Title: Device and method for retaining mercury source in low-pressure discharge lamps
Abstract: A device for retaining a mercury source in the discharge space of a low-pressure discharge lamp is disclosed. The mercury source retaining device comprises a holder, which has an inner space communicating with the discharge space and a receiver opening for receiving a mercury source. The retaining device further comprises resilient clamping means for clamping the holder in a tubular space segment of the discharge space and resilient retaining means at least partially blocking the receiver opening. The resilient retaining means are adapted for allowing a passage of the mercury source in a direction towards the inner space of the holder, but block the movement of the mercury source through the receiver opening in a direction out of the holder.
Patent Number: 6,906,460 Issued on 06/14/2005 to Busai, et al.
| Inventors:
|
Busai; Gyula (Budapest, HU);
Benkö ; Norbert (Tiszaujvaros, HU)
|
| Assignee:
|
General Electric Company (Schenectady, NY)
|
| Appl. No.:
|
064149 |
| Filed:
|
June 14, 2002 |
| Current U.S. Class: |
313/565; 315/248 |
| Intern'l Class: |
H01J 017/26; H05B041/16 |
| Field of Search: |
313/565,566,318.1,318.09,493,634
315/57,58,59,248,344
|
References Cited [Referenced By]
U.S. Patent Documents
Primary Examiner: Lee; Wilson
Assistant Examiner: A; Minh Dieu
Attorney, Agent or Firm: Fay, Sharpe, Fagan, Minnich & McKee, LLP
Claims
1. A device for retaining a mercury source in the discharge space of a low-pressure
discharge lamp, comprising
a holder comprising an inner space communicating with the discharge space and
a receiver opening for receiving a mercury source,
the holder includes resilient clamping means for clamping the holder in a generally
tubular space segment of the discharge space,
the holder further includes resilient retaining means at least partially blocking
the receiver opening, the retaining means adapted for showing a passage of the
mercury source in a direction towards the inner space of the holder, and blocking
the movement of the mercury source through the receiver opening in a direction
out of the holder.
2. The device of claim 1 in which the holder is made of a double coil, the ends
of the coil being turned towards a central axis of the coil and acting as the retaining means.
3. The device of claim 1 in which the holder is made of a sheet material formed
in an essentially cylindrical shape, the cylindrical holder comprises cylinder
segments, the cylinder segments are separated with slits extending substantially
parallel with a central axis of the cylinder, and the cylinder segments tilting
radially outward and acting as the clamping means.
4. The device of claim 3 in which ends of cylinder segments folding radially
inward and acting as the retaining means.
5. A device for retaining a mercury source in the discharge space of a low-pressure
discharge lamp, comprising
a holder comprising an inner space communicating with the discharge space, the
holder further comprising a receiver opening for receiving a mercury source,
resilient clamping means for clamping the holder in a generally tubular space
segment of the discharge space,
resilient retaining means at least partially blocking the receiver opening, the
retaining means adapted for allowing a passage of the mercury source in a direction
towards the inner space of the holder, and blocking the movement of the mercury
source through the receiver opening in a direction out of the holder, said holder
is made of a sheet material formed in an essentially cylindrical shape, said holder
comprises cylinder segments, the cylinder segments are separated with slits extending
substantially parallel with a central axis of the cylinder, said holder is formed
as a substantially frusto-conical barrel with a longitudinal slit formed substantially
along a generatrix of the barrel, and the retaining means are formed as tongues
extending radially inwards from an edge of the barrel.
6. The device of claim 1 in which a material of the device is selected from the
group containing stainless steel, molybdenum, tungsten or nickel.
7. A method for retaining a mercury source at a predetermined location in a discharge
space of a low-pressure discharge lamp, comprising the steps of:
inserting a retaining device into the discharge space, the retaining device comprising:
an inner space communicating with the discharge space and a receiver opening
for receiving a mercury source,
resilient clamping means for clamping the retaining device in a generally tubular
space segment of the discharge space, and
resilient retaining, means at least partially blocking the receiver opening,
the retaining means adapted for allowing a passage of the mercury source in a direction
towards the inner space of the retaining device, and blocking the movement of the
mercury source through the receiver opening in a direction out of the retaining
device;
clamping the retaining device at the predetermined location; and
inserting the mercury source into the retaining device through the receiver opening
and past the retaining means.
