EP2526563B1 - Method for producing an electrode for a high-pressure discharge lamp and high-pressure discharge lamp comprising at least one electrode thus produced - Google Patents

Description

Technical area

The present invention relates to a method for producing an electrode for a high-pressure discharge lamp according to claim 1.

State of the art

The emissivity of electrodes of discharge lamps has a decisive influence on the performance and geometrical design of such discharge lamps.

The prior art is the pasting with metal powders or mixtures by means of an organic binder and the subsequent sintering or baking to the electrode body. However, the pasted and sintered layer is mechanically less stable, which can lead to partial crumbling on contact.

From the WO 2008/090030 A1 For example, a method of processing an electrode of a discharge lamp is known. In this case, the electrode is oxidized in the region in which it is pinched gas-tight in the neck of a discharge space formed of glass. The oxidation is carried out by chemical routes in normal air atmosphere and ambient air pressure at a temperature between 700 and 1300 K. The oxide layer is then sublimated in a vacuum environment, the temperature during the sublimation between 1450 K and 1900 K is. By doing so, the electrode obtains a surface of fine roughness in the above-mentioned range, whereby the adhesion of the surface of this electrode portion to the discharge vessel material is reduced. This reduces the risk of cracking in the sealed area of the discharge vessel. During the sublimation step, the oxide layer also removes any contaminants from the surface of the electrode portion, thereby also reducing adhesion.

From the US 6,626,725 B1 a discharge lamp is known in which a rod-shaped electrode made of tungsten is partially introduced into a neck of a discharge vessel by a gas-tight pinch and extends in regions in a discharge space of the discharge vessel. In order to prevent cracking of the discharge vessel in the pinch region during operation of the discharge lamp, the surface of the electrode is processed. To produce an elementary tungsten layer on the surface of the electrode in the length range in which the electrode is arranged in the pinch region, an oxide layer is first produced on the surface. In this case, for example, a tungsten trioxide layer can be produced. To produce the elemental tungsten layer, the oxidized electrode is then heated at about 1200 ° C in a hydrogen furnace in which hydrogen is bubbled into water.

The EP 1 251 548 A1 teaches a method to improve the thermal radiation characteristics of electrodes in a high-pressure discharge lamp of the short arc type. For this purpose, gutters are in the surface of the electrodes brought in. The grooves have a depth that is less than or equal to 12% of the electrode diameter, with the ratio of the depth and spacing of the grooves being greater than or equal to two. For introducing the grooves, a laser device can be used. The grooves may be angular or curved, wherein the surface is ground to produce curved grooves and then electrolytically polished in a 10% sodium hydroxide solution. However, curved grooves can also be produced by heating to a high temperature in a vacuum, for example by heating the surface at 2000 ° C for 120 minutes.

Out DE102007015243 It is known to use laser radiation for sublimation of the filament surface of a halogen lamp or also for burning / depositing material on this surface.

Presentation of the invention

The object of the present invention is to provide a method for producing an electrode for a high-pressure discharge lamp, with which the highest possible emissivity for the electrodes can be achieved. The surface of the electrode should be as mechanically resistant as possible. The object further consists in providing a high-pressure discharge lamp with at least one electrode produced in this way.

These objects are achieved by a method having the features of claim 1.

The present invention is based on the finding that a high emissivity is basically feasible when the electrode has an improved thermal Has radiation behavior. The thermal radiation behavior can be improved by enlarging the surface of the electrode. However, it must be ensured that despite increased surface area of the electrode, the conductivity of the electrode is not affected.

