Note: Descriptions are shown in the official language in which they were submitted.
~342~
P~IN g633 l 16, 7~1980
"Electric lamp"
The invention relates to an electric :Lamp
having a quartz glass lamp envelope provided with current
supply conductors which ex-tend to an electric elernent
accommodated inside the lamp envelope, are guided in a
vacuum-tight manner through the wall of the lamp envelope
and have a circumferential coating of intermediate glass
over part of their length, between the ends of which
coating the wall of the lamp envelope is fusecl wi-th said
coating. Such a lamp is disclosed in British Patent Speci-
~ication No. 71OJ434~
Lamps which have a high operating temperatureare often manufactured with a lamp envelope of quart~ glass,
which term is used herein to indicate glasses having a
SiO2 content of at least 95~ by weight, and 1~i-th current
supply conductors of tungsten or molybdenum. These glasses
haYe a coefficient of thermal expansion (approx,
7 x 10 7 K ) which differs considerabl-y from that of
tungsten (45 x 10 7 K 1) and molybdenum (5~ x 10 7 K ).
Due to these large differences in coefficients of thermal
expansion, it is common practice to construct the current
supply conductors, at the location where they are incor-
porated in the wall of the lamp envelope in a vacuum-
tight manner, as a thin foil to which an internal and an
external current supply conductor are welded. ~Iowever,
during the manufacture of -the welded joint and also upon
sealing -the conductors in the wall of the lamp envelope,
rejects occur as a result of fracture of the foil. Other
disadvantages of this construction are that the welded
joints shoulcl always be checked for reliability~ that the
~ assembly of the current supply conductor is slack as a re-
sult of the presence of the ~oil so that it is cumbersome
to assemble the internal current conductor in the lamp
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PHN 9~33 2 16. 7.1980
envelope so as to be well positioned, and that the foil
restricts the permissible strength of the lamp current.
Notwithstanding these disadvantages of the construction
described, substantially all types o~ lamps with quartz
glass lamp envelope which are commercially available have
this construction. Only in lamps having a high current
strength, for e~ample short-arc discharge l&mps, is a
sealed wire necessarily used in practice as a current
supply conductor. From this it appears that there are
economic and technological restrictions to use sealed wires
as current supply conductors in other lamps also.
According to the said British Patent Specifi-
cation 710,1~34, a vacuum-tight sealing of the current
supply conductor in the wall of the quartz glass lamp
envelope is obtained by providing the current supply con-
ductor at the area o~ the sealing in the wall of` the lamp
envelope with a fused coating of an intermediate glass or
a number o~ intermedia-te glasses and to fuse the lamp
envelope therewith between the ends of said coating~
~lowever~ it is particularly difficult and time-
consuming to realize a good f`usion of` the wall of` the
lamp~envelope with the coating of the curren-t supply wire.
In practice, the quartz glass o~ the lamp envelope to be
formed is allowed to collapse on to the coating of` the
current supply wire. Although this can be accelerated by
pressing the quartz glass circumferentially against the
glass coating by means of a tool, that process is also
difficult to mechan:ize.
On the other ha~d it has been found that if` a
30 pinch seal is manufactured around the glass coa-ting, as is
usual in lamps in which a thin metal foil is used to rea-
lize a vacuum-tight seal of the lamp envelope, no reliable
seal ls obtained and fracture often occurs.
It is the object of -the invention to pro~ide
35 electric lamps having a quartz glass lamp envelope pI'O-
vided with current supply wires, which lamps have a robust
construction which is sim~le to realize and whlch does not
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3~2~i
PHN 9633 3 16. 7.1980
involve restictions of practical importance as regards
; the diameter of the current supply wires.
In lamps of the kind mentioned in the opening
paragraph this object is achieved in tha-t the lamp
envelope has at least one flattened pinch seal in which a-t
least one current supply wire is accommodated, which pinch~
seal on each of its two major side surfaces has, for each
current supply wire accommodated in the pinch seal, a
respective raised ridge extending above -the respective
wire over its entire pinched length.
