Properties of metals (II)

Strength with plasticity is the most important combination of properties a metal can possess. Strength is the ability of a material to resist deformation; plasticity is the ability to take deformation without breaking. Metals possessing this combination of properties may be used in main parts of structures or machine tools.

Strength as well as ease of shaping and low cost to a considerable extent determines the fact that steel is suitable for many structural purposes. Steel is used for the structural parts of buildings, rails, and ships. For automobile parts and where greater strength and toughness are required, more expensive special steels are used. Generally, if strength alone is the main consideration, nonferrous alloys should not be used. However, where the requirement for strength is combined with resistance to rusting, aluminium bronze may be used. There are purposes for which strength is not so important as ease of machining. In making screws, for example, another kind of steel or brass may be used. Where the finished form is to be produced by casting, and great strength is not required, cast iron or cast brass may find application.

Steel may be considered the most important of all metals. It can be made soft enough for machining or for cutting and forming to the desired shape, and then by heat treatment it can be properly hardened for use as a tool.

For making airplane parts, and in other applications where strength must be combined with light weight, metals such as aluminium or magnesium or their alloys are used. Metals vary greatly in their resistance to atmospheric and chemical corrosion. A list of the elements in the order of their resistance to corrosion will begin with gold and platinum, and it ends with potassium which burns in contact with water: platinum, gold, silver, copper, tin, lead, iron, zinc, aluminium, magnesium, and potassium.

But this list may not be used in practice, as both aluminium and zinc form protective coatings in the beginning of oxidation and are not destroyed any more, while iron or steel, if unprotected, will rust through. The so-called stainless steels are used in large quantities now without protective coatings and do not rust.

Copper and aluminium are the best conductors of electric current after silver, which has practically no resistance. Copper has less resistance than aluminium for the same size wire, but aluminium, being much lighter in weight, has less resistance per unit of weight.

2. Find in the text English equivalents to the following words and word combinations:

пластичність, деформація, жорсткість, сплави кольорових металів, виготовлення гвинтів, знаходити застосування, ржавіння, лита латунь, легка вага, магній, мідь, олово, свинець, залізо, калій, захисне покриття, опір, дріт, корозія, нержавіюча сталь.

3. Give synonyms for the following words:

to supplant, various, hard, small, to desire, clean.

4. Give antonyms for the following words:

active, destroy, able, large, solid, cold, brittle, strong, cheap, dark, little.

5. Translate the following groups of words:

to act — action — active — activity — to activate — activation; to consider — consideration — considerable — considerably; able — ability — to enable; to blow — a blow — blast; to destroy — destruction — destructive; a shape — to shape; to press — to compress — compression — compressive; to vary — variation — various — variety; to bear — bearing; to unite — union — a unit; to protect — protected — unprotected; to use — usable — unusable.

Дата добавления: 2015-07-25