There are 14 sand cores in the motor shell in total, and the assembly of sand cores is shown in Figure 1. In addition to the core of the gating system, the optimization design of No. 1 core, No. 2 core and No. 7 core is emphasized.
① Optimal design of core 1
No. 1 core is shown in Figure 2. In the original design, No. 1 core is made of furan resin sand, and four tile like cold irons are set in the outer circle of the sand core. Due to the strong cold ability of the cold iron, cracks are easy to form around the cold iron, and the sand casting is not dense where there is no cold iron. Since the chilling process is not used in this part, the workpiece is not dense, and cracks are easy to occur when cold iron is used, the chilling method with relatively weak chilling ability can be selected. The fire resistance of chromite ore is greater than 1900 ℃, and the thermal conductivity is several times greater than that of silica sand, but weaker than that of cold iron. Therefore, chromite ore is selected to replace cold iron. Embedded chromite sand is used within the thickness range of 30mm around the outer circle, and ordinary silica sand is used for the rest. The adhesive is alkaline phenolic resin and organic curing agent.
② Optimization design of core 2
The original No. 2 core adopts furan resin sand process, and there is no cold iron near the riser, but there is a stiffener with a thickness of about 60mm at this part, and there is a riser at the top, which forms a large hot spot. When the sand casting solidifies and shrinks, due to the late solidification of this part, the liquid steel is fed to the first solidified part, and at the same time, it is subject to the tensile stress caused by the solidification of other parts and risers. Because the stress is very concentrated, It is greater than the fracture strength of sand castings, and open cracks are basically formed at this part, with a depth of 10-20mm. In order to solve the problem of cracks in this part, 7 pieces of follow-up chill are added to core 2, as shown in Figure 3.
③ Optimal design of core 7
Figure 4 shows the original design of core 7. Two round steel cold irons are added at the fillet. Due to the mismatch between the round steel cold irons and the fillet here, the molding sand at the edge of the cold iron cannot be compacted and has low strength, which is easy to cause sand washing, and the sand castings have fleshy and sand inclusion defects. The round steel cold iron is designed as a follow-up cold iron with the same size as the arc here. During core making, the molding sand at the edge of the follow-up cold iron is easy to compact, which reduces the probability of sand inclusion in sand washing.
④ Optimal design of sand mold
The two cold irons on the sand mold column of the original lower box are designed to be 80mm thick and 70mm wide, and the length is the same as that of the column. Due to the strong chilling capacity of the cold iron, cracks appear at the edge of the cold iron, and shrinkage cavities appear in the middle of the column. If no chilling measures are taken here, large shrinkage defects will be formed due to the relatively thick column and slow solidification. In order to solve the problems of shrinkage and crack defects, the height of cold iron shall be shortened by half, and the upper part shall be cooled with chromite ore sand. In this way, the column will basically realize sequential solidification, and the cracks and shrinkage holes will be solved.
