Table of contents
Processing of metals by pressure
Metalworking is the process of changing the shape, sizes and qualities of metals and alloys. During the technological processes of processing of metals by various methods are changing the shape and size of metal, and can also change the physico-mechanical properties of metals.
For the treatment of metals in order of their changes and goals are different methods of processing metals.
The main methods of processing of metals are:
• Processing of metals by pressure
• Welding of metals
• Electric treatment
When the metal changes shape and dimensions of the metal parts to the desired shape using one or more methods of metal processing. The reliability of any production, any metal structure depends on the quality of performance of Metalworking.
Metal working is an essential part of many sectors of production, repair, and construction industries. The world economy and industrial level is constantly increasing, which means that the demand for the metal rises. She will be in demand as long as will function in the industry. And as equipment ages over time, or breaks down, the role of outsourcing is increasing as well as demand for these services. Benefits of Metalworking in outsourcing are quite obvious, for example, in construction: to outsource given the most popular operations and therefore it is possible to abandon burdensome phase in metal processing.
This process of metal treatment known to mankind for many centuries. Its essence consists in heating the metal to a liquid state with subsequent spill in the specified molds. Then the metal cools and hardens. It turns out the so-called casting, which exactly repeats the shape of the moulds.
The technological process of foundry production consists of several stages and steps:
• preparation of molding and core mixtures;
• making molds and cores;
• melting of metals;
• Assembly and die casting;
• removal of the casting from the mold;
• if necessary, heat treatment of castings
For the manufacture of a mold, the cavity of which represents the thumbprint of the future cast, use sand mix. As materials for forming molding compounds used (burnt) earth and quartz sand, modelling clay and additives: coal dust, sulfite liquor (waste from paper production) and others. The choice of composition of sand depends on the weight and thickness of the walls of the casting and chemical composition of molten metal.
In individual and small batch production of molds perform by hand, using wooden models or metal models. In mass production molds are made by special machine on the model plates, which is a metal plate with firmly attached parts of the model and in the two supports.
With the development of metallurgy, the casting process has been continuously improved. Now there are several types of casting, including casting with the additional application of pressure. The latest casting methods allow to produce castings of very small dimensions with unprecedented precision size.
Processing of metals by pressure
The essence of processing of metals by pressure is that the atoms of such material when exposed to external loads, the value of which exceeds the value of its elastic limit, can assume a new stable position in the crystal lattice. This phenomenon, which is accompanied by pressing of metal, called plastic deformation. In the process of plastic deformation of metal change not only its mechanical and physico-chemical characteristics.
Depending on the conditions under which the processing of metals by pressure, it can be cold or hot. Their differences are as follows:
1. Hot metal processing is performed at a temperature above the temperature of its recrystallization.
2. Cold metal, respectively, is performed at a temperature below the temperature at which they rekristallizatsiya.
Pressure treated metal depending on the technology in question:
5. bulk stamping;
6. sheet punching;
7. the processing performed by combined methods.
Welding is the process of permanent connections through the establishment of interatomic bonds between the welded parts in their heating or plastic deformation, or the joint action of both.
There are several methods of welding, but all of them can be divided into 2 large groups:
Welding with melting metal in the spot welding of the joined parts are heated to the melting temperature of metals. The liquid phase of the metals are mixed, forming a weld. Such a connection after cooling has high strength;
Welding plastic deformation – in this method, the parts are compressed, forming a weld. Sometimes parts are pre-heated locally.
As the source of heating used gas, electric current and other sources.
Welding as a high-performance process of making permanent joints finds wide application in the fabrication of permanent joints finds wide application in the manufacture of metallurgical, chemical and power equipment, various pipelines, mechanical engineering, production of building and other structures.
Large technological possibilities of welding have provided its wide application in the manufacture and repair of vessels, vehicles, aircraft, turbines, boilers, reactors, bridges, and other structures.
Electric metal processing is carried out using electric current. The two most common methods is:
Electrical discharge machining – creates an artificial discharge, which affects the metal. As a result, this impact occurs a local temperature increase of the metal to 8-10 thousand degrees Celsius;
Electrochemical machining – this method allows us to give the metal surface a brilliant form.
Modern electrical methods of metal processing are used in production quite extensively, as have a number of advantages over other technologies. First of all, they offer the opportunity to work with a very durable and solid materials that cannot be processed by other methods. Also technology can significantly reduce the consumption of materials, especially for the jewelry industry. For all tasks does not require the use of special tools, such as abrasives and crystals, which have high strength. All machines can be included in automated lines, what gives possibility to minimize human involvement in the process, therefore, the cost of maintaining skilled staff. Electrical methods of processing metals, however, have some drawbacks such as low processing speed and high energy consumption. Despite these factors, the technologies are rapidly developing and increasingly embedded in the production of various types.
Heat (or thermal) processing is the set of operations of heating, soaking and cooling of hard metal alloys with the aim of obtaining desired properties by changing the internal structure and structure. Heat treatment is used either as an intermediate step to improve machinability pressing, cutting, or as the final operation of the technological process, providing a given quality level of the product.
The total duration of heating of the metal during the heat treatment consists of the time self-heating to a predetermined temperature and holding time at this temperature. The heating time depends on the type of furnace dimensions of products, their installation in the furnace; the exposure time depends on the rate of occurrence of phase transformations.
Heating may be accompanied by interaction of the metal surface with a gaseous medium and lead to the decarbonization of surface layer and formation of scale. Decarburization leads to the fact that the surface of the product becomes less stable and loses its hardness.
Principal heat treatment:
• 1 kind of annealing (homogenization, recrystallization, strain relief). The purpose is to obtain the equilibrium structure. Such annealing is not associated with transformations in the solid state (if they occur, it is a side effect).
• Annealing 2 kind associated with transformations in the solid state. To the annealing of 2 kind include: full annealing, partial annealing, normalizing, isothermal annealing, patenting, annealing spheroidizing.
• Hardening is carried out with higher cooling rate with the aim of obtaining nonequilibrium structures. The critical cooling rate required for hardening depends on the chemical composition of the alloy. Hardening may be accompanied by a polymorphic transformation from the original high temperature phase formed a new non-equilibrium phase (e.g., the transformation of austenite to martensite in the hardening of steel). There is also quenching without polymorphic transformation, in which the recorded high temperature metastable phase (for example, in the hardening of beryllium bronze is the fixation of the alpha-phase, supersaturated with beryllium).
• Needs a vacation to relieve internal stresses and to give the material the desired mechanical and performance properties. In most cases, the material becomes more plastic at a somewhat reduced strength.
• Normalization. The product is heated to austenitic condition (at 30 to 50 degrees above AC3) and is cooled on calm air
• Dispersion hardening (aging). After the hardening (without polymorphic transformation) is carried out heating at a lower temperature to separate particles of the strengthening phase. Sometimes it is carried out step-aging at several temperatures, to identify a several kinds of hardening particles.
• Cryogenic treatment is a hardening heat treatment of steel under cryogenic ultra-low temperatures (below minus 153°C).
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Металлообработка [Электронный ресурс] // https://ru.wikipedia.org/wiki/Металлообработка - статья в интернете.
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Современные технологии термической обработки металлов[Электронный ресурс] // http://promtu.ru/obrabotka-metallov/protsess-termoobrabotki-metalla- статья в интернете.
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