Improved Methods of and Apparatus for Manufacturing Filaments for Electric Lamps.
Year: 1897

page_text: Date of Application, 11th Nov., 1897
Complete Specification Left, 10th Sept., 1898 --Accepted, 11th Feb., 1899
PROVISIONAL SPECIFICATION.
Improved Methods of and Apparatus for Manufacturing Filaments for
Electric Lamps.
I, HIRAM STEVENS MAXIM, of 18, Queen's Gate Place, in the County of Middle-
sex, Chevalier of the Legion of Honour, Civil and Mechanical Engineer, do hereby
declare the nature of this invention to be as follows:-
My invention relates to methods of and apparatus for manufacturing filaments
or conductors for incandescent electric lamps.
When pure carbon is used in the manufacture of such filaments their conduc-
tivity is so high that they have to be made very long and thin in order to
accommodate themselves to the high voltage now in use. When such materials
as carbide of silicon and carbide of boron are employed with the carbon, they are
liable to be volatilised and form a thin opalescent film on the inside of the glass
globe of the lamp. Now diamond powder is not subject to this objection, as it
will endure a very high temperature without being volatilised.
diamond powder (i.e. natural diamond reduced to powder) is too expensive, even
if made from the cheapest kind of stones that can be obtained.
But natural
One of the chief objects of my invention is to manufacture a species of carbon
which while closely, if not completely resembling the diamond will be less expen-
sive than natural diamonds; and an important feature of the said invention relates
to the obtaining of very high pressures by using together carbonic acid and a
hydrocarbon gas, and to the decomposition thereof which takes place in their sub-
jection to the voltaic are, that is to say, in causing the oxygen of the carbonic
acid gas to take up another measure of carbon, thereby converting the carbon
dioxide into the carbon monoxide, which is a much lighter gas and one that is
not easy to liquefy.
For the purpose of my invention I mount carbon pencils or electric conductors,
in a strong steel cylinder, so constructed as to endure an extremely high tem-
perature and a pressure of say from one to twenty tons per square inch. One of
the carbon conductors may be stationary and may be located in the centre of the
cylinder co-axially therewith, while the other carbon conductor may be attached
to a movable contrivance which is preferably in the form of a steel tube carrying
a copper conductor and provided with a stuffing box so as to prevent the escape
of the gases with which the cylinder is subsequently charged. This movable
carbon conductor is arranged in such a manner that its position may be varied
by a powerful screw.
In order to obtain the required pressure, I prefer to use carbonic acid gas and
gasoline. It is well known that carbonic acid or carbon dioxide (CO2) may be
retained in the liquid condition at a pressure of about from five hundred to six
hundred s. per square inch at ordinary temperatures, but if it is converted into
carbon monoxide, then the pressure required to prevent its increase in volume
is very much greater. In order to increase the pressure, carbonic acid in a liquid

page_text: condition, or in the condition of snow, is placed in the apparatus, together with a
quantity of gasoline or similar carbonaceous material. The apparatus is then
closed, and the voltaic are established between the aforesaid carbon conductors.
The voltaic arc very soon causes the decomposition of both the carbonic acid and
the gasoline, forming carbon monoxide. This decomposition, together with the
rise in temperature will produce the necessary pressure. By the use of this appar-
atus the temperature of the carbon can be raised very much higher than is possible
at the ordinary pressure of the atmosphere. In fact, the temperature is so
extremely high that the carbon in immediate contact with or near the conductors,
is converted into a species of diamond scales which will scratch glass, while all
the carbon is very much modified. In some instances all the ingredients for form-
ing the carbon filaments may be mixed together and then heated by being brought
near to, or in contact with the carbon conductors under a high pressure, and it
is thus possible to so change the constitution of the carbon as to make it highly
advantageous for the filaments of electric lamps; that is to say, by this process
the carbon from which the filaments are to be made and all the other materials
which might be employed therein, may be heated either singly or together to a
temperature very much above that to which they will be subjected in the lamp
itself. In this way an hydrous boracic acid may be reduced to a carbide without
being volatilised. The carbon also becomes modified so as to endure extremely
high temperatures, and if a considerable quantity of diamond carbon is present,
the electric resistance is of course very much increased.
