Suitability of the test results of micropitting tests acc. to FVA 54/7 for modern practical gear applications

A high load carrying capacity regarding micropitting is requested in many modern gear applications. The lubricant used has a great influence on the micropitting resistance of a gear-lubricant-system. As a result, it is highly recommended that a lubricant with a sufficient micropitting load-carrying capacity be used to avoid micropitting. Lubricants usually contain additives, which also have a strong effect on micropitting load-carrying capacity depending on operating temperature. As a result, the load-carrying capacity of gear lubricants cannot be determined theoretically and has to be determined by physical testing. A well-established test procedure to determine load-carrying capacity with regard to micropitting is the FVA/FZG-micropitting test according to FVA 54/7, which is also the basis of the recently published standard DIN 3990-16. This test method was defined about 30 years ago with standardized test gears, which differ from gears commonly used in modern applications. Therefore, the practicability of the test method needs to be reviewed and the suitability of the test results for modern practical gear applications needs to be verified. For this purpose, screening tests were conducted with case-hardened gears of materials 16MnCr5 and 18CrNiMo7‑6 to investigate the influence of the material on the results of the micropitting test. Additionally, the influence of test gears designed under consideration of practical applications on the test results was comprehensively examined. For this purpose, the micro-geometry (flank modifications), macro-geometry (helical gears) and grinding method (profile grinding) were altered. The results show that the results of the micropitting test according to FVA 54/7 with standard test gears made of 16MnCr5 can be applied to gears with the material, micro- and macro-geometry as well as grinding methods used commonly in practical applications. This paper presents and summarizes the results of these experimental investigations.