According to the number of blades of this kind of impeller, the complexity of structure and the technical requirements of castings, the production and research of this kind of impeller are also divided into simple and complex aspects.
a. Research status of impeller casting technology with simple structure and low technical requirements
For the large integral casting impeller with simple structure, easy mold taking and low technical requirements, as shown in Figure 1, considering the characteristics of the impeller and the advantages ofprocess, sand casting has become the preferred process in the production of casting enterprises.
In production, clay sand or sodium silicate sand is often used as molding materials according to different casting materials, and the overall pattern sand casting technology or scraper molding technology is often used as molding methods. Due to the large size and weight of the impeller, it is difficult to pour and feed, so the research on the design of this kind of impeller gating system and the feeding process method of the combination of riser and cold iron is a hot topic reported in the literature. Of course, for single piece impellers with low technical requirements, there are also reports of welding blades produced by sand casting to the hub.
Sand casting has the advantages of wide material sources and low price. Although it has been widely used in the production of such large and simple impellers, compared with investment casting, sand casting has the disadvantages of high scrap rate, rough surface and low casting precision due to the limitations of molding sand characteristics, model surface quality and modeling technology, Moreover, due to the limitation of molding technology and mold taking, sandis not suitable for the production of such large, complex and high quality impeller castings.
b. The research status of large-size impeller with large number of blades, complex shape and high technical requirements
In actual production, for the casting of large, complex, difficult to take mold and high technical requirements of stainless steel integral impeller, there are still great difficulties in modeling technology, setting up gating system and cutting gating and riser system. Especially for the larger size impeller with thicker hub, large number of blades, complex shape and high technical requirements, as shown in Figure 2, the modeling process is more difficult.
In terms of production, although there are also reports of using resin sand core assembly or core pulling molding sand casting technology for production, because this kind of impeller has the characteristics of large number of blades, difficult casting and high technical requirements, this kind of impeller casting is produced by investment casting or sand casting alone, The quality of the impeller can not meet the quality requirements due to the limitations of their respective processes.
In terms of process research, although there are many literatures on the casting process of this kind of impeller, there are few reports on the research of this kind of impeller, and there is no report on the research of investment mold sand mold composite casting process for this kind of impeller. Under this background, the investment mold sand mold composite casting process of large and complex impeller has become the research direction of this subject.