which of the drawings is more realistic explain
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ЗНАЕТЕ ЛИ ВЫ?
B Types of views used on drawings
АНГЛІЙСЬКА МОВА
Методичні рекомендації
для самостійної роботи студентів денної та заочної форм навчання зі спеціальності 8.10010203 " Механізація сільського господарства "
Миколаїв
УДК 811.111
ББК 81.2 Англ
Друкується за рішенням науково-методичної комісії факультету культури й виховання Миколаївського національного аграрного університету від 28.01.14 р., протокол № 5.
Укладачі:
О. В. Артюхова – канд. пед. наук, доцент кафедри іноземних мов Миколаївського національного аграрного університету.
А. Л. Лапчевська - викладач кафедри іноземних мов Миколаївського національного аграрного університету.
Рецензенти:
А. К. Солодка – канд. пед. наук, доцент кафедри іноземних мов факультету філології Миколаївського національного університету ім. В. О. Сухомлинського;
К. В. Тішечкіна – канд. філол. наук, доцент кафедри іноземних мов Миколаївського національного аграрного університету.
©Миколаївський національний
аграрний університет, 2013
ЗМІСТ
| Передмова ............................................................................... | |
| 1 Drawings ....................................................................................... | |
| 2 Design development ...................................................................... | |
| 3 Design solutions ............................................................................ | |
| 4 Horizontal and vertical measurements ....................................... | |
| 5 Locating and setting out ............................................................... | |
| 6 Dimensions of circles ................................................................... | |
| 7 Dimensional accuracy ................................................................... | |
| 8 Numbers and calculations ............................................................ | |
| 9 Area, size and mass ....................................................................... | |
| 10 Measurable parameters ............................................................... | |
| 11 Material types .............................................................................. | |
| 12 Steel ............................................................................................. | |
| 13 Non-ferrous metals ...................................................................... | |
| 14 Polymers ...................................................................................... | |
| 15 Minerals and ceramics ................................................................ | |
| 16 Concrete ...................................................................................... | |
| 17 Wood ........................................................................................... | |
| 18 Material properties 1 ................................................................... | |
| 19 Material properties 2 ................................................................... | |
| 20 Forming, working and heat-treating metal ............................... | |
| 21 Material formats .......................................................................... | |
| 22 3D component features ............................................................... | |
| 23 Machining 1 ................................................................................. | |
| 24 Machining 2 ................................................................................. |
ПЕРЕДМОВА
Методичні рекомендації та навчальний матеріал з іноземної мови для аудиторної та самостійної роботи призначено для студентів 5 курсу ОКР «Магістр» факультету механізації денної форми навчання за всіма напрямами підготовки.
Основною метою даних рекомендацій є формування необхідної комунікативної спроможності у сферах ситуативного професійного спілкування в усній та письмовій формах, забезпечення розвитку навичок аналітичного читання, розуміння та перекладу професійно-орієнтованих іншомовних джерел, написання рефератів, анотацій та інших документів іноземною мовою.
Основними завданнями методичних рекомендацій є формування у студентів умінь і навичок для практичного володіння діловою іноземною мовою під час усного та письмового професійного спілкування у конкретній галузі, користування усним монологічним та діалогічним мовленням у межах побутової, суспільно-політичної та фахової тематики, перекладу з іноземної мови на рідну текстів професійного спрямування.
Мотивацією для студентів піч час роботи з даними методичними рекомендаціями служить професійна потреба студента стати висококваліфікованим фахівцем з умінням спілкуватися іноземною мовою та здобути інформацію з новітньої іноземної літератури за фахом, аналізувати її та використовувати у своїй науково-дослідній роботі. Дисципліна « Іноземна мова за професійним спрямуванням» - важлива складова частина підготовки фахівців аграрного профілю в умовах постійного розширення міжнародних зв`язків України.
За кожну тему студент може отримати від 15-25 балів, що передбачено навчальною програмою з іноземних мов.
Методичні рекомендації розроблені згідно до вимог типової базової програми. Запропоновані вправи та завдання забезпечують швидке й ефективне засвоєння студентами лексичного матеріалу.
Для підготовки методичних рекомендацій використовувались матеріали з новітніх підручників, автентичних джерел та періодичних видань.
Drawings
A Drawing types and scales
In engineering, most design information is shown on drawings. Today, drawings are generally not drawn by hand. They are produced on computer, using CAD (computer-aided design) systems. A key factor on a drawing is the scale - that is, the size of items on the drawing in relation to their real size. When all the items on a drawing are shown relative to their real size, the drawing is drawn to scale, and can be called a scale drawing. An example of a scale is 1:10 (one to ten). At 1:10, an object with a length of 100 mm in real life would measure 10 mm on the drawing.
Most engineering designs consist of a set of drawings (a number of related drawings): General arrangement (GA) drawings show whole devices or structures, using a small scale.
This means objects on the drawing are small, relative to their real size (for example, a 1:100 drawing of an entire building).
Detail drawings show parts in detail, using a large scale, such as 1:5 or 1:2. Small parts are sometimes shown in a detail as actual size (1:1), or can be enlarged to bigger than actual size (for example, 2:1).
