Note: Descriptions are shown in the official language in which they were submitted.
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.LECTRIC LAMP INCI.UDIN& A CONTAINME~T COATING
AS PART TH~REOF
CROSS REF~RENCE TO A CO-P~NDI~G APPLICATION
In a co-pending Appllcation, having Canadian Serial No.
448,137-2 ("Electric Lamp With High Ou~er Envelope To Inner
Envelope Wall Thickness Ratio,~' Peter R. Gagnon), there is
defined a lamp having a relatively high outer-envelope to
inner-envelope wall-thickness ratio for the purpose of
substantially eliminating con~ainment failure of the lamp.
TECHNIC~L FIELD
This invention relates to electric lamps and more
particularly to such lamps employing light-source capsules
15 which operate at pressures other than atmospheric. Still
more particularly, this invention relates to such lamps
having containment means to substantiallly ellminate the
risk of a containment failure of the lamp.
BACKGROUND
The lighting industry is searching for a replacement
for the Edison-type incandescent lamp which is currently
the most popular type of lamp sold in the consumer market
in the United States. Tungsten-halogen and arc discharge
lamps, because of their superior performance
characteristics, are being carefully considered by various
lamp manufacturers as a replacement for the standard
incandescent lamp. ~Iowever, the remote possibility
of a minor dispersion of glass shards resulting
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from a fracture of the pressurized light ~ource ~ap~ule
contained within the la~p i6 a ~ub6tantial impedime~t in he
path of developing a feasible replace~ant in the consumer
market~ Althou~h occurrence of ~uch a fracture i~ ra~e,
neverthele66 ie could present a ~afety hazard to a person or
object in the immediate vicinity of the lamp (i.e., food
preparation). A tung~ten-~alogen lamp or an arc diccharge lamp
whic~ substantially eliminate~ the problem of shard disper6ion
upon the fracture o~ the light source capsule would constitute
an advancement in the art.
Method~ have been sugge~ted to improYe the ability of
tungsten-halogen and arc di~charge lamp~ to with~tand a
fracture of the inner light-source capsule. In one example the
shard~ are re~tricted from impacting with the outer envelope
through the use of a cylindrical body di~po6ed about the arc
tube, U.S. Patent No. 4,281,274, i6sued July Z8, 1981 to
Bechard et al. In addition, the practice of applying a coating
on the outside surface of a lamp envelope to hold the glas6
piece~ together upon envelope breakage, due to an impact by an
exte~nal force, i~ al60 know~ in the art. For example, Audesse
et al., in United Statss Patent No. 3,715,23~, i6~ued
February 6, 1973, di6clo~e~ the process of coating a lamp with
a 6ilicone rubber film for the above ~entioned purpose.
It i8 believed, therefore, that an electric lamp which
overcome~ the ~everal di6advantages a~sociated with the prior
art devi~es mentioned above would constitute a ~ignificant
advancement in the art.
DISCLOSURE OF THE INVENTION
It i~, therefore, a primary object of thi6 invention to
overcome the di~advantaqe~ of the prior art device~ 6uch a~
mentioned above.
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It is anot~er object of thi~ inventio~ to provide a mean~
of co~ainment for electric lamp6 whicll will ~ub~tantially
eli~inate t~e po~ibility sf a ~inor ~hard di6peEsion upon
fracture of a pre6~urized light ~ource ~apsule.
A urther ob~e~t of thi6 in~ention i6 to provide ~eans for
containment which doe~ not detract from the ae~thetic
appearance of lamps.
Another object of thi6 invention i~3 to provide mean6 for
containment which will cau~e little or no 1Q6~ of luminous
efficacy in lamp~ employing ~uch mean6.
Still another object of t~i6 invention i~ to overcome a
6ub~tantial impediment in the path o developing a replacement
for the ~tandard incandescent lamp in the con6umer ~arket.
