The role of medium temperature wax in the mainstream technology of producing precision castings at home and abroad.

At present, the silica sol shell method for medium temperature wax mold is the mainstream technology for producing precision castings at home and abroad. However, now the shell making cycle is long, and the casting is defective due to the defects of the surface mold shell. It is suggested to add anti crack agent in the surface glue, adopt large particle size silica sol to dry the surface layer, cancel the pre wetting before two layers of coating, and eliminate the staining of silica sol before coating, so as to improve the strength of the surface layer, reduce the surface layer defects, shorten the drying time of the coating film, and improve the one-time coating film qualification rate.

Investment casting medium temperature wax silica sol shell technology is suitable for precision parts with small surface roughness and high dimensional accuracy, and has become a widely used mainstream technology.

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笔记

This shell making technology has a long production cycle, especially due to the surface cracking, peeling, expansion, delamination and other defects, the occurrence of multiple surface defects of castings is puzzling the increase of output and the improvement of surface quality. The quality of the surface layer is directly related to the surface quality of castings and the first pass rate.

The process of silicasol shell crusting is actually the process of establishing strength inside the shell. When the coating is completely dry, the wet strength of the coating will be established after the gel of the silica sol is completed.

The anti cracking agent added to the surface slurry is a polymer with a molecular weight of long bond. It is modified and protected on the surface of the silica sol to reduce the electrode potential of the silica sol and the rebound force between the colloidal particles. During the dehydration of gel, due to the intertwining of polymer molecular chains, the silica sol clusters are close to each other. The results show that the gel process can start quickly under the action of the polymer and the small evaporation of the silica sol, Fast drying of surface layer

In addition, the polymer itself is also an adhesive, so it has alkaline water solubility, which can produce physical strengthening effect on the surface layer in the process of silica sol gel. With the excellent film forming performance of organic polymer, the adhesive can form a uniform and continuous film between the shell refractory materials, improve the whole bonding process, and finally make the shell form the same room temperature strength as the back layer.

In addition, the polymer bond has good flexibility, which can improve the covering condition of the adhesive in the powder and sand, effectively prevent the surface layer from cracking, swelling, delamination and other phenomena, and protect the surface layer. It can be proved by adding organic polymer shell and slurry to compare the section of the electron microscope photos. At present, the precision casting manufacturers continue to add anti crack agents in the production process.