технологических специальностей METLS Metls re mterils most widely used in industry becuse of their properties



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Тексты и упражнения для студентов механико-технологических специальностей

  1.  METALS

Metals are materials most widely used in industry because of their properties. The study of the production and properties of metals is known as metallurgy.

The separation between the atoms in metals is small, so most metals are dense. The atoms are arranged regularly and can slide over each other. That is why metals are malleable (can be deformed and bent without fracture) and ductile (can be drawn into wire). Metals vary greatly in their properties. For example, lead is soft and can be bent by hand, while iron can only be worked by hammering at red heat.

The regular arrangement of atoms in metals gives them a crystalline structure. Irregular crystals are called grains. The properties of the metals depend on the size, shape, orientation, and composition of these grains. In general, a metal with small grains will be harder and stronger than one with coarse grains.

Heat treatment such as quenching, tempering, or annealing, controls the nature of the grains and their size in the metal. Small amounts of other metals (less than one percent) are often added to a pure metal. This is called alloying (легирование) and it changes the grain structure and properties of metals.

All metals can be formed by drawing, rolling, hammering, and extrusion but some require hot-working. Metals are subject to metal fatigue and to creep (the slow increase in length under stress) causing deformation and failure. Both effects are taken into account by engineers when designing, for example, airplanes, gas turbines, and pressure vessels for high-temperature chemical processes. Metals can be worked using machine tools such as lathe, milling machine, shaper and grinder.

The ways of working a metal depend on its properties. Many metals can be melted and cast in moulds but special conditions are required for metals that react with air.

Vocabulary   [vэ'kæbjulэri]  Словарь

property  ['propэti]  свойство

metallurgy  [me'tælэd3i]  металлургия

separation  [sepэ'rei∫эn]  разделение, отстояние 

dense  [dens] плотный

arrangement  [э'reind3mэnt]  расположение

regularly  ['regjulэli]  регулярно, правильно

to slide  [slaid]  скользить

malleable  ['mæliэbl]  ковкий, податливый, способный деформироваться

bend  [bent] pp of bend  гнуть

to fracture  ['frækt∫э]  ломать

ductile  ['dAktail]  эластичный, ковкий

to draw  [dro:]  волочить, тянуть

wire  ['waiэ]  проволока

lead  [led]  свинец

iron  ['aiэn]  железо, чугун

grain  [grein]  зерно

to depend  [di'pend]  зависеть 

size  [saiz]  размер, величина

shape  [∫eip]  форма, формировать

composition  [kompэ'zi∫эn]  состав

coarse  [ko:s]  грубый, крупный

treatment  ['tri:tmэnt]  обработка 

quenching  [kwent∫iŋ)]  закалка

tempering  ['tempэriŋ]  отпуск после закалки

annealing  [э'ni:liŋ]  отжиг, отпуск

rolling  ['rouliŋ]  прокатка

to hammer  ['hæmэriŋ]  ковать (напр. молотом)

extrusion  ['ik'stru:3эn]  экструзия

metal fatigue  [fэ'ti:g]  усталость металла

creep  [kri:p]  ползучесть

stress  [stres]  давление, напряжение

failure  ['feiljэ']  повреждение, разрушение

vessel  ['vesl]  сосуд, котел, судно

lathe  [lеið]  токарный станок

milling machine  ['miliŋ mэ'∫i:n]  фрезерный станок

shaper  ['∫eipэ]  строгальный станок

grinder  ['graindэ]  шлифовальный станок

to melt  melt]  плавить, плавиться

to cast  [ka:st]  отливать, отлить

mould  [mould]  форма (для отливки)

Can you answer the following questions?

1. What are metals and what do we call metallurgy?

2. Why are most metals dense?

3. Why are metals malleable?

4. What is malleability?

5. What are grains?

6. What is alloying?

7. What is crystalline structure?

8. What do the properties of metals depend on?

9. What changes the size of grains in metals?

10. What are the main processes of metal forming?

11. How are metals worked?

12. What is creeping?

  1.  STEEL

The most important metal in industry is iron and its alloy – steel. Steel is an alloy of iron and carbon. It is strong and stiff but corrodes easily through rusting, although stainless and other special steels resist corrosion. The amount of carbon in a steel influences its properties considerably. Steels of low carbon content (mild steels) are quite ductile and are used in the manufacture of sheet iron, wire, and pipes. Medium-carbon steels containing from 0.2 to 0.4 percent carbon are tougher and stronger and are used as structural steels. Both mild and medium-carbon steels are suitable for forging and welding. High-carbon steels containing from 0.4 to 1.5 percent carbon, are hard and brittle and are used in cutting tools, surgical instruments, razor blades, and springs. Tool steel, also called silver steel, contains about 1 percent carbon and is strengthened and toughened by quenching and tempering.

The inclusion of other elements affects the properties of the steel. Manganese gives extra strength and toughness. Steel containing 4 percent silicon is used for transformer cores or electromagnets because it has large grains acting like small magnets. The addition of chromium gives extra strength and corrosion resistance, so we can get rust-proof steels. Heating in the presence of carbon or nitrogen-rich materials is used to form a hard surface on steel (case-hardening). High-speed steels, which are extremely important in machine-tools, contain chromium and tungsten plus smaller amounts of vanadium, molybdenum and other metals.

Vocabulary

alloy  ['æloi]  сплав

carbon  ['ka:bэn]  углерод

stiff  [stif]  жесткий

to corrode  [kэ'roud]  разъедать, ржаветь 

rusty  ['rAsti]  ржавый

stainless  [steinlэs]  нержавеющий

to resist  [rэ'zist]  сопротивляться

considerably  [kэn'sidэrэbli]  значительно, гораздо

tough  [tAf]  крепкий, жесткий, прочный

forging  ['fo:d3iŋ]  ковка

welding  ['weldiŋ]  сварка

brittle  ['britl]  хрупкий, ломкий

cutting tools   режущие инструменты

surgical instruments  ['sэ:d3ikэl]  хирургические инструменты

blade  [bleid]  лезвие 

spring  [spriŋ]  пружина 

inclusion  [in'klu:3эn]  включение 

to affect  [э'fekt]  влиять 

manganese  [mæŋgэ'ni:z]  марганец 

silicon  ['silikэn]  кремний 

rust-proof   нержавеющий 

nitrogen  ['naitrэd3эn]  азот 

tungsten  ['tAŋstэn]  вольфрам 

Can you answer the following questions?

1. What is steel?

2. What are the main properties of steel?

3. What are the drawbacks of steel?

4. What kinds of steel do you know? Where are they used?

5. What gives the addition of manganese, silicon and chromium to steel?

6. What can be made of mild steels (medium-carbon steels, high-carbon steels)?

7. What kind of steels can be forged and welded?

8. How can we get rust-proof (stainless) steel?

9. What is used to form a hard surface on steel?

10. What are high-speed steels alloyed with?

  1.  METHODS OF STEEL HEAT TREATMENT

Quenching is a heat treatment when metal at a high temperature is rapidly cooled by immersion in water or oil. Quenching makes steel harder and more brittle, with small grains structure.

Tempering is a heat treatment applied to steel and certain alloys. Hardened steel after quenching from a high temperature is too hard and brittle for many applications and is also brittle. Tempering, that is re-heating to an intermediate temperature and cooling slowly, reduces this hardness and brittleness. Tempering temperatures depend on the composition of the steel but are frequently between 100 and 650 0С. Higher temperatures usually give a softer, tougher product. The colour of the oxide film produced on the surface of the heated metal often serves as the indicator of its temperature.

Annealing is a heat treatment in which a material at high temperature is cooled slowly. After cooling the metal again becomes malleable and ductile (capable of being bent many times without cracking).

All these methods of steel heat treatment are used to obtain steels with certain mechanical properties for certain needs.

Vocabulary

to immerse  [i'mэ:s]  погружать

to apply  [э'plai]  применять

intermediate  [,intэ'mi:diit]  промежуточный

oxide film  ['oksaid]  оксидная пленка

annealing  [э'ni:liŋ]  отжиг, отпуск

cracking   растрескивание

Can you answer the following questions?:

1. What can be done to obtain harder steel?

2. What makes steel more soft and tough?

3. What makes steel more malleable and ductile?

4. What can serve as the indicator of metal temperature while heating it?

5. What temperature range is used for tempering?

6. What are the methods of steel heat treatment used for?

  1.  METHODS OF STEEL HEAT TREATMENT

Metals are important in industry because they can be easily deformed into useful shapes. A lot of metalworking processes have been developed for certain applications. They can be divided into five broad groups:

  •  Rolling
  •  Extrusion
  •  Drawing
  •  Forging
  •  Sheet-metal forming

During the first four processes metal is subjected to large amounts of strain (deformation). But if deformation goes at a high temperature, the metal will recrystallize –  that is, new strain-free grains will grow instead of deformed grains. For this reason metals are usually rolled, extruded, drawn, or forged above their recrystallization temperature. This is called hot working. Under these conditions there is no limit to the compressive plastic strain to which the metal can be subjected.

Other processes are performed below the recrystallization temperature. These are called cold working. Cold working hardens metal and makes the part stronger. However, there is a limit to the strain before a cold part cracks.

Rolling

Rolling is the most common metalworking process. More than 90 percent of the aluminum, steel and copper produced is rolled at least once in the course of production. The most common rolled product is sheet. Rolling can be done either hot or cold. If the rolling is finished cold, the surface will be smoother and the product stronger.

Extrusion

Extrusion is pushing the billet to flow through the orifice of a die. Products may have either a simple or a complex cross section. Aluminium window frames are the examples of complex extrusions.

Tubes or other hollow parts can also be extruded. The initial piece is a thick-walled tube, and the extruded part is shaped between a die on the outside of the tube and a mandrel held on the inside.

