Volume 6, Issue 7 (July 2009)
Foam Tests for Lubricating Oils: Limitations of Reliability and Reproducibility
The ASTM D892 foam test is a simple yet important method for evaluating the foaming tendency and stability of lubricating oils. Numerous interlaboratory studies have clearly shown the poor repeatability and reproducibility of this test. Often the quality of diffusers used in the test is questionable, yet many laboratories do not verify the diffuser quality. Perhaps using only the metal diffusers will improve the situation since these are machine made and can be fabricated to the required maximum pore size and permeability specifications. A review of the critical factors involved in conducting the ASTM D892 foam test is presented. Changes are proposed to the materials and procedures that will improve the precision of this important test method.