Calibration,and,Application,of,Actual,Tension,of,Low,Precision,20,High,Mill

时间：2023-06-13 20:00:14　来源：雅意学习网本文已影响人

ZHANG Chunjie, SONG Zheng, TONG Jianjia, MO Zhiying

(1. Tinplate Business Department of Shougang Jingtang Iron and Steel United Co., Ltd., Tangshan 063200, Hebei, China; 2. Steel Rolling Operation Department of Shougang Jingtang Iron and Steel United Co., Ltd., Tangshan 063200, Hebei, China)

Abstract:The rolling production of metal thin strips, especially the production of stainless steel and copper thin strips with high yield strength, due to the limitation of the minimum rolling thickness, multi roll mills with small working roll diameter are mostly used, and the 20 roll mill is the most common. Aiming at the problem that the actual tension of some 20 high rolling mills with long service time and low assembly accuracy has a large deviation from the set tension and is not accurate enough, this paper first designs the tension calibration device of the low precision 20 high rolling mill. Secondly, the calibration principle of the tension calibration device designed in this paper is described. Then, according to the calibration principle and specific implementation scheme, the actual tension tact of the strip steel is comprehensively determined, and the mapping relationship between the set tension tset and the actual tension tact of the 20 high mill is established, so as to improve the tension control accuracy of the 20 high mill and ensure the shape quality of the strip steel.

Keywords: tension calibration device; calibration principle; implementation plan; actual tension

In steel rolling,the output capacity of cold rolled strip steel plays a role in reviewing the national industrial level. The rapid development of Industrial Science and technology requires high-precision wide and thin silicon steel,stainless steel,alloy steel and other difficult to deform metal strips to have good quality and huge output. Due to the complicated structure of the roll system of the 20 high rolling mill and the problems of mutual disasters among various adjustment means,it is difficult to predict the results after adjustment on site. In addition to simple plate shape defects such as medium wave and small side wave,there are also high-order plate shape defects(which are easy to appear in the rolling process of thin gauge oriented silicon steel). The adjustment direction is unknown on site,and it is not easy to adjust. Therefore,it is necessary to systematically study the equipment accuracy and flatness control means,determine the law of shape control,and seek reasonable shape control schemes under different rolling conditions[1-4].

At present,some 20 high rolling mills with long service life and low assembly accuracy often have problems such as poor stability,large deviation between actual tension and set tension,and lack of accuracy. In the strip rolling of the 20 high rolling mill,the accuracy of the actual tension control is the necessary basic work to improve the shape quality and form the shape control technology[5-6]. In order to further improve the shape quality of stainless steel strip,a solution that can accurately calibrate the actual tension of 20 high rolling mill and improve the tension control accuracy of rolling mill is needed.

2.1 Overall design of tension calibration device

After long-term service of the 20 high mill,the deviation between the set tension and the actual tension increases,and the tension accuracy is low,which affects the rolling of plates and strips[7-10]. After research,as shown in Figure 1,a tension calibration device of the 20 high mill is proposed.

Figure 1 Schematic diagram of calibration device

Among them,one end of the counterweight frame is rotationally connected to the connecting shaft on the 20 high rolling mill,a reducer is respectively provided at the inlet and outlet of the 20 high rolling mill,and an inlet support roll is provided near the roll inlet where the strip steel enters the 20 high rolling mill. The counterweight frame is rotationally connected to the connecting shaft between the output shaft of the reducer and the inlet support roll,and can freely rotate around the connecting shaft in the vertical direction. The counterweight frame may be provided with a plurality of connecting mechanisms in sequence at certain intervals. The connecting mechanisms may be connecting holes or connecting beams for suspending the counterweight,which are not particularly limited. The space between the connecting mechanisms is configured according to specific needs,and is used to install or hang the counterweight. The counterweight may be a common counterweight. The pressure shaft is a structure similar to a pressure roller installed on the counterweight frame,and its position is close to the end where the counterweight frame is connected with the connecting shaft of the 20 high rolling mill. The vertical rotation of the counterweight frame around the connecting shaft presses the pressure shaft against the surface of the steel strip. At this time,the counterweight frame and the counterweight block exert a compressive stress on the steel strip under the action of gravity. The pressure shaft and the counterweight frame are connected by bearings. When the steel strip is running,it can drive the pressure shaft to rotate synchronously around the axis of the pressure shaft,so as to avoid scratching the steel strip during the tension calibration process.

