EP0602529A2 - High-pressure discharge lamp having a ceramic discharge vessel - Google Patents

Abstract

A ceramic high-pressure lamp has a bushing which is fitted into an end plug and is composed of at least two wires (23) or pins having a diameter of not more than 250 mu m. The bushing consists of a material which is not matched to the expansion coefficient of the end plug. <IMAGE>

Description

The invention is based on a high-pressure discharge lamp according to the preamble of claim 1.

These are essentially metal halide discharge lamps, the color rendering of which is improved by the use of a ceramic discharge vessel. Typical power levels are 50-250 W. However, the invention can also be used with other types of lamps, e.g. for high pressure sodium lamps.

A structure is known from the high-pressure sodium lamps in which the ceramic discharge vessel consists of Al₂O₃, to which small additions of other oxides, in particular MgO, may be added. At the ends of the vessel, a niobium tube is fitted as a passage in a ceramic stopper. The particular suitability of niobium is based on the fact that its thermal expansion coefficient corresponds to that of Al₂O₃ ceramic to a good approximation; for both materials it is approximately 8.10⁻⁶ K⁻¹.

A high-pressure lamp is known from EP-PS 34 113, in which a relatively high power (for example 400 W) and the associated higher current load are taken into account by means of a larger power cross section of the current feedthroughs, in that each bushing consists of several niobium wires, each with a maximum diameter of 600 µm. In this way, harmful thermal stresses between the bushing and the end plug are avoided.

From DE-OS 38 40 577 a high pressure lamp is known in which the discharge vessel is made of AlN. Solid tungsten pins are used as bushings because their expansion coefficient (5.10⁻⁶ K⁻¹) corresponds to that of AlN to a good approximation. The use of tungsten also has the particular advantage that this material is resistant to the highly corrosive effects of metal halides, which may be used here as a filler additive. Niobium does not have this property.

In order to improve the corrosion resistance in the area of seals, attempts have been made in metal halide lamps with discharge vessels made of Al₂0₃ to protect the usual niobium feedthroughs by special tricks, for example by deep insertion or by protective layers (for example EP-A 472 100), but this is very expensive . The use of electrically conductive cermets as end plugs does not help either (EP-A 142 202). Although these are more corrosion-resistant, their suitability is unsatisfactory because, over the course of their service life, the heating of the cermet, which acts as an ohmic resistance, causes microcracks, which spread further and ultimately cause the discharge vessel to leak.

The object of the invention is a high-pressure discharge lamp to create according to the preamble of claim 1, in which the sealing of the discharge vessel is improved and thereby the life of the lamp is extended.
This object is achieved by a high-pressure lamp with the characterizing features of claim 1. Particularly advantageous refinements can be found in the subclaims.

The high-pressure discharge lamp according to the invention has a discharge vessel made of Al₂0₃ or another translucent ceramic, the expansion coefficient of which, similar to Al₂0₃, is approximately 8.10⁻⁶ K⁻¹. For example, spinel (MgAl₂0₄) or Y₂0₃ comes into question. The ceramic can also be doped with other substances, e.g. MgO.

The discharge vessel is generally elongated, in particular cylindrical or bulged. But it can also be bent in a U-shape. At both ends it is closed with sealing means, which are also made of a suitable ceramic material. Discharge vessel and sealant do not necessarily have to be made of the same material. However, it should be roughly coordinated with regard to the coefficient of expansion.

The sealing means is often a separate end plug, for example in the form of a cylindrical disk, which in particular can have a widened edge or projection which serves as a stop when fitting into the discharge vessel. However, it can also be, for example, a suitably shaped integral end region of the discharge vessel.

The sealing principle according to the invention tries to take advantage of the corrosion resistance that some metals have with a relatively low coefficient of expansion of approx. 4 - 5.10⁻⁶ K⁻¹ (especially tungsten, molybdenum, rhenium and their alloys), also for bonding with ceramic materials to use, which have already proven to be particularly suitable for the manufacture of discharge vessels for high-pressure lamps, in particular Al₂0₃. The quality of the seal is primarily the material of the means for sealing, generally the end plug, because only this comes into direct contact with the implementation. The material of the discharge vessel itself is also important.

