Carburized gears have higher strengths and longer lives compared with induction-hardened or quench-tempered gears. But in big module gears, carburizing heat-treatment becomes time-consuming and expensive and sometimes cannot achieve good hardness due to the big mass-effect. Also, it is not easy to reduce distortion of gears during heat treatment. In order to achieve good surface hardness of the carburized layer, it is necessary to precisely control the carbon content distribution. The carburizing time is much longer for big module gears due to deeper case-depth requirements. So, after carburizing, it is necessary to have intermediate cooling to less than 6500C to get finer grain size and better mechanical properties. By using a carburizing furnace equipped with a fast cooling function, workpieces can proceed through intermediate cooling and heat up again to quench temperature inside the same furnace. This can remarkably reduce the total heat-treatment time, as well as costs. The distortion that comes from heat treatment is unavoidable. But, by improving the arrangement of a load of parts, we can reduce distortion and thereby reduce manufacturing costs.
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