Therefore, we analyze and sort out the causes of sand sticking in cast wear-resistant low alloy steel and the preventive measures. Compared with cast iron, the pouring temperature of cast steel is higher, sometimes as high as 1560 ~ 1620 ℃. The high pouring temperature is mainly to prevent the cold insulation of steel castings, but at the same time, such a high temperature has a long thermal action time on the sand mold and a large scouring force on the mold. The bucket tooth steel castings of excavators generally use an open gating system. The liquid steel is easy to oxidize and form oxides, which is easy to react with the sand mold and cause serious sand sticking.
① In the production of cast steel, in order to prevent carburization, the sand mold usually contains no or very little pulverized coal. Therefore, the mud content of cast steel green sand is lower than that of cast iron green sand, and the water demand is less. Under the same compaction rate, the moisture of cast steel green molding sand should be strictly controlled, and the moisture should be controlled at 4% ~ 5% or lower.
② In order to solve the problem of rough and unsmooth surface, raw sand with fine particle size should be selected. If a single sand molding is used, the clay content in the molding sand must be strictly controlled and cannot exceed the specified amount. Because the molding sand does not contain pulverized coal and the mud content is low, the air permeability is easy to be high. If it is a single sand, the air permeability should not exceed 120, and the air permeability of surface sand should be lower, so as to produce excavator bucket tooth castings with smooth surface and no mechanical sand sticking. The raw sand with particle size of 0.20 ~ 0.10mm (75 ~ 150 mesh) or 0.315 ~ 0.154mm (55 ~ 100 mesh) is selected. It is best to use fine high-purity silica sand instead of 0.40 ~ 0.20mm (45 ~ 75 mesh) coarse silica sand.
③ In order to prevent chemical sand sticking on the surface of bucket tooth castings of excavators, the SiO2 content of raw sand for large steel castings is mostly more than 96%. The SiO2 content of raw sand for thick wall castings and steel castings with high pouring temperature requirements should be higher. Due to the high SiO2 content of raw sand and the lack of buffer materials such as pulverized coal in molding sand, the bucket tooth steel castings of excavator have a greater tendency to produce sand inclusion and scab defects. It is better to use activated bentonite or natural sodium bentonite to improve the hot and wet tensile strength of molding sand and its ability to resist sand inclusion and scab.
④ In order to improve the surface air drying strength and toughness of molding sand and prevent sand hole defects, an appropriate amount of starch materials (such as dextrin α Starch, calcium lignosulfonate powder, water glass and other diluted aqueous solutions, or phenolic resin alcohol solution). If necessary, surface enhancer shall be sprayed on the surface of sand mold to improve the surface strength of molding sand.
In terms of molding sand, it is required to check and control the fire resistance of core sand, and select sand with high fire resistance to improve the fire resistance of core sand. The SiO2 content of raw sand is more than 96%, and the sand grain is correspondingly coarser. The higher the pouring temperature and the thicker the wall thickness, the higher the requirement for SiO2 content in raw sand. If sodium silicate sand is used, the moisture in sodium silicate sand shall be strictly controlled and not too high. Especially in winter, explosive sand sticking is easy to occur. When the moisture content is high, it is easy to absorb moisture, so it should be combined and poured in time after hardening.