The hottest mold level control system of Continuou

2022-08-17
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Design of continuous caster mold level control system based on fuzzy control decision

continuous caster has been widely used in iron and steel metallurgy industry, and the continuous casting ratio in China has exceeded 90%. In the field of continuous casting technology with the increasingly high requirements of modern social industry for products, the application Research of control technology in continuous caster is the most active. The crystallizer is a key equipment on the continuous caster, and its liquid level control accuracy is of great significance to improve steel output and reduce the accident rate of billet production. The author uses the fuzzy control strategy to control the mold liquid level, and applies the designed fuzzy controller to the actual control object

1 traditional crystallizer liquid level control system

1.1 overview

the traditional crystallizer liquid level control adopts the Co-60 control system [1], which controls the pulling speed of the tension leveler to control the crystallizer liquid level, but the liquid level control accuracy of this control system is low. Later, stopper rod was used to control the liquid level of crystallizer. This method is manual operation, with slow response speed and poor system stability. The traditional crystallizer level control system is shown in Figure 1-1

1.2 stopper control crystallizer liquid level

due to the long response time of stopper action, the nonlinearity of liquid level control is large, and even irregular phenomena may occur, resulting in instability of liquid level control and low control accuracy. There are mainly the following factors:

(1) the properties of stopper control have an impact. For example, when pouring steel flow with high aluminum content, the nozzle part is easy to bond, thus blocking the flow of steel flow

(2) in the pouring process, the stopper and nozzle are gradually melted, washed and eroded to change the size and shape of the steel flow channel, which will change the steel flow

(3) due to the change of process parameters, such as the temperature of molten steel and the amount of molten steel in the tundish, the level control of the crystallizer will be affected

1.3 casting speed control mold liquid level

control the liquid level by changing the casting speed, and its control characteristic curve is linear. Therefore, theoretically speaking, its control accuracy is very high. However, the casting speed is an important parameter in the continuous casting process, which depends on the following factors:

(1) the quality of the slab, and the casting speed should be designed according to the requirements of the solidification theory; Different steel grades, section sizes and superheat of molten steel determine the corresponding cooling degree and drawing speed. Therefore, the casting speed should have an upper limit on the premise of ensuring the slab quality. Help carry out the initial injection molding experiment ·

(2) in order to improve the production efficiency of slab, the drawing speed should have a lower limit

in order to meet the above two basic requirements, the pulling speed should be limited to a certain range. On the other hand, in order to meet the accuracy requirements of mold liquid level control, the casting speed should dynamically track the liquid level for adjustment. Therefore, the adjustment range of drawing speed should be limited to a small dynamic range

1.4 comparison of stopper control and casting speed control mold liquid level

when pouring ordinary carbon steel or steel with low quality requirements, both control methods [2] can be used, and the method of controlling casting speed should be preferred, because the casting speed control liquid level is approximately linear. When pouring special steel grades, two control methods should be used comprehensively, because at this time, the continuous casting process requires stable liquid level and stable casting speed. However, as long as there is no sudden change or great disturbance in the state of the continuous casting process, the method of controlling casting speed should be used. Even if there is a large disturbance, feedforward adjustment can be used in the casting speed control loop to eliminate the disturbance. Therefore, the control of crystallizer liquid level should be mainly controlled by casting speed

2 fuzzy controller design

2.1 control system structure analysis

Figure 2-1 is the system schematic diagram of controlling the liquid level with the pulling speed. The liquid level signal detected by the liquid level sensor is compared with the given liquid level signal, and the liquid level deviation and deviation change rate are calculated, fuzzified, fuzzy reasoning and decision-making are carried out. After the calculation of the adjustment factor, it is sent to the actual pulling speed liquid level PI controller for calculation, and its output controls the pulling speed of the tension leveler, So as to control the liquid level of the crystallizer. The block diagram of fuzzy control system is shown in Figure 2-2

2.2 fuzzification of precise quantity

the fuzzy controller selects two-dimensional input and one-dimensional output. The input variables are the positive mold liquid level error and the liquid level error change rate EC, and the output Z changes the P and I parameters of the speed PI controller. The corresponding fuzzy subset of language values is selected as: {h, m, Z, s, l}, where h= negative; M= negative small; Z= zero; S= positive small; L= positive. The integer universe of deviation month and deviation change rate EC is determined as: e:xe={-2, -1, 0, 1, 2}, ec:xec={-2, -1, 0, 1, 2}; The integer universe of output Z is: z:{-2, -1, 0, 1, 2}; P -- proportional control, I -- integral control

in order to obtain an error signal of a comprehensive performance index that tracks smoothly but reflects the elasticity, plasticity, strength and toughness of the material, the membership function of G and EC selects a triangle curve with equal distance cross distribution. As shown in Figure 2-3. The input Z and JC of the fuzzy controller are fuzzy discretized with the above membership function, as shown in table 2-1. The fuzzy table of the output Z has the same form

2.3 establishment of fuzzy control rules

according to the traditional speed PI controller to control the mold liquid level, according to the step response simulation curve of the second-order inertial system on the MATLAB platform that brings confidence to the extruder enterprise, and according to the control rules of the speed PI controller parameters introduced by the month and EC, the fuzzy control rule table is established, such as table and table. The table shows the proportional action fuzzy control rules of the speed n controller, and the table shows the integral action fuzzy control rules of the PI controller

table E and EC

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