Incandescent lamp leads of dispersion strengthened copper wires

Substantially completely deoxidized dispersion strengthened copper leads in incandescent electric lamps.

This invention relates to incandescent electric lamps, and particularly to 
improved lead wire for use in electric lamps. 
BACKGROUND OF THE INVENTION AND PRIOR ART 
The use of copper or various copper alloys as lead in wires in incandescent 
lamps has been in commercial practice for many years. More recently, 
dispersion strengthened copper has been used for such lead wires. (See 
McMillan U.S. Pat. No. 4,138,623). This dispersion strengthened copper 
wire was normally a "Glidcop" AL-20 wire or equivalent containing 0.20% 
aluminum oxide calculated as the metal equivalent and which had a thin 
copper (unstrengthened) sheath surrounding an inner core of the internally 
oxidized dispersion strengthened copper. This material, particularly when 
nickel plated to reduce release of contaminants from the underlying copper 
sheath, enabled lamp manufacturers to eliminate tie wires formerly used to 
support the plain copper or copper alloy leads and thus reduce cost. 
Graves et al in U.S. Pat. No. 4,208,603 found that to improve the 
resistance to embrittlement of the tungsten filament due to nickel plated 
on copper sheathed dispersion strengthened copper, removal of the copper 
sheath, or production of the wire without the copper sheath, enabled 
plating of nickel directly onto the bare dispersion strengthened copper 
wire and gave a superior bonding of the nickel deposit onto the copper 
alloy surface. This structure was found to be less prone to nickel 
migration during lamp operation. Nickel migration was believed responsible 
for early filament failure due to embrittlement. As shown in U.S. Pat. No. 
4,208,603, removal or omission of the copper sheath followed by nickel 
plating resulted in an improvement in filament life. 
A problem still remained, however, with attack on the tungsten filament as 
a result of residual hydrogen on the tungsten and residual free oxygen in 
the lead wire or within the environment of the bulb albeit in very low 
concentrations. These elements combine to form water. Water vapor present 
in the system reacts with tungsten under incandescent temperature 
conditions to form tungsten oxide and hydrogen ions. The oxide vaporizes 
and condenses on the inner surface of the envelope. Ambient hydrogen ions 
under the condition of the lower temperature of the envelope reduces the 
tungsten to the metal and regenerates water vapor thereby completing what 
is known in the art as the "water cycle". To control plating out of 
tungsten onto the glass envelope, it has become the practice to include a 
"getter" at the outer end of the lead wire in the lamp reactive with the 
oxygen to reduce the deleterious effect thereof, and interrupt the "water 
cycle". Zirconium metal is a "getter" material which can be used for this 
purpose. Obviously, however, the inclusion of a "getter" in a lamp 
increases cost not only in respect of the cost of the material, but also 
in the added operation of applying it to the lead wire. 
In the following discussion dispersion strengthened copper may be referred 
to as "DSC". Reference to an aluminum metal content of a given percentage 
will be understood as an equivalent amount of aluminum metal albeit 
present as the refractory oxide, aluminum oxide. 
Thus, the art has progressed to the point where it was using dispersion 
strengthened copper (DSC) wire leads, without tie wires. Because 
undeoxidized DSC containing refractory metal oxide to any extent contains 
residual free oxygen and is thus a source contributing to the "water 
cycle", control of contaminents from the wire was achieved by nickel 
plating with improved bond, or by use of any auxiliary getter, or a 
combination of both. 
Also, as known to those skilled in the art (See U.S. Pat. No. 4,138,623; 
Col. 2., Lines 2-14) lead wires are composed of three electrically 
conductive segments; an outer conductor and an inner conductor connected 
together through a short intervening segment of dumet wire. This segment 
is adapted and dimensioned to traverse the steam press portion of the 
glass stem to provide a seal between the inside and outside of the glass 
envelope. Dumet, which is a 40-43% nickel balance iron alloy, because of 
its favorable thermal expansion characteristics reduces the stresses due 
to differences in thermal radial expansion of the wire and the glass in 
the formation of the stem press and in actual use. The heat of softening 
the glass to make the stem press seal (about 1200.degree. F.) is 
sufficient to soften copper metal or copper alloys in a normal lead wire. 
A DSC wire is better able to withstand such temperature. It has now been 
found that use of nickel plating and/or use of an auxiliary use of nickel 
plating and/or use of an auxiliary "getter" and the attendant costs of 
each can be avoided while still maintaining the desired objective of 
eliminating the need for tie wires. This is achieved by use of a 
deoxidized internally oxidized dispersion strengthened copper wire, and 
particularly a deoxidized internally oxidized dispersion strengthened 
copper wire having a lower aluminum oxide (or equivalent refractory oxide) 
content than heretofore used. A principal source of free oxygen in the 
lamp environment is thereby substantially removed and the "water cycle", 
thus effectively controlled. Use of the lower oxide deoxidized DSC also 
presents advantages of greater ductility which facilitates fabrication and 
provides better electrical conductivity. A "getter" for any extraneous 
free oxygen can be incorporated in the body of the wire rather than 
topically applied after fabrication. 
