After being hot-dip galvanized in batches, iron and steel products can obtain better corrosion resistance and can have a life span of more than ten to several decades under atmospheric exposure. At the same time, due to the small investment in bulk galvanizing and the simple process, it can dip steel structures of various configurations, sizes and thicknesses, such as transmission towers, street light poles, highway guardrails, microwave towers, etc. Articles are an extensive and economical method of corrosion protection.
However, the surface of the galvanized sheet is relatively smooth when the surface of the galvanized sheet is not wiped with an air knife during batch galvanizing, and sometimes small hard particle protrusions appear on the surface of the galvanized sheet, and the surface of the galvanized layer is rough. These particles will seriously damage the surface appearance of the plated parts and affect the market competitiveness of the product.
According to analysis, the causes are:
1. The reason for the rough particles on the surface of the hot-dip galvanized steel products is that there are a large number of iron filings connected to the substrate on the surface of the substrate. After entering the zinc pot, these iron filings react violently with the zinc solution to produce explosive structures with extremely thick thickness. As a result, rough small particle defects are formed on the surface.
2. The cause of deep-level iron filings is caused by the "scaling of the scale" during the hot rolling of the substrate. In the subsequent pickling process, the scale that has been pressed into the substrate is dissolved by the acid, and the rest is lifted. Or raised iron sheet forms iron filings.
For the causes of rough particles on the surface of hot-dip galvanized steel products, the control measures are:
1. At the exit of the continuous casting slab or at the exit of the flat-plate heating furnace, a very thick scale ("primary scale") formed on the surface of the slab should be completely removed, so as not to cause a lot of surface quality problems in subsequent processes.
2. The high-pressure water descaling during the rough rolling process must be thorough, and the quality must be strictly controlled. The temperature of the slab during the rough rolling process is high, and scales are easily formed between passes ("secondary scale"). The effect of descaling by high-pressure water between passes, such as the scale is not cleaned, is brought into the finishing rolling process, which results in the "scale intrusion" defect.