[Abstract] This paper focuses on the development and application of the new 30000kN hot straightening machine from the French company VAI in the Jinan Iron and Steel Group's medium and heavy plate plant. It analyzes and explains the principle, system composition, system function, and equipment performance indicators of the straightening process. Specific descriptions are provided regarding the equipment's composition and process parameter settings. The paper mainly introduces the hydraulic HGC system, bending roll system, motor drive control system, and secondary model strategy analysis, offering valuable reference for the industry.
[Keywords] Hot straightening machine, hydraulic HGC, bending roll, two-stage model
Foreword
Given the severe oversupply and increasingly fierce market competition in the national medium and heavy plate industry, only by producing high-strength specialty plates and high-value-added specialty steels can companies better capture the market and achieve greater profits. The development and application of high-strength straightening machines are favorable conditions for adapting to the production situation of medium and heavy plate plants and increasing the production of specialty plates.
The principle of straightening is to stretch the product through reversible bending between rollers, with the aim of stretching the steel plate to make all fibers reach the same length. Its main functions are: ① To remove shape defects from the incoming steel plate. Shape defects such as edge waviness, center waviness, and quarter-warping can be removed by a straightening machine. ② To minimize residual stress within the steel plate in order to maintain its straightness.
1. Transmission control of the straightening machine
The hot straightener is controlled by two main motors (1# and 2#) to control 11 working rollers in groups. After the steel plate is bitten into the straightener, the main motor control system MASTER accelerates to the straightening speed of the steel plate. After straightening is completed, the deceleration control sends the steel plate out of the straightener.
When the tail of the steel plate is within the working rolls of the first control group, the torque limit of motor #1 decreases according to the position of the tail within the first group of rolls to prevent excessive torque on the shaft. The straightening speed is controlled by motor #1. Motor #2 maintains speed control, and its torque is kept within the normal range. When the tail of the steel plate reaches below the third roll of the first group of rolls, the acceleration of motor #2 decreases at a certain constant rate. This constant rate is calculated, and the acceleration is canceled when the tail exits the first group of working rolls. At this point, the torque limit of motor #2 is increased to the maximum motor torque, and the speed of the steel plate is then controlled by the second motor according to the S-RAMP speed curve.
When the tail of the steel plate is within the working rolls of the second control group, and when it exits the working rolls of the first control group, the second motor drive is speed-controlled. The torque limit of the second drive gradually decreases from the maximum transmission torque to the maximum torque at the final connection shaft. This decrease should be in accordance with the progress of the tail within the second group of rolls.
When the tail of the steel plate exits the straightener, the torque limit equals the maximum torque of the last connecting shaft. When CMD6 at the exit detects the tail of the steel plate, the speed controller MASTER uses S-RAMP to lower the speed reference of the straightener rollers, reducing the speed of the inlet/outlet roller conveyors to 0. When the steel plate stops, the pass is declared complete, and the steel plate is then conveyed out by the post-straightener conveyor rollers.
Motor #1 is the main drive control motor. The torque limit value of the main drive equipment is calculated by the PLC based on the L2 model data. This torque is equal to the sum of the torques generated by the straightening rollers that the steel plate actually contacts, as calculated by L2.
Motor #2 is a slave control motor. The torque limit of the slave drive equipment is transmitted through the main drive equipment and then multiplied by a coefficient in the PLC. This coefficient is calculated based on the position of the steel plate in the hot straightener and the data from the L2 model after the straightening rollers actually contact the steel plate. The calculation of the slave drive equipment coefficient is as follows:
2. Hydraulic HGC Roll Gap Control
The roll gap control of the straightening machine is achieved by a hydraulic HGC system. First, the position sensor of the hydraulic cylinder is calibrated to zero and automatically returns to zero. Then, the HGC system is set to CLOSELOOP control mode, and the roll gap control program is set to run on the PLC7-400 of the primary control system. This PLC is connected to the secondary computer via Ethernet TCP-IP. After receiving the preset data from the secondary model, the primary straightening machine controls the corresponding servo valves to achieve the set roll gap position.
