DE20210400U1 - Electrode system for metal halide lamp comprises electrically conducting bushing and electrode having unit for interlocking within connecting region consisting of recess in shaft of electrode - Google Patents

Abstract

Electrode system comprises an electrically conducting bushing (9) and an electrode with a shaft (16) connected to it. The bushing and electrode have a connecting region with fused material in which the electrode is embedded with its end of the shaft facing the bushing. The electrode has a shaft made from tungsten. The electrode has a unit for interlocking within the connecting region consisting of a recess in the electrode shaft. An independent claim is also included for a metal halide lamp with the above electrode system and containing a ceramic discharge vessel made from Al2O3.

Description

Patent Trust Company

for electric light bulbs mbH., Munich

Electrode system for a metal halide lamp and associated lamp

Technical area

The invention is based on an electrode system for a metal halide lamp and associated lamp according to the preamble of claim 1. These are in particular lamps with a power of at least 20 W, preferably from 100 W, up to powers of 400 W, possibly over 1000 W.

State of the art

EP-A 587 238 discloses a metal halide lamp with a ceramic discharge vessel in which a two-part feedthrough in an elongated plug capillary is sealed by means of glass solder at the end of the plug remote from the discharge. The outer part of the feedthrough is made of permeable material (niobium pin), the inner part of halide-resistant material (for example a pin made of tungsten or molybdenum). For higher lamp outputs (up to about 400 W), a different solution is used, namely replacing the inner Mo pin part with a cermet part. Its thermal expansion coefficient can be adjusted as required between that of other metal parts and that of the ceramic.

The disadvantage of such solutions is that the connection between the inner part of the feedthrough and the electrode is very susceptible to breakage. This applies both during further processing of the electrode system and in

Lifespan behavior of the system during lamp operation. Ultimately, kinked electrodes can cause the discharge vessels to burst during operation.

WO 01/82331 attempts to circumvent this by arranging the feedthrough in several parts. However, this does not solve the basic problem adequately. The diameter of the electrode is generally smaller than that of the inner part, and the two components are connected by melting the end of the inner part and embedding the end of the electrode in it. Melting is often done by brazing or laser soldering. The inner part is usually made of molybdenum or Mo-containing cermet. However, the melting amount on the inner part cannot be ensured in a reproducible manner within the required accuracy. This could be remedied by increasing the melting length. However, this is contradicted by the limitation of the maximum permissible "welding projection height". This refers to an elevation that results from a local accumulation of weld metal or solder in the area of the welding or soldering zone. It can also be slag (particularly in the case of a cermet joint). The maximum permissible degree of elevation is determined by the minimum permissible capillary inner diameter of the discharge vessel.

Description of the invention

It is an object of the present invention to provide an electrode system according to the preamble of claim 1, wherein the connection between the feedthrough and the electrode is designed in such a way that it can permanently withstand mechanical and thermal stresses.

This object is achieved by the characterizing features of claim 1. Particularly advantageous embodiments can be found in the dependent claims.

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According to the invention, a means for positive locking, in particular a notch or groove, is provided near the end of the electrode facing the feedthrough. It is provided so close to the end of the shaft that it is encased by the feedthrough material from the melting area. The means comprises at least one local depression or notch. A circumferential depression is preferred, which can be V- or U-shaped, rectangular or trough-shaped. The notch can be produced, for example, by grinding or punching.

This notch can be an irregular or regular reduction in the cross-section of the electrode. In particular, it is a circumferential notch or groove in a U or V shape. When connecting the feedthrough to the electrode, which is usually done by soldering (hard or laser soldering) or welding, an additional form fit is now achieved, which increases the mechanical load-bearing capacity of the connection. The amount of rejects resulting from an unacceptably large weld/solder zone elevation is also reduced, as a reservoir is now available for the excess melt or slag.

An additional advantage is that the recess offers a provisional fixing option for a possible coil at the end of an extended electrode shaft remote from the discharge, which is then finally and particularly securely fixed by melting the end region of the feedthrough, similar to the fixing option known from US-A 5 451 837.

The feedthrough can be made in one piece from the materials described above, or it can be constructed in two or more parts, with the outer part made of niobium or another hydrogen-permeable material, while the inner part has the properties explained above that favor the connection with the shaft. The inner part can be replaced by an extended shaft of the electrode, so that the inventive

appropriate connection technology is applied to the connection between the remaining outer feedthrough part and the correspondingly extended core pin.

The known structure of ceramic discharge vessels also comprises an elongated capillary tube (hereinafter referred to as a plug capillary), through which an electrically conductive, one- or two-part feedthrough, which consists of an inner part and an outer pin-shaped part with respect to the discharge, is passed in a vacuum-tight manner.

The feedthrough is usually sealed on the outside of the plug using glass solder. An electrode with its shaft is attached to the inside of the feedthrough and extends into the interior of the discharge vessel.

The lamp power is preferably between 20 and 400 W, but higher powers (2000 W and more) are also possible.