2.2 Counterweight frame design of tension calibration device

The counterweight frame is the main equipment of the calibration device. The counterweight frame is designed according to the fixed size of the existing roll system structure of the 20 high rolling mill in service in the rolling Center Laboratory of a university. As shown in Figure 2,the counterweight frame includes the pressure shaft,the counterweight frame and the connecting mechanism. Among them,the counterweight frame is 960 mm long,and a through-hole for hanging counterweight is reserved at the center of the intermediate plate every 160 mm. The counterweight frame is 200 mm wide,and one end is connected with the connecting shaft of the counterweight frame of the 20 high rolling mill. As shown in Figure 1,the pressure shaft on the counterweight frame is pressed on the tested steel strip to make the steel strips on both sides of the pressure shaft form a certain angleθ2. This angle varies with the counterweight and position. The counterweight frame′s own gravity(m1g)and the counterweight weights′gravity(m2gandm3g)form an acute angle with the counterweight frameα,The supporting forceF′of the strip steel reacting on the press shaft forms an acute angle with the counterweight frameβ.

Figure 2 Structure diagram of counterweight frame

2.3 Design of strip steel fixture

As shown in Figure 3,the steel strip holder is a welding structure designed according to the angle between the 20 high rolling mill platform and the steel strip in service in the rolling Center Laboratory of a university. The two sharp corners contacted by the strip steel shall be chamfered R5,and the top end shall be at an angle of 15°with the platform. The steel strip holder is fully welded with the platform of the 20 high rolling mill to ensure the maximum tension of the steel strip. Then press the steel strip with the cover plate and fix it on the steel strip fixing frame with 6 M12 high-strength bolts. In this way,the stability of the strip steel in the tension calibration process can be guaranteed.

Figure 3 Structural diagram of strip steel fixed fram

2.4 Check of output shaft of reducer

The output shaft of the reducer is made of Q345 and is subject to the pressure of the strip steel. When the output shaft radius of the reducer isr,the strip steel width isb,the strip steel thickness ish,and the actual tension of the 20 high rolling mill isT=600～3 000 N,as shown in Figure 4.

Figure 4 Schematic diagram of reducer output shaft stress

According to the balance equation in the coiling process of the cold rolled strip:

Pr=σ0

(1)

T=σ0br

(2)

Where,σ0is the bending stress per unit length of the strip steel acting on the output shaft of the reducer.

From formula(1)and formula(2),we can get

Pr=T/br

(3)

According to formula(3),whenTis the maximum value,the output shaft of the reducer receives the maximum compressive stressPmax. As shown in Figure 4a),the output shaft of the reducer is equivalent to a cantilever beam. When the middle is subjected to uniform pressureP,the torque and shear force at the fixed end are the largest,calculateMmax,and look up the table to get the maximum bending moment anti torsional section coefficientWzand the maximum bending normal stress[σ],Allowable shear stress[τ]. First,ensure the maximum bending normal stressσmax=Mmax/Wz≤[σ];Secondly,the maximum pressure on the fixed end of the cantilever beamFmax=Pmax×b×ω×r. Among them,ωis the center angle corresponding to the contact area of the steel strip on the output shaft of the reducer,the cross-sectional areaAof the cantilever beam,and the allowable shear stress[τ],Therefore,the maximum bending shear stress should be ensuredτmax=Fmax/A≤[τ].