In accordance with one a6pect of the present invention,
there i~ provided an electric lamp including a light-
transmitting envelope, a pres6urized light-60urce cap6ule
mounted within the envelope and containment mean6 for
containing within the lamp fragment6 of glas~ re6ulting from
fracture of the cap~ule. The containment means is disposed
substantially over the envelope and i6 of a sub6tantially light
tran~missive material. The containment mean6 has a high degree
of tensile ~trength at continuous service temperatures that are
6ubstantially egual to or higher than 190 Cel~iu~.
BRIEF DESCRIPTION OF THE DRA~ING
FIG. 1 is an elevational cro66-sectional view of an
embodiment of the lamp made in accordance with the teaching~ of
the present invention;
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PIG. 2 illu~trates an enlarged cro~s-~ectional vi~w o~ a
portion of the la~p with a fluoropolymer contain~ent coating:
and
FI~. 3 illu~trate6 an enlarged cros6-~eetion~l view of a
por~ion of the lamp with a 6ilicone rubber containment coating.
. BEST MOD~ ~OR CAR~YIN~ OUT THE INVENTION
For a better understanding of the present invention,
together with other and further object~, advantages, and
capabilitie~ thereof, reference is made to the following
di~clo6ure and appended claims taken in conjunction ~ith the
above-de~cribed drawings.
As used herein, the term "light-~ource capsule" denote6: a
tung~ten-halogen incandescent capsule, an arc tube of an arc
discharge lamp, or any light-emitting capsule within the outer
envelope of a lamp wherein the light-~ource cap~ule operate~ at
a pre~sure other than atmo6pheric and the possibility of minor
shard disper6ion upon fracture of the light 60urce capsule
exi~ts. The light-60urce cap6ule may be either a eingle-ended
or double-ended cap~ule.
The terms "contain" or "containment" as used herein mean
that the containment mean~ of the lamp, ~ade in accordance with
the teaching6 of the pre6ent invention, is not pierced as a
result of a fracture of the inner light-~ource cap6ule. Shard~
of ~he light-source cap6ule remain within the lamp and the
containment mean~ ~erves to prevent 6hard di6persion.
Referring now to ~he drawings with greater particularity,
FIG. l show6 an electric lamp lO made in accordance with the
~eaching6 of the present i~vention. ~lectric lamp lO includes
a light-transmissive outer envelope l2, containment ~ean~ 13
dispo~ed substantially over envelope 12 and a ba~e 14.
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Rnvelope 12, which ~a~ be for~ed of ~oda lime gla~s, has ~ body
15 and a neck 16. Lamp 10 further include6 a light-~our~e
capsule 18 ~ounted ~ithin envelope 12 on a fra~e a66e~bly 24.
Light-~ource capsule 1~ which may be for~e2 of quartz or hard
gla6~, ~as an en~elope 20 and a pre~6 ~eal end 22. Envelope 12
ha~ neck 16 runninq from ring 28 o brim 30. In addi~ion,
containment mean~ 13 should overlap or be attached to a por~ion
of base 14 to counteract the effects of ~ravity, by ~ervi~g as
a pouch or ~ack, in the event that envelope 12 break6.
In one embodiment of electric lamp 10, body 15 of envelope
lZ has a minimum wall thickne66, x. Envelope 20 ~a~ a maximum
wall thickne~s, y, of le66 than about 0.9 millimeter. In lamp
10, the ratio of x/y, whi~h hereinafter will be referred ~o as
the "~all-thickne66 ratio," is approximately equal to or
greater than 3. ~hen 6uch a relation6hip exi~t6, cap~ule 18
will be de~cribed herein a~ being "thin-walled" 'with re6pect to
envelope 12, and conver6ely envelope 12 will be de~crihed as
being "thick~walled" with re~pect to cap6ule 18. The
prescribed range of the wall-thickness ratio in6ure6 that these
comparative measure~ of "thick" and "thin" will be true by a
factor of approximately 3 or greater.
