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Welding Technology




















For permanent connection of welded components necessary to approximate the distance (S ~ 04/10 -10 m), which between them will overcome the energy barrier of the potential energy of the atoms of the surface layers are formed, and the general interatomic, interionic, and metallic bonds. Details closer to the desired distance prevent surface irregularities, as well as being her dirt and oxide films. In order to overcome their influence is necessary to expend the energy that is transferred during welding welded surfaces two physical processes: heat and pressure.
The relationships between temperature and pressure at which the possible formation of a welded joint
The figure shows a graph describing the relation between temperature and pressure at which the possible formation of a welded joint (the exact numerical values ​​depend on the characteristics of welded metal). The range of ratios is large enough. The metal can from the outside does not heat up and create a zone of high pressure welding (point A ). In this case the activation of the workpiece surfaces and the formation of a welded joint are due to the large plastic deformations. Under this scheme, formed connections with cold-welding , explosion welding . If the metal is heated to a certain temperature, to form a welded joint, you can use less pressure (point B ). This point, for example, corresponds to the friction welding in which heat is released due to friction during the rotation of one of the parts and their simultaneous squeezing. With further increase in temperature compressive force components needed for welding, continues to decline. For example, at relatively low pressures and heating temperature T N = 0,7 T square by diffusion welding (point C ).

When metal is heated to the melting point (point D ) for the welded joint is not necessary to apply pressure. The molten liquid metal spreads over the surface activated by heating the solid metal, wets it, and approaching at a distance sufficient to establish common bonds. After cooling, the permanent connection is formed.

Thus, all methods of welding can be divided into two groups: pressure welding and fusion welding. Welding pressure (region I in the figure) is characterized by a compression force of welded parts, which provides the plastic deformation of metal in the weld zone. Fusion welding (region II in the figure) is made ​​without pressure, and heating of the metal is above its melting temperature.

Pressure can be connected by welding metals, plastics, glass, ceramics (eg, diffusion welding). Fusion welding is typically used for metal compounds.

Technology fusion welding

Methods for fusion welding are usually classified according to three criteria: the source of heated metal, the method of protection of molten metal from the surrounding atmosphere, the degree of mechanization of the welding process. Depending on the source of heating metal fusion welding methods can be divided into the following:
  • arc welding (heat source of the metal - burning freely between the electrode and the workpiece an arc);
  • plasma welding (heat source of the metal - compressed electrical arc through which the supersonic gas is blown through acquiring properties of the plasma);
  • electroslag welding (heat source of the metal - molten flux (slag), in which electric current flows);
  • electron-beam welding (heat source of the metal - the kinetic energy of electrons moving in a vacuum under the influence of a powerful electric field);
  • laser welding (metal heat source - a laser beam (laser) in a light or infrared light);
  • gas welding (heat source of the metal - high-temperature flame, which is formed during the combustion of gas in a mixture with oxygen).
The first five methods are sometimes called electric fusion welding methods. The latter belongs to the flame treatment of metals, since the electrical energy for its implementation is not used. The most common method of fusion welding is arc welding.

To obtain a quality weld the molten metal during welding must be protected from the ambient atmosphere. Depending on the applied protection are following welding methods:
  • coated electrodes (the role of protecting the electrode surface does that decomposes when heated);
  • submerged (protection by using a special powder (flux), which is fed into the welding zone of the tank);
  • in protective gases (protection by means of gas, which is usually fed through the welding torch nozzle);
  • cored wire (security feature performs pre-buried in a tubular wire welding powder, which when heated decomposes to form gas and slag);
  • in a vacuum (the molten metal is isolated from the ambient air vacuum that is created in the chamber, where the welding).
For each welding method for the classification of the source of heat is applied one or another way of protection. Arc welding can be used all five ways to protect the molten metal from the atmosphere. Electron beam welding is performed only in a vacuum, electroslag - just submerged, plasma - only in the shielding gas.

Another sign of the classification, which is often used to refer to arc welding, is the degree of mechanization of the process. During the welding process to the basic operations include supply of electrode or wire in the welding zone and the movement of the arc along the welded edges. If both operations are performed manually welder, welding is manual . If mechanized wire feeding, welding, or call mechanized semi-automatic . If both operations are mechanized - and moving the wire feed arc welding is called automatic .

Thus, the full name of this method of manual welding will be as follows: manual arc welding with coated electrodes. In the full name includes all three features of classification: the degree of mechanization - Manual, according to the method of protection - coated electrodes, the source of heat - Arc.

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Cutting technology

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