Note: Descriptions are shown in the official language in which they were submitted.
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INLEAD AND METHOD OF
~ ~ ING A ~ISCHAROE LAMP
The invention reIates to an inlead for a discharge
lamp electrode and to a method of making a lamp. Both
are particularly suitable for use with miniature metal
vapor discharge lamps wherein accuracy in the length
and location of the interelectrode gap is most
important.
BACKGROUND OF THE INVENTION
Inleads containing a thin foil portion of a refrac-
tory metal such as tungsten or molybdenum have been com-
monly usea for sealing into quartz envelopes to pro-
vide current conductors to the electrodes. These metals
can withstand the very high templsratures necessary for
sealing into quartz. Provided the foil or ribbon por-
tions are~sufficiently thin, they will merely go into
tension when the bulb cools but will not rupture nor
crack the seals. Thè inlead may be composite comprising
a length of foil with a wire welded to each end, or it
may be made from a single piece of metal, for instance
by rolling a wire between pressure rolls as taught in
United States Patent 2,667,595, issued January 26, 1954
to Noel et al.
The electrode inlead assemblies used in high pres-
sure discharge lamps generally comprise an inlead ofthe foregoing kind having an electrode structure formed
on one end, as by winding a tungsten wire around the
shank portion. An arc tube comprises one such assembly
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sealed into each`end of a quartz tube. The common method
of sealing has been to stand the electrode inlead assem-
bly up on a spindle,` place one end of the quartz tube
around it, heat the quartz to softening temperature, and
then pinch or press the end o the tube shut between a
pair of opposed fast acting jaws. Reference may be made
to United States Patent 2,965,698, issued December 20, 1960
to Gottschalk for a fuller description of pinch sealing.
The foliated portion of the inlead must be very thin
in order to avoid shaling off and remain hermetically
bonded to the quartz. Thicknesses greater than .0015"
may give trouble with leaks and a thickness of .0009"
at the thickest portion of the foil is typical. The re-
sult has been that thé inlead is lacking in stiffness
and bends so readily that horizontal sealing has been
impractical. Vertical pinch-sealing has been the rule.
However, when an electrode inlead assembly is mounted
on a spindle preparatory to sealing, as shown for in-
stance at 6 in FIG. 2 of the Gottschalk patent, it can
barely stand vertical and electrode portion fre-
quently leans and sags over to on~ side or the other.
In conventional vertical pinch sealing, lack of inlead
stiffness is not too important; if the electrode should
lean over, the forceful movement of the viscous quartz
by the pressing jaws snaps the electrodes substantially
back into place at pinching. Furthermore, in prior art
high pressure metal ~apor lamps which generally were
ratedin excess of lOO watts, the arc gap or distance ~e-
tween the electrode tips would be several centimeters.
In such lamps a misplacement of the eIectrode in the end
by a millimeter or so would have no appreciable effect
on the electrical charact~ristics and performance of the
lamp.
In electric lamp manufacture, the arc voltage drop
is an important parameter which must be kept constant
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but it varies proportionally to the length of the inter-
electrode gap. Accordingly, as the size of lamp and
length of gap are reduced, the need for accuracy in gap
determination increases in importance. Also the heating
of the ends of the arc chamber is strongly influenced by
the extent to which the eIectrodes are inserted and pro-
ject into the arc chamber. Such heating determines the
extent of vaporization of the fill, particularly of the
~etal halides which tend to condense in the cooler ends.
Thus both the length and the location of the inter-elec-
trode gap are important and the need for precision in
its determination increases as the size of the lamp is
reduced.
In Canadian application Serial No. 306,479 filed
June 29, 1978 by Cap and Lake, entitled "High Pressurq
Metal Vapor Discharge Lamps of Improved Efficacy" and
which is assigned -to the same assignee as the present in-
vention, new lamp designs are disclosed utilizing shaped
enveIopes with small end seals for reducing end losses.
In these new lamps and particularly in the smaller sizes
having arc chamber volumes less than 1 cubic centimeter,
precision in hoth the length of the interelectrode gap
and its location within the bulb is essential.
SUMMARY_OF THÆ INVENTION
The general object of the invention is to provide
a ~oil type inlead ~or sealing into vitreous material,
particularly quartz, which has improved rigidity and
self-centering properties which facili-tate accurate
location of the electrodes in the arc chamber. A method
of making a lamp is sought which facilitates pro~er cen-
tering and axial alignment of the electrodes in a hori-
zontally supported envelope. The inleads must accommodate
themselves to envelope necks which are uniform in di-
ameter and large enough for either electrode inlead as-
sembly of the lamp to pass through. After the electrode
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inlead assemblies have been inserted and accurately lo~=cated, the inleads must hold them securely in place until
seals have been made.
