1 raw material surface defects. Such as scratches, pitting, soaking and so on. 

2 Health-grade pipe fittings material problems. The hardness is too low, it is not easy to be polished when polishing (poor polishing), and the hardness is too low, and the surface is prone to orange peel phenomenon during deep drawing, thereby affecting the polishing property. The polishing property with high hardness is relatively good. 

3 After deep drawing, the surface of the area with a large amount of deformation will also have small black spots and RIDGING, thus affecting the polishing property.