Lamp leads

Dispersion strengthened copper leads are used for inner and/or outer leads in electric lamps.

BACKGROUND OF THE INVENTION 
This invention relates to electric lamps and, in particular, to an improved 
lead wire for electric lamps. 
In the prior art, copper or various copper alloys have been used as the 
material for lead wire in electric lamps. A recurring problem has been the 
weakening or annealing of the copper during glass forming operations. As a 
specific example, in making incandescent lamps, the lead wires and exhaust 
tube are inserted into a flare and the smaller end of the flare is heated 
and pressed to make what is known as the stem. 
The stem press operation softens the lead wires to the point that tie wires 
are used to assure lamp reliability, particularly against shock. The 
button forming and tie wire operations add steps to the manufacture of 
lamps, increasing cost and adding possible source of shrinkage (rejected 
lamps). 
While a variety of materials have been tried as substitutes for the copper 
or copper-alloy lead wires, none had been found suitable. Metals or alloys 
that adequately withstand stem pressing at higher temperatures have too 
high a resistance, adversely affecting the efficacy of the lamp. While 
larger diameter wire might alleviate the problem somewhat, this solution 
causes other difficulties, such as increased cost and possible sealing 
problems. 
SUMMARY OF THE INVENTION 
In view of the foregoing, it is therefore an object of the present 
invention to provide an improved lead wire for electric lamps. 
Another object of the present invention is to provide a lead wire capable 
of withstanding higher stem press temperatures. 
A further object of the present invention is to provide an improved inner 
lead for electric lamps. 
Another object of the present invention is to provide an improved outer 
lead for electric lamps. 
A further object of the present invention is to provide a lead wire capable 
of withstanding higher stem press temperatures and having acceptable 
diameter and resistance characteristics. 
The foregoing objects are achieved in the present invention wherein it has 
been found that dispersion strengthened copper wire withstands elevated 
press seal temperatures and, when used for the inner lead wires, 
eliminates the need for tie wires due to its retained stiffness.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 illustrates a completed mount in accordance with the prior art. 
Specifically, the mount comprises a flare 11 having exhaust tube 12 and 
lead wires 13 and 14 inserted therein. As known to those of skill in the 
art, lead wires 13 and 14 each comprise three segments of conductive 
material. Specifically, lead wires generally comprise an outer conductor 
connected to an inner conductor by a short length of dumet wire which is 
positioned in pressed area 15 to provide a seal between the inside and 
outside of the glass envelope of the lamp. As illustrated in FIG. 1, the 
upper portion of the stem is inserted into the glass envelope. Thus, the 
portions of lead wires 13 and 14 extending upwardly from pressed area 15 
constitute the inner lead wires while the portions of lead wires 13 and 14 
extending downwardly from pressed area 15 constitute the outer lead wires. 
The ends of the inner lead wires are connected one each to each end of 
refractory filament 16, generally comprising tungsten. Encircling the 
central portion of filament 16 is support wire 17. Encircling each of lead 
wires 13 and 14 are tie wires 18 and 19, the other ends of which are 
embedded in glass button 20 formed in the end of the exhaust stem. 
In accordance with the prior art for low wattage gas-filled incandescent 
lamps, lead wires 13 and 14 generally comprise nickel-plated copper or 
copper alloy. In accordance with the present invention, illustrated in 
FIG. 2, the inner or outer leads may comprise what is known as a 
dispersion strengthened copper wire. Dispersion strengthening of metals is 
known in the art and, in particular, dispersion strengthened copper wire 
is known in the art and available from the Glidden Metals Division of SCM 
Corporation as "GlidCop" AL-20; the same material is available from GTE 
Sylvania, Inc., as DSC 200. This wire may be used for either the inner or 
outer leads and, for example, may comprise 10-mil diameter wire for the 
inner leads and 18-mil diameter wire for outer leads. As known by those of 
skill in the art, the outer surface of at least the inner lead wires 
comprises a nickel plate to eliminate contamination within the lamp due to 
the release of contaminants from the surface of the copper when the lamp 
is lighted. 
It has been found that dispersion strengthened copper wire as described 
above does not soften or anneal in the fires used to soften the flare and 
exhaust tube prior to pressing. As a result, the lead wires in a finished 
mount are stiffer in accordance with the present invention, and the need 
for tie wires 18 and 19 are possibly the center support wire 17 is 
obviated. 
A completed mount in accordance with the present invention, as illustrated 
in FIG. 2, therefore merely comprises a flare 11, exhaust tube 12, lead 
wires 13 and 14, and a suitable filament 16. The construction of the mount 
is thus simplified without compromising lamp performance. The lead wires 
previously described have a resistance and diameter comparable to that of 
lead wires of the prior art. In addition, lamps in accordance with the 
present invention can be manufactured at higher seal temperatures. 
As an inner lead for a standard incandescent lamp, ie. incandescent lamps 
used in what is known in the art as general service household lighting or 
general service illumination, lead wire in accordance with the present 
invention thus provides an improved lamp in which tie or support wires are 
unnecessary to help the lead wires tolerate shock or vibration.