A Short Procedure to Evaluate Micropitting Using the New AGMA Designed Gears


A Short Procedure to Evaluate Micropitting Using the New AGMA Designed Gears Dr. Kevin J. Buzdygon and Dr. Angeline B. Cardis, Exxon-Mobil Research and Engineering Company Encouraging results from a prototype micropitting test using specially designed gears (20:30 tooth ratio, tip relief, and a 560 mm radius pinion crown) on the standard FZG test rig were reported at the 1998 AGMA Fall Technical Meeting. Subsequently, the authors’ company purchased several sets of these experimental AGMA test gears and attempted to develop a new test procedure to evaluate micropitting as an alternative to FVA Procedure 54. The new relatively short test procedure involves running the test gears on the standard FZG test rig with oil circulation for 168 hours at load stage 10 and 1500 rpm. The 5-gallon reservoir of test oil is kept at 60 C throughout the test. The oil is cleaned by an in-line filter (200 =6 m) before it is injected into the gear mesh at 2 liters/minute. At the end of test, the gears are rated for micropitting, weight loss, pitting, and scuffing. The most common damage mode was micropitting, with only occasional occurrences of pitting and no occurrences of scuffing. Other modes of failure such as gear tooth bending did not occur at these conditions. The involute profile deviation of the gear teeth was not measured. Five commercially available ISO VG 320 gear oils, with performance in the FVA Procedure 54 micropitting test ranging from FLS 9-low to FLS >10-High, were evaluated using this procedure. The degree of micropitting coverage ranged from 34% to 7% in the new test procedure. Micropitting generally originated in the middle of the gear tooth, instead of the root or tip. Overall, there was excellent correlation of the degree of micropitting damage between the new test procedure and FVA Procedure 54.
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