1. Correction of gear distortion
After carburizing and quenching, generally speaking, the increase of internal and external diameter is related to the size of gear, the depth of carburizing layer and the ratio of internal and external diameter. The larger the gear is, the deeper the carburizing layer is, and the greater the increase of internal and external diameter is. Master the distortion law of each specification gear, and reserve the margin for expansion. But for bevel gears with large inner diameter, sometimes the inner and outer diameters shrink or increase or shrink very little. It is necessary to do detailed measurement work in production, and find out the distortion law of various gears, so as to reserve allowance correctly, so as to avoid scrapping due to the increase of internal and external diameters, which cannot be ground or corrected.
If the increase of inner and outer diameter exceeds the allowance and the grinding amount of inner hole becomes negative, the method of high-frequency induction heating or acetylene flame heating can be used to use the principle of thermal expansion and cold contraction, and the effect of inner diameter reduction is very good. The method is to heat the gear with tempering temperature, operate it quickly after being out of the furnace, heat the inner diameter to the temperature below the phase change point quickly, and air cool it to room temperature. For heating correction, due to large stress, the stress relief treatment with temperature no higher than tempering temperature shall be carried out in time. It is worth noting that if we use high frequency induction heating or acetylene flame to shrink the inner diameter without heating, not only the effect is poor, but also it is easy to crack. If the warpage of the large bevel gear cannot be corrected, a metal weight can be added to the plane concave of the bevel gear. The size of the weight depends on the warpage. Place the bevel gear on the special tooling, reheat and quench it, and the warped plane can be restored to the allowable distortion range.
2. Correction of tooth axis distortion
In the past, the distortion of the gear shaft was often corrected by press. This method can easily break the gear shaft or form micro cracks on the surface, which is difficult to see by naked eyes, which brings the hidden danger of fracture. Based on the principle of hot expansion and cold contraction, the effect of using hot spot to correct the bending of gear shaft is very good, and there is no danger of pressure breaking and using fracture. The method is simple and easy to use, and does not need press and other equipment. The method is to find out the bending high point, heat it to the temperature below the phase change point with acetylene flame, air cool it to room temperature, check the abnormal variables, if it is still out of tolerance, heat it again until it is qualified. Generally, 1-2 times can be corrected to be qualified. After heating correction, stress relief treatment with temperature no higher than tempering temperature shall be carried out in time.
After several years of production practice, the distortion law of carburizing and quenching of various specifications of gear and gear shaft of reducer has been preliminarily mastered, and some measures and correction experience for distortion control have been accumulated. However, due to the complex factors affecting the distortion of gear and gear shaft, and the limitations of equipment and tooling capacity, there are still many distortion problems that have not been solved. We will continue to work hard to further explore and study the distortion law, and strive to control the distortion within the minimum range.
