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Electric Automation Control Sytem of Mulit Rolls Straightening Machine
1. Technical advantages of stretch & bending straightening machine
The fundamental characteristic of stretch bending straightening is that the plastic extension of the strip can be produced when the tensile stress level is far below the yield limit of the material. In the bending straightening roller under the action of a small strip is in plastic state, while the rest of the tension between the rolls only generate elastic deformation, even in the strip plastic deformation area, is only a small part of the strip section of the plastic deformation in the state, it is not easy to break with defects at the edge of the strip. So the tension leveling method is especially suitable for thin strip, the strip does not need to be compared to the previous trimming, while its elongation is small (0.02%-0.2%) therefore required straightening tension than the tension levelling simple straight when smaller, so the tension roll assembly need smaller torque output, so as to ensure the the shape and physical properties of strip plate material.
FIG 1：Straightening layout
Elongation control of the main role is to compare the rate of strip detect actual elongation value and given, when the feedback extension rate is greater than a given elongation, the torque reduced s 4 tension roller straightening and reduce tension; when the detection value is less than the given torque increases S4 tension roll increase tension straightening thus, to achieve constant elongation control. Due to the small elongation of the unit (0.02%-0.2%), the torque adjustment is very small when the quantity of bending and straightening is certain.
The elongation control mainly consists of two links, one is the extension rate comparison and the other part is the extension rate regulation link. The role of the comparison link is to compare the difference between the actual extension rate and the set extension rate. When the absolute value of the difference is greater than or less than the dead zone of the error, the elongation control of the system can automatically enable or maintain.
Elongation is the percentage of the stretching length and the original length of the material
(3-1)
The main factors affecting the elongation of the strip are the curvature of the strip and the straightening tension when the stretch bending is straightened. The bending curvature is determined by the roll diameter of multiple bending rollers and the multi roll straightening rolls, and the penetration depth of the work rolls is regulated by the lower roller seat lifting and the oil cylinder adjustment. On the premise of the determination of the working roll diameter, the main factors of the stretch bending and straightening process of metal strip are determined by the straightening tension and the penetration depth of the straightening roller.
The basic principle of elongation control shows that only in real-time and accurate detection of elongation of strip in stretch bending straightening section, can accurate control of strip elongation be achieved. Although the formula (3-1) gives a simple and direct extension rate calculation method, but it is only suitable for the average extension calculation of a strip rate, not suitable for real-time calculation of elongation, so in the application of the general use of stretch bending straightening machine and the entrance exit strip line speed to indirectly get strip extension rate.
（3-2）
（3-3）
The straightening entrance and exit strip line speed can be obtained in elongation, bending and straightening unit, we use the S4 motor installed in the tension roller and a tension roller S5 motor encoder to detect the motor speed and then calculate the straightening entrance and exit line speed, and the elongation rate.
At present, the elongation control methods of tension leveller mainly include two kinds of direct control method and indirect control method. The extension rate of the unit is indirectly controlled by adjusting the cutting depth of the bending unit and straightening unit and adjusting the straightening tension to achieve elongation control.
FIG 2：Block diagram of elongation control system
6. Straightening tension control
Stretch bending straightening machine straightening section of tension is mainly composed of entrance tension roller group 3# (S1.1, S1.2, S1.3, S1.4) and group 6# export tension roller (S2.1, S2.2, S2.3, S2.4) of the 8 tension roller is generated, the entrance tension roller group 3# total output torque is directly determined by the direct tension, the main export tension roll set 6# is generated and the corresponding 3# tension roller group tension, tension and the opposite direction to that of 3#, while the 6# tension roll assembly running speed control line.
FIG 3： 3# Inlet tension rolls
7. Uncoiling and coiling tension control
Uncoiler and coiler adopts the control mode of the speed control force moment limiter, in order to ensure the speed and coil diameter change process in addition, coiling tension constant, the system through the accurate calculation of strip coil diameter, the uncoiler and Coiler of no-load torque and dynamic torque compensation. constant tension for the control of the entire process, thus ensuring a stable tension straightening section.
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