An Improved Process for the Manufacture of Filaments for Electric Incandescence or Glow Lamps.
Year: 1889

page_text: Date of Application, 3rd July, 1889-Accepted, 12th Oct.,
1889
COMPLETE SPECIFICATION.
[Communicated from abroad by ALEXANDRE DE LODYGUINE, of 48, rue de Bondy,
Paris, France, Electrician.]
An Improved Process for the Manufacture of Filaments for Electric
Incandescence or Glow Lamps.
I, ERNEST DE PASS, of 68 Fleet Street, in the City of London, Fellow of the
Institute of Patent Agents, 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, reference being had to the accompanying drawings
and to the letters and figures marked thereon, that is to say :-
This invention relates to an improved process of manufacturing filaments for electric
incandescence of glow lamps, substantially as hereinafter described.
In the accompanying drawings, Figs. 1 and 2 are side and edge views of a block of
lead upon which the blanks, from which the filaments or incandescents to be manu-
factured are placed, to expose them to the action of the fluoride of boron, as hereinafter
described.
Fig. 3-is a sectional view of the apparatus in which the blanks are exposed to the
action of the fluoride of boron.
Fig. 4 is a view partly in section shewing one form in which the apparatus may be
arranged.
My invention relates particularly to the process of manufacturing the filaments or
incandescents. I make use of any suitable organic substance such as bamboo, paper,
thread, piassaba, or any other organic material capable of the treatment hereinafter
mentioned. The organic material used is reduced to the required shape and size in
any of the well known ways for making the filaments or blanks from which such
incandescents are made. These filaments or blanks A, having the required dimensions
are bent upon a suitable form or block of lead B, fig. 1, to give them the required
finished shape, and they are fastened upon such block in any desired way, such, for
instance, as inserting their free ends into a suitable recess or slit C, in the side or edge
of the block, which recess is closed on the ends of the blank to hold it in place. The
form B, having the blank secured to it, is placed in a closed vessel in which it is
exposed to the action of fluoride of boron (B Fl.). In fig. 3 I shew a form of vessel D,
which may be used for this purpose. It is lined internally with lead to resist the
action of the fluoride of boron, and it has a shelf P upon which the blocks B with the
filaments or blanks secured thereto are placed. The chemicals from which the fluoride
is produced are placed in the lower part of the vessel, or a separate vessel may be used
for producing the gas, as shewn in fig. 4. The gas arising therefrom acts upon the
filaments or blanks secured to the forms B, and carbonizes them, driving off the
elements of water chemically combined therewith, preserving the original form and
structure of the filaments or blanks and imparting to them a uniform homogeneous
character, with the exception that the fluoride will combine with any foreign mineral
substances which may be contained in the material, forming fluoride salts.
A neck or tube F (see fig. 4), leads from the retort D, and terminates in a glass
vessel G, which is filled with naphtha or other liquid not containing the elements of
water, so that the gas will not combine therewith. The end of the tube F terminates
below the surface of the liquid so that the latter acts as a seal. The trap thus made,
while permitting the gas to pass through, effectually seals the retort from the entrance
of the atmosphere, and so prevents the strength of the fluoride of boron from being
wasted upon the moisture in the atmosphere. The glass vessel G is provided with a
filling orifice H through which the naphtha is poured into it. It is also provide with
an outlet I, from which a neck or tube K leads to a second glass vessel L containing
water, said vessel being connected with a third vessel L' also containing water and

page_text: .
provided with an exit opening M, communicating with the atmosphere. The ends of
the tube K terminate above the surface of the liquids contained in the vessels G and L,
the gas passing through the liquid contained in the vessel G, escapes therefrom
through the pipe K into the vessel L, where it combines with the water. The water
is capable of absorbing the gas up to the limit of 800 volumes of gas to one of water.
is
The opening M prevents the accumulation of pressure in the vessel L. The gas
destructive to life and the object of the vessel L is to render it harmless by pro-
viding for its absorption. The liquid contained in the vessel L after the absorption of
the gas is an acid which can be used for etching glass. Without the provision of the
vessel L, the pipe K should lead to a stack or other device by which it could be
conducted away to a safe place of discharge.
The heat in the retort should be not less than 300° and not more than 570°
Fahrenheit. The degree of heat is determined by a thermometer O, and the gas
flame is regulated by a cock. It is not necessary that the filaments or incandescents
should be treated in the same vessel in which the gas is produced, but, if desired,
the gas may be produced in one vessel and then led to another vessel in which the
filaments or incandescents are placed, as will be readily understood.
In order to prevent the liquid in the vessel G from being forced into the retort D
by the atmospheric pressure, when after the completion of the process, the retort N
is being cooled, a bulb Q is provided on the pipe F, of sufficient capacity to contain
all the liquid in the vessel G, so that when the latter is forced up the pipe by the
atmospheric pressure it will fill the bulb and be arrested thereby. In order to pre-
vent danger to the workmen from the gas when the retort D is open, after the
completion of the process, a branch pipe S, communicating with the pipe F, is
provided. This branch pipe leads to a vessel T containing water, and is provided
with a suitable cock. Before opening the retort D the workman opens the cock so as
to permit the gas to communicate with the water in the vessel, which will be of suffi-
cient quantity to absorb the gas remaining in the retort D, so that when the retort
is opened it will contain no gas injurious to the workmen.
Lead is used in forming the block B, because it is not affected by the action of
the fluoride of boron.
After this step in the operation the filaments or incandescents are removed from
the blocks B, and they are then placed in a furnace not containing oxygen, and
covered with graphite or powdered carbon, and are there exposed to a high tem-
perature for the purpose of eliminating any fluoride which may remain uncombined,
as well as the combinations which it may have formed on the filaments, and also any
other gases or substances contained therein which can be removed by the heat of the
furnace. Heat can be conveniently obtained by the use of a gas furnace, and a
gradually increasing temperature should be applied, say, during a period of about
thirty minutes, until the highest, temperature is reached, which may be continued
about two hours and then gradually reduced during a further period of about thirty
minutes.
When the filaments or incandescents are sufficiently cold they are removed from
the furnace and attached to temporary clamps or electrodes and placed in a suitable
chamber, from which the air has been removed, and there heated to a very high heat
in vacuo by passing a current of electricity through them. The filaments or incan-
descents in this operation should be exposed to as high a heat as they are capable of
withstanding without fracture. The purpose of this step of the operation is to drive
off all occluded gases from the filaments or incandescents and to complete the car-
bonizing operation. The perfect treatment by the fluoride bas the effect of increasing
the ability of the filaments or incandescents to withstand heat, and the effect of
subsequent super-heating by means of the electric current is to change the rather
amorphous carbon of the filaments or incandescents thus obtained into a highly re-
fractory homogeneous coke in which the form and structure of the original blank are
preserved. During this step of the operation the atmosphere of the chamber is being
continually drawn off, so that the gases which are expelled from the filaments or
incandescents by the high heat shall be carried away from and out of the chamber.

