(_a_) For electrical purposes.
(_b_) For engineering purposes.
(_c_) General industrial uses.
(_a_) _Electrical Uses._—Of late years the marked growth in the
consumption of copper has arisen very largely from its usefulness as
a conductor of electricity; the increased demand for the metal with
the development of electrical enterprise being a well-marked feature
in industrial progress. It is estimated that from 60 to 70 per cent.
of all the copper produced is utilised for this purpose, and metal is
specially prepared and sold under the designation of “high-conductivity
copper.” The demand has, to a large extent, increased irrespective of
price up to recent years, owing to the necessity of employing copper
for such purposes, though the natural economic factor that an enhanced
price of the metal tends to some discouragement of expansion and
of fresh electrical enterprise, has exerted considerable effect in
checking consumption.
It is merely necessary to enumerate some few of the present aspects
of electrical industry in order to realise the enormous absorption
of copper in this connection, as, for instance, electrical traction,
lighting, and power, the telegraph, and the telephone. With reference
to the use of the metal for this work, it is important that certain
mechanical as well as electrical requirements should be fulfilled,
for in many branches, considerable strength of the material is
also requisite. The demand of the electrical engineer is that as
a conductor, the copper shall offer a minimum of resistance to the
passage of the current, and for this requirement the metal must be
in a condition of very great purity. With but few exceptions, this
necessitates the purification of the copper by electro-deposition.
Electro-deposited metal as produced at the refineries is, however, not
immediately suitable for drawing into wire, owing to the weakness and
porosity inherent in the material prepared by this method. It must,
therefore, be melted, brought to pitch, cast into bars, and these bars
transformed into wire, which operations require to be conducted with
much care in order to keep the metal in as pure a condition as possible
for its work. It may be noted that within recent years, several
processes, notably those of Cowper-Coles and Elmore, have been put
into operation for the direct manufacture for electrical purposes, of
electrolytic-copper wire of the requisite strength.
The mechanical qualities demanded of the metal for such purposes as
telegraph work may be indicated by the two specifications of wire for
the British Post Office, which are appended:—
A. _Post Office Specification._
=Weight=, 150 lbs. per mile.
=Minimum diameter=, ·95½".
=Maximum diameter=, ·98".[1]
=Minimum breaking strain=, 490 lbs.
=Minimum number of twists=, 25 in 3 inches.
=Wraps required=, 6 times round wire of its
own diameter, unwrapped, and again wrapped without breaking.
=Maximum resistance per mile at= 60° =F.=, 5·857 ω.
B. _Post Office Specification._
=Weight=, 500 lbs. per mile.
=Minimum diameter=, ·135¼".
=Maximum diameter=, ·138¾".
=Minimum breaking strain=, 950 lbs.
=Minimum number of twists=, 30 in 6 inches.
=Wraps required=, 6 times round wire of its
own diameter, unwrapped, and again wrapped without breaking.
=Maximum resistance per mile at= 60° =F.=, 2·928 ω.
The following figures afford some indication of the increasing demand
for copper in two branches only of electrical industry:—
1902. 1907.
Mileage of wire for telegraph purposes, 3·9 5·3
" " telephone purposes, 10·9 28·2
(in million of miles)
(_b_) _Engineering Uses._—Metallic copper finds application in marine
shipbuilding and engine work, as well as in railway and locomotive
work, where the metal is particularly employed for steam pipes, and
for fire-box plates and stays, sometimes also for boiler tubes, on
account of its high conductivity for heat, combined with toughness.
The questions of suitable composition, and the other requirements
of the metal intended for these purposes, has been a subject for
discussion by some of the leading marine and locomotive engineers.
Useful information on the subject will be found in the reports of some
of these discussions at the Institution of Mechanical Engineers.
The following tests are required for copper plate (best quality)
intended for locomotive fire-boxes on the Lancashire and Yorkshire
Railway, taken from standard specifications given by their Chief
Mechanical Engineer at the Institute of Metals:—
_Bending Test._—Pieces of the plate shall be tested both
cold and at a red heat by being doubled over on themselves—
that is, bent through an angle of 180°—without showing
either crack or flaw on the outside of the bend.
_Flanging._—Plates must not show any defects in flanging.
_Tensile Test._—Ultimate breaking load, 14 tons per square
inch; Elongation, 35 per cent. in 8 inches.
_Analytical Test._—To be made at contractor’s expense.
The copper upon analysis to give the following results:—Arsenic, not
less than 0·35 per cent. nor more than 0·55 per cent.; other foreign
elements, exclusive of combined oxygen, not to exceed 0·25 per cent.
Clauses are also inserted as to stamping, inspection, and the giving of
testing facilities.