For electrical circuits, and pipe and duct networks, it is helpful to show designs in a simplified form. In this case, schematic drawings (often referred to as schematics) are used.
An everyday example is the map of a train network.
| Notes: | When written, drawing is often abbreviated to dwg. CAD is pronounced as a word: /kaed/. |
B Types of views used on drawings
1.1 Complete the sentences. Look at A opposite to help you.
1. Enlarged drawings show components larger than their .......... ........ .
2. For engineering drawings, 1:5 is a commonly used ........................ .
3. Whole machines or structures are shown on ...... ...... .drawings.
Electrical drawings don't usually show sizes. They're shown as .........
A ........ of drawings for a large project can consist of hundreds of pages.
Most drawings are produced on computers, using ........ software.
1.2 Match the descriptions (1-6) with the names of views used on drawings (a-f). Look at B opposite and Appendix I on page 98 to help you.
1. a 2D view of the side of an object
2. a 2D view inside an object, as if it is cut through
3. a 2D view, looking down on top of an object
4. a 3D view, showing an assembly taken to pieces
5. a 3D view, with the 2D face of the object at the front
6. a 3D view, with a corner of the object at the front
a. a plan
b. a section
c. an isometric projection
d. an oblique projection
e. an exploded view
f. an elevation
1.3 Write the full forms, in words, of the abbreviations and shortened terms below. Look at A and B opposite .
1. GA
2. CAD
3. dwg
4. 3D
5. section
6. 1:50
1.4Complete the sentences, taken from conversations about drawings, using the words and abbreviations in the box.
| 3D | detail | elevation | GA | plan | scale | schematic | section |
1. We need a...........through the bridge, showing the profile of the deck.
2. The only drawing we have is the.........,which is 1:100, so it obviously doesn't show things in detail.
3. On drawing 12, there's a large...........of the entire top deck of the ship.
4. This is the........showing the front face of the tower.
5. Modern CAD systems can produce.........drawings that look almost as realistic as photographs.
6. We don't need dimensions and positions at this stage. We just need a...........showing how many branches come off the main supply pipe.
Over to you
Imagine you are in a meeting at the start of a project. You and your colleagues are about to begin work on the design of a device, installation or structure you're familiar with. What types of drawing will be needed to communicate the design
Design development
A Initial design phase
A structural engineer from a firm of consulting engineers has sent an email to a more senior colleague, with an update on a project for a new airport terminal.
Stefan, We had our first design meeting with the airport authority and the architect yesterday. As you know, the client just gave the architect a short list of essential requirements for the terminal, so the design brief was pretty open. As a result, the ideas he's come up with form quite an adventurous concept. However, things are still at an early stage - there are no scale drawings yet, just eight sketches showing roughly what he wants the building to look like. So it wasn't possible to assess the design in detail. The next step is for the architect to develop the sketches into preliminary drawings. These are due at the end of April.
B Collaborative development
When a design team consists of engineers and consultants from different organizations, the design development process needs to be carefully co-ordinated.
Before the first draft (version) of a drawing is sent to members of the team, a decision is made about who needs a copy. Sometimes, a drawing will only be issued to certain specialists in the team. Sometimes, it will be circulated to all the team members.
After team members have received a drawing, they can comment on it, and may ask for the design to be changed. Following these comments, the drawing will be revised - that is, drawn again with the requested changes made to it. Every drawing is numbered, and each time a , drawing is amended (revised), the letter next to the drawing number is changed. Therefore drawing 110A, after a revision, becomes 11 OB. When revision B is issued, it becomes the current drawing, and A is superseded. With each new revision, written notes are added to the drawing. These describe the amendments that have, been made.
When engineers revise drawings during the early stages of the design process, they may have to go back to the drawing board (start again), and redesign concepts completely. For later revisions, the design should only need to be refined slightly.
After a preliminary drawing has been finally approved (accepted), a senior engineer can sign off (authorize) the drawing as a working drawing - that is, one that the production or construction team can work to.
However, this does not always mean the drawing will be final. Often, working drawings go through more revisions to resolve problems during production.
2.1 Find words in A opposite with the following meanings.
1. a description of design objectives
2. a rough, hand-drawn illustration
3. an initial diagram, requiring further development
4. an overall design idea
2.2 Put the words in the box into the table to make groups of verbs with similar meanings. Look at B opposite to help you.
| amend | circulate | redesign | revise | supersede |
| approve | issue | refine | sign off |
| change | send out | accept | replace |
| improve | distribute | agree | |
2.3 Choose the correct words from the brackets to complete the sentences about drawings. Look at B opposite to help you.
1. Has the drawing been revised, or is this the first (draft/refine)?
2. This has been superseded. It's not the (current/preliminary) drawing.
3. Has this drawing been signed off? Can they (circulate/work) to it in the factory?
4. I still need to (comment/note) on the latest set of drawings.
5. Construction can't start until the first (current/working) drawings have been issued.
2.4 Complete the email using the correct forms of the words in the box. Look at B opposite to help you. The first one has been done for you.\
| amendment | current | draft | issue | note | revision | supersede | work |
There seems to be a problem with dwg 1120, which you (1)....... issued ....... yesterday. The drawing is marked as (2)............ C, but there are no in the right-hand column detailing the (4) .........made. And on the actual drawing, there are no visible differences from the first (5)...... Has the (6)...... version (1120B) been sent accidently, incorrectly labelled as 1120C, instead of the new drawing? Please advise asap, as we are assuming this is not the (7)........ drawing, and I have therefore told the fabrication team not to (8)........ to it until we receive clarification.
