Note: Descriptions are shown in the official language in which they were submitted.
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84-1-0~5 -1-
BONDED BEAM L~MP
CROSS REFERENCE TO COPENDING APPLICATION
In Serial No. 461,058-0, entitled ~Par Spot Lamp" and
filed ~ugust 15, 1984 (William Thiry et al), ~here is
described a spot lamp having a curved lens member. the inner
surface of which has a series of radially disposed flutes
formed therein defining a fluted portion which surrounds a
centrally disposed stippled portion. The aforementioned
application was assigned to the same assignee as the instant
invention~
TECHN r CAL FIELD
The present invention relates in general to incandescent
light sources and particularly bonded beam lamps, having
two-piece envelopes, comprising a reflector and lens
assembled by adhesive means. The reflector has an internal
reflective coating for reflecting and directing light,
originating from a ligh~ source located within the envelope,
towards a coopexating lens through which the light is
transmitted.
BACKGROUND
It is well known in the art to utilize PAR (parabolic
aluminized reflector) or ER (eliptical reflector) lamps for
general spot or flood lighting applications~ In particular,
PAR and ER lamps have become exceptionally popular for short
to medium distance outdoor uses as well as indoor for
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di~play, ~ecoration, accent, in~pection and downlighti~g
applications. Such lamp6 are manufactured and ~old by the
as~ign~e of the in~tant :nvention. Typically, these lamps
are of hardglass and include a medium 6kirt (screw-type3 or
side prong base at the rear t~ereof for connecting the lamp
to the dasired power ~ource.
The produc~ion of 6uch a66embled 6ub6tantially circular
qlas6 reflector6 and lense6, however, can pre~ent numerous
problem6. For example, stres~e6 created in the glas6 len6e~
and reflector~ during a6sembly by fu6ion sealing [i.a., flame
6ealing) can cau~e cracking t~ereof. The proces6 of flame
~ealing is not only expensive but it require~ the u6e of
difficult-to-operate equipment. The thermally induced 6tres6
points can be the origin point o~ reflector or lens cracking
and ~ubsequent non-containment upon fracture of a ligh~
source capsule located within the lamp. The~e proble~s are
particularly evident in out6ide applications where the PAR or
ER lamp may be 6ubjected to extreme tharmal gradient~.
Experience gained in ~e te~ting involved with automobile
headlight design ha~ demonstrated ~hat the probability of
such tharmally induced stre6se~ can be 6ignificantly reduced
by using an adhesive, rather t~an flame sealing, to seal the
gla~ reflector and lens together.
In the de6ign of automobile headlights, the quality of
the lens-reflector ~eal depends largely on properly combining
the i~dex of thermal expan6ion of the len~ and reflector
material with the inde~ of thermal e~pansion of the adhesive
to be used. The typical indice6 of thermal expan~ion for
hardglas6 used in headlight~, 6uch as borofiilicate, and a
6uitable adhesive for bonding lamp gla~sware, such as an
epoxy polymer which has been flexibilized, can diffe~ by a
factor of about 10. The glas~-adhe~ive ~eal, when expo~ed to
a decrea~ing ambien~ temperature, can have glas6 portions
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thereo~ eontrac~ing at a muc~ different rate ~an ~he
adhesive portions thereof. Suc~ variations in coneraction
cause ~tre6~e6 that will ultimately lead to weakeni~q of ~he
lens to reflector 6eal or cracking of the gla68 . Li~ewi6e,
in ot~er lamps where a lens and reflector must be ~oined to
~orm ~ ~ealed envelope, the proper combination of indice~ of
thermal expansion o~ the lamp envelope material and adhesive
for the lens-reflector seal i~ important in order to obeain a
6trong long-lasti~g 6eal.
Ie is believed, therefore, that there i8 a need for a
lamp that can be a~6embled by a me~hod that 6ub6tantially
eliminate~ thermally induced 6train6 in either the len6 or
the reflector, unlike the traditional flame ~ealing
technigue. Such a lamp would be deemed an even fureher
advancement if a hig~er wattage capsule ~ould be u6ed,
without the cGncern that the additional heat generated would
cause a ~train induced failure.
DISCLOSURE OF THE INVENTION
T~erefore, it is a primary object of this invention to
enhance the art of incande~cen~ lamp6 and particularly bonded
beam lamps, operating at hi~her wattages, that are ~ubjected
to extreme thermal gradients.
It is another object of ~hi~ invention to provide a
bonded beam lamp that may be used more succe~fully in 6evere
outdoor application~ without the concern that an abrup~
temperature change will cause a lamp envelope failure.