8. The method of claim 7 in which the retaining device is inserted in the discharge
space before evacuating the discharge space.
9. The method of claim 7 in which the retaining device is pushed into an end
of an exhaust tube, in a position where the receiver opening of the retaining device
turns towards an outer end of the exhaust tube.
10. The method of claim 9 in which the mercury source is pushed through the receiver
opening with a pushing rod, whereby the mercury source is inserted in the retaining device.
11. The method of claim 9, in which the discharge space is filled with a filling
gas, and the mercury source is blown through the receiver opening with the filling gas.
12. The method of claim 9 in which the evacuated discharge space is sealed after
inserting the mercury source.
13. The method of claim 7 in which the mercury source is inserted in the retaining
device after evacuating the discharge space.
14. A low-pressure discharge lamp comprising a discharge space, a discharge electrode
and a mercury source located in a predetermined location of the discharge space,
in which the mercury source is retained in a retaining device, the retaining device comprising
a holder comprising an inner space communicating with the discharge space and
a receiver opening for receiving a mercury source,
resilient clamping means for clamping the holder in a tubular space segment of
the discharge space,
resilient retaining means at least partially blocking the receiver opening, the
retaining means adapted for allowing a passage of the mercury source in a direction
towards the inner space of the holder, and blocking the movement of the mercury
source through the receiver opening in a direction out of the holder.
15. The discharge lamp of claim 14 in which the retaining device is frictionally
retained in an end of an exhaust tube, the exhaust tube connects to a stem supporting
the discharge electrode.
16. The discharge lamp of claim 14 in which the mercury source is an amalgam.
17. The discharge lamp of claim 14 in which the mercury source is a pellet containing
liquid mercury.
18. A device for retaining a mercury source in a discharge space of a low-pressure
discharge lamp, comprising:
a holder comprising an inner space communicating with the discharge space and
a receiver opening for receiving a mercury source;
the holder includes resilient clamping members for clamping the holder in a tubular
space segment of the discharge space; and
the holder further includes resilient retaining members at least partially blocking
the receiver opening, the retaining members adapted for allowing a passage of the
mercury source in a direction towards the inner space of the holder, and blocking
the movement of the mercury source through the receiver opening in a direction
out of the holder.
19. A method for retaining a mercury source at a predetermined location in a
discharge space of a low-pressure discharge lamp, comprising the steps of:
inserting a retaining device into the discharge space, the retaining device comprising:
an inner space communicating with the discharge space and a receiver opening
for receiving a mercury source,
resilient clamping members for clamping the retaining device in a tubular space
segment of the discharge space, and
resilient retaining members at least partially blocking the receiver opening,
the retaining members adapted for allowing a passage of the mercury source in a
direction towards the inner space of the retaining device, and blocking the movement
of the mercury source through the receiver opening in a direction out of the retaining
device;
clamping the retaining device at the predetermined location; and,
inserting the mercury source into the retaining device through the receiver opening
and past the retaining members.
Description
BACKGROUND OF INVENTION
This invention relates to a device and a method for retaining a mercury source
in the discharge space of a low-pressure discharge lamp. The invention also relates
to a lamp equipped with the device.
A wide variety of low-pressure discharge lamps are known in the art. These lamps
contain small doses of mercury, which radiates under the influence of the discharge
arc. The mercury may be introduced into the discharge space of the lamp in a number
of ways. One possible method is the introduction of an amalgam, typically containing
bismuth, e.g. a Biln or BiSnPb compound. The mercury vapour necessary for the operation
of the lamp is released from the amalgam. The amalgam is optimally positioned near
a cold spot of the lamp, for example near a tip of the discharge tube. Another
method uses a so-called pellet, which contains liquid mercury. The mercury is released
from the pellet after the sealing of the discharge space with the help of a heat
treatment of the pellet. Both an amalgam or a pellet must be prevented from rolling
freely about in the discharge space, as it may collide with the electrodes and
it could scratch off the light emitting layer from the internal surface of the
discharge vessel.
A known method to position the amalgam is to insert it into an exhaust tube of
the discharge vessel. The amalgam is then held in a predetermined location with
various methods. In the method disclosed in U.S. Pat. Nos. 5,629,584 and 5,434,482,
the amalgam is held in place with indentations on the exhaust tube and glass balls
before and after the amalgam. However, this structure has certain disadvantages.