Still further, when the refractory oxide content in the DSC is as low as 
0.15% aluminum equivalent, it has been found that use of a dumet segment 
can be avoided, if desired. 
BRIEF STATEMENT OF THE INVENTION 
Briefly stated, therefore, the present invention is in an electric 
incandescent lamp having a translucent envelope for enclosing a resistive 
incandescent filament. The filament is electrically connected to and 
supported by a pair of lead wires. The lead wires comprise at least in 
part, substantially completely deoxidized internally oxidized dispersion 
strengthened copper wire. Such wire may contain aluminum oxide to the 
extent of 0.07% to 0.35% aluminum metal as the oxide. In preferred 
embodiments of the invention, I use deoxidized internally oxidized 
dispersion strengthened copper containing dispersed therein metal oxide 
refractory to the extent of no more than about 0.15% calculated as the 
metal equivalent. The wire may be unclad, or it may be clad with copper, 
nickel or other cladding metal or metal alloy, if desired. Desirably, the 
deoxidized internally oxidized dispersion strengthened copper also 
containing as a result of boron deoxidation, unreacted boron in an amount 
of from 0.001% to about 0.06%. It is preferred that the wire be formed by 
powder metallurgy techniques optionally with a thin copper sheath.

DETAILED DESCRIPTION OF THE PRESENT INVENTION 
Referring now more particularly to FIG. 1 there is shown in cross section 
an incandescent lamp 10 having a translucent envelope, for example, a 
frosted glass envelope 12, which is secured to a base member 14 to provide 
a housing assembly for a filament mount construction 16 upon which is 
supported the resistive incandescent filament 18 that serves as the 
illumination source in said lamp. An inert gas or a vacuum is further 
provided within the hermetically sealed envelope to protect against 
filament oxidation during lamp operation. The filament material is 
generally tungsten or some other suitable refractory metal including 
alloys thereof. The word "translucent" is used herein signifies the 
ability to transmit visible light, and contemplates coloration of the 
envelope material itself as well as coating the lamp envelope with 
materials which diffuse or reflect light. 
The filament mount construction 16 also preferably of glass and as better 
shown in FIG. 2, comprises a filament coil 18 disposed transverse to the 
axis of the lamp 10, and supported by a pair of lead wires 20 and 22 that 
are electrically connected at each end 24 and 26, respectively, to the 
filament coil 18. A central glass member 28 in the filament mount 
construction 16 is provided having a flared portion 30 which is sealed 
directly to a restricted neck portion 32 of the lamp glass envelope 12 at 
the base of the bulb portion 34 (FIG. 1). The translucent body 28 is in 
the form of a hollow tube 36 which includes an inner glass exhaust tube 38 
and with the glass body member 28 further including a stem press 40 at the 
opposite end of said member 28 from the flared portion 30 to provide a 
hermetic seal for the filament 18 and lead wires 20 and 22 in the lamp. It 
is through the stem press 40 that a dumet segment is commonly used for 
providing a better seal and more nearly matched coefficients of expansion 
between the glass and the metal. Protruding from the same end of the glass 
body member 28 as the lead wires 20 and 22 is an extension 42 which 
terminates in a button 44 used for securing tie wires (not shown) in the 
construction. The extension 42 has now become superfluous as filament 
support means and could be eliminated for simplification of the mount 
construction now being used. However, machinery is already in place which 
provides the extension 42. 
The improved glass mount construction shown in FIG. 2 utilizes lead wires 
20 and 22 made in accordance with the present invention. These lead wires 
need not be segmented to insert a dumet segment. In a specific embodiment, 
the lead wires 20 and 22 are constructed entirely from deoxidized 
internally oxidized dispersion strengthened copper alloy wire. In 
preferred embodiments, the deoxidized internally oxidized dispersion 
strengthened copper is characterized in that it contains a metal oxide 
refractory to the extent of no more than about 0.15% by weight aluminum 
and has been substantially completely deoxidized to reduce the free oxygen 
content to below about 0.002%. Any suitable deoxidizing means may be 
employed. I prefer, however, to utilize boron. One method of deoxidizing 
copper which is suitable for use in accordance with the present invention 
is described in U.S. Pat. No. 3,352,667 to Das et al. Alternatively to the 
Das et al process, boron in powder form can be blended with internally 
oxidized dispersion strengthened copper powder in an amount of about 0.02% 
to about 0.1% prior to compacting during extrusion and drawing of the wire 
to effect an internal sequestering of free oxygen. A slight excess of the 
boron over that required to completely deoxidize the wire is preferred to 
act as an integral "getter" for other extraneously introduced oxygen that 
may be present within the glass envelope. In general, an excess sufficient 
to yield from 0.001% to about 0.01% free boron in the final product is 
sufficient. 