It i~ ~till another object of this invention to provide a
bonded beam lamp ~hich will ~ucc2s~fully contain glas6
fragmene~ resulting from the fracture of a light ~ource
capsule located ~i~hin the lamp.
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In accordance wit~ one a~pect of t~e insta~t invent~on,
~here i6 provided an electric lamp co~pri6ing an envelope
having a reflector and a lens ~ade of su~antially the same
material ~ith a prede~ermined index of ~hermal expan6ion, a
lig~t ~ource diæpo~ed within the envelope and 6ub6~antially
~urrounded by the reflector, and adhe6ive ~ean~ di6po6ed
between and sealing the lens and reflector together, the
adhesi~e means having a curing ~emperature ~hat i6 equal to
or higher than the operating temperature of the lamp and a
higher index of thermal expansion than the len~ and reflector
material.
In accordance wit~ another aspec~ of the present
inve~tion, there i6 provided a method of making an electric
lamp, the lamp having an envelope formed ~rom a len6 and a
reflector, the len~ and reflector having ~ealing surface6 on
the lens and reflector peripheries, the method comprising the
steps of: alumini~ing ~he reflector, mounting a light source
within the reflector, disposing adhesive mean6 on t~e sealing
surface of the lens and joining ~he len6 6ealing 6urface with
the reflector sealing ~urface, the adhesive mean6 having a
curing temperature that i6 equal to or higher than the
operating temperature of t~e lamp and a highar index of
thermal expansion than ~he material Porming ~he lens and
reflector, curing t~e adhe6ive means to a temperature in the
range of about 148 Cel6iu6 to 190 Celsiu~ for a period of
time in the range of about 5 to 40 minutes ~ime.
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BRI~F D~SC~IPTION OP ~HE DRAWINGS
PI~. 1 is a s~dg ~levatio~al view, par~ly ~ sec~ion. of
an electric lamp const~uc~ed ~ accorda~ce wi~h the
principle~ o ~hi i~ven~io~; and
FIG. 2 ~s a ~a~mentary, ~ro~-sectional YieW of the l~ns
and reflec~or s~aling ~ur~aces ~ ac~ordance with ~he presen~
invention.
BEST ~ODE FOR CARRYING OUT TH~ INVENTION
For a better unders~andi~g o~ the present invention
together with o~er and further objects, advantages and
capabilities thereof, reference i~ ~ade to ~he ~ollowi~g
d~sclosure and appended clai~s in eonnectio~ wi~h the
above-deficribed drawings.
~it~ refareA~e ~ow to the dra~ing~, there is shown i~
FIG. 1 an elsctric lamp lO ~ade i~ accordance with the
teachings of ~e pre~e~t inventio~. Electric lamp lO
include~ an envelope 11, for~ed from a lens 12 and a
cooperating r~flec~or 14, a lig~t ~ource 16 and a base 18.
Both lens 12 and reflector 14 are jsined by ad~esive mean~ 15
to form a lens-reflector seal 19 ~or la~p lO. ~ens 12 and
reflector 14 can be formed by pressing ~ardgla~s in a mold
followed by an anneali~q pro~e~s. Lens 12 ~ypically ~a& a
slightly con~Y outer face and a~ optical pre~cription
provided, for example, by a ~erie~ of radially di~po~ed
flutes formed on ~he inner ~urface thereof defini~g a fluted
portion which ~urrounds a centrally di~po~ed ~tippled
portion, as deficribed in ~he aforementioned applicatio~
having Cana~ian Serial No. 461,058-0. Additionally, reflector 14
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has a concave inner surface 13 that includes a light
reflective coating typically comprised o~ aluminum or
silver. Reflec~or 14 is preferably a parabolic re~lector but
it can also be an eliptical reflector. Lens 12 and reflec~or
14 preferably have substantially circular peripheries and
sealing surfaces located approximately about these
peripheries, respectively.
As previously discussed, flame sealing, producad, for
example, by a flame trained on the glass reflector and lens
sealing surfaces, can crea~e unacceptable stress patterns in
envelope 11. In particular, stresses tend to concentrate
a~out the lens-reflector seal 19, resulting in cracks about
that area. The stresses created by flame sealing can be
substantially eliminated by interposing adhesive means 15
between the aforementioned peripheral sealing surfaces to
seal lens 12 to reflector 14. Acceptable adhesives for the
use indicated above are those having a curing temperature
that is equal to or higher than the operating temperature of
the lamp and a higher i.ndex of thermal expansion than the
lens and reflector material. Such an adhesive, a heat
curable epoxy, may be obtained from the Amicon Corp. of
Lexington, Massachusetts.