I sometimes modify my invention by employing with the carbon of the filament
some substance like pumice-stone which usually embodies several oxides, that is
to say it generally consists of silica, alumina, oxide of iron potassa and soda and
can resist extremely high temperatures. In fact, it may be said that as paraffin
is a hydro-carbon which very strongly resists decomposition on account of the
great length of time that it has lain in the earth, so pumice-stone, from the great
length of time it has been in the earth subjected to high temperatures, has also
become admirably suited for resisting high temperatures. Moreover, pumice-
stone when at a high temperature, is of a sticky, viscid and tenacious nature,
and serves admirably to impart coherence to the particles of carbon so that they
will adhere firmly together. The pumice-stone may be ground to a very fine
powder, and mixed directly with the carbon from which the filaments are to be
made; or it may be mixed in the form of a powder with carbide of silicon or car-
bide of boron, or both, the mass being fused into a button at an extremely high
temperature. The button may be then crushed and pulverised and mixed in
varying proportions with the carbon for the manufacture of filaments, the silicon
and boron serving to increase the resistance, while the pumice-stone forms
with the carbides a species of cement admirably calculated to prevent the disin-
tegration of the carbon. Such carbon filaments should be flashed at a temperature
very much higher than that employed in the lamp itself, so that if any decom-
position of carbon takes place, it will be that of the nascent carbon of the gases
used in flashing instead of the substance of the filament, itself. Where a very
high resistance is required, a considerable quantity of diamond dust, either
natural or artificial, may be employed alone or in conjunction with any suitable
combining material, such as pumice-stone or carbides of various materials.
The tendency at the present moment is to very high voltage, and in order to
meet the new requirements arising from this tendency it is necessary to increase
the resistance of the filament as much as possible, and this can only be done by
making it extremely fine and long, or by adding to it some highly refractory
non-conducting material.
'
In some instances it may be necessary to continue the high temperature for a
very long time in order to allow the carbon to crystallise out of the carbonaceous
gases. Of course, if the carbon be heated in carbonic acid gas alone, very little
effect would take place, and no very high pressure would be reached, whereas
if a too large quantity of hydrocarbon be employed, a loose, smutty and soft

page_text: deposit would be formed; but by having only a small excess of carbon i.e. just
sufficient to convert all the carbonic acid gas present into carbon monoxide, with
a little free hydrocarbon remaining, then the crystallisation may take place from
this residuum of gases, and, if the process is continued long enough, diamond
crystals or a species of diamond carbon may be formed. The diamond carbon
instead of being of a very low resistance, which is peculiar to carbon whose tem-
perature has been raised very high, will have imparted to it a high quality of
electric resistance, and in fact may be so perfectly crystallised as to prevent the
passage of an electric current through it. This of course depends upon the length
of time and the temperature employed. The carbon and the other ingredients
which are treated in the apparatus may be reduced to extremely fine powder,
mixed with suitable vehicles, such as tar, pitch, or sugar, and may be moulded
into filaments, and "retorted" and "flashed" in the usual manner.
By another modification of my invention, the filaments after being retorted in
the ordinary manner may be placed in the aforesaid high pressure furnace under
an extremely high pressure and heated to a temperature much higher than it is
possible to obtain where no pressure other than that of the atmosphere is em-
ployed. For this purpose a hollow carbon conductor may be employed, the
filaments being placed inside the said hollow carbon which is electrically heated
in the furnace under a high pressure as above stated. The temperature may
then be raised so high as to modify the carbon before it is placed in the lamp
so that it will endure a higher temperature than that to which it is ordinarily
subjected in the lamp.
This electric retorting operation may be effected either before or after the
flashing operation.
By my aforesaid methods I may obtain a large number of carbides which
cannot be readily formed under atmospheric pressure.
شدند
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HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C.,
Agents for the Applicant.
Improved Methods of and Apparatus for Manufacturing Filaments for
Electric Lamps.
I, HIRAM STEVENS MAXIM, of 18, Queen's Gate Place, in the County of Middle-
sex, Chevalier of the Legion of Honour, Civil and Mechanical Engineer, do hereby
declare the nature of this invention and in what manner the same is to be per-
formed to be particularly described and ascertained in and by the following
statement:-
1
My invention relates to methods of and apparatus for manufacturing filaments
for incandescent electric lamps.
The tendency at the present time in electric lighting is to use very high voltage,
and in order to meet the new requirements, arising from this tendency, it is
necessary to increase the resistance of the lamp filaments as much as possible;
this can only be done by making them extremely fine and long, or by adding
to the carbon of which they are composed some highly refractory non-conducting
material.
When such materials as carbide of silicon and carbide of boron are employed
with the carbon they are liable to be volatilised by the electric current when the

page_text: lamp is in use and to form a thin opalescent film on the inside of the glass globe
of the lamp. Now diamond powder is not subject to this objection, as it will endure
a very high temperature without being volatilised. Natural diamond powder
(i.e. natural diamond reduced to powder) is, however, too expensive to be used
for this purpose, even if made from the cheapest kind of stones that can be obtained,
but according to my invention I am able to manufacture a species of carbon
which, while closely if not completely resembling the diamond, will be less ex-
pensive than natural diamonds.
