EP0451647A2 - High-pressure discharge lamp and method for its manufacture - Google Patents

Abstract

In a discharge lamp which is pinched on two sides, the pinch seals are provided with constrictions (16) of the broad sides and reinforcements (17) of the narrow sides. In consequence, the heat localisation behaviour and the mechanical stability are improved. …<IMAGE>…

Description

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

Such lamps are lamps that are pinched on both sides with or without an outer bulb. They generally have a quartz glass discharge vessel and in particular have a metal halide filling. The lamps are preferably used in optical systems such as headlights and lighting systems, e.g. for floodlights, stage, film and television, with typical lamp powers of 400 to 4000 W. Smaller wattages can be used in shop window or general lighting (e.g. 150 W).

From US Pat. No. 4,396,857 and EP-OS 266 821, bilaterally squeezed miniature high-pressure lamps of low power (35 W) with outer bulbs with a discharge volume of less than 1 cm 3 are known. In order to avoid collecting the excess metal halide in the coldest places, in the space behind the electrodes, and to ensure precise electrode adjustment, these lamps have pinch seals, to which a cylindrical transition area towards the Connects discharge vessel. This transition area is constricted in the plane of the pinch seal, widened with respect to the narrow sides of the pinch seal. In comparison to the discharge vessel, the transition area has an increased wall thickness with an accumulation of glass mass. The result is an actually undesirable, relatively good heat conduction and heat dissipation to the pinch seals and also a relatively good heat radiation due to the large radiating surface of the cylindrical transition area. Overall, the heat build-up effect with these lamps is therefore not entirely satisfactory. In addition, the manufacture of such a lamp is relatively complicated since the transition region is produced in two process steps. The actual squeezing process takes place with two squeeze jaws.

Furthermore, from DE-GM 89 12 495 a double-sided pinched metal halide lamp of high power is known (1000-2000 W), which is operated without an outer bulb. Here, the heat accumulation behavior plays a particularly critical role, because otherwise the halide vapor pressure and the color temperature will not reach their optimally desired values. In some cases, therefore, a heat build-up must be used, but this increases the color dispersion of the lamps and causes shading. Another disadvantage of this type of lamp without an outer bulb is that the end regions break relatively easily at the transition points to the central region, since the end regions are capped directly.

It is an object of the present invention in a high-pressure discharge lamp, the heat accumulation effect to further improve the ends of the discharge vessel and to increase the temperature there and to provide a method for producing such a lamp.

This object is achieved by the characterizing features of claim 1 and the method steps of claim 11. Particularly advantageous designs can be found in the subclaims.

The lamps according to the invention can be produced particularly easily because a special transition region can be dispensed with and instead the constriction is designed as part of the pinch seal in a single process step during the pinching process.

The end regions designed as pinch seals are only constricted in the pinch plane, without in the transverse direction, i.e. in terms of the narrow sides to be thickened. In this way, the glass mass present in this area is considerably reduced. The radiating surface is also reduced. In this way, a significantly better heat accumulation effect can be achieved, which leads to an increase in the final burner temperature. Typical is e.g. an increase of 50 - 100 ° C. As a result, there is no need for heat accumulation, the color scatter is reduced, the light yield is increased (by 5 - 10%) and the color rendering is improved.

A particularly important advantage of the present invention is the significantly improved constancy of the color temperature, which is also significantly improved starting value is lower; Metal halide discharge lamps typically experience a sharp drop in color temperature during the first 500 hours of operation. The cause is that a metal halide sump gradually develops in the capillaries by diffusion, which exist along the electrode shafts between the foil and the discharge volume, since the thermal expansion coefficients of the electrode shaft made of tungsten and the quartz glass bulb differ greatly. This sump can no longer make a contribution to the vapor pressure in the discharge volume.

In the prior art, the use of a cylindrical transition area means that this capillary is inevitably lengthened and the disturbing drop in color temperature is therefore pronounced. In contrast to this, the present invention makes it possible to keep the length of the capillary extremely short despite the constriction, so that the drop in color temperature is considerably restricted. The length of the capillary is a maximum of about 10% of the length of the discharge volume along the longitudinal axis. In the case of lamps with a cylindrical transition region, the corresponding value deteriorates to approx. 28% in US Pat. No. 4,396,857 and approx. 54% (!) In EP-OS 266 821.

These advantages are particularly significant in the case of high-watt lamps without an outer bulb.

