Understanding of the relevant knowledge of coated sand casting.

Coated sand casting refers to a casting method in which a layer of solid resin film is covered with molding sand or core sand before modeling. There are two kinds of coating processes: cold method and hot method: the cold method is to dissolve the resin with ethanol, add additives during the sand mixing process, so that both are coated on the surface of the sand grains, and the ethanol volatilizes to obtain the coated sand; The sand is preheated to a certain temperature, resin is added to melt, stirred to coat the surface of the sand particles, aqueous solution and lubricant are added, cooled, crushed, and sieved to obtain coated sand. Generally used for steel castings and iron castings.

Coated sand casting mainly uses natural quartz sand as raw sand, and uses thermoplastic phenolic resin and reinforcing agents as raw materials. According to the different technical needs of users, the ratio of curing speed, mold release, fluidity, collapsibility, casting surface finish, storage, etc. should be adjusted appropriately. Coated sand casting is one of the modeling materials for automobiles, tractors, and hydraulic parts.

Main features of coated sand casting:

1. Vibration cleaning sand, high strength, small gas production, small expansion;

2. Castings have good dispersion and high surface finish;

3. The shell is not stratified, has good thermal stability, good thermal conductivity, good fluidity, and smooth casting surface;

4. High strength, high temperature resistance, low expansion, good mold release and sand resistance;

5. The shell layer is uniform and does not peel off, and the curing speed is fast;

The main function of additives used in coated sand casting is to improve the performance of coated sand casting. The widely used additives mainly include high temperature resistant additives, easily collapse additives, strengthening and toughening additives, anti-sticking sand additives and wetting additives. Many coated sand foundries have unique additive formulas. The performance of additives plays an important role in the production of coated sand casting and is one of the core competitiveness of the coated sand casting market.

Coated sand casting has gone through four stages: dry mixing method, cold coating method, warm coating method, and hot coating method. Almost all coated sand castings are produced by hot cladding. The hot coating process is to first heat the raw sand to a certain temperature, then mix and stir with the resin, polyurethane degradation product aqueous solution and calcium stearate, and then cool, crush, and sieve. Due to the different formulations, the mixing process is also different.