Excess Aluminum in Galvanizing Bath
Another type of surface defect, shown in the image below, is caused by an excess amount of aluminum in the galvanizing bath. This creates bare spots, seen as black marks, on the surface of the steel. The part may be repaired only if small areas of bare spots are evident. If this condition occurs over the entire part, the part must be rejected, stripped, and regalvanized.
We are facing the problem of Black spot in the packed GI sheets. While receiving from our supplier we are not finding such defects.This is happening at our customer end after we completing our process like Punching , Bending , Pemming , assemblly & packing in corrugated box. What we can do to elimiate such defects? pl. help me.
How does the Aluminum get into the hot dip galvanizing bath?
Suthkar,
For questions about galvanized sheet, the correct organization to contact is the Galv Info Center, who are a trade association for the galvanized sheet industry. Their website is www.galvinfo.com and their phone number is 888-880-8802.
The American Galvanizers Association (AGA) specializes in after-fabrication hot-dip galvanizing where the steel is fabricated, cleaned, and then dipped into a kettle of molten zinc. This process is very different than the process used to galvanize sheet steel.
Dave,
Aluminum is added directly to the kettle. It usually comes in special alloys with zinc to ensure even melting into the zinc kettle. Not all galvanizers use aluminum in their kettles.
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