It has been found experimentally that this
lamp has a reliable cons-truction and is easy to manufacture
in a mechanized process, even when current supply wires
¦ of o.6 to 0.8 mm diameter or more are used. In contras-t
therewith, lamps in which the larger side surfaces of the
pinch seal were not provided with such a raised ridge
showed cracks, in many cases even upon cooling right after
making the pinch seal.
The invention is based on the following
Z0 recognition. Intermediate glasses are generally understood
by those skilled in the art to mean glasses having a
coefficient of thermal expansion between the coefficients
of expansion of the materials to be joined, in this case
the metal of the current supply wire and the quartz glass of
the lamp envelope. Since due to their high SiO2-content
quartz glasses have a very low coefficient of expansion
and also a very high sof-tening point~ the intermediate
glasses must have a lower SiO2-content to reach a higher
coefficient of expansion and at the same -time they have a
lower softening temperature.
During the making of a flat pinch seal, the
intermediate glass has a temperature which differs only
little from the temperature o`f the quartz glass. As a re-
sult of this the intermediate glass has a comparatively
low viscosity, The pressure exerted by the pinching blocks
and transferred to the in-termediate glass by the quartz
glass causes the intermediate glass to flow easily, so that
,
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PHN 9633 4 16, 7~1980
the coating of the current supply w:ire is damaged, or
even disappears partly, upon making a normal pinch seal
in which the larger side surfaces are not provided with a
raised ridge as have lamps according to -the invention. The
current supply wire in the finished pinch seal is no
longer embedded in intermediate glass, which causes
stresses in the quartz glass which result in cracks.
By providing the facing surfaces of the
pinching blocks with respective grooves, the locations of
which are matched -to the location~s) of the current supply
wire(s) in the still open end of -the lamp envelope -to be
formed, the wall of the envelope in the region where it is
being pinched together is effectively shaped during the
pinching operation -to surround the supply wire(s), As a
result, the force applied to the intermediate glass
during pinching is very considerably reduced due to the
grooves.
As always when deforming glass, it is of im-
portance in this case also that the glasses are able to
~use together in such a manner that glass surfaces at the
area where they meet do not enclose acute angles. Depon-
~; dent on the way in which the sealing process is~carried out
i~ may therefore be recommendable to after-heat the pinch
seal.
It has been found that the glasses easily fuse
together if the quart~ g:Lass of the lamp envelope to be
formed is provided wi-th a coating of an intermediate glass
at the area where the pinch seal is to be reali~ed. Upon
making the pinch seal, said coating needs to fuse only
with the coating o~ the current supply wire, which easily
occurs as a result of the lower softening temperature of
intermediate glass.
The lamps embodying -the invention can be
manufactured easily, even in an automated manner~ They
have a very reliable construction and enable high curren-t
strengths with lo~ resistance losses. ~urther, the con-
struction enables several current supply wires -to be
.
26
PHN ~633 5 16. 7.1980
sealed in one pinch seal. Of course this is impossible in
the construction of the lamp disclosed in the above-
mentioned British Patent Specification, since in that
construction the sealing of the current supply wire is
rotationally s~nme-trical.
The lamp according to the invention may be
a discharge lamp, for example, a high-pressure ~nercury
vapour discharge lamp, in which case the said element
accommodated inside the lamp envelope is a pair of main
electrodes. A current supply wire to an auxiliary electrode
may be incorporated in a pinch seal in addi-tion to the
current supply wire to a main electrode. Alternatively, -the
lamp in accordance with the invention may have a filament
as the electric element, in which case the lamp may be
constructed as a -two-pinch or as a mono-pinch lamp, de-
pendent on its destined use.
It has beeen found that very good results are
obtained with intermediate glasses which over a temperature
range of 30-800oC have a coefficient of -thermal expansion
(~) in -the range of approx. 11 to 17 x 10 7 K 1.
