Analysis of Causes of Contusion Defects in Hot Rolling Sheet Flattening Production Line

　　In recent years, with the many applications of hot rolled coils, especially thin gauge products in the automotive industry, construction occupation, compressor occupation, etc., users have continuously improved the quality requirements of hot rolled coil shape. In order to achieve better shape quality, the hot rolling flat process is increasingly used in the improvement of the shape quality. However, the hot rolling flat process also brings a lot of appearance quality defects. In the meantime, the damage defects are the most extensive, and the impact on the appearance quality of the strip is also the most severe. As for the production of some thin standard plate strips, the disadvantages of injury often occur in the flat process.


　　The shortcoming of the damage is the silvery white scratch on the outer surface of the strip. It is mostly spread in clusters and flakes, and the damaged head is sharper. The damage is formed by the sliding inside the coil, which is presented together on the upper and lower sides of the strip. The damage defects are mainly presented on thin standard strips (thickness ≤ 3.0mm), which are less likely to appear on thick standard strips. Damage is a common shortcoming of the appearance quality of the flat production line. It not only has a great impact on the customer's application, but also greatly reduces the yield. Therefore, it is necessary to analyze the various influencing factors of the onset of injury defects, and adopt corresponding measures in the production to prevent the appearance of damage defects.


　　The whole process is: steel coil preparation station → unwinding machine unwinding → wearing belt → straightening machine → flat machine → coiling machine → unloading trolley → bundling, weighing, spraying → steel coil storage. In order to prevent the shortcomings of the flat process, the following preventive measures should be adopted.


　　In terms of material: hot-rolled strip head, tail contact and work roll bending force and balance force transformation, the shape of the plate is the worst, not only easy to lead to excessive gaps between the layers, and the wave-shaped peaks and troughs of the waves are more likely to cause damage. Therefore, it is necessary to continue to optimize the shape control function and make the balance force and the bending force as close as possible.


　　Flat unwinding operation: In addition to the relief of the shape of the plate and the shape of the roll, there is no useful way to prevent other elements that do not smooth the surface of the board; therefore, it is only possible to prevent the curl from being used as a layer to slide.


　　Roll-up operation: After the coil is placed on the unwinding mandrel, the operator manually rotates the unwinder together when the mandrel is expanded. When the mandrel is opened and forwarded to drive the outer ring of the coil, the operation is immediately suspended. The operating mandrel is retracted back to its original orientation. Repeat the above operation 3 to 5 times to wind the strip layer.


　　Tension control: In principle, the tension of the flat uncoiler should be less than the take-up tension of the hot-rolling coiler, but because the thin standard is simple and loose, the actual unwinding tension should be much smaller than the take-up tension. Together, the tension should be prevented from changing drastically. Especially when unwinding, the tension should change steeply. It takes 2~3s to progress from 0 to the set value.


　　Speed control: When the flat thin standard strip is used, the unwinding speed is too fast, which will cause the unwinding tension to shake sharply, so that the coil will slide between layers. Therefore, the flat speed should be appropriately lowered.


　　In summary, the causes of the injury shortcomings can be summarized as follows:


　　(1) The onset of injury defects, similar to the grinding effect, the two layers of steel stripped together are relatively sliding, and the plastic deformation of the meshing part reaches a critical value, and the part of each kneading shears slips and forms After the metal shavings, the metal shavings are continuously scraped and piled up, so that the damage defects are agile and deteriorate.


　　(2) The shape of the hot-rolled strip head and the tail part is poor, which not only makes the belt roll slide between layers, but also causes partial touch pressure.


　　(3) The radius of curvature of each circle of the coil is suddenly changed by the margin of the winding head, the tail part and the mandrel. When there is interlayer sliding, the partial pressure is too large and the damage is caused.


　　(4) After controlling the material condition and the precision flat operation, the layer slide between the rolls when the roll is opened can reach the intention of eliminating the defects of the damage.