Improvements in the Manufacture of Electrical Conductors.
Year: 1892

page_text: Date of Application, 10th Mar., 1892-Accepted, 16th Apr., 1892
COMPLETE SPECIFICATION.
Improvements in the Manufacture of Electrical Conductors.
I, GEORGE FREDERICK REDFERN, of the firm of G. F. Redfern & Co., The
General Patent Office, No. 4, South Street, Finsbury, in the County of London,
Patent Agents, do hereby declare the nature of this invention (a communication
to me by Sigmund Bergmann, of 21, Fennstrasse, Berlin, in the Empire of
Germany, Manufacturer) and in what manner the same is to be performed, to be
particularly described and ascertained in and by the following statement:-
This invention relates to the manufacture of an electrical main conductor which
contains within it two or more electrical conductors, the object being to completely
insulate cach conductor separately and the whole system which is extremely resistent
to external influences, the conductor occupying only a very small space.
The process of manufacture is based upon the idea of giving to the separate
conductors the form respectively of a copper rod and of tubes completely insulated
and sliding these tubes one upon the other, so that each successive conductor con-
stitutes a metallic sheathing for the protection of the conductors inside it, but is
separated from the latter by perfect insulation.
The new process is carried out in the following manner.
A paper tube impregnated with petroleum pitch, the inner and outer surfaces of
which are coated with a layer of fusible insulating substance is pushed over a
copper rod heated to the melting point of the insulating material. The insulating
material upon the inner surface of the tube is thus rendered fluid, and there results
from this an intimate union between the copper rod and the insulating substance
which is brought into contact with it. As soon as the cylindrical rod which results
is cool, a copper tube which has in the same way been heated to the melting point
of the insulating substance, and whose internal diameter corresponds with the
external diameter of the paper tube already employed, is pushed on to the latter,
so that again, but this time as regards the onter coating of the paper tube the
insulating mass is fused by the pushing on of the copper tube. Before the latter
is cold, however, a second paper tube of suitable diameter is pushed on, this tube
having been prepared exactly like the first paper tube, and being coated within
and without with the insulating substance. The still hot copper tube again causes
the fusion of the insulating layer upon the inner surface of the second paper tube
thrust over it, and if the copper tube be allowed to cool it is firmly united with the
paper tube thrust over it. The process is repeated in the same manner according
to the number of conductors which are to be united in the system, and the whole
conductor thus constructed is inserted in an iron tube heated to the melting point
of the insulating material. Thereupon again the outer layer of insulating material
upon the paper tube last employed is melted and an intimate union secured between
the iron tube and the paper tube. The system thus constructed therefore contains
two or more conductors which possess great mechanical strength and are in a
high degree protected against access of moisture, since each tube added, whilst in
itself a conductor, also serves as a protecting sheathing to the conductor which lies
beneath it.
By the previous high heating of the copper conductors and of the iron tube,
every trace of moisture and of atmospheric condensation is got rid of and as the
result of the melting of the insulating material upon the paper tube all small air
spaces between the tubes thus thrust within each other are got rid of and at the same
tire the access of air is prevented entirely.
By the employment of the process above described therefore, an electrical
conductor whose insulation is extremely complete is obtained. It is very important
that the paper tube should consist of one unbroken length along the whole extent of

page_text: the copper conductor since, otherwise, if a simple butt-joint is employed, the
insulation at this point will be lower than at other parts.
If, however, it is found impossible in practice to avoid constructing the paper
tube from two shorter lengths, the two ends of these must be reduced to an extent
sufficient to allow a ring constructed of the same material as the paper tube to be
placed over the butt-joint without increase of the external diameter of the paper
tubes so united.
The copper conductors must be of such a length that they project beyond the
protecting outer iron tube and the paper tubes which insulate the separate conductors
so far as to allow of their being joined to the conductors of the succeeding tube in
a suitable known manner.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is
The herein described process for the manufacture of compound electrical
conductors consisting in alternately thrusting into each other paper tubes coated
within and without with a fusible insulating material and a copper rod and tubes
heated to the melting point of this insulating material, thus bringing the inner and
outer insulating layers of a paper tube to the melting point, and causing intimate
union of the paper tube both with the copper rod or tube lying inside it and the
copper tube lying outside it, the whole being then pushed into an iron tube heated
to the melting point of the insulating material and which is so intimately united
with the outer paper tube that an electrical conductor is obtained which contains
within it two or several conductors, which are entirely insulated from one another
and are perfect in themselves.
Dated the 10th day of March 1892.
G. F. REDFERN & Co.,
4, South Street, Finsbury, London, Agents for the Applicant.