Методичка МТ-7 Шевченко Сварка (Методичка по сварке), страница 3

Read and translate the text. Retell the text.Text 3A. Submerged Arc WeldingAutomatic welding in conjunction with proper tooling hasthree broad types of applications: circular welds, linear welds,and mass production of identical parts. Automatic welding isreported to have been made possible due to the development ofwelding heads that strike the arc, feed the electrode, and maintain an arc of proper length and current. The metal electrodewire is coiled on reels and fed continuously.

These heads aremounted on adjustable supports that may move along the welded17joint, or the part to be welded may move under the head. Various kinds of equipment are available for clamping the parts intoposition, for positioning the part, and for feeding the wire electrode.The submerged arc is an important process used with automatic welding equipment.

The automatic submerged arc processes include:1) single ac or dc – straight or reverse polarity (this is themost common method);2) series arc – ac (used for cladding);3) three-phase, two-wire – ac, dc, or combination ac and dc;4) multiwire – ac for high deposition rates.Submerged arc welding is used in connection with automaticand semi-automatic welding equipment. The submerged arcprocess uses a mineral powdered flux that surrounds the electrode and arc. The electrode can melt rapidly and fuse with theparent metal under a protective atmosphere.

The flux is easilyremoved, no arc flash appearing. The operator judges the properlocation by observing the general direction of the wire and thewelded material. High current densities (up to 40,000 A/in.2)and high rates of metal deposition are possible with high quality,deep penetration, and high welding speed.Direct current automatic welding seldom uses currents above600 to 1000 A, and is used usually for alloy and stainless steels.Alternating current welding, which predominates, uses currentsup to 2000 A for standard equipment, and more for specialequipment; ac welding is usually used for low carbon steels.A manually operated submerged arc welder is known to havebeen developed for the flexibility of hand operation and for theadvantages of automatic welding.

The electrode wire (1/8 in.) isfed through a flexible tube up to 55 in./min, and with 450 A ofcurrent applied at the nozzle. The powdered flux is fed aroundthe electrode at the nozzle by compressed gas which carries the18powder through a tube connected to the nozzle. The operator issure to be much more comfortable because of the absence ofsmoke, spatter, and visible arc rays.Submerged arc welding is a high productivity weldingmethod in which the arc is struck beneath a covering layer offlux.

This increases arc quality since contaminants in the atmosphere are blocked by the flux. The slag that forms on the weldgenerally comes off by itself, and combined with the use of acontinuous wire feed, the weld deposition rate is high. Workingconditions are much improved over other arc welding processessince the flux hides the arc and almost no smoke is produced.The process is commonly used in industry, especially for largeproducts and in the manufacture of welded pressure vessels. Theprocess of arc welding is widely used because of its low capitaland running costs.III. Give the corresponding English equivalents from the text:минеральный порошковый флюс; поддерживает дугунадлежащей длины и ток; проволока наматывается на катушки и подается непрерывно; плакирование, покрытие;массовое производство одинаковых деталей; зажигает дугу;основной металл (сплава); отсоединяется; совместно с надлежащей инструментальной оснасткой; загрязняющие вещества; высокопроизводительный сварочный метод; низкиекапитальные затраты и эксплуатационные расходы; углекислый газ; на улице, на открытом воздухе; ручной сварочный аппарат для дуговой сварки под флюсом; низкоуглеродистая сталь; кольцевой (круговой) сварной шов; летучесть;легированная сталь; сварочная головка; хрупкость; сопло,наконечник (горелки).19IV.

Answer the following questions.1. What is meant by submerged arc welding?2. What do the automatic submerged arc processes include?3. What is the principle of operation of a manually operatedsubmerged arc welder?4. Where is the submerged arc welding used?V. Translate Participles I and II in the function of an attribute:burning gas; heat generated by electrical resistance; connecting bridge; controlled plastic deformation; members beingjoined; thermally ionized gaseous column; arc being formed between the base metal and the electrode; equipment used in afarm shop; unskilled operators; inherent regulating characteristics; vaporized metal; leading welding equipment suppliers;compressed gas tube connected to the nozzle; process used withautomatic welding equipment; mineral powdered flux; currentapplied at the nozzle; electrical equipment producing the current; originally developed for welding.VI.

Translate the sentences with Participles I and II in the function of an adverbial modifier.1. A small disk of indium and another of silver will bond atroom temperature when pinched between thumb and forefinger – but only if the surfaces are first abraded.2. A weld deposit builds up on the edge of a cutting tool,causing chatter or poor finish on the workpiece.3.