Over to you
Think about design development on a project you have worked on, or on a type of project you know about. Describe the key stages from the design brief to the issue and ongoing revision of working drawings. Say how designers, consultants and production teams are involved at each stage of the process, and explain what procedures are used.
Design solutions
A Design objectives
The web page below is from a manufacturing company's intranet.
Company design procedure ― the design brief A design brief for the proposed product should be drawn up by the project engineer. This should consist of a detailed list of technical objectives which the design team must work to, in order to produce a design solution. Key elements of the brief are: ● function - the product's intended use (what it is designed to do), including performance targets (strength, power, durability, etc.) ● constraints - limits on the design (for example, it must not exceed a maximum size or weight limit)comparative targets - how well the product should perform, compared with existing models (competing products already on the market, or the current model that the new product will replace) ● design features - specific things the new design must have (for example, rechargeable batteries, or a lid with a lock) ● budget - the cost limits that must not be exceeded, in order to make the design cost-effective.
B Design calculations
Design information is shown on drawings, and written in specifications - documents which describe the materials, sizes and technical requirements of components. In order to specify this detailed information, an engineer must evaluate - that is, identify and calculate - the loads (forces) that key components will have to carry. To do this, the engineer needs to determine (identify) the different loads, then quantify them - that is, calculate them in number form. Usually, each load is quantified based on a worst-case scenario - in other words, the engineer will allow for the maximum load, such as an aircraft making a very hard landing, or a bridge being hit by extremely high winds.
After maximum loads have been quantified, an engineer will apply a factor of safety. This is an extra margin to make the component strong enough to carry loads that are higher than the worst-case scenario. For example, a factor of 1.5 increases the load a component can carry by 50%. After this has been factored in, the engineer will then size the components - that is, calculate their required size.
Engineers are sometimes criticized because they overdesign things (add excessive factors of safety), which increases costs. However, according to Murphy's Law, 'Anything that can go wrong, will.' This suggests that belt and braces - an expression often used in engineering, based on the safest method of holding up trousers - is a sensible approach.
3.1 Complete the sentences from technical conversations using the words in the box. Look at A opposite to help you.
| budget | cost-effective | exceed | feature proposed |
| constraint | designed | existing | function |
1 Of course, money is limited. Cost limitations are always a ........... .
But some finance is available. A ....... has been allocated for the preliminary design phase - a total of $35,000. But we mustn't ..... that amount.
2 Obviously, if we have to spend ?70, that's not a ............. design solution.
3 The ........ of this detector is to locate underground cables by giving audio feedback. Since it's ....... to be used in noisy environments, the earphone is an important ........ .
4 Are these already on the market - are they ....... products? Or are we talking about ....... products that are still under development?
3.2 Choose the correct words from the brackets to complete the sentences. Look at B opposite to help you.
1. The types of loads that will be encountered must be (designed / determined).
2. Maximum loads are based on predicted (specifications / worst-case scenarios).
3. On top of maximum loads, additional safety margins are (factored in / sized).
4. For cost reasons, components shouldn't be (overdesigned / quantified).
5. The practice of overdesigning components can be described as the (belt and braces / factor of safety) approach.
6. (Quantifying / Sizing) components means calculating their dimensions.
3.3 Replace the underlined words and expressions with alternative words and expressions from A and B opposite.
Over to you
Think about overdesign in a field of engineering you are familiar with. How easy or difficult is it to predict and quantify loads? How serious are the consequences (human and financial) of technical failures? As a result, how high are typical factors of safety?
A Linear dimensions
The web page shows the key dimensions of the Airbus A380 in metres, and the explanations below it describe how they are measured. In the explanations, the word plane means an imaginary surface (not an aeroplane). On drawings, planes are shown as lines that indicate where dimensions are measured from and to, and are positioned to strike (touch) the faces (edges or surfaces) of components. Often, they are either horizontal planes or vertical planes.
Airbus A380 dimensions:
Overall length is a measurement of how long the aircraft is in total. The measurement is taken between the two points that are furthest apart (the front and rear extremities), along the length of the aircraft. The length is measured along a horizontal plane. It is the distance between a vertical plane striking the front of the nose, and a vertical plane striking the rear of the tail.
Wingspan is the total distance spanned by both wings. The span is measured as a straight line * between the two wingtips.
Overall height measures how tall the aircraft is. The dimension is measured vertically between the underside of the wheels and a horizontal plane striking the top of the tail.
Maximum fuselage width is the external width of the aircraft's body - how wide it is, measured horizontally between vertical planes striking the outside faces of the fuselage.