The attached table shows the dimensions for different lamp wattages (35, 70 and 150 W) of the following parts:

lamp Core pin AD
[μαιλειη] Groove depth
&Tgr;&iacgr;&mgr;&eegr;&eegr;&idiagr; Width
B γμ&igr;&tgr;&igr;&idiagr; End distance
[μαιλειη] execution AD [μαιδια] Melting
area Performance material 200 30 50 50 material 560 Length [μ&igr;&tgr;&igr;] 35 W 300 50 100 50 Mo or Nb 680 150 70 W 300 60 70 70 Mo or Nb 680 225 70 W 500 70 100 70 Mo or Nb 800 225 150 W 500 90 80 70 Cermet with Mo
or Nb 800 270 150 W Cermet with Mo
or Nb 250

Core pin: material and outer diameter in pm;

Groove in the core pin: depth T, width B and distance of the groove from the end of the pin remote from the discharge, each in μιδια;

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Implementation: material and outer diameter in pm;

Melting area: Length of the connection area between both components in pm.

The connection between the two components, feedthrough and core pin, is made by laser soldering.

Preferably, the ratio of the depth of the notch T and its width B is in the range B/T = 1:1, in particular it should be between 0.8 and 2.2. For stability reasons, the remaining outer diameter of the core pin in the area of the notch should be at least 60% of the original diameter, preferably 65 to 75%.

In the case of a two-part feedthrough, the inner end region of the feedthrough (hereinafter referred to as the melting region) which is in contact with the electrode is made of Mo, W, or a cermet which contains Mo or W in an amount which makes it weldable. The diameter of both parts to be connected can be approximately the same in this embodiment. The electrode is preferably made of tungsten. Its first end is embedded in the connection region, the second end faces the discharge. The shaft of the electrode can also be coated with a coil, preferably made of molybdenum, to limit the dead volume, as is known per se.

Alternatively, it is possible to replace the inner part of the current feedthrough by means of an extension of the electrode core pin (usually made of tungsten) to the outer feedthrough part (usually made of niobium), in accordance with EP-A 1 056 115. The thus extended shaft of the electrode can also be coated with a coil, preferably made of molybdenum, to limit the dead volume, as is also practiced with the 2-part current feedthrough (EP-A 587 238).

The feedthrough or at least its outer part in the case of a two-part feedthrough consists of an outer part (in particular a pin or tube made of niobium, but the use of tantalum is also possible) which is thermally expanded to match the (aluminum oxide) ceramic and permeable to H2 and O2, which is covered with glass solder and sealed.

In the case of a two-part feedthrough, the inner part of the feedthrough consists of a halide-resistant metal (preferably molybdenum or tungsten or their alloys) or a corresponding cermet. The material is preferably molybdenum. The inner part is only partially covered at its outer end with glass solder and melted in. The inner part is in particular a pin made of cermet or molybdenum or of the higher-melting tungsten. The tungsten can have a rhenium additive, either as an alloy or as a plating on the surface. The rhenium increases the high temperature load capacity and corrosion resistance of the tungsten. While molybdenum is particularly suitable for mercury-containing fillings, W is advantageously used for mercury-free fillings. In particular, W is also suitable for relatively low-wattage lamps from 70 W.

The inner part of the two-part feedthrough is connected on one side to the outer part (niobium pin or tube) and on the other side to the electrode. The inner part itself can be constructed in several parts, as described for example in WO 01/82331.

The stopper can be made of one piece or several pieces. For example, a stopper capillary can be surrounded by an annular stopper part in a manner known per se.

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Short description of the drawings

The invention will be explained in more detail below using several exemplary embodiments. They show schematically:

Figure 1 shows a metal halide lamp with a ceramic discharge vessel;

Figure 2 shows the electrode system of the lamp of Figure 1 in detail;

Figure 3 shows the connection area of the electrode system of Figure 2 with

differently shaped notches (a to d);

Figure 4 shows a further embodiment of the connection area;

Figure 5 shows a further embodiment of the connection area;

Figure 6 shows another embodiment of an end region.

Preferred embodiment of the invention

Figure 1 shows a schematic of a metal halide lamp with an output of 150 W. It consists of a cylindrical outer bulb 1 made of quartz glass that defines a lamp axis and is pinched (2) and capped (3) on both sides. The axially arranged discharge vessel 4 made of Al2O3 ceramic is cylindrical or bulbous in shape and has two ends 6. It is held in the outer bulb 1 by means of two power supply lines 7 that are connected to the base parts 3 via foils 8. The power supply lines 7 are welded to bushings 9, each of which is fitted into an end plug 12 at the end 6 of the discharge vessel. The plug part is designed as an elongated capillary tube 12 (plug capillary). The end 6 of the discharge vessel and the plug capillary 12 are, for example, directly sintered together.

The feedthroughs 9 each consist of two parts. The outer part 13 is designed as a niobium pin and extends into the capillary tube 12 up to about a quarter of the length. The inner part 14 extends inside the capillary tube 12 towards the discharge volume. It holds discharged

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electrodes 15 on the discharge side, consisting of an electrode shaft 16 made of tungsten and a coil 17 pushed onto the end of the shaft on the discharge side. The inner part 14 of the feedthrough is laser-soldered to the electrode shaft 15 on the one hand and laser-welded to the outer part 13 of the feedthrough on the other. The niobium pin 13 is inserted about 3 mm deep into the stopper capillary 12 and sealed using glass solder 10.

