One of the most important parameters in the iron mold sand coated casting process is the thickness of the sand shell. According to the thickness of the casting, the thickness of the sand shell generally adopts the empirical value of about 6-10mm. The numerical simulation calculation is carried out for the thickness of 8mm, 6mm and 4mm. The temperature field and solidification time at 500s are shown in Fig. 1 and Fig. 2 respectively.
When the thickness of the sand shell is 4mm, the surface temperature of the crank has dropped below 950 ° C at 500s, the temperature of the central axis and the hot spot is 1050 ° C, the time required for the complete solidification of the crank surface is about 80s, and the solidification time of the thicker parts such as the hot spot is about 300s. When the thickness of the sand shell is 8mm, the temperature on both sides of the crank surface is about 980 ° C at 500s, The temperature of the crank surface near the center and the central shaft is about 1080 ° C, and the temperature at both ends of the crankshaft is also high, which is about 1000 ° C. the time required for complete solidification of the surface is 130s, and the time for complete solidification of the central shaft and hot joint is about 400s. When the sand shell is 6mm, the temperature of the temperature field is between the above two, and the solidification time is basically the same as that when the thickness is 8mm.
The temperature field obtained by analysis and calculation shows that when the thickness of sand shell is 4mm, the cooling speed of casting is too fast, which is not conducive to mold filling and feeding. The sand shell is too thin and does not play the role of iron mold sand coating casting. When the thickness of sand shell is 6mm and 8mm, the temperature field changes little, and the solidification time is reasonable, which can be applied in practice. The thickness of sand shell can be selected according to the process conditions.