Basic Knowledge of Metal Casting
Metal casting has been widely used in our residential and industrial fields. Casting is the foundation of modern machinery manufacturing industry.
Casting process is to pour the melted metal into the mold, after the solidification by cooling, to get the curtain shape, size and performance of metal castings.
In 513 BC, we found the world's oldest iron casting - Cast Jin Ding, weighing about 270 kg. Europe began the production of cast iron around the eighth century AD. The emergence of cast iron expanded the application range of metal castings. For example, in the 15th to 17th Century, Germany, France and other countries have laid cast iron pipes to the residents drinking water. After the industrial revolution in 18th century, steam engines, textile machines, railways and other industries have developed very fast, so iron casting developed into a new period of industrial services for large industries. The casting technology began to have great development.
In 20th century, the development of casting is very fast, one important factor is the product of new technology, requires better casting with a variety of mechanical and physical properties, while still have good machining properties; Another reason is the mechanical industry itself and other industries such as chemicals, instruments and other development, all these factors created a favorable material conditions for the foundry industry. Such as the detection devices, to ensure the casting quality improvement and stability, and to provide the condition to the casting theory development. The invention of electronic microscope helped people to deep into the metal of the microscopic world, exploration of metal crystal mystery.
During this period, there was large development for various metal castings with superior performance, such as ductile iron, malleable welded cast iron, low carbon stainless steel, aluminum, copper, aluminum, aluminum-magnesium alloy, titanium-based, nickel-based alloys , and the invention of the gray cast iron inoculation of new technology, so that metal casting has a wider adaptability.
After middle of 20th century, there was high pressure molding with wet sand, chemical hardening sand molding and core making, molding and other special vacuum casting, shot blasting and other new technology to make castings with high shape, dimensional accuracy and good surface finish, foundry working conditions and environmental health is also greatly improved.
Since the 20th century, for foundry industry, gray iron inoculation treatment and chemical hardening sand molding process have two new special significance. These two inventions has broken the traditional methods for thousands of years, and has opened up new areas to improve the competitiveness of the casting.
Casting generally is divided into ordinary and special castings. Ordinary sand casting, including wet sand, dry sand, chemical hardening sand categories. Special casting material according to the different shapes can be divided into two categories: natural sand and gravel as the main form of mineral materials, such as investment casting, shell casting, vacuum casting, clay-type casting, solid casting, ceramics casting, etc.; a class of metal as the main mold material, such as metal casting, centrifugal casting, continuous casting, pressure casting, low pressure casting.
Casting process can be divided into three basic parts, namely, preparation of metal casting, mold preparation and casting processing. Metal casting is the production of metal castings for the cast, which is a metallic element as the main ingredient, and adding other metals or non-metallic elements and the composition of the alloy, traditionally known as the casting alloy, there are cast iron, Steel and cast non-ferrous alloys.
After the cooling, the castings have to be removed for the gate, riser and metal burrs, so the clean-up process is necessary. Equipments for such work are shot blasting machines, gate riser cutting machines. Some castings for special requirements have to be treated by post-casting processing, such as heat treatment, plastic surgery, anti-rust treatment, rough machining and so on.
Casting is an economical method of rough shape, complex shape parts for more demonstrated its economy. Such as automotive engine block and cylinder head, ship propellers and exquisite works of art. Somewhat difficult to cut the parts, such as nickel-based alloy gas turbine parts can not be formed without casting method.
In addition, the casting of the part size and weight to adapt to a wide range of metal species is almost unlimited; parts in the mechanical properties in general also has the wear and corrosion resistance, shock-absorbing and comprehensive performance. Sometimes, you can not get those characters by other metal forming methods such as forging, rolling, welding and punching, etc. So casting methods used in the machine manufacturing industry produced rough parts, in the number and tonnage thus far is the greatest.
Casting product development trend is to ask the cast a better overall performance, higher accuracy, less margin and more smooth surface. In addition, energy requirements and restore the natural environment of the community are increasingly vocal. To meet these requirements, the new cast alloy will be developed, refining new processes and new equipment will accordingly appear.
With the continuous improvement of the electronics and test methods, foundry workers will have deeper research for the metal crystals and in-depth exploration, to improve casting performance and internal quality. Robotics and computer will also become very popular in the field of casting production and management applications. Metal castings will have a better development and wider applications in the future.
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