In impact extrusion (also called back-extrusion – штамповка выдавливанием), the workpiece is placed in the bottom of a hole and a loosely fitting ram is pushed against it. The ram forces the metal to flow back around it, with the gap between the ram and the die determining the wall thickness. The example of this process is the manufacturing of aluminium beer cans.

Vocabulary

useful  ['ju:sful]  полезный

shape  [∫eip]  форма, формировать

rolling   прокатка

extrusion  [ik'stru:3эn]  экструзия, выдавливание

drawing  [dro:iŋ)]  волочение

forging  ['fo:d3iŋ]  ковка

sheet  [∫i:t]  лист

to subject  [sэb'd3ekt]  подвергать

amount  [э'maunt]  количество

condition  [kэn'di∫эn]  состояние, условие

perform  [pэ'fo:m]  выполнять, проводить

to harden  ['ha:dn]  отвердевать, упрочняться

at least   по крайней мере

common  ['komэn]  общий

billet  ['bilit]  заготовка, болванка

orifice  ['orifis]  отверстие

die  [dai]  штамп, пуансон, матрица, фильера, волочильная доска

cross section   поперечное сечение

window frame  [freim]  рама окна

tube  [tju:b]  труба

hollow  ['holou]  полый

initial  [i'ni∫эl]  первоначальный, начальный

thick-walled   толстостенный

mandrel  ['mændrэl]  оправка, сердечник

impact  ['impækt]  удар

loosely  ['lu:sli]  свободно, с зазором 

fitting   зд. посадка

ram  [ræm]  пуансон, плунжер

force  [fo:s]  сила

gap  [gæp]  промежуток, зазор

to determine  [di'tэ:min]  устанавливать, определять

Can you answer the following questions?

1. Why are metals so important in industry?

2. What are the main metalworking processes?

3. Why are metals worked mostly hot?

4. What properties does cold working give to metals?

5. What is rolling? Where is it used?

6. What is extrusion? What shapes can be obtained after extrusion?

7. What are the types of extrusion?

  1.  DRAWING

Drawing consists of pulling metal through a die. One type is wire drawing. The diameter reduction that can be achieved in one die is limited, but several dies in series can be used to get the desired reduction.

Sheet Metal Forming

Sheet metal forming (штамповка листового металла) is widely used when parts of certain shape and size are needed. It includes forging, bending and shearing. One characteristic of sheet metal forming is that the thickness of the sheet changes little in processing. The metal is stretched just beyond its yield point (2 to 4 percent strain) in order to retain the new shape. Bending can be done by pressing between two dies. Shearing is a cutting operation similar to that used for cloth.

Each of these processes may be used alone, but often all three are used on one part. For example, to make the roof of an automobile from a flat sheet, the edges are gripped and the piece pulled in tension over a lower die. Next an upper die is pressed over the top, finishing the forming operation (штамповку), and finally the edges are sheared off to give the final dimensions.

Forging

Forging is the shaping of a piece of metal by pushing with open or closed dies. It is usually done hot in order to reduce the required force and increase the metal's plasticity.

Open-die forging is usually done by hammering a part between two flat faces. It is used to make parts that are too big to be formed in a closed die or in cases where only a few parts are to be made. The earliest forging machines lifted a large hammer that was then dropped on the workpiece, but now air or steam hammers are used since they allow greater control over the force and the rate of forming. The part is shaped by moving or turning it between blows.

Closed-die forging is the shaping of hot metal within the walls of two dies that come together to enclose the workpiece on all sides. The process starts with a rod or bar cut to the length needed to fill the die. Since large, complex shapes and large strains are involved, several dies may be used to go from the initial bar to the final shape. With closed dies, parts can be made to close tolerances so that little finish machining is required.

Two closed-die forging operations are given special names. They are upsetting and coining. Coining takes its name from the final stage of forming metal coins, where the desired imprint is formed on a metal disk that is pressed in a closed die. Coining involves small strains and is done cold. Upsetting involves a flow of the metal back upon itself. An example of this process is the pushing of a short length of a rod through a hole, clamping the rod, and then hitting the exposed length with a die to form the head of a nail or bolt.

Vocabulary

to pull  [pul]  тянуть

reduction  [ri'dAk∫эn]  сокращение

to achieve  [э't∫i:v]  достигать

in series  ['siэriz]  серией, последовательно

beyond  [bi'jond]  выше, свыше

yield point  [ji:ld]  точка текучести металла

to retain  [ri'tein]  сохранять, удерживать

to bend  [bend]  гнуть 

shearing  ['∫iэriŋ]  обрезка, отрезание

edge  [ed3]  край 

to grip  [grip]  схватывать 

lower die   нижний штамп 

upper die   верхний штамп 

forming operation   операция штампования

dimension  [di'men∫эn]  измерение, размеры

required  [ri'kwaiэd]  необходимый 

increase  ['inkri:s]  увеличение 

open-die forging   ковка в открытом штампе (подкладном)

hammering  ['hæmэriŋ]  ковка, колотить

within  [wiin]  внутри, в пределах

to enclose  [in'klouz]  заключать 

rod  [rod]  прут, стержень

bar  [ba:]  прут, брусок

involved  [in'volvd]  включенный

tolerance  ['tolэrэns]  допуск

upsetting   высадка, выдавливание

blow  [blou]  удар

coining  ['koiniŋ]  чеканка

imprint  ['imprint]  отпечаток 

clamp  [klæmp]  зажим 

to hit  [hit]  ударять

Can you answer the following questions?

1. How can the reduction of diameter in wire drawing be achieved?

2. What is sheet metal forming and where it can be used?

3. What is close-die forging?

4. What is forging?

5. What are the types of forging?

6. What types of hammers are used now?

7. Where are coining and upsetting used?

8. What process is used in wire production?

9. Describe the process of making the roof of a car.

  1.  METALWORKING PROCESSES

An important feature of hot working is that it provides the improvement of mechanical properties of metals. Hot-working (hot-rolling or hot-forging) eliminates porosity, directionality, and segregation that are usually present in metals. Hot-worked products have better ductility and toughness than the unworked casting. During the forging of a bar, the grains of the metal become greatly elongated in the direction of flow. As a result, the toughness of the metal is greatly improved in this direction and weakened in directions transverse to the flow. Good forging makes the flow lines in the finished part oriented so as to lie in the direction of maximum stress when the part is placed in service.

The ability of a metal to resist thinning and fracture during cold-working operations plays an important role in alloy selection. In operations that involve stretching, the best alloys are those which grow stronger with strain (are strain hardening) — for example, the copper-zinc alloy, brass, used for cartridges and the aluminum-magnesium alloys in beverage cans, which exhibit greater strain hardening.

Fracture of the workpiece during forming can result from inner flaws in the metal. These flaws often consist of nonmetallic inclusions such as oxides or sulphides that are trapped in the metal during refining. Such inclusions can be avoided by proper manufacturing procedures.

The ability of different metals to undergo strain varies. The change of the shape after one forming operation is often limited by the tensile ductility of the metal. Metals such as copper and aluminum are more ductile in such operations than other metals.

Vocabulary

feature  ['fi:t∫э]  черта, особенность

to provide  [prэ'vaid]  обеспечивать

improvement  [im'pru:vmэnt]  улучшение

property  ['propэti]  свойство

eliminate  [i'limi,neit]  ликвидировать, исключать

porosity  ['po:'rositi]  пористость   

directional  [di'rek∫эnэl]  направленный 

to segregate  ['segrэgeit]  разделять 

casting  ['ka:stiŋ]  отливка 

elongated  ['i:lon'geitid]  удлиненный 

to weaken  ['wi:kn]  ослабевать, ослаблять 

transverse  ['trænzvэ:s]  поперечный 

flow  [flou]  течение, поток

finished  ['fini∫t]  отделанный 

thinning   утончение 

fracture  ['frækt∫э]  разрушение 

strain hardening   деформационное упрочнение

brass  [bra:s]  латунь 

beverage  ['bevэrid3]  напиток 

can  [kæn]  консервная банка 

to exhibit  [ig'zibit]  проявлять 

inner  ['inэ]  внутренний

flaws  [flo:z]  недостатки, дефекты кристаллической решетки

inclusion  [in'klu:3эn]  включение

trapped   зд. заключенный

refining  [ri'fainiŋ]  очищать, очистка

to avoid  [э'void]  избегать

to undergo  [Andэ'gou]  подвергаться

tensile ductility   пластичность при растяжении

Can you answer the following questions?

1. What process improves the mechanical properties of metals?

2. What new properties have hot-worked products?

3. How does the forging of a bar affect the grains of the metal?

4. What is the result of this?

5. How are the flow lines in the forged metal oriented and how does it affect the strength of the forged part?

6. What are the best strain-hardening alloys? Where can we use them?

7. What are the inner flaws in the metal?

8. Can a metal fracture because of the inner flaw?

9. What limits the change of the shape during forming operations?

  1.  MECHANICAL PROPERTIES OF MATERIALS

Materials Science and Technology is the study of materials and how they can be fabricated to meet the needs of modern technology. Using the laboratory techniques and knowledge of physics, chemistry, and metallurgy, scientists are finding new ways of using metals, plastics and other materials.

Engineers must know how materials respond to external forces, such as tension, compression, torsion, bending, and shear. All materials respond to these forces by elastic deformation. That is, the materials return their original size and form when the external force disappears. The materials may also have permanent deformation or they may fracture. The results of external forces are creep and fatigue.

Compression is a pressure causing a decrease in volume. When a material is subjected to a bending, shearing, or torsion (twisting) force, both tensile and compressive forces are simultaneously at work. When a metal bar is bent, one side of it is stretched and subjected to a tensional force, and the other side is compressed.

Tension is a pulling force; for example, the force in a cable holding a weight. Under tension, a material usually stretches, returning to its original length if the force does not exceed the material's elastic limit. Under larger tensions, the material does not return completely to its original condition, and under greater forces the material ruptures.

