M. Ibbotson - Professional english in use engineering (794233), страница 10
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As the term suggests,the glass is tempered - it's heated and kept hot for a certain time, to change its structure.Then if tempered glass is broken, it shatters - it breaks into tiny pieces. These are a lotsafer than the long, sharp pieces produced when annealed glass breaks.
The disadvantage oftoughened glass is that it can't withstand impacts from small objects, such as flying stones.So, for instance, that makes it unsuitable for vehicle windscreens. So in cases where impactsare a problem, another type of safety glass -laminated glass- is generally used. This is madeby laminating glass with a polymer- in other words, making a glass and polymer 'sandwich',with a sheet of polymer in the middle and sheets of glass at either side. The advantage ofhaving a laminated material is not just that it's very strong.
The layers of glass are bondedto a layer of polymer- they're stuck to the polymer- so if the glass does break, the brokenpieces are held together, and don't fly.'BrE: windscreen; ArnE: windshield36Professional English in Use Engineering15.1Decide whether the sentences below are true or false.
Then, change one word in each of thefalse sentences to correct them. Look at A opposite to help you.1 Minerals are organic.2 Minerals can be found in rocks.3 Silica is a compound containing silicon.4 Minerals can be metallic or non-metallic.5 Industrial diamond is an abrasive, metallic mineral.6 In order to become ceramics, materials must be vitrified.7 Clay can be fired to produce material with a glass-like structure.15.2Use the words and expressions in the box to describe each photo.
You will need to use somewords more than once. Look at B opposite to help you.annealed glasslaminated glasssafety glasstempered glasstoughened glasswindscreen315.3Complete the article about bulletproof glass from a science and technology magazine, usingwords from B opposite. Sometimes, more than one word is possible.'Bulletproof' is a loosely used word, suggesting something is totally unbreakable.
But technicallyspeaking, how accurate is the term 'bulletproof glass'? Outside of Hollywood movies, can glassreally stop bullets? The answer is, not on its own. But if several (1) ................................ of glass aresandwiched with a high-strength polymer to form (2) ................................ glass, a bullet-resistant, if notcompletely bulletproof. barrier can be obtained.The technique of sandwiching polymer and glass is nothing unusual. Car windscreens are made by(3) ................................
glass to a polymer, such as polyvinyl butyral (PVB), to form a type of safety glassUnlike the other main type of safety glass- (4) ................................ glass -laminated glass remainsintact on breaking. If a stone hits a windscreen, even though a small section of the glass on theoutside may crack, the polymer behind it will stop the stone, and also ensure the entire piece ofglass doesn't (5) ................................ Bullet-resistant glass uses the same principle, but must be muchtougher. A stronger polymer is therefore used - often polycarbonate - as well as a greater numberof (6) ................................ of glass and polymer.01Ove,r ..f-o tjou ~Think about the different ceramics and minerals used in your industry, or in an industryyou're familiar with. What types of material arc used, and why?Professional English in Use Engineering37Concrete-Concrete mix designCementSand - fine aggregateGravel - coarse aggregateCement is a key material in construction.
It consists of a very fine powder. When wateris added to cement, a chemical reaction occurs, and the cement begins to set - it starts tobecome solid. The most widely used cement-based material is concrete, which is made fromcement, fine aggregate (sand), coarse aggregate (gravel) and water.
After concrete has set,it needs time to reach its structural strength - the strength needed to perform effectively.Generally, engineers consider that this strength is reached after 28 days - a point called28-day strength.Concrete mix designs, which are specified by engineers, state the proportions of cement, fineaggregate and coarse aggregate to be used for specific structures. For example, a 1:2:4 (onetwo-four) mix consists of one part cement, two parts fine aggregate and four parts coarseaggregate. For mixing precise quantities- known as hatching- proportions are measured byweight. Mix designs also specify the water-cement ratio - the amount of water added relativeto the amount of cement used.
Excess water reduces the strength of concrete, so the quantityof water is kept to a minimum. But as drier concrete is more difficult to work with, anadditive (added chemical substance) called a plasticizer is often used. This helps the concreteto flow more easily. Other additives can also be used- for example, a retarder may be addedto delay setting, which gives workers more time to pour (place) the concrete.Reinforced concreteReinforced concrete (RC) structures containsteel bars. Steel reinforcement is needed mainlybecause concrete is weak in tension - that is, badat resisting stretching forces . As steel is strong intension, reinforcing bars overcome this weakness.In order to form the different parts of structures,formwork - sometimes also called shuttering - isused.
