冷轧薄板厚度检测及其自动控制(英)(DOC)

The Research and Application of Thickness Gauge and the Automatic Control System of Thickness in the Cold Rolled Sheet SteelZhang Lin1Yao Youling2（1、The Automation Department of Laiwu Steel Group，Laiwu ,271104,China; 2、The Cold Rolling Plant of Lai Steel Group, Laiwu,271104,China，+86-139******** lgzgyao@）Abstract: The paper relates the principle and the way of the automatic thickness measurement for cold rolled sheet and type selection of thickness gauge. The construction of the cold rolled sheet thickness automatic control system is discoursed. On the basis of measure result and measured thickness signal, we adopt intelligent control way to achieve the automatic gauge control(AGC) of the feedback AGC、the monitor AGC、the flow rate AGC. Through the emulation practical application of AGC system, its response speed and thickness accuracy all come to national standard, We apply this system on the thickness automatic control system of Laiwu Steel 1500mm cold rolling mill, it satisfies the needs of the user. It has higher economic benefit and promotional value.Keyword:automatic-control cold rolled sheet X-ray measure thickness1、IntroductionThickness accuracy is one important quality so as to obtain high-quality plates and higherindex. The thickness accuracy and evenness have a economic benefit. It is well known that the thick-direct bearing on the plate performance and market ness measuring accuracy is the key factor tosales status. In recent years, domestic and foreign realize the high-accuracy control of plate thickness related enterprises and scientific research institutions On the basis of drawing lessons from the similar plate strengthen the research on the control of plate thickness , the 1500mmUCM cold mill in the cold rolled plant of Shandong Laigang Group selects RM215 X-ray thickness gauge to measure the thickness of cold rolled plate online. It also implements alloy compensation to obtain a good thickness measuring accuracy. It combines with AGC control system to realize high-accuracy thicknesscontrol. The thickness accuracy of cold rolled sheetmeets the national standard and the requirements of users by practical application.2、Thickness measurementThe accurate thickness detection is the key step to produce high-quality cold rolled plate. Therefore, it is a very important work to select thesuitable thickness gauge for measuring the plate thickness.2.1 Model selection of thickness gauges[1]The thickness gauges which are used in strip mill for plate thickness detection can divided into two kinds, namely, contact type and non-contact type according to measuring mode. The contact type thickness gauge, for example, the basic “micrometer”, which is used to measure thickness off-line and is not realizing the closed-loop controlof thickness with the control system. Non-contract type thickness gauge can be used for online continual thickness measurement and carry on data processing, storage and output. It can realize the thickness closed-loop control with the control system conveniently and achieve the purpose of thickness automatic control (AGC). Therefore, at least one non-contract type thickness gauge that canrealize online continually measuring thickness shouldbe equipped on a cold rolled sheetproduction line. The non-contract thickness gauge can be divided into three types generally, namely: (1) optical thickness gauge; (2) isotopic thickness gage;(3) X-ray thickness gauge. Each thickness gauge has its advantages and disadvantages, its advantages and disadvantages are shown in the following table.The rolled pieces are relatively thin(0.1-6mm) , the milling speed is fast (over 15mm/s) and the requirement of measuring accuracy ≯±0.1% to cold rolling mill. In view of the above, the selection of the X-ray thickness gauge can only meet the requirements by combining the comparison of the several thickness gauge in the above table. Considering the radiation hazard of the ray, while measuring, anti-radiation measures should be taken. Furthermore, when it is notmeasuring, ray source will close automatically and it is safe to human body. The plate absorbs one part, it becomes I 1. According to the test, I 1 and I 0 has the following relation:k 1--- it is the mass absorption coefficient of the measured plates, this can be found in the handbook; ρ---it is the density of the measured plates, it canbe found in the metal handbook;h--- it is the measured plate thickness. Combining the equation (1) with (2) 10kh I I e -= (1)1k k ρ=⨯ (2)I 0---it is the X-ray intensity emitting by the raysource;I 1--- it is the X-ray intensity when the raypasses through the plate with the h thickness;k--- it is the linear absorption coefficient ofplates;and converting, we can get:0111ln I h k I ρ= (3) Then, according to the equation, it is very easy toget the thickness value of measured plate on the background computer. The value sends to thickness control system, the computer can realize automatic gauge control (AGC) comparing with the thickness set value in the system.3、Automatic gauge control system3.1 Brief introduction of AGCHydraulic AGC system is the key control system of single stand reversing cold rolled mill, its main function is to complete AGC, eliminate the exit vertical thickness tolerance of strips, maintain the relatively better flatness and ensure the high-speed, highly-efficient and steady rolling of mill. The advantages and disadvantages of the control system have direct relation to quality and rolling yield of cold-rolled products.The hydraulic AGC system is mainly composed of two sets of FM458 control devices, detecting and measuring instruments of roll gap, tension, pressure, thickness, speed, servo system, hydraulic push-up cylinder and other equipments. Its essence is to realize the automatic gauge control of strips by changing the actual position of roll gap, AGC are two parts including inner-loop control and outer-loop