FIGS. 3 and 4 show other forms of lead wires fabricated of deoxidized 
dispersion strengthened copper. In FIG. 3 there is shown a lead wire 20 
having three segments connected in tandem. In a preferred embodiment of 
FIG. 3, inner lead portion 44 and outer lead portion 46 are each formed of 
deoxidized 0.15% aluminum internally oxidized dispersion strengthened 
copper. Portions 44 and 46 are joined by a dumet segment 48 welded to 
confronting ends 45 and 47. The outer lead portions, e.g., portion 46 are 
adapted in the base 14 to be connected to opposite sides, respectively, of 
a source of electric current, not shown. 
FIG. 4 shows another lead wire 20 having 3 portions connected in tandem. 
Inner lead portion 50 and outer lead portion 54 are each formed of 
deoxidized 0.07% to 0.35% aluminum internally oxidized dispersion 
strengthened copper. Portions 50 and 54 are joined by a flattened segment 
52 also of the same dispersion strengthened copper. Where the lead is 
entirely of DSC, it is desirable to provide a thicker sheath of copper to 
better accommodate stress in the stem press portion. With thicker sheaths 
one would use a correspondingly higher aluminum content in the DSC to 
retain wire strength. copper. Segments 48 and 52 are desirably 
longitudinally dimensioned to match the depth of the stem press portion 40 
of the glass stem 16. (FIG. 2). The stem press traversing portion 52 may 
have a thickness of 0.1 to 0.2 millimeters compared to the normal wire 
diameter of 0.35 millimeters (0.014" or 30 gauge). The wires of FIGS. 3 
and 4 have no nickel cladding or plating, i.e., are nickel free. 
The internally oxidized dispersion strengthened copper may be produced in 
the form of a powder by the process described in the Nadkarni Pat. No. 
3,779,714. Although other methods of dispersion strengthened of copper 
than those described in the aforesaid U.S. Pat. No. 3,779,714 may be used 
to produce dispersion strengthened copper we prefer the process described 
and claimed in said patent. As indicated above, the amount of aluminum as 
aluminum oxide in the final product is desirably carefully controlled to 
be 0.15% or less down to about 0.07%. When the internally oxidized 
dispersion strengthened copper is deoxidized to remove free oxygen by a 
process such as described by Das (supra), it is substantially free of 
uncombined oxygen. 
The ordinary method for producing wire from such dispersion strengthened 
copper powder is to place the powder in a "can" which is then suitably 
sealed and reduced in size by any suitable means such as extruding and 
drawing, until the final diameter is approximately 0.014 inch. Wire 
extruded to this diameter from a 3/4 inch diameter can yields a 
substantially fully densified dispersion strengthened copper material 
contained within a very thin wall sheath. The sheath may be of copper, or 
of nickel. Alternatively, the copper sheath which is usually produced in 
making dispersion strengthened copper wire may be removed as described in 
the aforesaid U.S. Pat. No. 4,208,603, and a coating of nickel 
electroplated directly on to the dispersion strengthened copper wire. 
Thus, the deoxidized dispersion strengthened copper wire may be provided 
with or without a metal sheath. Reference may be had to U.S. Pat. No. 
3,179,515 to Grant for one method of forming dispersion strengthened 
copper wire. 
In use, the deoxidized internally oxidized dispersion strengthened copper 
wire of the present invention is utilized in exactly the same manner as 
taught in the aforesaid U.S. Pat. No. 4,208,603. No dumet segment is 
required although it may if desired by provided and the lead wires need 
not be supported by tie wires. Alternatively, because the 0.15% aluminum 
copper wire retains ductility, it may be flattened in the region of the 
stem press 40 to improve the sealing and thermal characteristics. It has 
been found that with such deoxidized internally oxidized dispersion 
strengthened copper wire, including a slight excess of boron over that 
required to react with free oxygen, the application of a "getter" such as 
zirconium metal at or near the point of attachment of the tungsten 
filament 18 to the free ends 24 and 26 of the lead wires 20 and 22, 
respectively, can be avoided. Filament life for the improved structure is 
substantially the same as that achieved with the system which contains a 
"getter". The cost of the "getter" and the operation for applying the 
"getter" to the insert assembly such as shown in FIG. 2 is thereby 
obviated. The use of a nickel coating can also be avoided, if desired. 
Still further, the use of a dumet segment can also be avoided particularly 
with the low oxide DSC. The low oxide DSC because of its ductility permits 
flattening of the stem seal traversing portion whereby a continuous wire 
lead may be produced from a single piece of DSC wire.