Maximum cabin width states the maximum internal width, measured between the inside faces of the fuselage. The measurement is equivalent to the external width, less the thickness of the fuselage at each side of the aircraft.20
| Notes: | When written, the words dimension and dimensions are often abbreviated to dim and dims. Span is also used to describe the distance crossed by a bridge, between its supports. If a bridge has a support at its centre (as well as at each end), then it has two spans. |
B Level and plumb
If a surface is described as being level, this means it is both horizontal and flat (smooth). However, a surface which is flat is not necessarily horizontal. A flat surface may be vertical, or inclined (sloping at an angle to the horizontal or vertical plane).
Faces that are vertical, such as those of the walls of buildings, are described by engineers as being plumb. Structures that are slightly inclined from vertical are said to be out of plumb.
4.1 Complete the key dimensions of the Millau Viaduct in France, using the words in the box. Look at A opposite to help you.
| height | overall | thickness | span | width |
1) ................................ length: 2,460 m
2) Maximum...............................between supports:342 m
3) ...............................of tallest support (ground to deck): 245 m
4) ...............................of deck: 32 m
5) ...............................of deck: 4.2 m
4.2 Decide whether the sentences about the viaduct are true or false, and correct the false sentences. Look at A and B opposite to help you.
1. The height of the towers is measured horizontally.
2. The overall span is measured along the width of the bridge.
3. The tops of the towers are at different levels, so a horizontal plane striking the top of one tower will not strike the tops of all the others.
4. The highest point of the structure is the top extremity of the highest tower.
5. The thickness of each tower decreases towards the top, so the faces of the towers are plumb.
6. The greatest thickness of each tower is its internal thickness at its base.
4.3 Circle the correct words to complete the text about extra-high voltage (EHV) power lines. Look at A and B opposite to help you. The first one has been done for you.
On EHV transmission lines, cables - called conductors - (1) incline /span between pylons, which are described as supports. The conductors are suspended from the supports by rods, called insulators. On straight sections of line, the insulators are (2) level / plumb, hanging vertically from the supports. At supports where the direction of the line changes, pairs of insulators are used. In this situation, the insulators are (3) inclined / striking from the vertical plane, as they are pulled (4) plumb / out of plumb by the conductors pulling in different directions. The higher the voltage being transmitted by the line, the greater the required distance between the conductor and the support, in order to provide effective insulation. The (5) length / width of insulators therefore varies, depending on the voltage. Higher voltages also mean that conductors must be located at a greater minimum (6) height / thickness above the ground, for safety. This distance is measured between the ground and the lowest point of the cable.
4.4 Read the text below. Can you answer the questions?
On long suspension bridges, when the distance between the vertical centres of the towers at either side of the bridge is measured horizontally, the distance between the tops of the two towers will be several millimetres longer than the distance between their bases. Does this mean the towers are out of plumb? Why is there a difference?
Over to you
Think of a product with a fairly simple shape. What dimensions would need to be specified on a drawing in order to allow the product to be manufactured?
Locating and setting out
A Centrelines and offsets
The drawing below shows the position of some holes for bolts. The distances between the holes can be shown as running dimensions or as chain dimensions. In both cases, the centreline (CL) - a line through the centre of the hole - is marked (drawn), and the distances between the centrelines are given. Distances between centrelines are called centre-to-centre (c/c) dimensions. The holes below are at 100 mm centres.
Centrelines are often used as reference points. These can be measured from, in order to locate - that is, give the position of - points on components. The measurements are offset from the centreline - each is at a certain distance from it, and the offsets are measured at a right-angle to the centreline (at 90 degrees to it).
| Notes: | We can say at a right-angle to X, at 90 degrees to X, or at right-angles to X. |
B Grids
In large designs, notably those of structures, grids are used for horizontal positioning. The gridlines have numbers and letters. All numbered gridlines are parallel with one another - that is, they are straight, and are regular distances apart. Lettered lines also run parallel with one another, and are perpendicular to (at a right-angle to) the numbered lines.
The plan below shows part of the floor of an office building. The perpendicular gridlines intersect at (cross at) the centres of columns. An opening (hole) in the floor is shown using coordinate dimensions. These allow the site engineer to set out (mark the position of) the opening by squaring off the gridlines - marking lines that run at a right-angle to them - and then measuring along these lines using a tape measure.
A theodolite - an optical device used for measuring angles - can be used to square off gridlines accurately. To double-check dimensions - that is, carry out an extra check - diagonal measurements can be used, as in the engineer's sketch below. The length of diagonals can be calculated using Pythagoras's Theorem.
5.1 Look at the sentences about the design of a ship. Replace the underlined words and expressions with alternative words and expressions from A opposite.
1. The handrail is fixed by 115 brackets, which are 175 mm apart, between their centres.
2. The dimensions are measured from the line down the middle of the ship.
3. How far is the widest point of the ship located away from the centreline?
4. Are the adjacent lengths of handrail at 90 degrees to each other?
5. These dimensions allow you to establish the position of the hole.
5.2 Look at the extracts from technical discussions on a construction site. Complete the sentences using the words in the box. Look at B opposite to help you.
| Gridline | intersect | parallel | perpendicular | set | out | quare | off |
1 According to this drawing ......... 8 runs along the external wall of the structure.
2 The positions were marked accurately - they were .......... by our site engineer.
3 The external wall runs along gridline I, and the internal corridor wall runs along gridline 2, so the walls are .........with each other.