Examples o:f such glasses are recorded in the
~ollowing table (composition in per cent by weight):
;
21 B203 A1203l CaO ¦~x 107 (K 1)
I a 86.9¦ g.ol 4~
~b 86.41 9.6j 4.0 1 ~ 13
c 81.9l 13.1 4.5 ~ o.5 ¦ 15
d 81.0¦ 10.9 ! 7.1 j 1.0 ~ 17
. . . ~ . . _ _ .
The in-termediate glasses can be sealed -to the
current supply wires of tungsten or molybdenum in a con-
ven-tional manner so as to ~orm a coating thereon. For
example, i:f glass in the form of a rod is used, the glass
may be applied to the wire in a flameO If -the glass is
available in tube form, -then it may be slid on the wire and
sealed to the wire, for example by inductive heating
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~3~26
P~ 9633 6 17.7.80
causing the tube to collapse on to the wire.
In lamps in which a vacuum-tight seal is
realized around a foil incorporated in a pinch seal, the
pinch seal is vacuum-tight only over a part of th0 length
of the foil which lies be-tween the ends of the internal
and external current conductors welded to the foil. In
order to lock this internal and external current con-
ductors mechanically in the pinch seal, the length of the
said pinch seal much be significantly larger than the
length of the vacuum-tight part. In lamps in accordance
with the invention, however, the pinch seal is vacuum-
tight over the whole pinched length of the current supply
wire. This enables lamps according to the invention to be
provided with considerably shorter pinch seals, which not
only involves a saving of quartz glass but also results
in a smaller lamp. As a result of this luminaires of
smaller dimensions and lower weight are made possible.
United States Patent Specification 3,742,2~3
discloses an electric lamp having a quartz g-ass lamp en-
velope provided with a pinch seal, in which the current
supply wires are enveloped by cermet over the part which
is situated in the pinch seal. On its major surfaces the
known lamp has a raised ridge extending above the current
supply1wires.
Although this lamp shows some resemblance with
the lamp according to the invention, there are diPferen-
ces which are of essential importance. The above United
States Patent Speci~ication states that only one cermet
will suffice when the current supply wires have a diame-
3n ter of approximately 300/um. When the thickness of the
current supply wires is 750/um or more, two or more con-
centric envelopes of different coefficients of thermal
expansion have to be used.
However, lamps having current supply wires of
300/um thickness are exceptional, so that the vast majo-
ri-ty of the lamps according to the United States Patent
Specif`ica~ion, must have two or more concentric envelopes
~ of cermet on the current supply wires. In addition, cer-
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P~ 9633 7 17.7 ~o
mets are difficult to process.
In the lamps according to the invention on the
contrary, one enveloping layer of glass, which can easily
: be provided, will always suffice.
The cermets which are used according to the
said ~nited States Patent Specification are more viscous
than quartz glass, also at high temperatures, because
they comprise a hi~h melting-point metal, for example
tungsten. The intermediate glass used in lamps according
to the in~ention is less viscous -than. quartz glass, since
it has a lower SiO2 content.
; In lamps according to the United States Patent
~: Specification a raised ridge is provided on the major
surfaces of the pinch seal above the current supply wires
so as to prevent that, upon making the pinch seal, the
comparatively little viscous quartz glass is pressed in
the longitudinal direction o~ the current supply wires
away from the very viscous cermet envelopes and lands be-
side the cermets on the bare parts of the current supply
wires. However, this could also be prevented in that the
: ` envelopes of cermets have such a length that the quart~
:~: glass cannot reach the bare parts of the current supply
wires.
In the lamps according -to the invention on the
contrary a raised ridge is provided 90 as to prevent the
quartz glass from pressing away the much less viscous in-
termediate glass and ~rom contacting, instead o~ the in-
termediate glass, a part o~ the current supply wire in
question which has become bare. Therefore, in the lamp
according to the invention a coating of intermediate
glass of larger length is no alternative for the use of a
: raised ridge.
