Note: Descriptions are shown in the official language in which they were submitted.
6.~3~
~RC TUBE FAB~ I CATION P~OC~SS
C~OSS REFERENCE TO OTHE~ APPLICATIONS
The following concurrently filed Canadian pate~t applications
relate to un~aturated vapor presfiure type high pres~ure ~odium lamps
and the fabrication thereof: 4~8,953-5, la48,955-1; 44~.916-1; and
~8,gl5-2.
TECHNICAL FIELD
This invention relate~ to the manu~acture of high pressure
sodium lamp~ of the unsaturated vapor type and more particularly to
a proce~s for fabricating arc tubes for use in high pressure sodium
lamps of the unsa~urated vapor types.
BACKGROUND A~T
In the manufacture of high pressure sodium la~ps, it i6 a nor~al
practice to provide a tubular ceramic arc tube which i6 6upported
within an evacuated envelope ~hich i6, in turn, affixed to an
ordinary ~crew-in type base member. Usually. the arc tube i~ filled
with an excess amount of ~odium in an attemp~ to compensate for
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undes;red losses thereof during operation of the lamp. Thus,
available high pressure sodium lamps are, for the most part, of the
so-called saturated vapor type and are known to provide undesired
. variations in lamp voltage and color rendition because of this
; ~ saturated condition.
In an effort to eliminate or at least reduce such undesired
effects, it has long been known that a lamp wherein the amount of
sod;um and ~ercury employed is only that which will become totally
vaporized would provide the desired result. In other words, a high
pressure sodium lamp of the unsaturated vapor type wherein sodium
and mercury are introduced in only such an amount as to become
totally vaporized is a highly desirable structure insofar as
efficiency, cost of manufacture and enhanced lighting capability are
concerned.
lS However, one of the major problems encountered in the
~abrication of unsaturated vapor high pressure sod;um lamps is the
introduction therein of the proper amounts of sodium and mercury.
Since the sodium content is of a relatively small amount and sodium
is such a chemically active material, it has been found most
difficult to dose or introduce the proper amount thereof into the
arc tube of an unsaturated vapor high pressure sodîum lamp.
One known suggestion for dosing an arc tube for a high pressure
sodium lamp with the proper amount of sodium and mercury is set
forth in U.S. Patent 4,156,550, issued to Furukubo et al on May 29,
1979. Therein, sodium azide (NaN3) was dissolved in a solvent,
placed in a container and the solvent evaporated. Also, a mercury
dispenser in the form of an Al-Zr-Ti-Hg alloy was placed in the
container. Thereafter, the container was positioned within one
exhaust pipe affixed to the arc tube, and this one exhaust pipe was
closed or pinched off. Another exhaust pipe or tube was affixed to
the other end of the arc tube and to an exhaust system. The exhaust
tube having the container therein was heated to decompose the sodium
and mercury-containing compounds and provide the desired sodium and
mercury within the arc tube. Also, the arc tube was evacuated and
re-filled with a starting gas.
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Although the above-described technique may or may not be
employed in an unsaturated vapor high pressure sodium lamp
fabrication process, it is submitted that the process leaves
something to be desired. More specifically, the process appears to
be relatively expensive of components, procedural steps and
apparatus. For example, the suggested exhaust tubes of niobium are
relatively expensive and not readily available in ordinary high
pressure sodium lamp manufacturing facilities.
OBJECTS AND SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved
high pressure sodium lamp manufacturing process. Another object of
the invention is to enhance the fabrication of an arc tube for use
in an unsaturated vapor high pressure sodium lamp. A further object
of the invention is to reduce the complexity of fabricating an arc
tube for an unsaturated high pressure sodium lamp.
These and other objects, advantages and capabilities are
achieved in one aspect of the invention by an arc tube fabricating
process wherein a first electrode is sealed into one end of a
tubular ceramic envelope, a sodium-mercury amalgam and an
oxygen-absorbing getter are disposed therein, the envelope is
exhausted and then filled with a low pressure noble gas and a second
electrode is sealed into the opposite end of the tubular ceramic
envelope.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an elevational view of an unsaturated vapor high
pressure discharge lamp of the invention;
FIG. 2 is an exploded isometric view of the arc tube of the
discharge lamp of FIG. l; and
FIG. 3 is an enlarged section of one end of the arc tube of
FIG. 2.
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BEST MODE FQR CARRYING OUT T~IE INVENTION
For a better understanding of the present invention, together
with other and further objects, advantages and capabilities thereof,:
reference is made to the following disclosure and appended claims in
; 5 connection with the accompanying drawings.
