Improvements in the Manufacture of Carbon Filaments for Incandescence Lamps.
Year: 1885

page_text: Improvements in the Manufacture of Carbon Filaments for
Incandescence Lamps.
I, ROBERT DICK, of Greenhead, Glasgow, Lanarkshire, Manufacturer, do hereby
declare the nature of my invention for "IMPROVEMENTS IN THE MANUFACTURE
OF CARBON FILAMENTS FOR INCANDESCENCE LAMPS," to be-as: follows:-
In the manufacture of carbon filaments for incandescence lamps a large
proportion of the filaments are damaged or destroyed in the process of car-
bonisation and by manipulation during the operation of preparing and connecting
or fixing them in place in the lamps. The object of my invention is to produce
filaments of much greater strength, and which may better withstand handling
than those prepared in the ordinary way, while also providing improved means of
connecting them to the conducting wires of the lamps.
According to my invention I form carbon filaments from strands of silk, cotton,
or other fibrous substances, or from strips of paper or parchment or of woven
fabrics, or of other materials commonly employed for the purpose, which strands
or strips enclose within tubes of copper, or other soft and ductile metal, which
I afterwards draw down through dies or otherwise to reduce the diameter of the
tubes and thereby to compress the materials within them. The strands or strips
may either be enclosed within solid tubes, or the tubes may be formed round or '
partially round them out of flat or channelled strips of metal. The compressed
filaments thus formed are then cut into suitable lengths, and bent or shaped to the
desired form, and are carbonised in the ordinary way. After carbonisation of the .
filament the copper tube or other metallic coating is removed from the greater
part of its length by immersion in nitric acid, or by electrolysis, or by other well-
known means, the metallic coating being however left at the ends to serve as a
convenient means of connecting the filament to the conducting wires of the lamp
by soldering, screwing, or clamping.
In some cases I form tubular filaments by placing a removable core or wire
within the material forming the filament before enclosing it within the outer tube,
so that the material may be compressed between the core and the tube, the wire
being removed before carbonisation, or it may be left in and decomposed by acid
after carbonisation, or when the wire is made of platinum it inay, be loft in.
The employment of the metallic tube serves the purposes of compressing within
it the material forming the filament, of maintaining the pressure and shape during
the carbonising process, of protecting the filament during the subsequent manipu-
lation required in connecting it to the lamp, and of forming a metallic connection
with the wires of the lamp.

page_text: Improvements in the Manufacture of Carbon Filaments for
Incandescence Lamps.
I, ROBERT DICK, of Greenhead, Glasgow, Lanarkshire, Manufacturer, do hereby
declare the nature of the said Invention, and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement in writing:-
In the manufacture of carbon filaments for incandescence lamps a large
proportion of the filaments are damaged or destroyed in the process of car-
bonisation, and by manipulation during the operation of preparing and connecting
or fixing them in place in the lamps.
The object of my Invention is to produce these carbon filaments of so much
greater strength and density that they will not only withstand the necessary
handling in their preparation and securing them in the lamps and to their
conducting wires, better than the filaments prepared in the ordinary way, but this
will also enable them to be made so much less in diameter for equal durability
and have less resistance that an electric current of less intensity will be required
to give an equal light, which will also save considerable loss of energy in power or
electricity.
According to my Invention I forin carbon filaments from strands of silk, cotton,
or other fibrous substances, or from strips of paper or parchment, or of woven
fabrics, or of other materials employed for the purpose. I find also some of the
natural grasses and the fibres of the Bass tree to answer well, and by preference
use the fibres of the Kitool plant (much imported and used as a substitute for hair
in the manufacture of the coarser class of brushes). In using this (or any other of
the natural vegetable or grass fibres) I first draw the fibres through fine steel
drawing plates or dies, as wire is drawn, only with sharp cutting edges, to
a uniform parallel size. These prepared or sized fibrous strands, threads, or strips,
I introduce or pass into or enclose within fine tubes of copper or other soft or
ductile metal, prepared or drawn as such tubes are usually made for Watchmakers,
Jewellers, Opticians, and others, preferably drawn on fine polished wires of a size
that when these are withdrawn, the fibres could be easily inserted, and all to the
desired sizes and length to suit the prepared strands or fibres. I afterwards draw
down these tubes, with the fibrous material in them, through dies, compressing
rolls, or otherwise, to reduce their diameter, and thereby compress the materials
within the tubes to the desired density. The compressed tubes with the filaments
thus formed in them, are then cut into suitable lengths and bent or shaped
approximately to the desired form the carbons are intended to retain in the lamps,
which admits of their being rolled into spirals or other shapes not possible in the
manufacture of carbons as heretofore made; in which state they are carbonised
within the tubes under pressure by heating them to bright redness in a crucible or
muffle of ground plumbago or other carbonaceous matter, in the ordinary way.
After this carbonisation of the filaments, the copper tubes or other metallic coating
is removed from the greater part of their length, or wholly removed, by immersion

page_text: in nitric acid, or by electrolysis, or by other well known means such as by melting;
part of the metallic coating may however be left at the ends to serve as
convenient means of connecting the filament to the conducting wires of the lamp,
by soldering, screwing or clamping.
The employment of the metallic tube serves the purposes of compressing the
material forming the filament placed within it, and of maintaining the pressure
and shape during the carbonising process.
The advantages obtained by this compression of the carbon forming material
during its formation and carbonisation are many, first, it strengthens the filament
mechanically, second, it enables the carbon to give a high specific amount of
luminosity per unit of energy expended on it in the lamp, thus rendering this
carbon filament a very durable and economical medium in incandescent lamps for
electric lighting.
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
.
First. The manufacture of carbon filaments for incandescent electric lamps
substantially as herein described.
Second. In the manufacture of carbon filaments for incandescent electric lamps,
the compression of the fibrous or other material within metal tubes; and the
carbonising of them within the tubes under compression substantially as herein
described.