The problem of over-galvanizing on the edges of galvanized steel plates seriously affects the normal operation of the production line, often resulting in a large number of defective products and significant material waste. Therefore, it is essential to address this issue from the perspective of reducing waste and improving production efficiency.
Reducing the production line speed can help minimize over-galvanizing on the side edges. Alternatively, you can first lower the air knife pressure to reduce overall galvanizing thickness. By producing products with slightly lower zinc coating content for a short period, it is possible to quickly resolve the issue without causing excessive waste.
Generally speaking, over-galvanizing at the edges most commonly occurs when the galvanizing amount is too high while the air knife pressure is too low. In such cases, appropriately increasing the air knife pressure often produces good results.
Next steps for diagnosis:
It is important to distinguish whether the problem is caused by raw material issues, zinc pot temperature problems, or improper air knife parameters.
- Raw material problems: If the edge appears rough, white, and lacks gloss, it is often due to slag or impurities in the zinc pot. Check the raw materials carefully for edge trimming issues, cracks, or jagged edges.
- Crystallization issues: If the edge of the steel strip shows signs of crystallization right after exiting the air knife, and the zinc flower on the edge appears particularly large after cooling, this is usually caused by low zinc pot temperature.
- Air knife parameter mismatch: If the edge of the galvanized steel plate is relatively smooth and the thickness 4-10mm away from the edge is normal, the over-galvanizing is likely due to improper air knife settings.
Recommended solutions:
At this stage, carefully adjust the air knife angle first, ensuring the front and rear angles of the air knife (especially domestic Kohler air knives) are offset by only 1°-2°. At the same time, minimize the distance between the air knife and the steel belt as much as possible.
If the above methods still cannot completely eliminate edge over-galvanizing, you should stop the line to further adjust the air knife gap at the edge position — making the gap larger to increase the zinc scraping force on the edges.
