Casting is generally classified according to the modeli […]
Casting is generally classified according to the modeling method, and is customarily divided into ordinary sand casting and special casting. Ordinary sand casting includes three types: wet sand type, dry sand type and chemically hardened sand type. Special castings can be divided into two categories according to different modeling materials: one is natural mineral sand as the main modeling material, such as investment casting, shell casting, negative pressure casting, clay casting, solid casting, ceramics. Casting, etc.; one type of metal as the main casting material, such as metal casting, centrifugal casting, continuous casting, pressure casting, low pressure casting, etc., the casting process can be divided into three basic parts, namely, casting metal preparation, mold preparation And casting processing. Cast metal refers to the metal material used for casting castings in casting production. It is an alloy composed mainly of a metal element and added with other metal or non-metal elements. It is customarily called cast alloy, mainly cast iron. Cast steel and cast non-ferrous alloys. Metal smelting is not only a simple melting process, but also a smelting process that allows the metal to be poured into the mold to meet the expected requirements in terms of temperature, chemical composition and purity. For this reason, various inspection tests for the purpose of controlling quality are carried out during the smelting process, and the liquid metal can be allowed to be poured after reaching various specified indexes. Sometimes, in order to achieve higher requirements, the molten metal is treated outside the furnace after being discharged, such as desulfurization, vacuum degassing, refining outside the furnace, gestation or deterioration treatment. Commonly used equipment for melting metal is cupola, electric arc furnace, induction furnace, electric resistance furnace, reverberatory furnace and the like.
Different casting methods have different mold preparation contents. Taking the most widely used sand casting as an example, the mold preparation includes two major tasks: modeling material preparation and modeling core making. Various raw materials used for molding cores in sand casting, such as foundry sand, sand binders and other excipients, as well as molding sand, core sand, paints, etc., which are formulated by them, are collectively referred to as modeling materials. The task of preparing materials is to follow castings. The requirements, the nature of the metal, choose the appropriate raw sand, binder and auxiliary materials, and then mix them into a certain type of molding sand and core sand in a certain proportion. Commonly used sand mixing equipment include a roller type sand mixer, a counter flow type sand mixer and a blade groove type sand mixer. The latter is designed for mixed chemical self-hardening sand, continuous mixing and fast speed. In the 20th century, the development speed of casting is very fast. One of the important factors is the advancement of product technology, which requires various mechanical and physical properties of castings to be better, while still having good mechanical processing performance. Another reason is the mechanical industry itself and others.
The development of industries such as chemicals and instruments has created favorable material conditions for the foundry industry. Such as the development of testing methods, to ensure the improvement and stability of casting quality, and to provide conditions for the development of casting theory; the invention of electron microscopy, etc., to help people penetrate into the microscopic world of metal, explore the mystery of metal crystallization, study the theory of metal solidification To guide casting production. During this period, a large number of new cast metal materials with superior performance and rich variety, such as ductile iron, weldable malleable cast iron, ultra-low carbon stainless steel, aluminum-copper, aluminum-silicon, aluminum-magnesium alloy, titanium-based, nickel-based alloy, etc. And invented a new process for the inoculation of gray cast iron, making the casting more adaptable. After the 1950s, there were new technologies such as wet sand high pressure molding, chemical hardening sand molding and core making, negative pressure molding and other special casting and shot blasting, which made the castings have high shape, dimensional accuracy and good surface finish. The working conditions and environmental sanitation of the foundry were also greatly improved. In the significant progress of the foundry industry since the 20th century, the two new processes of gray cast iron gestation treatment and chemical hardening sand molding have special significance. These two inventions have broken through the traditional methods that have lasted for thousands of years, opening up new fields for the casting process and having a major impact on improving the competitiveness of castings.