With the rise of lost foam casting, how to reduce the cost of castings, increase the yield and improve the quality is a problem. To solve such problems, the key is in the choice of sand type. Usually, in order to reduce the cost of sand, people will choose cheap quartz sand. However, due to the disadvantages of low refractoriness, poor gas permeability and poor fluidity, such sand has many casting defects during the casting process, such as: sand, pores. These defects are obvious in alloy steel casting. In addition, this kind of sand will generate a lot of dust in the subsequent treatment, which makes the environment of the production workshop very bad, the amount of waste sand increases, the sand is reduced, the sand recycling rate is low, and it is not durable. Therefore, from a comprehensive perspective, the cost of sand increases.
Nowadays, a new type of sand for lost foam casting has been widely concerned by the foundry industry and is known as the new sand “ceramic foundry sand” for green products. The major factors affecting the quality of castings and the excellent properties of ceramic foundry sand are summarized below.
Since the ceramic foundry sand is a spherical particle, its fluidity is very good, it is easy to compact when it is molded, and it can maintain good gas permeability, while quartz sand and forsterite sand are both polygonal sand, and the fluidity is poor. Originally, forsterite sand was used as the filling sand. Due to the poor fluidity of the polygonal sand, defects such as rat tail and scarring occurred many times. This phenomenon has been significantly improved after the use of ceramic foundry sand, improving the yield by 5%. Practice has proved that the fluidity of ceramic foundry sand is better than the existing various types of sand.
The ceramic foundry sand is made of high-quality aluminum bauxite from Shanxi and is made by melting in a high-temperature electric furnace. Ceramic foundry sand is a spherical particle, the main component is aluminum oxide (Al2O3), its refractoriness can reach 1900 °C. The main component of quartz sand is silica (SiO2), which has a refractoriness of less than 1700 ° C. Quartz sand will have various crystals at different temperatures, which will reduce the refractoriness of the sand again during the casting process.
Practice has proved that the use of ceramic casting sand can significantly reduce mechanical and chemical sand, greatly reduce the labor intensity of sand cleaning, and is not easy to produce sand, sand, porosity and other defects. For example, the high-manganese steel castings produced by Jilin Innovation Lost Foam Equipment Co., Ltd., before the use of ceramic foundry sand, the sand-sanding and sand-sanding phenomenon is very serious, and each time it takes a lot of manpower and material resources to clean and polish the surface of the casting. It not only increases the production cost of the casting, but also causes the surface quality of the casting to be unattractive. This type of casting defect has been eliminated after the use of ceramic foundry sand. To this end, the cost savings are 6%. The ceramic refining sand is comparable to chromite ore and is now widely used in the casting of raw chromite ore.
The permeability of the sand depends mainly on the size of the sand, the particle size distribution, the type of the grain and the type of binder. In the pouring process, if the permeability of the molding sand is poor, a large amount of gas generated by the internal heat due to high temperature cannot be immediately discharged, so that a bonfire phenomenon occurs, and defects such as pores, cold separation, and insufficient pouring are generated in the casting, and even scrapped.
Both quartz sand and magnesium olive sand are polygonal sands, which have poor gas permeability, while ceramic foundry sands are spherical particles with uniform particle size distribution and good gas permeability, which can avoid such casting defects. In the production of high-manganese wear-resistant steel castings, quartz sand and forsterite sand have been used successively, but the fruit is not ideal. Due to the poor gas permeability of the two sands, the molten bubble gas is not discharged, and a large number of knots are formed on the surface of the casting. Oh, and a large amount of gas generated by high-temperature heating during pouring cannot be discharged, resulting in defects such as porosity, crusting, and insufficient pouring, or the use of ceramic casting sand to solve this problem, and the yield is improved by 7%.
4. Thermal expansion coefficient
During the high-temperature casting process of castings, the thermal expansion of the molding sand will cause a slight change in the size of the molding sand, which in turn affects the accuracy of the casting size. The thermal expansion coefficient of the molding sand is too large, which may cause casting defects such as sand inclusion, crusting, and rat tail. The ceramic casting sand has a small coefficient of thermal expansion, and there is almost no expansion phenomenon during the casting process, which greatly improves the precision of the casting, and its performance is comparable to that of zircon sand. Henan Xinxiang has many manufacturers producing vibration equipment. There are many small holes in the wall panel. Due to its precision and refractoriness, zircon sand is used as casting sand. Ceramic casting sand is now used, and the cost of molding sand is reduced by 70%.
5. Reuse performance
Because quartz sand is polygonal sand, the strength is low, and the sand is easily broken during the modeling and sand treatment process. Not only will it generate a lot of dust, pollute the production environment, but also generate a lot of waste sand, which will make the sand not durable. According to statistics, The amount of waste sand cleared per pouring is about 5%. The ceramic foundry sand is spherical sand, which has high strength and is not easy to be broken. It can greatly reduce the amount of dust in the production workshop, reduce the labor intensity and production cost of the sand treatment workers, reduce the amount of waste sand, and increase the quantity of recycled sand. Thereby greatly reducing the amount of sand loss. According to statistics, the annual loss of ceramic foundry sand is below 5%. Therefore, the high cost caused by the high price of the ceramic foundry sand is directly offset, and the production cost is greatly reduced. According to the calculation of the manufacturer using the sand, the cost of the secondary increase can be recovered within 8-10 months.