Thermoplastics soften on heating, thenharden again when cooled. Thermoplastic molecules are alsocoiled and because of this they are flexible and easilystretched

Typical example of thermoplastics is polystyrene. Polystyrene resins are characterized by high resistance to chemical and mechanical stresses at low temperatures and by very low absorption of water. These properties make the polystyrenes especially suit­able for radio-frequency insulation and for parts used at low temperatures in refrigerators and in airplanes. PET (polyethene terephthalate) is a transparent thermoplas­tic used for soft-drinks bottles. Thermoplastics are also viscoelastic, that is, they flow (creep) under stress. Ex­amples are polythene, polystyrene andPVC.

2. Thermosetting plastics (thermosets) do not soften when heated, and with strong heating they decompose. In most thermosets final cross-linking, which fixes the molecules, takes place after the plastic has already been formed.

Thermosetting plastics have a higher density than thermoplastics. They are less flexible, more difficult to stretch, and are lesssubjected to creep. Examples of ther­mosetting plastics include urea-formaldehyde or polyurethane and epoxy resins, most polyesters, and phenolic polymers such as phenol-formaldehyde resin.

3. Elastomers are similar to thermoplastics but have sufficient cross-linking between molecules topreventstretching and creep.

Vocabulary:

carbon — углерод

flexible— гибкий

fibre— волокно, нить

chain— цепь

identical— одинаковый, идентичный

molecule— молекула

branch — разветвленный

to synthesize — синтезировать

chemicals — химические вещества

to soften — смягчать

cellulose — клетчатка, целлюлоза

wax — воск

thermosetting plastics — термореактивные пласт­массы

to harden — делать твердым

coil — спираль

stretched — растянутый

transparent — прозрачный

rubber — резина, каучук

to decompose — разлагаться

soft-drink — безалкогольный напиток

to subject — подвергать

polyurethane — полиуретан

resin — смола

similar — сходный, подобный

sufficient — достаточный

to prevent — предотвращать

General understanding

1. What is the definition of plastics?

2. What is the basic chemical element in plastics for­mula?

3. What do polymers consist of?

4. What are long-chain molecules made of?

5. What are the main types of polymers?

6. Give examples of plastics belonging to these types.

7. What plastics are the best electrical insulators?

8. Describe the difference between thermoplastics and thermosets.

9. What are the main types of structures of polymers?

10. What are the most important properties of plastics?

11. Give the examples of various uses of plastics be­cause of their characteristic properties.

Exercise 5.1. Find English equivalents in the text:

1. синтетические полимеры

2. молекулы с длинными цепями

3. характерные свойства полимера

4. синтезируются из органических химических ве­ществ

5. хороший электрический изолятор

6. размягчаться при нагревании

7. затвердевать при охлаждении

8. гибкий и легко растяжимый

9. течь под нагрузкой

10. более высокая плотность

11. менее подвержены ползучести

12. достаточная взаимосвязь между молекулами

Exercise 5.2. Translate into English:

1. Длинные цепи молекул полимеров состоят из одинаковых небольших молекул мономеров.

2. Сополимеры состоят из двух и более мономеров.

3. Пластмассы можно получать в виде листов, тон­ких пленок, волокон или гранул.

4. Молекулы полимеров могут быть линейными, ветвящимися или с поперечными связями.

5. Малый вес пластмасс и хорошие электроизоля­ционные свойства позволяют использовать их в радио­электронике и электроприборах, а также вместо ме­таллов.

6. Молекулы термопластов имеют извитую форму и, поэтому, они гибкие и легко растяжимы.

7. Эластомеры имеют большое число поперечных связей между молекулами.

Text В: «TYPES OF PLASTICS»

Epoxy resin.

Epoxy resin is a thermoset plastic containing epoxy groups. Epoxy resin hardens when it is mixed with solidifier and plasticizer. Plasticizers make a polymer more flexible.

Epoxy resins have outstandingadhesion, toughness, and resistance to attack from chemicals. They form strongbonds and have excellent electricalinsulationproperties. Large, complex,void-free castings can be made from them. They are also used as adhesives, and in composites for boat building and sports equipment.

