EP0887840A2 - Metal halide lamp with ceramic discharge vessel - Google Patents

Abstract

The lamp has a ceramics gas discharge envelope of aluminium oxide, with 2 opposite ends fitted with end seals (11) through which respective conductor leads (9) are fitted, for supporting the gas discharge electrodes. The end seal at at least one end (6a) of the gas discharge envelope is provided by at least 4 axial cermet layers (11a-11d) with a metal content which increases in the outwards direction, the conductor lead soldered to the outermost layer (11d).

Description

This registration is closely related to the following registrations: internal Case number 97P5541, 97P5542, 97-1-001, 93-1-480.

Technical field

The invention is based on a metal halide lamp with a ceramic Discharge vessel according to the preamble of claim 1. It is especially lamps whose operating temperature is relatively high, and is on the order of up to 1000 ° C.

State of the art

A major problem with such lamps is permanent sealing the implementation in the ceramic discharge vessel by means of a ceramic Stuffing. There are already many proposed solutions for this been. A tube or pin made of metal (tungsten or Molybdenum) as a feed-through in a ceramic stopper using glass solder / melting ceramic soldered or sintered directly. But this creates no connection layer between ceramic and metal, so that no permanent Sealing can be achieved. As a material for the stopper is therefore also proposed cermet, a composite material made of ceramic and metal (U.S. Patent 5,404,078 and U.S. Patent 5,592,049).

For better adaptation of the thermal expansion coefficient Also tried plugs that consist of several layers of cermet with a subtle There is a metal / ceramic ratio. From EP-A 650 184 is a non-conductive cermet plug known with axially arranged layers. However, the sealing is very complicated and uses a bushing with thread, an outer metal disc (flange) and a metal or Glass solder.

A metal halide lamp with a ceramic lamp is already known from US Pat. No. 4,602,956 Discharge vessel known, in which the electrode in a passage, which is designed as a disc made of electrically conductive cermet, sintered is. The implementation is also of an annular plug surrounded by cermet, the one with the ceramic discharge vessel Alumina is connected by means of glass solder. The glass solder is however through the aggressive filling components (especially halogens) corrodes. For these reasons, the lifespan is rather short. Disadvantage of this Arrangement is further that the embedding of the electrode in the cermet feedthrough to tensions and finally to cracks and cracks in the Cermet can lead. Due to the large diameter of the disc-like The discharge arc can also carry out, which is electrically conductive hit back slightly to carry out what for quick Darkness leads.

16 of US-PS 4 155 758 is a special arrangement for a Metal halide lamp with ceramic discharge vessel without outer bulb known in the implementation as a pin made of electrically conductive Cermet is trained. The electrode is sintered into the cermet. Of the Cermet stick is sintered into a plug made of pure aluminum oxide. This is connected to the discharge vessel by means of a glass solder. This arrangement has similar disadvantages as mentioned above.

EP-A 587 238 describes a metal halide lamp with a ceramic discharge vessel described that an extremely elongated capillary tube Aluminum oxide as the inner part of the plug, in which a glass solder is used pin-like metallic feedthrough at the outer end (melting area) is attached. It is crucial that the melting area is at a sufficiently low temperature. The implementation pin can consist of two parts, one of which faces the discharge Part made of electrically conductive cermet containing carbide, silicide or nitride, can be made. This sealing technique creates a large overall length of the discharge vessel. It is very complex to manufacture and based also on the corrosion-prone glass solder. A particularly serious one The disadvantage is that in the gap between the capillary tube and bushing A significant dead volume arises in which a large part of the filling condensed, so that on the one hand a considerable overdosing of the filling necessary is. In addition, the aggressive filling is intense from the start Contact with corrosion-prone components in the sealing area. This technique can only be used with small wattages (up to 150 W) because the difference in the case of larger inner diameters of the capillary tube coefficient of thermal expansion between the grommet cermet and the capillary tube become too large.

Presentation of the invention

It is an object of the present invention to use a metal halide lamp to provide a ceramic discharge vessel according to the preamble of claim 1, which has a long service life and almost on glass solder completely dispensed with. In particular, the sealing area should be vacuum-tight and resistant to high temperatures and not susceptible to corrosion.

