Improvements in Incandescent Electric Lamps.
Year: 1892

page_text: COMPLETE SPECIFICATION.
Improvements in Incandescent Electric Lamps.
I, FRANK STUART SMITH, Electrician of The Westinghouse Electric and
Manufacturing Company, of Pittsburgh, Pennsylvania, United States of America,
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.
This invention relates to the use of iron wire for the leading in conductors of
incandescent electric lamps in place of platinum wire heretofore generally
employed for this purpose in order to considerably reduce the cost of such lamps.
For this purpose an iron wire of the proper size is first carefully cleaned and
brightened by polishing with emery paper or in any other convenient manner.
Two wires, or the arms of a single piece of wire bent upon itself, are then held in
their proper relative positions for forming the stem. A small quantity of glass is
then fused upon the wires, fixing them in position. A sufficiently close joint
cannot be produced by fitting the wires into openings previously formed in the
glass and it is necessary that the glass be formed about or moulded upon the wires
by fusing or melting it. This can be done in a glass blower's flame; but as iron
oxidises very quickly when highly heated in this flame, care must be exercised to
guard against excessive heat and also against exposing the iron to the direct action
of the flame.
In practice, I usually, first pass the wires through a tube or tubes of glass and
then fuse one end of the tube upon the wires. The envelope thus formed protects
the wires from currents of air and from the direct action of the blow pipe flame.
The tube is then gradually fused along its length from the end so closed. Other
methods of applying the glass to the iron wires without excessive oxidation may
however be employed.
Even with these precautions in the process of coating the iron wires with glass,
a thin film or scale of oxide will usually form upon the wires and intervene between
them and the glass. This film or scale prevents the formation of the completely
air tight joint which is secured by the use of platinum leading in wires, but I have
found that by afterwards applying a suitable cement or plastic substance at the
point where the wires enter the glass a perfectly air tight seal is obtained. In
practice, I have obtained excellent results by the use of a sealing compound con-
sisting of a mixture of the yellow oxide of lead, one part by weight the red oxide
of lead, two parts, and the carbonate of lead, about five parts, all thoroughly
mixed and ground with boiled linseed oil sufficient to form a thick paste.
Other
vehicles than linseed oil may be used and the proportions may be varied somewhat.
Asphaltum varnish also gives good results and other suitable cements may be used.
The cement may be applied before or during the process of exhausting the bulb.
When the exhaustion has been effected, the lamp is sealed and removed from the
pump in the usual manner.
I have found that lamps constructed with iron leading-in wires in the general
manner described above and having the points where the wires pass through the
glass thus protected by a cement or suitable sealing compound, are in every way
as durable and efficient as those employing platinum leading-in wires, and at the
same time, the great saving in the expeuse is a matter of the utmost importance.
In the accompanying drawings, illustrating the invention,
nd
Figure 1 is an elevation of a complete lamp.
Figure 2 is an enlarged view of the leading-in wires and a portion of the bulb;

page_text: Figures 4 to 9 illustrate a method of applying glass to the iron wires in forming
the stem.
Referring to the figures, A represents a carbonised conductor prepared in any
suitable and well understood manner. This conductor is supported at the ends of
two leading-in wires B B, of iron.
The principal steps in the process of preparing the stem are illustrated in
Figures 4 to 9 inclusive. A bright clean piece of iron wire is bent into the shape
indicated in Figure 4. A short tube F of glass shewn in side and end view at
Figures 4 and 5 is then slipped over it and a flame is directed perpendicularly
against opposite sides of the tube F near one end f. This softens or fuses the glass
at that point, flattening it against the wires and completely embedding them.
The end of the tube is thus closed and circulation of air which would tend to
oxidise the iron is prevented. The parts are then in the form shown in Figs. 6
and 7. The flame is then directed toward other parts of the tube, causing it to
melt and close about the wires, the fusion being preferably continued from the
end toward the end f' until the entire tube is formed into a solid mass as shewn
in Figures 8 and 9. Throughout this process, care is taken to prevent, as far as
possible, the flame from coming against those portions of the iron which are to be
embedded in the glass. This prevents the formation of an excessive coating of
oxide upon the surface of the wire. A thin scale of film will however usually be
formed even if great care be exercised, but its presence is found not to be detri-
mental to good results, and it is possible that its presence may serve a useful
purpose in the completed lamp, in preventing the glass from being cracked by the
unequal expansion of the glass and the iron, the coefficient of expansion of the
latter being greater than that of glass.
In practice, it is convenient to employ a single piece of wire having the loop b
for forming the two wires B B, and, after the glass is fused upon the two arms,
the loop is cut open and the ends bent into the proper position to receive the ends
of the carbon conductor or the tips bb as the case may be. If the iron wires
themselves are to receive the ends of the conductor, then suitable sockets or
terminals may be formed on them. Certain of the methods of mounting carbon
conductors require the use of heat greater than that which iron can endure without
injury. When such processes are used the iron wires may be tipped with platinum
or other suitable metal having a higher fusing point. Such tips are shown at bb
(Figure 3) and they are attached by soldering or in any other suitable manner.
The wires having been embedded by fusion in the piece or stem of glass Fas
described, this is now introduced into the neck of the globe C, which is then
secured to the glass F by fusion as at Figs. 1 and 2, after which the entrance of
the wires into the globe is protected by a layer of cement or sealing compound D.
With the use of platinum leading-in wires it is customary to economise the
platinum outside the lamp-bulb by soldering thereto extensions of copper wire for
securing connections with the lamp bottom contacts. This extra step in the manu-
facture is not necessary when iron wires are used, but the iron wires are themselves
made of sufficient length to permit the attachments. To prevent the iron wires
from being injured by long exposure to the atmosphere or by the moisture from
the cement used to fasten the lamp bulb into the bottom, they may be varnished or
coated with suitable protecting material.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
1. Constructing incandescent electric lamps with leading-in conductors of iron
wire provided with a coating of glass fused thereon, on to which coating the glass
of the bulb is then fused, the entrance of the wires into the lamp being protected
by a cement or sealing substance at their point of entrance into the glass, sub-
stantially as described.
2. The method of forming a glass coating on iron leading-in wires for incan-

page_text: descent electric lamps consisting in passing the wire into a glass tube and first.
fusing one end of such tube on to the wire after which the remainder of the tube
is fused on to the same, substantially as described.
Dated this 20th And of March 1892
ABEL & IMRAY,
Agents for the Applicant.