According to the invention, therefore, first at least a part of the electrode surface for generating an oxide layer is coated with a suitable high-energy beam, for example an electromagnetic beam, in particular a laser beam, or an electron or ion beam. By appropriate choice of the energy density while at least a portion of the resulting oxide layer is already sublimated. As an intermediate result, an electrode surface is obtained which, although extremely rough, is oxidic, that is to say has a reduced conductivity. For this reason, in a subsequent step, the non-sublimated oxide layer is reduced to the metal. The result is an extremely rough surface with a high emissivity, whereby the emissivity is adjustable depending on the structuring and oxidation. The resulting surface is mechanically very strong and very resistant. Moreover, in contrast to the known from the prior art Bepastungsvariante no additional contamination is introduced.

In contrast to the production of an oxide layer by chemical means, only partial areas can be oxidized in the method according to the invention. This is particularly advantageous for defining different functional areas on the electrode.

In comparison to the defined introduction of grooves according to the teaching of the above-mentioned EP 1 251 548 A1 can be generated by the inventive method a much larger surface and thus realize a much higher emissivity.

For example, in step a) the coating is carried out at least on a part of the electrode which is not embedded in the glass of the glass bulb after mounting the electrode in the glass bulb of the high-pressure discharge lamp. The fact that the machining can be limited to the part of the electrode which is important for the emission results in a time saving and thus a reduction in the production costs. Preferably, step a) is carried out on the atmosphere, in particular oxygen-enriched atmosphere. Since the electrode is usually made predominantly of tungsten, i. In particular from doped tungsten, and tungsten is very reactive to oxygen, so can easily generate tungsten oxide.

Further preferably, step b) is carried out at the same time as step a). When overcoating, therefore, a part of the tungsten oxide already passes through the sublimation in the gaseous state, while another part of the tungsten oxide remains on the surface of the electrode.

Step c) is preferably carried out in a hydrogen-containing atmosphere, in particular in an argon-hydrogen mixture. A preferred argon-hydrogen mixture is known as VARIGON®. This provides particularly easy the possibility that the oxygen from the tungsten oxide with the hydrogen from the atmosphere in which step c) is performed, connects to water. The pure metal remains on the electrode surface.

As already stated, the electrode preferably comprises tungsten, wherein in step c) tungsten oxide is reduced to pure tungsten.

The coating is preferably carried out in step a) by means of a laser beam device. As a result, precisely that part of the electrode surface which is important for the emissivity can be processed with particular precision. In contrast to a chemical treatment, different areas of the electrode surface can be painted over differently. By varying the modifications made on the electrode surface by means of the laser beam device, a further optimization with regard to a high emissivity can be carried out. Scanning by means of a laser beam device allows a precise adjustment of a desired emissivity with regard to the adjustable parameters such as energy density, line spacing, focus, and the like.

In this context, the laser beam device is designed, in particular, to release an energy density which makes it possible to melt, oxidize and sublime at least part of the electrode surface.

In this case, in step a), the laser beam device with a frequency between 1 kHz and 100 kHz, in particular 10 kHz, are clocked. In step a), preferably rows with a line spacing between two adjacent lines are preferably interposed on the electrode surface 0.01 and 0.2 mm, in particular 0.1 mm generated. The laser beam device is preferably operated with a laser beam focus between 0.01 and 0.1 mm, in particular 0.02 mm. In this way, the electrode surface can be maximized, whereby at the same time the emissivity of the electrode becomes maximum.

Alternatively, the overcoating can also be done with other suitable blasting devices, e.g. Electron or ion beam devices

According to a preferred embodiment of the method according to the invention, step c) is carried out at a temperature between 700 ° C. and 2500 ° C., in particular 2200 ° C. Step a), however, is preferably carried out at ambient temperature, in particular a temperature between 15 ° C and 30 ° C, and ambient pressure.

Further preferred embodiments emerge from the subclaims.

The preferred embodiments presented with reference to the method according to the invention and their advantages apply correspondingly, as far as applicable, to a high-pressure discharge lamp having at least one electrode produced in this way.

