Derivation of Plastic Work Rate for Equal Area Yield Criterion and Its Application in Rolling

 Abstract: On the π-plane in Haigh Westergaard stress space the projection area of dodecagon intersected with Mises circle equals that of Mises, the dodecagon is called the equal area linear yield locus, and its equation is called equal area linear yield criterion or EA criterion for short. The criterion and its plastic work rate done per unit volume were first derived. Then, a generalized worked example of plate rolling was analyzed by the criterion and its corresponding plastic work rate. Finally, the precision of the solution was compared with measured roll separation force in plate finish rolling .It turns that the calculated results by EA criterion are little higher than those of measured and in good agreement with those by Avitzur’s.     

Optimization of Temperature and Force Adaptation Algorithm in Hot Strip Mill

Abstract： In the hot strip rolling control system, the temperature distribution and deformation resistance are the main parameters affecting prediction of rolling force. In order to improve the model prediction precision, an optimiza- tion algorithm based on objective function was put forward, in which the penalty function index was adopted. During the adaptation process, the temperature distribution and deformation resistance were taken as the optimized parame ters, and the Nelder-Mead simplex algorithm was used to search the optimal solution of the objective function. Fur thermore, the temperature adaptation and force adaptation were solved simultaneously. Application results show that the method can improve the accuracy of the rolling force model obviously, and it can meet the demand of the indus trial production and has a good application prospect.     

Simplified Weighted Velocity Field for Prediction of Hot Strip Rolling Force by Taking into Account Flattening of Rolls

The weighted velocity field was simplified for analysis of hot strip rolling. Using the field and GM （geometric midline） yield criterion, the deformation power, friction power and shear power were obtained respectively. Summing the partial power contributions, the total deformation power for strip rolling was presented. Then, by minimizing the power function, the rolling force was obtained; meanwhile, considering the effect of roll elastic flattening, iterative calculation of the roll radius was carried out until the radius was convergent. On line data were corn pared with the calculated results to verify the model accuracy. It was indicated that the calculated rolling forces were basically in agreement with the measured ones since the maximum error was less than 10.0%. Moreover, the effects of various rolling conditions such as thickness reduction, friction factor and shape factor, upon separating force, location of neutral angle, and stress state coefficient were discussed systematically.     

热连轧过程中的轧制力模拟

 对目前用于带钢热连轧过程分析中的几种屈服应力模型进行了对比,并在此基础上改进了模型：用Orowan公式计算轧制过程中轧件的应力-应变,用有限差分法计算轧件的温度变化,建立了热连轧生产过程中温度变化和塑性变形计算相耦合的力能参数预报模型。用此模型对某钢厂热轧板带生产过程中力能参数的变化进行了解析计算。计算结果表明,模拟值与现场实测值吻合较好。     

Two-Dimensional Transient Temperature Field of Finish Rolling Section in Hot Tandem Rolling

Comprehensively considering the factors such as descaling cooling, air cooling, watercooling, frictional heat and deformation heat in gap of every stand, heat conduction betweenwork roll and strip etc, a model of two-dimensional transient temperature field of finish rollingsection in hot tandem rolling was built with finite difference method to calculate the temperaturefields of strip and work roll. So two-dimensional accurate analysis and calculation of strip tem-perature were realized, and the theoretical basis for predicting and controlling strip temperaturewas provided. The simulated results show that the model is practical and reliable.     

Derivation of Plastic Specific Work Rate for Equal Area Yield Criterion and Its Application to Rolling

On the basis of the analysis of the hexagons inscribed and circumscribed of the Mises yield circle on the π-plane in Haigh Westergaard stress space,a new equation called equal area linear yield criterion or EA criterion was proposed,and its plastic specific work rate was derived.Then,a generalized worked example of plate rolling was analyzed by the criterion and its corresponding plastic specific work rate.Finally,the precision of the solution was compared with measured roll separation force in plate finish rolling process.It indicates that the calculated results by EA criterion are slightly higher than the measured ones.     

热连轧精轧过程中带材瞬态温度场的精确计算

基于热传导方程,考虑热连轧精轧区板带周期性地连续变形和连续冷却等复杂动态边界条件,利用有限差分法,在各机架变形区利用坐标映射关系建立三维瞬态温度场模型,在机架间非轧制区利用某横截面计算瞬态温度分布,这两种温度场模型互为条件,迭代求解。仿真结果表明,带材两侧边部有较大温差,易形成较大的局部热应力;带材越厚,压下量越大,带材高向温差越大,将会影响热连轧带材内部组织演变过程。仿真结果与实测数据吻合较好,表明模型能够精确预报热连轧精轧区板带的瞬态温度分布及终轧温度。     

Three-Dimensional Analysis of Rolling by Twin Shear Stress Yield Criterion

Using the twin shear stress yield criterion, the surface integral of the co-line vectors, and the integration depending on upper limit, Kobayashi＇s three-dimensional velocity field of rolling was analyzed and an analytical expression of rolling torque and single force was obtained. Through redoing the same experiment of rolling pure lead as Sims, the calculated results by the above expression were compared with those of Kobayashi and Sims formulae. The results show that the twin shear stress yield criterion is available for rolling analysis and the calculated results by the new formula are a little higher than those by Kobayashi and Sims ones if the reduction ratio is less than 30%.     

铝热连轧乳液的润滑特点及其实现

从润滑角度论述了轧制润滑机制，并据以研究。确定了热连轧乳液中乳粒尺寸、粘度和润滑成分的水平：乳粒尺寸在4～7μm之间，粘度在50～70mm^2／s之间，润滑成分需从高确定。表面质量良好。     

热连轧过程中温度场的模拟

考虑不同阶段各种因素对轧件温度的影响,采用有限差分法计算温度场,建立了带钢连轧生产过程轧件温度变化预报模型.其中,轧件应力应变采用Orowan公式计算,并引入迭代程序考虑轧件变形与温度变化间的相互影响.用此模型对某钢厂热轧板带生产过程中的温度场变化进行了解析计算,其预报值与实测值吻合较好.     

热连轧轧制减宽量对成材率的影响及改进

理论分析了轧制减宽量对带钢头尾部非稳定区长度的影响,通过合理的板坯设计和工艺优化减少减宽量,降低飞剪切头尾量,从而有效地提高了热连轧成品成材率。