The ASTM D942-19 standard, developed by the American Society for Testing and Materials (ASTM), describes a test method for determining the resistance of lubricating greases to oxidation when statically stored in an oxygen atmosphere in a closed system at high temperature under test conditions.
This test method measures the net change in pressure due to consumption of oxygen by oxidation and the gain in pressure due to the formation of volatile oxidation by-products. This test method is used for quality control purposes to indicate batch-to-batch uniformity. It predicts neither the stability of greases under dynamic service conditions, nor the stability of greases stored in containers for long periods of time, nor the stability of grease films on bearings and engine parts. It should not be used to estimate the relative oxidation resistance of different grease types.
Oxidation stability is a chemical reaction that occurs with a combination of lubricating oil and oxygen. Oxidation is accelerated by high temperatures, water, acids and catalysts such as copper. The rate of oxidation increases with time. The service life of a lubricant decreases with increases in temperature. Oxidation leads to an increase in oil viscosity and varnish and sludge deposits.
The oxidation rate varies depending on the additive package used, as well as the quality and type of base oil. Some synthetic compounds naturally exhibit better oxidation stability than mineral oils.
In general, oxidation halves the service life of a lubricant for every 60 degree increase in fluid temperature above 10 degrees Celsius.
Several methods are used to determine or evaluate the oxidation stability of an oil, generally regarded as the time until a certain increase in viscosity is noted or a certain increase in acid number.
Thanks to the consistency of lubricating greases derived from a lubricating fluid and a thickener, these products are developed for use in any machine with sliding or rolling contact, such as gears, speed joints or couplings.
Among the numerous tests, measurements, analyses, and evaluations our organization provides for businesses in various sectors, we also offer standard testing services for the oxidation stability of lubricating greases using the oxygen pressure vessel method under the ASTM D942-19 standard, thanks to our trained and expert staff and advanced technological equipment.
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