Note: Descriptions are shown in the official language in which they were submitted.
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High-pressure discharge lamp
Technical field
The invention proceeds from a high-pressure discharge lamp in accordance with
the preamble of claim 1. It is, in particular, metal halide lamps, chiefly
versions
with a base at one end, which are under consideration here. However, sodium
high-
pressure lamps or mercury high-pressure discharge lamps are also suitable.
Prior art
EP-A 566 975 has already disclosed a high-power high-pressure discharge lamp
in
which a discharge vessel is held in an outer bulb by means of a frame. In this
case,
at least one supply lead of the discharge vessel is connected in an
electrically
conducting fashion to a frame pari.
To date, welding (point welding or resistance welding) has been customary as
the
connecting technique. Hard soldering by means of a nickel-copper alloy (Ni-Cu)
is
used as an alternative. In the case of high currents, in particular those of
more than
20 A, both techniques turn out to be disadvantageous, because the high contact
2 5 resistance renders the thermal loading of the connecting point excessive.
The
service life of such lamps is therefore limited to 150 hours.
Summary of the invention
3 0 It is the object of the present invention to provide a high-pressure
discharge lamp
in accordance with the preamble of claim I which has a reliable connection,
which
can bear high loads, between electrically conducting parts and thereby permits
an
extended service life.
3 5 This object is achieved by means of the characterizing features of claim
1.
Particularly advantageous refinements are to be found in the dependent claims.
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According to the invention, use is now made of nickel and/or zirconium as
solder
between the electrically conducting parts to be connected. The thermal loading
of
the soldered joint is thereby substantially reduced, because the contact
resistance is
very low. Consequently, it is easily possible to achieve large-area contact
between
the lamp parts to be connected. The contact area is larger by at least a
factor of 10
than in the case of welding.
This technique can be applied particularly effectively in the case of parts
made
from molybdenum, since nickel makes a good connection with molybdenum. This
technique is also suitable whenever the diameter of the parts is relatively
large, in
particular larger than 2 mm. The parts to be connected are frequently wires
with a
diameter of 1 to 5 mm.
The solder made from pure nickel (or zirconium) is in this case firstly
applied as
wire in annular form or as a cylinder and then heated. Its melting point is at
more
than 1300°C (Ni: 1450°C; Zr: 1850°C). The soldered
connection is preferably
produced by induction. It is advantageous in this case when large-area contact
between the two parts to be connected is produced by winding the second part
2 0 around the first part.
In detail, the present invention relates to a high-pressure discharge lamp
having
electric current conductors and having an outer bulb in which a discharge
vessel is
held by means of frame parts, supply leads being led out at the ends of the
2 5 discharge vessel. At least one connection between two current conductors,
hereinafter referred to as a first and a second electrically conducting lead,
is
produced by a soldered connection which uses nickel and/or zirconium as
solder.
In particular, the first lead is a frame part and the second lead is a supply
lead.
3 0 However, the connection can also relate to two frame parts or various
parts of a
supply lead or lead-through. Of course, an arbitrary number of connections can
also be implemented inside the lamp, or also in the base region outside the
outer
bulb of the lamp by means of the soldered connection according to the
invention.
3 5 The leads are normally wires (and/or pins or bars) having a diameter of up
to 7
mm. A practical lower limit is 1 mm. However, differently shaped parts (for
example plates) can also be connected in this manner to other parts.
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At least one, preferably both leads are produced from molybdenum. The reason
for
this is that molybdenum makes a particularly intimate connection with nickel
and/or zirconium.
In a particularly preferred embodiment, the operating current of the lamp is
more
than 20 A. Currents of 100 A can also be managed.
The connection according to the invention is of great importance in the case
of a
lamp in which a discharge vessel sealed at two ends is held by means of a
frame in
an outer bulb sealed at one end.
In order to achieve a connection between the two parts to be connected over as
large an area as possible, it is advisable for one of the two leads to be
wound
around the other lead. Reliable contact is achieved with one to three turns.
Figures
2 0 The invention is to be explained in more detail below with the aid of a
plurality of
exemplary embodiments. In the drawing:
Figure 1 shows a metal halide lamp, partially in section.
2 5 Description of the drawings
Figure 1 represents the design of a high-pressure discharge lamp according to
the
invention with a base at one end. The high-pressure discharge lamp described
here
in the exemplary embodiment is a metal halide lamp for photooptical purposes
3 0 having a power consumption of 6 kW.
The high-pressure discharge lamp has a discharge vessel 1 sealed at two ends
and
made from quartz glass, in which an ionizable filling gas and two electrodes 2
are
enclosed.
The discharge vessel 1 is held by means of a bipartite frame 3, 4 in an outer
bulb 5
which is sealed at one end and evacuated (or also filled with nitrogen). The
outer
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bulb 5 is essentially axially symmetric. Its end 6 near the base is cemented
in a
ceramic base 7. The base 7 has a high-voltage endurance of more than 70 kV.
A long frame bow 3 runs along the discharge vessel 1 to the dome-shaped end 8,
remote from the base, of the outer bulb, and is connected there by means of
two
turns 10 to a supply lead 9 which is led out axially from the discharge
vessel. The
supply lead and the bow are soldered with the aid of nickel solder 11 in the
region
of the turns. This supply lead 9 remote from the base is fixed in an exhaust
tip 12
in the dome 8 of the outer bulb. The long bow 3 is partially sheathed in a
quartz
glass tube 13 which is inserted in an extension tube 20 in the end 6 of the
outer
bulb 5 near the base.
In a similar way, a short frame bow 4, which is arranged parallel to the long
bow 3,
is also surrounded by a quartz glass tube 14 and held in the end 6 near the
base.
The bow 4 is connected to the supply lead 15, which is led out from the end 6
of
the discharge vessel near the base, by virtue of the fact that here, as well,
the wire
of the bow 4 is wound around the supply lead 15. Here, as well, nickel solder
16 is
used for soldering in the region of the connecting point.
2 0 The bows 3, 4 made from molybdenum are connected in each case via solid
litz
wires 17 to contact pins 18 at the end of the base. The cavities inside the
base are
filled up with a ceramic sealing compound 19 with high-voltage endurance.
By comparison with a lamp of the same design with point welding as a
connection
2 5 between the supply lead and frame bow, this lamp achieved a service life
which
was longer by more than 300%. Instead of 150 hours, more than 600 hours are
reached.
In the case of a lamp of identical design in principle and having 10 kW,
zirconium
3 0 is used instead of nickel as the solder 11. The reason for this is that Zr
can be
subjected to even higher thermal loads, since it has a higher melting point.
It has
not been possible to date to use both solders, since it is necessary to ensure
very
rapid heating of the parts to be soldered so that excessive heating and
oxidation,
initiated thereby, of the adjacent parts are prevented. The best results can
be
3 5 achieved with the aid of a heating process operating inductively. The
overall
soldering operation (from melting of the annular solder up to the distribution
of the
solder as far as into the turns) lasts approximately 10 to 15 seconds.