Brief description of the drawings

Fig. 1

in schematischer Darstellung eine Hochdruckentladungslampe;

Fig. 2

einen Signalflussgraphen für ein Ausführungsbeispiel eines erfindungsgemäßen Verfahrens;

Fig. 3

einen Ausschnitt der Anode der in Fig. 1 dargestellten Hochdruckentladungslampe;

Fig. 4

eine erste vergrößerte Darstellung eines ersten Ausschnitts der in Fig. 3 dargestellten Elektrodenoberfläche;

Fig. 5

eine erste vergrößerte Darstellung eines zweiten Ausschnitts der in Fig. 3 dargestellten Elektrodenoberfläche;

Fig. 6

eine vergrößerte Darstellung des in Fig. 5 dargestellten Ausschnitts; und

Fig. 7

eine vergrößerte Darstellung des in Fig. 6 dargestellten Ausschnitts.

Hereinafter, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. Show it:

Fig. 1

a schematic representation of a high pressure discharge lamp;

Fig. 2

a signal flow graph for an embodiment of a method according to the invention;

Fig. 3

a section of the anode of in Fig. 1 illustrated high pressure discharge lamp;

Fig. 4

a first enlarged view of a first section of in Fig. 3 represented electrode surface;

Fig. 5

a first enlarged view of a second section of in Fig. 3 represented electrode surface;

Fig. 6

an enlarged view of the in Fig. 5 section shown; and

Fig. 7

an enlarged view of the in Fig. 6 section shown.

Preferred embodiment of the invention

In Fig. 1 schematically a section of a high-pressure discharge lamp 10 is shown. The high-pressure discharge lamp 10 comprises a discharge vessel 12 having a discharge space 14. In the discharge space 14, a first electrode 16 (anode) and a second electrode 18 (cathode) extend. At the oval in cross-section formed central part of the discharge vessel 12 close two diametrically opposite necks 20, 22 at. The electrode 16 is melted in the neck 22, the electrode 18 in the neck 20th

The electrodes 16, 18 are arranged on rods 24, 26, which are preferably formed from tungsten or a tungsten alloy. The electrodes 16, 18 themselves consist of doped tungsten.

The process according to the invention is illustrated in more detail using the example of the electrode 16, that is to say the anode. Of course, embodiments are conceivable in which, moreover, the cathode is processed according to the method according to the invention.

The method begins in step 100. In step 120, at least part of the surface of the electrode 16 is swept over by means of a laser beam device. The energy density is so high that a part of the electrode surface melts, oxidizes and sublimates. This means that a part of the resulting tungsten oxide goes into the gaseous state, another part of the tungsten oxide remains on the electrode surface. Step 120 is preferably carried out in an oxygen-enriched atmosphere. The laser beam device can be clocked at a frequency between 1 kHz and 100 kHz, in particular 10 kHz. Preferably, lines with a line spacing between two adjacent lines between 0.01 and 0.2 mm, in particular 0.1 mm, are produced on the electrode surface. In a preferred embodiment, the laser beam device is operated with a laser beam focus between 0.01 and 0.1 mm, in particular 0.02 mm. The laser beam device, for example, a power between 50 W and 200 W, preferably about 120 W, leave. The sweeping can, for example, at a speed between 10 mm / s and 100 mm / s, in particular 30 mm / s, take place. The temperature can be ambient temperature; the pressure is preferably ambient pressure.

A preferred laser beam device is known under the name rofin rsmarker and is operated with Galvo head. The power in this embodiment is about 120 W, whereby a current of about 38 A flows. The sweeping speed is approx. 30 mm / s.

Preferably, the electrode 16 is rotatably mounted, so that the entire circumference can be structured by the laser beam device.

The step 120 creates a very rough oxidic surface. This is not defined geometrically, as will be explained in more detail below with reference to the other figures.

