaminants in a lubricant.
Corrosion Inhibitor: An additive that protects lubricated metal surfaces against chemical attack by water or other contaminants.
Demulsibility: A lubricant’s ability to separate from water.
Detergent: An additive which chemically neutralizes acidic contaminants in the oil before they become insoluble and fall out of the oil to form sludge. Particles are kept finely divided so that they can remain dispersed throughout the lubricant.
Dielectric Strength: The extent to which a fluid can withstand electric voltage without failing. Dielectric strength is measured as the minimum voltage at which an electric arc passing through a fluid causes fluid breakdown. High dielectric strength may indicate that a fluid is a good electrical insulator, while low dielectric strength might possibly signal that a fluid is contaminated with water.
Diester: A category of base stocks typically used in reciprocating air compressors and vane compressors. Diesters mix with most glycols, polyalphaolefins (PAOs) and other fluids. Diesters offer excellent resistance to oxidation, varnish and carbon for a long fluid life. Their water separability is inferior to other synthetics, and their low viscosity indexes diminish cold-weather performance.
Dispersant: An additive that keeps insoluble contaminants dispersed (colloidally suspended) in a lubricant, preventing the particles from settling and accumulating. Dispersants help prevent the buildup of sludge, varnish and other deposits.
Dropping Point: The temperature at which grease passes from a semisolid state to a liquid state under specific test conditions.
Dry Running: A condition in which moving surfaces have no liquid lubricant between them. Dry running can lead to blistering, also known as the corona effect.
Elastomer: A rubber or rubber-like material used to make seals, hoses and other products. In the case of oil seals, lubricant selection depends in part on the compatibility between the lubricant and the elastomer.
Emulsifier: An additive that promotes the mixing of water and oil to form an intimate mixture of the oil and water (called an emulsion). Emulsions generally have a cloudy or milky appearance.
Entrainment: Describing a state of an immiscible fluid component. Minute quantities of a fluid (typically water) can be dissolved or absorbed into the oil, but excess quantities can be most harmful to equipment due to the entrainment leaving gaps in the lubricated areas.
Ester: A chemical compound typically formed through the reaction between an acid and an alcohol.
Extreme-Pressure Agent: An additive that prevents sliding metal surfaces from seizing in extreme-pressure conditions. It combines chemically with metal surfaces to form a layer of film that prevents welding and excessive wear of contacting metal parts under shock load.
Film Strength (Lubricity): The extent to which a lubricant is able to prevent the scuffing or scoring of metal surfaces.
Fire Point: Lowest temperature at which a combustible fluid will burst into flame in the presence of an extraneous ignition source. Very little additional heat is required to reach the fire point from the flash point.
Flash Point: Lowest temperature at which vapor from a sample of a petroleum product or other combustible fluid will “flash” in the presence of an ignition source. The flash can be seen in the form of a small spark over the liquid.
Foaming: A possible reaction of an oil when mixed with air. This entrained air can result in reduced film strength and a performance reduction.
Foam Inhibitor: An additive which causes foam to dissipate more rapidly. It promotes the combination of small bubbles into large bubbles which burst more easily.
Food-Grade Formulation: The USDA has established three food-grade designations, and a lubricant’s ingredients determine whether or not it meets the requirements for one of these designations: Fluids meeting the requirements for H1 applications may be used in food-processing environments where incidental food contact is possible. Fluids meeting the requirements for H2 applications may be used on equipment and machine parts in locations where there is no possibility of food contact. Fluids meeting the requirements for H3 applications are typically edible oils and are often used to prevent rust on hooks, trolleys and similar equipment.
Four-Ball Tests: Two test procedures on the same principle. The four-ball wear test is used to determine the relative wear-preventing properties of lubricants operating under boundary lubrication conditions. The four-ball extreme-pressure test is designed to evaluate performance under much higher unit loads.
Friction: Resistance to motion on a surface or by a substance as a result of its contact with another surface or substance. Sliding friction is that which occurs between two solid bodies, while fluid friction is that which occurs between the molecules of a fluid in motion. Both types of friction can be wasteful in power and energy, and sliding friction causes wear.
FZG Wear Test: A test to evaluate the anti-wear characteristics and load-carrying capacities of gear lubricants.
