Current status and future development of shape control technology for hot rolled wide strip
Abstract: 18 roll single frame mill after the production of vibration defects, check the hydraulic cylinder, transmission shaft coupling, electric control system, roller grinding process, etc., found the hydraulic cylinder vibration, pressure control speed is too fast, magnetic foot base welding, roller grinding process is unreasonable, by replacing the pressure hydraulic cylinder, specification transmission device inspection system, adjust the rolling pressure speed control gain, increase automatic shock detection function, optimize the roller grinding process, the machine after rolling strip vibration grain defects reduced by 91%, defect degradation 0.01%.
Key words: 18 rollers; vibration grain; side support; hydraulic cylinder; gain; grinding roller
After the 18-roller single frame mill was put into operation, the vibration pattern defect of the rolling strip was caused by the vibration of the rolling mill. Dense transverse printing can be seen on the strip surface, and the defects are more obvious after grinding, which seriously affects the surface quality of the product and brings a large number of degraded grades. The vibration grain defect brings great pressure to the production operation and cost benefit, and the order receiving ability of important varieties is greatly limited. The defect of rolling mill greatly affects the stability of production and quality of rolling mill.
The vibration of rolling mill has great influence on rolling mill production operation and product surface quality, and many professional institutions have studied it deeply. Peng Rongrong et al. [1] gave a nonlinear dynamic model for the rolling mill, The theoretical direction of suppressing the mill vibration is also given; Li et al [2] studied the causes of the vibration of the mill, After experimental testing, A rolling mill control model is given, It provides a theoretical basis for the control of rolling mill vibration; Zhang Yongshun et al. [3] studied the influence of the pressure system on the vibration of the rolling mill, It provides theoretical guidance to eliminate the vibration of the hydraulic system through simulation; Luan Zhaohua et al. [4], through the vibration test and simulation test, Find the vibration frequency, Control the occurrence of vibration by adjusting the pressure-down frequency; Lujie et al. [5] studied the effect of side support roller during rolling on rolling dense transverse pattern defects, The preliminary technology is explored by adjusting the rolling rules and equipment parameters. The literature data mainly studied the influencing factors and suppression methods of the vibration of the rolling mill, and mentioned the defects of the vibration lines after rolling, but did not do in-depth study.
This paper analyzes the vibration defects of the mill by optimizing the relevant measures.
1 Description of the vibration pattern problem
The company's 18 roll single rack mill began to find vibration defects two months after production. During the production of the last track replacement roller (Ra = 2.0 μ m), check the surface quality of the strip strip and find the vibration pattern defects as shown in Figure 1. Since then, similar conditions have long existed. High and low speed are the same spacing, the mill speed above 500 m / min, the rolling mill vibration phenomenon, the mill speed to 800m / min, the vibration is more serious, the last time is easier to vibrate, subsequent processing annealing and galvanizing process is not easy to eliminate this defect, after galvanized even has a tendency to enlarge the defect, the failure roll after galvanizing, the defect is more obvious.
Through long-term tracking, it is found that the occurrence frequency and severity of vibration grain defects gradually increase with the rolling speed, the increase below 500m / min is slow, and the incidence of defects over 500m / min increases substantially. At this stage, it is found that with the continuous improvement of rolling speed, the fluctuation problem of hydraulic cylinder position gradually begins to appear, and it is speculated that this problem may be related to the vibration grain defect of strip steel. The relationship between velocity and vibration pattern is shown in Table 1
After rolling, the strip surface will appear vibration defects, and the corresponding vibration lines will begin to appear on the surface of the side support working roll. The vibration pattern of the side support is shown in Figure 2. Therefore, the occurrence of vibration pattern defects takes a period of time to appear. During the installation and debugging, the production line only tested the 800m / min production.
The equipment and the process were inspected. The production line tested the process parameters, including tension, pressure rate and emulsion concentration, and replaced the rolled oil of different manufacturers, which had no obvious impact on the vibration lines. The inspection of the lower cylinder fixing bolt and the magnetic ruler found that the lower cylinder fixed bolt and the magnetic ruler were obviously loosened, and they were immediately tightened, but the vibration pattern problem was not significantly improved. A series of adjustment tests were carried out on the pressure control system, which did not solve the vibration pattern defects.
2. Cause analysis of vibration problems
2.1 Roller grinding process
Preliminary investigation of rollers and mechanical equipment was conducted. No obvious defects and suspected related defects were found. Carry out the comparative test of grinder grinding process, namely: roller grinding and top grinding vibration test [6].
1) grinding test: ① grinding wheel speed 24 m/s; diameter of grinding wheel 578mm; grinding wheel rotation 13Hz; diameter of rolling roll 169 mm; roller speed 50 r/min; vibration frequency 52,66,92 and 158Hz, the difference between four dominant frequencies of grinding wheel rotation; ② grinding wheel speed 19 m / s; grinding wheel rotation 10.5Hz; vibration advantage frequency 58,68,78,78 and 132Hz, the difference of four dominant frequencies are close to the multiple of grinding wheel rotation [7].
