Strip Shape Control And Optimal Design Of Roll Shape For HSM

High-quality automatic shape control is a goal which the hot rolling producers continusly pursues since long ago. Based on the international cooperation project of Kerea POSCO and RAL, Northeastern University,-"Development of CVC Roll Model and Thermal Crown Model for Hot Strip Mill", the project of BenSteel and RAL-"Research on improving strip shape control precision for BenSteel 1700mm HSM(Hot Strip Mill)", the project of GangLu and RAL-"Development of strip shape control system for GangLu 1250mm HSM", the basic theory and technology of strip shape control, optimization design and optimal allocation of roll shpe for HSM were researched by the numbers. The main works were shown as following:(1) The strip shape set up system for HSM was established. The control strategy of strip shape for HSM was analyzed at length. The strip entry crown was calculated to obtain strip target crown and keep strip shape well, the coordinating relationship of strip between the adjacent stand was considered.Calculation model of roll gap under load, roll shift location and roll bending force were built.The roll shift location and roll bending force were calculated. Deviation of strip crown and flatness of a rolling schedule was measured.(2) The mathematical models of roll system elastic deformation were set up with influence function method. The influence function of CVC roll bending force, roll elastic deformation, flattening between rolls and work roll flattening arised from the force were deduced. The equations of force balance, the relation between force and displacement and the deformation compatibility were obtained. The method to dispose of smoothed exponential and convergence index were bought forward, which solves effectively the calculation precision and the convergence problem of roll system elastic deformation.(3) The axial symmetry models of roll temperature field were built with FDM (Finite Difference Method). Roll surface temperature and roll expansion calculated by the models were good agreement with the measurements. The results show that models of roll temperature field and thermal crown have high accuracy. (4) The roll wear model was built with "slice method" and the roll shift location was considerd. Roll wear curves calculated by program were good agreement with the wear curves got by high-precision grinder. The results show that the roll wear model has high accuracy and should be applied in on-line prediction.(5) Take the minimal axial force as target function, the cubic CVC roll shape curve was designed and the range of roll shift location, roll equivalent crown, strip width and strip deviaton were considered. The comparison of optimization CVC roll shape, basic CVC roll shape and SmartCrown roll shape shows that the strip crown control requirement was satisfied and the minimal roll axial force could be got by optimization CVC roll shape.(6) Take the strip flatness in well and the uniform roll intermediate press as target, work roll shape was designed properly and the limit of roll bending force and strip crown at exit on each stand were considered. The application in production show that roll shape could satisfy different rolling schedule. The phenomenon of crack and flaking at end of backup roll occured for stress concentration was reduced and backup roll life was extended.