The reason of sand casting
5: the temperature is too high, casting speed is too fast, washed into the sand.
3: sand mold strength is not enough, caused by external force fall off. 4: pouring discontinuously or casting speed is too slow, resulting in the cavity sand can not float to the riser, and stay in a lower temperature place.
Main reason: 1: the sand in the cavity is not clean. 2: before pouring, from the sprue or riser opening into the sand.
