Study On Rolling Characteristic And Flatness Control Characteristic Of4-high Two-Stand Reversible Cold Rolling Mill

Based on the project of "Research on Flatness Control and Simulating Software Development of the Two Stand Reversible Cold Rolling Mill" in cold rolling plant of Jinan Iron&Steel Corporation, aimed at reducing the strip break rate and improving the strip flatness, the theory and mathematical model of the strip shape control system, the roll contour optimization and the rolling characteristic of the two stand reversible cold rolling mill were researched systematically. The main works are shown as follows:(1) In order to analyze the influence on the rolling characteristic of the rolling parameter variation and the rationality of the thickness and inter-stand tension control method in field application, the analysis model of steady state characteristic of the two-stand cold rolling mill was established. The main factors including rolling speed, roll gap, initial slab thickness, friction coefficient and deformation resistance influencing the strip thickness and the inter-stand tension with or without inter-stand tension control were researched. And then the thickness and the inter-stand tension control method were analyzed, the entry stand gap could be used for the strip thickness control, the exit stand gap and the speed of both the entry and exit stand could be used for inter-stand tension control, the control strategy was coincide with the one in filed application.(2) In order to analyze the transient process after parameter variation, the analysis model of dynamic characteristic of the two-stand cold rolling mill was established. The transient process of inter-stand tension and the strip thickness of parameter fluctuation, mill startup and mill acceleration process were analyzed with this model. The transient process of the inter-stand tension and the strip thickness with a step change of the parameter were in a step-like mode. The inter-stand tension fluctuation caused by the thickness thinning region in tension buildup process would cause a impact force to the strip, which was the main reason of the strip break in mill startup process. The startup mode was modified to reduce the thickness thinning and strip break in this stage was basically solved. According to the thickness thinning in the acceleration process, a compensation strategy of gap regulation for friction coefficient and oil film thickness of backup roll was established. The result showed that the compensation method could either reduce the thickness thinning or the inter-stand tension decreasing, which was a feasible and effective compensation strategy.(3) According to the special layout of the two-stand reversible cold rolling mill, the roll system stability was analyzed. The judging criterion of CVC work roll contact was modified, and the roll elastic deformation model of the4-high CVC mill was established with the influence function method considering the specific tension distribution and the work roll flattening. The result of the roll stability research showed a work roll offset to the inter-stand direction was more stable than that to the coil or uncoil. For the4-high CVC mill, the influence of the work roll shifting and bending force on the work roll deflection, the backup roll deflection, the inter-roll flattening and the flattening between work roll and strip were studied. The influence of CVC roll profile and the specific rolling force on strip crown were analyzed.(4) The roll thermal deformation and the roll wear of the4-high CVC cold rolling mill were analyzed. The contact arc was divided by equal division of the bite angle. The roll force and friction force in deformation area were calculated with the mix-fiction model. The heat transfer coefficients between roll and other mediums were calculated with empirical formula. The speed difference between each element and work roll was calculated by the mass flow rule. Then the roll temperature field and thermal crown calculating model were established with finite element method. The roll wear model was established considering the inter-roll force distribution and rolled length. The results of the roll temperature distribution and roll wear distribution both math well with actual data, which verified that the theory model is reliable.(5) Considering the rolls elastic deformation model, heat deformation model of work roll and rolls wear model, the shape preset model of the4-high CVC mill was established by the two-dimensional simplex search method. The field application showed that the flatness standard deviations of the two experimental strips decreased by0.44IU and1.58IU respectively when using the newly established shape preset model, and the distribution of which were more stable. It was to say that the shape control precision and the shape control stability were all improved with this model.(6) Based on a deep investigation of the CVC mill, the optimum design method of the CVC work roll and the corollary backup roll profile were studied. The axial force minimum method for calculating the first order coefficient of the CVC roll curve was improved considering the rolling schedule, and a new design method considering the roll gap effective area was established. A backup roll chamfer designing method was established for the purpose of even inter-roll force distribution, maximum oriental stiffness of roll gap and minimum axial force between work roll and backup roll. The field application showed that the newly designed backup roll chamfer made the unevenness of backup roll wear changed from1.5580to1.2179, that was to say the backup roll wear extent was more even.