EP1987531B1 - High-pressure discharge lamp having a ceramic discharge vessel - Google Patents

Description

Technical area

The invention is based on a high-pressure discharge lamp with a ceramic discharge vessel according to the preamble of claim 1. It can be high-pressure discharge lamps, as used in particular for general lighting.

State of the art

From the EP-B 639 853 For example, a metal halide lamp is known in which the dead volume in the ceramic discharge vessel, which has a capillary for receiving the leadthrough, is reduced by the fact that a tungsten electrode has a very long shaft which extends into the capillary. In this case, the relatively thin shaft is encased with a sleeve which is adapted to the inner diameter of the capillary.

Presentation of the invention

It is an object of the present invention to provide a high-pressure discharge lamp according to the preamble of claim 1, in which the risk of damage to the electrode is minimized. In addition, an extension of the life is desired.

These objects are achieved by the characterizing features of claim 1. Particularly advantageous embodiments can be found in the dependent claims.

The invention describes an electrode system for HID AC lamps, consisting of a W electrode, which consists of a rotationally symmetrical body and is divided into two parts with different diameters, such as an attached thereto implementation, which is arranged in a capillary. The invention reduces the dead volume in the capillary very reliably and with high accuracy.

Preferably, there is a welded joint between the electrode and the bushing. This is brought to an uncritical temperature by the length of the electrode, which projects far into the capillary. This reduces the risk of breakage or kinking of the electrode due to temperature influences.

In detail, according to the invention, a high-pressure discharge lamp with a ceramic discharge vessel is described, in which two electrodes and a light-emitting filling are contained, wherein at the ends of the discharge vessel capillaries sit, in which passages are sealed, which are each connected to an electrode made of tungsten. In this case, the electrode is pin-shaped and made up of two parts of different diameter, wherein the first part with a given diameter D1 forms the electrode tip and the second part with a diameter D2 sits in the capillary, wherein the diameter D2 of the second part at least 108% the total length L of the electrode is divided between the first part with a partial length L1 and the second part with a partial length L2, that L2 constitutes about 30 to 70% of the total length L, and wherein the beginning of the maximum diameter D2 coincides with the beginning of the capillary or deviates from it by a maximum of 10% of the length L.

Preferably, the diameter D2 of the second part is at least 95% of the inner diameter ID of the capillary, so that the dead volume is minimized.

In particular, the second part is connected to the passage through a weld. It is also recommended that the diameter of the bushing be at least 10% exactly the diameter of the second part.

In this case, the transition between D1 and D2 can be made abruptly by means of a step, but it can also be beveled, so that a gradual transition arises.

Since the electrode is made of one piece, the diameter D2 should not exceed 160% of D1, otherwise there will be too much waste.

Optimum thermal management can be achieved by providing additional thickening on the first part near the tip. These may be an integral head, or even a coil, which is pushed onto the first part. preferred is the integral head, since it can be easily made in one operation, which reduces the waste. Preferably, the maximum diameter of the head is therefore the same as that of the second part. The heat capacity can be adjusted over the length of the head. Alternatively, the diameter of the head, D3, may be between D1 and D2.

Preferably, the electrode and the electrode system is used for high-pressure discharge lamps, the filling of which contains metal halides.

Advantageously, the ratio of the diameters of the first and second part of the electrode can now be set very precisely and adjusted in particular so that the second part is closely matched to the inner diameter of the capillary. In particular, the values should be between 1.3 and 1.6. A typical value is a factor of 1.4.

On the first part often sits an electrode head, which in particular by a coil, a sleeve or massive thickening, as known per se, can be realized. But he can also be a pin without thickening.

At the diameter of the first, the plasma-facing portion of the electrode requirements are different from the larger diameter of the rear second, the melting facing part. The electrode is preferably made of tungsten or similar refractory material, especially a high tungsten compound.

The front, the plasma-facing first part of the W electrode should dissipate just enough heat that the temperature of the electrode tip on the one hand is not so high that unnecessarily high evaporation of tungsten, on the other hand, the heat dissipation should not be so large that in the cathode phase (AC operation) sputtering occurs. These requirements determine an optimum of the diameter of the W electrode tip in the front part.

For the optimal diameter of the rear part, namely the melting of the facing shaft portion of the electrode, other criteria apply. The optimum diameter is mainly due to the availability of the shank part with the cermet, molybdenum, Nb (Zr) - u./o. further conceivable Kapillardurchführungsbauteile determined in the direction Glasloteinschmelzung. These requirements set an optimum the diameter of the second part. It is determined by the condition that the ratio between the capillary feedthrough and the electrode stem portion is preferably between 0.5 and 1.0, including limits.

Inventive electrodes for discharge lamps are made of high temperature resistant metal. Tungsten, molybdenum, tantalum, rhenium or alloys thereof are particularly suitable, but also carbides of these metals, in particular tantalum carbide (TaC).

