Study And Application Of High Accuracy Gauge Control Strategy For Tandem Cold Rolling

The thickness accuracy is one of the main dimensional accuracy of tandem cold rolling strip, and the automatic gauge control is always considered as essential component of tandem cold rolling production. Based on a building project of 1450mm five-stand tandem cold mill of a certain cold rolled sheet plant, model setup system, hydraulic actuator control system, inter stand tension control system and automatic gauge control system were researched. Then a comprehensive gauge control strategy for tandem cold rolling was established and applied in practical production, which had good performance. The main research contents are as follows:(1)By evaluating the characteristics of tandem cold rolling techonology, the appropriate mathematical models for on-line rolling process control were developed. The simple finite unit method was adopted in rolling parameters calculate process, in order to not only guarantee the model setup precision but also solve difficult soluation of traditional method. A new mill spring model of tandem cold mill was adopted in order to improve precision of gap preset values. Taking all these important factors of tandem cold rolling process into consideration, a multi-object optimization method based on cost function was developed.(2)The hydraulic actuator control system and inter stand tension control system were researched. The position control mode, roll force control mode and individual control mode of screw down system were analyzed. The control strategies of hydraulic roll bending system and hydraulic roll shifting system were analyzed. Aiming at servo nonlinear and servo zero offset, corresponding compensation strategies were developed. A inter stand tension control strategy based on dynamic tension thresholds was presented, and the further research on conventional tension control loop and limiting tension control loop was carried out.(3)Taking the mill’s sensor configuration into account, an automatic gauge control system of five-stand tandem cold rolling was designed and developed. The most of large thickness deviation was eliminated by forepart stands, through setting many kinds of AGC at stand 1 and stand2. Several kinds of AGC control strategy were adopted at final stand, in order to satisfy the requirement of finished product thickness accuracy in different rolling strategies. A final stand roll force compensation control was developed not only to optimizing the control mode of gauge and tension but also to guaranteeing final stand roll force control accuracy. In order to avoid a certain stand overload occur, a dynamic load balance control was developed. A speed correction control was carried out to ensure that the stand speed adjustment process of AGC was performed efficiently and reasonably.(4)To the sake of improving the performance of monitoring AGC system, improved Smith prediction compensation control and feedback-assisted iterative learning control were introduced into monitoring AGC system. The theoretical model of inner loop of monitoring AGC system was established. Aiming at the low response speed and bad adjusting accuracy of conventional Smith prediction monitoring AGC system caused by unicity of controller, an improved control strategy of Smith predictor was developed. On the basis of above strategy, an improved Smith prediction monitoring AGC system based on feedback-assisted iterative learning control was designed, and the defect that the Smith prediction monitoring AGC system performance relied on the model accuracy was overcame. The simulation researches of these three monitoring AGC systems were carried out.(5)By using actual curves, the control results of screw down system and inter stand tension control system were analyzed, moreover, thickness control results of typical thickness specifications and thinnest tinplating coil were analyzed. A convincible evaluation for this gauge control strategy was made.The results of this study are practical for thickness control of tandem cold rolling process. The gauge control strategy has been applied successfully in five-stand tandem cold mill of a certain cold rolled sheet plant. It is significant for developing the tandem cold rolling gauge control system with independent intellectual property rights in China.