Present Situation of Large Steel Castings
Large steel castings usually need to pour dozens or even hundreds of tons of molten steel, and some sand cores are surrounded by a large amount of molten iron. The hot action time of molten steel on molding materials is very long, the static head is also very high, and the working conditions are extremely harsh. Therefore, chromite sand is widely used as surface sand in the production of large steel castings. At present, the chromite ore with good quality is high-quality foundry grade chromite ore imported from South Africa. Using chromite sand as the core material, although the expansion rate is low, the large angle coefficient of chromite sand, poor particle shape ratio and poor core fluidity will lead to poor permeability and collapsibility in the later stage. In some cases (such as some thin skin or blind hole sand cores), even chromite sand is difficult to clean out, which increases the cleaning work of castings accordingly.
The production of large steel castings in China has been using sodium silicate sand co-process since the 1970s. With the increasing requirements of users for product quality, this casting process has been difficult to meet the requirements for casting quality. In most cases, subsequent grinding and other means are required to meet the quality requirements of castings, which will not only increase the manufacturing cost of castings. It will also extend the production cycle of castings. The use of Fused ceramic sand in the parts of large steel castings that are easy to stick to sand, such as the included angle, groove, and the hot junction of slender holes, can eliminate the local sand sticking or iron coated sand phenomenon, reduce the cleaning cost of castings, and improve the surface quality of castings.
At present, many large steel casting manufacturers have carried out technical transformation, using alkali phenolic resin san, furan resin sand or ester hardened sodium silicate sand. Ester hardened alkali resin sand has been developed by British companies for nearly 40 years since the last century. Due to its advantages in environmental protection, more and more domestic steel casting plants have adopted this production process. Due to the superior physical and chemical properties of fused ceramic sand, the alkali phenolic resin Fused ceramic sand is widely used in the production of steel castings and has been well received by customers.
Characteristics of Fused Ceramic Sand
Fused ceramic sand is also known as electric melting ceramsite. It is mainly to spray the high-quality Calcined Bauxite raw materials in the molten state to obtain spherical or nearly spherical sand particles with smooth performance.
Fused ceramic sand has the advantages of high temperature resistance, good air permeability, collapsibility, acid-base corrosion resistance and low crushing rate, and its physical and chemical properties are relatively excellent.
From the comparison of Fused ceramic sand with chromite sand and silica sand, it can be seen that the bulk density of Fused ceramic sand is only 0.67 ~ 0.71 times that of chromite sand, and Fused ceramic sand is spherical in shape, with the smallest surface area and the smallest consumption of resin and curing agent; Fused ceramic sand is neutral and suitable for various steel castings (carbon steel, alloy steel, high manganese steel, etc.). In addition to the above advantages, fused ceramic sand has more advantages than chromite sand in terms of price and recycling.