Note: Descriptions are shown in the official language in which they were submitted.
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The invention is in the field of lamps and other
devices having current lead-in conductors sealed in and
through a bulb or envelope by means of current-conductive
foil members.
U. S. Patent No, 3,685,880 dated August 22, 1972
to John C. Sobieski, for example, discloses a lamp containing
a pair of electrodes each connected to a separate lead-in
conductor by a thin metal foil member, the foil members
being hermetically sealed in the lamp envelope at seal
regions, the end regions of the electrodes and lead-in
conductors being embedded in the seal regions. The
electrodes and lead-in conductors are attached to the
respective foil members by positioning their end regions to
overlap regions of the foil member, and spot welding
these regions together. Typically, the lead-in conductors
and the foil members are made of molybdenum, and, in an arc
lamp, the electrodes are tungsten rods. To improve the
spot-welded connections, both electrically and mechanically,
small platinum-coated foil pads have been placed at the
spot-weld locations, between the molybdenum seal foil
member and the tungsten electrodes and/or the molybdenum
lead-in conductors, prior to spot welding. The improvement
thus achieved is relatively greater for the welds of the
foil member to the tungsten electrode rods. However, it
has been found that this improvement in weld bonding is
accompanied by an increased tendency for cracking of the
envelope material at the seal region.
Object of this invention are to provide an improved
foil-type seal for lamps and the like, and to provide such
a seal which has good electrical and mechanical properties,
and good reliability of remaining intact without cracking.
The invention comprises, briefly and in a preferred
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embodiment, a lead-in seal having a thin conductive foil
member sealed into an envelope, such as into a stem integral
with a lamp bulb or housing, a thin conductive tab member
attached to the foil member and extending therefrom, and
an electrode attached to the extending portion of the
tab member and extending into the interior of the lamp bulb,
the attached end of the electrode being spaced from the
adjacent edge of the foil. Preferably, the width of the
tab member is about the same as the diameter of the electrode
to which it is attached, and may be thicker than the foil,
if required for conducting the lamp operating current without
overheating. The tab preferably is shaped in the form of
a double bend such that its end regions lie in parallel
planes. In the preferred embodiment, the electrode is
a tungsten rod, the tab member is a platinum-coated
molybdenum foil, and the seal member is molybdenum foil,
and a molybdenum lead-in conductor is attached to the
seal foil at the end thereof opposite from the tab,
the electrode and lead-in conductor being substantially
axially aligned.
FIG. 1 is a top view of a compact high intensity
arc lamp provided with a foil lead-in seal in accordance
with a preferred embodiment of the invention.
FIG. 2 is an enlarged side view of a lead-in
seal region of the lamp of FIG. 1.
FIGS. 3 and 4 are side and top views, respectively,
of a prior art type of foil seal arrangement.
The compact high intensity arc lamp 11 in FIG. 1
comprises an envelope of quartz or other suitable vitreous
material having a bulb portion 12 and stem portions 13 and
14 extending therefrom on opposite sides thereof, on a
common axis. Elongated tungsten rod anode and cathode
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electrodes 16 and 17 are positioned on the axis of the
lamp with the inner ends thereof spaced apart within the
bulb portion 12, and respectively extend into the anode
stem 13 and cathode stem 14. The tungsten anode rod 16
is part of the anode lead-in assembly, which further comprises
a molybdenum lead-in wire 18 having an end 19 spaced from
the outer end of the anode 16, the lead-in 18 and anode
rod 16 being substantially axiàlly aligned. The inner
end region 19 of the lead-in wire 18 overlaps and is spot-
welded to an end portion of a molybdenum thin foil member
21. The end region 19 of the lead-in wire may be swaged
or otherwise flattened to facilitate a good weld. A
thin foil tab member 22 has an end region 23 positioned
to overlap a portion of the other end of the foil 21, and
is spot-welded thereto. The remaining end region 24 of the
tab 22 is positioned to overlap an end region of the anode
rod 16, and is spot-welded thereto. Preferably, the tab
22 is provided with a double bend, as shown in FIG. 2, so
that the end regions 23 and 24 thereof lie in spaced apart
parallel planes, so that the anode 16 and lead-in wire
18 will be substantially in axial alignment. The inter-
mediate portion 26 of the tab 22 between its end regions
23 and 24 may be inclined at an angle of approximately
45~ as shown in FIG. 2.
