Why the surface of the steel shot is black after shot blasting

　　After the casting of our steel shot is completed, in order to improve the surface finish of the product, improve the service life and quality of the product, we generally have to process the casting, and this work is shot blasting. After shot blasting, different problems may also occur, such as blackening, so why is it blackening? Let's find out together.

　　Blackening performance of steel shot after shot blasting:

　　After the casting is sprayed, if the overall surface is black or there are obvious black spots or spots locally, it is a bit suspicious and thrown away, and some have been immersed in the casting matrix, and the area and position are not fixed.

　　Cause Analysis:

　　1. Defects brought by the die-casting process before spraying:

　　(1) Excessive black oil used in die casting;

　　(2) Punch oil splashes when opening the mold;

　　(3) Paint splashing during die casting;

　　2. The product has been placed for too long 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 shot-peened casting with his hands, resulting in fingerprints.

　　5. After spraying, put it for a long time, there will be dust on the surface or splash water and oil, and the environment will be humid and oxidized.

　　Corresponding measures:

　　1. Defects do not cover the entire steel shot surface, and the control and management are strengthened by the die-casting process.

　　(1) It is black oil and black in color;

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

　　(3) It is paint, the color of which is different from the color of the casting surface;

　　2. After spraying, the surface traces are shallow and cannot be removed because they have penetrated into 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 needs to be covered and protected, and placed in a suitable environment;

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

　　4. The operator is required to operate according to the operating instructions and wear gloves.

　　5. Shot peening should be done in a timely manner for final inspection, packing and warehousing. If it needs to be stored for a period of time, strict protection should be carried out.

　　There are many reasons for the blackening of the surface of the steel shot. One of the more intuitive ones may be the error in our operation method, which did not follow the prescribed requirements and conditions. Therefore, sometimes, we need to improve the quality of the product, and we need to start from the process, so everyone should pay special attention to it when operating.

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