# Selection of comprehensive average linear shrinkage of die cavity size of investment casting impeller blade

From the beginning of manufacturing the investment mold to the formation of the casting, the size of the impeller blade cavity needs to change three times: that is, the cooling shrinkage of the mold material after copying the size of the die cavity; The expansion of the mold shell in the roasting and heating process after copying the investment mold size, and the shrinkage of the investment casting impeller blade metal after copying the cavity and core size. Therefore, when determining the cavity size, we consider the average shrinkage of the mold ε 1. Average linear expansion rate of shell ε 2. Average linear shrinkage of impeller blade metal in investment casting ε 3。 Comprehensive average linear shrinkage of investment casting impeller blade in die cavity design ε First, calculate according to the formula.

ε1 The value is related to the composition of the mold material and the mold making process ε 1 greater than rosin based mold material, ε The variation range of 1 value is generally (0.38 ~ 2.05)%. The experiment adopts rosin based mold material and paste injection, so ε The value of 1 is 0.75%. ε 2. It is related to the material composition of the shell, shell making process and the temperature of the shell during pouring. Generally ε The value of 2 fluctuates in the range of (0.5 ~ 1.2)%. Because the composite shell of hexyl silicate and water glass is used in the experiment, it is difficult to ε The value of 2 is 0.5. ε The value of 3 is related to the alloy composition. Since the investment casting impeller blade is made of zg1cr18ni9ti, it ε 3 select 2.5.

Considering that the shrinkage rate of each part of the investment mold and the casting is different, the expansion rate of each part of the mold shell is also restrained by each other, resulting in different expansion. Therefore, the actual comprehensive shrinkage of each part of investment casting impeller blade ε S and ε The theoretical values of are different, so they are compared according to practical experience, ε S select 2.6%.

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