EP0901150A2 - Electrode, procedure and device for its manufacture - Google Patents

Abstract

The electrode (4) is made of wolfram material, which may be doped and has cylindrical shaft (5) with a conical point (9) which is formed by radial deformation of the shaft, e.g. using radial hammering or transverse rolling, for increasing the hardness in the vicinity of the point.

Description

Technical field

The invention is based on an electrode according to the preamble of the claim 1. It is in particular an electrode for high-pressure discharge lamps like xenon or mercury lamps.

State of the art

The process for making electrodes from tungsten is based on how known, on the pressing and subsequent sintering of the tungsten powder. The blank produced in this way then usually first undergoes forming and compression processes, for example by hammering and / or Rollers. It is a radial hammering of the cylindrical Blanks. These basics are, for example, in DE-OS 25 19,014 and US-A 4,859,239.

When a cylindrical blank is hammered radially, this becomes Material deforms as it passes through flat hammer jaws. The aim of this process is an even reduction in diameter of the blank while elongating the material. The same applies also for the process steps of rolling and drawing. Typical reductions hammering is 20% of the original per process step Diameter.

From a diameter of approximately 4 mm, the material can then be Drawing process can be further deformed if an even smaller final one Diameter is desired.

An electrode for high-pressure discharge lamps is already known from US Pat. No. 5,422,539 and a manufacturing process therefor. The production A tip on an electrode is then usually cutting shape, i.e. by turning or grinding. This can, according to the teaching of this document, by additional axial hammering (Upsetting) can still be improved, since this results in additional compression the top takes place.

According to this state of the art, the influence on the Stability of the structure of the blank electrode. The grain boundary structures run parallel to the wire axis, and not just in the area of the shaft, but also in the area of the tip of the electrode. If the geometry the electrode tip through the well-known cutting shape, such as e.g. by rotating and grinding, the grain boundary structure opens so evenly distributed on the sloping surface of the tip and breaks off there, as shown in Figure 1.

A redirection or centering of the grain boundary structure in the area the tip towards the axis or towards a plateau at the electrode tip was not possible so far. A disadvantage of the previous technology is also the large amount of waste that comes with machining Technology has to be accepted. The drop results from the difference between the shape of the finished electrode tip and the corresponding one cylindrical blank.

Presentation of the invention

It is an object of the present invention to provide an electrode according to the The preamble of claim 1 provide little waste in manufacture produced and shows an improved burning behavior in operation.

This object is achieved by the characterizing features of claim 1 solved. Particularly advantageous configurations can be found in the dependent ones Claims.

The technique of radial hammering to create a tip has so far been used only for very small opening angles (below 10 ° for sewing needles) for ductile Metals (iron) applied. Tungsten was considered to apply this Technology so far as too brittle. Opening angles over 10 ° were not considered makeable.

In the radial hammering according to the invention for generating a tip an electrode instead of flat jaws, as they are known for the cylindrical Hammering a sintered blank will be required, according to the desired tip shaped profiled hammer jaws used. Of the Process step takes place only after the sintered blank on its final diameter was transformed and then after that the individual blank electrode was cut to length.

The material of the electrode according to the invention consists of high-melting material, in particular tungsten material. In principle, for example, rhenium, osmium, tantalum (carbide) or the like. suitable. A dopant such as ThO ₂ can be added to it as an activation material. Dopants such as oxides of aluminum, potassium or silicon are also often added. However, alloys, especially tungsten, are also possible.

According to the invention, the electrode consists of a cylindrical base body, often also called a shaft, and a tapered tip, whereby the tip is essentially produced by radial forming.

a) Erhöhung der Stabilität des Gefüges im Spitzenbereich von Elektroden;

b) Orientierung der Korngrenzenstrukturen an der Spitze zur Achse der Elektrode hin, insbesondere zu einem Plateau an der Elektrodenspitze;

c) direkte gezielte Formgebung von Elektrodenspitzen;

d) Verringerung des Abfalls an Elektrodenmaterial;

e) gezielte Einstellung des Gefüges im Bereich der Elektrodenspitze;

f) Verringerung des Materialverschleißes bei den Werkzeugen für die Formgebung (z.B. bei Drehstählen, Schleifscheiben etc.).

The present invention offers a number of advantages:

a) increasing the stability of the structure in the tip region of electrodes;

b) orientation of the grain boundary structures at the tip towards the axis of the electrode, in particular towards a plateau at the electrode tip;

c) direct targeted shaping of electrode tips;

d) reducing the waste of electrode material;

e) targeted adjustment of the structure in the area of the electrode tip;

f) Reduction of material wear in the tools for the shaping (for example in turning steels, grinding wheels etc.).

