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Analysis of common defects in castings -- Sands

Source:adminRelease:2017-11-07【large In Small

A layer of shell material is firmly attached to the surface of the casting. It is called slime, and slime is one of the common surface defects of the mold casting. When the surface of the casting is sanding, it will not only make the surface cleaning of the castings difficult, but also increase the surface roughness of the castings. The formation of sands is a complex physical and chemical process. According to the main composition and characteristics of the clay sand, it is divided into two kinds of mechanical and chemical sands.

Mechanical sands are mainly due to the small surface tension of liquid metal, good fluidity, and the static pressure of liquid metal. It is formed in the pores between the particles of the shell material. It is obvious that the existence of pores on the inner surface of the shell is a prerequisite for the production of mechanical sands. The inner surface of the medium shell of the molten casting is made up of the dense coating layer. In general, the possibility of producing mechanical sands is less.

Chemical sands are common in mold casting. Chemical bonded sand is mainly composed of shell material composition, which is chemically active for casting alloys and oxides, and is formed by chemical interaction after pouring, which is adhered to the surface of castings.