Note: Descriptions are shown in the official language in which they were submitted.
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10~70~6
Thls lnvention relates in general to mercury
vapor lamps ~or use in photocuring applicatlon.
BACKGROUND OF THE INVENTION
A significant improvement in photopolymerization
processlng i~ realized when the chemical coating to be
cured is blanketed by an inert atmosphere during exposure
to ultraviolet radiation. The principle source of ultra-
vlolet energy ls a conventional mercury vapor lamp. Mer~
cury vapor lamps are relatively inexpensive and relatively
efficient as generators of electromagnetic radiation in ;~
the ultraviolet wavelength range.
In order to simultaneously provide a protective
atmosphere at the surface of the coating while the surface
is undergoing irradiation, it ls necessary to house the
mercury lamps in a confined enclosure in common with the
inerting assembly. However, when one or more mercury
vapor lamps, partlcularly lamp~ of high wattage, are
located in the confined enclosure of the inerting assem-
bly, sufficient heat is radiated to cause the ambient
temperature of the enclosure to rise considerably. The
elevated tAermal envlronment will in turn precipitate
failure of the lamps. Such failure has been attributed
to deterioration of the conducting element~ within the -~
lamps and more specifically to oxldation of the molybdenum
strips whlch are sealed to the quartz envelop at the
opposlte ends of the lamp and extend internally of the
lamp to the tungsten electrodes. Slnce the inerting
assembly is designed to pass inert gas into the con~ined
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enclosure~ it would be only natural to assume that the
design can be modified so that the inert gas provides
the additional function of cooling the ends of the rner-
cury vapor lamps. This would then be analogous to
other known mercury lamp systems which pass air over
and around the ends of the mercury lamps to provide
cooling. Nevertheless to provide adequate cooling in
this manner requires not only a relatlvely large flow
of gas but an inde~inite flow whlch will vary with the
number of lamps used and their wattage characteristic
and may not necessarily provide uniform cooling. Hence,
although ~easible, it is not compatible with efficient
inerting assembly design. Furthermore the requirement
o~ high gas flow is a serious economic disadvantage which
might prove fatal to the commercial viability of a
photocuring system dependent upon such flow. In ~act,
conslderable research effort has been expended t~ design
an inert gas blanketing system as taught in U.S. Patent
No. 3,~07,052 entitled Apparatus for Irradiation of a
Moving Product ln which the required lner~ atmosphere is
satisfied using a very low flow of inert gas and is one
o~ the princlple reasons why photopolymerization in
an inert atmosphere has become commercially acceptable.
The aforernentioned patent discloses an inerting assem-
bly including an enclosure having a treatment chamber,
which houses the source of radiation,such as a plurality
o~ mercury vapor lamps, and an lnlet and exit tunnel
extending from the treatment chamber. ~he dlsclosure
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70916
teaches the importance Or the geometry and location Or the
lnert ga~ inJector and its orientation withln the assembly
to achieve dynamic lnerting at low flows and emphasizes
the importance of a non-turbulent ~low of inert gas
throughout the enclosure.
It was theorlzed that the problem of overheating
at the sealed ends o~ the lamp could be prevented from
within the lamp by coupling the electrically conductive
elements at the opposlte ends of the lamp to a heat ex-
change medium external to khe lamp. Although this coupling
can be carried out in a number o~ ways the most pre~erred
is through a direct conductive coupling. This technlque
permit~ the direct transfer o~ heat ~rom the molybdenum
elements most susceptible to oxldation deterioration when
the lamp ls operating within an elevated thermal envlron-
ment without affecting the operating characteristlcs o~ the
lamp. It has been shown that by conductive coupling in a
predetermined manner not only i~ seal failure prevented but
the lamp is rendered substantially independent of the ex-
ternal thermal envlronment.
