Mass Quality Issues and Solutions in Gear Quenching and Cooling
Quenching and cooling are important steps during gear manufacturing, and they are also the critical stages which will effect the gear quality. In this process, various problems may arise, such as surface crack, personalization and distortion, machining allowance inability. To ensure the gear can meet the required requirements and working conditions, solutions to alleviate or eliminate these issues should be taken.
First of all, Gear quenching and cooling may result in surface crack because of different thermal expansion-contraction rates of gear’s material, often it is indicated by bushfire on gear’s tooth surface or flank, which is determined by alloy material and quenching-cooling media. To solve this problem, under the condition that no effective special heat treatment is available, the gear material should be selected as high-strength aluminum alloy and numerical control heat treatment equipment should be used. Moreover, coolant with low viscosity should be chosen in order to achieve fast cooling rate.
Secondly, it is also possible that gears undergo geometrical distortion in the quenching and cooling process. Usually, reasons causing this problem are unreasonable heat treatment parameters and poor equipment performance. To reduce thermal distortion and increase machining allowance rate, metal components must be heated evenly, and heat treatment temperature should be controllable. Those components under relatively large pressure in operation need to be heated at a lower temperature than that at which metal components are hardened, so that their stress potential is smaller. In addition, small steel parts need to be quenched in a special container to ensure even heating, and the container must be heated from a low temperature to avoid distortion of metal parts.
Finally, heat treatment also affects the machining allowance of the gear, which will affect the gear’s modulus and precision. Many factors can lead to machining allowance inability, such as processing gap between two or more parts that are in contact with each other. To reduce air gap and improve the machining allowance rate, when dealing with the gear’s tiny clearance, isotropic processing is required, especially for the complicated gear profile.
To sum up, good performance of gear relies on proper quenching and cooling process, which is not only related to heat treatment parameter but also related to equipment. By adopting higher-level technology and preserving suitable atmosphere and uniform speed during the process, the occurrences of problems mentioned above can be avoided. Quality attention should be paid at the same time to ensure the integrity and accuracy of the gear’s processing.
