Main reasons: when the sand box is under vacuum, the external air is sucked into the mold due to the damage of the mold during pouring; The strong air flow penetration process has penetration and rinsing force on the non solidified liquid metal to form the cutting phenomenon. We give this “negative pressure cutting” phenomenon, the negative pressure cutting defect diagram of steel castings. The main reasons for this phenomenon are as follows:
When pouring, the negative pressure is too high, the coating thickness is too thin or damaged, and the pressure holding time after pouring is too long. The process parameters are determined according to the factors such as the structure, size and quality of different castings. Generally, the negative pressure in the sand box is at the appropriate negative pressure degree during pouring, generally: – 0.025 ~ -0.045mpa, and the coating thickness is guaranteed to be 1.2 ~ 2.0mm. During pouring, the pouring height of the ladle shall be reduced as much as possible, the nozzle shall be close to the gate cup as much as possible, and the pressure holding time after pouring shall be controlled within 3 ~ 7 minutes.