For this purpose it is necessary to employ an extremely great pressure and a
high temperature and an important feature of my invention has reference to the
manner in which such great pressure and high temperature are obtained.
It is well known that carbonic acid or carbon dioxide (CO) may be retained
in the liquid condition at a pressure of about from five hundred to six hundred
pounds per square inch at ordinary temperatures, but that if it be converted into
carbon monoxide the pressure required to confine it is very much greater. I take
advantage of this fact to obtain the high pressure and temperature I require, by
placing in a strong tightly closing vessel, carbonic acid in the liquid or solid
condition, together with carbon, preferably a hydrocarbon such as gasoline. The
carbonic acid and the hydrocarbon are then decomposed by subjecting them to
the voltaic arc, the oxygen of the carbonic acid being thus caused to take up
another measure of carbon, and to be thereby converted from carbon dioxide
into carbon monoxide. This decomposition, together with the rise in temperature,
will produce the necessary pressure, the temperature of the carbon being at the
same time raised so extremely high that the carbon in immediate contact with
or contiguous to the electric conductors between which the voltaic arc is pro-
duced, will be converted into a species of diamond scales which will scratch glass,
while all the carbon will be very much modified.
In some instances it may be necessary to continue the high temperature for a
very long time in order to allow the carbon to crystallize out of the carbonaceous
gases. Of course, if the carbon or hydrocarbon be heated in carbonic acid alone,
very little effect would take place, as no very high pressure would be reached,
whereas if a too large quantity of hydrocarbon be employed, a loose, smutty and
soft deposit would be formed; but by having only a small excess of carbon i.c.
just sufficient to convert all the carbonic acid present into carbon monoxide, with
a little free hydrocarbon remaining, then the crystallization may take place from
the residuum of gases, and, if the process be continued long enough, diamond
crystals. or a species of diamond carbon may be formed. The diamond
carbon instead of being of a very low resistance, which is peculiar
carbon whose temperature has been raised
have
imparted to it a high quality of electrical resistance, in fact
very high, will
so perfectly crystallized as to altogether prevent the passage of an electric current
through it. This of course depends upon the length of time that the aforesaid
treatment is continued and the temperature employed during such treatment.
to
it may be
In some instances all the ingredients used for forming lamp filaments may be
mixed and subjected to the high temperature and pressure, or the said ingre-
dients may be treated singly. It will thus he possible to so change the constitu-
tion of the carbon or other ingredients as to render them highly advantageous
for the filaments of electric lamps; in any case the temperature to which they
are subjected is higher than that to which they will be subjected in the lamp
itself.
<
The carbon obtained or the ingredients treated by my method, are afterwards
reduced to extremely fine powder, mixed with suitable vehicles such as tar, pitch.
or sugar, and then moulded into filaments, which are retorted" and "flashed"
in the usual manner. It will be obvious from what has already been stated that
the electrical resistance of the filaments will be in proportion to the quantity of
the diamond carbon employed in their manufacture.

page_text: Figure is a side elevation.
Figure 2 a vertical section, and
Figure 3 a plan of one form of the apparatus for use in obtaining a high pres-
sure and temperature according to my invention.
Figure 4 is a vertical section and
Figure 5 a sectional plan of a modified construction of the said apparatus.
Referring more particularly to Figures 1 to 3:
A is a strong vessel of approximately cylindrical shape, furnished with trun-
nions A¹ A¹ by which it is pivotally supported in a frame A³. This vessel is
preferably made of steel lined with suitable refractory material to protect it from
the heat to which it is subjected internally when in use. The ends of the said
vessel are provided with strong detachable screw-covers or screw-stoppers A³ A¹
each, of which has a lever handle A5 to enable it to be conveniently unscrewed
when either of the said covers is required to be removed for the purpose of obtain-
ing access to the interior of the vessel.
B B' are carbon pencils or conductors mounted in metallic holders 6 6¹ form-
ing part of hollow stems 62 that extend through the aforesaid covers A³ A. The
carbon pencils are arranged co-axial with the vessel A, one of them being capable
of longitudinal movement with respect to the other, so that the distance between
their adjacent ends can be varied according to requirements For this purpose
the stem 62 of the holder 6 passes through a stuffing box a forming part of the
plug piece a¹. This stem 62 is connected at its outer end with another stem 63
which is screw threaded and passes through a nut 6. The said nut is mounted
in a cross piece 65 so as to be capable of revolving without sliding, the cross piece b
being connected by bolts 66 to a disc or bar a2 which is screwed to the aforesaid
plug piece a¹ and secures the latter to the cover A3 The nut is furnished with
lever handles 67 to permit of its being revolved, while the stems 62 63 are pre-
vented from revolving by a feather 68 on the carbon holder engaging with a longi-
tudinal groove 3 in the plug piece. This plug piece is insulated from the
surrounding metal by suitable insulating material a
The other carbon pencil B is carried by the stationary holder the stem 1,2
of which passes through the screw plug A and is insulated therefrom by insula-
ting material 6º.