This consists of moulds of the required sizeand shape, made from steel or timber, which areused to contain the concrete until it has set.In-situ reinforced concrete being pouredWhen wet concrete is cast (placed) in its final position, it is called in-situ concrete. Instead ofbeing cast in-situ, reinforced concrete elements can also be precast- cast at a factory - thendelivered to the construction site ready for assembly. Sometimes, precast concrete is alsoprestressed. With prestressing, tension is applied to the reinforcing bars, by machine, usuallybefore the concrete is poured.
The bars are then held in tension while wet concrete is pouredaround them. After the concrete has fully set, the bars become 'trapped' in tension. Thisincreases the concrete's ability to resist bending forces.38Professional English in Use Engineering16.1Find words and expressions in A opposite to match the descriptions (1-10).1 gravel used in concretesand used in concretepowder that enables concrete to setmixing concrete accuratelyspecification of concrete ingredientseffective structural capability of concreteaffects th e wetness and strength of concrete8 different types of chemical put in concrete9 allows concrete to stay wet fo r longer10 makes drier concrete easier to work with23456716.2Complete the tex tbook extract about a type of prestressed concrete using the words in thebox.
Look at B opposite to help yo u.castconcreteformworkin-situpourmgprecastprestressingreinforcementstructuralPrestressing techniquesIn the production of reinforced concrete components, the process of (1) ................................usually involves holding the (2) ................................ in tension while (3) ................................the concrete. This form of prestressing is called pre-tensioning, as tension is appliedbefore the concrete is poured .
The technique is often used in the manufacture of floorcomponents, which are small enough to fit on the back of a truck, and can therefore be(4) ................................ at a factory.A less common prestressing technique is post-tensioning (applying tension after theconcrete has set). This is more suitable for large elements, especially long beams, whichcannot be transported, and therefore need to be poured (5) .................................
Before theconcrete is poured, ducts (usually plastic tubes) are placed inside the (6) ............................... .along the length of the beam . These ducts contain steel cables. After the concrete hasbeen (7) ................................ and has gained sufficient (8) ................................ strength, the cablesare put in tension, using jacks at either end of the beam . This is only possible becausethe cables are free to move within the ducts- it is not possible with pre-tensionedreinforcing bars, which are held fast by the hard (9) ................................ surrounding them .The ends of the cables are then permanently anchored at either end of the beam.cable anchoredat each endcable inside ductPost-tensioned reinforced concreteOve,r .f-o t:tou~Think about a reinforced concrete structure in your area - for example, a building or abridge.
In what sequence do you think it was built? Do you think it was poured in-situ,or were its parts precast?Professional English in Use Engineering39WoodCategories of woodThe two main categories of wood are:•hardwood - usually from deciduous trees, which lose theirleaves in autumn, although some hardwood (for example,tropica l hardwood) comes from other types of tree•softwood - from coniferous trees, which remain green throughout the year.In engineering, wood can be categorized as:•solid wood - softwood or hardwood that has been sawn into specific shapes and sizes, butwhose natural structure, consisting of grain and knots, remains intact•engineered wood- made by bonding {sticking together) layers of solid softwood orhardwood, or by mixing quantities of wood particles and bonding them with resin.Notes: In ind ustry, wood is oft en referred t o as t imber (BrE) or lumber (AmE).In American Engl ish, tim ber genera lly means wood that is still growing in trees.Knot is pronounced /not / (the k is si lent).Solid structural timberThe text below is from a technical handbook about structural timber- wood intended tosupport loads in a structure.Generally, timbe r is cut to th e requ ired section- the width and depth tha t determin e its crosssection -at a sawmill, whe re a range of section sizes are produced.
Timber from sawm illsis generally supplied in rough-sawn sections. Thi s refers to the surface te xture produced bysawing timber with a circular saw. If the timber needs to have a smooth finish - for exa mple,because it will be visible in the structure- it can subsequ ently be planed to smooth its surface.Because the strength of wood varies , structural timber must be stress-graded . Th is means itsstrength is tested in order to give it a stress grade- a stand ard strength value which an engineercan use for design calculations .
Timber can be mechanically stress-graded, where its strengthis checked by machin e. It can also be visually stress-graded , where the wood is exam ined by aninspector w ho looks for pote ntial weaknesses- in part icular, the position of knots.Engineered woodEngineered wood covers a range of softwood and hardwood materials. It includes:•cheap, low-strength boards, such as particle board (often called chipboard) and mediumdensity fibreboard (MDF)•stronger boards suitable for structural use - primarily orientated strand board (OSB),which is made from strands of wood bonded with resin, and plywood, which consistsof several plies {layers) of solid wood, bonded so that the grain of each ply runs at 90degrees to that of the adjacent plies, to provide increased strength•glue-laminated sections- sometimes called glulams - which can be used as majorstructural elements, such as beams, in large buildings.Particle board or chipboard40Professional English in Use EngineeringOrientated strand board (OSB)Plywood17.1Match the two parts to make correct sentences about wood .
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