New Test Methods for the Evaluation of Wear, Scuffing and Pitting Capacity of Gear Lubricants


For maximum energy savings low viscosity lubricants are frequently used. Increasing transmitted power leads to higher temperatures and thus thinner lubricating films. These tendencies increase the failure probability in gear contacts with respect to wear, scuffing, micropitting and pitting performance. New test methods on modified FZG gear test rigs were developed to evaluate the load carrying capability of gear lubricants. For the low speed regime a wear test using C-type gears at low pitch line velocity of 0.05 m/s, and two different temperatures of 90 and 120 5C to consider different additive response at high loading of load stage 12 (C/0.05/90:120/12) was developed and applied to many different lubricants. New scuffing procedures for gear lubricants of scuffing performance between API GL 3 and GL 5 were developed. The step test A10/16.6R/90 uses A-type gears of 10 mm pinion face width at 16.6 m/s pitch line velocity with a driven pinion. A discrimination of all gear oils up to the level of API GL 4 is possible. A shock test S-A10/16.6R/90 with direct loading in the expected load stage discriminates between GL 4 and GL 5 lubricants. Different standard pitting tests are available for different lubricant viscosity grades using C-type gears at 8.3 m/s pitch line velocity and 90 5C in load stages 9 (PT C/9/90) or 10 (PT C/10/90). For automotive applications load spectrum testing is possible at low (PT C/LLS/90) and high (PT C/HLS/90) loads. For applications with long oil drain intervals a combined pitting and oil ageing test was developed (PITS C i85 TS) using C-type gears at variable load, speed and temperature conditions. At high temperature conditions between 120 and 150 5C the oil ageing properties together with their influence on pitting characteristics is evaluated in correlation to a reference oil. The test methods are described. Test results with different market products are discussed.
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