Carbon steel castings on the surface of sand is the oxidation of molten steel, the traditional casting paint only in the middle of the cylinder and mold to play a barrier to the role of anti-stick sand, but sometimes in the casting part or large area of sand. This is because the high temperature liquid metal is oxidized to produce metal oxide, the main product is ferrous oxide FeO, the melting point of 1370 ℃. FeO and the sand of the chemical reaction of SiO2, the formation of ferrous silicate, so the mobility is very good, even if the cylinder surface has solidified shell, the newly formed ferrous silicate is still liquid, easy to penetrate into the paint into the sand pore.
After the condensation of ferrous silicate on the castings, coatings and sand, have a strong bond, the sand can be firmly adhered to the casting surface, the formation of a series of low melting compounds, and thick and corners in the cylinder And so on, low melting point more, sticky sand layer later), resulting in castings sticky sand, it is called chemical sticky sand.
For this phenomenon, we are in the casting of liquefied petroleum gas cylinders must ensure that the casting wall thickness uniformity, can be appropriate to increase the fillet radius, try to reduce the hot circle, the use of cold iron. According to the thickness of the cylinder and the pouring temperature of the molten metal, the proper selection of the original sand grain size, the sand content of the surface sand and the binder is higher, or the quality of the molten metal is improved, and the casting temperature and pouring speed are appropriately reduced.