Improvements relating to Incandescent Electric Lamps.
Year: 1893

page_text: Date of Application, 10th Nov., 1893-Accepted, 20th Jan., 1894
COMPLETE SPECIFICATION.
Improvements relating to Incandescent Electric Lamps.
I, CHARLES JOHN PEACH ROBERTSON Member of the Institute of Electrical
Engineers (London), Managing and Technical Director of the Incandescent
Electric Lamp Company Limited, Brook Green Works, London, W., 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 :-
The object of this invention is to cheapen and improve the manufacture of
electric incandescent lamps, and applies to lamps in which the filaments or carbon
conductors have a mechanical support other than that afforded by their electrodes
or leading in wires, as, for instance, in the case of long, thin, or heavy filaments,
or carbon conductors, in lamps which are required to burn at various angles from
the vertical; or for supporting the filaments in lamps which are intended to
consume a small number of "Watts" per candle power, or so-called "Economic "
lamps. These supports may also be used for the mechanical strength they
afford to carbons or filaments during transport, as such supports prevent undue
breakage.
It is well known that filaments or carbon conductors of various dimensions will,
when out of the vertical and incandesced, gradually bend downwards, and may
touch the sides of the glass envelope, in which case a premature rupture of the
carbon ensues, or the glass envelope is cracked.
In mill lighting (through the frictional electricity developed by running belts),
trouble is caused by the carbons or filaments being attracted to the sides of the
bulb, and sticking thereto, thus causing undue breakage. In this case, thick
filaments of low voltage have hitherto been considered preferable, but this is not
always convenient or cheap, whereas, by the use of supports, filaments, however
thin, and of any voltage, may be used.
To maintain the filaments or carbons in their original position, small books or
eyes are used, which are suitably secured to the glass envelope. It has hitherto
been considered necessary to use platinum for these hooks or eyes, this platinum
being either affixed direct to the side of the bulb, or being first attached to a
small piece of glass, which latter is itself affixed to the bulb. Platinum has been
used hitherto for the reason that it is a non-oxidisable metal, and also because it
has about the coefficient of expansiou as the glass used for the bulbs or globes,
the non-oxidisability being essential in the operations of attaching it to the glass
bulbs or envelopes, in order to produce a vacuum tight junction.
If cheaper metals or alloys are operated in the same manner, they will become
coated with an external layer of oxide, and the presence of this oxide will prevent
the forming of a vacuum-tight junction with the glass globe or bulb. Such lamps
will therefore be likely to loose their vacuum, and also, owing to the different
expansibilities of the oxidised surface of the wire and the glass bulb, the latter are
very liable to crack at the point where the metals or alloys are attached.
Now I have found that by affixing my metallic hooks or supports to the bulbs
when the latter are evacuated, or free of any oxidising agent, can use cheap or
oxidisable metals or alloys for such hooks or supports. In fact, such metals as
iron, steel, nickel, copper, or suitable alloys of the cheaper and oxidisable metals,
can be used, equally as well, and as conveniently as platinum, and are much
cheaper for this purpose.

page_text: By adopting this plan of sealing the wires into the stempiece (or pip), or onto
the sides of the glass globe, whilst evacuated, I am actually heating such wires or
their glass attachments in a vacuum or non-oxidising medium, so that I
clean oxidisable metals without fear of tarnishing or oxidising their surfaces, and
obtain a clean and vacuum-tight junction.
may use
Of the cheaper metals, I prefer to use nickel, iron or copper wire, which I form
into eyes or hooks, and seal their opposite ends, either direct to the glass envelope
of the lamp, or first attach them to a short piece of glass, as before mentioned,
which latter is affixed to the glass envelope or bulb.
In the accompanying drawing, I have shewn in Figures 1 to 15 some of the
various forms the wires (from which the hooks or eyes are produced) may take,
the remaining figures illustrating the manner in which these supporting wires are
adapted to the glass bulbs, and these will be more particularly referred to in the
body of the Specification.
