1、 Causes:

1. The gas involved in liquid metal pouring exists in the casting in the form of pores after solidification of alloy liquid

2. Subcutaneous pores formed under the skin of the casting after the reaction of metal mold

3. The gas adhered to the slag oxide skin in the alloy liquid is mixed into the alloy liquid to form pores

2、 Solution repair

1. Prevent air getting involved during pouring

2. Before the alloy liquid enters the mold cavity, it passes through the filter screen to remove the slag, oxide skin bubbles in the alloy liquid

3. Change the mold material add the coating layer to prevent the alloy liquid reacting with the mold

4. Repair welding shall be carried out after the defects are cleared at the allowed repair welding parts