Tensile strength, 14·66 tons per square inch.
Elongation on 8 inches, 43·36 per cent. of original length.
Contraction of area, 45·9 per cent.
Close bend test, Double.
The effect of temperature and the influence of impurities on the
mechanical properties of the metal intended for engineering purposes
are of very great importance, and much attention has been devoted to
researches in this subject, particularly by Milton and Le Chatelier,
whose published experience gives important information of much
practical value. The main conclusions arrived at from practice have
had reference to the general effects of impurities in hardening the
metal, and the general tendency of heat to soften it and to increase
the ductility. The diverse effects of different impurities on strength
and ductility will be reviewed in detail at a later stage.
(_c_) _General Industrial Uses._—Copper as metal is also employed to
a considerable extent in certain important industries, as in textile
manufacture, where it is used for the rollers in calico-printing; and
it is in general industrial use in the form of copper heaters, vats,
coils, pans, and the like, and occasionally also for roofing and
sheathing.
=Uses of Copper Alloys.=—Between 20 and 30 per cent. of the copper
produced is employed in the form of alloys. The more important of these
are:—
=Brasses=; alloys of copper and zinc.
=Bronzes=; chiefly alloys of copper and tin.
=Coinage Alloys=; of gold and silver with copper.
=German Silver=; alloys of copper, nickel, and zinc.
=Special Bronzes=; alloys of copper with such metals
as aluminium and manganese.
It is further not unlikely that several classes of ternary alloys,
at present still under investigation, may have important industrial
application in the future. Among such alloys may be mentioned the
copper-aluminium series alloyed with other metals, Monel metal and the
Monel steel series, etc.
Of the above alloys, the brasses are by far the most widely used. It
may be recalled that the advantages possessed by alloys of copper and
zinc are in large measure due to their increased strength and hardness;
to the fact that they are more fusible, and more fluid when melted, and
so give good castings; that they are characterised by a good colour and
high lustre, as well as by the factor of cheapness resulting from the
addition of a less costly metal—zinc—in their manufacture.
The uses of the copper alloys may also be arranged in two classes—(_a_)
engineering uses, and (_b_) general uses. Of the brasses, those
containing upwards of 70 per cent. of copper may be rolled cold, whilst
the alloys with less than 70 per cent. are hot-rolled.
In the engineering industry large quantities of 70/30 brass are
utilised in the form of condenser tubes, whilst for the multifarious
requirements of general engineering work, very considerable amounts
of brass of lower tenor are employed in the forms of taps, pipes,
fittings, etc.
Muntz metal, the 60/40 brass, finds extended application for the
sheathing of ships, whilst the employment of brass and of the other
alloys for all manner of articles of general utility is a matter of
common knowledge.
The close connection between properties, constitution, and the
equilibrium diagram of these various classes of alloys has become
manifest to a marked degree within recent years, and the effects
of thermal treatment partly in modifying their constitution, and
thereby the properties, and also in controlling the condition and
distribution of the constituents, are at the present time having an
important bearing on the manipulation of these alloys in the industries
manufacturing them and adapting them for their various uses. The study
and application of these equilibrium diagrams are highly important to
those who have to deal with these alloys on an industrial scale.
[Illustration: Fig. 3.—Equilibrium Diagram, Cu-Zn Series.]
=The Properties of Copper.=—The properties of the metal which render
it of such service in the arts and industries are mainly its high
electrical conductivity, its great ductility, malleability, and
toughness, which enable it to be readily worked up into the different
forms in which it is employed, its high thermal conductivity, and its
resistance to the various agencies which lead to corrosion. These
are consequently the properties to which close study is directed.
Of perhaps still greater importance is a knowledge of the influence
exerted upon these properties by the circumstances which usually attend
working practice; such as, for example, the various common impurities,
and the variations of temperature, as well as the previous mechanical
and thermal treatment. These can only be indicated in general terms
here, references to authorities on the different branches being given
later.