Gray iron castings adopt the lost mold, resin sand casting process, equipped with large gas tempering kiln, artificial aging, tempering and releasing internal stress, etc., to improve the precision of castings after processing. For high-precision machine tools and large machine tools, the processing error caused by thermal deformation accounts for about 40~70%, because the thermal deformation can only be improved and can not be eliminated, for the machine tool to determine the case, generally only by controlling the cutting conditions of the machine tool to achieve the purpose of stabilizing the machine temperature, so as to avoid the impact of temperature changes on the processing accuracy. The basic characteristics of gray iron castings are: high clay content, low moisture and low pulverized coal addition. The basic feature of the high-density sand used for gray iron castings is that the addition of coal powder is also low, so the following points should be paid attention to when preparing the sand: clay content and mud content, moisture, and the particle size of the raw sand.