The blackening performance of castings processed by sand blasting and shot blasting in Dalian: after shot blasting, if the overall surface of the casting is blackened or there are obvious black marks and black spots in some parts, some can be thrown away, while others have been immersed in the casting matrix, and the area and position are not fixed.

Cause analysis: defects existing before shot peening brought by die-casting process: too much black oil is used in die-casting; Punch oil splashing during die opening; Paint splashing during die casting; The product is placed for a long time or the temperature is humid, and the surface is corroded, moldy or seriously dusty. The dust removal device of shot peening machine fails, and the steel shot contains more dust. The operator did not wear gloves as required, and directly contacted the casting surface after shot peening with his hands, resulting in fingerprints. After shot peening, it is placed for a long time, there is dust or splash on the surface, water and oil are added, and the environment is humid and oxidized.