The process requirements of hot-dip galvalume steel sheet during production id higher than galvanized steel, below are its main performance:
1. The hot-dip galvalume steel sheet has high melting temperature. And it also has high requirements to the fluctuations of plating bath temperature.
2. The temperature when steel sheet enter into pot during galvanization must be less than the temperature of the plating bath. And this can not adopt the method that raising the plate temperature to heat the solution. So the pot is normally in a heated state.
3. Al-Zn-Si melt also has a stronger corrosive effect on refractory material than Zn melt. The erosion loss on the pot, in particular the sensor channel is serious.
The higher temperature and aluminum content of Al-Zn-Si melt make the reaction of Fe and Al is very intense. This results in a large amount of Fe dissolved into the melt and forming a large number of slag. CAMELSTEEL found that their fundamental different with the galvanization is that the difference between the proportion of slag and melt.
Some iron-zinc compound slags have higher proportion than galvanizing zinc, sinking in the bottom of the pot to become the bottom slag. These have similar proportion with galvanizing zinc, suspending in liquid zinc and become floating slag. And they also have lighter proportion than galvanizing zinc, floating in the surface of cadmia and become the top slag.
However, the proportion of the Fe-Al compound slag is all larger than that of the melt, and mostly deposited on the bottom of the pot or on the parts inside the pot. The biggest danger of Fe-Al compound slag is to fall on the sinking roll and the stabilizing roller and forms accumulation tumor, then make the strip produce stamp. In serious cases, straightening machine can not flattening and affecting the final product quality.
Nodules formed by aluminizing are generally flaky lumps, rather than punctiform or clumpy during galvanization, with no sharp corners, and are relatively easy to remove when straightening. When nodular has been exist in the roll, staff can use slag scoop made of heat-resistant material to scrap. Its difficulty is slightly easier than the galvanized steel sheet.