Improvements in the Manufacture of Electrical Resistances.
Year: 1898

page_text: Date of Application, 23rd Aug., 1898-Accepted, 26th Nov., 1898
COMPLETE SPECIFICATION.
Improvements in the Manufacture of Electrical Resistances.
I, ADOLF VOGT, of I Lothringerstrasse 5, Vienna, Austria, Engineer, but at
present of Keysers Royal Hotel, Blackfriars, in the County of London, do here-
by declare the nature of this invention and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement:
My invention relates to the manufacture of an electrical resistance-material
capable of application in a variety of ways for regulating electrical currents, and
for the conversion of electrical energy into heat.
In a previous application for Letters Patent No. 15,238 of 1897, has been
described in Examples 1 and 2 set forth in the specification thereof, processes
for manufacturing electrical resistance materials. I have, however, found in my
subsequent experiments that these processes yield a material which, though to a
certain extent accomplishing the purposes for which it was intended, does not
possess those physical properties of density, hardness, and homogeneity, or that
accuracy of composition from an electrician's point of view, which are needed to
render it satisfactory for all such purposes. By my present invention these
defects are got rid of.
According to my present invention an intimate mixture, in a finely divided
state, of a non-conductor and a conductor is worked with water into a paste or
dough from which by moulding or by casting or otherwise, as for example, after
the manner in which potter's clay is handled, an article of the shape which it is
desired the resistance body should possess is made, such article after drying being
heated to a high temperature embedded in powdered carbon. For this purpose
the article and the carbon in which it is embedded are placed in a suitable box
or vessel which, except as hereinafter mentioned, is closed air tight and is heated
in an oven, either specially constructed for the purpose or as used in making
pottery.
The non-conductor may be any artificial stone, clay, cement, porcelain, mag-
nesia, or any refractory metallic oxide or mineral substance, which in the process
of manufacture of the resistance material does not suffer change. The conductor
may be carbon in the form for example, of graphite or powdered coke, a material
such as asphalt, tar, sugar, cellulose, bone-meal, which by heating is carbonised,
or a metal, or any metallic compound such as chromium silicide, iron silicide,
copper silicide which in the process of manufacture of the resistance material is
converted into a metal, otherwise than by reduction (i.e., otherwise than by
simple abstraction of oxygen). The proportions in which the constituents of
the resistance material are mixed will depend of course upon the resistance desired
and may vary within very wide limits.
In case asphalt or tar is used, the mixing of the same with the non-conductor
is carried out under application of heat, the temperature being raised until the
mixture ceases to become softer by further heating. In such case too, the precau-
tion should be taken when heating embedded in carbon, to carefully and slowly

page_text: raise the temperature and to provide means for the disengaged gas to escape by
using for the box or vessel containing the article embedded in carbon, a cover,
which although fitting fairly well does not close the same air-tight.
In cases other than when tar or asphalt is used, it is preferable to allow the
paste or dough to stand some months before moulding, or otherwise converting
it into the shape desired.
Inasmuch as the resistance of metal increases with the temperature, whereas
the resistance of carbon decreases with a rise of temperature, a material whose
specific resistance remains approximately constant for a considerable range of
temperature may be obtained.
In applying my invention to the production of such a material, a non-con-
ductor of the nature indicated previously in this specification is intimately mixed
in a finely divided condition with graphite and a metallic powder. The quantities
of the graphite and metallic powder one to another, must be proportioned with
a view to obtaining the desired result at the desired temperature. The exact
proportion in which the graphite and metallic powder should be used cannot be
given because, among other reasons the conductivity of different samples of
graphite varies considerably, however two or three experiments will determine in
what proportion any particular sample of graphite and any particular metal should
be used in order to prepare a material whose resistance shall at the desired tem-
perature te approximately constant. The mixture is worked up exactly as
indicated previously in this specification.
The resistance material manufactured according to my invention is sufficiently
compact to allow of its being polished, cut, turned, filed, bored, or provided
with screw threads. It may also if desired be galvanized glazed or enamelled.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I declare that what I
claim is:
1. The process of manufacturing an electrical resistance material from a mix-
ture of a conductor and a non-conductor, consisting in working such mixture into
a paste or dough with water, moulding casting or otherwise converting such paste
or dough into the shape desired, drying and finally heating embedded in carbon
to a high temperature substantially as described.
2. The process of manufacturing a resistance material having an approximately
constant conductivity throughout a considerable range of temperature from a
mixture of a non-conductor, graphite, and a metallic powder, consisting in
making a paste or dough of such mixture with water, moulding casting or other-
wise converting such paste or dough into the shape desired, drying, and finally
heating embedded in carbon to a high temperature, substantially as described.
3. In the processes hereinbefore claimed the substitution of a carbonizable
material for carbon in the composition of the mixture, due provision being made
for the escape of the gases generated during carbonization substantially as
described.
1
00 1 1
1000
ABEL & IMRAY,
Agents for the Applicant.