Rolling mill deviates, steel strip is unstable? Identify the cause and adjust it once and for all.
The most troublesome problem in the steel rolling workshop: The steel strip keeps deviating left and right while moving, constantly swaying and shaking. It sometimes scrapes the edges, forms waves, and has unstable width. It also easily causes steel piles and waste steel, which not only wastes raw materials but also delays production.
Many people blindly adjust the roll gap and forcefully manipulate the guide mechanism, making the situation even more chaotic with each adjustment. In fact, the deviation of the steel strip and the instability of its movement are not caused by random adjustments. The root cause lies in a few fixed points. Once the reasons are identified, the problem can be solved once and for all, and the stability can be maintained for a long time.
1. Uneven heating of the steel billet, inherent hardness and softness of the billet
There is a significant temperature difference between the left and right sides of the steel billet, and insufficient heating at the edges and corners. This can result in one side having good plasticity while the other side has high hardness. After entering the rolling process, the elongation rates are different, causing the steel strip to deviate towards the side with greater resistance. The overall sense of vibration of the steel strip is very strong. Solution: Standardize the movement path within the furnace to ensure uniform heating of the steel billet in all directions (left, right, and up and down), and completely eliminate uneven heating and black corner billets from being put into production.
II. Uneven wear of the rolls, inconsistent roll gap on the left and right
Severe wear on one side of the roll, imbalance in the roundness of the roll body, or asymmetry in the adjustment of the roll gap on both sides. One side has a large pressing force while the other has a small pressing force. The steel strip will be subjected to force imbalance and inevitably deviate towards the side with less pressure. Solution: Regularly inspect the wear of the rolls, promptly repair and replace the rolls; stop the machine to level the roll gaps on both sides and ensure that the pressing forces on both sides are uniform and consistent.
III. Asymmetry in cooling spray, imbalance of cold and hot stress
The flow rate, pressure and spray angle of the cooling water on both sides are different. One side has stronger cooling while the other side has weaker cooling. The contraction rates on both sides of the steel strip are different, resulting in internal stress, causing the steel strip to deviate while walking and warping and twisting on the surface. Solution: Uniformly calibrate the spray pipes and nozzle angles on both sides, block the nozzles and clear them in time to ensure balanced and synchronous cooling on both sides.
4. Roll alignment deviation, hidden load on bearings
Roll misalignment during installation, misalignment of the frame, elliptical wear of the bearing housing, and running with eccentric load. Although there seems to be no abnormal noise from the equipment, in fact, the centerline of the rolling process has shifted, causing the steel strip to lose its reference point and move erratically throughout the process. Solution: Regularly conduct checks on the coaxiality of the roll system and the alignment of the frame; when replacing bearings, always check for wear on the bearing housing to prevent eccentric and load-bearing issues that cause the steel strip to be misaligned.
V. Inconsistent matching between rolling tension and line speed
The speed ratio between the front and rear frames is unreasonable, and the tension fluctuates greatly. The steel strip is subjected to uneven pulling force. In mild cases, it may sway left and right and deviate; in severe cases, it may suddenly pile up steel, scrape the edges and be scrapped. Solution: Optimize the speed parameters of each frame, stabilize the micro-tension control, and avoid sudden acceleration and deceleration as well as forcibly pulling the steel strip.
Summary at the end of the text
If the rolling mill is running off-center and the steel strip is unstable, don't blindly adjust randomly. The core issues can be attributed to five main causes: uneven temperature of the billet, wear of the rolls, asymmetrical cooling, misalignment of the roll system, and imbalance in tension and speed. By systematically checking each of these points and identifying the root causes, the problem can be resolved in one go, ensuring that the off-centering does not result in waste of steel, while also stabilizing the quality of the finished product, reducing losses and avoiding unnecessary work.
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