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

According to the invention, the stopper is at at least one end of the discharge vessel from at least four axially layered layers from a cermet, consisting of aluminum oxide and metal (tungsten or molybdenum). The metal content decreases towards the outside (i.e. with increasing distance from discharge) to. Cermet is here for the sake of simplicity also an innermost or outermost layer made of pure aluminum oxide or to understand pure metal. It is essential for the invention that the outermost layer of the plug has such a high metal content, that it allows a weldability of this layer with the implementation. For this purpose, an electrical conductivity of this layer is of at least 5 mΩ required. This corresponds to a proportion of the metal from at least 50% by volume. As the number of layers increases, so too Metal content of the outermost layer can be raised. From a total number of six layers, the outermost layer can be made of pure metal, since the relative expansion differences are then kept sufficiently small can be.

With this last layer, the bushing is vacuum-tight by welding connected. This is from the other layers lying further inside Passage through a capillary gap (a few microns wide) spaced. Of the The advantage of sealing the discharge vessel by welding lies in the high corrosion resistance, high temperature resistance and high Strength of such a weld.

A pin or tube that is electrically conductive can be used as a feedthrough will. The material of the implementation should, at least what the thermal expansion coefficient concerns, as good as possible to the outermost Layer of the plug, especially adapted to its composition be. Ideally, it matches her, but there are deviations possible. For example, the outermost layer and also the feedthrough are made of pure metal. Alternatively, both can be made from weldable cermet with a metal content of at least 50% by volume.

The innermost layer of the stopper is with the end of the discharge vessel connected without glass solder. In general, this is done by direct sintering.

A key advantage of the present invention is that in the case of similarity for the outermost layer of the plug and for the implementation used material is guaranteed that no significant thermal Expansion differences occur. The seal is particularly durable, because a strong and permanent connection is achieved by welding is in this regard the technique of sintering or melting is superior. In addition, small differences in elongation lead to pure Metals such as molybdenum and tungsten and those highly enriched with metal Cermets do not crack as quickly because of tension due to elasticity of the metal are more easily mined. On the other hand, for the innermost Layer of the stopper can be selected a material that that of the discharge vessel resembles, so that the seal is permanent in this area.

The leadthrough can be a pin made of high temperature resistant metal, in particular tungsten or molybdenum, or from a cermet, which is made of a mixture of aluminum oxide and tungsten or molybdenum.

In a second embodiment, the bushing is made of a pipe high temperature resistant metal. This shape is for high watt lamps (typically 250 to 400 W) is particularly advantageous. The use of a Pipe as implementation has the advantage that even larger holes in Plugs for the passage of large electrodes for high-watt lamps are sealed without too much heat loss for the electrode can be. If you have an electrode system consisting of tubular feedthrough and electrode, used and this provisionally already together with the stopper in the end of the discharge vessel sinters, the tubular opening can be independent of the electrode size to get voted. In this case, this opening is only after the Filling closed with a filler pen, filling pen, tube and cermet in can be welded in one step. On a separate filling hole in the Plugging, as was often necessary in the past, can therefore be dispensed with entirely.

More specifically, the present invention is a metal halide lamp with ceramic discharge tube (made of aluminum oxide), which is usually surrounded by an outer bulb. The discharge vessel has two ends which are closed with sealing means. These are usually one- or multi-part plugs. At least with one The following construction is realized at the end of the discharge vessel. By a central bore of the sealant is an electrically conductive feedthrough passed vacuum-tight, on which an electrode with a Shaft is attached, which protrudes into the interior of the discharge vessel. The Implementation is a component made of a metal or a cermet, the Metal content is so high that it is weldable like a metal, the Carried out by means of a welded joint, i.e. without glass solder, in the stopper is attached. In addition, the stopper itself is without glass solder in the discharge vessel attached. This is usually done by direct sintering.

The ceramic part of the cermet consists of aluminum oxide, the metallic Part made from tungsten, molybdenum or rhenium. The basic structure of suitable materials for cermets is known per se, see for example the prior art mentioned at the beginning or the documents EP-A 528 428 and EP-A 609 477. The material of the suitable according to the invention However, the cermet component must be both weldable and electrically conductive be. A concrete example is a cermet with a share of 50 vol.% Molybdenum, remainder aluminum oxide. Other examples of this can be found in the parallel applications mentioned at the beginning.