2. PVC (polyvinyl chloride)

PVC (polyvinyl chloride) is a thermoplastic polymer made from vinyl chloride is a col­ourlesssolid with outstanding resistance to water, alcohols, and concentratedacids andalkalis. It is obtain­able as granules, solutions, lattices, andpastes. When compounded with plasticizers, ityields a flexible mate­rial moredurable thanrubber. It is widely used for ca­ble and wireinsulation, in chemical plants, and in the manufacture of protectivegarments. Blow moulding of unplasticized PVC produces clear, tough bottles which do not affect the flavour of their contents. PVC is also used for production of tubes or pipes.

Polystyrene.

Polystyrene is a thermoplastic produced by the polymerization of styrene. The electrical insulat­ing properties of polystyrene are outstandingly good and it is relatively unaffected by water. Typical applications include lightfixtures, toys, bottles,lenses, capacitordielectrics, medicalsyringes, andlight-duty industrial components. Extruded sheets of polystyrene are widely used for packaging,envelope windows, and photographic film. Its resistance toimpact can beimproved by the addition of rubbermodifiers. Polystyrene can bereadily foamed; the resulting foamed polystyrene is usedexten­sively for packaging.

4. Polythene (polyethene, polyethylene)

Polythene (polyethene, polyethylene) is a plastic made from ethane. It is one of the most widely used important thermoplastic polymers. It was first developed by the polymerization of ethane at a pres­sure of 2,000 bar at 200°C. This produced low-density poly­thene (LDPE). A relatively high-density form (HDPE) was synthesized in the 1950s using a complexcatalyst. Poly­thene is a whitewaxy solid with very low density,rea­sonable strength and toughness, but low stiffness. It is easily moulded and has a wide range of uses in contain­ers, packaging,pipes, coatings, and insulation.

Vocabulary:

adhesion— прилипание

adhesive — клей

bond — связи, узы

insulation — изоляция

casting — литье

void — пустота

solid — твердое тело, твердый

acid — кислота

alkali — щелочь

to obtain — доставать, получать

granule— гранула

solution — раствор

lattices — латексы

paste— паста

yield— выход

durable — прочный

rubber— резина, каучук

garment — предметы одежды

lens —линза

capacitor — эл. конденсатор

syringe— шприц

light-duty — неответственный

envelope — зд. обрамление

impact — удар

improved — улучшенный

modifiers — модификаторы

addition — добавление

readily — легко, с готовностью

foam — пена

catalyst — катализатор

wax — воск

reasonable — приемлемый, неплохой

coating — слой, покрытие

General understanding:

1. What are the types of plastics?

2. What are the features of the epoxy resin?

3. What is epoxy resin used for?

4. What is PVC usually used for?

5. What are the typical applications of polystyrene?

6. When was polyethylen synthesized?

7. Under what conditions is polyethylen synthesized?

8. What sorts of polyethylen can be synthesized?

Exercise 5.3. Translate into Russian:

1. Polythene is a plastic made from ethane.

2. Epoxy resins have outstanding adhesion, toughness and resistance to attack from chemicals.

3. PVC is a colourless solid with outstanding resist­ance to water, alcohols, and concentrated acids and al­kalis.

4. Polystyrene is a thermoplastic produced by the po­lymerization of styrene.

5. Polythene is a white waxy solid with very low den­sity, reasonable strength and toughness but low stiffness.

Exercise 5.4. Translate into English:

1. Эпоксидная смола затвердевает когда смешива­ется с отвердителем и пластификатором.

2. Эпоксидные смолы используются в качестве клея, а с добавками — в строительстве лодок и спор­тивного снаряжения.

3. ПВХ — бесцветное твердое вещество с выдаю­щейся устойчивостью к воздействию воды, спиртов, концентрированных кислот и щелочей.

4. ПВХ широко используется при производстве изоляции для проводов.

5. Выдувка непластифицированного ПВХ исполь­зуется при производстве прозрачных бутылок для на­питков.

6. Полистирол легко вспенивается и используется для упаковки.

7. Полиэтилен — воскообразное вещество белого цвета с очень низкой плотностью и малой жесткостью.

Text С: «COMPOSITE MATERIALS»

The combinations of two or more different materials are called composite materials. They usually have unique mechanical and physical properties because they combine the best properties of different materials. For example, afibre-glass reinforced plastic combines the high strength of thin glassfibres with the ductility and chemi­cal resistance of plastic. Nowadays composites are being used for structures such as bridges, boat-building etc.