Fatigue is the growth of cracks under stress. It occurs when a mechanical part is subjected to a repeated or cyclic stress, such as vibration. Even when the maximum stress never exceeds the elastic limit, failure of the material can occur even after a short time. No deformation is seen during fatigue, but small localised cracks develop and propagate through the material until the remaining cross-sectional area cannot support the maximum stress of the cyclic force. Knowledge of tensile stress, elastic limits, and the resistance of materials to creep and fatigue are of basic importance in engineering.

Creep is a slow, permanent deformation that results from a steady force acting on a material. Materials at high temperatures usually suffer from this deformation. The gradual loosening of bolts and the deformation of components of machines and engines are all the examples of creep. In many cases the slow deformation stops because deformation eliminates the force causing the creep. Creep extended over a long time finally leads to the rupture of the material.

Vocabulary

bar  [ba:]  брусок, прут

completely  [kэm'pli:tli]  полностью, совершенно

compression  [kэm'pre∫эn]  сжатие

creep  [kri:p]  ползучесть

cross-sectional area   площадь поперечного сечения

cyclic stress  ['saiklik]  циклическое напряжение

decrease  ['di:kri:s]  уменьшение

elastic deformation   упругая деформация

elastic limit   предел упругости

exceed  [ik'si:d]  превышать

external forces  [iks'tэ:nl]  внешние силы

fatigue  [fэ'ti:g]  усталость металла   

loosen  ['lu:sn]  ослаблять, расшатывать

permanent deformation     ['рэ:mэnэnt]  постоянная деформация

remaining  [ri'meiniŋ]  оставшийся

shear  [∫iэ]  срез

simultaneously  [simэl'teiniэsli]  одновременно

to stretch  [stret∫]  растягивать

techniques  [tek'ni:ks]  методы 

tension  ['ten∫эn] напряженность

to propagate  ['propэgeit]  распространяться

to bend  [bend]  гнуть, согнуть 

to extend  [iks'tend]  расширять, продолжаться

to meet the needs   отвечать требованиям

to occur  [э'kэ:]  происходить                

to respond  [ri'spond]  отвечать реагировать 

to suffer  ['sAfэ]  страдать 

torsion  ['to:∫эn]  кручение 

twisting  ['twistiŋ]  закручивание, изгиб 

volume  ['volju:m]  объем, количество

rupture  ['rApt∫э]  разрыв

Can you answer the following questions?

1. What are the external forces causing the elastic deformation of materials? Describe those forces that change the form and size of materials.

2. What are the results of external forces?

3. What kinds of deformation are the combinations of tension and compression?

4. What is the result of tension? What happens if the elastic limit of material is exceeded under tension?

5. What do we call fatigue? When does it occur? What are the results of fatigue?

6. What do we call creep? When does this type of permanent deformation take place? What are the results of creep?

  1.  MECHANICAL PROPERTIES OF MATERIALS

Density (specific weight) is the amount of mass in a unit volume. It is measured in kilograms per cubic metre. The density of water is 1000 kg/m3 but most materials have a higher density and sink in water. Aluminium alloys, with typical densities around 2800 kg/m3 are considerably less dense than steels, which have typical densities around 7800 kg/m3. Density is important in any application where the material must not be heavy.

Stiffness (rigidity) is a measure of the resistance to deformation such as stretching or bending. The Young modulus is a measure of the resistance to simple stretching or compression. It is the ratio of the applied force per unit area (stress) to the fractional elastic deformation (strain). Stiffness is important when a rigid structure is to be made.

Strength is the force per unit area (stress) that a material can support without failing. The units are the same as those of stiffness, MN/m2, but in this case the deformation is irreversible. The yield strength is the stress at which a material first deforms plastically. For a metal the yield strength maybe less than the fracture strength, which is the stress at which it breaks. Many materials have a higher strength in compression than in tension.

Ductility is the ability of a material to deform without breaking. One of the great advantages of metals is their ability to be formed into the shape that is needed, such as car body parts. Materials that are not ductile are brittle. Ductile materials can absorb energy by deformation but brittle materials cannot.

Toughness is the resistance of a material to breaking when there is a crack in it. For a material of given toughness, the stress at which it will fail is inversely proportional to the square root of the size of the largest defect present. Toughness is different from strength: the toughest steels, for example, are different from the ones with highest tensile strength. Brittle materials have low toughness: glass can be broken along a chosen line by first scratching it with a diamond. Composites can be designed to have considerably greater toughness than their constituent materials. The example of a very tough composite is fiberglass that is very flexible and strong.

Creep resistance is the resistance to a gradual permanent change of shape, and it becomes especially important at higher temperatures. A successful research has been made in materials for machine parts that operate at high temperatures and under high tensile forces without gradually extending, for example the parts of plane engines.

Vocabulary

ability  [э'biliti]  способность

amount  [a'maunt]  количество

absorb  [эb'zo:b]  поглощать

amount  [э'maunt]  количество 

application  [,æpli'kei∫эn]  применение

brittle  ['britl]  хрупкий, ломкий

car body   кузов автомобиля 

constituent  [kэn'stitjuэnt]  компонент 

crack  [kræk]  трещина

creep resistance   устойчивость к ползучести

definition  [,defi'ni∫эn]  определение

density  ['densiti]  плотность

ductility  [dAk'tiliti]  ковкость, эластичность

failure  ['feiljэ]  повреждение

gradual  ['grædjuэl]  постепенный

permanent  ['pэ:mэnэnt]  постоянный

rigid  ['rid3id]  жесткий

to sink  [siŋk]  тонуть 

square root  ['skwεэ 'ru:t]  квадратный корень

stiffness  ['stifnis]  жесткость   

strain  [strein]  нагрузка, напряжение, деформация

strength  [streŋθ]  прочность

stress  [stres]  давление, напряжение

tensile strength   прочность на разрыв

toughness  ['tAfnis]  прочность, стойкость

yield strength  [ji:ld]  прочность текучести

Young modulus   модуль Юнга

Can you answer the following questions?

1. What is the density of a material?

2. What are the units of density? Where is low density needed?

3. What are the densities of water, aluminium and steel?

4. A measure of what properties is stiffness? When is stiffness important?

5. What is Young modulus?

6. What is strength?

7. What is yield strength? Why is fracture strength always greater than yield strength?

8. What is ductility? Give the examples of ductile materials. Give the examples of brittle materials.

8. What is toughness?

9. What properties of steel are necessary for the manufacturing of:

    a) springs, b) car body parts, c) bolts and nuts, d) cutting tools?

10. Where is aluminium mostly used because of its light weight?

  1.  MACHINE-TOOLS

Machine-tools are used to shape metals and other materials. The material to be shaped is called the workpiece. Most machine-tools are now electrically driven. Machine-tools with electrical drive are faster and more accurate than hand tools: they were an important element in the development of mass-production processes, as they allowed individual parts to be made in large numbers so as to be interchangeable.

All machine-tools have facilities for holding both the workpiece and the tool, and for accurately controlling the movement of the cutting tool relative to the workpiece. Most machining operations generate large amounts of heat, and use cooling fluids (usually a mixture of water and oils) for cooling and lubrication.

Machine-tools usually work materials mechanically but other machining methods have been developed lately. They include chemical machining, spark erosion to machine very hard materials to any shape by means of a continuous high-voltage spark (discharge) between an electrode and a workpiece. Other machining methods include drilling using ultrasound, and cutting by means of a laser beam. Numerical control of machine-tools and flexible manufacturing systems have made it possible for complete systems of machine-tools to be used flexibly for the manufacture of a range of products.

Vocabulary

machine-tools   станки

electrically driven  [drivэn]  с электроприводом

shape  [∫eip]  форма

workpiece   деталь

accurate  ['ækjэrit]  точный

development  [di'velэpmэnt]  развитие

to allow  [a'lau]  позволять, разрешать

interchangeable  [,intэ'teind3эbl]  взаимозаменяемый

facility  [fэ'siliti]  приспособление

relative  ['relэtiv]  относительный

amount  [э'maunt]  количество    

fluid  ['fluid]  жидкость

to lubricate  ['lu:brikeit]  смазывать

spark erosion  [spa:k i'rou3n]  электроискровая обработка

discharge  [dis’ta:d3] разряд

by means of   посредством

beam  [bi:m]  луч

drilling   сверление

flexible  ['fleksibl]  гибкий

range  [reind3]  ассортимент, диапазон

  1.  LATHE

Lathe is still the most important machine-tool. It produces parts of circular cross-section by turning the workpiece on its axis and cutting its surface with a sharp stationary tool. The tool may be moved sideways to produce a cylindrical part and moved towards the workpiece to control the depth of cut. Nowadays all lathes are power-driven by electric motors. That allows continuous rotation of the workpiece at a variety of speeds. The modern lathe is driven by means of a headstock supporting a hollow spindle on accurate bearings and carrying either a chuck or a faceplate, to which the workpiece is clamped. The movement of the tool, both along the lathe bed and at right angle to it, can be accurately controlled, so enabling a part to be machined to close tolerances. Modern lathes are often under numerical control.

Vocabulary

lathe  [leið]  токарный станок

circular cross-section  ['sэ:kjulэ]  круглое поперечное сечение

surface  ['sэ:fis]  поверхность

stationary  ['stei∫эnэri]  неподвижный, стационарный

sideways  ['saidweiz]  в сторону

variety  [vэ'raiэti]  разнообразие, разновидность

depth  [depθ]  глубина

headstock  ['hed,stok]  передняя бабка

spindle  [spindl]  шпиндель

chuck  [tAk]  зажим, патрон

faceplate   планшайба

lathe bed   станина станка

to enable  [i'neibl]  давать возможность

tolerance  ['tolэrэns]  допуск

Can you answer the following questions?

