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Casting introduction

Casting is the process of melting metal into a liquid that meets certain requirements and pouring it into a mold, followed by cooling, solidification, and cleaning treatment to obtain castings with predetermined shapes, sizes, and properties. Casting is one of the fundamental processes in modern mechanical manufacturing industry.

Casting is a metal hot working process that humans have mastered relatively early, with a history of about 6000 years. China entered the heyday of bronze casting around 1700 BC to 1000 BC, and the craftsmanship had reached a considerable level. The 875kg Simuwu Fang Ding from the Shang Dynasty, the Yizun Pan from the Warring States period, and the translucent mirror from the Western Han Dynasty are all representative products of ancient casting.

Early castings were mostly tools or utensils for agricultural production, religion, and daily life, with a strong artistic color. At that time, the casting process developed in parallel with the pottery making process and was greatly influenced by pottery.

In 513 BC, China cast the earliest recorded cast iron piece in the world - the Jin Dynasty Cast Iron Cauldron, weighing about 270 kilograms. Europe also began producing cast iron parts around the 8th century AD. The emergence of cast iron has expanded the application scope of castings. For example, in the 15th to 17th centuries, countries such as Germany and France successively laid many cast iron pipes for supplying drinking water to residents. After the Industrial Revolution in the 18th century, industries such as steam engines, textile machines, and railways emerged, and castings entered a new era of serving large industries, with significant development in casting technology.

In the 20th century, the development speed of casting was very fast, and one of the important factors of stacker cranes was the advancement of product technology, which required castings to have better mechanical and physical properties while still having good mechanical processing performance; Another reason is that the development of the machinery industry itself and other industries such as chemical and instrumentation has created favorable material conditions for the foundry industry. The development of detection methods has ensured the improvement and stability of casting quality, and provided conditions for the development of casting theory; The invention of electron microscopes and other technologies has helped people delve into the microscopic world of metals, explore the mysteries of metal crystallization, study the theory of metal solidification, and guide casting production.

During this period, a large number of high-performance and diverse new casting metal materials were developed, such as ductile iron, weldable malleable iron, ultra-low carbon stainless steel, aluminum copper, aluminum silicon, aluminum magnesium alloys, titanium based, nickel based alloys, etc. A new process for incubating gray cast iron was also invented, making the adaptability of castings more extensive.

After the 1950s, new processes such as wet sand high-pressure molding, chemical hardening sand molding and core making, negative pressure molding, and other special casting and shot blasting cleaning emerged, which made castings have high shape and dimensional accuracy and good surface smoothness. The working conditions and environmental hygiene in the casting workshop were also greatly improved.

In the significant progress of the foundry industry since the 20th century, the inoculation treatment of gray cast iron and the chemical hardening sand molding process have special significance. These two inventions have broken through traditional methods that have lasted for thousands of years, opened up new fields for casting technology, and had a significant impact on improving the competitiveness of castings.

Casting is generally classified according to the molding method, and is habitually divided into ordinary sand casting and special casting. ordinary sand casting includes three types: wet sand mold, dry sand mold, and chemically hardened sand mold. Special casting can be divided into two categories based on different molding materials: one uses natural mineral sand and gravel as the main molding material, such as investment casting, shell casting, negative pressure casting, mud casting, solid casting, ceramic casting, etc; A type of casting material that uses metal as the main casting 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: straight arm high-altitude work platform, which includes metal preparation for casting, mold preparation, and casting processing. Cast metal refers to the metal material used in casting production to cast castings. It is an alloy composed mainly of one metal element and added with other metal or non-metal elements. It is commonly known as casting alloy and mainly includes cast iron, cast steel, and cast non-ferrous alloys.

Metal smelting is not just about simple melting, but also involves the smelting process to ensure that the metal poured into the mold meets the expected requirements in terms of temperature, chemical composition, and purity. For this purpose, various quality control inspections and tests must be conducted during the smelting process, and liquid metal can only be poured after reaching the specified indicators. Sometimes, in order to meet higher requirements, the molten metal also needs to undergo external treatment after being discharged from the furnace, such as desulfurization, vacuum degassing, external refining, inoculation or metamorphism treatment. The commonly used equipment for melting metals includes blast furnaces, electric arc furnaces, induction furnaces, resistance furnaces, reflection furnaces, etc.