A decisive advantage is that the gentle radial forming the grain boundaries, which act as channels for the dopant, tend to the axis aligned and practically exclusively in one area end close to the tip, so that the burning behavior is very calm. In the area of the grain boundaries, the doping promoting the emission may be preferred diffuse.

The tip is advantageously a truncated cone with a conical jacket and a Plateau, the grain boundaries in this case predominantly in the area of Plateaus end. In this case, the dopants are predominant transported to the plateau area. Conversely, losses through evaporation minimizes the dopants from the cone shell. This has a positive effect on the life of the lamp.

Radial forming allows electrode tips with simple geometries getting produced. Reshaping can advantageously be done either by radial hammering or by transverse rolling. Through this deformation work with free choice of the deformation parameters (e.g. Temperature, opening angle, degree of deformation) is a targeted additional Editing possibility for the structure created, which has a positive effect affects the burning behavior and the life of the electrode.

The general principle of cross rolling is already from VDI news, for example No. 20, May 17, 1996, p. 11. There it is, however, for components (Titanium alloy forgings) with large abrupt Jumps in diameter used. The cross roller is also included Round jaws equipped, which are profiled wedge-shaped. The profile is symmetrical. Round jaws are used for the application according to the invention, whose profile is asymmetrical. The profile forms the top of the Electrode off without sudden jumps occurring.

Radial hammering may result, depending on the diameter of the Electrode and the deformation parameters, a very fine structure (significant decrease in grain size) due to the additional deformation work is more solidified (significant increase in hardness, possibly also density). Grain size and density at the top can be compared typically change the stem by a factor of two or more, possibly even by a factor of 3 to 10.

The electrode is advantageously additionally doped, in particular with thorium oxide. It has now been shown that these additional dopants also the radial forming are crushed more. This results in a finer and more homogeneous dispersion of the dopants.

The structure at the tip can be influenced in a targeted manner by the deformation be so that the stability of the structure in the thermally highly stressed Tip area of the electrode can be improved. So opposite the desired structure due to the additional deformation can be set.

Due to the near-net shape, there are no machining steps, apart from any minor final corrections. Consequently the additional material consumption is significantly reduced (by 5 to 25%). The reduction, which depends on the opening angle, has a particular effect also favorable for thoriated materials because it is radioactive special waste waste to be treated is reduced.

At the same time, the need and wear of diamond grinding wheels, which are very expensive, drastically reduced.

The smaller the diameter of the electrode, the easier it is for the radial one Forming process, especially the hammering process. In principle, however, this method is also used for relatively large diameters applicable up to about 50 mm. Particularly good results can be seen in achieve application on DC-operated cathodes. But also Cathodes and anodes for AC-powered lamps can be manufacture with it.

Radial forming (hammering) always includes a tangential component. That is why peaks with an entire opening angle can be used Produce α of at most 90 °, preferred is α below 60 °. At a The deformation forces only act in the larger opening angle Near the surface. The core area remains unaffected. Here the layers near the surface slide off at the lower one Core area. This process can create unwanted voids form.

The tip is preferably conical or frustoconical. The latter is particularly preferred because here the grain boundaries along which the doping material is transported, end on a discharge-side plateau can.

characters

Figur 1

eine Elektrode aus Wolfram, im Schnitt, deren Spitze geschliffen ist (Stand der Technik);

Figur 2

eine Elektrode aus Wolfram, im Schnitt, deren Spitze radial gehämmert ist;

Figur 3

eine Prinzipdarstellung (Figur 3a) einer Elektrode gemäß Figur 2, wobei jeweils ein Bereiche an der Spitze (Figur 3b) und am Schaft (Figur 3c) vergrößert dargestellt ist;

Figur 4

ein Hämmerbackenpaar für das radiale Hämmern in Seitenansicht (Figur 4a), Frontalansicht (Figur 4b) und Perspektive (Figur 4c);

Figur 5

eine Hochdruckentladungslampe mit einer radial umgeformten Kathode gemäß Figur 2;

Figur 6

die Kathode aus Figur 5, vergrößert dargestellt.

The invention will be explained in more detail below with the aid of several exemplary embodiments. Show it:

Figure 1

an electrode made of tungsten, in section, the tip of which is ground (prior art);

Figure 2

a tungsten electrode, in section, the tip of which is hammered radially;

Figure 3

a schematic diagram (Figure 3a) of an electrode according to Figure 2, wherein an area at the tip (Figure 3b) and the shaft (Figure 3c) is shown enlarged;

Figure 4

a pair of hammer jaws for radial hammering in side view (Figure 4a), frontal view (Figure 4b) and perspective (Figure 4c);

Figure 5

a high-pressure discharge lamp with a radially formed cathode according to Figure 2;

Figure 6

the cathode of Figure 5, shown enlarged.

