The external dimension and microstructure of precision gear can be stabilized by low temperature treatment of industrial freezer. In order to control the noise of gear loading and transmission, the mesh cloth size is required to be stable, because the change of gear size affects the center distance of gear unit.
It has been found that when the content of retained austenite is increased from 17% to 40%, the life of gear can be prolonged by 166%. However, with the increase of fatigue life, the deformation of gear increases, that is to say, the noise in transmission increases.
The mechanism to improve the gear performance is to shear the austenite physically. The martensite produced by this method is more fine in structure than that formed by the thermodynamic method of deep freezing at – 79 ℃. The new structure design and system transformation are all based on the available life of materials, and the new alloy is used.
Precision gear materials are treated at – 79 ℃ and the effective microstructure is usually obtained by carburizing. In the field of materials, low temperature treatment has been successfully applied in different degrees. The technical requirements for the low temperature treatment of carburized parts are included in the technical conditions for the production of precision gears. The treatment can improve the dimensional stability, reduce the content of retained austenite to the minimum, and improve the surface hardness and wear resistance. Therefore, the low temperature treatment can be used to improve the performance of the gear.
In fact, deep handling below – 79 ℃ does not increase the processing process of parts, because the manufacturing process has included the process of freezing at – 79 ℃.
If the main purpose is to reduce the residual content, the treatment at – 79 ℃ is enough, but if the treatment at – 120 ℃ or lower can produce excellent performance, then it is necessary to choose ultra-low temperature industrial freezer. The lowest temperature of LNEYA’s ultra-low temperature industrial freezer can reach 150 ℃.
Recent researches and successful manufacturing processes provide valuable information for gear material cryogenic treatment. After cryogenic treatment, the sliding wear resistance of low carbon steel and cast iron is increased by 10%. The results of low temperature treatment for alloy steel are better than that for ordinary carbon steel. When the content of martensite is more than 70%, the presence of 10% – 15% residual in the microstructure is helpful to reduce the formation of cracks. The lower content of retained austenite can be transformed into martensite with good lattice structure after work hardening, which tends to hinder the formation of cracks on the surface. In addition, in some cases, the surface of carburized gear can obtain up to 25% of the retained austenite, which will help to expand its application range.
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