~ lectric lamp 10 includes a tungsten-halogen capsule 16
having an envelope containing an inert gas fill and a halogen
disposed within. Capsule 16 is disposed within and is
substantially surrounded by reflector 14 as well as being
substantially perpendicular to lens 12. Capsule 16 is
attached to and supported by mount 20. Reflec~or 14 has two
ferrule holes 22 ~hrough which the capsule-mount assembly
will be inserted and secured into place by an
eyelet-epoxy-washer combination. Each lead of mount 20 is
secured in each ferrule 22 by an eyelet 24, epoxy 26 and
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washer 28. Lamp 10 al60 includes a diode 30 and a fuse wire
32 ~oupled in serie6 with cap6ule 1~ and base 18. Envelope
11 of lamp 10 al60 includes an exhau~t hole tube 34 and a
small 6teel ball bearing 35 tha~ serve6 a~ a plug.
Envelope 11, a~ illu6trated in FIG. 1, is one example of
a lamp envelope t~at i~ al~o capa~le of con~aining glass
fragments re6ulting from a po6sible, but unlikely frac~ure of
cap~ule 16. Test re6ults ~ave shown t~at out of 60 lamp
envelope6 formed by the method described here, all of the
lamp6 6uccessfully contained glas6 fragment~ re6ulting from
intentionally induced capsule failures. Of the 50 lamp6 made
by the flame sealing technique, 3 lamp~ failed eo contain
after intentional inducement of capsule failure. Therefore,
the above described 6ealing technique results in a lamp
envelope that will reliably contain gla~s fragment~ from a
po~sible, but unlikely fracture of cap6ule 16.
Referri~g now to FIG. 2, there is illustrated a
fragmentary, cross-6ectional view of t~e len~-reflector seal
19 having a len6 ~ealing, channel-like surface A and a
reflector sealing ~urface B that are located about t~e
peripherie6 of lens 12 and reflector 14, respectively.
During a6sembly of electric lamp 10, ad~esive means 15 i8
placed between 6ealing 6urface6 A and B. Sealing 6urfaces A
and B are joined when lens 12 and reflector 14 are pre~ed
toge~er. Lamp 10 i6 then 6ubjected to a heat curing
temperature in the range of about 14B Celsius to 190
Cel~ui6 for about 5 to 40 minute~ in order to cure adhe6ive
means 15.
Contact between ~ealing surface6 A and B can degrade
quic~ly with time upon impropelly combining the different
indice6 of thermal expan~io~ of glas~ and adhesive mean~
used. For example, the index of thermal expan6ion for
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boro~ilicate glas6, conventionally used in sealed beam
auto~otive ~eadligh~, typically is about 40 ~ 10~7cm/cm/~C
(i.e., cm ~ centimeter C = Celsiu~). W~ereas ~he index of
ther~al expansion of a typically flexibilized ~poxy, suitable
for ~ealing headlight glas6ware, typically is about 40 X
10 6c~/cm/C. That i8, the indice6 of thermal expansion of
glass and adhe~ive means in a sealed beam headligh~ can
differ, by a actor of about 10. Therefore, temperature
changes, in particular decrea~ing temperature6, produce
different rates o~ contraction for t~e glas6 and interposed
adhesive mean~ creating more stre66 between the sealing
6urfaces thereby adver~ely affecting t~e gla~ lens to glass
reflector contact along the outermost ~ealing surface6 where
ad~esive means has been pre6sed away.
T~e sealing and ~tre~s problem~ found in automotive
headlights, due to t~e differing rates of contraction for the
lens and reflector ma~erial and interposed adhesive means,
also exist in PAR and ~R lamps. In addition, the sealing
problem in PAR a~d ER lamp6 i~ compounded by their higher
operating temperature ~140 Celsiu6 - 150 Celsiu~ a~
compared to headlights (about 120 Cel~iu~, which in turn
causes the failure of most adhe~ives having low toleraQce6 to
high temperature6. Adhesive means 15, of the present
invention, serve6 to alleviate 60mewhat the stre~se6 between
sealing surfaces A and B due eo it~ ability to withstand the
high compressive ~tres~ without breakdown at high operating
tem~erature6 of the lamp, and therefore provide an operative
lamp or an environment that varie6 frequently in temperature.
The present invenSion 6ignificantly reduces thermally
induced 6tresse~ by eliminating fla~e fiealing as a method of
creating a lens to reflector ~eal. Adhe~ive means 15, used
to join lens 12 and reflector 14 together, must have a curing
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temperature ~at is ~qual to or higher than the operating
temperature of lamp 10 and it must have a higher index of
thermal expansion than the material that form~ lens 12 and
reflector 14. Since the normal operating temperature of a
lamp 8UC~ as lamp 10 is u6ually abou~ 140 to 150 C~lsius,
the ad~e6i~e means used here will provide for a 6trong seal
at 6uch ~igh temperature6 due to it6 own high curing
temperature.