4 I've marked a cross on the concrete floor, showing where the two gridlines ............. .
5 We need to show the position of the corner of the staircase with coordinate dimensions. There should be two .......... dimensions, taken from two gridkines.
6 We'll use the theodolite to ......... the gridline and mark a ninety-degree offset.
Over to you
Choose a nearby object, or part of a building. Describe it, using language from A and B opposite. (You could also give approximate measurements) Then imagine you are designing the object or the part of the building. What dimensions and lines will be needed on the drawings in order to locate its features?
Dimensions of circles
A Key dimensions of circles
An engineer is giving a training course to a group of technical sales staff who work for a tyre manufacturer. During the talk, she mentions a number of dimensions relating to circles.
'Obviously, the outside edge of a tyre forms a circle, as you can see in this simple diagram. The outer circle in the diagram is the outside of the tyre, and the inner circle - the circle with the smaller diameter - represents both the inside of the tyre and the outside of the wheel. And, clearly, the inner circle is right in the middle of the outer circle - it's exactly in the centre. So because it's central, that means the inside and outside of the tyre form concentric circles. And as the tyre is circular, simple geometry tells us that measurements of the radius, taken from the centre of the circle to different points on its edge- points on the circumference - are equal. All the radii are the same. In other words, the tyre has a constant radius.'
'But when a tyre is fitted to a vehicle, it's compressed against the road surface. That means its geometry changes. So while the wheel the inner circle - obviously remains round, the circumference of the tyre - the outer circle - changes shape. It deforms. Before deformation, this part of the tyre forms an arc of the circle, between points A and B. So, as you can see in this diagram, it's not a straight line - it's a curved line. But after deformation, it's no longer a curve. The tyre becomes deformed between points A and B. It becomes a chord of the same circle, forming a straight line between A and B. However, the length of a chord and the length of an arc, between the same two points on a circle, are different. So the design of the tyre has to allow for this change in shape - from a rounded edge to a straight edge.'
B Pipe dimensions
Specific terms are used to describe the circular dimensions of pipes. The width of the inside of a pipe is called the inside diameter (ID). It can also be called the bore. The outside width is called the outside diameter (OD). When pipes are laid horizontally, the top of the outside of the pipe is called the crown, and the bottom of the inside of the pipe is called the invert.
6.1 Complete the notes, made by a salesperson attending the engineer's talk, using the words in the box. Look at A opposite to help you.
| arc | circular | constant | deformed | radius |
| chord | circumference | curved | diameter |
Before tyres are fitted to vehicles:
- shape is round - outside edge is perfectly (1) ......
- distance from centre of wheel to edge of tyre = (2) .......
- total distance across tyre = 2 x radius = (3) ....... of tyre
- all measurements from centre to points around tyre's (4) ....... are equal - tyre has (5) ...... radius
- bottom of tyre is (6)..... of a circle
When fitted to vehicle, bottom of tyre is compressed and (7) ......- changes from (8) ..... line to straight line. Straight line is (9) ....... of a circle.
6.2 Find words and expressions in B opposite with the following meanings. One question has two possible answers.
1. the highest point of a horizontal pipethe lowest point of the inside of a horizontal pipe
2. the maximum overall external width of a pipe
3. the maximum internal width between the pipe walls
6.3 Change one word in each of the sentences below to correct them. Look at A and B opposite to help you.
1. The distance travelled by the vehicle each time its wheels turn completely is equal to the radius of one of its tyres.
2. The diameter of the tyre is measured from the centre of the wheel to the outside edge of the tyre.
3. The radius of the curve in the motorway is constant, so the edges of the road follow chords of a circle.
4. The curve in the motorway has a constant radius, so the inside and outside edges of the road are arcs of two deformed circles that have the same centre.
5. The invert is on the circumference of the external face of the pipe, and therefore cannot be in contact with the liquid flowing inside the pipe.
6. The thickness of the wall at the bottom of the pipe, plus the distance between the invert and the crown of the pipe, is equal to the inside diameter of the pipe.
Over to you
Choose an object which has circular and/or curved shapes. Describe it using language from A opposite. (You could also give approximate measurements)
Imagine you are designing the object. What measurements and lines will be needed to define its circular/curved features?
Dimensional accuracy
A Precision and tolerance
It is impossible to produce components with dimensions that are absolutely precise, with sizes exactly the same as those specified in a design. This is because all production processes are imprecise to a certain extent. Therefore, the sizes of several components produced from the same design will vary (differ). Although the variation may only be a few hundredths of a millimetre, sizes will not be 100% accurate (exact) compared with the design.
Because engineers know that accuracy cannot be perfect, in designs they often specify tolerances - that is, acceptable variations in precision. Instead of giving one precise size, a tolerance specifies a range of acceptable sizes - an allowed amount of variation. This is often given as a deviation (difference) from a precise size.