In accordance with my invention, I provide foil type
inleads in which the thin foil portion is wider than the`
inside diameter of the neck into which it will be sealed.
The edges of the foil are reversely folded, that is bent
in opposite directions out of the medial plane, one up
and the other down, to stiffen it. The dimensions are
such that the foil edges are bent back'and the cross-
section tends toward a Z-shape as the inlead is forced
into the'tubular neck. This causes the'electrode-inlead
assembly to become centered in the neck and axially align-
ed upon entering the bulb portion of the envelope. Fur-
thermore,' the'frictional engagement of the foil in the
neck holds the electrode assembly in place while the
quart~ is heated and shrunk around the electrode and
finally collapsed around the foi:L itself to make the
hermetic seal.
DESCRIPTION OF I~RAWINGS
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; FIGS. 1 and la are plan and side views respectively of a rolled inlead and electrode assembly embodyins the
invention.
FIG. 2 is a cross section through the inlead of
FIG. 1 along lines 22.
FIG. 3 is an end view through a quartz neck show-
iny the electrode inlead assembly in place.
- FIG. 4 shows a composite inlead and electrode as-
' ~ ~ sembly embodying the invention.
FIG. 5 is an enlarged fragmentary view of a lamp
envelope in which an electrode inlead assembly is being
inserted through the bulb into the left hand neck.
FIG. 6 is a view similar to FIG. 5 in which metal
' halide pellets are being inserted into the bulb through
-' 35 the right hand neck.
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FIG. 7 is a view similar to FIGS. 5 and 6 in which
an electrode inlea~ assembly is being inserted into the`
right hand neck.
FIG. 8 shows a lamp envelope with electrode inlead
assemblies embodying the invention in place while the
necks are being shrink sealed.
FIG. 9 shows the'inished lamp being broken out
from the'neck fragments supported in the headstock 'and
tailstock of a glass lathe.
. DETAILED DESCRIPTION
Referring to FIGS. 1 and 2, an electrode inlead
assembly 1 embodying the invention comprises a one-piece
molybdenum wire portion 2, 3'originally of uniform cross
section throughout its entire length, for instance cir-
cular and .016" in diameter. The central portion 4 hasbeen foliated by longitudinal rolling to a thickness o
about .0009" at the center. A wire size is chosen in
respect of the tubular quartz neck in which it is to be
sealed which rolls into a foil portion appreciably wider
than the inside diameter of the nlsck. The edges of the
foil portion are reversely folded or bent in opposite
directions out of the medial plane, that is edge 5 is
bent up not quite to a right angle, about 75 as illus-
trated, and edge 6 is conversely bent down. The folds
are started at the points 7 in the tapering region 7a
of the inlead where the thickness of the foil is not yet
down to its ultimate least value. This provides an
overlap between the start of the folds and a foil region
of intermediate thickness in which the stiffening effect
of the folds begins. Beyond the points 7, that is in a
direction away from the central portion 4, the inlead
is thick enough to support the weight of the electrode
without bending. The folds in accordance with the in-
vention increase the stiffness of th inleads to the point
where the assembly will not bend from the weight of the
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electrode even while supported horizontally exclusively
rom the opposite end.
After the edges have been bent~ the overall trans-
verse dimension of the foil, that is the tip-to-tip di-
S agonal d shown in EIG. 2, is slightly greater than theinside'diameter of the aperture 23a through the quartz
neck ~3'in whïch it is to be sealed as shown in FIG. 3.'
By way of example,' a foil of width .070" may have a
diagonal d of .064" after the edges have been folded,
and will be suitable'for sealing in a quartz neck OL
tube from .052" to .056" in internal diameter. Tha re-
sult of this dimensioning and forming is that the folds
along the edges of the foil are bent into closer con-
formance with the curve of the inside wall of the neck
and the foil takes a Z-shape as it is forced into the'
nec]c.' This causes' the electrode inlead assembly to be-
come centered in the neck and axially aligned where it
ente.rs the end of the bulb. If the folds were not re-
versed one ~rom the other, the i.nlead could be stiffened
20 . but it would not be self-centeri.ng. In addition the
frictional engagement of the edges of the foil with the
neck wall serves to retain the assembly in place during
the interval between the time whèn the assembly was po-
: sitioned in the neck and the time when the neck is shrunk
around the` foil. This is particularly important in au-
tomated manufacture in which the lamp envelope'is in-
dexed at relatively high speed from station to station
while various manufacturing operations are being per-
- formed.