The tube section of the discharge vessel must be held in a vertical position, otherwise
the glass balls and the amalgam will not remain in the desired location during
the so-called tip-off, i. e. when the exhaust tube of the lamp is sealed and the
remaining excess length of the tube is removed. In certain production lines, this
is not always feasible, and there is a need for an amalgam retaining method where
the amalgam is held in place irrespective of the orientation of the tube, which
receives the amalgam.
A discharge lamp with an amalgam container is disclosed in U.S. Pat. No. 6,201,347.
In this known discharge lamp, the container is held in place with the help of a
resilient, coiled wire, which is attached to the container with the amalgam. The
container and the coiled wire are pushed into a tube within the discharge space
of the discharge lamp. The coiled wire acts as a clamping means, which substantially
prevents the movement of the container within the tube.
Another discharge lamp with an amalgam container is disclosed in U.S. Pat.
No. 6,137,236. In this known discharge lamp the container is held in place with
the help of a resilient body, which surrounds the container with the amalgam. The
resilient body is provided with radially extending portions, which press against
a wall of a tube within the discharge space of the lamp. The extending portions
of the resilient body keep the container in a predetermined location within the
tube. When the container is not inserted in the resilient body, the radially extending
portions of the body are somewhat retracted, and the resilient body may be inserted
into the tube with ease. The extending portions spread when the container is pushed
into the resilient body.
Though the retaining methods disclosed in U.S. Pat. Nos. 6,137,236 and 6,201,347
are practicable in any orientation of the discharge vessel, other problems remain.
For various reasons, it is desirable to insert the mercury source into the discharge
space only after an evacuation of the discharge vessel, and only shortly before
the final sealing of the discharge vessel. However, the containers with the amalgam,
as disclosed in U.S. Pat. Nos. 6,137,236 and 6,201,347, require relatively complicated
equipment, if the containers must be fed into the tube in the evacuated state of
the tube. Further, the containers need to be inserted into the tube in a predetermined
position (orientation) relative to the tube. This requires further specialised
positioning means in the feeding equipment, which must operate in vacuum. Such
an equipment is complicated, hence expensive[007]Therefore, there is a need for
a method for retaining a mercury source, which allows the insertion of the mercury
source into the discharge space in vacuum, and which does not require complicated
manufacturing facilities, and which may be integrated into all types of existing
production lines in a simple manner.
SUMMARY OF INVENTION
In an exemplary embodiment of the present invention, a device for retaining a
mercury source in the discharge space of a low-pressure discharge lamp comprises
a holder with an inner space. The inner space of the holder is in communication
with the discharge space. The holder further comprises a receiver opening for receiving
a mercury source, and resilient clamping means for clamping the holder in a tubular
space segment of the discharge space. The holder also comprises resilient retaining
means. The function of the resilient retaining means is to block the receiver opening,
at least partially. The retaining means are adapted for allowing a passage of the
mercury source in a direction towards the inner space of the holder, and blocking
the movement of the mercury source through the receiver opening in a direction
out of the holder.
In an exemplary embodiment of another aspect of the invention, a method for retaining
a mercury source at a predetermined location in a discharge space of a low-pressure
discharge lamp is provided. In this method, a retaining device as described above
is inserted into the discharge space of the discharge lamp. The retaining device
is clamped at the predetermined location in the discharge space. This is followed
by the insertion of the mercury source into the holder through the receiver opening
and past the retaining means.
In an embodiment of still another aspect of the invention, a low-pressure discharge
lamp comprises a discharge space, a discharge electrode and a mercury source located
in a predetermined location of the discharge space. In the lamp, the mercury source
is retained in a retaining device as described above.
The resilient retaining means of the retaining device makes it possible to insert
the retaining device into the discharge space in an early stage of the production,
while the mercury source itself may be fed into the retaining device in the very
last moment before the discharge space is sealed. In this manner, no or a negligible
amount of mercury vapour escapes from the discharge vessel during production, and
mercury contamination of the production equipment remains low.