1. What are machine-tools used for?

2. How are most machine-tools driven nowadays?

3. What facilities have all machine-tools?

4. How are the cutting tool and the workpiece cooled during machining?

5. What other machining methods have been developed lately?

6. What systems are used now for the manufacture of a range of products without the use of manual labour?

7. What parts can be made with lathes?

8. How can the cutting tool be moved on a lathe?

9. How is the workpiece clamped in a lathe?

10. Can we change the speeds of workpiece rotation in a lathe?

11. What is numerical control of machine tools used for?

  1.  MILLING MACHINE

In a milling machine the cutter (фреза) is a circular device with a series of cutting edges on its circumference. The workpiece is held on a table that controls the feed against the cutter. The table has three possible movements: longitudinal, horizontal, and vertical; in some cases it can also rotate. Milling machines are the most versatile of all machine tools. Flat or contoured surfaces may be machined with excellent finish and accuracy. Angles, slots, gear teeth and cuts can be made by using various shapes of cutters.

Drilling and Boring Machines

To drill a hole usually hole-making machine-tools are used. They can drill a hole according to some specification, they can enlarge it, or they can cut threads for a screw or to create an accurate size or a smooth finish of a hole.

Drilling machines (сверлильные станки) are different in size and function, from portable drills to radial drilling machines, multispindle units, automatic production machines, and deep-hole-drilling machines.

Boring (расточка) is a process that enlarges holes previously drilled, usually with a rotating single-point cutter held on a boring bar and fed against a stationary workpiece.

Shapers and Planers

The shaper (поперечно-строгальный станок) is used mainly to produce different flat surfaces. The tool slides against the stationary workpiece and cuts on one stroke, returns to its starting position, and then cuts on the next stroke after a slight lateral displacement. In general, the shaper can make any surface having straight-line elements. It uses only one cutting-tool and is relatively slow, because the return stroke is idle. That is why the shaper is seldom found on a mass production line. It is, however, valuable for tool production and for workshops where flexibility is important and relative slowness is unimportant.

The planer (продольно-строгальный станок) is the largest of the reciprocating machine tools. It differs from the shaper, which moves a tool past a fixed workpiece because the planer moves the workpiece to expose a new section to the tool. Like the shaper, the planer is intended to produce vertical, horizontal, or diagonal cuts. It is also possible to mount several tools at one time in any or all tool holders of a planer to execute multiple simultaneous cuts.

Grinders

Grinders (шлифовальные станки) remove metal by a rotating abrasive wheel. The wheel is composed of many small grains of abrasive, bonded together, with each grain acting as a miniature cutting tool. The process gives very smooth and accurate finishes. Only a small amount of material is removed at each pass of the wheel, so grinding machines require fine wheel regulation. The pressure of the wheel against the workpiece is usually very light, so that grinding can be carried out on fragile materials that cannot be machined by other conventional devices.

Vocabulary

milling machine   фрезерный станок

series  ['siэriz]  серия, ряд

cutting edge   режущий край, острие

circumference  [sэ:'kAmfэrэns]  окружность

to feed  [fi:d]  подавать

longitudinal  [,lond3i'tju:dinl]  продольный

horizontal  [,hori'zontl]  горизонтальный

vertical  ['vэ:tikl]  вертикальный

versatile  ['vэ:sэtail]  универсальный

flat  [flæt]  плоский

contoured  ['kontuэd]  контурный  

angle  ['ængl]  угол

slot  [slot]  прорезь, паз

gear teeth  [giэ ti:θ]  зубы шестерни

drill  [dril]  дрель, сверло, сверлить

hole  [houl]  отверстие

to enlarge  [in'la:d3]  увеличивать

thread  [θred]  резьба

portable  ['po:tэbl]  портативный

unit  ['ju:nit]  единица, целое, узел

previously  ['pri:vjэsli]  ранее

to slide  [slaid]  скользить

stroke  [strouk]  ход

lateral  ['lætэrэl]  боковой

displacement  [dis'pleismэnt]  смещение

straight  [streit]  прямой

idle  ['aidl]  на холостом ходу

workshop  ['wэ:kop]  цех, мастерская

to mount  [maunt]  крепить

holder   держатель

to execute  ['eksikju:t]  выполнять

simultaneous  [simэl'teiniэs]  одновременный

multiple  ['mAltipl]  многочисленный

grinder  ['graindэ]  шлифовальный станок

wheel  [wi:l]  круг, колесо

bonded  [‘bondid] скрепленый

to remove  [ri'mu:v]  удалять

pass  [pa:s]  проход

fine  [fain]  точный

conventional  [kэn'ven∫эnl]  обычный

device  [di'vais]  устройство, прибор

fragile  ['fræd3ail]  хрупкий

Can you answer the following questions?

1. What is the shape of a cutter in a milling machine?

2. What moves in a milling machine, a table or a cutter?

3. What possible movements has the table of a milling machine?

4. What kind of surfaces and shapes may be machined by a milling machine?

5. What can we use a drilling machine for?

6. What kinds of drilling machines exist?

7. What is rotated while boring, a cutter or a work-piece?

8. Describe the work of a shaper (planer).

9. What must be done to execute multiple simultaneous cuts on a planer?

10. What is the working tool in a grinder?

11. Can we obtain a very smooth surface after grinding and why?

12. Can we grind fragile materials and why?

  1.  DIES

Dies are tools used for the shaping solid materials, especially those employed in the pressworking of cold metals.

In presswork, dies are used in pairs. The smaller die, or punch, fits inside the larger die, called the matrix or, simply, the die. The metal to be formed, usually a sheet, is placed over the matrix on the press. The punch is mounted on the press and moves down by hydraulic or mechanical force.

A number of different forms of dies are employed for different operations. The simplest are piercing dies (пробивной штамп), used for punching holes. Bending and folding dies are designed to make single or compound bends. A combination die is designed to perform more than one of the above operations in one stroke of the press. A progressive die permits successive forming operations with the same die.

In coining, metal is forced to flow into two matching dies, each of which bears a engraved design.

Wiredrawing Dies

In the manufacture of wire, a drawplate (волочильная доска) is usually employed. This tool is a metal plate containing a number of holes, successively less in diameter and known as wire dies. A piece of metal is pulled through the largest die to make a coarse wire. This wire is then drawn through the smaller hole, and then the next, until the wire is reduced to the desired measurement. Wiredrawing dies are made from extremely hard materials, such as tungsten carbide or diamonds.

Thread-Cutting Dies

For cutting threads on bolts or on the outside of pipes, a thread-cutting die (резьбонарезная плашка) is used. It is usually made of hardened steel in the form of a round plate with a hole in the centre. The hole has a thread. To cut an outside thread, the die is lubricated with oil and simply screwed onto an unthreaded bolt or piece of pipe, the same way a nut is screwed onto a bolt. The corresponding tool for cutting an inside thread, such as that inside a nut, is called a tap (метчик).

Vocabulary

chip  [t∫ip]  стружка

sharp  [∫a:p]  острый

friction  ['frik∫эn]  трение

content  ['kontэnt]  содержание

range  [reind3]  диапазон

inexpensive  [inik'spensiv]  недорогой

to permit  [pэ'mit]  позволять, разрешать

common  ['komэn]  обычный

tungsten  ['tAŋstэn]  вольфрам

ingredient  [in'gri:diэnt]  ингредиент

diamond  ['daiэmэnd] алмаз

tips   наконечники

ceramic  [si'ræmik]  керамический 

truing  ['truiŋ]  правка, наводка, заточка

die  [dai]  матрица, штамп

matrix  ['meitriks]  матрица

to employ  [im'ploi]  применять

to pierce  ['piэs]  протыкать, прокалывать

to punch  [pAnt∫]  пробивать отверстие

matching  ['mætiŋ]  сочетающийся, парный

coarse  [ko:s]  грубый

wire  ['waiэ]  проволока

to draw  [dro:]  тащить, волочить

thread  [θred]  резьба

hardened  ['ha:dnd]  закаленный

to lubricate  ['lu:brikeit]  смазывать

to screw  [skru:]  привинчивать

nut  [nAt]  гайка

outside  [,aut'said]  наружный, внешний 

inside  [,in'said]  внутри, внутренний  

  1.  WELDING

Welding is a process when metal parts are joined together by the application of heat, pressure, or a combination of both. The processes of welding can be divided into two main groups:

• pressure welding, when the weld is achieved by pressure and

• heat welding, when the weld is achieved by heat. Heat welding is the most common welding process used today.

Nowadays welding is used instead of bolting and riveting in the construction of many types of structures, including bridges, buildings, and ships. It is also a basic process in the manufacture of machinery and in the motor and aircraft industries. It is necessary almost in all productions where metals are used.

The welding process depends greatly on the properties of the metals, the purpose of their application and the available equipment. Welding processes are classified according to the sources of heat and pressure used.

The welding processes widely employed today include gas welding, arc welding, and resistance welding. Other joining processes are laser welding, and electron-beam welding.

Gas Welding

Gas welding is a non-pressure process using heat from a gas flame. The flame is applied directly to the metal edges to be joined and simultaneously to a filler metal in the form of wire or rod, called the welding rod, which is melted to the joint. Gas welding has the advantage of using equipment that is portable and does not require an electric power source. The surfaces to be welded and the welding rod are coated with flux, a fusible material that shields the material from air, which would result in a defective weld.

Arc Welding

Arc-welding is the most important welding process for joining steels. It requires a continuous supply of either direct or alternating electrical current. This current is used to create an electric arc, which generates enough heat to melt metal and create a weld.

Arc welding has several advantages over other welding methods. Arc welding is faster because the concentration of heat is high. Also, fluxes are not necessary in certain methods of arc welding. The most widely used arc-welding processes are shielded metal arc, gas-tungsten arc, gas-metal arc, and submerged arc.