According to the vibration grain spacing of strip steel, the corresponding vibration frequency corresponds to 60~80 Hz, and the vibration of test 1 and test 2 is close to it. It is preliminarily estimated that the vibration may be generated by the rotating parts of the grinding wheel. As the grinding amount decreases, the vibration is gradually decreased. The vibration frequency of the grinding test test is shown in Figure 3. The upper curve of the grinding test is the ground frequency curve of the grinding test, and the lower part is the vibration frequency curve of the grinder.
2) grinder top grinding test: ① grinding wheel speed is 24 m/s, grinding wheel diameter is 578mm, grinding wheel rotation frequency is 13Hz, roll diameter is 169mm; roll speed is 50r / min, vibration frequency is 294Hz; ② grinding wheel speed is 19 m/s, grinding wheel rotation frequency is 10.5Hz, and the vibration frequency is 200~300 Hz.
In the case of top grinding, the vibration frequency of the grinder is mainly concentrated at 200~300 Hz, and the vibration frequency is relatively high, and there is no obvious correspondence with the roll vibration grain interval. The vibration frequency of the grinding machine top grinding test is shown in Figure 4. The upper curve of Figure 4 is the ground frequency curve of the top grinding test, and the lower part is the vibration frequency curve of the grinder.
2.2 Mechanical and equipment problems
Check the position fluctuation of the mill hydraulic cylinder. The position fluctuation of the hydraulic cylinder is usually in the high-speed operation stage of above 500 ppm, the fluctuation range is between 15 and 70 μ m, and the maximum fluctuation value is above 50 μ m. The fluctuation range of the response speed of the system under the controller gain and the pressure is reduced, and the large fluctuation value is generally within 50 μ m.
2.3 Problems of the electronic control system
Rolling mill line products with transverse shock grain, can not be judged. After analysis, it was found that the control system of the rolling mill fluctuates during the production process, causing high frequency shaking of the roll joint, bringing shock lines to the strip steel, and the damage of the support bearing on the downline side was obvious. Therefore, it is proposed to optimize and debug the pressure control system of the production line to eliminate the swing.
1) Control system investigation. The operating side and driving side of the mill have a set of independent position detection device, program control system and hydraulic actuator respectively, and the program control algorithm on both sides is the same. The hydraulic actuator has two sets of servo valve, and one set of servo valve performs the fine adjustment function of the position of the pressure cylinder, called slow valve, proportional control; a set of servo valve performs the adjustment of the pressure cylinder, called fast valve, its algorithm has two: ① according to the deviation of the actual position and the target position, the more difference, the more output; less difference, less output; when the required action speed is less than 3.7 mm/s closed. This algorithm is not used in steel rolling production; ② when the slow valve output exceeds 80%, the control fast valve output a maximum less than 10% adjustment volume, similarly the more slow valve exceeds, the greater the fast valve adjustment volume.
First of all, for the fast valve, considering the problem that the fast valve regulation speed is easy to cause shock, the function of the fast valve exceeds 80% in the program chain, with no improvement.
Secondly, the parameters of the pressure control system of the slow valve were adjusted, the manual gain coefficient and automatic gain coefficient were gradually reduced, and the butterfly compensation control function was turned off. The manual gain coefficient decreased from 2500 to 1800, and the automatic gain coefficient decreased from 4500 to 3600, with only a slight improvement.
Finally, by checking the output adjustment of the slow valve at the normal time through the curve, it is found that it is basically within the range of about ± 27%, taking the measure to limit the output of the slow valve at the production time to ± 30%. At this time, the curve shows that the output of the slow valve fluctuates in the range of ± 30%, but the shock amplitude of the roller seam is significantly reduced, about ± 50 μ m. It shows that the oscillation of the control system will aggravate the oscillation of the roller joint position;
2) Magnetic tape inspection. In the 18 roll down system, the position detection is adopted, with an accuracy of 1 μ m. The whole magnetic meter detection system includes SONY magnetic tape, cable, MD50 processor and signal board card.
Check the components of the magnetic meter detection system; the indoor MD 50 processor and signal card are normal without alarm; the special plug at both ends of the cable is in good contact and not loose; observe the field magnetic meter without abnormality, and the excitation line and signal line resistance are measured within the normal range.
The magnetic meter check started from the site where problems were most likely. First, the cable from the site to the electrical room was replaced, which had no effect. So organize the replacement of the site magnetic tape. During the disassembly process, it was found that the fixed magnetic rod base connected to the hydraulic cylinder was welded. The open welding of the magnetic ruler fixed sleeve rod base is shown in Figure 5.
After rewelding, the original magnetic meter was reinstalled and all the previously modified control parameters were restored. Start production, drive side shock problem disappeared, return to normal.
3. Optimization measures and application effects
3.1 Optimization of the grinding process
From the beginning of the single frame, the vibration grain defects were found on the surface of the strip steel. After adopting a series of technological measures, the vibration grain defects failed to be solved essentially. The grinding working roll mode is changed from support grinding to top grinding to eliminate the possible defects [8-10] of the coaxial error of roll diameter and roll body in the roll machining process.