Composite materials usually consist of synthetic fi­bres within a matrix, a material that surrounds and is tightly bound to the fibres. The most widely used type of composite material ispolymer matrix composites(PMCs). PMCs consist of fibres made of a ceramic mate­rial such as carbon or glass embedded in a plastic matrix. Usually the fibres make up about 60 per cent by volume. Composites with metal matrices or ceramic matrices are calledmetal matrix composites (MMCs) andceramic matrix composites (CMCs), respectively.

Continuous-fibre composites are generally required for structural applications. Thespecific strength(strength-to-density ratio) andspecific stiffness (elastic modulus-to-density ratio) of continuous carbon fibre PMCs, for example, can be better than metal alloys have. Composites can also have other attractive properties, such as high thermal or electrical conductivity and a low coefficient of thermalexpansion.

Although composite materials have certain advan­tages over conventional materials, composites also have some disadvantages. For example, PMCs and other com­posite materials tend to be highlyanisotropic— that is, their strength, stiffness, and other engineering proper­ties are different depending on the orientation of the com­posite material. For example, if a PMC is fabricated so that all the fibres are lined up parallel to one another, then the PMC will be very stiff in the direction parallel to the fibres, but not stiff in the perpendicular direction. The designer who uses composite materials in structures subjected to multidirectional forces, must take these anisotropic properties into account. Also, forming strong connections between separate composite material com­ponents is difficult.

The advanced composites have high manufacturing costs. Fabricating composite materials is a complex proc­ess. However, new manufacturing techniques are devel­oped. It will become possible to produce composite mate­rials at higher volumes and at a lower cost than is now possible, accelerating the wider exploitation of these materials.

Vocabulary:

fibreglass— стекловолокно

fibre — волокно, нить

reinforced — упрочненный

expansion — расширение

matrix — матрица

ceramic — керамический

specific strength — удельная прочность

specific stiffness — удельная жесткость

anisotropic — анизотропный

General understanding:

1. What is called «composite materials»?

2. What are the best properties of fibre-glass?

3. What do composite material usually consist of?

4. What is used as matrix in composites?

5. What is used as filler or fibers in composites?

6. How are the composite materials with ceramic and metal matrices called?

7. What are the advantages of composites?

8. What are the disadvantages of composites?

9. Why anisotropic properties of composites should be taken into account?

Exercise 5.5. Find equivalents in the text:

1. композитные материалы

2. уникальные механические качества

3. полимерные матричные композиты

4. составлять 60% объема

5. углепластик

6. привлекательные качества

7. структура, подвергающаяся воздействию разнонаправленных сил

Exercise 5.6. Translate into Russian:

1. PMC is fabricated so that all the fibres are lined up parallel to one another.

2. Forming strong connections between separate com­posite material components is difficult.

3. Fabricating composite materials is a complex process.

4. Composite materials have certain advantages over conventional materials

5. Nowadays, composites are being used for structures such as bridges, boat-building etc.

6. Continuous-fibre composites are generally required for structural applications.

FAMOUS INVENTORS

Alfred Bernhard Nobel was a famous Swedish chem­ist and inventor. He was born in Stockholm in 1833. Af­ter receiving an education in St. Petersburg, Russia, and then in the United States, where he studied mechanical engineering, he returned to St. Petersburg to work with his father in Russia. They were developing mines, tor­pedoes, and other explosives.

In a family-owned factory in Heleneborg, Sweden, he developed a safe way to handle nitroglycerine, after a factory explosion in 1864 killed his younger brother and four other people. In 1867 Nobel achieved his goal: he produced what he called dynamite динамит. Не later produced one of the first smokeless powders (порох). At the time of his death he controlled factories for the manufacture of explosives (взрывчатое вещество) in many parts of the world. In his will he wanted that the major portion of his money left became a fund for yearly prizes in his name. The prizes were to be given for merits (заслуги) in physics, chemistry, medicine and physiol­ogy, literature, and world peace. A prize in economics has been awarded since 1969.

UNIT 6

WELDING

I. Text A: «Welding», Text В: «Other types of welding»