In a preferred embodiment, the end region is shaped like a double T. The means that the narrow sides of the pinch seal are widened and form edge beads in relation to the level of the pinch seal. In a particularly preferred embodiment, the edge beads widen as additional struts towards the central area, in particular over the entire length of the constriction. In this way, the pinch seals are additionally mechanically stabilized at their point of attachment to the central area. The end areas are reliably prevented from breaking off. Both the constriction and the bracing is particularly important for lamps without an outer bulb. The combination of both measures also leads to a particularly happy interaction during manufacture, since the glass mass saved in the constriction can be redistributed to the struts during the crushing process.

An exact centering of the electrode systems is ensured in particular if at least one centering knob is attached to at least one broad side of the pinch seal. The centering knob is also produced without additional effort only during the squeezing process, in that at least one of the squeezing jaws has at least one cavity in the squeezing surface.

In a particularly advantageous manner, the area of the central area directly adjoining the end areas is shaped during the squeezing process by appropriately designed squeeze jaws. Tangential bevels are embossed on the ends of the central area, which reduce the discharge volume behind the electrodes.

The manufacturing process for this lamp is characterized by time savings and the greatest possible simplicity. Both the shape of the constriction and the struts as well as the centering of the electrode system can be carried out in a single process step, the crimping process with four crimping jaws. These are two main pinch jaws that form the broad side of the pinch seal, at least one of which has a hollow for the centering knob and which have bevels for the struts. In addition, two side crushing jaws are used, which have a roof-shaped protruding nose at the end facing the central area, which shape the constrictions and struts. Particularly good shaping of the pinch seals is achieved by briefly delaying the side pinching process compared to the main pinching process.

Figur 1

eine Hochdruckentladungslampe mit einer Leistungsaufnahme von 2000 W in Seitenansicht

Figur 2

die Lampe gemäß Figur 1 um 90° gedreht sowie ein Querschnitt durch eine Quetschdichtung (Fig. 2a) unter Weglassung des Sockels

Figur 3

die Farbtemperatur dieser Lampe als Funktion der Betriebsdauer

Figur 4

die Temperaturverteilung in der Quetschdichtung einer derartigen Lampe

Figur 5

eine Hochdruckentladungslampe mit einer Leistungsaufnahme von 400 W in Seitenansicht

Figur 6

dieselbe Lampe in um 90° gedrehter Seitenansicht

Figur 7

die Quetschbacken zur Herstellung derartiger Lampen

The invention will be explained in the following using several exemplary embodiments. Show it

Figure 1

a high-pressure discharge lamp with a power consumption of 2000 W in side view

Figure 2

the lamp according to Figure 1 rotated 90 ° and a cross section through a pinch seal (Fig. 2a) with omission of the base

Figure 3

the color temperature of this lamp as a function of the operating time

Figure 4

the temperature distribution in the pinch seal of such a lamp

Figure 5

a high-pressure discharge lamp with a power consumption of 400 W in side view

Figure 6

the same lamp in a side view rotated by 90 °

Figure 7

the crimping jaws for the manufacture of such lamps

1 and 2 show a 2000 W high-pressure discharge lamp 1 with a length of approximately 190 mm, which does not require an outer bulb. It is intended for use in a reflector, not shown here, in which it is inserted axially. It has a piston 2 which consists of a central region and two end regions which extend in diametrically opposite directions. The very good approximation isothermal discharge vessel 3 made of quartz glass with a wall thickness of approx. 2 mm (or 2.5 mm), which forms the central area, is designed as a barrel body, the generatrix of which is an arc with a radius of curvature of 38.25 mm. The largest outer diameter of the barrel body is 36 mm, the axial length about 51 mm. The outer diameter at the barrel ends 4, on each of which an end region 5, which forms a pinch seal, is approximately 16 mm, so that a discharge volume of approximately 22 cm 3 results. The rod-shaped tungsten electrodes 6, the tips of which are spaced 30 mm apart, are each held axially in the end region 5 and have a double-layer coil 7 in the vicinity of the electrode tip. The end regions 5 have a length of approximately 40 mm and a width of approximately 16 mm. The electrodes 6 are connected via molybdenum foils 8, which are melted into the pinch seal in a vacuum-tight manner, to current leads (not visible) which are in contact with strands 9 of two sleeve bases. The molybdenum foils 8 have a length of approximately 30 mm and a width of 8 mm. On the ends of the pinch seals 5 remote from the base, the two ceramic sleeve bases 10 are fastened with cement, which consists of a slotted cylindrical holding part 11 and a flattened end body 12 facing the socket.