Shielded Metal Arc

In shielded metal-arc welding, a metallic electrode, which conducts electricity, is coated with flux and connected to a source of electric current. The metal to be welded is connected to the other end of the same source of current. An electric arc is formed by touching the tip of the electrode to the metal and then drawing it away.

The intense heat of the arc melts both parts to be welded and the point of the metal electrode, which supplies filler metal for the weld. This process is used mainly for welding steels.

Vocabulary

to join  [d3oin]  соединять

pressure welding   сварка давлением

heat welding   сварка нагреванием 

instead  [in'sted]  вместо, взамен 

bolting  [boultiŋ]  скрепление болтами 

riveting  ['rivitiŋ]  клепка 

basic  ['beisik]  основной

to manufacture  [,mænju'fakt∫э]  изготовлять 

to depend  [di'pend]  зависеть от

purpose  ['pэ:pэs]  цель

available  [э'veilэbl]  имеющийся в наличии

equipment  [i'kwipmэnt]  оборудование

source  [so:s]  источник

gas welding  газосварка

arc welding   электродуговая сварка

resistance welding   контактная сварка 

laser welding   лазерная сварка

electron-beam welding  электронно-лучевая сварка

flame  [fleim]  пламя

edge  [ed3]  край

simultaneously  [simэl'teiniэsli]  одновременно

filler  ['filэ]  наполнитель

wire  ['waiэ']  проволока

rod  [rod]  прут, стержень

to melt  [melt]  плавить(ся)

joint  [d3oint]  соединение, стык

advantage  [эd'va:ntid3]  преимущество

to require  [ri'kwaiэ]  требовать нуждаться

surface  ['sэ:fis]  поверхность

coated  ['koutid]  покрытый

flux [flAks]  флюс

fusible  [fju:zэbl]  плавкий

to shield  [∫i:ld]  заслонять, защищать

touching  ['tAtiŋ]  касание   

tip  [tip]  кончик

Can you answer the following questions?

1. How can a process of welding be defined?

2. What are the two main groups of processes of welding?

3. How can we join metal parts together?

4. What is welding used for nowadays?

5. Where is welding necessary?

6. What do the welding processes of today include?

7. What are the principles of gas welding?

8. What kinds of welding can be used for joining steels?

9. What does arc welding require?

10. What is the difference between the arc welding and shielded-metal welding?

  1.  OTHER TYPES OF WELDING

Non-consumable Electrode Arc Welding

As a non-consumable electrodes tungsten or carbon electrodes can be used. In gas-tungsten arc welding a tungsten electrode is used in place of the metal electrode used in shielded metal-arc welding. A chemically inert gas, such as argon, helium ['hi:liэm], or carbon dioxide is used to shield the metal from oxidation. The heat from the arc formed between the electrode and the metal melts the edges of the metal. Metal for the weld may be added by placing a bare wire in the arc or the point of the weld. This process can be used with nearly all metals and produces a high-quality weld. However, the rate of welding is considerably slower than in other processes.

Gas-Metal Arc

In gas-metal welding, a bare electrode is shielded from the air by surrounding it with argon or carbon dioxide gas and sometimes by coating the electrode with flux. The electrode is fed into the electric arc, and melts off in droplets that enter the liquid metal of the weld seam. Most metals can be joined by this process.

Submerged Arc

Submerged-arc welding is similar to gas-metal arc welding, but in this process no gas is used to shield the weld. Instead of that, the arc and tip of the wire are submerged beneath a layer of granular, fusible material that covers the weld seam. This process is also called electroslag welding. It is very efficient but can be used only with steels.

Resistance Welding

In resistance welding, heat is obtained from the resistance of metal to the flow of an electric current. Electrodes are clamped on each side of the parts to be welded, the parts are subjected to great pressure, and a heavy current is applied for a short period of time. The point where the two metals touch creates resistance to the flow of current. This resistance causes heat, which melts the metals and creates the weld. Resistance welding is widely employed in many fields of sheet metal or wire manufacturing and is often used for welds made by automatic or semi-automatic ['semi,o:tэ'mætik] machines especially in automobile industry.

Vocabulary

gas-tungsten   сварка оплавлением вольфрамовым электродом в среде инертного газа

inert  [i'nэ:t]  инертный

edge  [ed3]  край

bare  [bεэ]  голый

rate  [reit]  зд. скорость

gas-metal arc   аргоно-дуговая сварка

considerably  [kэn'sidэrэbli]  значительно, гораздо

surrounding  [sэ'raundiŋ]  окружающий

carbon dioxide  ['ka:bэn dai'oksaid] углекислый газ  

droplet  ['droplit]  капелька

liquid  ['likwid]  жидкость, жидкий

beneath  [bi'ni:θ]  под, ниже, внизу

layer  ['leiэ]  слой

weld seam  [si:m]  сварной шов

resistance  [rizistэns] сопротивление

clamp  [klæmp]  зажим, зажимать

sheet  [∫i:t]  лист

fusible  ['fju:zэbl]  плавкий

granular  ['grænjulэ]  плавкий

semi-automatic  ['semi,o:tэ'mætik]  полуавтоматическая

to create  [kri:'eit]  создавать

to submerge  [sэb'mэ:d3] погружать

Can you answer the following questions?

1. What is the difference between the arc-welding and non-consumable electrode arc welding?

2. What are the disadvantages of the non-consumable electrode arc welding?

3. How is electrode protected from the air in gas-metal arc welding?

4. What is submerged arc welding?

5. What is the principle of resistance welding?

6. Where is semi-automatic welding employed?

  1.  AUTOMATION

Automation is the system of manufacture performing certain tasks, previously done by people, by machines only. The sequences of operations are controlled automatically. The most familiar example of a highly automated system is an assembly plant for automobiles or other complex products.

The term automation is also used to describe non-manufacturing systems in which automatic devices can operate independently of human control. Such devices as automatic pilots, automatic telephone equipment and automated control systems are used to perform various operations much faster and better than could be done by people.

Automated manufacturing had several steps in its development. Mechanization was the first step necessary in the development of automation. The simplification of work made it possible to design and build machines that resembled the motions of the worker. These specialized machines were motorized and they had better production efficiency.

Industrial robots, originally designed only to perform simple tasks in environments dangerous to human workers, are now widely used to transfer, manipulate, and position both light and heavy workpieces performing all the functions of a transfer machine.

In the 1920s the automobile industry for the first time used an integrated system of production. This method of production was adopted by most car manufacturers and became known as Detroit automation.

The feedback principle is used in all automatic-control mechanisms when machines have ability to correct themselves. The feedback principle has been used for centuries. An outstanding early example is the flyball governor, invented in 1788 by James Watt to control the speed of the steam engine. The common household thermostat is another example of a feedback device.

Using feedback devices, machines can start, stop, speed up, slow down, count, inspect, test, compare, and measure. These operations are commonly applied to a wide variety of production operations.

Computers have greatly facilitated the use of feedback in manufacturing processes. Computers gave rise to the development of numerically controlled machines. The motions of these machines are controlled by punched paper or magnetic tapes. In numerically controlled machining centres machine tools can perform several different machining operations.

More recently, the introduction of microprocessors and computers have made possible the development of computer-aided design and computer-aided manufacture (CAD and CAM) technologies. When using these systems a designer draws a part and indicates its dimensions with the help of a mouse, light pen, or other input device. After the drawing has been completed the computer automatically gives the instructions that direct a machining centre to machine the part.

Another development using automation are the flexible manufacturing systems (FMS). A computer in FMS can be used to monitor and control the operation of the whole factory.

Automation has also had an influence on the areas of the economy other than manufacturing. Small computers are used in systems called word processors, which are rapidly becoming a standard part of the modern office. They are used to edit texts, to type letters and so on.

Automation in Industry

Many industries are highly automated or use automation technology in some part of their operation. In communications and especially in the telephone industry dialling and transmission are all done automatically. Railways are also controlled by automatic signalling devices, which have sensors that detect carriages passing a particular point. In this way the movement and location of trains can be monitored.

Not all industries require the same degree of automation. Sales, agriculture, and some service industries are difficult to automate, though agriculture industry may become more mechanized, especially in the processing and packaging of foods.

The automation technology in manufacturing and assembly is widely used in car and other consumer product industries.

Nevertheless, each industry has its own concept of automation that answers its particular production needs.

Vocabulary

automation  [,o:tэ'mei∫эn]  автоматизация

previously  ['pri:vjэsli]  ранее

sequence  ['si:kwэns]  последовательность

assembly plant   сборочный завод

non-manufacturing  непроизводственный

device  [di'vais]  устройство, прибор

resemble  [ri'zembl]  походить

efficiency  [i'fi∫эnsi]  эффективность

flyball governor   центробежный регулятор

steam engine   паровоз

household thermostat  [‘θэ:mэ,stæt] бытовой термостат

facilitate  [fэ'siliteit]  способствовать

punched  [pAnt∫t]  перфорированный 

aid  [eid]  помощь

dimension  [di'men∫эn]  измерение, размеры

Can you answer the following questions?

1. How is the term automation defined in the text?

2. What is the most «familiar example» of automation given in the text?

3. What was the first step in the development of automaton?

4. What were the first robots originally designed for?

5. What was the first industry to adopt the new integrated system of production?

6. What is feedback principle?

7. What do the abbreviations CAM and CAD stand for?

8. What is FMS?

9. What industries use automation technologies?

  1.  TYPES OF AUTOMATION

Applications of Automation and Robotics in Industry

Manufacturing is one of the most important application area for automation technology. There are several types of automation in manufacturing. The examples of automated systems used in manufacturing are described below.

