Masatoshi Yoshizaki

Effect of Abnormal Surface Layer on Tooth Surface Strength Increase of Gas Carburized Gears

Gas carburizing has been widely applied to power transmission gears in mass production. Gas carburized gears have so called abnormal surface layers on their surfaces that are generated during the carburizing process. Although the influence of the abnormal surface layer on the bending strength of the gear tooth has already been reported (Lyu et al., 1994), that on the tooth surface strength has not been clarified. The authors have carried out experiments to study the influence of the layer on the tooth surface strength. As a result of the experiments, it was found that the layer on the tooth surface has an effect to increase the tooth surface strength and that the effect of the layer greatly depends on its characteristics. By examining the layer microscopically five characteristics were given, and their suitable conditions that increase the tooth surface strength were discussed. Furthermore, experiments were carried out to examine whether the tooth surface strength of Cr-Mo alloy steel (JIS SCM420H) can be increased by improving the characteristics of the abnormal surface layer. A trial material was prepared by modifying the chemical composition of the Cr-Mo alloy steel. From the experiments with the gears made of the modified Cr-Mo alloy steel, it is demonstrated that the tooth surface strength of the gas carburized gears can be increased by improving the characteristics of the layer. Presented at the 57th Annual Meeting Houston, Texas May 19–23, 2002

Influence of Oil Viscosity, Chemical Oil Structure, and Chemical Additives on Friction Loss of Spur Gears (Concerning the Influence of Synthetic Oil and Mineral Oil)

The friction loss of gears and its quantitative estimation are important problems because of their relevance to energy conservation and load-carrying capacity. Recent research results do not provide satisfactory estimates of friction loss of spur gears. Therefore, the authors carried out experiments to study the influences of lubricating oil viscosity and additives, as well as base oil type and load and rotational speed on friction loss of spur gears

Effect of Fine Particle Bombarding Process on Tooth Surface Properties and Tooth Surface Strength of Carburized Gears (2nd Report, Effect on Tooth Surface Strength and Influencing Factors)

Recently the application of fine particle bombarding process (denoted as FPB) has been getting wider because of its superior effects compared to conventional shot-peening ; however, the influence on the tooth surface strength of gears has not been clarified. The purpose of this study is to determine quantitatively the effect of FPB on the tooth surface strength of carburized gears and to clarify the factors influencing on the tooth surface strength. First, the author examined the tooth surface properties such as residual stress, roughness, hardness, surface texture, etc. using test gears processed by the FPB under three different conditions of arc height. A test gear performed by conventional impeller-type shot-peening was also used for comparison with the FPB. These results have been described in the 1st report. Next, durability tests were carried out using the gears to measure the tooth surface strength. The results showed that the FPB is effective to increase the tooth surface strength by 1.21 to 1.28 times in Hertzian stress compared to conventional impeller-type shot-peening. Then, the following factors caused by the FPB that influence on the tooth surface strength increase were discussed. (1) Produced high residual compressive stress, (2) Increased hardness, (3) Good conformability on the tooth surface, (4) Micro hollows on the tooth surface generated during running. It was found that the latter two are unique factors caused by the FPB process. In the 2nd report, the effect of the FPB on the tooth surface strength is described.