The films are arranged within the pinch seals so that the distance on the discharge side of the film end from the end of the pinch seal is approximately 4 mm. Only over this short distance can a capillary form in the pinch seal along the tungsten electrode 6, which captures the metal halide sump. The broad sides 13 of the pinch seal have beads 14 on the edges towards the narrow sides, so that the pinch seal 5 has a double T-shaped cross-section (ie two "T" abut it Base together). The thickness of the pinch seal is approximately 4 mm, the thickness of the edge beads 14 on the narrow sides 15 is approximately 7 mm (cf. FIG. 2a). Towards the central region, the broad sides 13 have constrictions 16 in the form of two bevels over an axial length of 5.5 mm, so that the broad side 13 tapers to 12 mm at the attachment of the end region to the central region without the thickness of the pinch seal changing. At the same time, the thickness of the edge beads 14 widens towards the central area, so that struts 17 are primarily formed in the area of the bevels. The thickness of the edge beads gradually increases from originally approx. 7 mm to approx. 8 mm at the break point 18 of the bevels and finally reaches approx. 10 mm at the starting point of the struts 17 in the central region.

The broad sides 13 of the pinch seals are provided with corrugation (not shown) and furthermore have elongated centering knobs 19a, b at the level of the electrodes 6 and the outer current leads 9. In the region of the central region adjoining the end regions, a total of four zones are formed as flat surfaces 20 with approximately square dimensions in the direction of the broad sides 13 and the narrow sides 15 of each pinch seal, said quasi approximations of the curvature of the central region as tangents. These tangential surfaces 20 form an obtuse angle with the planes of the broad sides 13 or the narrow sides 15, in particular approximately 150 ° or 130 °. In this way, the discharge volume behind the electrodes is additionally narrowed, which increases the temperature of the cold spot.

The discharge vessel 3 contains a filling of an inert gas (argon) as the ignition gas and mercury as the main component (approx. 220 mg) as well as the rare earths DyBr₃ (1 µmol and TmBr₃ (0.5 µmol) per cm³ discharge volume, also 1 µmol TlBr, 2 µmol CsBr and 0.5 µmol ThJ₄. The thorium can be replaced by hafnium. Overall, this filling gives an initial color temperature of approximately 5700 K (previously 5900 K) with a color rendering index of 92 (previously 90). The specified rare earth filling has the values x = 0.333, y = 0.346 as the color locus and the operating pressure is approximately 15 bar.

With a supply voltage of 380 V and a lamp current of 10.3 A, an operating voltage of 225 V is achieved.

The favorable overall design of the 2000 W lamp makes it possible to increase the total light output from 100 lm / W to 105 lm / W and to achieve an extremely long service life of approx. 2000 hours. The specific arc power is 67 W / mm.

The isothermally designed discharge vessel has a maximum bulb temperature of approx. 1030 ° C (hot spot), which drops to 1000 ° C (previously approx. 940 ° C) at the cold spot (behind the electrodes at the end of the vessel). At the end of the film, the temperature has dropped to 230 ° C (instead of 250 ° C earlier) (free-burning). In the headlight, this corresponds to a temperature of 330 ° C (previously 350 ° C). The term "earlier" refers to an identical lamp without constriction.

The special design of the pinch seal leads to significant improvements in the operating data of this lamp compared to conventionally designed pinch seals due to the heat accumulation effect of the constrictions. In addition, the tangential surfaces at the end of the central area increase the temperature in the volumes behind the electrodes (area of the cold spot).

The luminous flux remains almost constant at the initial value of 205,000 lm over the operating period (maintenance). The drop is only around 5% (previously around 15%). The color temperature (Fig. 3) shows an initial value of 5700 K (solid curve), which means a reduction of 200 degrees compared to earlier (dashed curve). At the same time, the drop in color temperature (ΔT = 500 K) during the operating period is much less pronounced than before (ΔT = 900 K after 1500 operating hours). Further advantages are the improved burning voltage (now approx. 5 - 10% higher) and the better stabilized re-ignition peak (340 V) at the beginning of the lamp's operating life.