Different casting methods have different mold preparation contents. Taking sand casting, which is widely used, as an example, mold preparation includes two major tasks: material preparation and core making. The various raw materials used for molding cores in sand casting, such as casting sand, sand binders, and other auxiliary materials, as well as the sand, core sand, coatings, etc. formulated from them, are collectively referred to as molding materials. The task of preparing molding materials is to select suitable raw sand, binders, and auxiliary materials according to the requirements of the casting and the properties of the metal, and then mix them in a certain proportion to form molding sand and core sand with certain properties. The commonly used sand mixing equipment includes roller type sand mixer, counter current sand mixer, and blade groove sand mixer. The latter is specifically designed for mixed chemical self hardening sand, with continuous mixing and fast speed.

Core molding is carried out based on casting process requirements, after determining the molding method and preparing the molding materials. The accuracy of castings and the economic efficiency of the entire production process mainly depend on this process. In many modern casting workshops, the molding and core making have been mechanized or automated. The commonly used sand molding and core making equipment includes high, medium, and low pressure molding machines, sand throwing machines, boxless injection molding machines, core shooting machines, cold and hot core box machines, etc.

After the casting is taken out of the self cooled casting mold, there are gates, risers, and metal burrs and gaps. Castings made by sand casting also adhere to sand, so they must go through a cleaning process. The equipment used for this type of work includes shot blasting machines, sprue and riser cutting machines, etc. Sand casting cleaning is a process with poor working conditions, so when choosing the molding method, it is important to consider creating convenient conditions for sand cleaning. Due to special requirements, some castings also need to undergo post-processing, such as heat treatment, shaping, rust prevention treatment, rough machining, etc.

Casting is a relatively economical method of forming blanks, and lifting trucks can better demonstrate their economy for complex shaped parts. Such as the cylinder block and cylinder head of car engines, ship propellers, and exquisite artworks. Some difficult to cut parts, such as nickel based alloy parts for gas turbines, cannot be formed without casting methods.

In addition, the adaptability range of the size and weight of the cast parts is very wide, and the types of metals are almost unrestricted; Parts not only have general mechanical properties, but also comprehensive properties such as wear resistance, corrosion resistance, and shock absorption, which cannot be achieved by other metal forming methods such as forging, rolling, welding, punching, etc. for aluminum alloy high-altitude work platforms. Therefore, the raw parts produced by casting methods in the machine manufacturing industry are still the largest in terms of quantity and tonnage.

The materials commonly used in casting production include various metals, coke, wood, plastics, gas and liquid fuels, molding materials, etc. The required equipment includes various furnaces for smelting metals, various sand mixers for sand mixing, various molding machines and core making machines for molding and core making, as well as sand dropping machines and shot blasting machines for cleaning castings. There are also machines 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 its wide adaptability, the need for more materials and equipment, and environmental pollution. Casting production produces dust, harmful gases, and noise that pollute the environment more severely than other mechanical manufacturing processes, and measures need to be taken to control them.

The trend in the development of casting products requires castings to have better comprehensive performance, higher precision, less allowance, and smoother surfaces. In addition, the demand for energy conservation and society's call for restoring the natural environment are also increasing. To meet these requirements, new casting alloys will be developed, and new smelting processes and equipment will correspondingly emerge.

As the mechanization and automation level of casting production continues to improve, it will also develop more towards flexible production to expand its adaptability to different batches and varieties of production. New technologies that save energy and raw materials will be given priority for development, and new processes and equipment that produce little or no pollution will be given priority. There will be new developments in quality control technology in the detection, non-destructive testing, and stress measurement of each process.

Under the continuous advancement of electronic technology and testing methods, foundry workers will conduct more in-depth exploration of theories such as metal crystallization solidification and sand compaction, in order to study effective ways to improve the performance and internal quality of castings. The application of robots and electronic computers in the fields of casting production and management will also become increasingly widespread