IMPROVEMENTS IN THE MANUFACTURE OF CARBON FILAMENTS FOR INCAN- DESCING ELECTRIC LAMPS
Year: 1883

page_text: LETTERS PATENT to George Bowron of Maida Vale and Walter Hibbert of
Crawford Street, both in the County of Middlesex. for an Invention of
"IMPROVEMENTS IN THE MANUFACTURE OF CARBON FILAMENTS FOR INCAN-
DESCING ELECTRIC LAMPS
"
PROVISIONAL SPECIFICATION left by the said George Bowron and
Walter Hibbert at the Office of the Commissioners of Patents on the
12th February 1883.
GEORGE BOWRON of Maida Vale and WALTER HIBBERT of Crawford Street
both in the County of Middlesex " IMPROVEMENTS IN THE MANUFACTURE OF
CARBON FILAMENTS FOR INCANDESCING ELECTRIC LAMPS
"
Our Invention has for its object the production of carbon filaments for incan-
descing electric lamps of a more homogenous structure than has been heretofore
attainable whereby increased durability and greater illuminating power for a given
unit of surface are obtained.
In carrying out our Invention in order to effect this object we make the carbon
filaments of a mixture of carbon in a very fine state of division and a viscous liquid
of an organic nature or holding organic substances in solution.
The carbon which we may employ for the purpose is graphite, lamp black or
vegetable black, or charcoal derived from sugar or any equivalent carbon yielding
substance. The viscous liquid which we prefer to employ is a strong solution of
sugar. The relative proportions of the carbon and viscous liquid may be varied
but we have found in practice that with the use of graphite in a very fine powder
a quantity of solution of sugar equal to say from about thirty to sixty per cent.
of the weight of graphite used gives good results, the solution containing say about
from sixty to seventy per cent. of sugar. The exact proportions will however
depend upon the nature, and state of division of the carbon. For example with
vegetable black a larger proportion of sugar should be used.

page_text: The carbon and sugar or its equivalent mixed in suitable proportions as before
mentioned so as to form a pasty consistence, is introduced into a vessel or receptacle
having a very minute orifice, through which the material is forced by means of a
plunger, and issues in the form of a continuous and flexible filament. This con-
tinuous filament is then cut up into the required lengths and bent into a suitable
form for the filaments of incandescing lamps, which filaments are then allowed to
dry by exposure to the air, and afterwards beated in a close vessel at a bright red
heat so as to carbonize the sugar or its equivalent forming one of the constituents
of the filaments. The filaments are then ready for connection to the leading-in
wires of the lamp to which they may be attached by adhesion and carbonization
of a small quantity of the paste of which the filaments are made or in any other
suitable manner. If preferred the filaments may be attached to the leading-in
wires before carbonization, or the continuous filament may be first dried and
carbonized and afterwards cut up into lengths for the finished filaments
If desired the filaments may be placed in an atmosphere of hydro-carbon vapour
and raised to incandescence in the well known manner.
Our Invention is applicable both to the production of solid filaments and tubular
filaments. When tubular filaments are required they may be produced by the
addition of a filamentous core to the die or plunger the core occupying the centro
of the orifice.
The carbon filaments may be used in exhausted bulbs in the usual manner

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said George Bowron & Walter Hibbert in the Great Seal Patent
Office on the 10th August 1883.
GEORGE BOWRON of Maida Vale and WALTER HIBBERT of Crawford Street
both in the County of Middlesex "IMPROVEMENTS IN THE MANUFACTURE OF
CARBON FILAMENTS FOR INCANDESCING ELECTRIC LAMPS "
Our said Invention has for its object the production of carbon filaments for
incandescing electric lamps of a more homogeneous structure than has been
heretofore attainable whereby increased durability and greater illuminating power
per unit of surface will be obtained, and it consists in making such filaments of
a mixture of carbon in a very fine state of division and a solution of sugar or
other viscous liquid of an organic nature, or holding organic substances in solution,
in the manner and by the means substantially as hereinafter described.
In carrying out our said Invention we take graphite or lamp black, or vegetable
black, and mix therewith the viscous liquid by preference a strong solution of
sugar, the two ingredients (the carbon and the solution of sugar or other viscous
liquid) being employed in such relative proportions that their commixture shall
form a pasty consistence. As this condition is the result which is to be sought
the exact proportions of the two ingredients may be readily arrived at by testing
in small quantities, it being obvious that as the proportions must necessarily be
varied according to the nature and state of division of the carbon, it is not possible
to give definite proportions which will be applicable in all cases. It should be
observed however that no more of the viscous liquid should be used than is
necessary to make a homogeneous paste presenting a dry appearance. We have
found the following approximate proportions to give good results in practice:
viz_
With the use of graphite in a very fine powder, a quantity of solution of sugar
may be employed equal to say about sixty per. cent. of the weight of graphite
used, the solution containing say about from sixty to seventy per. cent. of sugar.
With lamp black, or vegetable black also in a very fine powder, a larger pro-
portion of solution of sugar may be employed viz: about two hundred per cent of
the weight of lamp black or vegetable black used, the solution of sugar being of
the same strength as before.
In lieu of employing graphite, or lamp black, or vegetable black, charcoal derived
from sugar or any equivalent carbon-yielding substance may be used, but as the
results so far obtained with it have been inferior to those obtained with graphite,
or lamp black, or vegetable black, we do not recommend its use but prefer to employ
the forms of carbon first mentioned.
In lieu of using a solution of sugar we may employ other viscous liquids of an
organic nature or holding organic substances in solution. For example when
vegetable black is employed, a solution of resin in turpentine may be used, but
in this case we have always found it advantageous to add to the carbon used
a proportionate quantity of sugar. This is most conveniently done by mixing a
suitable quantity of solution of sugar with the carbon, and then evaporating to
dryness, the carbon and granular sugar resulting, being afterwards mixed with the
solution of resin in turpentine..
Good results have been obtained by mixing with the vegetable black a quantity
of pure sugar equal to about thirty per. cent. of the weight of vegetable black used,
the sugar being added in the form of a weak solution containing say about five
per cent of sugar, and after evaporation, mixing the vegetable black and sugar

