What kind of situation is called blackening after shot blasting

　　After the casting is shot peened, the whole surface is blackened or there are obvious black marks and black spots locally. Some can be thrown away, while others have been immersed in the casting matrix. Area and location are not fixed.

　　Cause Analysis:

　　1. Defects that existed before the shot peening brought by the die casting process:

　　(1) Too much black oil is used in die casting;

　　(2) Punch oil splashes when the mold is opened;

　　(3) Paint splashes during die casting;

　　2. The product is placed for a long time or the temperature is humid, and the surface is corroded, moldy or dusty.

　　3. The dust removal device of the shot blasting machine fails, and the steel shot contains a lot of dust.

　　4. The operator did not wear gloves as required, and directly touched the surface of the casting after shot peening, resulting in fingerprints.

　　5. After shot peening, it will be placed for a long time, and there will be dust or splashes on the surface with water and oil, and the environment will be humid and oxidized.

　　Corresponding measures:

　　1. Defects are not spread over the entire casting surface. Strengthen the control and management by the die-casting process.

　　(1) It is black oil, the color is black;

　　(2) It is punch oil, dark red in color;

　　(3) It is a paint, and the color is different from the light color of the casting surface;

　　2. After shot peening, the surface traces are shallow and cannot be removed because they have been immersed in the casting matrix. Strengthen the management of product placement, and it should not be too long. If it needs to be placed for a long time, it must be covered and protected and placed in a suitable environment;

　　3. The color of the entire casting surface is black and dark. Restore dust removal or replace with new steel shot;

　　4. The author must operate according to the operation instructions. Gloves must be worn.

　　5. Final inspection, packing and storage should be carried out as soon as possible for shot peening. If it needs to be stored for a period of time, strict protection must be carried out.