At present, the manufacturing processes of excavator bucket teeth in China mainly include sand casting, forging manufacturing and precision casting. In the market, the mainstream manufacturing process of bucket teeth is precision casting. First, the price is lower than that of forged bucket teeth. Second, the shape is better and the size is accurate, and the cost is moderate. Third, as long as the raw materials are well controlled, the quality and wear resistance of precision casting bucket teeth even exceed that of forged bucket teeth.
Due to the lowest cost of sand casting, there is still a great demand in the market, but its production quality is not as good as precision casting and forging parts. Zgmn18 is mostly used as the material of bucket teeth in sand casting. This kind of steel casting can basically meet the service conditions after water toughening treatment. However, the thermal expansion coefficient of high manganese steel castings is about 50% higher than that of ordinary steel, and the thermal conductivity of high manganese steel castings is poor. Therefore, transverse cracks (thermal cracks) are easy to appear in the casting process, resulting in the easy tearing and disconnection of excavator bucket teeth along the stress concentration during operation, which significantly reduces the service life of excavator bucket teeth. In order to solve this problem, technical measures such as reducing the content of manganese (WMN = 6% ~ 8%), adding WMO = 1% and WCR = 1.5%, reducing the austenitic layer, improving the work hardening ability of austenitic manganese steel, and strengthening heat treatment have been adopted; Some also use zgmn18vtimo low alloy cast steel. Wear resistant low alloy steel can obtain plate and strip martensite structure through appropriate heat treatment. It not only has high strength, but also has good plasticity and toughness. It can fundamentally overcome the disadvantage that high manganese steel must be work hardened in advance to obtain high hardness. However, the common casting defect of sand mold casting of wear-resistant low alloy steel is sand sticking.
Sand sticking refers to the sintering layer on the surface or part of the casting covered with metal or the mixture (or compound) of metal oxide and molding material, which makes the surface of the casting rough. This kind of sand sticking cannot be eradicated when it is serious, especially the inner cavity of the casting is directly scrapped due to iron clad sand. It is a common problem to use sand mold to cast wear-resistant low alloy steel. Bucket teeth castings of excavators are simple and easy to make in terms of shape. As for wall thickness, they are thin castings as alloy steel. They are not easy to form at low temperature, and sand sticking will occur when the temperature is too high. To make the casting surface smooth, coarse-grained sand cannot be used. Silica sand is mostly used in casting production, but its fire resistance is low and sand sticking is easy to form.
When the pouring temperature is increased, the liquid FeO in the metal infiltrates into the gap between sand particles, resulting in the sand sticking layer formed 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 the mechanical permeability sand sticking is produced after the chemical reaction, and the two types of chemical sand sticking and mechanical penetration sand sticking coexist at the same time. In the upper part of the bucket tooth of the excavator, the sand core is surrounded by high-temperature liquid steel, so the sand core 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. Zirconium sand was used to replace silica sand, and the pouring test was carried out under the same other conditions. Only about 3% of the bonded sand was produced, and the effect was very obvious.