What is the reason for sand formation on the surface of alloy steel precision castings?

Precision castings will form sand after being used for a period of time. Why? Let us introduce the reasons for sand formation on the surface of alloy steel precision castings. Let us take a look.

The sand on the surface of alloy steel precision castings is caused by the oxidation of molten steel. The traditional casting coating only plays a blocking and isolation role between casting and casting to achieve the purpose of preventing sand from adhering, but sometimes it can also be found in the casting part or Large areas of sticky sand. This is because high-temperature liquid metal is oxidized to produce metal oxides. The main product is ferrous oxide FeO at 1370 degrees Celsius. Feo reacts chemically with SiO2 in the molding sand to produce ferrous silicate. The melting point of ferrous silicate It is very low, only 1220 degrees Celsius, so the fluidity is very good. Even if there is a solidified shell on the surface of the casting, the newly produced ferrous silicate is still liquid and can easily penetrate into the sand pores.

Condensed ferrous silicate has strong adhesion to precision castings, coatings and molding sand. It can firmly adhere the molding sand to the surface of the casting, forming a series of low melting point compounds on the thick walls and corners of the casting, with more low melting points. Melting point sand sticking layer), resulting in sand sticking to castings, which is called chemical sand sticking.