The casting of aluminum castings is a kind of surface defects commonly encountered in sand casting, such as sand inclusion, scarring, rodent tail and burr defects. It is caused by the arch and surface cracks on the surface of the casting when the surface of the casting is not solidified or the strength of the solidified shell is very low. The main problem is the quality of the molding sand and the modeling operation. The sand surface sand layer is heated to expand, at this time whether the grain is rearranged is determined by the ability to absorb the stress.

Metal is poured into the sand after casting surface drying thin layer drying, then produce high water, the wet tensile strength of sand body in low humidity far. The surface of the mold is heated and expanded, and the high water layer of low strength produces stress concentration and cracks, which is further developed into sanding scar from the tail of the rat. Because of the high strength water mold is low, and the casting surface dry layer expansion and mould body separated, can freely slide, thus draws the conclusion: sand knot, the most prone to the condition is pouring time, aluminum casting wall thickness and the shape of flat. The degree of sanding scars is related to the time of crack on the surface of the molding sand. If the high temperature and tensile strength of high water sand is high, it can extend the cracking time of dry sand. If the molten metal is completely filled with molding sand and has not formed cracking, then the sand inclusion and scarring defect of the casting will not be formed. The longer the dehiscence of all types of sand, the smaller the possibility of producing sands and scars.