In a particularly preferred embodiment, the implementation is a Pen made of electrically conductive cermet, the shaft of the electrode on the End face of the pin is butt welded. The pen itself is with the stopper welded. The advantage of this arrangement is that the thermal expansion difference between pin and plug is relatively small. Furthermore cermet is not as good a heat conductor as metal. Finally allows a pen made of cermet that fewer layers of the plug are needed. Instead of five or six layers for the stopper, which is a metallic Four layers are sufficient.

The implementation is recessed into the plug, so that contact with the filling is minimized and the temperature load is reduced becomes.

In a second particularly preferred embodiment, which is particularly Suitable for small-watt lamps, the bushing is an electric one conductive pin made of metal. The pen itself can serve as an electrode shaft or be connected to it. It can also protrude beyond the plug to facilitate the connection to the external power supply. This lead-through pin is preferably made of tungsten or molybdenum.

characters

Figur 1

eine Metallhalogenidlampe mit keramischem Entladungsgefäß, teilweise im Schnitt,

Figur 2

eine Darstellung des Endbereichs des Entladungsgefäßes der Lampe nach Figur 1,

Figur 3

ein weiteres Ausführungsbeispiel eines Endbereichs für ein keramisches Entladungsgefäß, vor (Figur 3a) und nach (Figur 3b) dem Einsetzen der Durchführung

Figur 4

ein weiteres Ausführungsbeispiel eines Endbereichs für ein keramisches Entladungsgefäß,

Figur 5

ein weiteres Ausführungsbeispiel eines Endbereichs für ein keramisches Entladungsgefäß.

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

Figure 1

a metal halide lamp with ceramic discharge vessel, partly in section,

Figure 2

2 shows a representation of the end region of the discharge vessel of the lamp according to FIG. 1,

Figure 3

a further exemplary embodiment of an end region for a ceramic discharge vessel, before (FIG. 3a) and after (FIG. 3b) the insertion of the bushing

Figure 4

another embodiment of an end region for a ceramic discharge vessel,

Figure 5

a further embodiment of an end region for a ceramic discharge vessel.

Description of the drawings

A metal halide lamp with an output of 150 W is shown schematically in FIG. It consists of a cylindrical outer bulb 1 made of quartz glass which defines a lamp axis and is squeezed (2) and base (3) on two sides. The axially arranged discharge vessel 4 made of Al ₂ O ₃ ceramic is bulged in the middle 5 and has two cylindrical ends 6a and 6b. 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 are welded to bushings 9, 10, which are each fitted in a plug 11 at the end of the discharge vessel.

The bushings 9, 10 are cermet pins with a diameter of approx. 1 mm. The cermet is conductive and weldable and consists of approximately 50 vol .-% tungsten (or molybdenum), the rest aluminum oxide.

Both bushings 9, 10 are on the outside of the stopper 11 and hold Electrode 14 on the discharge side, consisting of an electrode shaft 15 Tungsten and a helix 16 pushed on at the discharge end. The bushing 9, 10 is in each case with the electrode shaft 15 and with the outer power supply 7 butt welded. The diameter of the Wendel is slightly smaller than that of the feedthrough, so the whole electrode system subsequently in the corresponding central hole in the stopper can be introduced.

In addition to an inert ignition gas, the discharge vessel is filled, e.g. Argon, from mercury and additives to metal halides. Is possible for example, the use of a metal halide filling without Mercury, whereby a high pressure is selected for the ignition gas xenon.

The end plugs 11 essentially consist of an axially layered cermet with the ceramic component Al ₂ O ₃ and the metallic component tungsten or molybdenum. They are sintered directly into the ends 6.

An end region of the discharge vessel is shown in detail in FIG. 2. Of the Plug 11 consists of four axially stacked circular rings, Layers or layers, the innermost of which faces the discharge. The innermost Annulus 11a consists of pure aluminum oxide or a cermet with low metal content. Preferably, the cermet contains the innermost Circular ring maximum 8 vol .-% metal, rest aluminum oxide. The circular ring 11a is partially inserted in the end 6a of the discharge vessel and with the cylindrical Sintered directly at the end 6a of the discharge vessel (i.e. without glass solder). The second annulus 11b contains 10 to 25 vol .-% metal, the third Circular ring 11c between 25 and 40 vol .-% metal. The fourth annulus 11d contains at least 50 vol .-% metal and is therefore weldable. He is at his External surface connected to the bushing 9 by laser welding.