SUMMARY OF THE INVENTION
In accordance wlth the present invention lt was
discovered that accelerated fallure of a mercury vapor
lamp due to its conrlnement in an optically enclosed space
re~ulting in a high temperature environment can be over-
come by conductlvely coupling the lnternal electrlcally
conductive elements of the lamp to an externally located
heat slnk and controlllng the temperature of the heat sink
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BO a~ to maintain a "seal temperature" of below 400C at
the opposite ends of the lamp. The expresslon seal
temperature 1~ hereinafter de~lned a~ the temperature
at the sealed lnter~ace between the molybdenum conduc-
tive strlp and the 3urrounding ~uartz at the end~ of
the lampO
Accordingly, one aspect o~ the present inven-
tion is dlrected to a method for continuously operatlng a
hlgh wattage mercury vapor lamp ln a con~ined enc~osure.
with ~aid lamp having an elongated quartz envelop sealed
.. ..
at each end; the lmprovement comprising the steps of:
^onnectin~ each sealed end of said lamp to
a thermally conductive heat slnk;
maintalning sald heat ~ink at a temperature
o~ below 10~C; and
locating said heat sink in such physical
proxlmity to the s~aled ends of said
quart2 envelop ~o that the seal temperature
is held to below 400C.
Another a~pect of the present lnvention ls
directed to a method for continuou~ly operatlng a plural-
lty of hlgh wattage mercury vapor lamps ln combination
a~ a ~ource o~ ultraviolet radiation ln a con~lned enclo-
~ure wlthin wh~ch a non-turbulent inert gas atmosphere ls
maintained, each of ~aid lamps having an elongated quartz
envelop sealed at each end about an electrlcally conduc-
tive molybdenum strip; comprislng the ~teps o~:
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~(~47~)9~
connecting said electrically conductlve
molybdenum strip at the end3 o~ each
lamp ln a serles circuit relationship
wlth a ~ource Or alternating current;
intercoupling a thermally and electric-
ally conductive heat ~ink into the
serie~ circuit of each lamp re~pec-
tively;
maintainlng the heat sink at a tempera-
ture of below about 100~; and :~
placlng the heat ~ink ln each circuit
ln such phy~lcal proximlty to 3ald
~ealed ends 80 that the temperature
of the molybdenum strlp at the sealed
end of each lamp i~ malntained at :;
below 400~C. ^ ~:Yet another aspect o~ the present invention ls
directed to an improved mercury vapor lamp ~or generating ~:
ultravlolet light lncludlng an elongabed quartz envelop :
surrounding two tung ten electrode~ located at opposite
end~ of the envelop, with each end sealed in lnt~mate
contact about an electrically conductive molybdenum ~trip
coupled to one o~ sald electrode and an electrlcal con-
ductor extendlng from each sealed end, the improvement ~;
comp~lsin~: terminal mean~ located ad~acent each opposite
end o~ the envelop and being ln electrical and thermal
contact with each of said electrical conductors, means -:-
for electrlcally coupllng ~aid terminal means acro~ a
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7~g~
~ource of alternatlng current and meanR for pa~ing a
cooling liquid through ~ald termlnal means,
A ~urther aspect o~ the present invention i9
directed to the combination of a mercury vapor lamp
having an elongated quartz envelop ~urroundlng t~o tung-
sten electrodes located at opposite end~ of the envelop
with each end sealed in intimate contact about an elec-
trically conductive molybdenum strip coupllng one of
said electrodes, and an electrical conductor extending
from each sealed end~ and a means ~or electrically
coupling ~a~d conductor to a source of alternatlng
current, sald means being located ad~acent a sealed
end and being o~ relatively high thermal conductivity,
and conduit means located contiguou~ to said coupllng
mean~ an~ adapted for pa~sage o~ a coollng liquid.
AccordlnglyJ it is the sole ob~ect o~ the pre~-
ent invention to provide a mercury vapor lamp which can
operate ln an optlcally conPinëd space substantially
independent o~ its surrounding thermal environment.
Other advantages o~ the present lnvention wlll
become apparent ~rom the followlng detailed description
o~ the pre~erred embodiment when taken in con~unctlon
wlth the accompanylng drawings realizlng that variatlons ~ ~-
and modl~icatlons may be made to the preferred embodiment
wlthout departlng from the spirit and scope of the novel
concept of the di2closure.
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BRIEF DESCRIPTION OF TXE DRAWIN~S
Figure 1 i~ a longitudlnal ~ectional view lllus-
trating the combined mercury vapor lamp and terminal assem-
bly of the present invention;
Figure 2 ig a slmllar view to that o~ Figure 1
with the apparatus rotated ninety degrees (90) about a
horizontal axis ~rom the position shown in Flgure 1;
Figure 3 is a substantlally enlarged view of one
of the sealed ends o~ the lamp ~hown in Flgures 1 and 2;
and
Figure 4 ls a diagrammatlc lllustration of the
pre~erred inertlng apparatus housing the mercury vapor lamp
and terminal a~sembly hown in Figures 1 and 2.