The drawing below shows a shaft with a specified diameter of 88 mm, plus or minus (+) 0.05 mm. This means the diameter may deviate 0.05 mm either side of this size. Therefore, diameters of 87.95 mm and 88.05 mm, which are slightly inaccurate, are still permissible (allowed), as they are within tolerance. However, diameters of 87.94mm or 88.06mm are not permissible - they are outside tolerance.
When the permissible deviation in size is very small, we say it is a tight tolerance (or a close tolerance). A large permissible deviation is a loose tolerance. For example:
Machining a metal component to a tolerance of ±0.1 mm is relatively easy to do, so this tolerance is loose. But a tolerance of just ±0.01 mm is a tight tolerance in metalworking.
In a concrete structure, ±10mm is a loose tolerance. But ±lmm is tight, because it is difficult to place wet concrete accurately.
B Fit
When one component goes through another, such as a shaft or a bolt going through a hole, the two must fit together - their sizes and shapes must match. The key question is, how tightly (or loosely) should they fit together? There are two main types of fit:
A clearance fit allows a component to slide or turn freely, by leaving clearance (a gap) between itself and the sides of the hole. This distance must be quite precise. If there is insufficient clearance - if the gap is too small - the component will fit too tightly. As a result, the component will bind - it will not be able to slide or turn freely. In other words, there will not be enough play. However, if there is too much clearance, there will be too much play and the component will be able to move too much.
An interference fit is a very tight fit which does not allow a component to move freely inside a hole. This type of fit can be achieved by forcing the component into the hole. Alternatively, the metal around the hole can be heated so that it expands (increases in size due to heat). After sufficient expansion, the component is placed in the hole. The metal then cools and contracts (decreases in size due to cooling). The contraction results in a tight fit. An example of an interference fit is a train wheel fitted on an axle.
7.1 Find words and expressions in A opposite with similar meanings to the words and allowed exact differ exactness not exact expressions below (1-10). Sometimes there is more than one possible answer. The first one has been done for you.
1. allowed permissible
2. exact
3. differ
4. exactness
5. not exact
6. deviation between maximum and minimum
7. an acceptable deviation
8. an unacceptable deviation
9. little deviation allowed
10. large deviation allowed
7.2 Match the related sentences. Look at B opposite to help you.
1. It'll bind.
2. It'll contract.
3. It'll expand.
4. There'll be too much play.
5. It needs a clearance fit.
6. It needs an interference fit.
a. The bolt will have to turn in the hole.
b. The bolt won't be able to turn freely enough in the hole.
c. The bolt won't fit tightly enough in the hole.
d. The wheel will have to fit very tightly on the axle.
e. The hole will widen with the high temperature.
f. The shaft will shorten and narrow slightly as it cools.
7.3 Complete the article about engine blueprinting using the words in the box. Look at A and B opposite to help you.
| clearances | minus | plus | range | variation |
| fit | permissible | precise | tolerances | within |
Blueprinting for performance since they are manufactured, not to perfectly (2) .......... dimensions, but to specified (3) ......... . Although these differences may only be (4) ........ or (5) ....... a few hundredths of a millimetre, they will nevertheless result in a slight performance gap between any two engines.
One way round this problem (if you have the cash) is to have your engine blueprinted. The process is perfectly legal, as the sizes of all parts remaim (6) ....... the tolerances that are (7) ...... for the standard engine specification. However, by carefully matching pairs or groups of parts that are all in either the lower or upper half or the tolerance (8) ......, a blueprinted engine is built to (9) ....... together very precisely, thanks to almost perfect (10) ..... between moving parts.
Over to you
Think of a type of product or structure you're familiar with. Imagine you're designing it, and are discussing the tolerances required for different components. Say what tolerances are permissible, both for production (not too tight due to cost), and for quality (not too loose). Say which parts require the tightest tolerances, and explain why.
Numbers and calculations
A Decimals and fractions
A manufacturer is thinking about giving both metric measurements (for example, millimetres) and imperial measurements (for example, inches) in its product specifications. One of the company's engineers is giving his opinion on the idea in a meeting.
'One problem is, when you convert from metric to imperial you no longer have whole numbers - you get long decimal numbers. For example, one millimetre is nought point nought three nine three seven inches as a decimal.
So to be manageable, decimals have to be rounded up or down. You'd probably round up that number to two decimal places, to give you zero point zero four. Now, you might say the difference is negligible - it's so small it's not going to affect anything. But even if it's just a tiny fraction of a unit - one hundredth of an inch (1/100), or one thousandth of an inch (1/1000) - and those numbers are then used in calculations, the rounding error can very quickly add up to give bigger inaccuracies.'
Over to you
Write down a few examples of some calculations you did recently, or ones that you do frequently, and then explain them.
Area, size and mass
A Area.
Over to you
Talk about different materials that are suitable for specific engineering uses due to their density - because they are either very dense, or verу lightweight
Measurable parameters
Material types
A Metals and non-metals
Engineering materials can be divided into:
■ metals - examples of metallic materials are iron (Fe) and copper (Cu)
■ non-metals - examples of non-metallic materials are carbon (C) and silicon (Si).