The platinum supports as heretofore used, have been so affixed to the carbon
filaments or conductors, that they have been unduly restrained in their expansion
and contraction, and in many cases this restraint has been sufficient to cause
rupture of the carbon at its point of contact with the platinum hook or eye.
The support has taken the form of a single turn round the carbon, in many
cases being tightly affixed thereto; or simple hooks have been used, the upper
or lower end of which has been allowed to depress or elongate the carbon filament
or conductor.
Such restraints to the contraction or expansion of the carbon lengthwise, are
detrimental to the life of a lamp, and are also liable to cause undue breakage at
the point of contact of the wire with the carbon conductor or filament.
To overcome this difficulty, I form the hooks or eyes of 'such dimensions as to
allow of the carbon conductor or filament having a certain amount of free space
for its expansion and contraction, that is to say, the hooks or eyes are made of an
elongated form, as shewn in the various figures, and I find it best, in order to keep
the same attached to the filament in the glass-blowing operations, to bend the end
of this eye or hook, round again upon itself, as shewn at B-(Figures 1 and 3,
and 5 to 15), or when using thicker wires, it can be a simple hook, as in Fig. 2.
In the process of manufacture, it is necessary that care be taken that the filament
or carbon conductor may (in the finished lamp) take up a position somewhere in
the middle of these hooks or eyes; in any case, care must be taken that the upper
end A does not hang on, or drag the filament downwards, or that the end B should
not abut on the filament or carbon conductor, and thus prevent its free expansion,
when incandesced, but it is immaterial if the sides X and Y touch the filament.
To facilitate the fixing of these hooks or eyes in the proper relative position, I
may provide a boss or shoulder on the wire, which will rest on the walls of the
glass envelope, and thus regulate primarily the central position of the carbon in
its hook, and, secondarily, the depth to which the wire shall project into the pip or
stem end C of the lamp, as indicated at Fige. 16 and 20, and also steady it in
position before sealing. This boss or shoulder may take the form of a kink N in
the wire M, as shewn at Figs. 5, 8, 9, and 12; or a piece of glass G fused to the
wire M, as shewn at Figs. 3, 4, 7, 14, and 15, as before referred to, or it may be a
combination of both the kink N and the piece of glass G, as shewn at Figs. 6, 10,
11, and 13. It is thus easy, by adjusting the lengths of wire hooks, etc., to obtain
the filament or carbon conductor in a free position inside the hook or eye. It is
also possible, but requires considerable practice, to seal-in hooks or cyes without
shoulders, Figs. 1 and 2, by strongly heating at the point C, Fig. 18, and allowing
the glass, together with the metallic hook, to be pressed inwards a slight distance
by the pressure of the external air; but this operation is more likely to produce
subsequent cracks at the sealed pip or joint.
Another method I may employ, when using hooks without shoulders, such as
those in Figs. 1 and 2, is to introduce some wool, grains, or pieces of glass, into the
upper part of the exhaust tube, as in Fig. 17. The position of this glass wool is so

page_text: arranged that the lower end of the stem of the metallic hook or eye rests thereon
in such a manner, that the filament embraced by such hook takes up a position in
the centre thereof. These hooks or eyes (in all cases of a pre-arranged length, to
suit the length of each bulb and filament), are affixed to the mounted filaments or
carbon conductors before the latter are sealed into their bulbs or other glass
envelopes. The filaments or carbon conductors, with these hooks attached, are
introduced into the glass bulbs, and then sealed in by the ordinary glass blowing
methods after the bulbs have been exhausted, or during the operation of exhausting;
or, the wire supports may be sealed into the lamps while the bulbs contain a non-
oxidising medium, which will be introduced to expel the air, such, for instance, as
an inert gas, say, nitrogen, the bulbs being then attached to the pump to be evacuated
in the usual way. The presence of a non-oxydising medium may of course be had
in any case, if desired, the oxydising of the oxidisable metals being thereby
obviated.
