Note: Descriptions are shown in the official language in which they were submitted.
i~-23,804 So
METHOD OF DISPENSING MOORER INTO A FLUORESCENT
LAMP AND LAMP no OPERATE WITH METHOD
TECHNICAL FIELD
This invention relates to arc discharge lamps which include
mercury and to a method for dispensing the mercury into the tamp.
It has particular application to fluorescent lamps.
BACKGROUND ART
In the past, it has been common to dispense liquid mercury into
a lamp through an exhaust tabulation. Since this procedure has on
occasion been considered an environmental hazard, as well as being
wasteful, other techniques, involving the release of mercury from a
solid after the lamp has been evacuated and sealed, have been
employed.
These other techniques have involved the use of radio frequency
(RF) induced currents in order to heat the mercury target. This has
required the use of a metal antenna loop in order to intercept and
convert the RF energy into an RF heating current.
In one such method the antenna took the form of a disintegration
shield encircling the lamp coil. This shield contained an
inter metallic Tip Hug alloy applied to one side of an oval-shaped
ribbon loop made of a base metal such as nickel or stainless steel.
The metal ribbon had a width of about 0.25 inches
Another method of mercury dispensing employing the
disintegration shield RF antenna principle was to position the
mercury target across a gap in the ribbon shield. The mercury was
contained in either a glass or metal capsule. In the case of the
glass capsule a fine wire was either wrapped around the capsule or
passed through it. The ends of the wire were then welded to each
side of the shield gap to complete the loop current path. In the
case of the metal capsule the capsule itself is welded across the
gap to complete the loop current path.
D-23,804
Previous dispensing techniques involving metal ribbon shields
have relied on the heat generated by the RF current to raise the
temperature of the metal loop or the wire or capsule across the
shield gap to the level required for mercury release. The required
temperature varied depending on the type of mercury target. The
Tip Hug alloy releases mercury by thermal decomposition within a
temperature range of 600~C to Luke. The release lime will be
lower at the higher temperature. A release time of 25 seconds is
achieved for a temperature of 900C. In the case of the glass
capsule, the wire temperature required to crack -the glass is about
Luke, and Hug release times are between 5 and lo seconds. For the
metal capsules, the mercury release is obtained when the vapor
pressure within the capsule increases to the bursting point of the
capsule design. This can vary considerably depending on the capsule
material as jell as the wall thickness. Release times of about 5
seconds have been reported using stainless steel capsule of 2 - 3
mix wall thickness.
All of these previous methods require the use of a closed loop
metal antenna to convert the RF energy to RF heating current. This
adds to the expense of the lamp and limits the minimuln release time
since a two-stage energy conversion process is required.
DISCLOSURE OF THE Invention
It is, therefore, an object of the invention to obviate the
disadvantages of the prior art.
It is another object of the invention to enhance mercury release
within an arc discharge lamp.
Yet another object of the invention is the achievement of faster
mercury release times at the expenditure of less energy.
These objects are accomplished, in one aspect of the invention,
by a mercury release mechanism Lucia includes the direct electron
heating of a mercury containing target. The mercury release is
accomplished after the exhaust, fill, and tip-off operations have
D-23,804 I I
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been performed. Imp mount modifications are employed to position
the mercury containing target in an appropriate location to receive
the electron stream.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic view of an electrical circuit
employable with the invention;
FIG. 2 is a diagrammatic view of one form of fluorescent lamp
utilizing a particular electrical connection to release mercury;
FIG. 3 is diagrammatic view of a lamp similar to the lamp of
FIG. 2 employing an alternate electrical connection; and
FIG. 4 is a diagrammatic view of an alternate lamp configuration
with an appropriate electrical connection.
BEST MODE FOR CARRYING OUT THE JNVENTIO~
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
taken in conjunction with the aDove-described drawings.
Referring now to the drawings with greater particularity, there
is shown in FIG. 1 a fluorescent lamp 10 formed of a tubular glass
envelope 11 and having ends 12 and 14.
Lamp 10 (see FIG. 2) has mounts 16 and 18 sealed within ends 12
and 14. Mount 16 comprises a glass stem 20, Lyon conductors 22
and 24 and an electrode 26 connected to the lead-ins and supporter
thereon.
Mount 18 comprises a glass stern 28, lead-in conductors 30 and 32
and an electrode 34.
A mercury containing target 36, such as a disc of lit Hug, is
mounted upon a relatively rigid support 38 which is electrically
connected to one of the lea ins, for example, 32 of mount 18. In
the embodiment shown in FOG. 2, the target 36 is positioned beyond
the plane of electrode 34: i.e., toward the center of lamp 10.