The material used to form lens 12 and reflector 14 i6
usually hardglass, and the predetermined index of Shermal
expansion for such a material is about 40 ~ 10 7cm/cm/~C.
Adhesive means 15 of the present invention include~ an epoxy
having a curing temperature that i6 in ~he range of about
148 Cel~ius to 190 Cel6iufi with an index of thermal
expansion in the range of about 75 - 300 X 10 7cm/cm/C.
The curing time of the epoxy îs about 5 to 40 minutes. The
epoxy currently in use has an index of thermal expan6ion of
about 150 X 107cm~cm/C, a curing ~emperature of about 160
Celsius and a curing time of about 5 minute6. In addition,
adhesive means 15 may also include ultraviolet cured epoxies
that have similar expansion and temperature charactari6tics
as the acceptable heat cured epoxie6 de6cribed earlier.
Since t~e epoxy used ~ere ha6 an index of expansion
greater t~an the hard~la~s forming the lens and reflector, a
stronger seal will result due to a compre~sive 6tress being
formed around t~e lens-reflec~or 6eal when the lamp i6 placed
in an environment with a temperature below ~at which it was
cured. This would occur during most, if not all, operating
condition~ with the lamp on or off. In addition, the need
for a specialized 6hape or form for sealing 6urfaces A and B
of lens 12 and reflector 14 is obviated by the use of the
sealing technique6 taught by the pre~ent invention. In one
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embodi~ent of the present invention, ehe lens sealiny
surface A has a channel or rece6sed por~ion and reflector
6eali~g 6urface B has a fla~ge, thereby creating a
self-aligning relationship when the lens 12 and rsflector 14
are ~ealed together by adhesive means 15 (6ee FIG. 2).
To assemble lamp 10, reflector 14 i~ fir6t of all
aluminized by placing a light reflective coating on the inner
surface 13 of reflector 14, typically comprised of aluminum
or silver. Reflector 14 i6 aluminized in such a way as to
provide an aluminum-free area near the reflec~or base where
ferrule holes 22 are lo~ated. Eyelets 24 are then placed in
ferrules 22 and a small amount of thermally cured epoxy 26 is
injected around eyele~s 24. Washer6 28 are then placed about
eyelets c4 whereupon eyelets 24 are s~aked. Capsule 16,
which i6 attached to mount 20, is then inserted into ferrules
22 and then supported by the eyelet-epoxy-washer
combination. The capsule-mount a~embly is then soldered
into place. Adhesive mean6 15, which i8 preferably a
thermally cured epoxy, i6 then a~plied to len6 12 whic~ i~
then joined with reflector 14, such that a self-aligning
relationship is c~eated. The lens-reflector as6e~bly is then
placed in an oven and brought to and kept at the requi~ite
curing temperature (about 160 Celsius~ until such time a6
the epoxy is cured (about 5 to 40 minutes). Lamp 10 i~ then
~ubjected to a brief nitrogen flu~h through exhau6t tube hole
34 located in reflec~or 14. Exhaust tube hole 34 is
thereafter plugged by using small 6teel ball bearing 35 and
an ultraviolet cured epoxy. The diode-fu~e assembly and base
18 are then ~oldered into place.
Thus, there has been 6hown and described an improved
electric lamp and method of making such a lamp which
6ubstantially reduces or eliminate6 thermally induced strain
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~n ei~er the len6 or the re~lector once ~hey have been
~oined together, unlike the ~raditional flame ~ealing
technigue. The advantages of a strain-free PAR or ~R lamp
include the following: a hig~er wa~tage tungsten-halogen
capsule may be u~ed wi~hout ~he concern that the additional
heat generated will ~au6e a 6train induced failure: t~e lamp
may be used ~ore succe6s~ully i~ severe outdoor applications
without t~e concern that a ~hermal shock will cause a lamp
envelope failure and envelope failures due to a fracture of
.lO a tungsten~alogen cap~ule will be ~ub6tantially eli~inated
in bonded beam lamps . The above de~cribed invention may be
utilized wherever the flame 6ealing technique is used in a
lamp to seal two corre~ponding and opposing members together
to form a single member.
~hile there have been shown and de6cribed what are at
present considered the preferred embodiments of the
invention, it will be obvious to those ~killed in the art
that variou~ change6 and modifications may be made therein
without departing from the scope of the invention as defined
by the appended claims.
