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Defects that Easy to Occur on Galvalume Steel Coil



Due to the process characteristics of the galvalume steel coil, it is prone to occur some defects. In addition to the surface, the coating is loose, the galvalume steel coil is also prone to occur the following defects:


1. Skip plating

Due to the high melting point of the aluminum-zinc alloy, the oxide film on the surface is thick, aluminum-zinc melt has poor wettability to the strip. So the hot-dip galvalume steel sheet is easy to cause skip plating defects. Because of the tension of the liquid coating on the edge of the strip is big, it is easy to be peeled off from the strip and leave a bare strip. And the black edge will be seen after coiling.


2. White coating

The reaction of Al-Zn is violent, and despite the addition of silicon can suppress its reaction, this reaction will still proceed rapidly. If the reaction time is too long, the temperature is too high, it will make the compound layer between the coating and the strip thickness. The coating has a bad binding force with strip, that forms the white coating. And it is very easy to dissolve during processing.


3. Dross and stamping

Another result of the intense aluminum-zinc reaction is more production of slag. A large amount of iron dissolved in the melt, forming a lot of aluminum and iron compound slag. Its density is greater than the aluminum-zinc melt, so all sink in the lower part of the plating pot and become the bottom slag, it must be regularly salvaged. At the same time, a large number of slag sticks to the sinking roll and the stabilizing role, creating a stamp on the strip.


4. Scratch

During the production of galvalume steel sheet, due to the more slag, complex composition, serious segregation, there is easy to occur scorification or solidification in furnace nose, affecting the strip through the line and scratch the strip.


5. Small dimples

Small dimples are unique defects of hot dip galvalume steel sheet. It refers to the round pit that irregularly distributes on the surface of the galvalume steel sheet. Its diameter is 0.5 ~ 1.5 mm, and the cladding material of pits is lower than somewhere else.


6. Strip breakage

As the corrosion of aluminum-zinc-silicon liquid to steel strip is very serious, such as the malfunction of the production line. The strip is easy to be corroded if the time in the zinc pot soaking is slightly longer, resulting in strip breakage.



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