page_text: It is better to admit a small quantity of illuminating gas or other suitable gas into
the chamber before the beginning of this step of the process, for the purpose of
reducing the amount of oxygen contained in the chamber, as the effect of the admis-
sion of the gas is to reduce the quantity of atmospheric air which may be present.
This operation of heating by means of an electric current occupies but a short time,
being in the case of ordinary sized filaments or incandescents from thirty seconds to
two minutes.
The filaments or incandescents are then removed from the temporary clamps or
holders and so much of the ends as were not fully exposed to the high heat of the
electric current, may be broken off. After this the filaments or incandescents are
secured to the platinum clamps or holders which constitute their permanent electrodes
in the finished lamp, and placed in a receiver from which the atmosphere is exhausted
and to which an atmosphere of carbonaceous gas not containing oxygen, say for
instance, gasoline or rhigoline, is admitted. An electric current is then passed
through the filaments or incandescents for the purpose of building it up by the
deposition of carbon, and thereby imparting to them a uniform resistance. This
step of the process does not differ from that usually practised in the manufacture
of fibrous filaments for incandescence lamps, except that it follows instead of preceding
the operation of driving off the occluded gases. The advantage of driving off the
occluded gases before the process of building up the carbon by deposition is that
if the latter operation be first performed, the hard deposit or shell thereby made
upon the filaments or incandescents has a tendency to prevent the escape of the
gases, so that a greater or less quantity remains in the filaments or incandescents,
and the effect of their presence is to endanger the filaments or incandescents, and to
increase the blackening of the bulb of the lamp when in use and shorten its life.
The filaments or incandescents are then taken and sealed into the lamp bulbs in
the usual way, and the latter is either exhausted or filled with an artificial atmo-
sphere in the way practised in the manufacture of incandescence lamps.
I have referred somewhat to the construction of apparatus used in this process
and also to periods of time which may be occupied by some of the steps, but I do
not limit myself to any particular form of apparatus, or to any particular order or
periods of time in the various operations. These things, together with the form
and construction of the apparatus which is necessary in the process, will be readily
understood by persons familiar with the art, and it is not necessary to encumber
this specification with any further description of or reference to them.
The action of the fluoride of boron is to decompose the organic substance composing
the filaments or incandescents by hydrating them, leaving practically nothing in the
case of a vegetable material but the carbon with which they have no chemical affinity,
and in case of an animal substance leaving only the carbon and nitrogen. There are
other chemical agents, known to chemists which have such an affinity to water that
they will decompose and carbonize organic substances, among which agents are sul-
phuric acid, fluorohydric acid, chlorine gas, caustic soda, and caustic potash.
Such chemical agents are more or less adapted to use in my improved process, and
I include them as chemical equivalents of the fluoride of boron, although not so power-
ful for the purpose. The manner of using them to dehydrate and decompose organic
substances is familiar to the skilful chemist and need not be here described.
The advantages of my improved process consist in the fact that the filaments or
incandescents are very free from a tendency to blacken the lamp when in use, and
require with the same life and candle-power a smaller expenditure of energy than
filaments or incandescents made by any other process known to me.
Having now fully described and ascertained my invention, and in what manner the
same is to be performed, I claim :-
The process of manufacturing carbon filaments or incandescents for electric glow
lamps from organic material, consisting in dehydrating and decomposing the filaments
or incandescents by the action of a chemical agent, then subjecting them to a high
temperature with the exclusion of oxygen, expelling the occluded gases from the

page_text: filaments or incandescents by subjecting them to a high temperature by the passage of
an electric current, and finally giving them the required resistance by the deposition of
carbon, substantially as described.