Through the above-mentioned verification method of the reducer output shaft,the bending normal stress and bending shear stress of the reducer output shaft under the maximum set tension can be controlled within the safe range,which can improve the safety and stability of the 20 high rolling mill in the tension calibration process.

Based on the rolling principle of the 20 high rolling mill,the coiling principle is studied[11-15]. According to the overall design diagram of the calibration device,the calibration principle flow chart is sorted out in Figure 5.

Figure 5 Calibration principle flow chart

When different weights of counterweights are selected and connected to different positions on the counterweight frame,the actual tension corresponding to the current set tension of the 20 high rolling mill is calculated. The specific calibration principle is as follows:

1)Obtain the set tension Tset of the current 20 high rolling mill and the massm1of the counterweight frame;

2)Determine the massm2of the counterweight and the connecting position of the counterweight on the counterweight frame. Wherein the distance between the connecting mechanism connecting the counterweight and the connecting shaft isL;

3)Determine the included angle between the counterweight frame and the vertical directionα,included angle of strip steel on both sides of the pressing shaftθand the included angle between the stress direction of the steel strip reacting on the press shaft and the counterweight frameβ;

4)According tom1,m2,L,α,β,θ,determine the current actual tension tact of the strip steel;

(1)According tom1,m2,L,α,β,as shown in Figure 1,according to the moment balance,calculate the stress of the strip steel acting on the press shaft,that is

F′=(km1g+Lm2g)×sinαisinβ

(4)

(2)According to the stressF′(F′=F)andθ,as shown in Figure 6.

Figure 6 Actual tension conversion diagram

The current actual tension Tact of the strip steel is determined according to the force balance,that is

(5)

5)Changing the set tension Tset of the 20 high rolling mill,repeating the above steps to obtain a mapping relationship between the set tension and the actual tension;

6)Control strip steel production according to the mapping relationship.

4.1 Actual tension calculation steps

This paper refers to the relevant 20 high mill control literature[16-20],and then designs the specifications of the counterweight frame according to the actual dimensions of the 20 high mill in the rolling Center Laboratory of a University(Figure 1),the length of the counterweight frame is 960 mm and the width is 200 mm. The counterweight frame is provided with 6 connecting beams for hanging counterweights. According to the distance from the connecting axis,the distance from each connecting beam to the connecting axis isa,b,c,d,e,fin the order from near to far. The spacing betweena-fis 160 mm. The weight of the counterweight frame itself ism1=12.5 kg,and two counterweights are prepared using the counterweight. Their weights arem21=20 kg,m22=40 kg. 0.8 mm×100 mm can be selected for tension calibration,surface roughnessRaless than 0.8 μm of 304 stainless steel flexible belt. When connecting counterweights of different weights to different positions on the counterweight frame,the actual tension corresponding to the current set tension of the 20 high rolling mill is as follows:

1)The included angle formed by the steel strips on both sides of the compression shaft isθ1. The included angle between the stressF′and the counterweight frame isα1. The included angle between the counterweight frame gravitym1gand the counterweight frame isβ1. Taking the connecting shaft connected with the counterweight frame as the axis point,according to the principle of moment balance,the following is obtained as

F′1=3m1g×sinα1/sinβ1

(6)

Where,k=3 is the constant actually determined according to the current counterweight frame and counterweight specifications. Then,according to the force balance,the actual tension of the strip steel at this time can be obtained as

(7)

2)Install the configuration weight with massm21=20 kg(i.e. the connecting beam with distanceL=afrom the connecting shaft)at pointa. At this time,the included angle formed by the steel strips on both sides of the compression shaft isθa21;the included angle between stressF′and counterweight frame isαa21;the included angle between the counterweight frame gravitym1g,the counterweight weight weight gravitym2gand the counterweight frame isβa21,with the connecting shaft connected with the counterweight frame as the axis point,according to the principle of moment balance

F′a21=(3m1g+am21g)×sinαa21/sinβa21

(8)