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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Bactericide – Additive included in the formulations of water-mixed fluids to inhibit the growth of bacteria. 

Base Number – The number of milligrams of acid required to neutralize one gram of an oil sample. ASTM D974 uses hydrochloric acid and a color-indicator titration. ASTM D2896 uses perchloric acid in a potentiometric titration

Base Stock
– A primary refined petroleum fraction, usually lubricating oil, into which additives and other products are blended to produce finished products.

Bearing – Basic machine component designed to reduce friction between moving parts and to support a moving load.

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.

Bleeding – Separation of a liquid from lubricating grease.

Boundary Lubrication – A form of lubrication between two rubbing surfaces without development of a full-fluid lubricating film. 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. 

Brookfield Viscosity – A measure of the viscosity characteristics of a lubricant under low temperature and low shear conditions. The apparent viscosity of oil, usually determined by test method ASTM D2983. The apparent viscosity of a non-Newtonian fluid is valid only for the shear rates and 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 (centipoise) by a conversion factor or equation.

Bulk modulus – The measure of a fluid’s resistance to compressibility—the reciprocal of compressibility.