TOPIC 11. NON-MECHANICAL JOINTS

Text 1

 

1.Обратите внимание на перевод следующих слов и словосочетаний:

welding - сваривание;

filler - наплавочный материал;

discontinuity - разрывность;

residual stress - остаточное действующее напряжение;

weld zone -     зона сварки.

 

2.Прочитайте текст и переведите при помощи словаря незнакомые слова и словосочетания.

 

3.Прочитайте и переведите весь текст:

 

WELDING

Welding means permanently joining two pieces of material by heating the joint between them. The heat melts the edges of the components being welded together, and once the material has become molten (liquid), fusion occurs. When the joint fuses, material from each component is mixed together, joining to form a solid weld. Metal is often welded. It is also possible to weld plastic.

Welding is usually used to join components of the same base metal- that is, the metal the components are made of. It is possible - though more difficult - to weld certain dissimilar materials. For example, copper can be welded to steel. Often, a filler is added during welding. This is new material, of the same type as the base metal, which is melted into the weld pool - the molten metal at the joint during welding.

One problem in welding is discontinuity, where joints are not completely solid. Another problem is residual stress. This is force- for example, tension- which is 'trapped' around the joint. This problem occurs after welding, as a result of contraction in the weld zone (or fusion zone) -the area that was the weld pool. It can also occur in the heat-affected zone (HAZ) -the material close to the weld pool which was subjected to high temperature, and was modified by the heat.

 

TEXT 2

 

1.Обратите внимание на перевод следующих слов и словосочетаний:

shielded metal arc welding - дуговая сварка плавящимся электродом в защитной атмосфере;

arc welding - электродуговая сварка;

stick welding - дуговая сварка плавящимся покрытым электродом;

flux - огнеупор (контактирующий с расплавом);

shielding gas - защитная атмосфера;

gas metal arc welding - дуговая сварка металла в защитной атмосфере;

oxyfuel - кислородное топливо;

gas fuel - газообразное топливо;

consumable electrode - плавящийся электрод;

weld pool - сварочная ванна;

gas tungsten arc welding - газ-вольфрамовая дуговая сварка;

Metal Inert Gas - газ, инертный к металлу.

 

2.Прочитайте текст и переведите при помощи словаря незнакомые слова и словосочетания.

 

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COMMON GAS AND ARC WELDING TECHNIQUES

Shielded metal arc welding (SMAW), generally called arc welding or stick welding, involves striking an electric arc between the workpiece and an electrode – an electrical conductor. The heat from the arc melts the base metal. The electrode consists of a welding rod – a stick of metal of the same type as the workpiece – which provides filler. The welding rod is therefore consumable - it is used up. The rod is also coated with a material called flux. When heated, this produces a shielding gas, which protects the molten metal from oxygen. Without this gas, the hot metal would combine with the oxygen in the air, and this would weaken the weld.

In gas welding, heat comes from a torch which burns oxyfuel - a mixture of oxygen (02) and a gas fuel. The gas fuel burns much hotter in oxygen than it would in the air. The most common fuel is acetylene (C2H2) called oxyacetylene when mixed with oxygen. Welding rods provide filler but flux is not required, as the

burning oxyfuel produces carbon dioxide (C02) which acts as a shielding gas.

In gas metal arc welding (GMAW) - often called MIG welding (Metal Inert Gas) - an arc is struck between the workpiece and a wire which is made of the same metal

as the base metal. The wire acts as a consumable electrode, supplying filler. A shielding gas, often argon (Ar), is blown onto the weld pool.

In gas tungsten arc welding (GTAW)- often called TIG welding (Tungsten Inert Gas) – an arc comes from an electrode made of tungsten (W). However, the tungsten is non-consumable -it does not melt, and is not consumed as filler during the welding process. A separate welding rod is used to supply filler, if required. As with MIG welding, a shielding gas such as argon is blown onto the weld.

 

4.Используйте эти слова, чтобы дополнить текст: base, discontinuities , dissimilar

fuse, heat –affected, materials, metal, molten, pool, residual, stresses, together

weld, welded, zone

It is possible for components made of different metals to be (1). For instance, steel can be welded to copper and to brass. However, it is much more difficult to weld components made of two (2) than it is to weld those made of the same (3). While there is no difficulty in melting two different metals and mixing them together in a (4) state, problems occur once the hot, liquid metal forming starts to cool. As this process takes place, the two metals will not necessarily (6) properly. Once the joint has cooled, this can result in (7), such as cracks, at the heart of the (8) In addition, as the metals contract at different rates (due to different coefficients of thermal expansion), powerful (9) can build up, not only in the joint, but also in the wider (10) near the joint.