DETAILED DESCRIPTION OF THE INVENTION
The apparatu~ o~ the present invsntlon ls shown
ln Figure~ 1 and 2~inclusive, and includes ln combinatlon
a conventlonal mercury vapor lamp 10 and a pair of terminal
assemblies 12 and 14 located adJacent each end Or the lamp
10 re~pectively.
The mercury vapor lamp 10 i~ a typical commer~
cially available 2.2 kw lamp manu~actured by Sylvania
Electric Products Inc. and commercially ldentl~ied by the
No. H2200~4/24Q. Although a medium pres~ure lamp of the ~ ;;
partlcular con~iguratlon shown 1~ illustrated ln the
drawings, the pre~ent lnvention ls not to be consbrued ~
a~ limlted thereto. In ~act, any conventional mercury ~ -
vapor lamp may be u~ed o~ any conflguratlon and ~pec-
lf`lcatisn,
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The illu~trated mercury vapor lamp 10 i~ sealed
at each end 30 and 32 definlng therebetween an arc envelop
16 of ~used quartz which surrounds a pair of tungsten
electrode~ 18 and 20 located at the opposite ends of the
lamp lO. The electrode 18 i5 connected at the sealed end
30 ko the power conductor 22 through an intermediate strip
of material 24. The sealed interconnection between the
conducting elements consisting o~ the tungsten electrode
1~, the intermedia~e ~trip 24, and the power lead 22 i~
Ishown more clearly in ~lgure 3. Likewisej electrode 20
is connected at the sealed end 32 o~ lamp 10 to the power
conductor 26 through an intermediate strip o~ material 28.
Each ~trip of material 24 and 28 is compo ed of a ductile
materlal which i9 electrically conductive and has a high
melting point such as molybdenum. The sealed ends 30 and
32 are rormed,a~ter the lamp ls filled with argon gaæ and
a ~mall amount of mercury, us~ng conventlonal method~ ;
æuch as, ~or example, by mechanically compressing each end
o~ the lamp lO into intimate contact about the conducting
strips 24 and 28 re~pectively. By compressing the enda ~;
together to ~orm a ~eal, the end geometry becomes substan-
tially rectangular. Alternatively, the ends o~ the lamp
10 may be vacuum drawn ~orming an extended neck which in-
timately enclose~ the molybdenum strips. It i~ also con-
ventional to encap~ulate the ~ealed end~ 30 and 32 respec-
tively in ceramic material 35. Moreover, a metal7ic con-
ductlve cap may be placed over the ~ealed ends 30 and 32
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~047096
of lamp lO and u~ed a~ a ~ubstltute for the external
power leads 22 and 26 respectlvely.
The terminal a~semblles 12 and 14, shown in
Figures 1 and 2 inclusive, are prs~erably ldentlcal in
structure with each es~entially represented by a member
shown in the ~orm o~ a block whlch ls thermally and pref-
erably elect~ically coupled to the molybdenum strips 24
and 2~ respectively of lamp 10. The terminal as~emblies
12 and 14 although primarlly lntended a~ heat sinks also
~unction to shleld the sealed ends 30 and 32 ~rom radiation
as will be explained in more detail hereafter a~ well as -~ -
to transmit the alternating current to the tungsten elec-
trode~ 18 and 20.
The physical configuration and materials o~
construction ~or each terminal assembly 12 and 14 is
not critlcal to the invention provided they adequately
per~orm the ~unction o~ a heat slnk 90 as to drive su~
~lcient heat ~rom the internal conductive elements o~ -
the lamp lO, and more particularly ~rom the molybdenum
strips 24 and 28, to prevent ~allure. To ful~ill thls
requirement each terminal assembly must be constructed
o~ a reasonably good the~mally conductive ma~erial and be
o~ a con~lguratlon so as to permlt efflcient tran~er o~
heat. It is particularly pre~erred to use the power con-
ductors 22 and 26 to ~unctlon as the lntermediate heat
tran~fer medium from the molybdenum strlps 24 and 28 to
the terminal as~emblles 12 and 14 respectively. The
phy~ical placement of each terminal assembly 12 and 14
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9616
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to each sealed end 30 and 32 respectively of lamp 10 ls
critical ln that lf there is too ~ar a separation the
necessary cooling to overcome oxldation at the sealed
endc wlll not be achleved. It ha~ been found that the
locatlon o~ the termlnal assemblles 12 and 14 must be in
such close proximity to the sealed ends 30 and 32 to keep
the seal temperature below 400C and pre~erably not above
350C. To maintaln the seal temperature at this level
it has also been found necessary to lnsure that the temp-
erature o~ the termlnal as~emblies 12 and 14 be held to
a temperature significantly lower than 350C and prererably
not above about 100C. To sati~fy the latter requirement
the terminal assemblles 12 and 14 must be cooled with a
cooling liquid such as water. The sxtent of such cooling
wlll determine the heat drlvlng ~orce.