In an analogous manner, this consideration also applies to the case that the sealing means consists of several parts, only one of which is in direct contact with the bushing.

The invention is based on the consideration that it is not possible per se to permanently connect two substances with different thermal expansion in a vacuum-tight manner when they are exposed to such large temperature fluctuations (approx. 800-1000 ° C.) as in the operation of a lamp. However, it should not be overlooked that the comparison of the expansion coefficients only gives the relative expansion differences. A second parameter of equally great importance, however, is the absolute value of the expansion differences. So make the dimensions of one seal partner as possible small, the relative expansion differences are no longer significant.

The functionality of this general principle is shown in discharge vessels made of quartz glass, in which lamellar, extremely thin molybdenum foils are used. Surprisingly, it has been shown that this principle can be concretized in ceramics in that a commercially available wire or pin with a diameter of at most 250 µm is used as the basis for the implementation. The diameter can preferably also be considerably smaller; diameters between 50 and 130 µm are well suited.

Depending on the desired power level of the lamp, the current load of the bushing is taken into account by increasing the cross-sectional area of the bushing by arranging a plurality of wires parallel to one another. At high power levels, up to nine or more wires can be used. A particularly advantageous side effect when using multiple wires is the improved stabilization of the implementation. In particular, it is possible to twist the part of the wire bundle projecting into the discharge vessel into a strand.

In the case of small-watt lamps, a decisive advantage can be derived from this. This is because the strand can be fused to form an electrode tip with a high heat capacity, in particular to form a spherical tip. Tungsten is particularly suitable as a lead-through material for such an arrangement, since it is particularly heat-resistant. A separate Electrode, which first has to be connected to the feedthrough, can be omitted. The ball diameter of such an electrode tip can be adjusted over the length of the strand section melted back in an arc (generated by plasma torch or laser).

In the simplest case, it is sufficient to pass this bundle of wires, possibly loosely twisted, through a single, closely matched hole in the sealant and to seal this hole in a vacuum-tight manner using glass solder. Individual wires or different wire bundles can also be guided in two or more closely matched holes. The only decisive factor for the sealing effect is that each individual wire is surrounded by glass solder. This is ensured in the case of several, even loosely twisted, wires in a bore by the capillary action of the gaps present between the wires. The advantage of using wire bundles is the easier and faster threading into the holes.

When making the seal, it should be noted that the bore is normally so narrow that a spherical electrode tip would not fit through it. For this reason, a loosely twisted wire bundle is first passed through the single hole in the end plug and sealed with a glass solder. A ball is only created at the electrode tip by applying an overcurrent. The filling takes place, for example, by means of a lateral bore in the wall of the discharge vessel.
An alternative is to start with the wire bundle insert into the bore of the end plug, which has not yet been inserted, and then shape or fasten the electrode tip. Only then, after the discharge vessel has been filled by the upper end, is this structural unit inserted into the still open end, and both the gap between the end of the discharge vessel and the stopper and the hole in the stopper containing the wire bundle in the stopper are sealed by means of glass solder. This technique can also be used if the end plug has multiple holes for individual wires or wire bundles.
Alternatively, the direct sintering technique can be used to seal individual wires in separate holes in the end plug, which has not yet been used. This technique works better the thinner the wire diameter. Here the electrode tip can be braided into a strand and a ball tip can be formed or an electrode tip can be attached later. This unit can then be inserted into the second, still open end of the discharge vessel, similarly to the last exemplary embodiment, when the filling process is complete. The annular gap between the end plug and the end of the discharge vessel is then closed using a glass solder. With this technique, the use of glass solder is minimized so that the corrosive effect of the filling on the glass solder can be neglected. In any case, it is advisable to use a glass solder that is as halogen-resistant as possible.
Direct sintering in of the end plug in the end of the discharge vessel is also possible, while at the same time direct sintering in of the lead-through wires in the end plug. However, there must again be a lateral one Filling hole can be created in the wall of the discharge vessel.
This technique also allows multiple wires to pass through a separate hole if a special material with a reduced coefficient of expansion is used for the sealant.