3.1.1 Operation steps of top grinding mode
1) After the top grinding, the original support bracket shall remove the head and tail top of the grinder to cover the central holes at both ends of the roller shaft;
2) In order to prevent deflection during the roll grinding process, three pneumatic center frames are used for the roll support, and the whole direction is shifted by 20mm according to the position and position of the roll;
3) The top of the grinder is fixed, which cannot be manually adjusted, so the installation error chain needs to be manually removed before grinding;
4) The startup procedure is normal for grinding.
3.1.2 Comparison between top grinding and support grinding
Test grinding roller pair, the grinding process is as follows:
1) Comparison of the installation error. Installation error value of roll head and tail coordinate difference. The installation error of top mill is 0.028 mm; because the mill can be manually adjusted manually, the installation error chain value is 0.031mm and the installation error is about 0.035 mm. The installation error of the two grinding methods is not much different, both meet the error requirements;
2) Comparison of the grinding results. Roll error 0.005mm, 0.002mm, 0.001mm; Roll error 0.009mm, 0.002mm, 0.001mm. Compared with the two grinding methods, the roller error is much smaller than the grinding, and the roller accuracy is higher;
3.1.3 Problems with top grinding
The top mill wears the grinder top more seriously, the top can see obvious wear groove, and the top cooling is insufficient, and the center hole of the roll has heating phenomenon. By increasing the shaft head cooling nozzle, the heat dissipation capacity of the shaft head is increased to avoid the high temperature produced by the grinding process affecting the grinding precision.
3.2 Mechanical and equipment
Replace two main pressure down cylinders by inspection, and inspect and tighten the anchor bolts with a torque of 1560 NM.
Check the tooth splines of the coupling. Check the wear of the gear head and spline of the middle roll coupling of the rolling mill to wear and apply grease. The coupling tooth face has no visual visible wear, and the middle roller spline has slight wear [11-13].
Check the universal joint bearings for wear and apply grease. Check the oil level in the bearing tank. Check the wear of the roller bearings. Check the clearance between the support roller bearing seat and the memorial arch. The gap between the supporting roller bearing seat and the archway is 1.1 to 1.2 mm.
3.3 Optimization of the electronic control system
3.3.1 Adjust pressure control
The automatic gain coefficient of the pressure control of 3 # rolling mill has always used the fixed value of 5000 in production. On the curve, the thickness control has large fluctuations under different speeds, and the system under the pressure causes the system instability [14]. The automatic gain coefficient of the pressure system is optimized to establish a set of output coefficient changing automatically with the speed. The higher the speed is, the output percentage is lower; when the speed is low, the output percentage is higher. This effectively reduces the intensity of high speed adjustment, the overshoot of pressure control is lower, and the system operation is more stable. Limit the output opening of the servo valve under the pressure system, and the output opening in the normal production does not exceed 30%. In the pressure down system, the butterfly compensation control is optimized, and the shock range is significantly improved.
3.3.2 Add the automatic vibration detection function
Analyanalyzing curve of vibration history data, developed automatic detection function and adjusts corresponding control measures according to vibration. The controller identifies the vibration [15] by accumulating the number of position deviation per unit time and the output of the servo valve. When the vibration occurs, the controller automatically triggers, adjusts the automatic gain coefficient of the system to 30% of the original value, and triggers the automatic deceleration program of the mill to reduce the speed by 50m / min. Develop the shock detection program, automatically reduce the gain coefficient, deceleration and other control. If the shock is detected below 650m / min, the gain coefficient is automatically reduced to 30%, and the speed fluctuates above 650 m / min. In addition to reducing the gain coefficient to 30%, the speed is reduced by 50 m / min.
3.4 Application effect
One month after the implementation of the above measures, the production data of 30d will be continuously counted to analyze the occurrence trend of defects. Through the test, it is found that the vibration frequency of the grinder is close to the vibration pattern frequency, and the vibration frequency of the grinder and the vibration pattern frequency. Then the vibration pattern defect is reduced by 26%; the functional accuracy and lubrication inspection of the transmission device are reduced by 31%; the automatic gain coefficient of the system is optimized, and the automatic vibration detection and control function is increased, and the vibration pattern defect is reduced by 34%. After the implementation of the above measures, the vibration defects were reduced by 91%, the reduction trend was obvious, and the vibration defects were effectively controlled.
4 Conclusion
This paper studies the defects of vibration pattern, analyzes the causes of mill vibration and takes relevant measures.
1) Optimize the roll grinding process, the roll grinding process is changed from support grinding to top grinding, and the vibration pattern defects are reduced by 26%;
2) By replacing the pressure hydraulic cylinder and standardizing the transmission device inspection system, the vibration grain defects are reduced by 31%;
3) Adjust the speed control gain of the rolling mill under the press, increase the automatic detection and shock detection function, and reduce the vibration grain defects by 34%.
After the implementation of the above measures, the vibration grain defects of the strip steel were effectively controlled, the vibration grain defects were reduced by 91%, and the defect degraded products were less than 0.01%.
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2024/04/12 13:19:01
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