a. Sand casting pattern
(1) Selection of pattern material forof impeller investment mold sand mold composite molding
Because the impeller casting is produced by single piece, batch and manual molding, in order to improve the geometry of the casting and the relative position accuracy of the casting during mold closing, reduce the original imbalance and facilitate operation, the wooden pattern was selected in the experiment.
(2) Determination of pattern size of sand casting for impeller investment mold sand mold composite molding
The determination of pattern size of impeller casting is the most important content in pattern design. The most important of all dimensions is the working dimension of the pattern, which directly forms the dimension of the casting.
The working dimension of impeller casting pattern is calculated according to the formula:
In the formula:
Am – working dimension of pattern (mm);
AC – part size of the product (mm);
At – additional dimension of part(mm);
ε— Linear shrinkage of casting (%), taken as 2.2%.
(±) – the size of convex part is marked with + and the size of concave part is marked with -.
When determining the additional dimension at of the impeller casting process, the machining allowance of the upper and lower surfaces of the parts and the machining allowance of the center hole shall be considered. In addition to the above formula, the clearance value s of the core head shall be added to the core head size of the impeller casting pattern. The main dimensions and shapes of impeller sand casting pattern are shown in Figure 1.
b. Core box
The core box is a special process equipment for manufacturing sand core. When designing the core box, the structural form and size of the core box shall be determined according to the casting process drawing, production batch and the conditions of the core making equipment and the structural shape and size of the sand core. Since the impeller is produced in a single piece and small batch, the wooden core box is selected to make the core, and the schematic diagram of the core box is shown in Figure 2.