M. Ibbotson - Professional english in use engineering (794233), страница 17
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Look at A opposite to help you.basediscontinuitiesdissimilarfuseheat -affectedmaterialsmetalmoltenpoolresidualstressestogetherweldweldedzoneIt is possible for components made of different metals to be ( I) ............................... ................................. . For instance, steel can be welded to copper and to brass. However, it ismuch more difficult to weld components made oftwo (2) .............................................................. ..than it is to weld those made of the same (3) ................................................................. While there isno difficu lty in melting two different metals and mixing them together in a (4) ...............................
.state, problems occur once the hot, liquid metal forming the (5) .............................. .................................. starts to cool. As this process takes place, the two metals will not necessari ly(6) ................................ properly. Once the joint has cooled, this can result in (7) ................................ ,such as cracks, at the heart of the (8) .................................................................
In addition, as themetals contract at different rates (due to different coefficients of thermal expansion),powerful (9) ................................ ................................ can build up, not only in the joint, but also in thewider ( I0) ................................ ................................ near the joint28.2 Match the two parts to make eleven correct sentences about welding techniques. You willneed to use some parts more than once. Look at B opposite to help you.Shielded metal arc welding uses2 Gas welding uses3 Gas metal arc welding uses4 Gas tungsten arc welding usesa burning gas.b a consumable electrode.c a non-consumable electrode.d a separate welding rod which is not an electrode.e a special coating on the welding rod which produces a shielding gas.f a separate gas supply, blown onto the weld as a shielding gas.g a shielding gas generated by burned oxyfuel.h a gas whose purpose is to increase the temperature of the welding process.28.3Match each of the substances (1-6) to the description (a-h) above that uses the substance.Look at B opposite to help you.flux2 argon3 oxygen4 tungsten5 acetylene6 carbon dioxideOve,r ..f-o 1:1otc,fJ1Think about the different techniques used for welding metals in the industry you work in, orin an industry you know about.
In what specific situations are different techniques used, andwhy are they suitable?Professional English in Use Engineering63_,.I! I Non-mechanical joints 2~-Specialized welding techniquesThe web page below, from a technical guide to welding techniques, explains some morespecialized welding methods.Resistance welding involves passing an electric current through metal componentsthat are touching. This heats the metal and welds it.
The technique can be usedfor spot welding - welding a number of small points between the surfaces of thecomponents . It can also be used for seam welding, to make long, narrow welds.Ultrasonic welding uses high-frequency acoustic vibrations (sound vibrations) tomake the touching surfaces of two components vibrate. This generates friction, heatingthem and fusing them. The technique is often used to weld plastics.-Brazing and solderingIn brazing, brass- an alloy of copper (Cu) and zinc (Zn)- is melted using an oxyfuel torch, andadded 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, solderingis often used. Solder is a metal filler which melts at quite alow temperature. Like brazing, soldering forms joints withoutmelting the base metal. Soldered joints are therefore weakerthan welds, and also generally weaker than brazed joints.In soft soldering, an alloy- of tin (Sn) and lead (Ph), or oftin and copper- is melted using an electrically heated rodcalled a soldering iron . In hard soldering, a solder containingcopper and silver (Ag) produces slightly stronger joints.
Thehigher melting point of silver means a flame - usually from anoxyfuel torch - is used instead of a soldering iron.Soft soldering-AdhesivesAdhesive - 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 bondbetween them. Most adhesives are liquids, which can be applied to (put on) the surfaces thatneed to be glued together.Adhesives can create adhesion between surfaces in two main ways.
One is by allowingwet adhesive to be absorbed by the components. After drying and hardening, this formsa mechanical bond, as adhesive is anchored into each component's substrate (the materialbelow the surface). Adhesion may also be created by a chemical bond, from a chemicalreaction between the adhesive and the materials.Many types of adhesive harden by drying. They contain a solvent- water or a liquidchemical -which gives a workable mixture. After the adhesive has been applied, the solventevaporates - turns from a liquid to a gas - to leave solid adhesive. An example of this typeis polyvinyl adhesive (PVA), a wood glue.
Other types, such as epoxy resins (see Unit 14 ),are two-part adhesives, supplied as separate chemicals in two containers. When mixed andapplied, 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 thesurfaces are brought together. A bond then occurs when the surfaces touch.64Professional English in Use Engineering29.1Make word combinations with welding using words from A opposite. Then match thecombinations with the descriptions (1-4) below.1 components are joined by several small welded points2 the weld is in the form of a very thin line3 high-frequency vibrations are generated by sound, causing friction and subsequent fusion4 both components are connected to an electrical supply in order to be joined by spotwelding or seam welding29.2Tick one or more of the boxes to show which technique(s) each sentence applies to, or leaveall three boxes empty if the sentence applies to none.
Look at B opposite to help you.Copper is used in the filler material.2 A soldering iron is used to melt the filler.3The filler material contains silver.4 The base metal is melted to fuse with the filler.Heat is provided by a flame, often from oxyfuel.Tin is used in the filler material.7 This produces stronger joints than welding.5629.3brazingsoft solderinghard soldering000000000000000000000Choose the correct words from the brackets to complete the sentences about adhesives. Lookat C opposite to help you.1 Surfaces can be glued together by applying different types of (adhesive I adhesion).2 When adhesive-covered surfaces touch, they (adhere to I apply to) each other.3 If an adhesive reacts with the material which the components are made from, it forms a(chemical bond I mechanical bond) with the material.4 An adhesive that is applied to the surfaces of both components, then allowed to dry beforethey are joined, is called a (contact adhesive I two-part adhesive).5 In order to form an effective mechanical bond, an adhesive must be absorbed quite deeplyinto the (solvent I substrate) of the material.6 When two-part adhesives are mixed, they react chemically, which enables them to (cure Ievaporate) and form a hard, strong material.••A tube of adhesiveov~r .f-o t:fou ~Think about the adhesives used in assemblies you're familiar with.
Use language from Copposite to explain how the adhesives are used, and how they work.Professional English in Use Engineering65sm-load, stress and strainLoadW hen engineers design a machine or structure, they need to know wha t forces will be exertedon it (p ut press ure on it ). In engineering, forces are called loads. Usually, several differentloads will act on - app ly fo rce to - the components in a machine, or the members (parts) ofa structure.
A component or member which is des igned to carry (or bear) a load is call ed aload-bearing component or member.To predict what will happen when components are loaded, engineers calculate the magnitude(size) of each load, and also work out the direction of the load -for example, verticallydownwards. Load is therefore a vector quantity (or vector)- that is, a measurementwith both a magnitude and a direction.
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