In the specific case of Figure 2, the plug 11 consists of an innermost Layer 11a with 7.5 vol% molybdenum. The second layer 11b has 15% by volume Molybdenum, the third (11c) 30% by volume, the outermost (11d) 50% by volume.

In Figure 3a, 3b is another embodiment of such End area shown. The bushing 20 is a pin made of pure molybdenum. Here, the plug 21 consists of six layers of a cermet each form a circular ring. The innermost layer 21a contains 5 to 8% by volume Molybdenum, remainder aluminum oxide. The second annulus 21b contains 10-25 Vol .-% molybdenum, the third annulus 21c between 25 and 40 vol .-%. Of the fourth circular ring 21d contains 50 to 70 vol .-% molybdenum, the fifth 21e 70 to 90 vol%. The outermost annulus 21 f consists of pure molybdenum and is therefore very easy to weld. It is with a collar-shaped extension piece 21g equipped, which is about 1 mm in length and a wall thickness of about 0.5 mm. The bushing 20 is slightly above this collar 21g and has a lateral thickening 23 at its outer end (such as a cutting burr or weld spot) that is performing 20 fixed in the plug 21. The outermost annulus 21f including the collar 21g is in shape with the bushing 20 by a weld 19 connected to a melting ball.

In a specific case, the plug 21 consists of an innermost layer 21a with 5 vol.% Molybdenum. The second layer 21b has 15% by volume of molybdenum, the third (21c) 30% by volume, the fourth (21d) has 55% by volume, the fifth (21e) approximately 80 vol%. The outermost layer 21f including the collar 21g is made of pure molybdenum or a weldable cermet with a high molybdenum content. In this embodiment, the relative differences very low in coefficient of thermal expansion.

In this variant, the feed-through pin 20 is so far into the central one Bore 22 of the plug inserted until it is fixed by the thickening 23 is. Closing is carried out by welding (19 denotes the Sweat bead) of the end of the pin with the last cermet layer 21f inclusive the collar 21g. The contacting of an external power supply (7), see Figure 1, can easily here directly on the collar 21g of the outermost layer of the plug because it is also highly conductive. Figure 3a shows that the bore itself was first used for evacuation and filling becomes. Only then (Figure 3b) the pin itself is inserted and welded on the outside. This welding technique is quick compared to the sintering technique and easy to run and does not require high temperatures outside of the welding area.

In a further exemplary embodiment (FIG. 4), 6a and 6b of the discharge vessel performing a molybdenum tube 30, which in a six-layer cermet plug 31 welded in at the outer end (19) is.

The molybdenum tube 30 holds the electrode 32 by means of a crimp 33 into which the electrode is welded gas-tight. Again, the hole in the Plug used first for filling. Only then will the tubular electrode system inserted and the annular gap welded closed at the outer end.

The feed-through tube 35 made of molybdenum can be used in a further exemplary embodiment a high-watt lamp with 250 W power (Figure 5) also be cylindrical throughout. At its discharge end the electrode 32 with a wide head 39 (two-layer coil) is eccentric on the outside attached. For the provisional fixation in the plug 37, the outermost one Layer 37f of the plug with the molybdenum tube 35 first by sintering connected.

After evacuation and filling, the tube 35 is filled with a metal pin 36 closed, which is welded to the tube 35. The tube 35 will welded to the outermost layer 37f of the plug 37 at the same time. The means that the permanent, permanent sealing of the bore of the plug by welding, since this technique is superior to direct sintering is.

The use of a tube as a feedthrough has the advantage that on it the electrode can be attached very easily. That has the extra Advantage that the relatively wide electrode is nevertheless by means of a much smaller one Bore in the plug can be made in the discharge vessel. Here the plug is inserted into it together with the one previously loosely Electrode system inserted into the end 6 of the discharge vessel and directly sintered in. At the same time, provisional sintering takes place the passage in the outermost end of the stopper (last layer of the stopper). Alternatively, the end of the implementation can be done with a transverse stop be provided to achieve a provisional bracket.

The size of the electrode is therefore not limited by the plug bore. In addition, the tubular bushing is used before the metal pin is inserted 36 as a filling opening.

In particular, this ensures that the filling opening is independent of the electrode size, which depends on the wattage of the lamp can.