- Referring to the drawings, FIG. 1 illustrates an unsaturated
vapor high pressure sodium lamp having a hermetically sealed and
evacuated glass envelope 5 formed to fit into an ordinary screw-type
base member 7. A glass stem member 9 is sealed to the envelope 5
and projects therein~ Electrical conductors, 11 and 13
respectively, are sealed into and pass through the stem member 9 to
provide electrical connections from the interior to the exterior of
the glass envelope 5.
An electrically conductive support member 15 is affixed to one
of the electrical conductors 11 and has a pair of crossbars 17 and
1~ affixed thereto at either end. Also, a plurality oF spring-like
members 21 are affixed to the support member 15 and formed for
contact with the glass envelope 5. Moreover, a pair of getters 23
and 25 are attached to the support member 15 and serve to insure the
2U integrity of the evacuated envelope 5.
~ Disposed within the glass envelope 5 and supported by the
; crossbars 17 and 19 is an arc tube 27. This arc tube 27, preferably
of a materîal such as polycrystalline alumina for example, includes
an electrode 29 and 31 at either end thereof. One electrode 29 is
affixed to and supported by the crossbar 17 while the other
electrode 31 is insulat;ngly supported by the other crossbar 19, but
electrically connected to the electrical conductor 13 passing
through the stem member 9. Heat conserving elements 33 may be
wrapped about the arc tube 27 at each end thereof in the vicinity of
the electrodes 29 and 31 in order to reduce the heat differential
thereat from the center of the arc tube 27.
As to fabrication of the above-mentioned arc tube 27, reference
is made to the exploded view of FIG. 2 and enlarged view of FI~. 3.
A ceramic envelope 35 of a material, such as a polycrystalline ~
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alumina for example, has an apertured end of reduced diameter 37 and
39 affixed to either end thereof. A first electrode member 41 has a
support portion 43 with outwardly extending fins 45 and an attached
electrode portion 47.
An apertured ceramic wafer ~9 is telescoped over the electrode
portion 47 and placed in contact with the outwardly extending fins
45. Then, an apertured glass frit wafer 51 is telescoped over the
; electrode portion 47 and into contact with the apertured ceramic
wafer 49. Thereafter, the electrode portion 47 of the first
electrode member 41 is inserted into the ceramic envelope by way of
the apertured end 37. Heat is applied to the one end of the
envelope 35, apertured wafer 37, glass frit wafer 51, apertured
ceramic wafer 49 and electrode member 41 in an amount sufficient to
hermetically seal the electrode member 41 ;nto the cera~ic
envelope 35.
The ceramic envelope 35 having a hermetically sealed end portion
is usually trans~erred to an inert atmosphere, such as a we11-known
inert atmosphere glove box. Therein, a sod;um-mercury amalgam is
introduced into the envelope 35 by way of the opposite or unsealed
end of the envelope 35. Moreover, the mercury may be in the form of
a metal alloy or mercuric oxide decomposable to provide the desired
mercury vapor.
Also, an ~xygen-absorbing getter is introduced into the ceramic
envelope 35 by way of the opposite or unsealed end thereof. The
getter is a metal alloy which is preferably selected from the metal
group consisting of aluminum, titanium, scandium, hafnium, cerium,
lanthanum, thorium, yttrium and z;rconium. Also, other rare earth
or actinide metals are applicable so long as the oxygen-absorbing
capabilities are present.
Follow;ng, a second electrode member 53 having a support portion
55 with outwardly extending fins 57 and an attached electrode
portion 59 has an apertured ceramic 61 telescoped over the electrode
portion 59 and ;nto contact with the outwardly extending fins 57.
An apertured frit wafer 63 is also telescoped over the electrode
portion 59 and contacts the apertured ceramic 61. The electrode
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portion 59 of the second electrode member 53 is placed in the other
end of the ceramic tube 35 with the frit wafer 61 in loose contact
therewith.
A noble or rare gas such as xenon is introduced into the ceramic
envelope 35 by way of the unsealed end whereat the second electrode
member 53 is loosely located. Preferably, the noble or rare gas is
employed to flush the ceramic prior to being introduced there;n at a
given desired pressure. Thereafter, the second electrode member 53
is frit sealed into the opposite end of the ceramic envelope 35 to
provide a desired arc tube 27. Moreover, the arc tube 27 is
supported within an evacuated glass envelope, in a manner well known
in the art to provide an unsaturated vapor high pressure sodium lamp.
While there has been shown and described what is at present
considered the preferred embodiments of the invention, it will be
obvious to those skilled in the art that various changes and
modifications may be made therein without departing from the
invention as derined by the appended claims.
