Definition of casting (GB/T5611-1998)
Casting - smelting metal, making a mold, pouring molten metal into a mold, and solidifying to obtain a metal part blank having a certain shape, size and performance
Casting is a process in which a metal is smelted into a liquid that meets certain requirements and poured into a mold, which is cooled and solidified and subjected to a treatment to obtain a casting having a predetermined shape, size and performance. The casting blank is nearly shaped, and it is free of machining or a small amount of processing, which reduces the cost and reduces the production time to some extent. Casting is one of the basic processes in the modern equipment manufacturing industry.
Casting classification
There are many types of castings, which are customarily divided according to the modeling method:
1 Ordinary sand casting, also known as sand casting, sand turning, including wet sand type, dry sand type and chemical hardening sand type.
2Special casting, according to the modeling material, can be divided into special castings with natural mineral sandstone as the main modeling material (such as investment casting, clay casting, shell casting, negative pressure casting, solid casting, ceramic casting, disappearing Mold casting, etc.) and special castings with metal as the main casting material (such as metal casting, pressure casting, continuous casting, low pressure casting, centrifugal casting, etc.).
According to the molding process, it can be divided into:
1. Gravity casting: sand casting, hard molding. The molten metal is poured into the cavity by gravity. 2. Pressure casting: low pressure casting, high pressure casting. The molten metal is instantaneously pressed into the casting cavity by an additional pressure.
The casting process usually includes:
1 mold (to make liquid metal into a container for solid casting) preparation, the mold can be divided into sand type, metal type, ceramic type, mud type, graphite type according to the materials used, and can be divided into disposable type and semi-permanent type according to the number of times of use. And permanent type, the advantages and disadvantages of mold preparation are the main factors affecting the quality of castings; 2 melting and casting of cast metal, casting metal (casting alloy) mainly has various types of cast iron, cast steel and cast non-ferrous metals and alloys; 3 casting treatment And inspection, casting treatment includes removal of cores and foreign objects on the surface of castings, resection of risers, burrs and burrs and other projections as well as heat treatment, shaping, anti-rust treatment and roughing.
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.
What is casting heat
The heat of casting is an acute exothermic reaction caused by the inhalation of highly dispersed zinc oxide fumes produced during the smelting of copper. It has been reported that metal oxide smoke such as lead, tin, antimony, nickel, etc. can also cause this disease. Preventing the escape of metal fumes is the fundamental way to prevent casting heat. In the operation of smelting, casting, etc., it is necessary to strengthen the airtightness, install a local exhaust dust removal equipment, and recover zinc oxide. Strengthening overall ventilation and wearing smoke masks can be used as an auxiliary measure.
Process flow introduction
With the advancement of technology and the booming of the foundry industry, different casting methods have different mold preparation contents. For example, in the most widely used sand casting, the mold preparation includes two major tasks: preparation of the molding material, molding, and core making. Various raw materials used for molding and core making in sand casting, such as foundry sand, sand binder and other excipients, as well as molding sand, core sand, and coatings prepared by them are collectively referred to as modeling materials, and the task of molding materials preparation According to the requirements of the castings and the nature of the metal, the appropriate raw sand, binder and auxiliary materials are selected, and then they are mixed into a certain type of molding sand and core sand according to a certain ratio. Commonly used sand mixing equipment include a roller-type sand mixer, a counter-flow sand mixer and a continuous sand mixer. The latter is designed for mixed chemical self-hardening sand, continuous mixing, and quick mixing.
Modeling and core making are based on the requirements of the casting process, based on the determination of the modeling method and the preparation of the modeling materials. The accuracy of the casting and the economics of the entire production process depend mainly on this process. In many modern foundry workshops, styling and core making are mechanized or automated. Commonly used sand-type molding core equipments include high, medium and low pressure molding machines, air punching molding machines, boxless injection molding machines, cold core box core machines, hot core box core machines, and coated sand core machines.
After the castings are taken out of the cast-cooled mold, the castings with gates, risers, metal burrs, and crevices are also adhered to the sand, so they must be cleaned. Equipment for performing such work includes a sander, a shot blasting machine, a pouring riser, and the like. The sand falling of sand castings is a process with poor working conditions. Therefore, when selecting the modeling method, it should be considered to create convenient conditions for the falling sand cleaning. Some castings are subject to special post-processing requirements such as heat treatment, shaping, anti-rust treatment, roughing, etc.
Industry characteristics
Casting is a relatively economical method of forming blanks, which is more economical for parts with complex shapes. Such as the cylinder block and cylinder head of the car engine, ship propellers and fine art. Some hard-to-cut parts, such as nickel-base alloy parts of gas turbines, cannot be formed without casting.
In addition, the size and weight of the cast parts are wide, and the metal types are almost unlimited. The parts have general mechanical properties, and also have comprehensive properties such as wear resistance, corrosion resistance and shock absorption. Other metal forming methods such as forging , rolling, welding, punching, etc. can not be done. Therefore, the number of blank parts produced by the casting method in the machine manufacturing industry is still the largest in terms of quantity and tonnage.
Materials commonly used in foundry production are various metals, electricity, coke, wood, plastics, gas and liquid fuels, modeling materials, and the like. The equipment required is various furnaces for smelting metal, various sand mixers for sand mixing, various molding machines for core making, core making machines, sand falling machines for cleaning castings, and shot blasting machines. Wait. There are also machines and equipment for special casting and many transportation and material handling equipment.
Casting production has different characteristics from other processes, mainly due to its wide adaptability, the need for materials and equipment, and pollution of the environment. Casting produces dust, harmful gases and noise that pollute the environment. It is more serious than other mechanical manufacturing processes and requires measures to control it.
For casting engineers and mechanical structural design engineers, heat treatment is a very meaningful and highly valuable method for improving the quality of materials. Heat treatment can change or affect the structure and properties of cast iron, while achieving higher Strength, hardness, and improved wear resistance and so on.
Due to different purposes, there are many types of heat treatment, which can be mainly divided into two categories. The first type is that the tissue structure does not change or should not be changed by heat treatment, and the second is the change of basic organizational structure. . The first heat treatment procedure is mainly used to eliminate internal stresses, which are caused by different cooling conditions and conditions during the casting process. The structure, strength and other mechanical properties are not significantly changed by heat treatment. For the second type of heat treatment, the alkyne has undergone significant changes, which can be roughly divided into five categories: (1) softening annealing: its purpose is mainly to decompose the carbide, reduce its hardness, and improve the processing performance. In the case of ductile iron, the purpose is to obtain more ferrite structure. (2) Normalizing treatment: The main purpose is to obtain pearlite and sorbite structure to improve the mechanical flaw of the casting. (3) Quenching: Mainly to obtain higher hardness or wear strength, and at the same time to very high surface wear resistance. (4) Surface hardening treatment: mainly to obtain a surface hardened layer, and at the same time obtain a very high surface wear resistance. (5) Precipitation hardening treatment: mainly in order to obtain high strength, the elongation does not change drastically.
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