The trick of assembling the sealant from several parts, in particular from a central part contacting the seal and a peripheral part which surrounds the central part, has proven particularly successful in terms of production technology. This arrangement has advantages both when inserting the bushing and when sealing as well as when forming a strand. The central part is expediently designed in particular as a multi-hole capillary, in which each wire is passed individually through a bore. A separate central part simplifies handling when threading the wires. The twisting of the wires in the area of the electrode tip can expediently only take place after threading, as can the formation of a ball on the electrode tip. A decisive advantage is that the seal between the bushing and the central part can be made before it is installed in the end of the discharge vessel. In particular in the case of direct sintering, that is to say without glass solder, there is no need to take account of the discharge vessel and, above all, of the filling that may already be contained in the temperature load required for this during the sintering process.

A central part and in particular a multi-hole capillary also offer a particularly elegant solution for the problem of filling the discharge vessel because the the bore receiving the central part in the peripheral part can initially be used as a filling opening. The first end of the discharge vessel is initially completely closed, while a filling opening is left at the second end, which is only closed after the evacuation and filling. Alternatively, the multi-hole capillary can also have a hole which is superfluous compared to the number of wires and which can serve as a filling opening.
Details on the technique of direct sintering and the filling process by means of an opening to be subsequently closed are set out in EP-PA 92 114227.9 and PCT / DE92 / 00372 (Article 54 (3) EPC), to which express reference is made.

There are particular advantages in the case of metal halide discharge lamps with a ceramic discharge vessel and sealant, the service life of which has hitherto been greatly restricted by the aggressive fillers. Bushings made of tungsten or molybdenum according to the invention have proven particularly useful here since they are corrosion-resistant.

Figur 1

ein erstes Ausführungsbeispiel einer Metallhalogenid-Entladungslampe, teilweise geschnitten

Figur 2

ein weiteres Ausführungsbeispiel des Endbereiches des Entladungsgefäßes

Figur 3

ein weiteres Ausführungsbeispiel des Endbereichs der Lampe in Seitenansicht (geschnitten) (Figur 3a) und im Querschnitt (Ausschnitt) (Figur 3b), sowie deren Herstellung (Figur 3c und 3d)

Figur 4

weitere Ausführungsbeispiele von Kapillaren mit Durchführungen im Querschnitt.

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

Figure 1

a first embodiment of a metal halide discharge lamp, partially cut

Figure 2

a further embodiment of the end region of the discharge vessel

Figure 3

another embodiment of the end region the lamp in side view (cut) (Figure 3a) and in cross section (detail) (Figure 3b), and its manufacture (Figure 3c and 3d)

Figure 4

further embodiments of capillaries with bushings in cross section.

A metal halide discharge lamp with an output of 100 W is shown schematically in FIG. It consists of a cylindrical outer bulb 1 made of quartz glass which defines a lamp axis and which is squeezed 2 and base 3 on two sides. The axially arranged discharge vessel 4 made of Al₂0₃ ceramic is bulged in the middle 5 and has cylindrical ends 6. However, it can also consist of a cylindrical tube, for example. It is held in the outer bulb 1 by means of two power leads 7, which are connected to the base parts 3 via foils 8. The power supply lines 7 made of molybdenum are welded to bushings 9, which are sintered directly into a ceramic end plug 10 of the discharge vessel, that is to say without soldering glass. The end plugs are also made of Al₂0₃. In addition to an inert ignition gas, such as argon, the discharge vessel is filled with mercury and metal halide additives. The first bushing 9a is arranged at the first end 6a, which serves as the pump end when the lamp is being filled. It consists of two molybdenum wires, each with a diameter of 220 μm, which are guided through two bores of the end plug 10a at a distance from one another. They hold an electrode 11 in the interior of the discharge vessel, consisting of an electrode shaft 12 made of tungsten and a spherical tip 13 formed at the discharge end.