T~e importance of the pre6cribed range of the wall-
thick~e66 ratio i6 a6 follow6. When a thin-walled capsule
frac~ures into ~hard6, each shard i~ relatively thin and
25 pos6e~ses les6 ~a~6 than would be the ca6e if the cap6ule were
not thin-walled. When thefie low-mass 6hards i~pact with the
out~r envelope, the impact energy per colli6ion i6 reduced
because energy i~ proportional to mas6. The thinner shard~
tend to ~hatter them6elve6 thereby dis~ipating colli~ion energy
harmle~61y. There i6 evidence from observations that
thin-walled capsules fracture into grea~er numbers of ~maller
~hards than do cap6ules with greater wall thickne66e6 under
6imilar operating conditions. The grea~er the number of 6hard~
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D-24,44q
-6-
impa~ting with the outer envelope, the more the to~al energy of
the fracture will be 6pread uniformly oYer t~e outer envelope.
The ultimate result of these factors i~ that the out~r envelope
ha6 the ability to contain a~ inner cap~ule fracture when She
wall-thickne~s ratio i6 wit~in tbe pre6cribed range.
Con~ainment mean6 13 will preserve the integrity of the outer
envelope of the la~p where the wall thicknes~ ratio is ~ot
wi~hin the pre~cribed range.
In an alternative embodiment of the electric lamp, outer
envelope 12 has a concave top 26 opposed to neck 16. the word
"concave'~ means t~a~ the radiu6 or radii of curvature of top 26
fall~ on the exterior of envelope 12. The concave ~shape of top
26 diverts shards and energy of a fracture of eapsule 18 ~o~ard
ba~e 28 where they are least likely to cause damage; in 80
doing, top 26 shatter6 many shard6 which further dissipate~
fracture energy. Top 26 also reinforces the portion of
envelope 12 that lies above cap~ule 18. This re.gion of
envelope 12 may require rein~orcement for two reasons. First,
top 26 may be the portion of envelope 12 closest to capsule
18. Second, there is the po~sibility that capsule 18 may
fracture such that the upper portion of capsule 18, i.e., the
portion of capsule 18 closer to top 26, may be propelled
again~t top 26. Thi~ type of ~racture may occur if envelope 20
of capsule 18 i8 fractured near pre~s seal 22. If ~uch a
fracture should occur, the high pre66ure withi~ cap6ule 18 may
propel the portion of capsule 18 above pres6 ~eal 2Z toward top
26. It is believed that the region of capsule 18 where
envelope 20 joins pre6s seal 22 may be particularly susceptible
to thermally induced fracture~ because of the ~ub~tantial
temperature gradient in this region cau~ed by the high
operating temperature of envelope 20 and the relatively cool
operating temperature o pre~s fieal 22.
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D-24,444 _7_
In another embodiment of the electric lamp, minimum
wall thickness, z, of neck 16 is approximately equal ~o or
greater than 2.5 millimeters. The extra thickness of
neck 16 facililates the mounting of frame-assembly 24 on
neck 16 by means of elastic and frictional forces. For a
de~ailed explanation of the means for mounting
frame-assembly 24 with capsule 18 thereon within envelope
12, reference is made to co-pending Canadian Patent
Application having Serial No. 44~,138 1, filed
10 Pebruary 23, 198~ and assigned to ~he present assignee.
I.ight source capsule 18 oper~tes with fill pressures
other than atmospheric, typically about 5 to about ZO
atmospheres. At such pressures, and where the
wall thickness ratio i6 less than 3 ~i.e., the outer
envelope has a wall thickness similar to a standard
incandescent bulb)~ a fracture of capsule 18 would result
in a dispersion of shards from the capsule that would
pierce t~le outer envelope where containment means 13 was
absent from tbe exterior of the electric lamp:.
Containment means 13 (see FIG. 1) includes a coating, that
is disposed over envelope 12 of lamp lO, for containing
fragmen~s resulting from fracture of capsule 18.