The electrodes are made of blanks of appropriate dimensions by turning, grinding, drilling, etching, etc. Particularly preferred is a laser method as in DE 42 06 002 described. Optionally, deformation work is additionally introduced by suitable manufacturing processes, such as rolling and hammering, in order to increase the structural stability of the electrode materials. High-temperature-resistant metals, such as, for example, W, Ta, Mo, Re or their alloys, which are in some cases additionally doped, are used as electrode materials in order to increase the structural stability of the materials. The doping is preferably carried out to stabilize the structure with elements such as K, Al and Si and additionally with oxides, carbides, borides, nitrides and / or the pure metals (or their alloys) of rare earth elements, lanthanides, actinides such as La, Ce, Pr, Nd, Eu, Th, but also Sc, Ti, Y, Zr, Hf. They serve not only to stabilize the structure, but also to lower the electron work function.

In a particularly preferred first embodiment, one-piece electrodes, in particular made of tungsten, are produced, wherein the complex contour may have a rear part as a second part, which is cylindrical, and a front part as a first part, which may have a head.

It is possible to produce high-density bodies with typically 98% (even up to more than 99%) of the theoretical density.

In particular, an optimization of the heat flow behavior of electrodes is achieved. Machining here is often purely mechanical through cutting tools. So far, a drop of up to about 60% had to be accepted for such electrodes. Here, however, a laser sublimation method can be applied, which is based on the specifications of DE-A 42 06 002 based. In particular, the shaft length of the W electrode can now be designed to be completely variable. So far, the problem is known that the junction between the previously used two parts, which is usually a weld, is thermally overloaded when too close to discharge in lamp operation. This is the case when the connection of W electrode for implementation is placed too close to the end of the capillary in the direction of discharge volume. Care must be taken so far that the temperature at the junction is not more than 1500 K, more preferably not more than 1300 K. The result is then a kinking of the W electrode at the connection point, which is usually a weld. If the W electrode touches the inner wall of the capillary, cracks in the capillary occur, through which the filling escapes from the discharge vessel. This shortens the life and the lamp goes out.

The different requirements for the two parts of the W electrode are now best met by the fact that the electrode is integral and that the tungsten material is removed in the front first part of the W electrode. This is best done by mechanical, chemical or thermo-mechanical methods such as laser ablation.

The present application also relates to a high-pressure discharge lamp with such an electrode, in particular with metal halide filling, as of the type forth already from the EP-A 1 056 115 is known.

Extending the electrode into the capillary without increasing the diameter of the second part produces a very large dead volume with the known negative consequences. This dead volume usually leads to larger Farbtemperaturstreuungen, which in turn can be compensated only by a load increase. An increase in charge in turn results in an increase in Wiederzündspitzens voltage. As a result, the risk of premature extinguishment of the lamp increases.

The diameter of the second part should therefore be adapted to the inner diameter of the capillary as well as possible and so fill the dead volume. The end of the electrode can be moved as far back into the capillary, up to 70% of the total length L of the electrode.

characters

Figur 1

eine Metallhalogenidlampe mit keramischem Entladungsgefäß;

Figur 2

eine Elektrode gemäß der Erfindung im Detail;

Figur 3 - 4

je ein weiteres Ausführungsbeispiel einer Elektrode im Detail;

Figur 5

den Endbereich der Lampe der Figur 1 mit Elektrodensystem im Detail;

Figur 6

ein weiteres Ausführungsbeispiel eines Elektrodensystems.

In the following the invention will be explained in more detail with reference to several embodiments. Show it:

FIG. 1

a metal halide lamp with a ceramic discharge vessel;

FIG. 2

an electrode according to the invention in detail;

FIGS. 3 to 4

each a further embodiment of an electrode in detail;

FIG. 5

the end of the lamp FIG. 1 with electrode system in detail;

FIG. 6

another embodiment of an electrode system.

Description of the drawings

In FIG. 1 schematically a metal halide lamp with a power of 150 W is shown. It consists of a lamp axis defining cylindrical outer bulb 1 made of quartz glass, which is squeezed on two sides (2) and socketed (3). Of course, the lamp can also be closed on one side and be provided, for example, with a screw base. The axially arranged discharge vessel 4 made of Al ₂ O ₃ ceramic is cylindrical or bulbous and has two ends 6. It is held in the outer bulb 1 by means of two power supply lines 7, which are connected to the base parts 3 via foils 8. The power supply lines 7 are welded to bushings 9, which are each fitted in an end plug at the end 6 of the discharge vessel. The end plug is designed as a long capillary tube 12 (plug capillary). The end 6 of the discharge vessel and the stopper capillary 12 are, for example, directly sintered together. An electrode 15 is located on the discharge side on the bushing.

The passage 9 is in each case designed as a multi-part pin and projects into about three quarters of the length of the capillary tube 12 into this. A two-part electrode shaft 16 made of tungsten extends within the capillary tube 12 towards the discharge volume and has a helix 17 which is pushed onto the discharge-side end.

