M. Ibbotson - Professional english in use engineering (794233), страница 16
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Answerthe following questions about the technical characteristics of the joints:•How accurately must preload be adjusted?•Are the bolts designed to resist shear forces, or do they work as HSFG bolts?•Arc any types of washer used? What is their purpose?Professional English in Use Engineering59mMechanical fasteners 2-ScrewsScrews have threaded shafts with heads. They may be screwed into a predrilled hole- drilledfor the screw to enter. Self-tapping screws do not require predrilled holes. They cut their ownhole as they are screwed in. Unlike bolts, screws are not used with nuts and- generally- arenot screwed into threaded holes. Most screw heads are designed to be screwed in using ascrewdriver. The most common types are slot head screws and crosshead screws.A screwdriverA slot head screwA crosshead screw,Phillips typeA crosshead screw,Pozidriv typeSmall-diameter bolts, which can be used with nuts or screwed into threaded holes, are sometimescalled machine screws.
Bolts that hold components in place by pressing the end of the boltagainst the component, in order to generate friction and prevent sliding, are called set screws orgrub screws. Examples of uses are holding a wheel on a shaft, and connecting electric wires.-Screw anchorsFasteners designed to fix objects to walls are called screw anchors.
These fit into predrilledholes. A simple screw anchor is a plastic tube called a wall plug (or plug). It is inserted in ahole, and a screw or bolt is then screwed into it. As it enters the plug, the plug expands (itsdiameter increases). This increases friction, allowing the plug to resist pullout forces- theforces which would cause it to be pulled out of the hole if it were not firmly anchored. Anexpansion anchor is another type of anchor. It consists of a bolt fitted inside a metal sleeve.The sleeve expands as the bolt is tightened in the hole.In cases where pullout forces are very high, chemical anchors can be used.
These are studsthreaded bars, onto which nuts can be screwed. The studs are set in - that is, held in the holeby an adhesive. Most chemical anchors are set into holes using a strong adhesive called epoxyresin (see Unit 29 for more on adhesives).-RivetsRivets are permanent fasteners - they cannot be unscrewed. A solid rivet consists of a short,solid shaft of metal with a head at one end, called the factory head. The rivet is insertedthrough a pre-drilled hole, then a special tool is used to deform (change the shape of) theother end of the rivet, flattening and widening it to form a second head, called the shop head.Solid rivets are widely used in aircraft.Blind rivets (or pop rivets) are made from hollow tubes, and arefitted using a tool called a rivet gun.
Blind rivets are not suitablefor high-strength joints.A cross-section of a solid rivet60Professional English in Use EngineeringA blind rivetSolid rivets after installation27.1Make word combinations with screw using words from A and B opposite. Then match thecombinations with the descriptions (1-5) below. One description can be used twice.1 A ................................ screw2 A ................................ screw3 A ................................
screw4 A ................................ screw5 A ................................ screw2 7.2is a thin bolt.does not require a predrilled hole.has a straight groove cut into the top.fits screwdrivers with an X-shaped profile at the end.applies pressure at its end to hold a component in place.Complete the article from a home improvements magazine using the words in the box. Lookat A and B opposite to help you .crossheadexpandheadplugpulloutscrewset inscrewdriverHow NOT to use wall plugs•••You check the diameter of hole required, then choosea drill bit one millimetre narrower. You've tried drillingthe specified hole size many times in the past, onlyfor it to be too big, leaving the (1) ...............................
.spinning in the hole when you try to tighten the(2) ................................. You decide it's better to ensurea tight fit So you drill a smaller hole than suggested,then attempt to hammer in the plug. It bendssideways, useless. You try again. And again.Eventually, you manage to get a plug into the hole.You insert the end of the screw, pick up your(3) ................................
and get to work. It certainly is a tightfit. And hard work. And as the screw goes in, and theplug starts to (4) ................................ ,the going gets harder.By the time the screw's halfway in, the screwdriver has slipped off the screw so manytimes that what used to be a (S) ................................ pattern on the screw (6) ................................now looks more like a smooth, round hole. It's impossible to screw it in any further.Or unscrew it. So you take a pair of pliers, grip the end of the screw, and attempt to dragthe whole thing out of the walL But the (7) ................................
force is beyond the power ofyour now-aching arms. The screw might as well be (8) ................................ with epoxy resin.27.3Match the descriptions (1-5) to the terms (a-e). Look at C opposite to help you.1 a type of fastener that is hollow2 a type of fastener that is not hollow3 a tool used for installing a type of fastener4 the wide part at the top of a rivet, present when the rivet is supplied5 the wide part at the bottom of a rivet, formed after the rivet is insertedov~r 1-o 11ouabcderivet gunshop headfactory headsolid rivetblind rivet•Think of an assembly or installation you know about, where screws are used as fasteners.Say what types of screw are used, and suggest why each type was specified.Professional English in Use Engineering61.,J:,•4lliiliil Non-mechanical joints 1-WeldingWelding means permanently joining two pieces of materia l by heating the joint betweenthem.
The heat melts the edges of the components being welded together, and once thematerial has become molten (liquid), fusion occurs. When the joint fuses, material from eachcomponent is mixed together, joining to form a solid weld. Metal is often welded. It is alsopossible to weld plastic.Welding is usually used to join components of the same base metal- that is, the metal thecomponents are made of. It is possible - though more difficult - to weld certain dissimilarmaterials. 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.
Anotherproblem is residual stress. This is force- for example, tension- which is 'trapped' aroundthe joint. This problem occurs after welding, as a result of contraction in the weld zone (orfusion 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, andwas modified by the heat.-Common gas and arc welding techniquesShielded metal arc welding (SMAW), generally calledarc welding or stick welding, involves striking an electricarc between the workpiece and an electrode - anelectrical conductor.
The heat from the arc melts thebase metal. The electrode consists of a welding rod - astick of metal of the same type as the workpiece - whichprovides filler. The welding rod is therefore consumable-it is used up. The rod is also coated with a materialcalled flux.
When heated, this produces a shielding gas,which protects the molten metal from oxygen. Withoutthis gas, the hot metal would combine with the oxygenin the air, and this would weaken the weld.In gas welding, heat comes from a torch which burnsoxyfuel - a mixture of oxygen (0 2 ) and a gas fuel. Thegas fuel burns much hotter in oxygen than it would inthe air.
The most common fuel is acetylene (C2H2)called oxyacetylene when mixed with oxygen. Weldingrods provide filler but flux is not required, as theburning oxyfuel produces carbon dioxide (C02) whichacts as a shielding gas.Shielded metal arc welding~,~~I/~In gas metal arc welding (GMAW)- often called MIGwelding (Metal Inert Gas) - an arc is struck between the•workpiece and a wire which is made of the same metalGas welding using oxyacetyleneas the base metal.
The wire acts as a consumableelectrode, 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) - anarc 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 separatewelding rod is used to supply filler, if required. As with MIG welding, a shielding gas such asargon is blown onto the weld.Note: MIG and TI G are said as words: /rrug/ and /tlg/.62Professional English in Use Engineering28.1Complete the extract from a technical document about welding using the words in the box.You will need to use some words twice.
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