1. Fixed automation, sometimes called «hard automation» refers to automated machines in which the equipment configuration allows fixed sequence of processing operations. These machines are programmed by their design to make only certain processing operations. They are not easily changed over from one product style to another. This form of automation needs high initial investments and high production rates. That is why it is suitable for products that are made in large volumes. Examples of fixed automation are machining transfer lines found in the automobile industry, automatic assembly machines and certain chemical processes.

2. Programmable automation is a form of automation for producing products in large quantities, ranging from several dozen to several thousand units at a time. For each new product the production equipment must be re-programmed and changed over. This reprogramming and changeover take a period of non-productive time. Production rates in programmable automation are generally lower than in fixed automation, because the equipment is designed to facilitate product changeover rather than for product specialization. A numerical-control machine-tool is a good example of programmable automation. The programme is coded in computer memory for each different product style and the machine-tool is controlled by the computer programme.

3. Flexible automation is a kind of programmable automation. Programmable automation requires time to re-program and change over the production equipment for each series of new product. This is lost production time, which is expensive. In flexible automation the number of products is limited so that the changeover of the equipment can be done very quickly and automatically. The reprogramming of the equipment in flexible automation is done at a computer terminal without using the production equipment itself. Flexible automation allows a mixture of different products to be produced one right after another.

Vocabulary

equipment  [i'kwipmэnt]   оборудование

sequence  ['si:kwэns]   последовательность

initial  [i'ni∫эl]   первоначальный, начальный

investment  [m'vestmэnt]   инвестиция, вклад

to facilitate  [fэ'siliteit]   способствовать

rate  [reit]   скорость, темп

assembly machines    сборочные машины

quantity  ['kwontiti]   количество

non-productive    непроизводительный

changeover  ['teind3,ouvэ]   переход, переналадка

Can you answer the following questions?

1. What is the most important application of automation?

2. What are the types of automation used in manufacturing?

3. What is fixed automation?

4. What are the limitations of hard automation?

5. What is the best example of programmable automation?

6. What are the limitations of programmable automation?

7. What are the advantages of flexible automation?

8. Is it possible to produce different products one after another using automation technology?

  1.  ROBOTS IN MANUFACTURING

Today most robots are used in manufacturing operations. The applications of robots can be divided into three categories:

1. material handling

2. processing operations

3. assembly and inspection.

Material-handling is the transfer of material and loading and unloading of machines. Material-transfer applications require the robot to move materials or work parts from one to another. Many of these tasks are relatively simple: robots pick up parts from one conveyor and place them on another. Other transfer operations are more complex, such as placing parts in an arrangement that can be calculated by the robot. Machine loading and unloading operations utilize a robot to load and unload parts. This requires the robot to be equipped with a gripper that can grasp parts. Usually the gripper must be designed specifically for the particular part geometry.

In robotic processing operations, the robot manipulates a tool to perform a process on the work part. Examples of such applications include spot welding, continuous arc welding and spray painting. Spot welding of automobile bodies is one of the most common applications of industrial robots. The robot positions a spot welder against the automobile panels and frames to join them. Arc welding is a continuous process in which robot moves the welding rod along the welding seam. Spray painting is the manipulation of a spray-painting gun over the surface of the object to be coated. Other operations in this category include grinding and polishing in which a rotating spindle serves as the robot's tool.

The third application area of industrial robots is assembly and inspection. The use of robots in assembly is expected to increase because of the high cost of manual labour. But the design of the product is an important aspect of robotic assembly. Assembly methods that are satisfactory for humans are not always suitable for robots. Screws and nuts are widely used for fastening in manual assembly, but the same operations are extremely difficult for a one-armed robot.

Inspection is another area of factory operations in which the utilization of robots is growing. In a typical inspection job, the robot positions a sensor with respect to the work part and determines whether the part answers the quality specifications. In nearly all industrial robotic applications, the robot provides a substitute for human labour. There are certain characteristics of industrial jobs performed by humans that can be done by robots:

1. the operation is repetitive, involving the same basic work motions every cycle

2. the operation is hazardous or uncomfortable for the human worker (for example: spray painting, spot welding, arc welding, and certain machine loading and unloading tasks)

3. the workpiece or tool are too heavy and difficult to handle

4. the operation allows the robot to be used on two or three shifts.

Vocabulary

handling  ['hændliŋ]  обращение 

transfer  ['trænsfэ:]  передача, перенос 

location  [lou'kei∫эn]  местонахождение 

pick up   брать, подбирать

arrangement  [э'reind3mэnt]  расположение

to utilize  ['ju:ti,laiz]  утилизировать,

 находить применение

gripper  ['gripэ]  захват

to grasp  [gra:sp]  схватывать

spot welding   точечная сварка

continuous  [kэn'tinjuэs]  непрерывный

arc welding   электродуговая сварка

spray painting   окраска распылением

frame  [freim]  рама

spray-painting gun   распылитель краски

grinding   шлифование

polishing   полирование

spindle   шпиндель

manual  ['mænjuэl]  ручной

labour  ['leibэ] труд

hazardous  ['hæzэdэs]  опасный

shift  [∫ift]  смена

Can you answer the following questions?

1. How are robots used in manufacturing?

2. What is «material handling»?

3. What does a robot need to be equipped with to do loading and unloading operations?

4. What does robot manipulate in robotic processing operation?

5. What is the most common application of robots in automobile manufacturing?

6. What operations could be done by robot in car manufacturing industry?

7. What are the main reasons to use robots in production?

8. How can robots inspect the quality of production?

9. What operations could be done by robots in hazardous or uncomfortable for the human workers conditions?

120100 – Технология машиностроения (Manufacturing Engineering)

GEAR (7574 characters)

Gear is a toothed wheel or cylinder used to transmit rotary or reciprocating motion from one part of a machine to another. Two or more gears, transmitting motion from one shaft to another, constitute a gear train. At one time various mechanisms were collectively called gearing. Now, however, gearing is used only to describe systems of wheels or cylinders with meshing teeth. Gearing is chiefly used to transmit rotating motion, but can, with suitably designed gears and flat-toothed sectors, be employed to transform reciprocating motion into rotating motion, and vice versa.

Simple Gears

The simplest gear is the spur gear, a wheel with teeth cut across its edge parallel to the axis. Spur gears transmit rotating motion between two shafts or other parts with parallel axes. In simple spur gearing, the driven shaft revolves in the opposite direction to the driving shaft. If rotation in the same direction is desired, an idler gear is placed between the driving gear and the driven gear. The idler revolves in the opposite direction to the driving gear and therefore turns the driven gear in the same direction as the driving gear.

In any form of gearing the speed of the driven shaft depends on the number of teeth in each gear. A gear with 10 teeth driving a gear with 20 teeth will revolve twice as fast as the gear it is driving, and a 20-tooth gear driving a 10-tooth gear will revolve at half the speed. By using a train of several gears, the ratio of driving to driven speed may be varied within wide limits.

Internal, or annular, gears are variations of the spur gear in which the teeth are cut on the inside of a ring or flanged wheel rather than on the outside. Internal gears usually drive or are driven by a pinion, a small gear with few teeth. A rack, a flat, toothed bar that moves in a straight line, operates like a gear wheel with an infinite radius and can be used to transform the rotation of a pinion to reciprocating motion, or vice versa.

Bevel gears are employed to transmit rotation between shafts that do not have parallel axes. These gears have cone-shaped bodies and straight teeth. When the angle between the rotating shafts is 90°, the bevel gears used are called mitre gears.

Helical Gears

These gears have teeth that are not parallel to the axis of the shaft but are spiralled around the shaft in the form of a helix. Such gears are suitable for heavy loads because the gear teeth come together at an acute angle rather than at 90° as in spur gearing. Simple helical gearing has the disadvantage of producing a thrust that tends to move the gears along their respective shafts. This thrust can be avoided by using double helical, or herringbone, gears, which have V-shaped teeth composed of half a right-handed helical tooth and half a left-handed helical tooth.

Hypoid gears are helical bevel gears employed when the axes of the two shafts are perpendicular but do not intersect. One of the most common uses of hypoid gearing is to connect the drive shaft and the rear axle in motor cars. Helical gearing used to transmit rotation between shafts that are not parallel is often incorrectly called spiral gearing.

Another variation of helical gearing is provided by the worm gear, also called the screw gear. A worm gear is a long, thin cylinder that has one or more continuous helical teeth that mesh with a helical gear. Worm gears differ from helical gears in that the teeth of the worm slide across the teeth of the driven gear instead of exerting a direct rolling pressure. Worm gears are used chiefly to transmit rotation, with a large reduction in speed, from one shaft to another at a 90° angle.

Bearings

Bearing is a mechanical device for decreasing friction in a machine in which a moving part bears – that is, slides or rolls on another part. Usually in a bearing the support must allow the moving part one type of motion, for example, rotation, while preventing it from moving in any other way, for example, sidewise. The commonest bearings are found at the rigid supports of rotating shafts where friction is the greatest.

Bearings were invented early in history; when the wheel was invented, it was mounted on an axle, and where wheel and axle touched was a bearing. Such early bearings had surfaces of wood or leather lubricated with animal fat. Modern bearings have been arbitrarily designated as friction bearings and antifriction bearings. The first comprises sleeve or journal bearings; the second, ball and roller bearings. Neither type of bearing is completely frictionless, and both are highly efficient in reducing friction. A large, modern aircraft engine, for example, has more than 100 bearings, including both types; yet the total power consumed in overcoming bearing friction is less than one per cent of the total power output of the engine.

Friction bearings of the sleeve or journal type are simpler than antifriction bearings in construction but more complex in theory and operation. The shaft supported by the bearing is called the journal, and the outer portion, the sleeve. If journal and sleeve are both made of steel, the bearing surfaces, even if well lubricated, may grab or pick up, that is, rip small pieces of metal from each other.