The lamps may be sealed onto the pumps in a vertical position, their electrodes
or leading-in wires being uppermost, as indicated in Figs. 17, 18, and 19, and the
operator, by gently shaking or tapping the lamps, can readily arrange such hooks
in their proper positions (as shewn in the various figures). This is most con-
veniently performed just before sealing-on or affixing the lamp to the vacuum
pump. The plane of the hooks, loops, etc., should be, as near as possible, at right
augles to the plane of the filament, in order to leave the latter free to move without
being pinched between the two sides of the metallic hook or eye.
By forming the hook or eye oval at its upper end, the tapping or shaking
previously mentioned, enables such hook to automatically take up a position at
right angles to the plane of the filament.
In this position, the lamps are evacuated and incandesced on the pumps in the
usual manner. When the lamps are fully exhausted, they are sealed off in the usual
manner, at C, Figs. 16, 17, 18, 19, and 20, a small blowpipe being directed against
this point, to melt the glass, which immediately closes fast on to the end of the
wire, or the glass extension, which has been adjusted so as to project into the
thinned end of the exhaust tube (as shewn at Fig. 20).
The pressure of the outer air facilitates the ease and success of this operation,
and, by a gentle upward movement (whilst C is still hot), the lamp is easily
detached from the pump.
This is, in fact, the method usually practised with lamps having no hooks or eyes.
A finished lamp is shewn at Fig. 16. Or the whole fork on which one or more
lamps have been previously affixed, can be sealed off from the pump at H, as shewn
in Figs. 17, 18, and 19, and the individual lamps can then be sealed off at C, singly,
from this detached fork, by a glass blower seated at a table; or the lamps can be
sealed off singly at a point below C, as shewn at K, Fig. 20; and the final operation
at C can be done at a glass-blower's table.
It is advisable when hooks, eyes, loops, etc., formed wholly of metals other than
platinum be used, that the lower end of the wire shall not project outside the end
of the finished glass pip, as it might thereby induce leakage and subsequent
deterioration of the vacuum.
Fig. 16 shews a section of a finished lamp, with its pip or stem piece containing a
wire support sealed-in to the same.
Fig. 19 shews a form of hook supported on projections D in or upon the exhaust
tube, prior to being sealed in at the point C, as before explained.
Fig. 21 is a section on the line 1-2 of Fig. 16, shewing the approximate relative
positions of the hook and the filament which it embraces.
It will be obvious that the hook or eye may be attached to the side of the lamp,
instead of the pip, or in any other position, but in any case after evacuation.
I would here remark, that the illustrations herein given are by way of example
only, as it is obvious that the invention may be applied in other ways, without
departing from the nature thereof.

page_text: Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I wish it to be understood
that I do not confine myself to the particular arrangements hereinbefore set forth,
but that what I claim is :
1. Sealing metallic supports for the carbons of incandescent electric lamps into
the bulbs or globes during exhaustion, or after the air has been exhausted there-
from, as and for the purpose set forth.
2. In the manufacture of incandescent electric lamps, the use of oxidisable metals,
or metallic alloys, for the supports of the carbon filaments, the said oxidisable
supports being sealed into the bulbs or globes during exhaustion, or after the air
has been exhausted therefrom, substantially as and for the purposes set forth.
3. Sealing metallic supports for the carbons of incandescent electric lamps into
the bulbs or globes in the presence of a non-oxydising medium, either before, during,
or after exhaustion, as set forth.
4. Sealing or melting the supports for the carbons of incandescent lamps direct
into the pip of the bulbs, simultaneously with the ordinary operation of sealing the
lamps off the pumps, substantially as and for the purposes herein described.
5. A metallic support for the carbon filaments or conductors of incandescent
lamps, having an elongated loop or eye, and a boss or shoulder, substantially as and
for the purposes herein described.
6. The various methods herein described for fixing the metallic supports for the
carbon conductors or filaments of incandescent electric lamps, such supports being
so formed and arranged as to relieve the filaments or carbon conductors of all
unnecessary and harmful strains, and to allow such carbons or luminous conductors
to have a free space for their expansion and contraction, substantially as herein set
forth.
Dated this 10th day of November 1893.
NEWTON & SON,
Agents for the Applicant.