The heat accumulation effect of the constricted pinch seal can be demonstrated directly with the aid of FIG. 4. It shows the broad side of the pinch seal for a lamp without constriction (FIG. 4a) and with constriction (FIG. 4b). The temperature distribution is characterized by lines of the same temperature (isotherms), where a denotes the highest and g the lowest temperature. The temperature d corresponds absolutely to about 350 ° C. The pinch used earlier (Fig. 4a) shows a relative steep gradients over their length, at the end of which a relatively high temperature d remains. As a result of the constriction (FIG. 4b), the pinch seal as a whole is subjected to considerably less temperature stress (e), and the stress is moreover distributed more evenly over the length of the pinch seal, in particular over the critical area of the melted film. Overall, the temperature at the end of the base is thus reduced, the sealing effect of the melt-in of the film is improved and the melt-in is less stressed. For reasons of measurement technology, the discharge-side edge zone of the pinch seal is not recorded in FIGS. 4a, b.

Because of the struts, bruises no longer occurred.

In a substantially identical lamp for 1000 W nominal power, in which previously a heat-dust coating made of ZrO₂ at the ends of the discharge vessel was appropriate, this coating can now be dispensed with, so that its shadowing effect is eliminated. As a result, the luminous efficiency could be improved by approx. 5 - 10% to values corresponding to the 2000 W lamp.

In a further exemplary embodiment of a metal halide lamp with a nominal output of 400 W, the design of the lamp bulb corresponds approximately to FIGS. 1 and 2. However, the lamp bulb is accommodated in an outer bulb and is smaller overall. With a total length of 86 mm in total, the press seals each have a length of approximately 20 mm, of which 4 mm are in the area of the constriction. The film with a length of 13 mm is melted into the middle of the pinch seal, so that the electrode shaft and the external power supply are each embedded about 3.3 mm into the pinch seal.

The width of the pinch seal of 16 mm is reduced to 9 mm in the constriction. The thickness of the press seal is approximately 2 mm and increases to 4 mm in the area of the edge beads. The edge beads themselves widen to 6 mm over the length of the constriction, forming the struts towards the central area.

Another exemplary embodiment of a metal halide lamp is shown in FIGS. 5 and 6. It has a cylindrical outer bulb 21 made of hard glass, which is provided at one end with a screw base 22 and at the other end with a dome 23. Coaxially with the outer bulb, a quartz glass bulb 24 with two axially opposite electrodes is arranged as a discharge vessel, which is held by means of a frame 25 including two current leads 26 and is melted into the outer bulb 21 in a gas-tight manner. The discharge vessel has a tubular central body 27, the two ends of which are enclosed by a box-like crimp 28, i.e. without ridges, is sealed.

The width of the pinch corresponds to the outer diameter of the central body 27. Similar to the first exemplary embodiment, the pinch has a constriction 29 which reduces the width of the pinch from 16 mm to 9 mm. The thickness of the pinch is about 2 mm. The narrow sides of the bruises widen to struts 30, which on Approach the central area to a thickness of 4 mm.

The lamp is manufactured from a blank for the quartz glass bulb with, for example, a barrel-shaped central region (cf. FIG. 1) and two tubular end regions. The pump stem is placed in the middle of this. Then an electrode system, consisting of an electrode, a molybdenum foil and an external power supply, the electrode and the external power supply being welded to the molybdenum foil, is inserted from below into the tubular end region and held there with an interchangeable holder.

After purging with argon gas, the end area is brought to squeezing temperature (approx. 1700 ° C) by two gas burners. The part of the piston that is still in the deformation area should also reach the pinch temperature. The end area is finally squeezed with a four-jaw squeezing machine while flushing with argon. The two main pinch jaws 31 (FIG. 7a) form the broad sides of the pinch seal. The pinch surface 32 of the main pinch jaws has two recesses 33 for centering the electrode system, which appear as centering knobs on the pinch seal. At the upper end 34 of the main crimping jaws facing the central region, two lateral bevels 35 are attached to the crimping surface in order to enable an engagement with two side crimping jaws 36. A third bevel 37 takes the squeeze surface 32 back close to its upper edge 34 by approximately 60 °. This slope 37 serves for the tangential shaping of the central area. Steps 38 are formed on the lateral edges of the squeeze surface, which produce the edge beads.

