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Welding

Welding is a process when metal parts are joined to­gether by the application of heat, pressure, or a combi­nation of both. The processed of welding can be divided into two main groups:

pressure welding, when the weld is achieved by pressure and

heat welding, when the weld is achieved by heat. Heat welding is the most common welding process used today.

Nowadays welding is used instead of bolting and riv­eting in the construction of many types of structures, including bridges, buildings, and ships. It is also a basic process in the manufacture of machinery and in the mo­tor and aircraft industries. It is necessary almost in all productions where metals are used.

The welding process depends greatly on the proper­ties of the metals, the purpose of their application and the available equipment. Welding processes are clas­sified according to the sources of heat and pressure used.

The welding processes widely employed today include gas welding, arc welding, and resistance welding. Other joining processes are laser welding, and electron-beam welding.

Gas Welding

Gas welding is a non-pressure process using heat from a gas flame. The flame is applied directly to the metal, edges to be joined and simultaneously to a filler metal in the form of wire or rod, called the welding rod, which is melted to the joint. Gas welding has the advantage of using equipment that is portable and does not require an electric power source. The surfaces to be welded and the welding rod are coated with flux, a fusible material that shields the material from air, which would result in a defective weld.

Arc Welding

Arc-welding is the most important welding process for joining steels. It requires a continuous supply of either direct or alternating electrical current. This current is used to create an electric arc, which generates enough heat to melt metal and create a weld.

Arc welding has several advantages over other weld­ing methods. Arc welding is faster because the concen­tration of heat is high. Also, fluxes are not necessary in certain methods of arc welding. The most widely used arc-welding processes are shielded metal arc, gas-tung­sten arc, gas-metal arc, and submerged arc. Shielded Metal Arc

In shielded metal-arc welding, a metallic electrode, which conducts electricity, is coated with flux and con­nected to a source of electric current. The metal to be welded is connected to the other end of the same source of current. An electric arc is formed by touching the tip of the electrode to the metal and then drawing it away. The intense heat of the arc melts both parts to be welded and the point of the metal electrode, which supplies filler metal for the weld. This process is used mainly for weld­ing steels.




«OTHER TYPES OF WELDING»

Non-consumable Electrode Arc welding

As a non-consumable electrodes tungsten or carbon electrodes can be used. In gas-tungsten arc welding a tungsten electrode is used in place of the metal electrode used in shielded metal-arc welding. A chemically inert gas, such as argon, helium, or carbon dioxide is used to shield the metal from oxidation. The heat from the arc formed between the electrode and the metal melts the edges of the metal. Metal for the weld may be added by placing a bare wire in the arc or the point of the weld. This process can be used with nearly all metals and pro­duces a high-quality weld. However, the rate of welding is considerably slower than in other processes. Gas-Metal Arc

In gas-metal welding, a bare electrode is shielded from the air by surrounding it with argon or carbon dioxide gas and sometimes by coating the electrode with flux. The electrode is fed into the electric arc, and melts off in droplets that enter the liquid metal of the weld seam. Most metals can be joined by this process. Submerged Arc

Submerged-arc welding is similar to gas-metal arc welding, but in this process no gas is used to shield the weld. Instead of that, the arc and tip of the wire are sub­merged beneath a layer of granular, fusible material that covers the weld seam. This process is also called electron-beam welding. It is very efficient but can be used only with steels.

Resistance Welding

In resistance welding, heat is obtained from the re­sistance of metal to the flow of an electric current. Elec­trodes are clamped on each side of the parts to be welded, the parts are subjected to great pressure, and a heavy current is applied for a short period of time. The point where the two metals touch creates resistance to the flow of current. This resistance causes heat, which melts the metals and creates the weld. Resistance welding is widely employed in many fields of sheet metal or wire manufac­turing and is often used for welds made by automatic or semi-automatic machines especially in automobile industry.
















Vocabulary:

1.
to join [djom] —
соединять

pressure welding — сварка давлением

heat welding — сварка нагреванием

instead [m'sted] — вместо, взамен

bolting [baultin] — скрепление болтами

riveting ['nvitin] — клепка

basic ['beisik] — основной

to manufacture [maenju'faektfa'] — изготовлять

to depend [di'pend] — зависеть от

purpose f'paipas] — цель

available [a'veibbl] — имеющимися в наличии

equipment [I'kwipmsnt] — оборудование

source [so:s] — источник ,

gas welding — газосварка

arc wading — электродуговая сварка

resistance welding — контактная сварка

laser welding — лазерная сварка

electron-beam welding — электронно-лучевая сварка

flame [fleim] — пламя

edge [£d3] — край

simultaneously [simal'teiniosli] — одновременно

filler [fib] — наполнитель

wire ['waia'] — проволока

rod [rod] — прут, стержень

to melt [melt] — плавить(ся)

joint [d3omt] — соединение, стык

advantage [ad'vcr.ntichi] — преимущество

to require [n'kwaia'] — требовать нуждаться

surface ['s3:fis] — поверхность

coated ['ksutid] — покрытый

flux [fUks] — флюс

fusible [fju:zibl] — плавкий

to shield [/i:ld] — заслонять, защищать

touching ['tAt/in] — касание

tip [tip] — кончик

2.

gas-tungsten — сварка оплавлением вольфрамовым электродом в среде инертного газа

inert [i'na:t] — инертный

edge [ed3] — край

bare [Ьеэ'] — голый

rate [reit] — зд. скорость

gas-metal arc — аргоно-дуговая сварка

considerably [ksn'sidarabli] — значительно, гораздо

surrounding [sa'raundin] — окружающий

carbon dioxide ['kcubsn dai'oksaid]— углекислый газ

droplet ['droplit] — капелька

liquid ['hkwid] — жидкость, жидкий

beneath [bi'ni:6] — под, ниже, внизу

layer ['leia] — слой

weld seam [sbm] — сварной шов

resistance — сопротивление

clamp [klaemp] — зажим, зажимать

sheet [Ji:t] — лист

fusible ['fju:zabl] — плавкий

granular ['graenjula] — плавкий

semi-automatic ['semi ,o:t3'maetik] — полуавтомати­ческая

to create [kri:'eit] — создавать

to submerge {sab'm3:c^] — погружать







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