Improvements in the Manufacture of Filaments for Incandescent Electric Lamps.
Year: 1892

page_text: Date of Application, 29th Mar., 1892
Complete Specification Left, 23rd Dec., 1892-Accepted, 18th Feb., 1893
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of Filaments for Incandescent
Electric Lamps.
I, MORITZ BOEHM of 64 Oranienburger Strasse, Berlin, N. in the Empire of
Germany Broker do hereby declare the nature of this invention to be as follows:-
The object of this invention is to cheapen the cost of production of filaments
suitable for use in incandescent electric lamps by so varying the material of which
they are made that certain advantages may be had in simplifying the process of
the manufacture and in lessening the percentage of waste due to spoilt filaments.
In place of using a fibre or fibres of organic matter as heretofore and carbonizing
this fibre by which a large percentage usually is spoilt and rendered unfit for
further treatment, this invention consists in employing as a basis for the con-
struction of the filament, an extremely fine wire made of a suitably soft but
tenacious metal or alloy or mixture of metals. A suitable metal or alloy for
this purpose has been found to be one consisting of two parts of fine cast iron
with one part of aluminium, this being fairly rich in carbon, sufficiently ductile
and porous, and not an especially good conductor of electricity. This thin wire
is boiled in a suitable heavy fluid hydrocarbon, one of a very high boiling point,
so that the latter may soak as much as possible into the pores of the wire. From
such wire the lengths for the filaments are cut off and bent into the form desired
in order to be provided with a coating of deposited carbon by heating them in
an atmosphere of hydrocarbon in the usual way, but before they are so coated
they are provided with a varnish the purpose of which is to cause the deposited
carbon to adhere. This varnish may be made of coal-tar suitably diluted with
alcohol and thickened with a little graphite or soot or lamp black. Directly the
varnish is applied it is preferable to place the filaments (in their holders) in a
vessel from which the air may be drawn by an air pump.
While the air pump is
in action a weak electric current is passed through the filament, not sufficient to
cause the filament to glow, but only to heat it sufficiently to evaporate the volatile
matters from the varnish. This done, the filaments may be transferred to a second
vessel, with the least delay. This second vessel is in connection with an air pump
and also with a retort in which the hydrocarbon may be evaporated, the pipe
from the latter extends down into the base of the aforesaid vessel and there
terminates in an open bell mouth directed downwards. The air pump is set in
action to withdraw the air and the heavy vapour of the hydrocarbon gradually fills
the vessel. A sufficiently strong current is then passed through the filament and
the carbon from the gas is deposited thereon in the usual way, the operation being
continued until the filament has attained the desired thickness.
Dated this 29th day of March 1892.
HERBERT & Co.,
Agents to Applicant.

page_text: COMPLETE SPECIFICATION.
Improvements in the Manufacture of Filaments for Incandescent
Electric Lamps.
I MORITZ BOEHм of 64 Oranienburger Strasse, Berlin N. in the Empire of
Germany, Broker do hereby 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 :-
The object of this invention is to cheapen the cost of production of filaments
suitable for use in incandescent electric lamps by so varying the material of which
they are made that certain advantages may be had in simplifying the process of
the manufacture, in lessening the percentage of waste due to spoilt filaments and
in securing greater uniformity in the product so as to obviate the necessity of such
careful sorting as is now requisite.
In place of using a fibre or fibres of organic matter as heretofore and carbonizing
this fibre by which a large percentage usually is spoilt and rendered unfit for further
treatment, this invention consists in employing as a basis for the construction of
the filament, an extremely fine wire made of a suitably soft but tenacious metal
or alloy or mixture of metals. A suitable metal or alloy for this purpose has been
found to be one consisting of two parts of fine cast iron with one part of aluminium,
this being fairly rich in carbon, sufficiently ductile and porous and not an especially
good conductor of electricity. This thin wire is boiled in a in a suitable heavy
fluid hydrocarbon, one of very high boiling point, so that the latter may soak as
much as possible into the pores of the wire. From such wire the lengths for the
filaments are cut off and bent into the form desired in order to be provided with a
coating of deposited carbon by heating them in an atmosphere of hydrocarbon in
the usual way; although this process alone would have the effect of giving a
more or less adherent coating of deposited carbon, yet in order to give greater
adherence to the deposit, the wires after they are cut off and bent into form, and
before they are coated are provided with a varnish the purpose of which is to
cause the deposited carbon to adhere. This varnish may be made of coal tar
suitably diluted with alcohol and thickened with a little graphite or soot or lamp-
black. Directly the varnish is applied it is preferable to place the filaments (in
their holders) in a vessel from which the air may be drawn by an air pump.
While the air pump is in action, a weak electric current is passed through the
filament, not sufficient to cause the filament to glow, but only to heat it sufficiently
to evaporate the volatile matter from the varnish. This done, the filaments may
be transferred to a second vessel, with the least delay. This second vessel is in
connection with an air pump and also with a retort in which the hydrocarbon may
be evaporated, the pipe from the latter extends down into the base of the aforesaid
vessel and there terminates in an open bell mouth directed downwards. The air
pump is set in action to withdraw the air and the heavy vapour of the hydrocarbon
gradually fills the vessel.
A sufficiently strong current is then passed through the filament and the carbon
from the gas is deposited thereon in the usual way, the operation being continued
until the filament has attained the desired thickness.
The drawings hereto appended illustrate a suitable vessel A for the previous
low heating of the filament a for exhausting the air and volatile matters from the
varnish, a vessel B for submitting the filament taken from the vessel A to the action
of a stronger current in the atmosphere of hydrocarbon evolved from the contents
of the retort C.

page_text: 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. A filament for employment in an incandescent electric lamp having an inner
core composed of metallic wire.
2. A filament for employment in an incandescent electric lamp having an inner
core composed of wire made of an alloy of cast iron and aluminium.
3. A filament for employment in an incandescent electric lamp having an inner
core composed of metallic wire previously boiled in a heavy liquid hydrocarbon of
high boiling point.
4. A filament for employment in an incandescent electric lamp having an inner
core composed of a metallic wire upon which a deposit of carbon has been made in
the usual manner after previous application of a varnish for causing adherence of
the deposited carbon.
Dated this 23rd day of December 1892.
HERBERT & Co.,
18, Buckingham Street, Strand, London, W.C., Agents to Applicant.