3Q Electrode inlead assembly 1 shown in FIG. 1 is in-
tended as an anode and includes a tungsten pin or wire'
portion 8 attached at 3 to the end of the molybdenum
wire portion 2 and terminated at its distal end by a
ball 10. The join 9 between molybdenum and tungsten
may be effected by a laser butt weld which maintains
~ both parts on the 'same axis and makes a symmetric
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structure as taught in patent ~,136,298 - Hansler, 1979.
The ball 10 is readil~ formed by starting with a tungsten
wire 8 longer than necessary and directing a plasma torch
on the end to melt it back while it is held upright. Such
an anode i5 suitable for use in a miniature metal halide
lamp operating on direct current, for instance a 35-watt
lamp such as disclosed in the aforementioned Cap and Lake
application. In a d.c. lamp the anode is simply an elec-
tron collector but it must have sufficient heat-dissipating
capacity to avoid rapid erosion of the tip durinq oper-
ation. The ball 10 performs this function and, by way
of example, it may have a diameter of about 25 mils~ A
~ Z-cross section foil in accordance with the invention
; will remain centered in the neck and hold the relative-
ly heavy anode ball or the spudded on cathode substan-
tially on axis even in a lamp which is being supported
horizontally during manu~acture.
The foliated or flattened portion 4 in the inlead
assembly of FIG. 1 has been produced by longitudinal roIl-
2.0 ing of the wire. Such a portion may also be produced bycross rolling and by swaging or hammering of the original
wire. One may also use a composite ~oil, by way of ex-
ample comprising, as illustrated in FIG. 4, a cut length
of molybdenum foil 11 to one end of which is welded a
molybdenum wire 12 and to the other end a t~mgsten wire
13. The end of wire 12 may be somewhat flattened or
spade-shaped at 14 to facilitate welding to the foil~
A platinum tab 15 is interposed between foil 11 and tung-
sten wire 13 to facilitate welding and also serves to
stiffen the foil to which it is welded or brazed. In
this composite assembly, the edges of the foil 11 are
folded in opposite directions out of the medial plane
in the fashion previously described, that is edge 5 is
bent up not quite at right angles and edge 6 is bent
down to a corresponding extent.
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In a longitudinally rolled foil as in FIG. 1, there
is a gradual taper over the sections 7a startiny from the
full thickness of the wire and going down to the thickness
of the central oliated portion 4~ In a cross-rolled foil
~not shown) a region of gradual taper may be provided by
suitabIe shaping of the rolls. In either case the re-
verseIy folded edges 5 and 6 should begin before the foil
thickness drops down to its minimum. This will assure an
overlap between the region wherein the bent edges pro-
vide stiffening and the region where the foil thicknessis great enough'to support the weight of the electrode
withbut any help. 'In the composite'foil embodiment of'
FIG. ~}, the bent edges 5', 6' are long enough to have
overlaps with the weld or braze regions of increased stif-
ness juxtaposed to the spade terminal 14 or to the plat-
inum tab 15 and thereby achieve sufficient stiffness over-
all. In a variant o~ thè composite foil which'is wide-
ly used, the outer lead portion is of molybdenum and
the inner end is tapered down into a foil by longitu-
dinal rolling. To the foliated end, a tungsten wireconductor such as 13`in FIG. 4 may be attached by weld-
ing or hrazing. In such case, the folded edges should
at least partly overlap the tapered region at one end
and the` region of the weld at the other end.
~5 For some applications it is not necessary that tha
entire inlead electrode assembly be stif~ and it may
suffice to have sti~fness starting at the foil region
- and going forward to the electrode at the distal end.
In such case the folded edges need not be e~tended into
an overlap with a region of greater stiffness at the
outer end. My improved leads are of general utility
and may be used to advantage in conventional pinch
~ealing as in the Gottschalk patent. When an electrode-
inlead assembly according to the invention is stood
on a spindle for pinch sealing, it stands straight and
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vertical and this assures an improved lamp in which the
electrodes are more accuratel'y loca~ed.
The utility and versatility o~ my improved leads
are most noticeable in conn~ction with automated dis-
charge lamp manufacture on equipment which supports thelamp horizontally as shown in FIGS. 5 to 9. The lamp
comprises' an arc tube or lamp body 21 made from a piece
of fused silica or quartz'tubing having a hollow bulbous
midportion 22 which defines an arc chamber ~or containing
a high pressure discharge. In this particular instance,
the arc chamber is generally spherical and has-a volume'
of less than 1 cubic centimeter, but it may be'of various
shape~ such as ellipsoidal or cylindrical and it may vary
greatly in size. ~oined to and extending in dlametrical-
ly opposite'directions from the mid-portion 22 are two
tubular neck portions 23 and 24. Each neck is general-
ly cylindrical and uniform in cross section throughout
its length and of course smaller in cross section than
thè bulbous mid-portion. During the manufacturing op-
erations considered here, the lamp body may be supportedhorizontally in a glass lathe as shown in FIGS. 8 and 9.
