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Automatic control of plate shape for cold rolling of plate and strip steel

Plate and strip steel products are indispensable raw materials for the automobile, construction, home appliance and other industries, and the plate shape automatic control system plays a vital role in the preparation process of plate and strip steel. The characteristics of modern plate and strip cold rolling technology are reflected in the fact that there are many physical quantities involved in the multi-variable rolling process, which change with time and space, and there is a strong coupling between these system variables, which is very important for the development and application of The plate shape automatic control system based on the above variables in the cold rolling production of plate and strip steel has put forward newer and higher requirements.



Automatic control, cold rolling, plate, strip steel


1. Automatic thickness optimization control system


The Automatic Gauge Control System (AGC system for short) is an important part of the automatic control system for cold rolling plates and strip steel. It is responsible for automatically controlling the thickness accuracy of the plate and strip steel, thereby making the thickness of the plate and strip steel The difference is in line with industrial standards while improving the yield of steel plates and strips. This article mainly introduces an improved automatic thickness optimization control system, which can not only solve the mutual coupling effect of multiple variables but also optimize the control of the plate and strip steel rolling mill system, thereby ensuring product quality and improving the production efficiency of the rolling mill. Taking a common plate and strip steel rolling mill system as an example, the entire rolling mill system consists of rolling mill equipment, automatic thickness control systems and thickness sensors. This control method can be combined with the rolling speed to obtain the optimal rolling speed. On the one hand, it ensures the product quality. Quality, on the other hand, can improve rolling mill efficiency.


1.1 Control mode of automatic thickness control system


(1) Tension control mode


In the tension control mode of the automatic thickness control system, the closed-loop control of the strip steel thickness is mainly carried out through the uncoiling tension. In this control mode, the tension output directly controls the drive module of the rolling mill, so that the armature current of the unwinding drive motor is adaptively adjusted. The actual tension of the metal coil is generally obtained through calculation or measurement, but in practice, it is also obtained through the armature current of the motor, which requires the armature current to be proportional to the absolute tension. This tension automatic thickness control mode can be used in the rolling process of medium-thickness and small-thickness plate and strip steel.


(2) Speed feedforward control mode


The main function of velocity feedforward is to minimize the disturbance of outlet thickness caused by velocity changes. This mode can be implemented by converting changes in speed into adjustments to the tension set value or pressure (roller gap) set value through a feedforward transformation gain. In practice, the change of the set value is achieved by subtracting the speed change from the set value, which can largely offset the impact of the speed change and achieve decoupling control. If the thickness is too thin, the speed can be reduced at the same time through control. If the thickness is too thick, the speed can be increased at the same time through control. In this case, the speed feedforward control mode will not be activated.


1.2 Optimization mode of automatic thickness control system


(1) Speed optimization control


The main principle of speed optimization control is that during the uncoiling process of the rolling mill, a certain method is used to cause the rolling speed to increase linearly in a short period of time until the thickness value drops below a preset value. During normal operation of the rolling mill, the system can be used to maintain the tension control within an allowable operating range. If the tension is greater than the upper limit of the operating range, the system can increase the speed through control, thereby making the tension smaller. If the tension is less than the lower limit of the operating range, the system can reduce the speed through control, thereby increasing the tension. In the tension control mode of the automatic thickness control system, the purpose of speed optimization is to make the uncoiler tension work at the minimum value of tension, which allows a sufficiently high speed while leaving sufficient tension in any direction for the control range.


(2)Pressure optimization control


The purpose of pressure optimization control is to optimize the load of the rolling mill so that the rolling mill operates at the maximum allowable rolling speed. Usually, the pressure of the rolling mill will stabilize the uncoiling tension at a value within its allowable range, so that the tension can maintain a sensitive and rapid response to thickness errors in both directions. The pressure optimization control system works together with the tension automatic thickness control system and speed optimization control. If the tension exceeds the upper limit of the required intermediate range value, the pressure is increased through the control system. If the rolling speed is smaller than the set value and the tension is less than The tension limit allows speed growth and the control system will reduce the pressure to allow maximum mill speed.


2. Automatic position control system


Automatic Position Control (APC) is another important component of the plate and strip steel rolling mill profile automation control system. The automatic position control system stores various rolling procedures in the system in advance, and during the actual operation process, it automatically or manually selects the rolling conditions according to the required plate and strip steel rolling conditions (such as steel type, ingot type, billet, etc.) The rolling process is based on the conditions and the rolling mill is automatically controlled according to this process. The control accuracy and stroke time are its main indicators. In order to meet the requirements of rolling mill production and better complete the automatic control of position, relevant personnel to calculate its control rules and design efficient and reliable programs. The software design of automatic position control is based on this goal. Its performance indicators mainly include two aspects, one is fast response time, and the other is high positioning accuracy, that is, small positioning error.

In the entire system, because the pressing position is driven by the motor, you can consider detecting it with the help of an auto-angle machine or encoder with coaxial transmission of the motor. The pressing position can be set manually on the operating table or automatically by the system. The principle of pressing position control is a three-loop control system with position-sensing feedback, in which the position regulator can be implemented through PLC programming. The control functions of the automatic position control system mainly include the following points.


(1) Inter-device communication function


Taking the TMEIC-GE transmission equipment as an example, the PLC and the transmission communicate through the TC-NET network. The PLC transmits the data to the transmission device through the TC-NET network and then controls the motor action. If communication is not used, analogue signals can be collected directly through the PLC, and data reception and transmission between the PLC and the transmission device can also be achieved.


(2) Press hard protection


In order to prevent the occurrence of “seat roller” and “top punch” failures, a limit switch can be set at the upper limit and lower limit position of the roll. If the limit switch action is detected, the power supply of the DC transmission device should be disconnected. The automatic position control system will reset the speed given the signal to the transmission device to zero and display the type of fault on the HMI screen, thereby preventing “seating”. The occurrence of “roller” and “top punch” failures.


3. Automatic tension control system


In the cold rolling process of plate and strip steel, tension is an important process parameter. Fluctuations in the tension value caused by any factor will not only destroy the balance of the stand but also destroy the balance of the rolling mill system through the downstream and countercurrent flow of plate and strip steel. Therefore, keeping the tension between the cold rolling mill stands constant is of great significance for improving the thickness and shape accuracy of the product.

In order to ensure the stability of the tension between the stands and the quality of the produced plate shape in the three different working cycles of low speed, coiling and rolling mill adjustment, the automatic tension control system can usually be divided into two working modes according to different situations: Speed ATC control mode (low-speed ATC) and depress ATC control mode (high-speed ATC). The control of tension between racks is mainly used to keep the tension within a fixed range close to the given value, thereby avoiding the occurrence of belt breakage to a large extent.

In practice, a tensiometer is installed between each frame to provide tension feedback. Changes in speed and roll gap position between the two frames will directly affect the tension between the frames. Decreasing the speed of the upstream frame or increasing the position of the roller gap of the downstream frame will increase the frame tension. On the contrary, increasing the speed of the upstream frame or decreasing the position of the roller gap of the downstream frame will reduce the tension of the frame.

The application of the pattern automation control system in the cold rolling production of plate and strip steel has solved some difficult problems in the production process and can achieve higher control accuracy and control effects, thereby saving energy, reducing consumption, and improving production efficiency.

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