As iron is such a widely used material, metals can be divided into:
■ ferrous metals - those that contain iron
■ non-ferrous metals - those that do not contain iron.
C Composite materials
The article below is from an engineering journal.
Over to you
Think of some of the materials used to make products or structures you know about. Say whether the materials are elements, compounds, mixtures, alloys or composites. If they are composites, what materials are used (a) as the matrix, and (b) as reinforcement?
Steel
A Carbon steels
This extract from an article in an engineering journal is about different types of steel.
Steel is the most widely used engineering material. Technically, though, this well-known alloy of iron and carbon is not as simple as one might think. Steel comes in a huge range of different grades, each with different characteristics. For the inexperienced, it can be difficult, to know where to begin.
A good place to start is with the two main types of steel. The first, carbon steels, consist of iron and carbon, and contain no significant quantities of other metals. Carbon steels can be divided into three main grades:
- Mild steel - the most widely used grade - is a low carbon steel which contains up to approximately 0.3% carbon.
- Medium carbon steel contains between approximately 0.3% and 0.6% carbon.
- High carbon steel contains between approximately 0.6% and 1.4% carbon.
| Notes: | The chemical symbol for iron = Fe, and carbon = C. |
B Alloy steels
The article goes on to look at alloy steels.
The second main category of steel is alloy steels, which consist of iron, carbon and one or more alloying metals. Specific grades of alloy steel include:
- low alloy steels, which contain 90% or more iron, and up to approximately 10% of alloying metals such as chromium, nickel, manganese, molybdenum and vanadium
- high strength low alloy steels (HSLA), which contain smaller quantities of the above metals (typically less than 2%)
- stainless steels, which contain chromium as well as other metals - such as nickel - and which do not rust.
- tool steels, which are extremely hard, and are used in cutting tools. They contain tungsten and/or cobalt. A widely used grade of tool steel is high-speed steel, which is used in cutting tools that operate at high temperatures, such as drill bits.
| Notes: | The terms carbon steel and alloy steel can cause confusion, as carbon steels are also alloys, and alloy steels also contain carbon. The chemical symbol for chromium = Cr, cobalt = Co, nickel = Ni, manganese = Mn, molybdenum = Mo, tungsten = W, and vanadium = V. |
C Corrosion
One weakness of mild steel is that it corrodes - its surface progressively deteriorates due to a chemical reaction. This reaction takes place between the iron in the steel and the oxygen (O2) in the air, to form iron oxide. When iron corrodes, we say that it rusts. In some metals, such as aluminium (Al), the presence of corrosion is not a problem, as the layer of oxide around the metal remains hard, which prevents it from oxidizing any further. However, when mild steel goes rusty, the rust on the surface comes off continuously, and a new rusty layer forms, progressively 'eating into' the metal.
12.1 Decide whether the sentences below are true or false, and correct the false sentences. Look at A and B opposite to help you.
1. Steel is an alloy of iron and carbon.
2. Mild steel is a high carbon steel.
3. Alloy steels contain carbon.
4. Chromium and nickel are used as alloying metals in steel.
5. Low alloy steels contain more chromium than iron.
6. Stainless steel is an alloy steel.
7. Tungsten is added to steel to make it softer.
8. High-speed steel is suitable for making cutting tools that get very hot.
12.2 Use the words to complete the sentences below. There is more than one possible answer. Look at C opposite to help you.
1. When steel is exposed to air and water, it… .
2. A brown/red material on the surface of steel is called …… .
3. The strength of steel is reduced if it is … .
12.3 Complete the article about a special type of steel, using words from A, B and C opposite
. Weathering steel
The perennial problem with mild (1)….. is that it when exposed to air and water. Generally, the only solution is either to apply a protective coating, or to use another (3) ….. of steel that is resistant to the (4) ….... process - the most well-known being (5)….. steel, which contains significant quantities of (6) …... and, often, nickel.
There is, however, an alternative solution. So-called weathering steel is a special alloy suitable for outdoor use. But rather than being completely protected from corrosion, the surface of the steel is allowed to go (7) …... . Once a layer of (8) …... has formed on the surface, it stabilizes and forms a hard protective layer. This layer differs from ordinary (9) …. oxide, as it does not continue to eat into the metal. While not everyone may like the 'rusty look', weathering steel has been widely used in architectural applications and outdoor sculptures.
Over to you
Think about some items you're familiar with are made of steel, but which are not protected (for example, by paint). How serious is the potential problem of corrosion? How is it prevented or limited - for example, by using a specific grade of steel?
Non-ferrous metals
Over to you
How are non-ferrous metals used in your industry, or an industry you're familiar with? Is electroplating common? If so, what kinds of metals are used for plating, and why are these specific metals chosen?
Polymers
Over to you
Talk about specific types of polymer that are used in your industry, or an industry you're familiar with. How are they used? Which of the categories mentioned in A and B opposite do the polymers belong to?
Minerals and ceramics
B Glass
A technical adviser for a glass manufacturer is giving a briefing to a group of engineers at a trade fair.