The sleeves of most bearings therefore are lined with brass, bronze, or Babbitt metal. Sleeve bearings are generally pressure-lubricated through a hole in the journal or from the housing that contains the bearing. The sleeve is often grooved to distribute the oil evenly over the bearing surface.

Typical clearance (difference between the diameters of journal and sleeve) is nominally 0.0025 cm for every 2.54 cm of journal diameter. When the journal is rotating, it may be about 0.0000001 cm from the sleeve at the side with the greatest load. The journal is thus supported on an extremely thin film of oil, and the two parts have no actual contact. As the rotational speed increases, other variables remaining constant, the oil film becomes thicker, so that the friction increases in less than direct proportion to the speed. Conversely, at lower speeds the oil film is thinner if other factors are unchanged. At extremely low speeds, however, the film may rupture and the two pieces come into contact. Therefore, friction is high when the machine is started in motion, and the bearing may fail if high stresses are put on it during starting. Ball bearings, on the other hand, have low starting friction.

Jewel bearings are used to mount very little shafts such as those found in fine watches. They are friction-type bearings in which the ends of the shafts are mounted in extremely hard substances. The bearing is lubricated with a microscopic drop of fine oil.

In a ball bearing, a number of balls rotate freely between an inner ring, which is rigidly fixed to a rotating shaft, and an outer ring, which is rigidly fixed to a support. Both balls and rings are made of hardened alloy steel, usually finished to extremely fine tolerances. The balls are generally held in position by a cage or separator that keeps them evenly spaced and prevents them from rubbing against each other. The bearing is lubricated with grease or oil.

A roller bearing is similar to a ball bearing, except that small steel cylinders, or rollers, are substituted for the balls. A needle bearing is a roller bearing in which the rollers are extremely long and thin. An ordinary roller bearing may have 20 rollers – each twice as long as it is wide – whereas a needle bearing may have 100 needles, each 10 times as long as it is wide. Needle bearings are particularly useful when space is limited.


120500 – Оборудование и технология сварочного производства

(The Eqiupment and Engineering of the Welding Fabrication)

BASIC PRINCIPLES OF WELDING  (7712 characters)

A weld can be defined as coalescence of metals produced by heating to a suitable temperature with or without the application of pressure, and with or without the use of a filler material.  

In fusion welding a heat source generates sufficient heat to create and maintain a molten pool of metal of the required size. The heat may be supplied by electricity or by a gas flame. Electric resistance welding can be considered fusion welding because some molten metal is formed.

Solid-phase processes produce welds without melting the base material and without the addition of a filler metal. Pressure is always employed, and generally some heat is provided. Frictional heat is developed in ultrasonic and friction joining, and furnace heating is usually employed in diffusion bonding.

The electric arc used in welding is a high-current, low-voltage discharge generally in the range 10-2,000 amperes at 10-50 volts. An arc column is complex but, broadly speaking, consists of a cathode that emits electrons, a gas plasma for current conduction, and an anode region that becomes comparatively hotter than the cathode due to electron bombardment. Therefore, the electrode, if consumable, is made positive and, if non-consumable, is made negative. A direct current (dc) arc is usually used, but alternating current (ac) arcs can be employed.

Total energy input in all welding processes exceeds that which is required to produce a joint, because not all the heat generated can be effectively utilized. Efficiencies vary from 60 to 90 percent, depending on the process; some special processes deviate widely from this figure. Heat is lost by conduction through the base metal and by radiation to the surroundings.

Most metals, when heated, react with the atmosphere or other nearby metals. These reactions can be extremely detrimental to the properties of a welded joint. Most metals, for example, rapidly oxidise when molten. A layer of oxide can prevent proper bonding of the metal. Molten-metal droplets coated with oxide become entrapped in the weld and make the joint brittle. Some valuable materials added for specific properties react so quickly on exposure to the air that the metal deposited does not have the same composition as it had initially. These problems have led to the use of fluxes and inert atmospheres.

In fusion welding the flux has a protective role in facilitating a controlled reaction of the metal and then preventing oxidation by forming a blanket over the molten material. Fluxes can be active and help in the process or inactive and simply protect the surfaces during joining.

Inert atmospheres play a protective role similar to that of fluxes. In gas-shielded metal-arc and gas-shielded tungsten-arc welding an inert gas—usually argon – flows from a tube surrounding the torch in a continuous stream, displacing the air from around the arc. The gas does not chemically react with the metal but simply protects it from contact with the oxygen in the air.

The metallurgy of metal joining is important to the functional capabilities of the joint. The arc weld illustrates all the basic features of a joint. Three zones result from the passage of a welding arc: (1) the weld metal, or fusion zone, (2) the heat-affected zone, and (3) the unaffected zone. The weld metal is that portion of the joint that has been melted during welding. The heat-affected zone is a region adjacent to the weld metal that has not been welded but has undergone a change in microstructure or mechanical properties due to the heat of welding. The unaffected material is that which was not heated sufficiently to alter its properties.

Weld-metal composition and the conditions under which it freezes (solidifies) significantly affect the ability of the joint to meet service requirements. In arc welding, the weld metal comprises filler material plus the base metal that has melted. After the arc passes, rapid cooling of the weld metal occurs. A one-pass weld has a cast structure with columnar grains extending from the edge of the molten pool to the centre of the weld. In a multi-pass weld, this cast structure maybe modified, depending on the particular metal that is being welded.

The base metal adjacent to the weld, or the heat-affected zone, is subjected to a range of temperature cycles, and its change in structure is directly related to the peak temperature at any given point, the time of exposure, and the cooling rates. The types of base metal are too numerous to discuss here, but they can be grouped in three classes: (1) materials unaffected by welding heat, (2) materials hardened by structural change, (3) materials hardened by precipitation processes.

Welding produces stresses in materials. These forces are induced by contraction of the weld metal and by expansion and then contraction of the heat-affected zone. The unheated metal imposes a restraint on the above, and as contraction predominates, the weld metal cannot contract freely, and a stress is built up in the joint. This is generally known as residual stress, and for some critical applications must be removed by heat treatment of the whole fabrication. Residual stress is unavoidable in all welded structures, and if it is not controlled bowing or distortion of the weldment will take place.

Arc Welding

Shielded metal-arc welding accounts for the largest total volume of welding today. In this process an electric arc is struck between the metallic electrode and the workpiece. Tiny globules of molten metal are transferred from the metal electrode to the weld joint. Arc welding can be done with either alternating or direct current. A holder or clamping device with an insulated handle is used to conduct the welding current to the electrode. A return circuit to the power source is made by means of a clamp to the workpiece.

Gas-shielded arc welding, in which the arc is shielded from the air by an inert gas such as argon or helium, has become increasingly important because it can deposit more material at a higher efficiency and can be readily automated. The tungsten electrode version finds its major applications in highly alloyed sheet materials. Either direct or alternating current is used, and filler metal is added either hot or cold into the arc. Consumable electrode gas-metal arc welding with a carbon dioxide shielding gas is widely used for steel welding. Metal transfer is rapid, and the gas protection ensures a tough weld.

Submerged arc welding is similar to the above except that the gas shield is replaced with a granulated mineral material as a flux.   

Weldabllity of Metals

Carbon and low-alloy steels are the most widely used materials in welded construction. Carbon content largely determines the weldability of carbon steels. Low-alloy steels are generally regarded as those having a total alloying content of less than 6 percent. There are many grades of steel available, and their relative weldability varies.

Aluminum and its alloys are also generally weldable. A very thin oxide film on aluminum tends to prevent good metal flow, however, and suitable fluxes are used for gas welding. Fusion welding is more effective with alternating current when using the gas-tungsten arc process to enable the oxide to be removed by the arc action.

Copper and its alloys are weldable, but the high thermal conductivity of copper makes welding difficult. Metals such as zirconium, niobium, molybdenum, tantalum, and tungsten are usually welded by the gas-tungsten arc process. Nickel is the most compatible material for joining, is weldable to itself, and is extensively used in dissimilar metal welding of steels, stainless steels and copper alloys.

(Copyright © 1994-2000 Encyclopædia Britannica, Inc.)


180400 – Электропривод и автоматизация промышленных установок и технологических комплексов

(The Electric Drive and the Automatization of the Commercial Plants and Production Process Complexes)

         

AUTOMATION IN INDUSTRY.

FIXED AND PROGRAMMABLE AUTOMATION (7823 characters)

Automated Production Lines

An automated production line consists of a series of workstations connected by a transfer system to move parts between the stations. This is an example of fixed automation, since these lines are set up for long production runs, making large number of product units and running for several years between changeovers. Each station is designed to perform a specific processing operation, so that the part or product is constructed stepwise as it progresses along the line. A raw work part enters at one end of the line, proceeds through each workstation and appears at the other end as a completed product. In the normal operation of the line, there is a work part being processed at each station, so that many parts are being processed simultaneously and a finished part is produced with each cycle of the line. The various operations, part transfers, and other activities taking place on an automated transfer line must all be sequenced and coordinated properly for the line to operate efficiently.

Modern automated lines are controlled by programmable logic controllers, which are special computers that can perform timing and sequencing functions required to operate such equipment. Automated production lines are utilized in many industries, mostly automobile, where they are used for processes such as machining and pressworking.

Machining is a manufacturing process in which metal is removed by a cutting or shaping tool, so that the remaining work part is the desired shape. Machinery and motor components are usually made by this process. In many cases, multiple operations are required to completely shape the part. If the part is mass-produced, an automated transfer line is often the most economical method of production. Many separate operations are divided among the workstations.

Pressworking operations involve the cutting and forming of parts from sheet metal. Examples of such parts include automobile body panels, outer shells of laundry machines and metal furniture More than one processing step is often required to complete a complicated part. Several presses are connected together in sequence by handling mechanisms that transfer the partially completed parts from one press to the next, thus creating an automated pressworking line.

