Читать книгу Material science. Жаратылыстану факультеттерінің студенттеріне арналған әдістемелік құрал - Шолпан Гумарова - Страница 5

Aluminium is a major representative of light metals (with densities below 5,000 kg/m3); the density of cast aluminium is around 2,600 kg/m3, and rolled aluminium 2,700 kg/m3. Aluminium is thus about 3.5 times lighter than copper.

The resistivity of aluminium is approximately 1.63 times that of copper, and therefore aluminium cannot always be substituted by copper, especially in radio electronics. However, an aluminium wire of the same length and resistance as a copper wire would be almost half as heavy as the latter, though thicker. That is why in fabricating the wire of one and the same conductance per unit length, it would be more profitable to use aluminium than copper, if the former is no more than two times as high in cost per ton as the latter. Also of importance is the fact that aluminium is more readily available than copper.

A grade A1 aluminium that has no more than 0.5 % impurities is used for general electrical purposes. A grade AB00 aluminium that average 99.97 % pure goes for aluminium foil, electrodes and castings of electrolytic capacitors. The highest purity aluminium, grade AB000, has 0.004 % impurities.

Aluminium is rolled, and annealed in the same manner as copper. It can be rolled into thin foil, down to 6 to 7Mm, which is used for plates of paper and film capacitors.

The surface layer of aluminium readily oxidizes to form a thin oxide film of high resistance. This film protects aluminium against further corrosion, but builds up a high contact resistance (where aluminium wire come in contact) and makes ordinary soldering methods unsuitable for aluminium. This difficulty is obviated by employing special brazing pastes or ultrasonic soldering bits.

Exercises:

I. Memorize the following words and word combinations:

II. Find the Kazakh (Russian) equivalents to the following word combinations:

А) the density of cast aluminum; casting of electrolytic capacitors; aluminum is annealed; plates of film capacitors; builds up a contact resistance; employing special brazing pastes.

В) создавать переходное сопротивление; корпус электроли-тических конденсаторов; плотность литого алюминия; приме-нение специальных паст припои; отжиг алюминия; обкладки пленочных конденсаторов.

С) өтпелі кедергі жасау; электролитті конденсаторлар ғимараты; құйылған алюминидің тығыздығы; арнайы жабсыру пасталарын қолдану; алюминиді күйдіру; қабыршықты конденсатор орамдары.

III. Translate into English using the active vocabulary of the lesson:

VI .Translate at sight