Box collapse defects are sometimes referred to as collapse defects or mold collapse. as far as casting defects are concerned, they usually occur in the process of pouring or solidification. the main feature is that the casting can not be formed or locally succulent because of the local collapse and collapse of the mold. In order to solve the casting collapse defects, measures can be taken from the following aspects: 

1. If the buoyancy produced by the liquid metal is too large, the mold sand in the upper part of the mold will be easily deformed, resulting in local collapse. In order to prevent the box from collapsing caused by the large buoyancy of the liquid metal, the method of increasing the sand consumption on the top of the mold or adding pressed iron at the top of the mold can be adopted. 

2. during the casting process, the decomposition of the casting pattern produces too much and urgent gas, and the exhaust speed of the mold is too late to lead to the collapse of the mold, so it is necessary to choose low-density mold material to make the pattern to reduce the amount of gas generation. 

3. After liquid metal replaces the shape of the casting and fills the cavity, the dry sand is supported by the coating coating. When the coating strength or fire resistance is not enough, the local mold will collapse, so it is necessary to choose the coating with high strength, high fire resistance and good air permeability as far as possible. 

4. The gating system should be designed reasonably, the area of straight gate and inner gate should be suitable, the pouring process should be reasonable, the pouring temperature should be reduced as much as possible, the pouring speed should be controlled, and the flow should not be cut off. 

5. In order to avoid the collapse of the box caused by the flash flow of liquid metal, the casting can be reinforced with ceramic or self-hardening sodium silicate sand in the area with severe erosion of liquid metal.