As a further important advantage, the suggested retaining device remains in its
position—practically in an exhaust tube of the discharge vessel—,
in an arbitrary orientation of the exhaust tube. This advantage may be exploited
especially at horizontal manufacturing of linear fluorescent lamps, which in turn
results in increased productivity of the manufacture.
BRIEF DESCRIPTION OF DRAWINGS
The invention will now be described with reference to the enclosed drawings where
FIG. 1 is a perspective view of a low-pressure discharge tube manufactured according
to the method.
FIG. 2 is an enlarged cross section of an end portion of the lamp shown in FIG.
1, with an embedded electrode assembly, taken along the plane II—II of FIG. 1.
FIG. 3 is an enlarged view of an exhaust tube in the end portion shown in FIG.
2, with the inserted retaining device and the mercury source within the retaining device,
FIG. 4 is a cross section of the exhaust tube and a top view of the retaining
device, seen in the plane IV—IV in FIG. 3.
FIG. 5 is another cross section of the exhaust tube and a bottom view of the
retaining device, seen in the plane V—V in FIG. 3.
FIG. 6 illustrates a ball-formed mercury source being inserted in the retaining
device in a view similar to FIG. 6.
FIG. 7 is a perspective view of another embodiment of the retaining device.
FIG. 8 shows a cross-section of the exhaust tube with the retaining device of
FIG. 7 being inserted, in a view similar to FIG. 6.
FIG. 9 is a perspective view of yet another embodiment of the retaining device.
FIG. 10 illustrates the insertion of the retaining device into the exhaust tube
of the discharge lamp.
FIG. 11 is an enlarged view of a part of FIG. 10.
FIG. 12 illustrates a first step during the insertion of a mercury source into
the retaining device, in partial cross-section.
FIG. 13 illustrates a subsequent step in the insertion of a mercury source into
the retaining device, following the step shown in FIG. 12.
FIG. 14 illustrates another insertion method for the insertion of the mercury
source into the retaining device.
FIG. 15 is a cross-section of the end of the discharge tube with inserted mercury
source and the sealed exhaust tube.
DETAILED DESCRIPTION
Referring now to FIGS. 1 to
3, there is shown a low-pressure discharge
lamp
1 in the form of a straight light tube. The lamp
1 has a sealed
discharge vessel
2. A cap
4 covers the ends
22 and
24
of the discharge vessel
2, and also holds the electric contacts
8
of the lamp. The contacts
8 are mechanically supported by an insulating
plate
6, which latter is embedded in the cap
4. The contacts
8
are welded to the ends of lead-through wires
10 and
12. The wires
10,
12 connect to a filament
14.
The discharge vessel
2 of the low-pressure discharge lamp
1 encloses
a discharge space
16. The filament
14 functions as a discharge electrode,
which is located in the discharge space
16. For the proper operation of
the discharge lamp
1, a mercury source
18 is also provided in the
discharge space
16. In the shown embodiment, the mercury source
18
is an amalgam, for example made of a BilnPb compound, which is capable of forming
an amalgam alloy with mercury.
The mercury source
18 is located in a predetermined location of the discharge
space
16. In the shown embodiment, the mercury source
18 is located
in an end of an exhaust tube
20. The exhaust tube
20 connects to
a stem
26 supporting the discharge electrode, i. e. the filament
14.
This arrangement of the stem
26 and the exhaust tube
20 at the ends
of the discharge vessel
2 is well known in the art, and needs no further explanation.
In order to retain the mercury source
18 in the predetermined location
of the discharge space
16, the discharge lamp
1 comprises a retaining
device
30, which will be explained in detail below. The mercury source
18
is retained in the retaining device
30, and in this manner it permanently
remains in the predetermined location.
In the embodiment shown in FIGS. 3 to
6, the retaining device
30
is made as double wire coil
31 as best seen in FIG.
3. The central
windings and the ends of the coil
31 act as a holder, which surrounds the
mercury source
18. In this manner the holder of the retaining device
30
comprises an inner space, which communicates with the discharge space
16.
This is necessary to allow an unhindered passage of the mercury vapours from the
mercury source
18 into the discharge space
16.