Description of the drawings

In Figure 1 is an electrode made of tungsten material, with an addition of Potassium, silicon and aluminum, with a diameter of 1.5 mm in Detail shown, the tip of which was ground. It is more conventional Formed with a diamond grinding wheel.

In comparison, an electrode made of the same is doped in FIG Tungsten material with a diameter of 1.5 mm shown in detail, the Tip is hammered round. It is in the manner according to the invention Radial hammers have been formed.

Figure 3 shows one possibility using the example of thoriated tungsten material the targeted structure influence by radial hammering in the area the conical tip. The electrode 4 has a diameter of 3 mm and an opening angle of 40 ° at the tip. Figure 3a shows the location of two Image sections in the area of the tip 9 (deformation zone) and the shaft 5. At the tip (FIG. 3b), a round kneading structure is formed by the shaping, that is recrystallized in operation. This structure is much finer than that in the area of the shaft (FIG. 3c), which is the usual previously known drawing structure trains. This also applies after a recrystallizing annealing treatment.

The electrode according to the invention is produced by using the tungsten powder as usual, first pressed and then sintered. Subsequently the sintered rod blank is rolled, hammered and, if necessary, pulled until the desired final diameter has been reached. On the generated The blank electrode now becomes the tip of the electrode by radial hammering generated, with the desired geometry of the Tip is incorporated as a profile.

Figure 4 shows a pair of hammer jaws 15 in three views. They exist from cuboid tool bodies, the ones facing the electrode shaft Front 16 with a semicircular cavity 17 that runs along the narrow side 14 runs, is equipped. The cavity 17 narrows down inside, basically conical. The cavity 17 consists of three sections, an input opening 18, which tapers conically, a guide shaft 19 (for the electrode shaft), the diameter of which is kept constant and a tip molding 20 that is tapered with the desired one Opening angle of the tip of the electrode approaches. The cylindrical blank electrode protrudes for processing between the two still spaced Narrow sides 14 of the jaws 15. Before radial hammering, the Blank electrode as usual on a suitable for processing Temperature. Then the tip 15 by means of the jaws hammered.

A xenon short-arc lamp operated with direct current is shown schematically in FIG 1 shown with 150 W power for photo-optical purposes. The elliptical Discharge vessel 2 made of quartz glass contains an anode 3 and a cathode 4. Each electrode has a shaft 5 which is connected to a molybdenum foil 6 is. This is melted in a vacuum-tight manner into the ends of the discharge vessel 2.

The cathode 4 is shown enlarged again in FIG. It consists of tungsten which is doped with 0.4% by weight of ThO ₂ . In order to ensure a high degree of arc stability, the cylindrical base body of the cathode forming the shaft 5 tapers in the manner of a truncated cone to a tip 9, the cone jacket 11 of which ends in a plateau 10 on the discharge side. The tip 9 is produced by radial hammering and has the structure shown in FIG. 3. The opening angle α is 20 ° here. Only the plateau 10 is subsequently treated by grinding.

Claims (10)

Electrode (4) made of refractory material, in particular tungsten material, for a high pressure discharge lamp, with a cylindrical Shaft (5) and a tapered tip (9), characterized in that that the tip (9) essentially by radial shaping is made. Electrode according to claim 1, characterized in that the tungsten material is endowed. Electrode according to claim 1, characterized in that the forming by radial hammering or by transverse rolling. Electrode according to claim 1, characterized in that the hardness and possibly also the density in the area of the tip (9) compared to that in the Shaft (5) is raised. Electrode according to claim 1, characterized in that the tip (9) opens into a plateau (10). Electrode according to claim 1, characterized in that the middle Grain size in the area of the tip is smaller than in the area of the shaft. High-pressure discharge lamp with an electrode according to one of the preceding Expectations. Process for producing a tungsten electrode for high-pressure discharge lamps, the electrode having a shaft (5) and a Has conical tip (9), characterized in that the tip (9) is essentially generated by radial forming. A method according to claim 8, characterized in that the radial Forming is done by hammers or cross rolls. Device for radially hammering an electrode according to claim 1, consisting of a pair of rectangular hammer jaws (15), with a front side (16) and a narrow side facing the electrode (14), with a semicircular-like cavity (17) that follows narrowed inside to accommodate part of the electrode from the front (16) extends along the narrow side (14).

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