Two side crushing jaws 36 (FIG. 7b) act transversely to the main crushing jaws, the crushing surface 39 of which forms the narrow sides of the crushing seal. At the upper end of the crushing surface, a nose 40 projects like a roof, the ridge 41 running parallel to the upper edge of the crushing surface. The lower roof slope 42 protruding from the crushing surface is inclined by 30 ° from the plane of the crushing surface 39, the upper roof slope 43 has an inclination of 50 ° in this regard. The lower roof slope 42 creates the constriction, while the upper roof slope 43 forms the two remaining tangential surfaces of the central area. The upper edge of the main crimp jaw closes with the ridge of the side crimp jaw.

The struts in the edge beads result from the fact that the side slopes 35 of the main crushing jaws have a different inclination (19 °) than the lower roof slopes 42 of the side crushing jaws. It has proven particularly favorable if the side crushing jaws work with a slight time delay (approx. 0.5 sec) compared to the main crushing jaws.

The glass flask is then turned over and the second end area is closed using the same technique. The pumping stem is used to pump out, rinse and fill the discharge vessel in a manner known per se.

Claims (18)

High-pressure discharge lamp consisting of - An elongated glass bulb (2) with a central region (3) which encloses a discharge volume, and two end regions (5) which extend in diametrically opposite directions and which are used as compression seals with two flattened broad sides (13) and two narrow sides (15) are trained - A pair of electrodes (6) which is arranged in the discharge volume and which is connected to power supply lines which extend through the pinch seals to the outside - an ionizable filling characterized in that each pinch seal (5) has constrictions (16) on the broad sides at its end facing the central region (3) without the thickness of the pinch seal changing. High-pressure discharge lamp according to Claim 1, characterized in that the pinch seals (5) have the shape of a double T in cross section, the base points of the two T abutting one another, so that the flattened broad sides (13) are equipped with edge beads (14) which form the narrow sides (15) widen. High-pressure discharge lamp according to Claim 1 or 2, characterized in that the narrow sides (15) and possibly the edge beads (14) widen towards the central area (3) and thereby form struts (17). High-pressure discharge lamp according to Claim 3, characterized in that the struts (17) are formed in the region of the constrictions (16). High-pressure discharge lamp according to Claim 1, characterized in that the broad sides (13) of the pinch seals are equipped with one or more centering knobs (19) for the electrodes (6) and / or current leads (9). High-pressure discharge lamp according to Claim 1, characterized in that the region (6 ') of the electrode which is embedded in the pinch seal (5) is very short and lies entirely in the region of the constriction (16). High-pressure discharge lamp according to Claim 1, characterized in that the width of the flattened sides (13) is reduced by approximately 30 - 50% due to the constrictions (16). High-pressure discharge lamp according to Claim 1, characterized in that the constrictions (16) form bevels. High-pressure discharge lamp according to Claim 3, characterized in that the narrow sides (15) widen by approximately 30%. High-pressure discharge lamp according to claim 1, characterized in that the length of the constriction accounts for approximately 10-25% of the total length of the press seal. High-pressure discharge lamp according to Claim 1, characterized in that the central region (3) is bulged, flat surfaces (20) being formed on the attachment of the central region to the pinch seal, which are quasi-approximate to the curvature of the central region as tangent surfaces. High-pressure discharge lamp according to Claim 1, characterized in that the lamp bulb is the only bulb. High-pressure discharge lamp according to Claim 1, characterized in that the filling contains metal halides. A method for producing a high-pressure discharge lamp according to claim 1 with the following method steps - Provision of a glass bulb with a central area and two end areas - Squeezing a first electrode system into a first end region - Squeezing a second electrode system into a second end region - Pumping out, rinsing and filling the discharge volume characterized in that the constriction is formed by squeezing with two main crushing jaws (31) which have lateral bevels (35) on the crushing surface and with two side crushing jaws (36), each having a bevel (42) projecting from the crushing surface . Method according to Claim 14, characterized in that struts are formed on the narrow sides in that the lateral bevels (35) on the main crushing jaws (31) and the projecting bevels (42) on the side crushing jaws have different inclinations. Method according to Claim 14, characterized in that tangential surfaces are formed at the base of the central region in that the main crushing jaws (31) in the vicinity of the upper edge (34) of the crushing surface (32) have a surface (37) receding obliquely backwards and / or that the side crushing jaws (36) have roof-like lugs (40). Method according to claim 14, characterized in that the squeezing process of the side jaws is carried out with a time delay compared to the squeezing process of the main squeezing jaws. A method according to claim 14, characterized in that the main crimping jaws have depressions (33) for centering the electrodes and / or current leads which form the centering knobs.

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