The filling of the discharge vessel is in addition to an inert ignition gas, such as argon, from mercury and additives to metal halides. It is also possible, for example, the use of a metal halide filling without mercury, wherein As ignition gas, for example xenon and in particular a high pressure, well above 1.3 bar, can be selected.

The pin 9 is inserted into the stopper capillary 12 and sealed by means of glass solder 19.

In FIG. 2 For example, an electrode 15 is shown in detail. It is important that the electrode is an integral component. The diameter of the front part 25 is D1 and the diameter of the rear part 26 is D2. The total length of the electrode is L. The length of the first part 25 is L1 and the length of the second part 26 is L2. The transition between the two parts is a step 27.

In FIG. 3 For example, an electrode 15 is shown in which the first part 25 has a head 28 which is also made integral. Its diameter is D3, its length is L3, where D1 <D3 ≤ D2.

In FIG. 4 For example, an electrode 30 is shown in which the head is a separate coil 31. It is further shown that between the first part 25 and the second part 26, a slope 33 is used as a transition.

In Fig. 5 the electrode system 35 is shown in detail in the plug 36. As a passage 9 is a pin, for example, as in FIG. 6 shown a two-piece pin, the first part near discharge 38 is a cermet of Mo and Al ₂ O ₃ , and the second part 39 consists of niobium or NbZr or MoV. The implementation may for example also be partially encased by a helix. The second part 26 of the electrode has approximately the same diameter as the pin and is welded thereto. This is followed by the discharge side of the first part 25, whose diameter is significantly smaller, both parts are made of one piece. The first part may be pin-shaped, or may have a solid part or a coil as the head. In this case, the diameter of the second part should preferably be at least 10%, at most 60% greater than the diameter of the first part. The minimum value applies in particular if the electrode is pin-shaped. The step 27 between the two parts should coincide approximately with the end of the capillary. The mismatch A should be less than 10% of the length L. A typical value for A is 1 mm.

In FIG. 6 a further embodiment of an electrode system in the capillary is shown. It is preferred that the diameter D2 of the second part 26 of the electrode is between 120 and 140% of the diameter D1 of the first part 25. The diameter D2 of the second part should preferably approach as close as possible to the inner diameter ID of the capillary. It should be at least 95%, preferably at least 98% thereof.

Also important is the relative assignment in the axial direction. It should preferably, based on the beginning of the capillary, the second part of the electrode approximately flush or slightly recessed or be prominent, so for example, be used in a depth A up to 1 mm, in the capillary.

It is also advantageous that the connection point 40 is located as deep as possible in the capillary for implementation. It should have a depth T of for example 3 to 6 mm, this value also depends on the Wattage of the lamp.

The implementation is in particular made up of two parts, namely a cermet as an inner and a niobium pin as a further outer part. Both parts of the bushing preferably have approximately the same diameter as the second part of the electrode and should deviate a maximum of 10% thereof. Thus, the dead volume is minimized throughout.

Welding, but also mechanical fitting into a groove, etc. come into question as the connection technology between the second part and the bushing. However, a weld is preferred because it provides the safest hold.

Claims (9)

1. High-pressure discharge lamp having a ceramic discharge vessel, in which two electrodes and a light-producing filling are contained, capillaries resting at the ends of the discharge vessel, in which capillaries leadthroughs are sealed off, which leadthroughs are each connected to an electrode made from tungsten, rhenium or a mixture or alloy of the two elements, possibly with an addition of conventional dopings, characterized in that the electrode is in the form of a pin and integrally comprises two parts with different diameters, the first part with a given diameter D1 forming the electrode tip, and the second part with a diameter D2 resting in the capillary, the diameter D2 of the second part making up at least 108% of the diameter D1 of the first part, the total length L of the electrode thus being split between the first part with a part length L1 and the second part with a part length L2, with L2 making up approximately 30 to 70% of the total length L, and the beginning of the maximum diameter D2 coinciding with the beginning of the capillary or deviating from this by a maximum of 10% of the length L.
2. High-pressure discharge lamp according to Claim 1, characterized in that the diameter D2 of the second part is at least 95% of the inner diameter ID of the capillary.
3. High-pressure discharge lamp according to Claim 1, characterized in that the second part is connected to the leadthrough by means of welding.
4. High-pressure discharge lamp according to Claim 1, characterized in that the diameter of the leadthrough corresponds to the diameter of the second part to an accuracy of at least 10%.
5. High-pressure discharge lamp according to Claim 1, characterized in that the transition between D1 and D2 takes place suddenly by means of a step.
6. High-pressure discharge lamp according to Claim 1, characterized in that the diameter D2 makes up at most 160% of D1.
7. High-pressure discharge lamp according to Claim 1, characterized in that an additional thickened portion is fitted on the first part in the vicinity of the tip.
8. High-pressure discharge lamp according to Claim 1, characterized in that the filling contains metal halides.
9. High-pressure discharge lamp according to Claim 1, characterized in that the electrode material is doped with at least one of the elements K, Al, Si, Y.

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