The holder of the mercury source
18 also has a receiver opening
32
for receiving the mercury source
18 as will be explained with reference
to FIGS. 12 to
14. In the embodiment shown in FIGS. 3 to
5, the receiver
opening
32 is defined as the opening surrounded by the last windings and
the two ends
34,
36 of the coil
31. The receiver opening
32
is best seen in FIG. 6, which shows the retaining device
30 from the ends
34,
36 of the coil
31. As it is apparent from FIG. 5, the distance
between the ends
34,
36 of the coil
31 are only slightly smaller
than the diameter of the ball-shaped mercury source
18. As a comparison,
the tip
38 of the coil
31, where the two strands of the coil
31
are joined, substantially closes the inner space in the holder of the retaining
device
30, and prevents any passage of the mercury source
18 between
the windings of the coil
31.
The retaining device
30 is equipped with resilient clamping means. These
serve to clamp the mercury source holder in a tubular space segment of the discharge
space, typically in the exhaust tube
20 as shown in FIGS. 2 and 3. In the
embodiment where the retaining device
30 is made as the double coil
31,
the central windings
40,
42 of the coil
31 act as the resilient
clamping means. In the non-stressed state of the coil
31, the external diameter
of the central windings
40,
42 is slightly larger than the internal
diameter D of the exhaust tube
20. In this manner, when the coil
31
is inserted into the exhaust tube
20, the central windings
40,
42
are compressed, and press against the internal surface
44 of the exhaust
tube
20. Due to the friction between the coil
31 and the wall of
the exhaust tube
20, the retaining device
30 remains at the location
where it has been inserted.
The retaining device
30 is further equipped with resilient retaining means.
In the embodiment shown in FIGS. 3 to
6, the retaining means is embodied
by the ends
34 and
36 of the coil
31. The ends
34 and
36 are folded back, so they partly turn towards a central axis of the coil
31. In this manner, the retaining means, i.e. the ends
34 and
36
are at least partially blocking the receiver opening
32, as best seen in
FIG.
5. The retaining means are adapted for allowing a passage of the mercury
source
18 in a direction towards the inner space of the holder. At the same
time, the retaining means are blocking the movement of the mercury source
18
through the receiver opening
32 in a direction out of the holder. In the
embodiment shown in FIGS. 3 to
6, this works as follows: the flexible resistance
of the ends
34,
36 is relatively easily surmounted, and the ends
34,
36
yield to the external force and spread, when the mercury source
18 is pushed
in the inner space of the retaining means
30 between the two ends
34,
36
of the coil. This is shown in FIG. 6, which shows the ends
34,
36
as they spread while the mercury source
18 passes between them. However,
when the mercury source
18 would move out of the retaining device
30,
for example under the force of gravity, or because of its inertia, the retaining
means, i. e. the folded ends
34,
36 of the coil
31 show sufficient
resistance for preventing the movement of the mercury source
18 out of the
inner space of the retaining device
30. It is assumed that the mercury source
18 inserted into the retaining device
30 is itself not capable of
exerting a force that is large enough to press it again out from the retaining
device
30.
In the embodiment shown in FIGS. 3 to
6, the retaining device
30
is made of resilient wire material, typically made of stainless steel, molybdenum,
tungsten or nickel. As explained above, in this case the mercury source holder
of the retaining device is constituted by the double coil
31 itself, where
the ends
34,
36 of the coil are folded back, and turned at least partly
towards a central axis of the coil
31. In this manner, the ends
34,
36
act as the retaining means of the retaining device
30 embodied by the coil
31.
Another embodiment of the retaining device
30 is shown in FIGS. 7
and 8. This retaining device
30 also comprises a holder part with an inner
space and receiver opening, resilient clamping means for clamping the holder in
a tube of the discharge space
16, and resilient retaining means at least
partially blocking the receiver opening.
In the retaining device
30 of FIG. 7 and 8, the mercury source holder
is
a substantially cylindrical capsule
130. The capsule
130 is made
of a sheet material formed in an essentially cylindrical shape. In order to facilitate
the insertion of the retaining device
30, i. e. the capsule
130 into
the exhaust tube
20, the external diameter of the capsule
130 at
the closed end
132 is positively smaller than the internal diameter D of
the exhaust tube
20. As best seen in FIG. 7, the cylindrical holder of the
capsule
130 comprises cylinder segments
134 and
136. In the
shown embodiment, one cylinders segments
134 are relatively wide, while
other segments
136 are somewhat narrower. The cylinder segments
134,
136
are separated with slits
138. The slits
138 are substantially parallel
with a central axis of the cylinder.
