The role of the sand core in the casting process is to form cavities in castings of various shapes.
The sand core is mainly used to form the inner hole and cavity of the casting. Fix the sand core in a specific position in the sand mold, and then pour. After the casting is completed, the sand core is wrapped in the casting (of course not completely wrapped, there must always be a mouth), and the sand core is broken, the cavity part in the casting is formed.
Some shape parts that hinder mold release and are not easy to produce sand can be formed with sand cores. The working conditions of the sand core are harsh, so the requirements for the sand core:
1) Have sufficient strength and rigidity;
2) Good exhaust performance;
3) Good concession;
4) Low contraction resistance;
5) Self-disintegrating, easy to sand.
Sand core design includes: determining the number of sand cores, the shape and size of each sand core; the number, shape and size of core heads; core braces and core bones; exhaust method; core sand types and core making methods, etc.
The materials used for manufacturing cores in foundry production are generally made by mixing molding materials such as foundry sand, molding sand binder and auxiliary additives in a certain proportion. The core is mostly surrounded by high-temperature liquid metal in the mold, and the size of the support positioning part is generally small.
Therefore, in addition to the performance of general molding sand, core sand also requires higher strength, air permeability, yield and collapse. Core sand is divided into clay core sand, water glass core sand, oil core sand, synthetic core sand, resin core sand, etc. according to different binders used.
The core sand of casting process using resin as a binder includes self-hardening resin core sand, ester hardened water glass core sand, coated sand core sand, hot core box core sand, cold-core box core sand. The production of small-batch castings can use self-hardening binder core sand. The production of large batch castings should use hot core box core sand (hot core box core shooting machine) and cold-core box core sand. For special requirements, castings can use coated sand core sand.