Containment coating 13 should be relatively transparent
so as to allow a substant;al amount of light to pass
through it. In addition, coating 13 should be resistant to
degradation by high temperature and ultraviolet radiation.
According to the present invention, the containment coating
material is preferably either a fluoropolymer or a sillcone
rubber base material. Coating 13 can be applied to an
outer envelope of any wall thickness in order to provide
containment capabilities. The coating material~ used here
also exhibit a high degree of tensile strength at high
te~peratures.
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Referr~ns now to ~IG. 2, one embodiment of the
fluoropolymer containment coatin~ of the present ~nventlon i~
illuxtrated a6 coati~ 13A ove~ a portion of envel4pe 12. In
one 6pecif~c u~e, ~oating 13A consi6ted of a ~erPluoroalkoxy
re6in i.e., P.F.A. Teflon material ~"Teflonl' being a trademark
of E.I. du Pont ds Nemour~ Co.). The visible ligh~
~ransmiæ~ion of thi~ coating was fou~d to be about 99~ of that
of a ~lear outer envelope without such a coating. The
perfluoroalkoxy resin material has a continuous ~ervi~e
temperature rating of about Z63 Celsiu~, and i~ es~entially
unaffected by ultraYiolet radiation. Other fluoropoly~er
materialfi such as fluorinated ethylene-propylene copolymer
(i.e., F.E.P. re6in~ and polychlorotrifluoroethylene (i.e.,
P.C.~.F.E. resin) al~o ~a~e similar containment capabilitie~
and are unaffe~ted by ultraviolet radiation, but do vaLy in
6ervice temperature rating. These ma~erial6 have a 6ervice
temperature of about 190~ Celsius.
In an alternative embodiment of the fluoropolymer
containment coating, the fluoropolymer coating could be applied
in cnmbination with a reinforcing material to provide either
improved protection or to minimize the quanti~y of coating
material required. One example of such a reinforcing ~aterial
consist6 of using short gla~s fiber~ ~le~ than 0.30 inch in
length) mixed in suspen~ion within the fluoropolymer material.
Thi~ combination al~o has the advantage of providing inherent
diffusion of the light emitted from lamp 10 where de~ired, due
to t~e glas~ fibers. The thickness of ~he aforementioned
fluoropolymer coating~ are normally in the range of abou~ 0.001
to 0.006 inch.
The fluoropolymer coatings of the pre6ent invention also
provide lamp 10 with means for refiisting thermal shock induced
fracture, a~ mig~t be caused by water droplet~ falling on t~e
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_9,_
lamp while it i~ in operation. In additio~, the coating a~ds
i~ ~aking a "tamper-re6i6tant" lamp ~y reinforcing ~he outer
envelope to preven~ breakage from rou~h handling or from a
minor i~pact by an~external force while the la~p is i~
opera~ion. ~anufacturing ~tep~ in making ~he lamp ca~ be
reduced by formulating a ~oating that can either diffu~e he
light e~itted from tbe lamp (a6 in frof;ted o~ ~mo~ w~ite
lamp6~ or be colored for decorative la~p purpo~e~. ~he
fluoropolymer coating~ m2ntioned above can be applied by
conventional technique~ 6uch as electrostatic powder coati~g,
fluidized bed coating or wet 6pray coating.
Referring now to FIG. 3, one embodiment of the ~ilicone
rubber containment coating of the pre~ent invention i~
illu6trated a~ coating 13B o~er a portion of outer envelope
12. The 6ilicone rubber containment coating 13B comprises
coa~ing envelope 12 of lamp 10 with more ~han one layer of
mate~ial. Two or more layer6 of material with differing moduli
of elasticity are applied on envelope 12 of la~p 10. The
combination of layer~ 13c and 13d, made of material6 having
high ~13c) and low (13d) moduli of ela~ticity, provide~ a high
de~ree of containment for lamp 10 due to the re6i6tance of the
multi-layer system to tear propagation. Each layer of
tranfiparent 6ilicone rubber i8 for~ula~ed to have a different
modulu~ of elasticity. Each layer i6 applied by the proce~s of
dip coating. The thickne66 of each layer i~ in the range of
about 0.001 to 0.003 inch. The overall ~hickness of the
~ilicone rubber coating i~ in ~he range of a~out 0.002 to 0.006
inch. The 6ilicone rubber containment coating 13B will al~o
provide containment capabilitie~ for a lamp having the wall
thickness of a standard incande~cent light bulb.
