Mill Surface Defects

Buildup

This defect looks like thick bands of zinc lines or a single mottled band along a coil edge. It can also look like lines of zinc in the center width of the coil. This defect is also known as spooled edge, lines in zinc, or heavy zinc. This defect can occur if the air knife that’s positioned above the zinc bath becomes extremely plugged by debris. As a result, the zinc does not blow off evenly across the surface which gives the lathered, appearance. The defect is usually worse on a coil edge and leads to spooling and wavy edges. This defect is what galvanizing line pot operators try to correct when they make a die clean out mark or air knife clean-out mark. Learn about other mill surface defects.