Glossary of Lubrication Terms

This glossary is designed to help the understanding of some of the terms used in Tribology and Lubrication Engineering. Quickly look up a definition or explanation for a topic.
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Carbon Residue – The measure of the coke-forming tendency of oils at high temperatures.  

– A cancer-causing substance. Certain petroleum products are classified as potential carcinogens under OSHA criteria. Suppliers are required to identify such products as potential carcinogens on package labels and Material Safety Data Sheets.

Catalyst – A substance that contributes to a chemical reaction without, itself, undergoing any change.

Cavitation – The 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 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.

Channel Point – A measure of the lowest temperature at which a gear lubricant may be used safely.

Chlorinated Paraffins (CPs) – A complex group of man-made compounds, primarily used as coolants and lubricants in metal forming and cutting. They also are used as plasticizers and flame-retardants in rubber, paints, adhesives, sealants and plastics.

Chlorinated Wax – Certain solid hydrocarbons treated with chlorine gas to form straight-chain hydrocarbons with a relatively high chlorine component.  Chlorinated waxes are used primarily as polyvinyl chloride plasticizers, extreme-pressure additives for lubricants, and formulation components for many cutting fluids.

Circulating Lubrication System – A system in which oil is recirculated from a sump or tank to the lubricated parts, in most cases requiring a pump to maintain circulation. Circulating lubrication makes possible extended lubricant use and usually requires high-quality rust and oxidation inhibited (R&O) oil.

Clay Filtration – A refining process using fuller’s earth (activated clay), bauxite or other mineral to adsorb minute solids from lubricating oil, as well as remove traces of water, acids and polar compounds.

Cloud Point – The temperature at which a lubricant appears hazy due to wax formation when a sample is cooled under standard conditions.

Cold Cranking Simulato
r – A viscometer used to predict the ability of an engine lubricant to allow cranking during cold starts.

Compounded Oil – A mixture of 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.

Consistency (Grease) – A basic property describing the softness or hardness of a grease (i.e., the degree to which a grease resists deformation under the application of force). Consistency is usually measured by means of a cone penetration test. The consistency of a grease depends on the viscosity of the base oil and the type and proportion of the thickener. It can also be affected by recent agitation. To take this phenomenon into consideration, grease is usually subjected to working (a standard churning process) prior to measuring its penetration value.

Corrosion – A chemical attack on a metal or other solid by contaminants in a lubricant.  Common corrosive contaminants are (1.) water, which causes rust of ferrous materials, and (2.) acids, which may form as oxidation products in a deteriorating oil, or may be introduced into the oil as combustion byproducts in piston engines.

Corrosion Inhibitor – An additive for protecting lubricated metal surfaces against chemical attack by water or other contaminants. There are several types of corrosion inhibitors. Polar compounds wet the metal surface preferentially, protecting it with a film of oil. Other compounds may absorb water by incorporating it in a water-in-oil emulsion so that only the oil touches the metal surface. Another type of corrosion inhibitor combines chemically with the metal to present a non-reactive surface.

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 lighter grades for wet, saturated, or low-pressure steam. Some grades are compounded for service in excessive moisture. Cylinder oils lubricate on a once-through basis.