~he prererred structural arrangement ~or each
terminal a~sembly 12 and 14 ac shown in ~igures 1 and 2
com~rises a two section constructlon with each seckion
50 and 52 respectively composed of a material which is
thermally and pre~erably electrically conductlve such as
copper or aluminum. The two sectlons 50 and 52 are ln-
tended to be coupled by bolts 54 so as to ~it about an end
o~ the lamp 10. Each section 50 and 52 includes drillings
for formlng, when the two sections are combined, two con-
centrically reces~ed portions 56 and 5~, into which the
ceramlc co~ering 35 at each ~ealed end 30 and 32 o~ lamp
10 is ~eated before ~irmly securlng the ~ectlons, and a
bore through whlch the power conductor at each end is
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~ ~'7~ 6
entrained. It is also desirable to hold a fairly close
tolerance in order to achleve good surface contact,
between the sealed ends 30 and 32, at their terminatlons
with the power conductors 22 and 26 respectively, and the :
sectlons 50 and 52 Or each terminal assembly 12 and 14
reRpectively. A passageway 60 is located ln the upper
section of each assembly for passing the cooling water
~rom a source (not shown) through each terminal assembly.
The pas~ageway 60 should be located suf~iciently close to
the conductlng power lead3 22 and 26 to maintain an effec~
tive heat transfer gradlent between the.conductive strlps -~
24 and 2~ and the terminal assemblies. ~-
AC power is applied to the lamp lO ~rom a source .
62 connected acros~ the terminal assemblies 12 and 14. ;~
Alternatively, AC power may be applied directly across the ;~
power conductors 22 and 26 in which case the terminal ;~
assemblles nee~ not be electrically conductive. .
. The recessed portions 56 and 58 into whlch the
sealed ends of the lamp are seatod are pre~erably of a
length su~ficient to form a radiatlon shield about the
molybdenum ~trips 24 and 2~ respectively. Shielding the :
molybdenum strips from reflectlve radiat.ion limits the
extent o~ internal coolln~ of the lamp 10 that would :
otherwise be necessary to maintaln the seal temperature
at below 400C.
~e pre~erred system in which a plurality o~
lampR lO are used as a source o~ ultraviolet radiation
in an inert enclosure 1~ schematically iIlustrated in
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96~6
47C1~6
Figure 3~ A product P is intended to pass through the
inert enclosure 70 at a predetermined speed. The enclos-
ure 70 includes a radiation chamber 72 which houses a
plurality of lamps 10, only one of which is shown, and
an inlet and exit tunnel 74 and 76 respectively. Each
lamp 10 is seated as shown in Figure 1 in a terminal
assembly 12 and 14 respectively which is in turn affixed
to the chamber 72. A reflector 78 partially covers the
lamp 10 for redirecting radiated light toward the passing
product P. The cooling water passing through the terminal
assemblies 12 and 14 may also be used to cool the reflector
78. The atmosphere within the enclosure 70 is exclu-
sively controlled by the passage of inert gas fed from the ~ ;
plenum chamber 80 through the inert gas injector 82 into
the enclosure 70. The method by which the inert gas may
be fed at a predetermined low flow rate to maintain an
inert atmosphere above the moving product is taught in
U.S. Patent No. 3,936,950 and entitled Method of Inerting
The Atmosphere Above A Moving Product. A non-turbulent flow
of inert gas is malntained throughout the enclosure.
By following the teachings of the present invention
so as to conductively transfer heat out from the elec-
tr~cally conducting elements within each of the lamps 10
a substantial degree of thermal independerlce is achieved
between each of the lamps 10 and the ambient temperature
within the optically enclosed radiatlon chamber 72.
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