The lathe comprises headstock 25 and tail-stock 26 each
journaling a chuck 27 accommodating a collet 28 in which
thè neck portions 23, 24 are received and gripped. A
driveshaft 29, partly shown only, couples the headstock
and tailstock in known manner to make them rotate in
unison. The lamp body is rotated while it is being
heated or during sealing as indicated by the curbed
arrows 20.
In manufacturing the lamp, a cathode assembly 30
is transported through the right neck 24 and into the
left neck 23 by means of a transporter 31 and a push
rod 32 which holds the assembly in place as shown in
FIG. 5, until the transporter is withdrawn. The cathode
assembly comprises a folded edge inlead 4 as previously
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described, to the distal end of which is spudded a cath-
ode structure comprising a coil 33'of tungsten wire ter-
minating in a rounded tip 34. Reference may be made to
Canadian Patent application Serial No. ~ ,/7~ , filed
5 ~a~ /6~ f~ by Dvorak and Fridrich, "Ele-ctrode'
for High Pressure Metal ~apor Lamp", assigned like'this
application, for a more complete'description of the sub-
ject el'ectrode.
In automated lamp making equipment, the glass lathe
10' holding the lamp body would now be indexed into anothèr
station, as represented by FIG 6, at which`metal halide
pellet's 35 are put into the bulb. This may be accomplisb-
ed by inser-ting a tubular needle 36 through'the right
hand neck 24, stopping the needle when its tip 37 is
near the'center of the bulb~ The needle communicates
with a low pressure source of dry inert gas whose flow
expels the pellets through the dc~wnwardly opening port
38 near the end of the needle. Following release of
the halide'pellets 35, the needle 36 is withdrawn, tbe
glass lathe indexed to another st:ation, and a globule'
of mercury 39 is released into the bulb by means of an-
other needle similar to the needle 3~ previously des-
cribed.
The glass lathe is then indexed to yet another sta-
tion represented by FIG. 7 where an anode assembly 1corresponding to that illustrated in FIG. 1 is positioned
in the right neck 24 by means of a transporter 41 and a
push rad (not shown) corresponding generally to those
` used for the insertion o~ the cathode assembly 30. Mean-
while dry argon has been flushed through the bulb both
of whose nec~s have been open~ The tailstock 26 may now
be opened and withdrawn to the right and the right necX'
24 heated to seal it off at 40 as shown in FIG. 8.
The glass lathe is again indexed and thè right neck
24 may now be'gripped anew in colle~ 28 oE the tailstock
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26. While the bulb is rotating in the glass lathe, the
cathode inlead assembly 30 is hermetically sealed into
the'neck 23 by heating the quartz and reducing the in-
ternal pressure to cause the quartz to collapse around
S the foil portion 4 o the inlea'd. This may be done for
example by a laser, schematically represented at 42,
which traverses along an appropriate length of the'neck
to cause'the'quartz to collapse as illustrated in FIG~ 8.
At the same'time the bulb portion 22 is cooled by ad-
vancing a shroud 43 to partially surround it. The shroudcontains a sponge which engages the bulb and which is
kept wet by water supplied by tube 44 while aspirator
tube 45 removes excess water. Thereafter the anode'as-
sembly 1 is hermetically sealed into neck 24 in the same
fashion. F~nally the lathe is indexed into the station
illustrated in FIG. 9 where a head 46 carrying a pair of
scoring tools 47 is advanced into an operative position
adjacent the lamp body. The tools 47 are located to
score the end portions of the necks 23 and 24 beyond the
sealing regions of the inlead oils so that the end pox-
tions subsequently may be broken away to expose the in-
leads.
The use of the folded edge inleads according to my
invention allows the electrode inlead assemblies to be
transported through the necks of the lamp body and to re-'
main firmly in place after having once been positioned.
The inleads are self-centering which allows the initial
positioning to be precise. The accurate gap deter,mina-
tion which is achieved thereby is maintained throughout
the subsequent indexes of the glass lathe and lamp body
~rom station to station~ The frictional engagement is
such that no movement occurs notwithstanding the rota-
tion of the lamp body during the heating and during the
shrinking of the necks upon the foils. My invention
thus makes possible the high speed mass production of
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miniature metal vapor discharge lamps with the accuracy
in inter-eLectrode gap determination and the precision
~n electrode placement necessary for satisfactory lamp
performance.
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