Reasons for pot defect of polished aluminum sheet metal

The polished aluminum sheet metal is among the most popular aluminium mirror sheets for its excellent performance and luxurious color. In a previous article we discussed several reasons for pot defect of the sheet. Here we will proceed to deal with the other two reasons: damp wrapping paper board and inappropriate cleaning process.

Paper or cardboard is used to separate or wrap aluminium mirror glass sheets to avoid scratches. Damp paper leads to corrosion of the sheet surface. Paper (board) corrosion is caused by acid radicals, which are present in the paper. Therefore, the use of paperboard without chloride and sulfate and avoiding water seepage is an effective method to solve paper corrosion.

When an aluminium sheet is washed by alkali, sulfuric acid or chemically polished, the star wash or radiation spots sometimes appear. The corrosion depth left on the surface of a mirror finish aluminum sheet is very shallow, and the cleaning water might have been seriously polluted or the flow rate of the overflow water washing might be low. The reason is that the zinc in the aluminum material reacts with other chemical elements in the washing water. Adding 1% HNO3 with nitric acid deashing or washing water will eliminate the spots.