Research status of casting technology of small impeller

a. Research status of casting technology of small and simple impeller

For the casting impeller with small size, light weight and simple shape as shown in Figure 1, the selection of casting process is often determined according to the production batch size and technical requirements. When the production volume is large and the technical requirements are high, the investment casting process of medium and low temperature integral wax mold, water glass, ethyl silicate and silica sol coating has been widely used for production. The quality of impeller castings produced by this process can not only fully meet the technical requirements of products, but also show incomparable advantages over other casting methods in terms of cost; When it is single piece, small batch production and low technical requirements, ordinary sand casting process is often used for production. There are also reports about the production of small aluminum alloy impellers by pressure casting process. The production technology of this kind of cast impeller has been basically mature, so the technology of this kind of cast impeller is not the focus of current research and report.

b. Research status of casting technology of small and complex impeller

As shown in Figure 2, the cast impeller with small size and complex shape is mainly produced by investment casting in actual production.

Investment casting is a casting process with little or no cutting. It is an excellent process technology in the casting industry, and it is widely used. It is not only applicable to the casting of various types and alloys, but also produces castings with higher dimensional accuracy and surface quality than other casting methods, and even investment casting can be used for complex, high temperature resistant and difficult to process castings that are difficult to be cast by other casting methods.

Compared with sand casting, investment casting has higher dimensional accuracy and lower surface roughness, and can cast medium and small parts with very complex structure. In fact, investment casting has become the only and most economical production method for a considerable number of precision parts. Especially for the impellers, blades and ordnance parts used in shipbuilding, electric power, aviation and aerospace, precision casting has greater practical value. Therefore, from the application and process characteristics of investment casting, it can be seen that investment casting has incomparable advantages in the production of this kind of impeller casting. In actual production, for small, complex and high quality impeller castings, the application of investment casting method has been the first choice for this kind of impeller casting production.

Due to the complex shape and high quality requirements of this kind of impeller casting, the design of die and the manufacturing process of investment mold are still quite difficult in production. At present, the research work in this aspect mainly focuses on the development of new mold materials, the design of molding, the use of soluble core, the preparation of impeller casting pattern by core pulling or separately pressed blade and hub assembly welding process. Of course, there are many research reports on coating preparation, coating process, melting and gating system process improvement. The use of these research projects has greatly promoted the application of investment casting technology in the production of this kind of impeller castings and the improvement of quality.

As far as the investment casting process is concerned, although the small and complex impeller castings can obtain high-quality impeller casting blanks by using the investment casting method in production, due to the strength of the investment mold and shell and the coating process of fire-resistant coating, there are still great restrictions on the weight of the castings, so it is still very difficult to cast the larger impeller, It can’t even be produced.

Moreover, in the shell making process, for most of the thick hot joints on the casting, due to the limitation of the coating process of precision casting, it is not suitable to set up a complex gating system and a large riser or use cold iron for feeding and chilling of the hot joints. Therefore, although investment casting shows incomparable advantages over other casting methods in the production of such small and complex castings, the application of conventional investment casting in large impeller casting is still quite difficult.