The discharge vessel is filled with an inert ignition gas, e.g. argon, mercury and metal halide additives. It is also possible to use a metal halide filling without mercury, for example, whereby xenon is the preferred ignition gas and a high pressure, well over 1.3 bar, can be selected.

An electrode system is shown in detail in Fig. 2. A system consisting of a niobium pin (or tube) as the outer part 13 and a molybdenum pin as the inner part 14 serves as the feedthrough 9.

The niobium pin 13 is butt-welded to the inner part 14 made of molybdenum on the discharge side. On the discharge side, the inner part 14 is soldered to the electrode shaft 16 in the same way.

The alternative is to use an inner part 14 made of cermet with a high content of Mo, balance AI2O3.

The shaft 16 has a diameter of 0.4 mm. The diameter of the inner part is 0.8 mm, that of the outer part is 0.88 mm. The inner part 14 therefore has a diameter 100% larger than the electrode shaft 16.

Figure 3a shows the principle of the connection according to the invention. Depending on the lamp power in question, a circumferential groove 18 is provided approximately 0.5 mm to 2 mm from the feedthrough-side end of the electrode shaft 16. It has, also depending on the power, a

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Depth of 0.5 to 2 mm and a width of 0.5 to 2 mm. During laser soldering (arrow), the melting area 25 extends beyond the groove 18, which is rectangular here. The melted molybdenum serves as solder for embedding the tungsten shaft 16. The groove enables additional form-fitting and serves as a reservoir for excess melt or the slag produced when cermet is separated.

Alternatively, the groove can also have a circumferential recess with a differently shaped cross-section, in particular a V-shaped recess 26 (Fig. 3b) or a trough-shaped recess 27 (Fig. 3c). A further alternative is a form-locking means consisting of two opposing notches 28 in the shaft (Fig. 3d).

In a particularly preferred embodiment (Figure 4), a coil 20 made of molybdenum is applied to the shaft 36, which is greatly extended and therefore replaces the inner lead-through part, to displace the dead volume. The last coil 21 is held in the groove 18. During manufacture, this provides a provisional fixation until laser welding is carried out to produce the melting area.

Figure 5 shows an embodiment in which the feedthrough 30 (made in one piece from niobium) is brazed or welded to the extended core pin 31 made from tungsten. Both components have approximately the same outside diameter. The means for the positive locking is a notch 32. The connection area 33, which can contain material from both components, is shown here very schematically.

Figure 6 shows a further embodiment in which, in addition to the first groove 37 remote from the discharge, a second groove 38 near the front, discharge-side end of the shaft 39 ensures that the second coil end can also be fixed. The coil is not shown. Advantages

This is particularly due to the simplification of the automatic position orientation for the subsequent laser soldering. Both notches 37 and 38 are groove-shaped with sloping side walls.

Claims (12)

1. Electrode system for a metal halide lamp, comprising an electrically conductive feedthrough ( 9 ) and an electrode connected thereto with a shaft ( 16 ), wherein the feedthrough and the electrode have a connection region with melted material, in which the electrode is embedded with its end of the shaft facing the feedthrough, and wherein the electrode has a shaft made of tungsten, characterized in that the electrode has a means for positive locking within the connection region, which consists of at least one recess in the shaft of the electrode. 2. Electrode system according to claim 1, characterized in that the feedthrough consists of an inner part ( 14 ) and an outer part ( 13 ), wherein the electrode is connected to the inner part. 3. Electrode system according to claim 2, characterized in that the inner part consists of a weldable cermet. 4. Electrode system according to claim 1, characterized in that the feedthrough and the electrode shaft are cylindrical, the diameter of the feedthrough being 80 to 200% of the diameter of the electrode shaft. 5. Electrode system according to claim 1, characterized in that the means for positive locking is a local or circumferential recess or groove on the shaft. 6. Electrode system according to claim 5, characterized in that the recess is U- or V-shaped 7. Electrode system according to claim 6, characterized in that the maximum penetration depth T is 25 to 40% of the diameter of the shaft. 8. Electrode system according to claim 1, characterized in that the means is spaced 0.1 to 2 mm from the end of the shaft facing the feedthrough. 9. Electrode system according to claim 1, characterized in that the electrode additionally comprises a coil at the end remote from the discharge, which coil encases the shaft, wherein the end of the coil facing the feedthrough is anchored in the recess on the shaft. 10. Metal halide lamp with an electrode system according to claim 1 11. Metal halide lamp according to claim 10, characterized in that the lamp contains a ceramic discharge vessel, in particular made of Al ₂ O ₃ . 12. Metal halide lamp according to claim 11, characterized in that the discharge vessel has two ends ( 6 ) which are closed with ceramic stoppers, each of which contains an elongated capillary tube ( 12 ), hereinafter referred to as stopper capillary, and wherein an electrically conductive feedthrough ( 9 ) is led through this stopper capillary ( 12 ), wherein an electrode ( 16 ) with a shaft ( 15 ) is fastened to the feedthrough and projects into the interior of the discharge vessel.