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Handling grease: A no-mixer

Keeping grease clean and dry is a no-brainer. And as a general rule, greases should never be mixed; however, sometimes it is unavoidable.


June 30, 2011
Kathy Smith

Keeping grease clean and dry is a no-brainer. And as a general rule, greases should never be mixed; however, sometimes it is unavoidable.

Several types of incompatibilities can occur that are not solely dependent on the thickener system, and they are difficult to predict. Exhaustive testing is recommended to prevent significant cost overruns arising from long-term maintenance problems or equipment damage.

Nicolas Samman, the manager of grease product development for Petro-Canada Lubricants Inc. in Mississauga, Ont., recommends ASTM D6185 as the primary test procedure. It’s best performed in service or in a test that simulates field service, and it should be preceded by an ASTM D217 test to determine grease consistency.

Reasons for the incompatibility of greases are base oil differences and oil blends, thickener systems, formulation or additive incompatibilities and incompatibilities resulting from loss of additives synergy.
Watch for decreases in physical properties and in heat resistance, changes in product consistency, decrease in shear stability and a general decrease in additive performance. Obviously, incompatibility affects in-service performance. Grease mixtures will often run out of the bearings, the dropping point can be drastically reduced and, at worst, catastrophic losses are possible.

Samman says if grease pairs are compatible or borderline, it’s generally safe to proceed. Remember to check other performance factors besides the thickener system. Greases become less compatible with increases in operating temperature.

From a presentation and discussion at the Toronto Section of the Society of Tribologists and Lubrication Engineers (STLE).