1. Casting [Explanation]
The process of smelting metal into a liquid that meets certain requirements and pouring it into a casting mold. After cooling, solidification, and cleaning, a casting (part or blank) with a predetermined shape, size and performance is obtained. The basic technology of modern machinery manufacturing industry. The cost of the blank produced by casting is low, and it can show its economical efficiency for parts with complex shapes, especially with complicated inner cavities; at the same time, it has wide adaptability and better comprehensive mechanical properties. However, there are more materials (such as metal, wood, fuel, modeling materials, etc.) and equipment (such as metallurgical furnaces, sand mixers, molding machines, core making machines, sand shakers, shot blasting machines, etc.) required for casting production, and Will produce dust, harmful gases and noise and pollute the environment.
Casting is a kind of metal thermal processing technology that mankind has mastered earlier, with a history of about 6000 years. In 3200 BC, copper frog castings appeared in Mesopotamia. Between the 13th and 10th centuries BC, China has entered the heyday of bronze castings, and the craftsmanship has reached a very high level, such as the 875 kg Simuwu Fang Ding of the Shang Dynasty, the Zenghou Yizun plate of the Warring States Period and the Western Han Dynasty. Translucent mirrors are all representative products of ancient casting. Early casting was greatly influenced by pottery. Most of the castings were tools or utensils used in agricultural production, religion, and life, with a strong artistic color. In 513 B.C., China cast iron castings, the earliest found in written records in the world, the Jin Kingdom Casting Tripod (approximately 270 kilograms weight). Around the 8th century, Europe began to produce iron castings. After the Industrial Revolution in the 18th century, castings entered a new period of service to large industries. In the 20th century, the rapid development of casting has developed. Nodular cast iron, malleable cast iron, ultra-low carbon stainless steel, aluminum-copper, aluminum-silicon, aluminum-magnesium alloy, titanium-based, nickel-based alloy and other casting metal materials have been developed. A new process for inoculation of cast iron. After the 1950s, new technologies such as green sand high-pressure modeling, chemical hardening sand modeling and core making, negative pressure modeling, and other special casting, shot blasting, etc. appeared.
2. Casting Types Are Divided Into Habit Of Modeling Methods
- 1. Ordinary sand casting, including 3 types of green sand, dry sand and chemically hardened sand.
- 2. Special casting, according to the modeling material, can be divided into special casting with natural mineral sand and gravel as the main modeling material (such as investment casting, clay casting, casting workshop shell casting, negative pressure casting, solid casting, ceramic mold Casting, etc.) and special casting with metal as the main mold material (such as metal mold casting, pressure casting, continuous casting, low pressure casting, centrifugal casting, etc.).
3. The Casting Process Usually Includes
- 1. Preparation of casting molds (containers that make liquid metal into solid castings). The casting molds can be divided into sand molds, metal molds, ceramic molds, clay molds, graphite molds, etc. according to the materials used, and can be divided into disposable, semi-disposable, and semi-disposable types according to the number of uses. Mold and mold, the pros and cons of mold preparation are the main factors affecting the quality of castings.
- 2. Melting and pouring of cast metals. Cast metals (casting alloys) mainly include cast iron, cast steel and cast non-ferrous alloys.
- 3. Casting processing and inspection. Casting processing includes removal of foreign bodies on the core and surface of castings, removal of pouring risers, shoveling and grinding of burrs and drape seams and other protrusions, as well as heat treatment, shaping, anti-rust treatment and rough machining.
4.The Development Of Large-Scale Casting Technology
Casting is a process in which metal is smelted into a liquid that meets certain requirements and poured into a casting mold. After cooling, solidification, and cleaning, a casting with a predetermined shape, size and performance is obtained. Because the casting blank is almost formed, it can achieve the purpose of avoiding machining or a small amount of processing, reducing the cost and reducing the time to a certain extent. Casting is one of the basic processes of modern machinery manufacturing industry.
