Studies on Improvement of Surface Durability of Case-Carburized Steel Gear - Effects of Surface Finish Processes upon Oil Film Formation


It is very difficult to precisely finish a gear tooth surface to the extent of a few sub-micron with grinding. Even if possible, the grinding time of the tooth surface will be very long and a grinding burn may often occur. The authors have adopted a barreling process as a final finish process in order to improve the ground and/or shot peened surface. Though the barrelling process is economical from the viewpoint of the manufacturing process, there was a very important question whether or not the process is applicable to gears with complex configurations. The authors have found that the barrelling process is very effective for the improvement of gear tooth surface roughness without changes in tooth profiles and tooth traces, which may have small tooth tip relief and/or crowning. In the present research, the surface durability of the high quality gear manufactured by a proposed new method was also investigated using a gear testing machine, which can measure the condition of oil film formation between a pair of gears during running. As the results of durability test, it was confirmed that the configuration of tooth surface of the barrelled gear scarcely changed after running, but that of the shot peened gear remarkably changed. The condition of the oil film formation in a running test conducted using barrelled gears was very good even during start-up. Also, the duration of oil film formation in the case of the barrelled gear was superior to the one in the case of the ground or shot peened ones, because of the difference of metallic contact condition.
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