Sand cores are used to form the inner cavity, the hole and the parts that cannot be realized by the outer mold. Most of the sand cores in the intake cylinder will be covered with three or more working faces by molten iron. Under the thermal action of high temperature molten iron, the working conditions are bad. In terms of process design requirements, the sand core design should not only meet the requirements of precise casting size, sufficient strength and stiffness, easy to set exhaust channel, but also not hinder the shrinkage during casting solidification; in terms of operation requirements, sand core design should not only meet the requirements of convenient operation, reduce the number of cores, but also require the shape to adapt to the actual core making method. Improper design of sand core will lead to casting size deviation, sand inclusion, low operation efficiency, and even lead to casting scrap. The dimensional accuracy grade of the drawing of the inlet cylinder casting is ct11, and there are many sand cores, and it is difficult to make and lower the core of some slender sand cores. Therefore, it is difficult and important to ensure the accuracy of core assembly size through reasonable design and effective control measures.

(1) Selection and determination of datum.

In order to reduce the operation difficulty of core making and ensure the accurate positioning of sand core, the inner cavity of inlet cylinder is formed by 1 ᦇ core as a whole. The upper threading hole and the profile of volute shell are all based on 1 ᦇ core, and the template is used to control to ensure the integrity of the inner cavity size of the casting.

(2) Inner chamber sand core design.

1 ᦇ core can be accurately positioned through the lower core head; 4 pieces of 2 ᦇ core are connected with 1 ᦇ core through reserved welding fastening points of 1 ා core, and resin sand is filled at the position of connecting core head, which can ensure that the size of cantilever hole in inner cavity is accurate and the wall thickness meets the requirements, reducing skin seam and facilitating core laying. The 3 ᦇ core forms the vortex shell profile at the inlet side, and the four bracing bars are formed by the 4 ᦇ core embedded in the 3 ා core.

(3) Outer profile sand core design.

7, 8 and 9 cores form the outer contour of the casting. The design scheme of sectional manufacturing sand core can effectively solve the problem of casting size control. At the same time, the design of the sand core can ensure that the casting has a spacious tamping surface, which is easy to fill and pound sand, and is convenient to place the core and take exhaust measures. According to the above design principle, a total of 25 sand cores are designed for the inlet cylinder. The design and layout of sand cores are shown in the figure.