The pipe technology is also very suitable for large wattages where the Electrode has a large diameter and large transverse dimensions. The pipe diameter is relatively uncritical because the difference in thermal expansion behavior between bushing and outermost Layer at the end of the stopper can be kept very small. In doing so, Pipe and outermost layer of the plug a similar material, in particular the same material, chosen.

The welding of the annular gap between pipe and plug or pipe and Filler pen is also possible with large diameters of these parts.

For large wattages, pipes are preferred as feedthroughs because pins that are adapted to the required large diameter of the electrode, too much Would remove heat. This would cause considerable start-up difficulties when lighting the lamp. This is the pipe technology presented here for the first time able to use metal halide lamps with ceramic Discharge vessel reliable even with large wattages (more than 150 W) to seal. As is known, the size of the electrode increases (in particular their outer diameter) with the performance, but according to the invention the diameter of the bushing must no longer be appropriate be enlarged.

In a particularly preferred embodiment, the implementation is finished pure molybdenum (pin or tube). The stopper consists of a cermet with six layers. The metal part of the cermet is tungsten, since with this metal because of its larger expansion compared to molybdenum the thermal expansion coefficient of each layer is easier can be controlled. The innermost layer consists of 2 vol .-% tungsten (corresponding to 10% by weight of tungsten), balance aluminum oxide. It is that Very well adapted end of the discharge vessel, that of pure aluminum oxide consists. The second layer contains approximately 15% by volume of tungsten, correspondingly 46 wt% tungsten. The third layer contains about 28 vol% tungsten, corresponding to 67% by weight of tungsten. The fourth layer contains about 42 Vol .-% tungsten, corresponding to 78 wt .-% tungsten. The fifth layer contains about 56% by volume of tungsten, corresponding to 88% by weight of tungsten. The outermost Layer contains about 69 vol .-% tungsten, corresponding to 90 wt .-% tungsten. This last layer is therefore the coefficient of thermal expansion ideally adapted to the bushing made of molybdenum.

The above values are chosen so that the difference in the coefficient of thermal expansion about the same distance for all layers of the stopper to each other. The load is therefore evenly distributed. Here is a temperature of 1000 ° C taken as a benchmark.

Claims (10)

Metal halide lamp with a ceramic discharge vessel (4) Alumina, wherein the discharge vessel has two ends (6), the are closed with plugs (11), and through which plugs a electrically conductive bushing (9, 10; 20; 30; 35) passed through in a vacuum-tight manner on which an electrode (14) with a shaft (15) is attached is, which protrudes into the interior of the discharge vessel, the Plug consists of axially arranged layers or layers, wherein the material of the layers consists of cermet, the metal content of increases inside out, characterized in that the stopper at least at one end (6) of the discharge vessel from at least four axially arranged layers or layers, and that the outermost Layer (11d) of the plug made of a weldable material with at least 50 vol .-% metal (rest ceramic), the Carrying out (9) with the outermost layer of the stopper through a Weld (19) is connected and wherein the innermost layer (11a) of the Plug without glass solder is attached in the end of the discharge vessel. Metal halide lamp according to claim 1, characterized in that the implementation of a pin (9, 10) made of high-temperature-resistant metal, in particular tungsten or molybdenum, or from electrically conductive Cermet is, in particular the material of the pen approximately matches that of the outermost layer of the cermet stopper. Metal halide lamp according to claim 1, characterized in that the stopper consists of up to six layers, the metal content of which increases on the outside. Metal halide lamp according to claim 1, characterized in that the outermost layer of the plug is made of pure metal. Metal halide lamp according to claim 1, characterized in that the innermost layer of the stopper is made of pure aluminum oxide. Metal halide lamp according to claim 1, characterized in that the innermost layer (11a) of the stopper in the end of the discharge vessel is sintered directly. Metal halide lamp according to claim 1, characterized in that the implementation of a tube (30; 35) made of high temperature resistant Metal, especially tungsten or molybdenum. Metal halide lamp according to claim 7, characterized in that the electrode head is wider than the outside diameter of the tube. Metal halide lamp according to claim 1, characterized in that a filler pin (36) is inserted into the tubular feedthrough (35). Metal halide lamp according to claim 7, characterized in that the tubular bushing for a lamp with a high wattage, in particular at least 150 W is used.

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