Numerical Control

Numerical control is a form of programmable automation in which a machine is controlled by numbers (and other symbols) that have been coded on punched paper tape or an alternative storage medium. The initial application of numerical control was in the machine tool industry, to control the position of a cutting tool relative to the work part being machined. The NC part program represents the set of machining instructions for the particular part. The coded numbers in the program specify x-y-z coordinates in a Cartesian axis system, defining the various positions of the cutting tool in relation to the work part. By sequencing these positions in the program, the machine tool is directed to accomplish the machining of the part. A position feedback control system is used in most NC machines to verify that the coded instructions have been correctly performed. Today a small computer is used as the controller in an NC machine tool. Since this form of numerical control is implemented by computer, it is called computer numerical control, or CNC. Another variation in the implementation of numerical control involves sending part programs over telecommunications lines from a central computer to individual machine tools in the factory. This form of numerical control is called direct numerical control, or DNC.

Many applications of numerical control have been developed since its initial use to control machine tools. Other machines using numerical control include component-insertion machines used in electronics assembly, drafting machines that prepare engineering drawings, coordinate measuring machines that perform accurate inspections of parts. In these applications coded numerical data are employed to control the position of a tool or workhead relative to some object. Such machines are used to position electronic components (e.g., semiconductor chip modules) onto a printed circuit board (PCB). It is basically an x-y positioning table that moves the printed circuit board relative to the part-insertion head, which then places the individual component into position on the board. A typical printed circuit board has dozens of individual components that must be placed on its surface; in many cases, the lead wires of the components must be inserted into small holes in the board, requiring great precision by the insertion machine. The program that controls the machine indicates which components are to be placed on the board and their locations. This information is contained in the product-design database and is typically communicated directly from the computer to the insertion machine.

Automated Assembly

Assembly operations have traditionally been performed manually, either at single assembly workstations or on assembly lines with multiple stations. Owing to the high labour content and high cost of manual labour, greater attention has been given in recent years to the use of automation for assembly work. Assembly operations can be automated using production line principles if the quantities are large, the product is small, and the design is simple (e.g., mechanical pencils, pens, and cigarette lighters). For products that do not satisfy these conditions, manual assembly is generally required.

Automated assembly machines have been developed that operate in a manner similar to machining transfer lines, with the difference being that assembly operations, instead of machining, are performed at the workstations. A typical assembly machine consists of several stations, each equipped with a supply of components and a mechanism for delivering the components into position for assembly. A workhead at each station performs the actual attachment of the component. Typical workheads include automatic screwdrivers, welding heads and other joining devices. A new component is added to the partially completed product at each workstation, thus building up the product gradually as it proceeds through the line. Assembly machines of this type are considered to be examples of fixed automation, because they are generally configured for a particular product made in high volume. Programmable assembly machines are represented by the component-insertion machines employed in the electronics industry.

INDUCTION MOTORS FOR SPEED AND POSITION CONTROL

From Electric Motor

On a constant-frequency supply, an induction motor is essentially a near-constant speed drive. Induction motors, however, can be used to provide accurate speed and position control in either direction of rotation by furnishing a controllable-voltage, controllable-frequency three-phase supply. This is done by means of an electronic inverter. Using semiconductor switches (e.g., transistors or thyristors), the utility supply is converted into a set of three near-sinusoidal inputs of controlled voltage and frequency to the stator winding. The speed of the motor will then approach the synchronous value of 120 f/p revolutions per minute for a controlled frequency of f cycles per second.

Reversal of the phase sequence from abc to acb reverses the direction of the torque. For accurate control of speed or of position, the speed of the shaft can be monitored by a tachometer or position sensor and compared with a signal representing the desired value. The difference is then used to control the inverter frequency. Generally, the voltage varies directly with the frequency to keep the magnitude of the magnetic field constant.

(Copyright © 1994-2000 Encyclopædia Britannica, Inc.)


72000 – Стандартизация и сертификация в машиностроении

(The Standardization and Certification in Machine-Building)

STANDARDIZATION   (7934 characters)

Standardization in industry is the development and application of standards that permit large production runs of component parts that can be readily fitted to other parts without adjustment. Standardization allows for clear communication between industry and its suppliers, relatively low cost, and manufacture on the basis of interchangeable parts.

A standard is that which has been selected as a model to which objects or actions may be compared. Standards for industry may be devices and instruments used to regulate colour, size, weight, and other product attributes, or they may be physical models. Standards may also be written mathematical or symbolical descriptions, drawings, or formulas setting forth the important features of objects to be produced or actions to be performed. Standards that are applied in an industrial setting include engineering standards, such as properties of materials, fits and tolerances, terminology, and drafting practices; and product standards intended to describe attributes and ingredients of manufactured items and embodied in drawings, formulas, materials lists, descriptions, or models.

Certain fundamental standards among firms are required to prevent conflict and duplication of effort. The standards activities of governmental departments, trade associations, and technical associations serve in part to meet national standards needs, but one specialized standardizing organization is needed to co-ordinate the diverse standardization activities of many different types of organizations and promote general acceptance of basic standards.

In the United States the American National Standards Institute (ANSI) performs this function. It does not initiate or write standards but provides the means by which national engineering, safety, and industrial standards can be co-ordinated. All interested groups may participate in the decision-making process, and compliance with the national standard is voluntary. The international body that serves this function is the International Organization for Standardization (ISO). Developing an international standard presents the greater challenge because of the breadth of representation and the diversity of needs and viewpoints that must be reconciled.     

The International Organization for Standardization

The International Organization for Standardization is a specialized international organization founded in Geneva in 1947. It is concerned with standardization in all technical and nontechnical fields except electrical and electronic engineering (the responsibility of the International Electrotechnical Commission). Its membership extends to more than 100 countries, and each member is the national body "most representative of standardization in its country" – in Western industrial countries usually a private organization, such as the American National Standards Institute (ANSI) and the British Standards Institution (BSI), but in most other countries a governmental organization.

Standardization affects units of measurement; alphabetization and transliteration; specifications for parts, materials, surfaces, processes, tools, methods of testing, and machines; and even the form in which specifications are presented. Upon request, the ISO establishes international "technical committees" to investigate and resolve specific issues of standardization and publishes the results as "International Standards" (IS). Because of technological evolution, ISO standards are optimally reviewed (and, if necessary, revised) every five years.

(Copyright © 1994-2000 Encyclopædia Britannica, Inc.)

MEASUREMENTS

Metric System

Metric System is a decimal system of physical units, named after its unit of length, the metre, the metric system is adopted as the common system of weights and measures by the majority of countries, and by all countries as the system used in scientific work.

Weights and Measures

Length, capacity, and weight can be measured using standard units. The principal early standards of length were the palm or hand breadth, the foot, and the cubit, which is the length from the elbow to the tip of the middle finger. Such standards were not accurate and definite. Unchanging standards of measurement have been adopted only in modern time.

In the English-speaking world, the everyday units of linear measurement were traditionally the inch, foot, yard and mile. In Great Britain, until recently, these units of length were defined in terms of the imperial standard yard, which was the distance between two lines on a bronze bar made in 1845.

In Britain units of weight (ounces, pounds, and tons) are now also derived from the metric standard — kilogram. This is a solid cylinder of platinum-iridium alloy maintained at constant temperature at Sevres, near Paris. Copies, as exact as possible, of this standard are maintained by national standards laboratories in many countries.

International System of Units (SI)

International System of Units is a system of measurement units based on the MKS (metre-kilogram-second) system. This international system is commonly referred to as SI.

At the Eleventh General Conference on Weights and Measures, held in Paris in 1960 standards were defined for six base units and two supplementary units:

Length

The metre had its origin in the metric system. By international agreement, the standard metre had been defined as the distance between two fine lines on a bar of platinum-iridium alloy. The 1960 conference redefined the metre as 1,650,763.73 wavelengths of the reddish-orange light emitted by the isotope krypton-86. The metre was again redefined in 1983 as the length of the path travelled by light in a vacuum during a time interval of 1/299,792,458 of a second.

Mass

When the metric system was created, the kilogram was defined as the mass of 1 cubic decimetre of pure water at the temperature of its maximum density or at 4.0 °C.

Time

For centuries, time has been universally measured in terms of the rotation of the earth. The second, the basic unit of time, was defined as 1/86,400 of a mean solar day or one complete rotation of the earth on its axis in relation to the sun. Scientists discovered, however, that the rotation of the earth was not constant enough to serve as the basis of the time standard. As a result, the second was redefined in 1967 in terms of the resonant frequency of the caesium atom, that is, the frequency at which this atom absorbs energy: 9,192,631,770 Hz (hertz, or cycles per second).

Temperature

The temperature scale is based on a fixed temperature, that of the triple point of water at which it's solid, liquid and gaseous. The freezing point of water was designated as 273.15 K, equalling exactly 0° on the Celsius temperature scale. The Celsius scale, which is identical to the centigrade scale, is named after the 18th-century Swedish astronomer Anders Celsius, who first proposed the use of a scale in which the interval between the freezing and boiling points of water is divided into 100 degrees. By international agreement, the term Celsius has officially replaced centigrade.

One feature of SI is that some units are too large for ordinary use and others too small. To compensate, the prefixes developed for the metric system have been borrowed and expanded. These prefixes are used with all three types of units: base, supplementary, and derived. Examples are millimetre (mm), kilometre/hour (km/h), megawatt (MW), and picofarad (pF). Because double prefixes are not used, and because the base unit name kilogram already contains a prefix, prefixes are used not with kilogram but with gram. The prefixes hecto, deka, deci, and centi are used only rarely, and then usually with metre to express areas and volumes. In accordance with established usage, the centimetre is retained for body measurements and clothing.

In some cases certain other units are allowed for a limited time, subject to future review. These include the nautical mile, knot, angstrom, standard atmosphere, hectare, and bar.

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