 

Text 3

 

1.Обратите внимание на перевод следующих слов и словосочетаний:

resistance welding - контактная электросварка;

spot welding - точечная сварка;

seam welding - шовная сварка;

ultrasonic welding - ультразвуковая сварка.

 

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SPECIALIZED WELDING TECHNIQUES

Resistance welding involves passing an electric current through metal components that are touching. This heats the metal and welds it. The technique can be used for spot welding - welding a number of small points between the surfaces of the components. It can also be used for seam welding, to make long, narrow welds.

Ultrasonic welding uses high-frequency acoustic vibrations (sound vibrations) to

make the touching surfaces of two components vibrate. This generates friction, heating them and fusing them. The technique is often used to weld plastics.

 

Text 4

 

1.Обратите внимание на перевод следующих слов и словосочетаний:

brazing - пайка среднеплавким припоем;

soldering - спаивание;

soft soldering - низкотемпературная пайка;

soldering iron – паяльник.

 

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BRAZING AND SOLDERING

   In brazing, brass- an alloy of copper (Cu) and zinc (Zn)- is melted using an oxyfuel torch, and added as filler to form the joint. Unlike welding, the base metal of the components is not melted, so the components are not fused. Brazed joints are therefore not as strong as welded joints.

For some pipe joints and for electrical connections, soldering is often used. Solder is a metal filler which melts at quite a low temperature. Like brazing, soldering forms joints without melting the base metal. Soldered joints are therefore weaker than welds, and also generally weaker than brazed joints. In soft soldering, an alloy- of tin (Sn) and lead (Ph), or of tin and copper - is melted using an electrically heated rod called a soldering iron. In hard soldering, a solder containing copper and silver (Ag) produces slightly stronger joints. The higher melting point of silver means a flame - usually from an oxyfuel torch - is used instead of a soldering iron.

 

Text 5

 

1.Обратите внимание на перевод следующих слов и словосочетаний:

adhesive - клейкий или вязкий материал;

solvent - растворитель;

epoxy resins - эпоксидные смолы.

 

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ADHESIVE

Adhesive - called glue in everyday language -can be used to bond (permanently join) components together. Its purpose is to adhere to the surfaces being joined, to create a bond between them. Most adhesives are liquids, which can be applied to (put on) the surfaces that need to be glued together.

Adhesives can create adhesion between surfaces in two main ways. One is by allowing wet adhesive to be absorbed by the components. After drying and hardening, this forms a mechanical bond, as adhesive is anchored into each component's substrate (the material below the surface). Adhesion may also be created by a chemical bond, from a chemical reaction between the adhesive and the materials.

Many types of adhesive harden by drying. They contain a solvent- water or a liquid chemical -which gives a workable mixture. After the adhesive has been applied, the solvent evaporates - turns from a liquid to a gas - to leave solid adhesive. An example of this type is polyvinyl adhesive (PVA), a wood glue. Other types, such as epoxy resins, are two-part adhesives, supplied as separate chemicals in two containers. When mixed and applied, the two parts react, then cure- harden due to a chemical reaction.

Contact adhesives must be applied to both components, then left to dry for a time before the surfaces are brought together. A bond then occurs when the surfaces touch.

 

 4. Дополните предложения, выбрав нужное слово:

 

1 Surfaces can be glued together by applying different types of (adhesive/ adhesion).

2 When adhesive-covered surfaces touch, they (adhere to/apply to) each other.

3 If an adhesive reacts with the material which the components are made from, it forms a (chemical bond/mechanical bond) with the material.

4 An adhesive that is applied to the surfaces of both components, then allowed to dry before they are joined, is called a (contact adhesive/two-part adhesive).

5 In order to form an effective mechanical bond, an adhesive must be absorbed quite deeply into the (solvent/substrate) of the material.

6 When two-part adhesives are mixed, they react chemically, which enables them to (cure/evaporate) and form a hard, strong material.