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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Immiscible – Incapable of being mixed without separation of phases. Water and petroleum oil are immiscible under most conditions, although they can be made miscible with the addition of an emulsifier.

Industrial Lubricant – Any petroleum or synthetic-base fluid or grease commonly used in lubricating industrial equipment such as gears, turbines and compressors.

Infrared (IR) Analysis
– A form of absorption spectroscopy that identifies organic functional groups present in a used-oil sample by measuring their light absorption at specific infrared wavelengths; absorbance is proportional to concentration.  The test can indicate additive depletion, the presence of water, hydrocarbon contamination of a synthetic lubricant, oxidation, nitration, and glycol contamination from coolant. Fourier Transform Infrared (FTIR) permits the generation of complex curves from digitally represented data.

Inhibitor – An additive that improves the performance of a petroleum product through the control of undesirable chemical reactions.

Insolubles – A test for contaminants in used lubricating oils such as test method ASTM D893.  In this method, the oil is first diluted with pentane, causing the oil to lose its solvency for certain oxidation resins, and also causing the precipitation of such extraneous materials as dirt, soot, and wear metals. These contaminants are called pentane insolubles. The pentane insolubles may then be treated with toluene, which dissolves the oxidation resins (benzene was formerly used). The remaining solids are called toluene insolubles. The difference in weight between the pentane insolubles and the toluene insolubles is called insoluble resins. Testing for grease insolubles is described in ASTM D128.

ISO Viscosity Classification System – An 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.