The structure of the product drawing shows that, except for several hole processing parts and one side plane processing, the rest are non-processing surfaces. The key slot hole and the two opposite holes parallel to the key slot hole are the main processing parts and the main stress parts of the pumping unit crank. According to the part drawing and the standard requirements of GB/T 6414-2017 Dimensional Tolerances, Geometric Tolerances and Machining Allowances for Castings, the sand casting drawing is designed and drawn, as shown in the figure. At the right two bumps ϕ The 39 mm machining hole diameter is small, so it is not cast. The machining allowance is set at the other machining holes and the machining plane, and the process allowance is set at the key slot hole. The sand casting weighs 220 kg.

It can be seen from the figure that except for the hole, there are large hot spots in other parts, especially around the key slot hole and ϕ 90 The hot spot between the two holes of the machined hole is large, up to about 130 mm. The overall structure of the crank of the pumping unit is a thick-walled plate-like piece, and the surrounding arcs and bevels are connected. From the analysis of the sand casting process of the product structure, the product can only be cast horizontally, while the thick wall plate parts can not form effective feeding gradient due to the small difference in the flow of molten metal at each part, and the effective feeding efficiency of the riser will be reduced. Therefore, it is the key and difficulty to ensure the internal quality of the stressed part of the crank key of the pumping unit of the sand casting steel parts.