Page 102 - Gear Technology Solutions

measurement results of the ground ring gear. The center graphic in Figure 10
shows the alteration which occurred after a 300-mile break-in. The surface
roughness value Ra dropped to about 50% of the original roughness. Also, the
value Rz dropped below 70% of the value after grinding.

Figure 10: Surface roughness of: ground, broken-in and super-finished flanks

The bottom graphic in Figure 10 shows the surface-finish after super finishing
the freshly ground ring gear. The roughness value Ra dropped to 12% of the
ground pinion surface. Also, the value Rz reduced significantly to only 15% of
the original number.

The roughness characteristic as it is created by the break-in process has ad-
vantages for the buildup of a stable oil film with a high load carrying properties
versus the super finished gearset. It can be noticed, comparing the center and
the bottom graphic in

Figure 8 that the oil pockets provided by the roughness valleys have complete-
ly disappeared during the super finishing treatment. Single flank tests with slow
RPM and high RPM microphone recordings also proved that the operating
noise at the most critical low load conditions is lower for conventionally broken-
in gearsets compared to the super finished version.

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