Grease: A type of lubricant composed of a fluid (typically lubricant oils) thickened with a material that contributes a degree of plasticity (typically soaps). Just as viscosity is the basic property of lubricating oil, consistency is the basic property of grease. Consistency is measured in terms of penetration, tested in terms of tenths of a millimeter that a standard cone acting under the influence of gravity penetrates the sample under controlled test conditions. The greater penetration, the softer the grease.
Hazard Analysis Critical Control Point (HACCP): A systematic approach to identify, evaluate and control food-safety hazards. It addresses physical, chemical and biological hazards with the goal of preventing hazards before products enter the food supply. From a lubrication standpoint, an HACCP plan generally involves conducting a lubrication survey, which is a thorough examination of potential lubrication-related food-contamination risks in a facility.
Hydrocarbon: A compound of hydrogen and carbon of which petroleum products are typically examples. Petroleum oils are generally grouped into two parts: Naphthenics possess a high proportion of unsaturated cyclic molecules; paraffinics possess a low proportion of unsaturated cyclic molecules.
Hydrodynamic Lubrication: A type of lubrication effected solely by the pumping action developed by the sliding of one surface over another in contact with an oil. Adhesion to the moving surface draws the oil into the high-pressure area between the surfaces, and viscosity retards the tendency to squeeze the oil out. If the pressure developed by this action is sufficient to completely separate the two surfaces, full-fluid-film lubrication is said to prevail.
Hydrolytic Stability: The ability of a lubricant to resist chemical decomposition in the presence of water (a condition known as hydrolysis).
Hydro-Treating: A Gulf-patented process used to make lubricant base stocks. In the process, lubricant feed stocks are reacted with hydrogen in the presence of a catalyst at very high temperature (800°F) and pressure (3200 psig). The process displaces impurities and unsaturated hydrocarbons.
Hygroscopic: Describes substances, such as certain lubricants, that readily absorb and retain moisture.
ISO Viscosity Grades: A grading system approved by the International Standards Organization (ISO) to evaluate the viscosity of a lubricant.
Lubrication: The control of friction and wear between two moving, touching surfaces by placing a friction-reducing substance between them.
Lubrication Survey: An examination of potential lubrication-related food-contamination risks in a facility, generally conducted as part of an HACCP (hazard analysis and critical control point) plan.
Lubricity (Film Strength): The capacity of a substance for reducing friction.
Metal Deactivator: An additive that reduces the catalytic effect of metals and their salts on the rate of oxidation.
Mineral Oil: Any oil derived from a mineral source, such as petroleum.
Miscible: Capable of being mixed in any concentration without separation of phases.
Naphthenic: Asphaltic or “sour” crude oil. It has poor low-temperature fluidity as a result of a low viscosity index. It has good solvency properties.
Neutralization Number: An indication of the acidity or basicity (alkalinity) of an oil. The neutralization number is expressed in milligrams of potassium hydroxide or hydrochloric acid needed to neutralize any acid or base in one gram of oil. The total acid number (TAN) test uses potassium hydroxide as the neutralizing agent, and the total base number (TBN) test uses hydrochloric acid as the neutralizing agent.
NLGI Grades: A grading system established by the National Lubricating Grease Institute to evaluate the consistency or thickness of a grease.
Oxidation: A form of chemical deterioration to which all petroleum products are subject to, and involves the addition of oxygen atoms resulting in degradation. It is accelerated by higher temperatures above 160°F, with the rate of oxidation doubling by each 20°F increase. With fuels and lubricant oils, oxidation produces sludge, varnish, gum and acid, all of which are undesirable.
Oxidative Stability: Resistance of a petroleum product to oxidation, thereby increasing its potential service or storage life. Since the life of many lubricants can be well over a year, simulations are used to show the time required for a sample to develop a specified degree of oxidation under accelerated conditions.
Paraffinic: Waxy or “sweet” crude oil. It is the most common type of base oil in production. It has a poor pour point due to the tendency to form wax molecule chains. It typically has excellent oxidation stability and a high viscosity index.
Particulate: A substance made up of a concentration of separate, minute particles.
Phosphate Ester: A category of base stocks with an alkyl subcategory typically used in aircraft hydraulic fluids, and an aryl subcategory typically used in compressor oils, metal production/mining hydraulic fluids, steam and gas turbine power generation. Phosphate esters offer low volatility, good chemical stability and fire resistance/good fire-extinguishing capabilities. They are sensitive to moisture and high density, and they have selective seal and paint compatibility. They can be considered toxic/hazardous in large quantities.