In order to keep the carbon holders cool I make the said stems 62 63 of the
movable holder b and also the stem 2 of the fixed holder 61 hollow and arrange
within them a central pipe or tube 610 with an annular space 6" around it. The
extremities of the stems are provided with inlet and outlet nozzles 612 613 one of
which communicates with the pipe 610 and the other with the annular space 611
Cold water can thus be allowed to circulate through the carbon holders and the
parts directly connected therewith.
The apparatus illustrated by Figures 4 and 5 is provided with a lining A upon
which the vessel A is shrunk, the said lining having a spiral water course A?
around it for the circulation of cold water which enters at A8 and escapes at A'.
The plug piece a¹ is likewise formed with a hollow head a communicating with
longitudinal passages and with inlet and outlet nozzles a 8 for enabling cold
water to circulate through said plug piece and keep it cool. The screw stopper A³
is in this example provided with an obturator A* for assisting in rendering the
vessel A gas tight. It is also provided with a toothed segmental portion A
adapted to gear with a worm All mounted on an axle furnished with a crank
handle A for revolving it. The said upper stopper A³ is formed with interrupted
screw threads so that by giving approximately a quarter turn thereto it will be
released from engagement with the corresponding interrupted screw threads on
the vessel A. To permit of its then being readily removed from the vessel, the
said worm and the crank handle are adapted to be disconnected by forming the
worm with a longitudinal central hole of rectangular shape to receive the axle,
which is also of rectangular shape at the part where the worm fits it. The end A¹³

page_text: of the said axle and the portion A are made.cylindrical to fit the bearings A15,
When the axle has been revolved a sufficient number of, times to turn and release
the stopper as aforesaid, the said axle can be withdrawn longitudinally from the
bearings A15 and also from the worm, whereby both these parts are at one operation
detached from the vessel A.
In using the apparatus, the carbon or hydrocarbon is placed within the vessel A
together with a quantity of carbonic acid preferably in its solid or snow-like .con-
dition. The vessel is then hermetically sealed by tightly, screwing, on the screw-
stoppers and the, electric current is then allowed to pass between the carbon
pencils. As the temperature rises by the heat generated by the electric current
the solid carbonic acid in the presence of the carbon will be converted into carbon
monoxide and a great pressure be thereby generated within the vessel as afore-
said. The continuance of such high temperature and great pressure will convert
the carbon into a very hard and crystalline condition which, after its removal
from the vessel, is crushed, into fine powder for use with the carbon employed.in
the manufacture of the filaments as already explained above.
..
I do not confine myself to the use of the said apparatus for obtaining carbon
in a hard and crystalline condition as above, stated, as the said apparatus, may be
used for treating other substances requiring to be subjected to high temperature
and pressure. For instance ordinary lamp filaments after being retorted; in the
usual manner may be treated in the apparatus so, as to heat them to a much
higher temperature than is possible when they are heated at atmospheric pres-
sure. In this case I prefer to employ a hollow carbon conductor to contain the
filaments.
When treating carbon or other. ingredients employed. in the manufacture, of
lamp filaments I prefer to enclose the same in small crucibles surrounding the
ends of the carbon pencils, and in order to retain the crucibles in position I sur-
round them with or embed them in some non-conducting material which acts as
a packing.
By my aforesaid methods I can obtain a large number of carbides which cannot
be readily formed at atmospheric pressure.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is;-
1. The method of obtaining carbon in à hard or crystalline condition by sub-
jecting carbonic acid and carbon or a hydrocarbon to the voltaic are in a closed
vessel for the purpose specified.
2. A method of obtaining great pressure and high temperature by subjecting
solid or liquid carbonic acid and carbon or a hydrocarbon to the voltaic are in a
closed vessel so as to convert the carbon dioxide into carbon monoxide substanti-
ally as described.
3. The manufacture of electric lamp filaments from substances consisting of
or containing materials that have been subjected to high temperature and great
pressure in the manner substantially as herein before described.
4. The subjection of electric lamp filaments to a high temperature substan-
tially as described and for the purpose specified.
5. Apparatus for use with my method of obtaining high temperature and great
pressure substantially as described with reference to Figures 1 to 3 or Figures 4
and 5 of the accompanying drawings.
Dated this 10th day of Santambon 1200
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C.,.
Agents for the Applicant.