Rougher Tooth Surfaces Give Longer Gear life?

摘要

T.C. Jao and his co-authors reach the startling conclusion that gears with rough tooth surfaces have longer macropitting life. How can this be when all other research seems to show smoother surfaces give longer life? As it turns out, the devil is in the details. They tested FZG PT-C macropitting gears and FZG GF-C micropitting gears, which are the same in all respects except PT-C gears have a tooth surface roughness of R{sub}a = 0.3μm, whereas GF-C gears have a tooth surface roughness of R{sub}a = 0.5μm. PT-C and GF-C gears are peculiar because they have no profile modification, such as tip or root relief. Consequently, under the high loads used in FZG tests, the tips of the gear collide with the flanks of the pinion. The collision creates a severe dent at the start of active profile (SAP) on the pinion. It is this dent, together with the difference in tooth surface roughness, that causes the difference in macropitting life between the PT-C and GF-C gears.