Performance comparisons of open-gear lubricants using different FZG test conditions

摘要

The standard FZG -test (A/8, 3/90) was developed to determine the scoffing load capacity of gear oils (1) and is performed using type 'A' gears at a circumferential speed of 8,3 m/s with an initial sump temperature of 90℃. For testing fluid open- gear greases, this test is often performed at 2,76 m/s (2). In order to conduct the test under more representative operating conditions and to accommodate most lubricant technologies, gear speed was reduced to 0,8 m/s and the method of lubrication of the gear surfaces was changed from dip-lubrication to dripping the lubricant directly into the meshing gears (3). The purpose of the present article is twofold, namely to compare performance of 10 open-gear greases using the 2,76 m/s test with that of the 0,8 m/s test and to establish a means of evaluating wear performance of open-gear greases using the FZG test. In the FZG test for gear oils, failure due to lubricating film breakthrough is determined either by means of a specified increase in mass loss per load stage compared with the average mass loss over the preceding load stages, or by visual evaluation of the damage on the gear tooth faces. When evaluating an open gear lubricant on the FZG-machine, a drastic breakthrough of the lubricating film is often not evident. When gear teeth are inspected, tooth surfaces are polished due to abrasive action of solid particles present in the lubricant. Abrasion causes a relatively large, gradual mass loss without the sudden mass loss characteristic of film breakthrough. An alternative failure criterion than failure load stage is therefore required when evaluating open-gear lubricants on the FZG-machine. Such a criterion should relate the wear rate observed during the test to the expected wear of gear surfaces over the design lifetime of the gears.