What are the reasons for the formation of sand on the surface of precision castings


After a period of use of precision castings, there will be sand formation. Why? As an excellent precision casting manufacturer, Junlong has rich experience. Let me introduce the reasons for the sand formation on the surface of carbon steel precision castings. Everyone Let's find out together.
The sand formation on the surface of carbon steel precision castings is caused by the oxidation of molten steel. The traditional foundry coating only acts as a barrier and isolation between the casting and the mold to achieve the purpose of preventing sand from sticking, but sometimes it also sticks to the casting part or a large area. This is because the high temperature liquid metal is oxidized to form metal oxides, the main product is ferrous oxide FeO, whose melting point is 1370 °C. FeO reacts chemically with the SiO2 of the molding sand to form ferrous silicate. The melting point of ferrous silicate is extremely low, only 1220 ℃, so the fluidity is very good. Even if the surface of the casting has a solidified shell, the newly formed ferrous silicate Still in a liquid state, it is easy to penetrate the paint into the pores of the sand mold.
The condensed ferrous silicate has strong adhesion to precision castings, coatings and molding sand, and can firmly adhere the molding sand to the surface of the casting to form a series of low-melting compounds [at the thick walls and corners of the castings. Etc., there are more low-melting substances, and the sticky sand layer is later), causing the casting to stick to the sand, which is called chemical sticky sand.