In the embodiment shown in FIGS. 7 and 8, the clamping means of the retaining
device
30 is constituted by the wide cylinder segments
134. In the
non-stressed state of the capsule
130, the segments
134 are tilting
radially outward. When the capsule
130 is inserted into the exhaust tube
20, the segments
134 press against the internal surface of the exhaust
tube
20, and thereby hold the capsule
130 in place.
At the same time, the resilient mercury source retaining means of the capsule
130 are constituted by the free ends
140 of the narrow cylinder segments
136. These free ends
140 are folding radially inward, toward a central
axis of the capsule
130. In this manner the receiver opening
32 of
the mercury source holder is surrounded by the free edges
142 of the cylinder
segments
134, and the ends
140 protrude into the receiver opening
32, at least partly blocking it. The ends
140 of the segments
134
are folded slightly towards the inner space of the capsule
130, and the
ends
140 also act as resilient retaining means which are adapted for allowing
a passage of the mercury source
18 through the receiver opening
32
in a direction towards the inner space of the holder. At the same time, the ends
140 are capable of blocking the movement of the mercury source
18
through the receiver opening in a direction out of the capsule
130.
Similarly to the coil
31, the capsule
130 may be manufactured
of stainless steel, molybdenum, tungsten, nickel, or any other material which is
suitably resilient, and which does not destroy the discharge atmosphere in the
discharge space
16.
Another embodiment of the mercury source retaining device
30 is shown
in FIG.
9. Here, the mercury source holding part of the retaining device
30 is formed as a substantially frusto-conical barrel
230. As with
the capsule
130, the retaining device
30 constituted by the barrel
230 is made of a resilient sheet material. The clamping of the barrel
230
in the tubular segment of the discharge space
16 is ensured by the flexibility
of the external shell of the barrel
230. A longitudinal slit
232
is formed substantially along a generatrix of the barrel
230, which means
that the circumference and thereby the diameter of the barrel
230 may decrease
when the barrel
230 is inserted into the exhaust tube
20 of the discharge
vessel
2.
The retaining means of the retaining device
30 constituted by the barrel
230 are formed as tongues
240. The tongues
240 extend radially
inwards from an edge
242 of the barrel
230, substantially towards
the principal central axis of the barrel
230. The tongues
240 function
substantially in the same manner as the folded ends
140 of the segments
134 of the capsule
130. This means that the receiver opening
32
of the barrel
230 is defined by the surrounding edge
242, and this
receiver opening
32 is partly blocked by the tongues
240, because
the diameter of an included circle between the tips
244 of the tongues
240
is smaller then the external diameter of a ball-shaped mercury source
18
(not shown in FIG.
9). However, the tongues
240 also yield to an
external pressing force when a ball-shaped mercury source
18 is pressed
into the inner space of the barrel
230 between the tongues
240.
The mercury source retaining device
30 is suitable for retaining a mercury
source
18 at a predetermined location in the discharge space
16 of
the low-pressure discharge lamp
1. The method, in which the retaining device
30 is used, is explained with reference to FIGS. 10 to
15. These
illustrate the use of a retaining device
30 formed as a double-ended coil
31, but the other embodiments of the retaining device
30 are used
in a similar manner.
In a first step, as shown in FIG. 10, the retaining device
30 is inserted
into the discharge space
16. More precisely, the retaining device
30
is inserted into its final position, in the shown embodiment into that end of the
exhaust tube
20, which is closer to the stem
26 holding the filament
14. In this manner, the mercury source
18 is located in a relatively
cold place, which is sufficiently far from the discharge arc and also far from
the thermal load which arises when the other end of the exhaust tube
20
is sealed.
The retaining device
30 is pushed into the exhaust tube
20 by a
suitably formed tool, e.g. a rod
50 with a positioning pin
52 at
the end thereof. The diameter of the rod
50 and that of the pin
52
is selected to ensure a loose fit in the exhaust tube
20 and in the retaining
device
30 during insertion. In this manner the rod
50 is easily withdrawn
from the exhaust tube
20 and also from the retaining device
30, while
the latter remains in the exhaust tube. As the retaining device
30 is inserted,
the wall of the exhaust tube
20 slightly compresses the windings
40
and
42 of the coil
31. If necessary, the rod
50 and the coil
31 may be rotated during insertion in order to make the compression of the
coil
31 even easier (in the shown embodiment the rotation is counter-clockwise).
