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Because gray cast iron has relatively high casting performance, is easy to cut, has good wear resistance and toughness, and is relatively low in cost, it is often used for open gears with low production speed and low load-carrying capacity. The grades of cast iron parts are different, and the heat preservation temperature required by the produced gears is also different. The speed of annealing and cooling is determined by the accuracy of the cast iron parts and the matrix structure. During annealing, the temperature is lower than that during heating. According to the performance of the gray cast iron gear, the processed gear needs to be quenched and heat-treated by a high-frequency induction heating machine to better improve its technical characteristics.
First of all, gray cast iron gears need to undergo preparatory heat treatment, that is, normalizing or annealing. For some gray cast iron gears with small thickness, especially those with less carbon and silicon, the purpose of normalizing them is to improve the strength and wear resistance of the gears. During the cooling process of the gray casting gear, because the cooling speed of each part is different, internal stress will be generated, and the internal stress will cause deformation and cracks in the gear during the cooling process, so in order to remove the residual stress of the gray casting, avoid Or to reduce the deformation of the gear, it will be annealed to stabilize the size of the gear. However, it should be noted that the speed must be slowed down during annealing and cooling to prevent secondary stress on the gear.
Then the finished gray cast iron gear undergoes final heat treatment, that is, overall quenching or surface quenching. During overall quenching, the temperature of the high-frequency induction heating machine should be around 870°C, and the quenching medium can be oil or water-soluble solution. The temperature during surface quenching should be around 900°C, which is slightly higher than that of overall quenching, and the quenching medium is generally cooled by water or the like. The purpose of both is to improve the strength, hardness, and anti-friction ability of gray cast iron gears.
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