Casting is a kind of metal thermal processing technology that mankind has mastered relatively early, and it has a history of about 6000 years. China has entered the heyday of bronze castings between 1700 and 1000 BC, and the craftsmanship has reached a very high level. The Simuwu Fangding Ding weighing 875 kg in the Shang Dynasty of China, the Yizun plate of Zenghou in the Warring States Period, and the translucent mirror of the Western Han Dynasty are all representative products of ancient casting.
Most of the early castings were tools or utensils used in agricultural production, religion, life, etc., with a strong artistic color. At that time, the casting process developed in parallel with the pottery process and was greatly influenced by the pottery.
In 513 BC, China cast iron castings, the first found in written records in the world—the Jin Kingdom cast-shaped tripod, weighing about 270 kilograms. Europe also began to produce iron castings around the eighth century. The emergence of iron castings has expanded the scope of application of castings. For example, in the 15th to 17th centuries, Germany, France and other countries successively laid many cast iron pipes to supply drinking water to residents. After the Industrial Revolution in the 18th century, industries such as steam engines, textile machinery, and railways emerged, castings entered a new period of service to large industries, and casting technology began to develop greatly.
Entering the 20th century, the rapid development of casting, one of the important factors is the advancement of product technology, requiring better mechanical and physical properties of castings, while still having good mechanical processing performance; another reason is the machinery industry itself and other The development of industries such as chemicals and instrumentation has created favorable material conditions for the foundry industry. For example, the development of testing methods has ensured the improvement and stability of casting quality and provided conditions for the development of casting theory; the invention of electron microscopes has helped people to penetrate into the microscopic world of metals, explore the mysteries of metal crystallization, and study the theories of metal solidification. , To guide casting production.
During this period, a large number of new cast metal materials with superior performance and rich varieties were developed, such as ductile iron, weldable malleable cast iron, ultra-low carbon stainless steel, aluminum copper, aluminum silicon, aluminum-magnesium alloy, titanium-based, nickel-based alloys, etc. , And invented a new technology for inoculation treatment of gray cast iron, which makes the adaptability of castings more extensive.
After the 1950s, new technologies such as green sand high-pressure modeling, chemical hardening sand modeling and core making, negative pressure modeling and other special castings, shot blasting cleaning, etc. appeared, so that castings have high shape, dimensional accuracy and good surface finish. The working conditions and environmental sanitation of the foundry have also been greatly improved.
In the significant progress of the foundry industry since the 20th century, the two new processes of inoculation treatment of gray cast iron and chemically hardened sand modeling have special significance. These two inventions broke through the traditional methods that lasted for thousands of years, opened up a new field for the casting process, and had a significant impact on improving the competitiveness of castings.
Casting is generally classified according to modeling methods, and is customarily divided into ordinary sand casting and special casting. Common sand casting includes three types: green sand, dry sand, and chemically hardened sand. According to the different molding materials, special casting can be divided into two categories: one type uses natural mineral sand and gravel as the main molding material, such as investment casting, shell casting, negative pressure casting, clay casting, solid casting, ceramics Mold casting, etc.; one type uses metal as the main mold material, such as metal mold 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. Casting metal refers to the metal material used for casting castings in the production of casting. It is an alloy composed of a metal element as the main component and adding other metals or non-metal elements. It is customarily called a casting alloy, mainly including cast iron, Cast steel and cast non-ferrous alloys.
Metal smelting is not only a simple melting, but also includes a smelting process, so that the temperature, chemical composition and purity of the metal poured into the mold meet the expected requirements. For this reason, various inspections and tests for the purpose of quality control must be carried out during the smelting process, and the liquid metal can only be allowed to be poured after reaching the specified indicators. Sometimes, in order to meet higher requirements, the molten metal has to be processed outside the furnace after being discharged, such as desulfurization, vacuum degassing, refining outside the furnace, inoculation or deterioration treatment, etc. Commonly used equipment for smelting metals includes cupola, electric arc furnace, induction furnace, resistance furnace, reverberatory furnace, etc.
