At present, the manufacturing processes of bucket teeth of excavators in China are sand casting, forging and precision casting. In the market, the mainstream manufacturing technology of bucket teeth is precision casting bucket teeth. Compared with forging bucket teeth, it has the advantages of low price, good shape, accurate size and moderate cost. Due to the lowest cost of sand casting, there is still a great demand in the market. Most bucket teeth are made of zgmn18, which can basically meet the service conditions after water toughening treatment. A company in Pingxiang, Jiangxi has been using ordinary sand casting to produce wear-resistant low alloy steel bucket teeth. During cleaning, it is found that the sand casting is seriously stuck with sand, which needs to be solved.
Sand sticking is that the surface of sand casting is covered with metal or a mixture of metal oxide and molding material, or a layer of sintered compound, which makes the surface of sand casting rough. Sand casting defects such as sand sticking of wear-resistant low alloy steel bucket teeth by sand casting are common problems, but they are only distinguished between serious and mild, easy to clean and difficult to eradicate. Bucket tooth castings belong to simple sand castings in terms of shape and thin castings in terms of wall thickness for alloy steel. They are not easy to form at low temperature, and sand sticking will occur at high temperature.
According to the sand sticking situation of sand castings on the production site of the foundry provided by ZHY casting, it is preliminarily judged that the increase of pouring temperature is due to the infiltration of liquid FeO in the metal into the gap between sand particles, and the sand sticking layer generated by its interaction with SiO2 in the molding sand. The vertical section is thin at the top and thick at the bottom. Therefore, it is considered that mechanical permeability bonded sand is produced after chemical reaction, and chemical bonded sand and mechanical permeability bonded sand coexist at the same time.
The sand core at the upper part of the bucket tooth is wrapped around by high-temperature liquid steel, which is very easy to overheat and be easily melted by high-temperature liquid steel, resulting in melting corrosion and sand sticking. In serious cases, the liquid steel infiltrates into the sand core. This is due to the low melting point and low heat storage coefficient of silica sand for sand core, so it is easy to form melting corrosion. Zircon sand in non silica sand is used to replace silica sand. The pouring test is carried out under the same other conditions. Only about 3% of the sand is bonded, and the effect is obvious. Therefore, we analyze and sort out the main reasons for sand sticking of sand casting wear-resistant low alloy steel bucket teeth.
Practice has proved that high-grade silica sand with SiO2 > 96% should be used to prevent sand sticking of steel castings. The surface of the sand mold shall be coated with anti sticking sand coating to cover the gap of the mold. In order to reduce the gap of the mold, the mold needs to ensure sufficient compactness.