Bearings gall when overloaded or underlubricated.4. The parts of an instrument that rub together while unfolding from a satellite in space bond together despite the cold.5. For example, a TIG torch that has a rating (номинальныйпредел) of 250 A when used with straight polarity (dcsp) must20be de-rated (разгрузить) to 15 to 25 A when used with reversepolarity (dcrp-electrode positive).VII. Read and translate the text. Put three questions to the text.Text 3B. Gas Metal Arc WeldingGas metal arc welding, sometimes referred to by its subtypesmetal inert gas (MIG) welding or metal active gas (MAG) welding, is a semi-automatic arc welding process in which a continuous and consumable wire electrode and a shielding gas are fedthrough a welding gun.

Shielding gases (argon and carbon dioxide) are necessary for gas metal arc welding to protect the welding area from atmospheric gases such as nitrogen and oxygen,which can cause fusion defects, porosity, and weld metal embrittlement if they come in contact with the electrode, the arc, or thewelding metal.

At constant voltage, direct current power sourceis most commonly used with gas metal arc welding, but directcurrent systems, as well as alternating current ones, can be used.Originally developed for welding aluminum and other nonferrous materials in the 1940s, gas metal arc welding was soonapplied to steels because it allowed for lower welding timecompared to other welding processes.

The cost of inert gas limited its use in steels until several years later, when the use ofsemi-inert gases such as carbon dioxide became common. Further developments during the 1950s and 1960s gave the processmore versatility and as a result, it became a highly used industrial process. Today, gas metal arc welding is commonly used inindustries such as the automobile industry, where it is preferredfor its versatility and speed.

Unlike welding processes that donot employ a shielding gas, such as shielded metal arc welding,it is rarely used outdoors or in other areas of air volatility.VIII. Name and explain which of the four arc welding processesis the most popular one now.21UNIT 4I. Learn the words below:circuit – контур; цепь; схемаconsistent – 1) подходящий; совместимый; 2) последовательныйconsistency – 1) стабильность; 2) последовательность; 3) согласованностьresistivity force – (удельное) давлениеimpedance – полное сопротивлениеto necessitate – 1) требовать; 2) неизбежно влечь за собойmating parts – сопряженные деталиshot – выплеск; заряд (тока); ввод; взрывresistance weld – соединение, полученное контактной сваркойbutt welding – стыковая сварка; сварка встыкflash welding – стыковая сварка оплавлениемpercussion welding – ударная сваркаprojection welding – рельефная сваркаseam welding – шовная сваркаspot welding – точечная сваркаII.

Read and translate the text.Text 4A. Resistance Welding (Part I)Resistance welding is the heating of material аt the junctionto bе welded bу local resistance to passage of electric current.Spot, projection, seam, flash, percussion, and butt welding areforms of resistance welding. The material is raised to а temperature that causes it actually to melt and, under pressure, it is fusedor forged together. The principle is the same as that used in аnуblacksmith-forged joint.22The amount of heat depends upon the amount of current andthe length of time it is applied (Н = I 2RТ). The amount of current depends upon the voltage applied and the total resistance orimpedance of the circuit; therefore, voltage must bе consistentregardless of variations in the power required. Some weldingequipment, especially that used for welding aluminum, placesheavy demands оn power lines and often requires special feedersand transformers to maintain suitable electrical capacity andvoltage.

The total resistance or impedance of the welding orwelding equipment's circuit depends upon the following factors.1. The impedance of the welding circuit varies as the positionof the part within the welder changes. If the part is magnetic, thelines of force will pass through the material and reduce the current. Therefore, if а resistance weld is made when а small portion of the part is near the electric circuit, it will receive morecurrent than it does when the part is moved, so that а large portion is included in the electric circuit.2. The resistance оr impedance of the electrical equipmentproducing the current influences the amount of current.

Theseparts can bе designed with suitable electronic control, so thatvariations in current can bе compensated for, to а great extent,even variations in position of part, line voltage, and resistance ofthe joint.3. Resistance of the joint is composed of:a) contact resistance between electrodes оr clamps and material;b) contact resistance аt joint of mating parts;c) base resistance of mating material;d) resistance of the electrodes.Contact resistances (3.а and 3.b аbоvе) аrе significantly affected bу the surface conditions such аs cleanliness, uniformity,and freedom from oxides and other compounds. Also, contact23resistances аге directly related to the resistivity of the materialsbeing joined and resistivity force.The base material resistance is proportional to the resistivityof the metal and the length of the current path.III.