control. The system includes h-AGC、H-AGC、MF-AGC、T-AGC etc.3.1.1 Inner-loop controlThe inner-loop control is the control system of roll gap in the mill, it is responsible for the adjustment and control in the rolling process. If the inner-loop control takes the feedback of displacement sensor in screw-down device as the control objective, it is called position control loop –APC. If the inner-loop takes the feedback of pressure sensor in screw-down device as the control objective, it is called pressure control loop – APC. In APC control, displacement sensor of detecting the roll gap position can be installed on the press-up oil cylinder of mill. There are two feedback signals for acquiring the position on the operating side and driving side of mill, then the two signals are averaged to generate a signal standing for the central position. Comparing the average value with the given signal of roll gap, the servo valve is driven by the differential value of the two, the differential value should be close to zero by adjusting the press-up oil cylinder.In AFC control, the pressure sensor installed on the press-up oil cylinder checks the pressure in oil cylinder, after converting, the feedback signal of rolling force for the mill is obtained. The signal compares with the pressure given signal, the differential value of the two is driven the servo valve, the differential value should be close to zero by adjusting the press-up oil cylinder. The pressure control is mainly used for AGC control of pressure – tension, pro-pressing zero adjustment of mill, mill commissioning and fault diagnosis.3.1.2 Outer-loop controlThe outer-loop control is the quality control system of the mill, it is responsible for the thickness control of strip in the rolling process. The outer-loop control includes h-AGC、T-AGC、H-AGC、MF-AGC, outputs the thickness control adjusting signal to inner-loop and adjusts the press-down position of hydraulic pressure to control the finished product thickness.strip3.1.3 Mathematical model of cold rolling thickness[3]The thickness is one of the most key indexes for the overall quality index of cold rolled plate. The compensating measures should be taken to various factors that influence the control accuracy of thickness in order to improve the thickness control accuracy.The following main factors should be considered: ○1 The thermal expansion and abrasion of roll and mill in the milling process of mill;○2 After the rolls are added bending force, it not only causes the changes of section profile of strip, but also influence s the exit thickness in order to improve the profile;○3 After the milling force and bending force are added, the changes of oil film thickness for oil film bearing influence the plate thickness. Therefore, the thickness control can be written as To a specific rolling, while rolling a certain pass, it can be considered that the three variables T 、τb 、τf are constants, so the partial differential is done to the equation (6), the linear part is chosenthe following form:00mo G T p F mP F P F F h S h S h C C C +-=++++++ (4) The equation (4) reflects the influences of rolling force and rolling fore on the rolled thickness. Considering the influence of slight fluctuation of various diameters to be analyzed on exit thickness variation, T o G h S h 、、 can be considered to be invariable.Therefore, the equation (4) can be written as the following incremental form:mp F mF P F h S C C C δδδδδ=+++ (5) In the equation: S δ--set roll gap dynamicvariation quantity.The metallic pressure equation can be written as thefollowing form:P=f(H ,h , τb , τf ,T ) (6) In the equation ： H —incoming material thickness; h —exit thickness of rolling pieces; τb — tensile stress of backward machine; T —rolling deformation heat produces temperature rise; τf 一tensile stress of forward machine.and gotten:δP =h hP H H P δδ∂∂+∂∂ (7) Bring the equation (7) to the equation (5), makemathematical manipulation and obtain: δh =1mP F mF P P F S H h C H h C C δδδδδ∂∂⎛⎫++++⎪∂∂⎝⎭ Suppose the stiffness coefficient of rolling pieces plastic deformation is Q, according to the metal plastic deformation principle and beam on elastic foundation theory,=Q h P ∂∂-=H P ∂∂，make thegraphical method ，sort out the above equation and get the thickness model equation: δh =()()P P P m P P P F P mC C C Q S H F F C Q C Q C Q C C Q C δδδδ+++++++ (8)In the above equation, Q can be obtained by calculating the rolling pressure P , incomingmaterial thickness H and exit thickness h ；For the stiffness coefficient of mill C P and stiffness coefficient of bending roll C F 、C m, currently, the methods of actual extruded aluminium plate or copper rod on specific mill and increasing the operation of bending roll force are adopted, then using the theory to calculate and get.4、Actual application effectThe exploited system is applied to automatic gauge control (AGC) of 1500mm six roll reversing cold rolling mill in Laigang. According to the specification of production plan, the thickness curves of 0.37×1000、0.36×1000 and 0.38×1200 finished product pass. The thickness values of finished products are automatically checked bythickness gauge and manually checked by adopting high-accuracy micrometer. To the products of three specifications, absolute errors of their thickness are all within the±0.005mm. These meet the requirements of users and national standard.Figure2 AGC Objective Curve5、ConclusionThe detection method and control means researched in the article is used to control plate thickness of 1500mm single stand reversing cold rolling mill.The system detection is accurate, systemrunning is stable, the response speed is fast, control accuracy is high and it reaches the aim and requirement by the proof of actual application.References[1] Written by V.B. Ginzburg，Translated by Jiang Mingdong and Wang Guodong, High-accuracy Strip Rolling Theory and Practice，, Beijng, Metallurgical Industry Press，2002，110~112。