How to reduce gear distortion and cracking

How to reduce gear distortion and cracking

    The purpose of heat treatment is to improve the hardness and wear resistance of the gear, and thus increase the service life of the gear. However, improper quenching will also cause cracking and deformation of the customized product of the gear. So, how to reduce the quenching crack and deformation?

    First of all, the gear material should be properly selected and the tooth shape should be properly designed. For gears with complex shapes, it is better to use gear steel with higher hardenability so that it can be cooled in a slow cooling quenching medium to reduce internal stress. For gears with higher precision requirements, bottom deformed steel can be used and graded or austempered. When designing the gear, try to reduce the thickness of the section and avoid the sharp corners; make the transition as smooth as possible at the junction of the thick and thin gears. 

    For large gears, separate and inlay structures should be used to create conditions that can be mechanically modified after heat treatment.  Secondly, it is necessary to properly perform preliminary heat treatment and casting. The gear blank should be subjected to appropriate preliminary heat treatment, such as normalizing, annealing, quenching and tempering, etc. to obtain a satisfactory structure to meet the requirements of machining and heat treatment. When casting gear blanks, it is necessary to minimize casting defects, which are easily caused by cracking and deformation of the gear during quenching. And to use a reasonable heat treatment process. When heating, try to achieve uniform heating to reduce the thermal stress during heating; for large gears, preheating should be used. Choose the appropriate quenching temperature, and generally choose the lower limit temperature of quenching. Correct selection of quenching medium and cooling method, under the premise of meeting the performance requirements, should use a more moderate quenching medium, or use fractional quenching, austempering, etc.

    After the large gear is machined, there are many small areas on the gear that are not sufficiently hard. These areas are called cushions. The soft point is often the center of gear wear or fatigue cracking, which reduces the service life of the gear, so soft spots are not allowed on the finished product of the gear.