Polyalkylene Glycol (PAG): A category of base stocks typically used in air and gas compressors, textile lubricants, automotive air-conditioning compressors and marine oils. They are available in water-soluble, water-insoluble and food-grade varieties. They have very high viscosity indexes.
Polyalphaolefin (PAO): A category of base stocks often used in air compressor lubricants, engine oils, transmission fluids and gear lubricants. They offer excellent oxidative resistance for a very long fluid life, very high viscosity indexes for enhanced lubrication at hot and cold temperatures, excellent seal compatibility and excellent water separation. They are not compatible with glycols and other specialty chemicals. They have limited additive solubility.
Polyol Ester (POE): A category of base stocks typically used in air and refrigeration compressors, jet aircraft engines, hydraulic systems and high-temperature change lubricants. They are compatible with most non-silicone lubricants. They offer excellent resistance to carbon formation and oxidation for a long fluid life. They have excellent low-temperature fluidity as well as enhanced protection at high temperatures, but they have a tendency to absorb water.
Pour Point: A widely used low-temperature flow indicator, depicted as 5°F above the temperature to which a normal liquid petroleum product maintains fluidity. It is a significant factor in cold-weather start-up.
Rust Inhibitor: A lubricant additive for protecting ferrous (iron and steel) components from rusting caused by water contamination or other harmful materials from oil degradation. Some rust inhibitors operate similarly to corrosion inhibitors by forming inert films on metal surfaces. Other rust inhibitors absorb water by incorporating it into a water-in-oil emulsion so that only oil touches the metal surfaces.
Shear Stress: A unit of frictional force overcome in sliding one layer of fluid along another. This is typically measured in pounds per square foot, with pounds representing the frictional force, and square feet representing the area of contact between the sliding layers.
Silicone: A category of base stocks with three subcategories: Dimethyl silicones resist moisture and some chemicals and are ideal for low loads and low speeds. Phyenylmethyl silicones resist moisture, oxidation and corrosion, and they are ideal for low-to-moderate loads and moderate-to-high speeds. Fluorosilicones, typically used in harsh chemical and solvent environments, are ideal for moderate-to-high loads and moderate-to-high speeds.
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 to dissolve into a solution producing a homogeneous physical mixture. The degree of solvency varies along with the rate of dissolution depending on the amount of heat added to the solution.
Specific Gravity: The density of a substance divided by the density 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.
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.
Synthetic Hydrocarbon: A category of base stocks commonly used in engine oils and other automotive applications, hydraulic fluids, air compressors, pump fluids, and chain and gear fluids. They offer excellent thermal and oxidative stability, lubricity and water separation, but they will not mix with glycols.
Thermal Stability: The ability to resist chemical degradation under high-temperature operating conditions.
Timken Extreme-Pressure Test (Timken OK Load Test): A test to determine the extreme-pressure capabilities of a lubricant. It measures the heaviest load a lubricant can sustain without scoring the test block. Results may be expressed in pounds or kilograms.
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.
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.
Tri-ester: A compound containing three ester groups. (An ester is a chemical compound typically formed through the reaction between an acid and an alcohol.)
Two-Stage Hydrocracking: A refining process that utilizes high-pressure hydrogen to break apart and reform most or all of the aromatic molecules into preferred chemical structures and strip virtually all sulfur and nitrogen from the oil, creating a far more stable chemical structure and a fluid that is 99.9 percent pure.
Vapor Pressure: The measure of a liquid’s volatility. The higher the pressure at a standard test temperature, the more volatile the sample, and the more readily it will evaporate.
Varnish: A deposit resulting from oxidation and polymerization of fuels and lubricants. Similar to, but softer than, lacquer.
Viscosity: Measure of a fluid’s resistance to flow. This is typically measured as the time required for a standard quantity of fluid at a certain temperature to flow through a standard orifice. The higher the value, the more viscous the fluid. Viscosity varies inversely with temperature, so the measurements are always expressed together. Tests are typically conducted at 40°C and 100°C.
Viscosity Dilution: The reduction of lubricant viscosity caused by contamination with water or other substances.
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 less of a change in viscosity there will be over a given temperature range. In determining the viscosity index, two temperatures of viscosity are taken, one at 40°C and the other at 100°C.
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.