JPH087837A - Metallic vapor discharge lamp - Google Patents

Abstract

PURPOSE:To obtain a metallic vapor discharge lamp with a long service life by sealing conductive cermet caps to both ends of a single crystal alumina tube, penetrating the centers of cylindrical ceramic compacts to the inner surface ends of the caps, and burying electrodes and external leads. CONSTITUTION:At both ends of a single crystal alumina tube 1, projecting form of conductive cermet caps 2 made of alumina-tungsten are sealed airtight by a glass frit 3. Tungsten electrode arbors 4 are buried at the center in the tubes of the caps 2, an alumina membrane is coated to cover the exposed surfaces in the tubes, cylindrical alumina compacts 6 with the diameter about half of the outer diameter of a luminous tube are sintered integrally thereover, and the electrode arbors 4 are penetrated to the centers of the compacts 6 and buried integrally. And an excessive additive of a metal halogenation substance is added. In this case, the arbors 4 are a little longer than the projecting length of the compacts projecting into the inner side of the caps. By such a constitution, the lamp starting is improved, a tube wall blackening by the spattering of the electrode substance and the like at the starting is not generated, and a long service life is realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal vapor discharge lamp using a single crystal alumina tube as an arc tube, and more particularly to improvement of electrodes at both ends of the arc tube.

[0002]

2. Description of the Related Art Instead of a quartz arc tube, a translucent ceramic tube having higher heat resistance than quartz, chemical stability and pressure resistance can be used as the arc tube of a metal halide lamp. It is proposed as No. 52-71695. FIG. 3 shows an example thereof, in which reference numeral 21 is a ceramic arc tube, and end caps 22 made of a conductive cermet made of alumina and tungsten metal are provided at both ends of a straight tubular pipe with glass frits 23 as a sealing agent. The end cap 22 has an electrode mandrel 25 having a tungsten coil 24 at the tip thereof, and a lead rod 26 buried and fixed on the outer side thereof. The metal halide is enclosed in the tube together with mercury and a rare gas. Also, JP-A-63-2571
No. 79 discloses a range of arc lamps between both electrodes, a tube wall load or a tube inner diameter, in which the luminous characteristics and operating voltage of the lamp are optimally designed values in the same arc tube as described above.

When designing such an arc tube, the ceramic tube length and tube diameter are restricted by the end sealing structure and the sealing method. Therefore, the method of sealing the arc tube shown in FIG. 3 will be described. An additive is placed in an arc tube in which one end opening of a ceramic tube is sealed in advance with a conductive cermet cap through a glass frit, and the mixture is placed in a rare gas atmosphere. A method of sealing the other end opening with a cap is also performed. In the final sealing, when the glass frit molded body is heated, the other end where the additive stays is cooled in order to prevent the mercury and the additive encapsulated before heating from scattering. This cooling must be maintained until the glass frit in the heated portion is melted and the solidification is completed. However, if the heating part and the cooling part are close to each other, that is, if the light emission length is short, the temperature of the mercury to be cooled rises due to the heat of the heating part and scatters. In addition, the larger the heated portion, the more difficult it is to heat, and the diameter of the arc tube is also restricted.

On the other hand, in the case of an optical lamp in which the luminous intensity density of the arc between the electrodes of the arc tube and the brightness of the arc tube are important, the lamp is not for general illumination, and the arc tube has a small linear transmittance. It is useful as a short arc length lamp that uses a single crystal alumina tube having a large linear transmittance in place of the photoceramic tube to increase the brightness of the arc tube and increase the emission density of arc discharge.

[0005]

In the case where both ends of a single crystal alumina tube are hermetically sealed with a conductive cermet cap through a glass frit, in order to enhance the airtightness and halogen resistance, which are the characteristics after the glass frit is melted and solidified. In this case, the heating rate of temperature rise and the rate of temperature decrease are important. Further, although the single crystal alumina tube and the conductive cermet cap chemically react with the glass frit component to be bonded, the temperatures of both the single crystal alumina tube and the conductive cermet cap must be raised.

In order to hermetically seal one end of a single-crystal alumina tube with a conductive cermet cap, and enclose mercury or a metal halide in the alumina tube, and then to seal the other end with a conductive cermet cap, the first sealed enclosure. It is necessary to cool the area where the material is accumulated. However, since the other end is cooled during the second seal heating, the temperature of the heated portion does not easily rise, and the distance between the heating portion and the cooling portion is large in order to heat at the predetermined heating rate. The temperature rises more easily. For this reason, in order to perform good sealing, the arc tube has to be long in spite of the short arc length.

On the other hand, starting of the arc tube shifts from discharge of argon and mercury between facing electrodes to glow discharge and arc discharge. From glow discharge to arc discharge, the temperature must rise until thermionic electrons are emitted at the electrode tip.
However, since the arc tube length cannot be shortened indefinitely from the above-mentioned sealing method, in the short arc length lamp, the electrode length embedded in the conductive cermet cap must be increased. For this reason, in the glow discharge, there is a problem that glow discharge does not occur between the electrode tips, glow discharge occurs from the middle of the electrode mandrel or in the vicinity of the base, the temperature of the electrode tip does not rise, and arc discharge cannot be performed. Further, the glow discharge at this time sputters tungsten as an electrode material, and the arc tube is blackened.

The present invention has been made in view of the above, and has a good starting characteristic in a short arc lamp made of a single crystal alumina tube, and has a long life without the blackening of the arc tube wall. The purpose is to provide a lamp.

