Optimization On Quenching Process Of Large Backup Rolls Based On Taguchi Method

Backup roll is one of the most important parts of blooming mill. Quenching process is the key technology to adjust the inner organization, residual stress and improve the life-cycle of the backup roll. Therefore, it is of great significance to do some research on quenching process and develop proper experimental designs and statistical methods of backup roll.First of all, Cr5 forged backup roll was taken as a investigated subject in this paper, a three dimensional mutual coupling calculation model on temperature, microstructure and stress of Cr5 forged backup rolls during the quenching process was built by the use of finite element numerical simulation technology. After that, hexahedral meshes for large Cr5 forged backup roll were generated by the finite element software HYPERMESH, then the finite element software DEFORM was utilized to simulate its spray quenching process. The distribution rules of temperature, microstructure and stress field can be obtained after the simulation.Then, According to shortcomings such as the lack of hardened layer depth, the excessive temperature gradient on middle section of backup roll and the higher residual stress from the simulation results, the quenching process of Cr5 forged backup was optimized by using Taguchi method. During the process, the temperature difference between surface and center after quenching, the depth of hardening layer and the residual axial stress were selected as quality index. Then quenching temperature, cooling method, cooling time and temperature of quenchant were chosen as control factors, and transfer time, environment temperature, deviation of quenching temperature measurement were chosen as noise factors. through the analysis of variance, the significant factors influencing the target was found in this paper, and the influence factors were classified into four types. Through the analysis above, the most optimum processing parameters during quenching process are obtained.Next, temperature, microstructure and stress of Cr5 forged backup rolls were compared before and after the optimization process. The results showed that the optimization process could effectively improve the hardened layer depth, while reducing the residual stress and temperature gradient. The physical simulation experiment was carried out on the optimization results, which verified the accuracy and effectiveness of the Taguchi method and numerical simulation results.This paper also simulated the tempering process, and analyzed the internal stress distribution and evolution.The research achievement of the paper has a certain guiding significance on developing and improving quenching process of backup roll.