The lamp according to the invention thus has a
construc-tion which is simpler and more universal and can
be made more easily. The raised ridge above the current
supply wires have a different effect.
Embodiments of lamps according to the invention
will now be described wlth reference to the accompanying
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PHN 9633 8 17,7,80
drawing. In the drawing
Figure 1 is a longitudinal sectional view
through a high-pressure mercury vapour discharge lamp,
Figure 2 is a sectional vîew through the lamp
shown in Figure 1 taken on the line II-II,
Figure 3 is a side elevation of a mono-pinch
halogen incandescent lamp,
Figure 4 is a cross-sectional view t,hrough the
pinch seal o~ the lamp shown in Figure 3 taken on the
line IV IV,
Figure 5 is a side elevation of a two-pinch
halogen incandescent lamp, and
Figure 6 is a sectional view through the lamp
shown in Figure 5 -taken on the line VI-~I.
I~ Figure 1, a quartz glass lamp envelope 1 has
flat pinch seals 2 and 3. A current supply wire 4 is
passed through pinch seal 2, around which wire 4 the
pinch seal 2 has the same geometry as pinch seal 3 around
a current supply wire 5~ Over a part of its length cur-
rent supply wire 5 has a circum~erential coating of in-
termediate glass 6 of the composition b in the above
table, which i5 fused to the wire 5. Between the ends o~
the coating 6 the quartz glass of the pinch seal 3 is
fused therewith. The current supply wire 5, which con-
sists of tungsten and as a diameter of 800/um, has tung-
sten wire turns 8 at its end 7 so as to form a main elec-
trode. Adjacent the wire 5 in pinch 3, is a tungsten wire
10 provided with a coating 9 of the same intermediate
glass. The end 11 of wire 10 forms an auxiliary elec-
trode.
In Figure 2 the shape of the flat pinch seal 3is clearly visible. The pinch seal 3 has smaller side
sur~aces 12 and 13 and larger side surfaces 14 and 15.
On the latter are present raised ridges 16 ancl 17, res-
pectively, each situated above the current supply wire 5and its coating 6 and extending over-its entire pinched
length. Raised ridges 1~ and 19, respectively, are also
present above the current supply wire 10 and its coating
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PI~ 9633 9 17.7 80
9.
In Figure 3, molybdenum current supply wires
32 and 33, respecti~ely, of 600/um diameter are incor
porated in a vacuum-tight manner in the flat pinch seal
30 of a quartz glass lamp envelope 31. The wires have
coatings 34 and 35, respectively, of intermediate glass
of the composition d from the table. The current supply
wires 32 and 33 support a tungsten filament 46.
It is visible in Figure 4 that raised rilges
38, 39, 40 and 41, respectively~ are present above each
of the current supply wires 32 and 33, respectively, in-
corporated in the ~lat pinch seal on the major side sur-
~aces 36 and 37 of the pinch seal. They extend over the
whole pinched length of the current supply wires 32 and
lS 33. The lamp shown may be used for projection purposes.
In Figure 5 the quartz glass lamp envelope 50
has flat pinch seals 51 and 52 of the same geometry. A
tungsten current supply wire 53 of 700/um diameter is in-
corporated in pinch seal 52, on which wire a coating 54
of composition a from the table is sealed. Between the
ends of coating 54 -the glass of the pinch seal 52 is fus-
ed therewith. At its end situated inside the lamp ~essel
50 the current supply wire has a few tungsten wire turns
55 which are screwed in the filament 56c The lamp may be
used as a floodlight lamp.
Fig~lre 6 shows raised ridges 59 and 60 present
above -the current sL1pply wire 53 and its coating 54 on
the respective larger side surfaces 57 and 58 of the
pinch seal 52, which ridges extend o~er the whole length
o~ the current supply wire 53.