Different casting methods have different mold preparation contents. Taking the most widely used sand casting as an example, mold preparation includes two major tasks: molding material preparation and molding core making. The various raw materials used in sand casting to form the core, such as foundry sand, sand binder and other auxiliary materials, as well as the moulding sand, core sand, paint, etc. prepared from them are collectively referred to as moulding materials. The task of preparing moulding materials is to follow the castings According to the requirements of the metal and the nature of the metal, select the appropriate raw sand, binder and auxiliary materials, and then mix them into molding sand and core sand with certain properties in a certain proportion. Commonly used sand mixing equipment includes roller type sand mixer, counter-current sand mixer and blade groove type sand mixer. The latter is specially designed for mixing chemical self-hardening sand, continuous mixing and fast speed.
Modeling core is carried out on the basis of determining the modeling method and preparing the modeling materials according to the requirements of the casting process. The accuracy of the casting and the economic effect of the entire production process mainly depend on this process. In many modern foundry workshops, sculpting and core making have been mechanized or automated. Commonly used sand moulding core making equipment include high, medium and low pressure moulding machines, sand blasting machines, boxless injection moulding machines, core shooting machines, cold and hot core box machines, etc.
After the casting is taken out from the pouring and cooling mold, there are gates, risers, and metal burr drape seams. The sand castings still adhere to the sand, so they must go through the cleaning process. The equipment for this kind of work is shot blasting machine, gate riser cutting machine and so on. The falling sand cleaning of sand castings is a process with poor working conditions. Therefore, when choosing the molding method, it should be considered as far as possible to create convenient conditions for falling sand cleaning. Due to special requirements, some castings have to undergo post-casting treatments, such as heat treatment, shaping, anti-rust treatment, and rough machining.
Casting is a relatively economical method of forming blanks, and it can show its economy more for parts with complex shapes. Such as the cylinder block and cylinder head of automobile engine, ship propeller and exquisite artwork. Some hard-to-cut parts, such as nickel-based alloy parts for gas turbines, cannot be formed without casting.
In addition, the size and weight of the cast parts are suitable for a wide range, and the types of metals are almost unlimited; while the parts have general mechanical properties, they also have comprehensive properties such as wear resistance, corrosion resistance, and shock absorption. They are other metal forming methods such as forging. , Rolling, welding, punching and so on. Therefore, the number and tonnage of the blank parts produced by the casting method in the machine manufacturing industry are still many.
The materials often used in foundry production include various metals, coke, wood, plastics, gas and liquid fuels, and modeling materials. The required equipment includes various furnaces for metal smelting, various sand mixers for sand mixing, various molding machines and core making machines for modeling and core making, and sand shakers and shot blasting machines for cleaning castings. Wait. There are also machinery and equipment for special casting, as well as many transportation and material handling equipment.
Casting production has different characteristics from other processes, mainly due to wide adaptability, many materials and equipment required, and environmental pollution. Casting production will produce dust, harmful gases and noise to the environment, which is more serious than other mechanical manufacturing processes, and measures need to be taken to control it.
The development trend of casting products is to require castings with better comprehensive performance, higher precision, less margin and smoother surface. In addition, the requirements for energy conservation and the society’s call for restoration of the natural environment are also increasing. In order to meet these requirements, new casting alloys will be developed, and new smelting processes and new equipment will appear accordingly.
While the degree of mechanization and automation of foundry production continues to improve, it will develop more flexible production to expand its adaptability to different batches and multi-variety production. New technologies that save energy and raw materials will be given priority for development, and new processes and equipment that produce less or no pollution will be given priority. There will be new developments in quality control technology in the inspection of various procedures, non-destructive testing, and stress determination.
Under the conditions of continuous advancement in electronic technology and testing methods, foundry workers will conduct more in-depth explorations on theories of metal crystallization and solidification and sand compaction to study effective ways to improve the performance and internal quality of castings. The application of robots and electronic computers in the field of foundry production and management will also become increasingly widespread. Huazhu CAD is one of the domestic foundry software, which is developed on the CAD platform. In addition, there are some similar softwares in Korea and the United States.
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