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on tune embodiment Chilean in FIG. 3 and 4, one of the mounts, for
example, aye, includes a third lead-in 40 which mounts the target
36. In this instance the target 36 it positioned between electrode
34 and stem 28.
The basic circuit arrangement For utilizing electron current to
release the mercury is shown in FIG. 1 as comprising a do power
supply 42 and a variable resistor 44. The end of the lamp 10
containing the mount to which the mercury target is attached it
connected to the positive side of the pudgier supply 42 while the
other end of the lamp 10 is connected to the negative side of the
power supply I
The current drawn through fluorescerlt lineup 10 is essentially
electron current. The primary source of electron current in the
lamp 10 is the lamp cathode which in the do circuit sown is the
electrode 26 connected to the negative side of the power supply 42.
The primary electron current generates secondary electrons through
an ionization process in the positive column of the evacuated,
filled and sealed lamp. These electrons have a random thermal
velocity as well as a drift velocity established by the tamp field
in the direction from cathode-to-anode. Electrons arriving at the
positive end of the lamp will be collected by the electrode 34, the
lead-in wires, and the mercury target 36. The electron collection
process converts the kinetic energy of the electron current into
heat energy. The quantity of heat energy produced Jill depend on
the kinetic energy of the electrons itch is directly relatable to
tile anode sheath voltage. The anode sheath voltage is related if.
the lamp current and the electron collector surface area by equation
(1) -
Us q or A
Do no
-!-
where:
Us = Anode sheath voltage
K = Boltzman gas constant
To = Electron gas temperature
q = Electron charge
= Natural logarithmic function
IL = Lamp current
Jr = The random thermal electron current density
A = The electron collector surface area.
lo By increasing the lamp current and reducing the size of the
collector surface the value of the sheath voltage is increased
The power dissipated in the anode will be equal to the product
of the sheath voltage an the lamp current.
P = V IL = - e L ~-Jr---hC (2)
In using the anode heating process-for mercury release it is
important that the mercury target 36 be positioned on the mount
structure 18 or aye in a manner which will maximize the value of
heating power. This will minimize the required release time which
is of critical importance in high speed lamp making equipment.
Optimum positioning of the mercury target 36 can be done by two
means. The first method involves use of a three-lead-wire-mount
structure aye. The mercury target 36 is attached to the isolated
third lead-in wire 40 which is then connected to the positive side
of the do power supply. This arrangement is shown in FOGS. 3 and
4. This configuration assures that the entire electron current will
be collected by the mercury target. Tiffs method will result in the
fastest mercury release time for a specified activation current
since all the current will be drawn to mercury target 36 and the
_._
collector surface area A will be limited to that of the target 36
itself. Both these factors can be seen to increase the heating
power in equation (2).
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Two variations of the three-lead-wire circuit are shown in Fogs.
3 and 4. In FIG. 4 the cathode of the discharge (the electrode 26)
is located at the lamp end opposite to tune mercury target 36. In
FIG. 3 the cathode is the electrode 34 which is at the same end of
the lamp 10 as the mercury target 36.
FIG. 2 shows the positioning of the rrlercury target 36 on a
standard two-lead-in mount structure 18. The target 36 is positioned
above the plane of the electrode 34 and close to the electrode clamp
on a lead-in wire 32. This location will result in a higher
percentage of the lamp current being collected by the mercury target
at the expense of the electrode 34 and lead-in wires 30 and 32.
This is important if the heating power in equation (2) is to be
maximized.
Activation of the mercury target 36 requires a current of
between 500 to 1000 ma depending on the size of the target 36 and
the mercury release time desired. In one test of the procedure
cylindrical stainless steel capsules were utilized having a wall
thickness of 3 miss, a length of 160 miss, and a diameter of 22
miss. The capsules were flat on the bottom and filled with 20 my of
liquid mercury and then hermetically welded at the top end. At an
activation current of 1000 ma mercury release was accomplished in
3.5 seconds.
The target 36 also may consist of a metal capsule containing
either liquid mercury, a powdered inter metallic mercury alloy, or a
solid form of the mercury alloy. Alternately, the target 36 might
consist of a glass ampule containing either the liquid mercury, or a
powdered or solid form of a mercury alloy. The glass ampule would
be contained within a cylindrical metal holder loosely crimped at
the ends or a wire-type mesh holder fashioned to hold the ampule in
place. In yet another embodiment, the mercury target 36 might
comprise a piece of metal ribbon onto which a mercury alloy has been
applied.
While there have been shown and described what are at present
considered to be the preferred embodiments of the invention, it Pill
be apparent to those skilled in the art that various changes and
modifications can be made herein without departing from the scope of
the invention as defined by the appended claims.