'Sheets of glass, which are obviously flat and thin, are called float glass. This refers to the manufacturing technique where molten glass is floated on molten tin, to produce flat sheets. Usually, after float glass has been formed, it's annealed - it's left to cool slowly. But if it's left in this state, and the glass later gets broken, it breaks into dangerous, sharp pieces. So for most engineering and architectural uses, annealed glass is unsuitable. We need to use what we call safety glass.'
'One type of safety glass is toughened glass, also called tempered glass. 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 lot safer than the long, sharp pieces produced when annealed glass breaks. The disadvantage of toughened 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 impacts are a problem, another type of safety glass - laminated glass - is generally used. This is made by 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 of having a laminated material is not just that it's very strong. The layers of glass are bonded to a layer of polymer - they're stuck to the polymer - so if the glass does break, the broken pieces are held together, and don't fly.'
15.1 Decide whether the sentences below are true or false. Then, change one word in each of the false 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.
15.2 Complete the article about bulletproof glass from a science and technology magazine, using words from В opposite. Sometimes, more than one word is possible.
'Bulletproof is a loosely used word, suggesting something is totally unbreakable. But technically speaking, how accurate is the term 'bulletproof glass'? Outside of Hollywood movies, can glass really stop bullets? The answer is, not on its own. But if several (1) .........of glass are sandwiched with a high-strength polymer to form (2) ......... glass, a bullet-resistant, if not completely 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 glass.
Unlike the other main type of safety glass - (4) ......glass - laminated glass remains intact on breaking. If a stone hits a windscreen, even though a small section of the glass on the outside may crack, the polymer behind it will stop the stone, and also ensure the entire piece of
glass doesn't (5) ......... . Bullet-resistant glass uses the same principle, but must be much tougher. A stronger polymer is therefore used - often polycarbonate - as well as a greater number of (6) ....... of glass and polymer.
Over to you
Think about the different ceramics and minerals used in your industry, or in an industry you're familiar with. What types of material are used, and why?
Concrete
A Gravel - coarse aggregate
Cement is a key material in construction. It consists of a very fine powder. When water is added to cement, a chemical reaction occurs, and the cement begins to set - it starts to become solid. The most widely used cement-based material is concrete, which is made from cement, 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 called 28-day strength.
Concrete mix designs, which are specified by engineers, state the proportions of cement, fine aggregate and coarse aggregate to be used for specific structures. For example, a 1:2:4 (one- two-four) mix consists of one part cement, two parts fine aggregate and four parts coarse aggregate. For mixing precise quantities - known as batching - proportions are measured by weight. Mix designs also specify the water-cement ratio - the amount of water added relative to the amount of cement used. Excess water reduces the strength of concrete, so the quantity of water is kept to a minimum. But as drier concrete is more difficult to work with, an additive (added chemical substance) called a plasticizer is often used. This helps the concrete to flow more easily. Other additives can also be used - for example, a retarder may be added to delay setting, which gives workers more time to pour (place) the concrete.
B Reinforced concrete
Reinforced concrete (RC) structures contain steel bars. Steel reinforcement is needed mainly because concrete is weak in tension - that is, bad at resisting stretching forces. As steel is strong in tension, reinforcing bars overcome thisweakness.
In order to form the different parts of structures, formwork - sometimes also called shuttering - is used. This consists of moulds of the required size and shape, made from steel or timber, which are
used to contain the concrete until it has set. In-situ reinforced concrete being poured
When wet concrete is cast (placed) in its final position, it is called in-situ concrete. Instead of being cast in-situ, reinforced concrete elements can also be precast - cast at a factory - then delivered to the construction site ready for assembly. Sometimes, precast concrete is also prestressed. With prestressing, tension is applied to the reinforcing bars, by machine, usually before the concrete is poured. The bars are then held in tension while wet concrete is poured around them. After the concrete has fully set, the bars become 'trapped' in tension. This increases the concrete's ability to resist bending forces.
16.1 Find words and expressions in A opposite to match the descriptions (1-10).
| 1. | gravel used in concrete | ...... |
| 2. | sand used in concrete | ....... |
| 3. | powder that enables concrete to set | ..... |
| 4. | mixing concrete accurately | ...... |
| 5. | specification of concrete ingredients | .... |
| 6. | effective structural capability of concrete | ...... |
| 7. | affects the wetness and strength of concrete | ..... |
| 8. | different types of chemical put in concrete | ..... |
| 9. | allows concrete to stay wet for longer | .... |
| 10. | makes drier concrete easier to work with | ..... |
16.2 Complete the textbook extract about a type of prestressed concrete using the words in the box. Look at B opposite to help you.
| cast | formwork | pouring | prestressing | structural |
| concrete | in-situ | precast | reinforcement |
Prestressing techniques
In the production of reinforced concrete components, the process of (1)
usually involves holding the (2) .....in tension while...the concrete. This form of prestressing is called pre-tensioning, as tension is applied before the concrete is poured. The technique is often used in the manufacture of floor components, 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 offer the concrete has set). This is more suitable for large elemen
which of the drawings is more realistic explain
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