[0009]

According to the present invention, a conductive cermet cap in which an electrode mandrel and an external lead are embedded is sealed at both ends of a single crystal alumina tube through glass frits, and an ionizable gas is sealed inside. The electrode mandrel is formed by penetrating through a central portion of a cylindrical ceramic molded body formed on the inner end surface of the conductive cermet cap and having a length shorter than the electrode mandrel.

[0010]

According to the present invention, glow discharge at the start of the arc tube is generated from the tip of the electrode, the temperature of the tip rises quickly, and the transition time to arc discharge is shortened. Also, the sputtering of the electrode material is reduced, and the blackening of the tube wall is reduced.

[0011]

EXAMPLE A metal halide lamp which is an example according to the present invention will be described with reference to FIG. A conductive cermet cap 2 made of alumina-tungsten having a convex shape is hermetically sealed to both ends of the single crystal alumina tube 1 via a glass frit 3 serving as a sealing agent. Also, the cap 2
An electrode mandrel 4 made of tungsten is embedded in the center of the tube. Further, an alumina layer 5 having a thickness of 1 mm or less is deposited on the exposed surface of the inside of the tube of the cap 2, and a cylindrical alumina molded body 6 having a diameter of about half the outer diameter of the arc tube is integrally formed thereon. The electrode mandrel 4 is integrally sintered by penetrating through the center of the molded body 6. In addition, 7 indicates a surplus additive of a metal halide. Here, the electrode mandrel 4 projects by about 2 mm longer than the projecting length of the molded body 6 to the inner surface of the cap.

The reason why the electrode mandrel 4 is covered with the alumina molded body 6 which is an insulator excluding the tip end is that the length of the electrode mandrel projecting from the inner surface of the cap is longer than the arc length. The reason is that the method of sealing both ends of the arc tube is required. Therefore, this sealing method will be described with reference to FIG. First, the opening at one end of the single crystal alumina tube 1 is sealed with a conductive cermet cap 3a formed by integrally sintering the alumina compact 6a via the glass frit 2a. Next, it is placed in a water-cooled metal holder 11 with the sealing part facing downward, and additives such as mercury and metal halides are sealed from the other end opening, and a ring-shaped glass frit is attached to the end surface of the opening. The alumina molded body 6b is integrally sintered with the cap 3b sandwiching the 2b so as to be inserted into the alumina tube. Then, the pipe-shaped metal heater 12
Are arranged on the outer circumference of the end portion. The lower end A-A of this heater 12
Is the BB 2 to be sealed from the top of the alumina tube 1.
It is placed in a double length position. The distance between the heater 12 and the outer surface of the alumina tube 1 is 6 mm. Under this heater installation condition, the heater is heated to 1500 ° C. in about 1 minute by high frequency heating, and the radiant heat heats the alumina tube 1, the glass frit 2b and the cap 3b to 1450 ° C.

Here, when the distance between the end surface on the cooling side and the end surface on the heating side of the alumina tube is 20 mm or less, the glass frit melts, but thereafter the heat in the heating section conducts and mercury as an additive evaporates. It was confirmed that the pressure inside the arc tube increased and the molten glass frit could not flow into the gap between the alumina tube and the cap, and could not be hermetically sealed.
Further, it is considered that the evaporation of mercury can be prevented by lowering the temperature of the cooling part, but the temperature rise of the heated part becomes slower,
The glass frit becomes difficult to melt. Thus, the length of the single-crystal alumina tube is required to be 20 mm, and if the sealing length of the cap is 2.5 mm and the arc length is 3 mm, the electrode length protruding from the conductive cermet cap is 6 mm.

In an arc tube having an electrode projecting from the cap inside the arc tube of 6 mm and an arc length of 3 mm, a pulse of 13 KV, 60 PPS was generated at the time of starting, comparing the case where there was no ceramic molded body covering the electrode mandrel. And the time from the start of glow discharge to the transition to arc discharge using a power source with no load voltage of 280 V when there is no ceramic compact 3
It took about 10 minutes, but if a ceramic molded body is provided, it will take about 10 minutes.
The time was shortened to seconds, and the blackening of the inner surface of the alumina tube due to the glow discharge sputtering of the electrode was prevented.

[0015]

INDUSTRIAL APPLICABILITY As described above, the metal vapor discharge lamp according to the present invention is most suitable as a short arc type optical lamp consisting of a single crystal alumina tube, and the starting of the lamp is good and the electrode material There is an advantage that blackening due to sputtering does not occur and the life is long.

[Brief description of drawings]

FIG. 1 is a side view showing an embodiment of a metal vapor discharge lamp according to the present invention.

FIG. 2 is likewise an explanatory view showing a lamp manufacturing process.

FIG. 3 is a side view showing a conventional discharge lamp.

[Explanation of symbols]

 1 Single Crystal Alumina Tube 2 Conductive Cermet Cap 3 Glass Frit 4 Electrode Mandrel 5 Alumina Layer 6 Alumina Molded Body 7 Additive 11 Single Crystal Alumina Tube 12 Glass Frit 13 Conductive Cermet Cap 14 Metal Holder 15 Additive 16 Ring Glass Frit 17 Conductive cermet cap 18 Heater

Claims (1)

[Claims] 1. A conductive cermet cap, in which an electrode mandrel and external leads are embedded via glass frit, is sealed at both ends of a single crystal alumina tube, and an ionizable gas is sealed inside the electrode mandrel. Is a metal vapor discharge lamp that is formed on the inner end surface of a conductive cermet cap and is embedded through a central portion of a cylindrical ceramic molded body that is shorter than the electrode mandrel length.