In the industry, galvanized sheet is a common equipment, widely used in construction, household appliances, vehicles and ships, container manufacturing, mechanical and electrical industry and other industries. So, in the use of galvanized steel processing, appear blackening is caused by what reason? Next, Jinan galvanized sheet will take you to know:
Causes of blackening of galvanized sheet
Jinan galvanized sheet
1、 Types of blackening on the surface of pure zinc coated steel plate
There are two common types of surface blackening: dirt (foreign matter attached to the surface of the coating) and processing (change of coating surface characteristics during processing). Of course, in actual cases, these two types may exist at the same time.
2、 Identification of dirty black spots
The most common source of dirt is oily zinc dust, such as the oil accumulated on the cutting felt.
Identification: this kind of black spot belongs to the foreign body attached to the surface, so it can be reduced or removed by wiping. Even when it's dry, you can see a sharp outline.
Black spots of dirt can often be identified by observing parts.
3、 Identification of machining black spots
There are many reasons for black spots in processing. The surface roughness of zinc coating is changed due to friction, or zinc powder accumulation caused by friction or oxidation of hot-dip galvanized coating (affected by coating composition) may form black spot morphology.
Identification: the black spots in processing must be analyzed in combination with the production process. When the black spots are found on the parts, the law on the parts should be determined first, whether the whole part appears uniformly or a certain position rule appears.
After determining the law, reverse check on the processing line to find out the process without black spots at the inlet and outlet. The black spots in machining are usually caused by friction between steel plate and equipment. The adjustment also focuses on reducing the clamping force of clamping device, reducing the roughness of concave convex die, improving lubrication, shortening the cleaning cycle of mould and adjusting the belt speed.