1.If the scratch occurs in the longitudinal direction of the tempered glass: 

Check whether there is debris on the rollers in the heating oven and cooling section; 

Check if there are foreign objects or broken glass pieces between the rollers in the heating oven and cooling section; 

Check if the heating oven door is in contact with the upper or lower surface of the glass.

2.If the scratch occurs in the lateral direction of the tempered glass: 

Check whether the glass in the heating oven bumps into the furnace door; 

Check if the drive encoder of the furnace works properly; 

Check if the data of the photoelectric switch at the entrance of the furnace is correct.