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20040 ~~-
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~ oraa~ce ~i h o~e e~bo~ent o~ ~e ~ra6~t ~en~ionO
the e~terior of ~n A 19 bulbo ~onta~ni~q ~ T-4 ~ze
tun~sten-~alo~en cap~le, ~ade o alumino611i~ate or hara gla~
~a~erial, ~t about 10 atmo~phere~ ~reæ~urer wa~ ~oat~d wi~h a
0.005 i~h ~ k coa~ing of per~luoroal~oxy resi~. S~e ~oat~ng
reliably contained ~e glass ~raymen~6 of ~e purpo~ely
fr~c~ured T-4 ~ize haloqen capsule. Vi~ible liqht tran~mis~ion
of thi~ coating wa~ ~ou~d to be abou~ 99~ of tha~ of a lamp
with a ~lear envelope or bul~. Th~ perfluoroalkoxy resin had a
continuou6 6er~ice temperature rating of about 260~ Cel6iu~.
I~ accordance with another e~bodiment of the pre~ent
invention, an outer envelope of the lamp wa~ ~ormed from
6oda-lime gla66 with a concave top. The envelope had a minimum
wall t~ickne6~ of about 1.9 ~ imeterB. The T-~l 6ize
tung6ten-halogen cap6ule ~ithin the lamp, which was ~ade of
alumi~o6ilicate gla6~, was at 10 atmo6phere6 pres6ure and had a
volume of about two cubic centimeter~. The perfluroalkoxy
resin coating on the outer envelope was about O.OOl inc~ in
t~ic~nes6. The coating here reliably ~ontained the glax~
ragment~ of the purpo~ely ~ractured halogen cap~ule.
In accordance with 6till anot~er embodi~ent of the pre~ent
invention, an A-l9 bulb containing a T-4 ~ize tung6ten-halogen
capsule at about lO atmo6phere~ pre6~ure wa6 coa~ed ~it~ an
overall 0.006 i~ch thic~ layer of 6ilicone rubber mate~ial.
The ~oating was compri6ed of two layer6 of ~ilicone rubber
~aterialO each layer having a difering moduli of ela~ticity.
One layer ~ad a high modulus of ela~ticity and ~he other had a
low ~odulu~ cf ela~icity. The layer6 ~ere applied by the
proce~6 of dip ~oati~g. ~e coa~i~g here reliably co~tained
t~e glas6 fragment6 of the purposely fractured halogen capsule.
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Thu~, there ha been shown and de~cribe~ an improved
cont2inment ~eans for containi~g frag~ents of gl~66 within a
lamp re6ul~ing from t~ fra~ture cf a light ~ource capsule
within the lamp. The contain~ent means consi6t~ of a coating
of eit~er a fluoropolymer material or ~ 6ilicone rubber
material that i~ difipv6ed over the outer envelope of the lamp
and is of a 6ubstantially light-tran~mi~sive material. The
coating~ al~o exhibit a hig~ degree of tensile strength at high
temperature~. The coating ~hould be re~istant ~o hi~h
temperature~ (about 190 Cel6ius or higher) and be unaffected
by ultraviolet radia~ion.
~ hile there have been shown what are at present con6idered
to be the preferred embodiments of the invention, it ~ill be
appa~ent to those skilled in the art that variou6 change~ and
modification~ can be made herein without departi.ng from the
scope of the invention as defined in the appended claims.
