There are mainly sand casting and special casting. Special casting can be divided into special castings with natural mineral sand and gravel as the main modeling material according to the modeling materials (such as investment casting, mud casting, shell casting, negative pressure casting, solid mold casting). Casting, ceramic mold casting, etc.) and special casting with metal as the main casting material (such as metal mold casting, pressure casting, continuous casting, low pressure casting, centrifugal casting, etc.)
Casting classification:
1.Ordinary sand casting uses sand as the mold material,
also known as sand casting and sand foundry, including green sand molds, dry sand molds and chemically hardened sand molds. However, not all sand can be used for casting. The advantage is that the cost is lower because the sand used in the mold can be reused; the disadvantage is that the production of the mold is time-consuming and the mold itself cannot be reused and must be destroyed before the finished product can be obtained.
1-1. Sand mold (core) casting methods: green sand mold, resin self-hardening sand mold, water glass sand mold, dry mold and surface dry mold, solid mold casting, negative pressure molding.
1-2. Sand core manufacturing method: It is selected based on the size, shape, production batch and specific production conditions of the sand core. In production, it can be generally divided into manual core making and machine core making.
2. Special casting,
according to the modeling materials, can be divided into special castings using natural mineral sand and gravel as the main modeling materials (such as investment casting, mud casting, shell casting, negative pressure casting, solid casting, ceramic mold casting, Lost foam casting, etc.) and special castings using metal as the main casting material (such as metal mold casting, pressure casting, continuous casting, low pressure casting, centrifugal casting, etc.).
2-1. Metal mold casting method
Use metal with a higher melting point than the raw material to make casting molds. It is subdivided into gravity casting, low pressure casting and high pressure casting. The metals that can be cast are also limited by the melting point of the mold.
2-2. Lost wax casting method
This method can be outer film casting method and solid casting method. The object to be cast is first copied with wax, then immersed in a pool containing ceramic (or silica sol) and left to dry. The wax replica is covered with a ceramic outer film. The steps are repeated until the outer film is sufficient to support casting. process (about 1/4 inch to 1/8 inch), then melt the wax in the mold and pull out the mold. Subsequently, the mold needs to be heated to high temperatures several times to enhance the hardness before it can be cast.
This method has good accuracy and can be used for casting of high melting point metals (such as titanium). However, since the price of ceramics is quite high, and the production requires multiple times of heating and is complicated, the cost is quite expensive.
3.Sand casting methods can be further divided into:
green sand machine molding method, self-hardening resin sand molding core making, water glass sand molding core making, dry molding and surface dry molding, solid mold casting, negative pressure molding, and manual molding.
4. The manufacturing method of the sand core is selected based on the size, shape, production batch and specific production conditions of the sand core. In production, it can be generally divided into manual core making and machine core making.
Casting molding process:
- Gravity casting: sand casting, die casting. The molten metal is poured into the mold cavity by the metal’s own gravity.
- Pressure casting: low pressure casting, high pressure casting. The additional pressure is used to instantly press the molten metal into the casting cavity.
The casting process usually includes:
① Preparation of casting molds (containers that turn liquid metal into solid castings). Casting molds can be divided into sand molds, metal molds, ceramic molds, clay molds, graphite molds, etc. according to the materials used. Casting molds can be divided into disposable types and semi-permanent types according to the number of uses. And permanent mold, the quality of mold preparation is the main factor affecting the quality of castings;
②The melting and pouring of cast metals. Cast metals (cast alloys) mainly include various types of cast iron, cast steel and cast non-ferrous metals and alloys;
③ Casting processing and inspection. Casting processing includes removing foreign matter on the surface of the core and casting, cutting off the pouring riser, shoveling burrs and seams and other protrusions, as well as heat treatment, shaping, anti-rust treatment and rough machining.
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 pouring castings in foundry production. It is an alloy composed of one metal element as the main component and adding other metal or non-metal elements. It is customarily called casting alloy. It mainly includes cast iron, Cast steel and cast non-ferrous alloys.
Metal smelting is not just a simple melting, but also includes a smelting process so that the metal poured into the mold meets the expected requirements in terms of temperature, chemical composition and purity. For this reason, various inspections and tests for the purpose of quality control must be carried out during the smelting process. Liquid metal can only be poured after reaching various specified indicators. Sometimes, in order to meet higher requirements, the molten metal needs to be treated outside the furnace after being discharged from the furnace, such as desulfurization, vacuum degassing, refining outside the furnace, incubation or deterioration treatment, etc. Commonly used equipment for smelting metals include cupola furnaces, electric arc furnaces, induction furnaces, resistance furnaces, reverberatory furnaces, etc.
About the Author: Gavin Xia