page_text: with a quantity of solution of resin in turpentine equal to say about ninety per
cent of the weight of the mixture of vegetable black and sugar used, the solution
containing say from about forty to fifty parts of resin in one hundred parts of the
solution.
The carbon and solution of sugar or other viscous liquid having been mixed
together in suitable proportions as before mentioned so as to form a pasty con-
sistence the same is introduced into a vessel or receptacle having a very minute
orifice through which the material is forced by means of a plunger and issues in
the form of a continuous and flexible filament.
+
The accompanying drawings illustrate some convenient forms of apparatus to be
used in the manufacture of the filaments
Figure 1. represents a vertical section of one form of apparatus.
A, is a hollow cylinder, the interior a, of which is bored true, smooth and
cylindrical for the greater part of its depth for the reception of a plunger B, but
slightly conical at its lower end for the insertion of a conical plug C, the chamber b
of the latter terminating in a very minute orifice c. In operating with the
apparatus the plug C being in its place and the plunger B withdrawn, a suitable
_ quantity of the mixture of carbon and solution of sugar or other viscous liquid,
in the condition of a pasty consistence is introduced into the interior a of the
cylinder A, the plunger B is then inserted, and pressure applied at its upper end
by means of a screw press or otherwise, whereby the material is forced out through
the orifice c, and issues in the form of a continuous and flexible filament.
- This arrangement is adapted for the production of solid filaments. When tubular
filaments are required they may be produced by the addition of a filamentous core
to the die or plunger, the core occupying the centre of the orifice.
Figure 2 is a vertical section of an apparatus intended for the production of
tubular filaments.
A, is the cylinder with its bore a terminating at its lower end in a conical
portion, in which are fitted two plugs C, C, a short distance apart so as to leave
a space d, between them. The plug C is formed with an orifice c whilst the plug C¹
carries a filamentous core e which occupies the centre of the orifice c, grooves or
passages being provided on the periphery of the plug C' (see detail Figure 2) for
the passage of the material. The operation is performed by the application of
pressure to a plunger B as before.
Figure 3 shows a similar apparatus in which the plug C is dispensed with, the
orifice c being formed in the cylinder A. The plug C₁ (shown in detail in Fig. 3ª)
with its pendent filamentous core e is used as before.
"
The continuous flexible filament whether solid or tubular, issuing from the
apparatus may then be cut up into the required lengths and bent into a suitable
form for the filaments of incandescing lamps, or it may be lightly wound or allowed
to fall around or over a suitable "former" in such a manner as to approximate
to the shape of the filaments, and be then cut up or otherwise severed. Figures
4, and 5. represent respectively an elevation and section (drawn to a reduced scale)
of a former" D, by turning which and moving it slightly longitudinally as the
filament g descends from its point of egress A, the filament will become lightly
wound round it, the several filaments being subsequently severed at h. Or the
device shown on a reduced scale in Figures 6, 7, 8, and 9, may be conveniently
adopted, of which Figures, 6, 7, and 8, are diagrammatic sectional views illustrating
three different positions, and Figure 9 is an elevation. A, represents the point of
egress of the filament from its cylinder, and D, the "former". The continuous
filament first descends down one side of the "former" D as shown in Figure 6,
the "former" is then moved to the left so that the filament will descend in a loop-
form down the opposite side as shown in Figure 7. after which the "former" is
moved to the right, and the loop descends down the other side, and so on in
succession until as the former is gradually moved longitudinally the whole
length of the "former" is covered with loops which only require severing to
produce filaments of a form suitable for use in incandescing lamps. It is obvious

page_text: "3
that the shape of the formers is to be varied to suit the form of filaments
required. The filaments having been cut or severed, may be at once subjected to
the action of the carbonizing apparatus, or, as we prefer, they are first allowed to
dry by exposure to the air, and then carbonized.
The filaments are then ready for connection to the leading-in wires of the lamp
to which they may be attached by adhesion, and carbonization of a small quantity
of the paste of which the filaments are made, or in any other suitable manner.
If preferred the filaments may be attached to the leading-in wires before car-
bonization; or the continuous filament may be first dried, and carbonized, and
afterwards cut up or severed into lengths for the finished filaments,
If desired the filaments may be placed in an atmosphere of hydro-carbon vapour
and raised to incandescence in the well known manner.
The carbon filaments may be employed in exhausted bulbs in the usual
manner.
Having now described and particularly ascertained the nature of the said
Invention and the manner in which the same is or may be used or carried into
effect we would observe in conclusion that what we consider to be novel and original
and therefore claim as the Invention secured to us by the hereinbefore in part
recited Letters Patent is :-
The manufacture of carbon filaments for incandescing electric lamps from a
mixture of carbon in a fine state of division, with a solution of sugar, or other
viscous liquid of an organic nature, or holding organic substances in solution, in the
manner, and by the means substantially as herein before described.
In witness whereof we the said George Bowron and Walter Hibbert have
hereunto set our hands and seals this sixth day of August in the year
of our Lord, one thousand eight hundred and eighty three.