Study of Forming Mechanism of Non-Filling Holes in Blades of Semi-Solid Cast Impellers

Abstract

The semi-solid casting process has a lot of advantages in controlling casting defects. High quality impellers have been produced successfully by the semi-solid process for several years. The semi-solid processed impellers have uniform microstructure and premier mechanical properties, and therefore excellent durability. Further improvement of performance of the impellers is demanded and achieved by increasing curvature and length of blades of impellers. These changes create potential trend of casting defects in blades of impellers, such as non-filling holes. In our recently work, castings were made in different conditions, including two-step plunger velocity and one-step plunger velocity. The experimental results show that the change of plunger velocity played a decisive role in the forming of non-filling holes. Entrapped gas is the direct reason of the non-filling holes. With the increasing of plunger velocity, the area of non-filling holes increased. The non-filling holes in blades could be avoided by eliminating the plunger velocity’s changing during filling blades.