Operators can also manually set the roll gap according to actual conditions by manually inputting the roll gap value on the HMI. The HGC system can then receive the command and automatically move to the corresponding position. Alternatively, the HGC system's position can be operated using a joystick. The servo controllers employ P-type (proportional) and D-type (differential) controllers with good response characteristics. The control diagram is shown in Figure 2 below:
(Figure 2: HGC loop control)
3. Bending Roller Control Principle
The bending roller system is used to compensate for the deviation between the straightening rollers and the box body during the straightening process. The bending roller system keeps the straightening rollers parallel during straightening. A schematic diagram is shown in Figure 3.
(Figure 3: Schematic diagram of the bending roller function)
The upper straightening roll and support roll housing are mounted on a split, closable frame. This frame is divided into two parts connected by a movable joint. An eccentric device at the top of the frame separates these two parts, causing the straightening roll to bend. A hydraulic cylinder with an internal position sensor activates this eccentric device. Two pressure sensors provide pressure feedback to the hydraulic cylinder. A servo proportional valve drives the bending roll cylinder, controlling its position and providing overload protection.
The eccentric motion of the split frame is irreversible. The bending roller cylinder can only change position when the straightener is unloaded, so bending roller operation is not allowed under load.
4. Human-Machine Interface (HMI)
The HMI displays the upstream and downstream equipment and steel plate tracking information of the hot straightener, focusing on the main area of the straightener. It shows all relevant data and parameters of the straightener and provides a detailed description of the process route and material tracking.
Operators monitor the system based on the preset process values and setpoints displayed on the HMI. Normally, the control system automatically completes the steel plate straightening process. However, in case of abnormalities or discrepancies with actual site conditions, operators are allowed to manually intervene and modify parameters. The main monitoring content includes multiple operation screens such as: roller conveyor control (power on/off/speed display/fault information), main drive system (power on/off/speed display/fault information), HGC system, bending roll system, hydraulic station system, roll changing system, oil-air lubrication system, and fault alarm system. Operators are allowed to start/stop the equipment and view the operating status of various equipment displays. See Figure 4 below:
(Figure 4: Manual operation interface)
5. Two-level model control strategy
The secondary model calculation of the hot straightening machine is based on the PDI (basic data) information of the steel plate. The model uses the temperature of the steel plate measured by the temperature measuring instrument at the inlet of the straightening machine to calculate the thermal evolution of the steel plate, and performs inter-pass calculations based on the actual steel grade, chemical composition characteristics, etc. during the straightening process.
Based on the geometric characteristics of the steel plate and the steel grade properties at different temperatures in each pass, the working position (roll gap value) of the upper roller box, as well as the position of the first guide roller at the inlet and outlet of the straightener, are calculated. Within the design limits, the preset values of torque and straightening force are calculated to obtain the straightening strategy.
After the control system applies these preset values to straighten the steel plate, the primary control system sends the measured values of torque and straightening force to the secondary model. Based on these measurement feedback values, the secondary model automatically adjusts and optimizes using its self-learning function to improve the straightening quality of the next steel plate. The secondary model strategy analysis is shown in Figure 5 below:
(Figure 5: Second-level model strategy analysis)
The main functions of the second-level model are as follows:
Steel plate tracking: Receives data from the second stage of the finishing mill, mainly including information about the steel plate: steel plate ID number, chemical composition, steel grade, rolling temperature, current temperature, thickness, length and width, etc.
Data recording and reporting: Calculate the straightening mathematical model based on the received data, store the actual straightening data and equipment status, and issue a straightening report.
Human-Machine Interface (HMI): Through the human-machine interface, operators can see whether the data calculated by the model matches the actual application, and can make manual interventions and modifications.
Model calculation: Based on the steel plate data and information from the finishing mill, the corresponding data during straightening are calculated, such as roll gap value, straightening speed, and straightening pressure.
6. Summary
The application of hot straightening machines has improved the shape quality of steel plates. The main functions of the straightening machine's control system include transmission control and hydraulic system control, as well as the improved application of the secondary model, which greatly enhances the straightening quality of steel plates. Currently, medium and heavy plate plants can use this hot straightening machine to produce more than 30 types of high-strength plates, such as JG670DB, X70, and SS400, providing reliable technical support for the production of high-end medium and heavy plate products, bringing benefits to enterprises, and thus possessing certain promotional value.
Author: Yue Linping, female, senior electrical engineer, mainly engaged in the field management and maintenance of computer control and automation instruments. Mobile: 13864172994
Address: No. 21, Gongye North Road, Licheng District, Jinan City, Shandong Province, 250101, China
Email: [email protected]