The outer end of the cathode rod is shown
.: ~
spot-welded directly to a molybdenum seal foil 31, and
~ol~bden 4~7
a cathode lead-in wire 32, preferably of 3norybdenu, is
spot welded to the remaining end region of the foil 31, the
welded end region 33 of the lead-in wire 32 having been
flattened or swaged to facilitate the welding.
After the anode and cathode lead-in electrode
assemblies have been prepared, they are properly positioned
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with their inner ends within the bulb portion 12, and the
bulb is evacuated and filled with suitable gas, and a
metal halide such as indium triiodide, if desired, and the
end regions of the stems 13 and 14 are heated and flattened
by pairs of jaws, for example as disclosed in the above-
referenced Sobieski patent, to form anode and cathode seal
regions 36 and 37, respectively, in which seal regions the
quartz material of the bulb wets the foils 21 and 31, thus
providing hermetic sealing.
The foil tab 22 of the invention is preferably
molybdenum coated with platinum, similar to the spot-
welding pads that have been used previously. The tab 22
preferably has a width approximately equal to the
diameter of the tungsten rod 16 to which it is welded,
and the tab 22 may be thicker than the seal foil 21, in order
to adequately carry the operating current of the lamp without
overheating. In a practical embodiment, the platinum-
plated molybdenum tab 22 is 3/1000 of an inch thick, and
the molybdenum sealing foil 21 is 9/10,000 of an inch thick.
The invention, comprising the elongated
connector tab 22 between the sealing foil 21 and the electrode
16, achieves its objective of considerably reducing the
number of seals 36 which crack during operation of the
lamp, the anode seal 36 having been particularly prone
to cracking. This achievement is believed due not only to
the elongated feature of the tab 22, but also due to its
double bend which provides the oblique intermediate section
26. Both of these features appear to reduce stress in the
seal 36 af~er the lamp is completed. The reason for this
improvement is believed due to a tendency for a stress to
develop and remain in the seal region 36 when the former
technique was employed of positioning a foil platinum-coated
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pad between the sealing foil 21 and electrode 16. Tabs
similar to the tab 22 can be interposed between the foil 21
and lead-in wire 18, and between the foil 31 and electrode
17 and lead-in wire 32, respectively.
FIGS. 3 and 4 illustrate this prior construction,
in which a platinum-coated molybdenum foil pad 41 was inter-
posed between the wld regions of the anode 16 and the
sealing foil 21 prior to the step of spot welding these
members together. It is believed that during the spot welding,
the the foil pad 41 curled slightly upwardly at its edges,
toward the round rod 16, causing narrow spaces between
these curled edges and the sealing foil 21, and also
narrow spaces between these curled edges and the electrode
rod 16, and during the sealing operation the quartz material
of the envelope was unable to adequately penetrate into
and fill these narrow spaces, which resulted in setting up
a stress in the seal. It should be noted that, due
to its extreme hardness, it is relatively difficult to swage
or flatten the spot-welded end of the tungsten rod 16, as
can more readily be done at the spot-welded end 19 of
the molybdenum lead-in wire 18, to provide a broader
area of spot welding.
Another achievement of the invention is the
prevention of corrosion of the molybdenum seal foil 21 by
metal halide or other corrosive vapor contained in the
bulb 12 and which can seep along the electrode 16 within
the stem 13, to the outer welded end of the electrode.
The platinum coating on the tab 22 resists corrosion, and
the corrosion-prone molybdenum foil 21 is completely sealed
and encased by the quart~ housing mat:erial so the corrosive
vapors cannot reach it. The use of a single platinum-
coated foil interconnecting the members 16 and 18 is
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undesirable because platinum is not wetted by quartz as
well as is bare molybdenum foil.
While preferred embodiments of the invention
have been shown and described, various other embodiments
and modifications thereof will become apparent to persons
skilled in the art and will fall within the scope of the
invention as defined in the following claims.
