1. Scratches caused by zinc pot rolls
Scratches caused by zinc pot rolls are an important cause of galvanized product scratches, which account for most of the scratch problems. In general, the zinc pot roll is mainly sunk
The roller is composed of a correction roller and a stabilizing roller. It is in a special position in the zinc solution, which is not conducive to setting a motor to realize transmission. For this reason, many zinc pot rollers are passive rollers, mainly using the steel surface and the stick surface of the zinc pot roller. The frictional force between the rollers and the strip steel rotates at the same speed. However, due to the changes in the composition of the zinc solution and the application of the zinc pot roller and other related factors, the relative friction between the steel strip and the sinking roller due to insufficient transmission friction force caused the zinc pot roller to be scratched.
2. Air knife streak problem
If the air knife nozzle is partially blocked, the zinc layer at the corresponding position of the strip will pass through and produce streaks. The occurrence of streak is generally due to the sudden change of the pressure of the air knife when the production line speed changes greatly, resulting in the zinc liquid splashing, which blocks the air knife, or the distance between the air knife and the strip is relatively small, and the incoming material scoops The uneven heating of the strip and the tension of the strip are too small, etc. will cause the scraper of the strip to block, resulting in streaks. In this regard, the staff should effectively control the amplitude during the lifting process of the production line, and pay attention to the shape of the incoming material. If the shape is relatively poor, the air knife spacing should be adjusted in time, and the tension and stabilizing roller should be adjusted. Complete reasonable adjustments to ensure that the strip can obtain a relatively good straightness in the middle of the air knife nozzle to avoid blockage of the strip steel scraper. If the air knife streak is generated, the air knife should be quickly opened at the weld and cleaned up with professional equipment.
3. Missing plating point
The missed plating point mainly refers to the unplated area that appears incompletely wetted during the hot dip plating process. In the process of hot-dip galvanizing, only by thoroughly eliminating the scale and oxides of the substrate rolling and the cleaning liquid, and at the same time exposing the relatively clean substrate surface, can we ensure good wettability. Under normal circumstances, steel rolling mills produce automotive outer covers in zinc solutions with Al content exceeding 0.2%. The hot-dip galvanized steel sheet produced in this type of zinc pot is relatively bright, but when the zinc solution reaches the Al content, in order to obtain good wettability, there are stricter requirements on the cleanliness of the substrate surface. Steel plates with relatively high strength usually have related alloying elements such as C, P, and Si. At the same time, these alloying elements may segregate during the heat treatment process, thereby forming oxides on the surface of the steel plate. In this regard, the Si contained in the substrate will cause more leaked plating points, which seriously affects the wettability.
4. Pit
The coating at the pit defect location is much thinner than the nearby coating, which is caused by the abrasion of the solidifying coating when passing through the air knife and small zincification equipment. Judging from the morphology angle, the pit is mainly caused by the impact of small droplets formed by the small zincation equipment. When the coating passes through the air knife, the solid particles will be blown out of the coating by air, because the coating is already reflowed or semi-cured, and the copper wire pits are difficult to be flattened by the nearby coating.