For this purpose, the rod
50 may comprise suitable extensions to cause the
simultaneous rotation of the coil
31. Thereby the coil is "screwed" into
the exhaust tube.
The retaining device
30 is pushed into the exhaust tube
20 in a
position where the receiver opening
32 of the retaining device
30
turns towards an outer end of the exhaust tube
20. This means that in the
shown embodiment, the receiver opening
32 is to the right, and the positioning
pin
52 of the pushing rod is inserted into the retaining device
30
through the receiver opening
32. When retaining devices in the form of the
capsule
130 or the barrel
230 are to be inserted, the positioning
pin
52 may comprise suitable grooves, which loosely receive the ends
140
of the segments
134 or the tongues
240, without positively engaging
those. In this manner the rod
52 may be withdrawn, without pulling out the
capsule
130 or the barrel
230 from the exhaust tube
20 while
the retaining device
30 is clamped at the predetermined location of the
discharge space
16.
Advantageously, the retaining device
30 is inserted in the
discharge space
16 before the discharge space
16 is evacuated. This
means that the equipment, which feeds the retaining devices
30 into the
production line and onto the rod
50, need not be in vacuum. This makes the
feeding and positioning of the retaining devices
30 easier.
Following the insertion of the retaining device
30, the mercury
source
18 is inserted into the holder of the retaining means
30.
The mercury source
18 is inserted through the receiver opening
32
and past the retaining means, i. e. past the ends
34,
36 of the coil
31 in the shown embodiment. This may also take place before evacuation,
but it is preferred to insert the mercury source
18 in the holder of the
retaining device
30 after evacuating the discharge space. Thereby the emission
of mercury vapours into the ambient atmosphere is minimized.
The mercury source
18 may be pushed through the receiver opening
32
of the retaining device
30 with another, suitably formed pushing rod
60.
For the sake of proper positioning and feeding of the mercury source
18,
the pushing rod
60 may comprise an external sheath or sleeve
62,
the end
64 of which snugly receives the ball-shaped mercury source
18.
The sleeve
62 and the rod
60 are pushed until the unit reaches the
retaining device
30. Thereafter the rod
60 pushes the mercury source
18 out from the end
64 of the sleeve
62, and into the retaining
device
30 through its receiver opening
32.
In another version of the method, the mercury source insertion process utilises
the energy of a filling gas, such as argon. After evacuation of the discharge vessel
2, which is symbolised with the flange
70 of the evacuating equipment,
the filling gas is fed into the discharge space
16 before the latter is
sealed. The mercury source
18 is inserted into the input end of the exhaust
tube
20, and thereafter the mercury source
18 is blown through the
receiver opening
32 with the filling gas. This is illustrated in FIG.
14.
For this purpose, the mercury source
18 needs to develop sufficient inertia
to surmount the resistance of the resilient retaining means, which block the receiver
opening
32.
Finally, as illustrated in FIG. 15, the evacuated discharge space
16
is sealed at the outer end
28 of the exhaust tube
20 after the insertion
of the mercury source
18 into the retaining device
30. The sealing
is done in a known manner, by melting the outer end
28 of the exhaust tube
20.
In the above embodiments, the mercury source
18 was an amalgam. However,
the retaining device and method is also applicable if the applied mercury source
is a so-called pellet, which contains liquid mercury. Such pellets are activated
after the sealing of the discharge space. The carrier materials of such pellets—e.g.
zinc—are known in the art. The release of the mercury from the pellet is
normally activated with a short thermal pulse. With suitable adjustment of the
production equipment, the thermal pulse may be delivered during the sealing of
the exhaust tube.
The invention is not limited to the shown and disclosed embodiments, but other
elements, improvements and variations are also within the scope of the invention.
It is clear for those skilled in the art that the same principles may be applied
to other types of low-pressure discharge lamps, and not only to straight light
tubes such as shown in FIG.
1. For example, the proposed mercury source
retaining device is applicable with all types of mercury vapour lamps
*