In step 140, the electrode 16 is preferably inductively heated in a VARIGON atmosphere. As a result, the oxidized parts of the surface are reduced by the existing hydrogen to metallic tungsten and water. The result is a metallic, very rough electrode surface with an emissivity that can be adjusted by the degree of treatment. The surface is free from contamination since, in contrast to the prior art, no binder has to be used in a pasting process. The electrode has a very good coupling-in behavior during inductive heating and is mechanically stable, ie the electrode surface shows no tendency to decay. Step 140 is preferably carried out at a temperature between 700 ° C and 2500 ° C, in particular 2200 ° C, performed.

The method according to the invention ends in step 160.

By means of the method according to the invention, it is possible to produce electrodes with an emissivity of the generated surface of up to 0.6. Thus, the range that could be achieved in the state of the art with paste, even slightly exceeded.

Fig. 3 shows an enlarged view of the area of the surface of the electrode 16 of FIG Fig. 1 in which the shape changes from cylindrical to conical. The magnification is 10: 1. The tracks of the laser processing, in particular also the overlapping areas of the laser structure, which have arisen due to the fact that the beam has run out during the application of the parallel lines in the conical region of the electrode 16, can be clearly recognized.

Fig. 4 shows an enlarged view of a section of Fig. 3 in the transition region cylindrical cone-shaped. The magnification is 1: 30. At the same magnification shows Fig. 5 a section of Fig. 3 in the cylindrical area.

With further enlargement to the factor 1: 200 shows Fig. 6 an enlarged section of the illustration in Fig. 5 , There are clearly visible ribs, with the irregularity of the surface striking the eye. Due to the irregularity results in a significant increase in the electrode surface, which can achieve high emissivities.

Fig. 7 finally, the detail of a rib shows the representation of Fig. 6 , The magnification is 1: 1000.

This illustration emphasizes the high roughness of the tungsten surface of the electrode.

Claims (12)

1. Method for producing an electrode (16) comprising tungsten for a high-pressure discharge lamp (10), comprising the following steps:

   a) scanning at least part of the electrode surface using a high-energy beam for producing an oxide layer (step 120);

   b) at least partially sublimating the oxide layer formed in step a) (step 120); and

   c) reducing the rest of the oxide layer (140).
2. Method according to Claim 1,
   characterized
   in that step a) is carried out in atmosphere, in particular in an oxygen-enriched atmosphere (step 120).
3. Method according to one of the preceding claims,
   characterized
   in that step b) is performed at the same time as step a) (step 120).
4. Method according to one of the preceding claims,
   characterized
   in that step c) is performed in a hydrogen-containing atmosphere, in particular in an argon/hydrogen mixture (step 140).
5. Method according to one of the preceding claims,
   characterized
   in that tungsten oxide is reduced to form pure tungsten in step c) (step 140).
6. Method according to one of the preceding claims,
   characterized
   in that the scanning in step a) is effected by means of a laser beam, electron beam or ion beam apparatus (step 120).
7. Method according to Claim 6,
   characterized
   in that the laser beam, electron beam or ion beam apparatus is designed to release an energy density which makes it possible for at least part of the electrode surface to be melted, oxidized and sublimated.
8. Method according to either of Claims 6 and 7,
   characterized
   in that, in step a), the laser beam apparatus is clocked at a frequency of between 1 kHz and 100 kHz, in particular 10 kHz (step 120).
9. Method according to one of Claims 6 to 8,
   characterized
   in that lines with a spacing of between 0.01 and 0.2 mm, in particular 0.1 mm, between two adjacent lines are produced on the electrode surface in step a) (step 120).
10. Method according to one of Claims 6 to 9,
    characterized
    in that the laser beam apparatus is operated with a laser beam focus of between 0.01 and 0.1 mm, in particular 0.02 mm.
11. Method according to one of the preceding claims,
    characterized
    in that step c) is carried out at a temperature of between 700°C and 2500°C, in particular 2200°C (step 140).
12. Method according to one of the preceding claims,
    characterized
    in that step a) is carried out at ambient temperature, in particular at a temperature of between 15°C and 30°C, and at ambient pressure (step 120).

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