The casting is prone to porosity defects

1. The high mud content of the molding sand will lead to the decrease of the permeability of the molding sand, the increase of water, and the porosity defect of the casting is easy to appear.

 If the silica sand, bentonite and pulverized coal used in the foundry are of poor quality, and the old sand lacks effective dust removal, the mud content will be too high due to the increase in ash content.

2. In addition to affecting the permeability and moisture, it will also cause the toughness of the molding sand to become worse, the molding is difficult to draw, and the molding sand corners are fragile, resulting in the defect of sand holes in the casting. If the casting enterprise produces the castings of the core, there are a large number of collapsed coated sand cores mixed in the old sand, resulting in the sand at the most suitable compaction rate, the moisture is too low, and the strength and other properties will fluctuate significantly, making the sand difficult to accurately control. Therefore, some casting enterprises will add an appropriate amount of a starch to the molding sand to reduce the sensitivity of the sand to water.