Упражнения

Упр.1. Найдите в тексте английские эквиваленты следующих слов и словосочетаний:

1. Высокий коэффициент расширения; 2. металл склонен уходить от пламени; 3. пока он сохраняет пластичность; 4. запасные прутки; 5. Обязательно прогреть; 6. небольшие порции металла; 7. сама окись растворяется в соответствующем флюсе. 8. охвачен пламенем; 9. ненужное излучение тепла; 10. нормальное пламя.

Упр.2. Подберите в тексте синонимы к следующим словам:

1. Normally; 2. shrinkage; 3. to mix; 4. ductile; 5. to cover; 6 in touch with; 7. fume.

Упр.3. Переведите на английский следующие предложения:

1. Цветные металлы и их сплавы при нагреве вступают во взаимодействие с окружающим воздухом гораздо сильнее, чем черные металлы. 2. Большинство цветных металлов имеют большую теплопроводность, чем сталь. 3. Чистая медь пластична и легко поддается деформации даже в холодном состоянии. 4. Алюминий легко вступает в реакцию с атмосферными газами. 5. Сплавы меди (бронза, латунь) резко меняют физико-механические свойства. 6. Окись алюминия, быстро появляющаяся на его поверхности, защищает металл от атмосферного воздействия, но мешает прокладке шва. 7. Свариваемости алюминия мешают пыль, жир, и другие загрязнители на кромках свариваемых деталей. 8.Введение в медь примесей и легирующих элементов определяет физико-химические свойства сплава. 9. Сварку меди и ее сплавов выполняют в среде защитного газа, в качестве которого служит азот, аргон, гелий, а также их смеси. 10. При дуговой сварке меди наибольший эффект достигается при использовании азота в качестве защитного газа.

Unit 27. COLD WELDING

Cold welding is a process performed at room temperature that uses mechanical force or pressure to bring two metallic surfaces in intimate contact until inter-atom-ic forces are developed to complete the weld, while considerable plastic deformation is taking place. The need for metal distortion and flow to perform cold welding excludes that brittle materials could be joined by this process. However, many combinations of ductile dissimilar metals can be joined by cold welding, even those that could never be joined by fusion welding. There is no fusion of either metal, so that cold welding is included into the class of solid state welding processes.

To be successful cold welding must provide for the disruption of surface oxides if they are present, reducing them to separate tiny particles that do not interfere with the process. Shattering of the oxides during material flow is due to their brittle nature. Microscopic observations confirm that the interface becomes a phase boundary and that oxides are not interfering with the soundness of the bond.

Many varieties of the basic cold welding process are known to have been implemented. Deformation can be made in lap or butt configuration and can involve press forming, drawing and extrusion. Roll welding is a variant that should be dealt with separately.

Lap cold welding could be explained as a variant of resistance spot welding where two overlapping sheets are joined at separate spots, except that no current and no heating is involved, and there is no fusion. Instead considerable deformation is generated in the transversal direction to that of the applied pressure.

Cleaning should be performed just before cold welding, especially with easily oxidized materials like aluminum, because it is a critical requirement.

Various thicknesses can be joined, from 0.1 to 15 mm, provided sufficient striking force is available. Cold welding is performed by clamping the sheets to be joined between two dies and by striking a powerful blow that deforms a definite region of the material. The meeting protrusions that appear in the interface result welded together by the pressure. Different shapes of dies generate a round spot or a circular ring or a linear joint, depending on requirements.

Butt cold welding is done on bars of compatible materials by upsetting jointly both of their ends. The bars are clamped in suitable fixtures to be moved axially one against the other. The lining force will cause buckling of the bar extension. If an acceptable weld is not achieved with that force in a single strike, it is possible to perform the weld in steps, moving the clamp position accordingly between steps. The pressure generated in the drawn materials between the die and the mandrel (or the solid bar) produces the metallurgical weld, provided the surfaces are clean as required.

One of the quality problems affecting this and other pressure welding processes is the lack of reliable non-destructive tests for evaluating production. The suggested procedure consists of performing destructive tests on suitable test pieces, and that in assuring process control by striking to the parameters developed and recorded.

Cold welding can occur also as an unwanted casual accident when two surfaces come into contact in the absence of a lubricant and stick locally together. Such an event, capable of substantial destructive damage, can be the source or the consequence of mechanical failures. Examples of failures due to destructive cold welding are found in ball or roller bearing running dry, although substantial heat can be generated by friction.

VOCABULARY

Cold welding – холодная сварка

Interatomic forces – межатомные связи

Upsetting - осадка

plastic deformation – пластическая деформация

metal distortion – деформация металла

metal flow – пластичность металла

ductile – ковкий, пластичный

disruption, shattering - разрушение

interface – поверхность контакта свариваемых деталей

phase boundary – межфазная граница

soundness – плотность шва, отсутствие дефектов

lap configuration – соединение внахлест

butt configuration – стыковое соединение, соединение встык

press forming - прессовка

drawing - прокатка

extrusion – экструзионная прессовка ( выдавливание)

roll welding – сварка прокаткой

transversal direction – перпендикулярно \ поперек

welding die – контактная колодка

protrusion - выступ

fixture – зажимное приспособление

clamp position – место, положение зажима

drawn materials – свариваемые части \материалы

mandrel - оправка

solid bar – неподвижный брусок

non-destructive tests – неразрушающие методы контроля

test piece – образец для испытаний

ball \ roller bearing – шарико-\ роликоподшипник