Various types of sand casting have many advantages. And these advantages are especially obvious in large batch and standard shape castings. However, when sand casting is used to produce castings with small batch, complex shape and high quality (such as cast steel joints and complex impellers), there are still considerable difficulties.
Although clay sand casting has the advantages of low price, simple sand mold manufacturing process, easy reuse of used sand, easy to realize automatic production and so on. However, there are still many problems in the production of cast steel joints and complex impellers by clay sand casting. First, because of the high quality of the casting, the requirement of the strength of the mold is high, and the large mold leads to the difficulty of compaction. Second, the shape of the casting is very complex, and the molding process is difficult. Third, because of small batch production or even single piece production, the mold investment is very high, resulting in increased costs. Therefore, clay sand casting is not suitable for the production of cast steel joints and desulfurization pump impeller.
Water glass sand casting is very suitable for the production of large-scale steel castings. Using water glass as binder is non-toxic and harmless, which can ensure the material of castings and is conducive to obtaining high-quality castings. By using the method of organic grease hardening, the mold has high strength and the hardening process is convenient. Therefore, the cast steel joint produced by Beijing Institute of mechanical and electrical engineering has always been made of sodium silicate sand. However, the biggest difficulty of using water glass sand casting is that the spatial structure of the joint is relatively complex, and there are some problems such as difficult to take out the mold and lower the core when using the traditional wood mold modeling and core making. In addition, the mold making process is relatively difficult, and the cast steel joint is basically a single production, so the wood mold can only be used once, forming a great waste. Generally speaking, there are still many areas worthy of improvement in the production of cast steel joints by water glass sand casting.
Resin sand casting has the advantages of good collapsibility, low wet strength, good fluidity of molding sand, easier molding, convenient recovery of used sand, etc. At present, this kind of impeller is mainly produced by resin sand core molding sand casting technology. The impeller manufacturer studied in this paper is Shijiazhuang industrial pump factory, which adopts the method of resin sand core group. The sand core is divided into five parts, each part is made of wooden core box. Assemble the core in sequence. But at present, the serious defects of this method are: high working intensity, long modeling time, and large positioning error, which directly affect the dynamic balance performance of impeller.