Castings are metal molding objects obtained by various casting methods, that is, molten liquid metal is injected into prepared casting molds by pouring, injection, suction or other casting methods, and the objects with certain shapes, sizes and properties are obtained after cooling and polishing.
Casting has a long history of application.People used to make castings and some utensils of life in ancient times.In modern times, castings were mainly used as rough parts of machine parts, and some precision castings were also used as parts of machine directly.Casting accounts for a large proportion in mechanical products, such as tractors, casting weight accounts for about 50 ~ 70% of the total weight of the machine, agricultural machinery accounts for 40 ~ 70%, machine tools, internal combustion engines and other up to 70 ~ 90%.Among all kinds of castings, mechanical castings have the largest variety, the most complicated shape and the largest dosage, accounting for about 60% of the total production of castings.Followed by the metallurgical ingot mold and engineering pipe, as well as some tools in life.
Casting is also closely related to daily life.For example, frequently used door handles, door locks, heaters, water pipes, iron pans, gas stove racks, irons, etc., are castings.
Classification of the casting
Castings are classified into steel castings, cast iron castings, cast copper castings, cast aluminum castings, cast magnesium castings, cast zinc castings and cast titanium castings.Each type of casting can be further divided into different types according to its chemical composition or metallographic structure.For example, cast iron can be divided into gray cast iron, nodular cast iron, vermicular cast iron, malleable cast iron, alloy cast iron, etc.According to different casting methods, castings can be divided into ordinary sand casting, metal casting, die-casting, centrifugal casting, continuous casting, investment casting, ceramic casting, electroslag recasting casting, bimetallic casting, etc.Among them, ordinary sand casting is the most widely used, accounting for about 80% of the total casting output.And aluminum, magnesium, zinc and other non-ferrous metal castings, mostly die casting.
Directions for use
The theory of liquid metal casting is often called casting. Casting technology has a long history.As early as more than 5000 years ago, our ancestors were able to cast copper and bronze products.Casting is the most widely used liquid metal forming process.It is a method to pour liquid metal into the mold cavity and obtain the blank or part of a certain shape after cooling and solidification.
In machine equipment, liquid forming parts account for a large proportion, in machine tools, internal combustion engines, mining machinery, heavy machinery, liquid forming parts account for 70%~90% of the total weight;In the automobile, the tractor occupies 50%~70%;Account for 40%~70% in agricultural machinery.Liquid forming process can be so widely used because it has the following advantages:
(1) it can produce blank with inner cavity and complicated shape.Such as a variety of boxes, machine tool bed, cylinder body, cylinder head, etc.
(2) the process has great flexibility and wide adaptability.The size of the liquid form is almost unlimited, its weight can be from a few grams to several hundred tons, its wall thickness can be from 0.5mm to about 1m.In industry, all metal materials that can be dissolved into liquid state can be used for liquid forming.For cast iron with poor plasticity, liquid forming is the only way to produce the blank or part.
(3) low cost of liquid forming parts.Liquid molding can directly use waste parts and chips, lower equipment costs.At the same time, liquid parts processing allowance is small, saving metal.
However, the liquid metal forming process, and it is difficult to accurately control, so that the quality of casting is not stable.Compared with forgings of the same material, internal shrinkage cavity, porosity and porosity are easy to occur due to loose structure and coarse grain of liquid forming.Its mechanical properties are low.In addition, labor intensity, poor conditions.Has the fine mechanical, the physical performance, it may have each kind of different strength, the hardness, the toughness coordinate the synthesis performance, also may hold concurrently one kind or many kinds of special performance, like wear-resisting, the high temperature and the low temperature, the corrosion resistance and so on.
The weight and size range of the casting are very wide, the weight of the lightest is only a few grams, the heaviest can reach 400 tons, the wall thickness of the thinnest is only 0.5 mm, the thickness can exceed 1 meter, the length can be from a few millimeters to more than 10 meters, can meet the requirements of different industrial sectors.
Castings have been widely used in hardware and the whole mechanical and electronic industry, and their use is becoming an expanding trend.Specific use, construction, hardware, equipment, construction machinery and other large machinery, machine tools, ships, aerospace, automobiles, locomotives, electronics, computers, electrical appliances, lamps and other industries, many are ordinary people all day long contact, but do not understand the metal objects.