The second bushing 9b is arranged at the second end 6b, which is designed as a blind end. It consists of a solid niobium pin, which is inserted 14 into the bore of the end plug 10b. For the purpose of evacuation and filling, a filling bore 15 is provided near the pump end 6a, which is closed after filling by a glass solder or a ceramic ceramic 16. In this version, attention must be paid to the firing position in order to keep the corrosion small even when using a niobium bushing.

In a second embodiment, both ends 6a, 6b are equipped with the same multi-wire feedthrough, the burning position being irrelevant.

FIG. 2 shows a further exemplary embodiment in which a continuous, loosely twisted bushing 9a 'is passed through a bore in the ceramic end plug 10a. It consists of four individual wires, which are fused to a ball 13 at the tip. The bushing 9a 'is melted into the bore by means of glass solder 16'. The end plug 10a is in turn melted into the end 6a of the discharge vessel by means of glass solder 16 ″. A separate filling hole in the side wall as in FIG. 1 can be omitted, since the end plug 10a is only inserted into the discharge vessel 6a after the discharge end has been evacuated and filled.

Another embodiment is shown in FIG. 3a. It is just a section, namely the area of one end 6.

The ceramic end plug 20 consists of two concentric parts, an outer peripheral part 21, which is shaped like a ring, and an inner central part 22 in the form of a cylindrical four-hole capillary with an outer diameter of 1.2 mm. Both parts consist of pure Al₂0₃. Four tungsten wires 23, each with a diameter of 100 μm, are passed through the four bores in the capillary, each with an inner hole diameter of 200 μm. They are twisted into a strand 24 in the interior of the discharge vessel, which is fused at the tip to a ball 25 of approximately 700 μm in diameter. This bushing is suitable for currents of approx. 1.2 A. FIG. 3b shows a top view of the capillary 22 with the wires 23.

The ends of the wires 23 are surrounded by a niobium coil 27 on the outside 26 of the end plug. A conical end part 28 made of niobium is fitted into the coil 27 so that it clamps the wires 23 on the inside of the coil 27. The central part 22 is generously sealed by means of glass solder 29 in the peripheral part 21, the wires 23 in the bores of the central part 22 also being sealed by the glass solder 29. Finally, the niobium coil 27 is also attached to the outside 26 of the end plug by the glass solder 29.

The sealing of one end of the discharge vessel with a bushing according to FIG. 3a is explained in more detail in FIG. 3c. First, the wires 23 are threaded into the bores of the capillary 22 and on the discharge side Twisted end to a strand 24. The electrode tip 25 is then formed by melting the strand back. Then the niobium coil 27 is inserted over the wire ends 23 at the end of the capillary remote from the discharge. The wire ends 23 are clamped in the helix 27 with the conical end part 28, which is fitted into the helix 27 from above (arrow). The helix 27 is spread somewhat. To better guide the wires, the end part 28 can have grooves 30 in the conical surface.

The preassembled electrode system 31 including the capillary 22 is inserted (FIG. 3d) into the central bore of the peripheral part 21 already connected to the end of the discharge vessel (arrow), the niobium coil 27, which advantageously projects somewhat laterally on the capillary 22, as a stop for the electrode system 31 can serve if it is positioned in the central plug bore before it melts. A glass solder ring 32 is then placed on the outer surface 26 of the end plug 20 and the end 6 locally heated to such an extent that the glass solder 32 melts and runs into the cavities, thereby sealing the bores of the end plug and fixing the coil 27, as shown in FIG. 3a. The coil 27 must be made of niobium or another metal with a coefficient of expansion similar to that of niobium, e.g. Tantalum, since otherwise it cannot be connected to the glass solder ring 32 without cracks.

FIG. 4 shows in cross section further exemplary embodiments of a multi-hole capillary 17, for example for a 150 W lamp. According to the higher occurring here Current (1.8 A), eight wires 18 are sintered directly into eight holes in FIG. 4a. Furthermore, the capillary 17 has an extra large bore 19 in the middle, which can be used to fill the discharge vessel. Accordingly, there is no need for a separate filling hole in the wall of the discharge vessel. The hole 19 is closed after filling with glass solder or ceramic.

