Description: Discuss the deviation of the strip due to various factors, and analyze and solve the deviation of the strip during the production process of the pickling mill.
Keyword: Mill rolls, rolling rolls, hot rolling strip
Related Product: https://lmmrolls.com/
The pickling and tandem rolling mill of the cold-rolled plate factory connects the front and rear coils of strip steel through the welding machine in the population section, so that the strip steel of the production line can run continuously, but the total length from the population uncoiler to the export coiler is about More than 1,000 meters, various equipments are required on the way, and strip deviation is prone to occur. Although there are 8 sets of CPC correction devices on the production line, which can automatically correct the strip steel, in actual operation, it is found that the strip steel in the looper often deviates seriously and cannot be corrected by the correction device, forcing the production line to have to Reduced speed or even shutdown has seriously affected production output, product quality and equipment safety. For this reason, it is necessary to analyze the deviation of strip steel and adopt effective methods to control it.
Reasons for strip deviation
During operation, the strip deviates from the center of the production line and moves to one side of the roller, which is called “strip deviation”. The strip runs on the conveyor roller. As long as the strip is in contact with the surface of the roller and is within a certain frictional resistance limit, the points on the strip will travel at right angles to the center line of the roller. Assuming that the strip has a good shape and a uniform section thickness, the tension on the strip is evenly distributed, and the rollers are kept parallel and perpendicular to the running direction of the strip. Then the strip will not run off the rollers. That is, the strip runs at the center of the production line at all times.
However, in the actual production process, there will be various factors that affect the normal running trajectory of the strip steel, which will cause the strip to deviate.
- The influence of the defects of the strip itself
If the thickness of both sides of the strip is different, the strip itself forms a sickle shape. When the strip runs as shown in Figure 1(a), the ideal strip operation is shown in Figure 1(b), assuming that the strip has the left Convex sickle bend, the situation shown in Figure 1(e) will appear. The CD line is the tangent contact line between the strip and the roller when the A’C section of the strip turns to the roller. When A’B’ reaches the roller , The point A’on the left will fall on the left of point C. At this time, the deviation distance of the A’C section of the strip after entering the steering roller is f= A’C×sinβ. Similarly, when the strip has the right When the convex sickle bends, it will cause the strip to move to the right on the steering roller. The amount of deviation is related to the degree of the sickle bend, the spacing of the steering rollers, and the size of the strip tension.
There are also various other plate defects, such as middle wave, edge wave, longitudinal bending, transverse bending, etc., plus the difference in width, thickness, hardness, and surface roughness everywhere, so that the strip can not be evenly attached to the steering On the roll, these asymmetry factors will produce a lateral force perpendicular to the running direction on the surface of the strip in contact with the steering roll. Under the action of this lateral force, the strip slips laterally, which causes the strip to deviate.
- The influence of the roller
The roll is processed into a cone shape during manufacturing, or the single-sided abrasion caused by the edge wave of the strip steel is tapered, which makes the strip tension distribution uneven, so the strip steel always deviates to the thick end. The amount of deviation is related to the taper.
In addition, the surface quality of the roll surface will also affect the deviation of the strip, such as uneven surface roughness, damage to the roll surface, oil stains on the roll surface, and so on. In severe cases, the strip will slip on the steering roller, further aggravating the deviation.
- The influence of other factors
There are other interference factors such as strip temperature, tension fluctuation, equipment installation accuracy, etc., which will also affect strip deviation, and these factors are intertwined and interact, so accurate analysis is very difficult. Through long-term and careful observation, we can see that when all other working conditions remain unchanged, increasing the strip tension will reduce the amount of strip deviation. Under the condition that all other working conditions remain unchanged, the deviation caused by the long free conveying section of the strip is larger than the deviation caused by the same length with a steering roller in the middle.
Analysis and solution of the problem of strip deviation in the looper
The 3# and 7# sample deviation correction devices are used to correct the strip steel in the population looper and the 2# exit looper, and the correction range is ±150mm. During the observation, it was found that due to the longer length of the looper, about 200 or 300 meters, and the large number of support rollers, the strip steel deviated more and more severely after passing through these rollers, which has exceeded the deviation correction range of the deviation correction device, resulting in The production line stops automatically. as shown in picture 2. As long as we can find ways to reduce the deviation of the strip in the looper and control it within the allowable range of the correction device, the normal operation of the production line can be guaranteed.
Since the bearing seat bracket of the support roller is fixed in the original design, the support roller cannot be adjusted (see Figure 3a). For this reason, we modified the original fixed bearing bracket bracket, and added 2 waist-shaped holes on the bracket so that the rollers can be adjusted (as shown in Figure 3b). In this way, we can rotate the supporting rollers that were perpendicular to the centerline of the production line to a certain angle, and install several pairs of eight-shaped rollers in the looper. As shown in Figure 4, assuming that the linear velocity of the roller surface is V, under the action of the friction between the strip steel and the support roller, a sub-velocity VlVl (V1=V×sina) will be generated for the strip steel, so that the strip steel is in There is a tendency to slide toward the center in the lateral direction, and this tendency increases with the angle and the contact surface between the strip and the roller. In this way, the strip can be self-centered when running on this kind of support roller, thereby greatly reducing the deviation of the strip in the looper.
Before the transformation, due to the deviation of the looper, the production line slowed down, and even manual operation problems occurred every month, ranging from a few times to as many as a dozen times, and it was even more frequent for thick steel strips above 3.5 mm. . After the transformation, the problem of strip deviation in the looper has been effectively solved, and it has been completely controlled within the allowable range. From the completion of the equipment transformation to the present, there has been no accident that caused production due to strip deviation. . It can be said that the transformation has been a complete success, effectively ensuring the safe, stable and high-speed operation of the production line.