Flow stress equation in range of intermediate strain rates and high temperatures to predict roll force in four-pass continuous rod rolling
(1. Department of Mechanical Engineering, Dong-A University, Busan 604-714, Korea;
2. Department of Mechanical Engineering, Chung-Ang University, Seoul 156-756, Korea)
2. Department of Mechanical Engineering, Chung-Ang University, Seoul 156-756, Korea)
Abstract: A flow stress equation was proposed to compute the roll force in the finishing stands of an actual rod mill where the strain rate and the temperature of the material range from 100 to 400 s-1 and from 900 to 1050 °C, respectively. The underlying idea is to modify the Shida model and Misaka model, which provide flow stress equations (constitutive equations) frequently used to depict deformation behavior of high temperature material at different strain rates. The modified model was coupled with finite element method to compute the roll force during four-pass continuous rod rolling, where strain rates are in the range of 100-400 s-1 at high temperatures (900-1050 °C). The roll forces and the surface temperatures of the material at each stand were measured, and the measured data were compared with the computed values. Results reveal that the Misaka model is better than the Shida model for high temperatures and intermediate strain rates. The roll force error was -5.7 % when the Misaka model was used at 900 °C. However, the error increased by -15.2% at 1050 °C. When the modified Misaka model was used, the error was reduced to 1.8% on average. It can consequently be deduced that the modified Misaka model can be used to depict the deformation resistance behavior in intermediate ranges of strain rate and high temperature ranges in continuous rod rolling process.
Key words: roll force; strain rate; deformation resistance; rod rolling; Shida model; Misaka model