Hot rolling force ratio mode load distribution method
Abstract: Whether the load distribution of each stand in finishing mill group is reasonable or not directly affects the load bearing capacity of the whole unit and the stability of strip rolling process, and also directly affects a series of quality indexes such as plate shape control. On the basis of studying the load distribution method of rolling force ratio mode, the main factors affecting the load distribution of the rolling force under this mode are obtained by calculating the rolling force.
Key words: hot rolling; Load distribution; Rolling force ratio
1. Introduction
The purpose of hot strip rolling process control is to optimize the rolling process, and to calculate the control parameters online by mathematical model and self-adaptation. The core of parameter calculation is the load distribution of each frame. The practical load distribution methods at home and abroad have three kinds of distribution coefficient methods, such as reduction rate, rolling force and power, and the common one is reduction rate distribution coefficient method. The following mainly introduces the rolling force ratio distribution method and the main factors that affect the reduction schedule distribution under this method [1].
2. Basic algorithm of rolling force ratio distribution method
The load distribution of the finishing mill group is to calculate the strip thickness between the stands hi (i =1,...) according to certain rules when the incoming thickness h0 and the target thickness hn (n is the number of finishing mill stands) are known. , n-1). The distribution rule is that the load (rolling force or rolling power) of each frame is in a certain proportion:
Where pik is the load value (rolling force or rolling power) calculated by k iterations of the i frame; Target load distribution ratio for rack i.
The rolling load pi of any frame is a function of the thickness HI-1 at the entrance and the thickness hi at the exit of the frame. In order to solve the thickness hi of the exit of each frame, Newton-Raphson method was used to combine the equations in equation (1), give a certain initial thickness distribution, and solve the iterative calculation.
3, manual intervention load adjustment
In order to ensure the instability caused by the change of product development or factors, the operator is left with enough modification rights in the secondary interface to ensure the smooth rolling. Manual intervention is also divided into two modes: the first is to adjust the ratio coefficient of rolling force; The second is to specify a pushdown mode for a frame.
3.1 Adjustment of rolling force ratio coefficient
The actual load ratio of rolling force is the comprehensive calculation result of the standard value in the model layer table and the operator's adjustment value, where, is the temporary calculation value of the rolling force ratio of the i frame; Is the model table value of rolling force ratio of frame i; Is the operator's correction of the rolling force ratio of frame i [2].
The temporary calculation value of rolling force ratio determined by the above process needs to be nominally processed. The frame load ratio with the maximum rolling force ratio is nominally reduced to 1, and the nominal rolling force ratio of each frame is:
In formula (4), ri-- the nominal rolling force ratio of frame i, (i= 1,2,... , L (end frame))
Below, a concrete example is used to illustrate the calculation process of determining the final used rolling force distribution ratio according to the standard rolling force distribution ratio obtained by searching the layer table and the rolling force ratio correction value entered by the operator at the secondary interface, as shown in Table 1.
3.2 Specify the pushdown mode
The pushdown procedure for some racks can be calculated from the target pushdown value. If a target pushdown value other than 0 is entered in the target pushdown table, the pushdown procedure for this frame is calculated as the target pushdown. For other frames, the rolling force ratio is still used to calculate the rolling force ratio.
4. Factors affecting rolling force
Because the ratio distribution method of rolling force is a certain ratio of rolling force, but the reduction will fluctuate due to the change of rolling conditions. The relationship between rolling force and reduction is as follows:
P=pmb average (R △ h) 1/2 In equation (5) : pm is the average unit pressure; b average is the average strip width before and after rolling; R is the radius of the work roll; △ h is the amount of reduction.
It can be seen that under the premise that the total rolling force P is certain, the b average, the average unit rolling force and the roll diameter (radius) are the three factors that determine the reduction rate of each frame.
The factors affecting the unit pressure can be divided into two categories: the first type is the factor affecting the performance of the strip itself, namely, the plastic deformation resistance; The second category is the factors affecting stress state conditions. The size of deformation resistance depends on the chemical composition and microstructure of the metal material, deformation temperature, deformation speed, deformation degree and so on. The factors affecting stress state conditions include friction coefficient, tension and so on. The factors affecting the friction coefficient also include the composition of the oxide sheet, the material of the roll, the input of rolling oil, the thickness of the strip, the diameter of the roll, etc. [3].
The rolling force ratio distribution method ensures the stability of the rolling force, so it greatly improves the stability of the belt through, but the change of the reduction rate will affect the rolling state of the strip body and the strip end, so this is a comprehensive problem.
5. Closing remarks
It is proved in practice that the load distribution of finishing mill group directly determines the rolling stability and shape quality of finishing mill. The ratio distribution mode of rolling force ensures the stability of the rolling force through the belt of each frame, but there are many factors affecting the rolling force, and the unreasonable reduction rate will also lead to the instability of the belt body and the tail. Therefore, in addition to the self-adaptation of the automatic control system, it is necessary for the model personnel to improve the ratio coefficient of rolling force timely and reasonably, which is a long-term work.
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