In FIG. 4b, bundles 33 of three wires 34 each are guided in a bore 35 in the capillary 17. The wires 34 are spaced apart. The total of three bores 35 are sealed in a vacuum-tight manner by means of glass solder 36, so that each individual wire 34 is surrounded by glass solder 36.

In FIG. 4c, bundles 37 of four wires 38 each are guided in a bore 39 of the capillary 17 and sintered there directly. However, this is only possible under the special condition that the thermal expansion coefficient of the end plug, in particular of the central part 17, is better matched to the metallic bushing. For this purpose, the end plug or at least the capillary can contain up to 40% additives (eg tungsten) in addition to the basic ceramic matrix (Al₂0₃). Because of the lower relative expansion difference, it can then be accepted that a plurality of wires 38 are arranged directly next to one another in a bore 39. The bore 39 is then advantageously adapted to the cross section of the wire bundle. In the case of a bundle of four wires, a cloverleaf-like cross section of the bore 39 is therefore used.

The invention is not restricted to the exemplary embodiments shown. In particular, it can be advantageous to let the capillary protrude somewhat at the end of the end plug on the discharge side, since this improves the ignition and operating behavior of the lamp. Any condensate from filling components then only wets the protruding collar of the capillary, but not the bushing.

Claims (13)

High-pressure discharge lamp with a discharge vessel (4) made of translucent ceramic, which encloses a light-generating filling, the discharge vessel (4) having two ends (6a, 6b) which are closed with ceramic means (10) for sealing, and by which means one electrically conductive bushing (9) is passed through in a vacuum-tight manner and connects an electrode (11) in the interior of the discharge vessel to an external electrical feed line, characterized by the following features: - At least the means (10) for sealing consist essentially of Al₂0₃, Y₂0₃, MgAl₂0₄ or mixtures thereof, at least at one of the two ends (6) of the discharge vessel, the feedthrough (9) consists of a metal whose coefficient of thermal expansion is considerably smaller than that of the ceramic means for sealing, - This implementation (9) consists of at least two, preferably several, thin wires (23) or pins, each with a diameter of at most 250 microns. High-pressure discharge lamp according to Claim 1, characterized in that the bushing (9) consists of tungsten or molybdenum or rhenium or mixtures thereof. High-pressure discharge lamp according to Claim 1, characterized in that the individual wires (23) or pins are passed separately through the sealing means (10). High-pressure discharge lamp according to Claim 1, characterized in that the individual wires (23) or pins are twisted into a strand (24) at least within the discharge vessel. High-pressure discharge lamp according to Claim 1, characterized in that the bushing (9) in the means (10) for sealing is melted in by a glass solder (29) or is sintered in directly. High-pressure discharge lamp according to one of the preceding claims, characterized in that the means (20) for sealing consists of several parts and has a tubular separate part (22) which surrounds the leadthrough (9). High-pressure discharge lamp according to Claim 6, characterized in that the separate part is a capillary (22) with a plurality of bores. High-pressure discharge lamp according to Claim 1, characterized in that the outer ends of the wires (23) or pins projecting from the means (20) for sealing are surrounded by a ring-like resilient element (27), an electrically conductive end part (28) having a conical one Partial surface is fitted into the resilient element so that the outer ends of the wires or pins between the resilient element (27) and the end part (28) are mechanically clamped and thereby ensure an electrically conductive connection between the bushing and the end part. High-pressure discharge lamp according to claim 8, characterized characterized in that at least the resilient element (27) is made of niobium. High-pressure discharge lamp according to Claim 8, characterized in that the resilient element is a filament (27). High-pressure discharge lamp according to Claim 4, characterized in that the end of the strand (24) on the discharge side is fused to form an electrode tip (25) with a high heat capacity. High-pressure discharge lamp according to Claim 1, characterized in that the light-generating filling contains metal halides High-pressure discharge lamp according to Claim 1, characterized in that the means for sealing or at least one of its parts contains up to 40% additives.

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