JPH09129178A - Sintered type electrode for metal vapor discharge lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal vapor discharging sintered type electrode having a long life and excellent lamp characteristics by forming a tip protrusion portion of a specific dimension relationship in a sintered body made of high melting point metal powder and an electron radiative substance. SOLUTION: Mixed powder of high melting point metal powder such as tungsten or the like and an electron radiative substance such as barium calcium tungstate or the like are pressed so as to stick to a tungsten rod, and the same is sintered in vacuum so as to obtain a sintered type electrode composed of a sintered body 1, the tungsten rod 2, and the tip protrusion portion 3 thereof, and used for a metal vapor discharge lamp. The protrusion portion 3 is formed so as to meet a formula 1>=(R-r)/2, where the diameter of the sintered body 1 is R, the diameter of the protrusion portion 3 is (r), and the length is (l). Thereby, it is possible to completely prevent the occurrence of the blackening of a light-emitting tube inner face caused by the splash of the electron radiative substance from the sintered body by electron impact during the operation of the discharge lamp.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of a sintered electrode used in a metal vapor discharge lamp.

[0002]

2. Description of the Related Art Sintered electrodes are usually formed by pressing mixed powder of refractory metal powder such as tungsten, tantalum, molybdenum, etc. and electron emissive material such as tungstate onto a tungsten rod etc. It is made by heating the body in a vacuum and sintering it. Compared with the coil type electrode, the sintered type electrode can secure a large amount of the electron emissive substance, and thus has an advantage that the life of the metal vapor discharge lamp can be extended.

When a metal vapor discharge lamp in which sintered electrodes are sealed at both ends of an arc tube is produced, an electron radioactive substance is scattered from the sintered body due to an electron impact during the operation of the discharge lamp to release the metal vapor. There is a problem that the light adheres to the inner surface of the arc tube of the electric lamp, resulting in blackening of the end of the arc tube and a decrease in the luminous flux during lighting. This is more noticeable in high wattage lamps with high current values.

[0004]

For this reason, JP-A-52
No. 11677 proposes to prevent the sintered body from scattering and evaporating from an electron impact by providing a protruding portion of a tungsten rod at the tip of the sintered body. However, even with a metal vapor discharge lamp that uses a sintered electrode with a protrusion, depending on the size of the sintered electrode, electron emissive material may scatter from the sintered body due to electron impact during operation, resulting in May adhere to the inner surface of the arc tube.

The present invention has been made in view of the above, and by defining the length of the protruding portion, it is possible to completely suppress the scattering of the electron emissive material from the sintered body due to the electron impact, and to prolong the life. It is an object of the present invention to provide a sintered electrode for a metal vapor discharge lamp having excellent lamp characteristics.

[0006]

The present invention provides a tip for use in a metal vapor discharge lamp which is obtained by heating and sintering a mixed powder of a refractory metal powder such as tungsten and an electron emissive material such as barium calcium tungstate. In a sintered electrode provided with a protrusion, when the diameter of the sintered body is R, the diameter of the protrusion is r, and the length of the protrusion is 1, l ≧ (R−r) / 2 In addition, a protrusion is formed.

[0007]

With the above construction, the sintered electrode according to the present invention can completely prevent the scattering of the electron emissive material from the sintered body due to electron impact during the operation of the metal vapor discharge lamp. At this time, the optimum value of the diameter R of the sintered body is obtained from the inner diameter of the arc tube, the lamp input, and the like. The diameter of the protruding portion is defined by the lamp current value and the like.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory diagram of a sintered electrode used in a metal vapor discharge lamp such as a high pressure sodium lamp. In FIG. 1, 1 is a refractory metal such as tungsten, tantalum, molybdenum, and an electron emitting substance such as barium calcium tungstate. Is a sintered body. Reference numeral 2 is a tungsten rod (core rod) whose main component is tungsten, and a protrusion 3 from the sintered body 1 is formed at the tip of the tungsten rod 2.

In such a sintered electrode, a mixed powder of a refractory metal powder such as tungsten, tantalum and molybdenum and an electron emissive material such as tungstate is pressed on a tungsten rod and fixed, and the pressed body is fixed. It is created by heating in a vacuum and sintering. At this time, the tungsten rod may be thoriated tungsten having tungsten as a main component. In the present invention, when the mixed powder is pressed and fixed to the tungsten rod, the diameter of the sintered body of the sintered electrode is R, the diameter of the protrusion is r, and the length of the protrusion is l. , L ≧ (R−r)
Pressing is performed so that it becomes / 2, and one end of the tungsten rod is provided as a protruding portion.

[0010]

Next, an experimental example will be described. 80% by weight of tungsten powder, Ba ₂ Ca as an electron emitting substance
A mixed powder of WO ₆ 20% by weight was mixed with l = 0.8 mm and R =
The tungsten rod was pressed and fixed so that 2.5 mm and r = 0.9 mm. A 220 watt high pressure sodium lamp was used with this sintered electrode.
I made a lamp. When this lamp was turned on for 12000 hours, no blackening at the end of the arc tube was observed. Further, when the luminous flux maintenance factor from the initial stage was obtained, it was found that it was maintained at 95% on average, and the sintered type electrode without a protrusion or the length l of the protrusion
Was higher than that of a lamp using a sintered electrode in which 1 <(R-r) / 2.

In the present invention, the length l of the protruding portion is set to l ≧ (R−r)
However, if it is less than this, the electron emissive material scatters from the sintered body after long-time lighting, blackening of the arc tube occurs, and the luminous flux maintenance factor lowers. It has a short life. The optimum value of the diameter R of the sintered body is determined from the inner diameter of the arc tube and the lamp input. Further, the diameter of the protruding portion is defined by the lamp current value of the arc tube and the like. Although the high-pressure sodium lamp has been described as the discharge lamp, substantially the same result is obtained when the sintered type electrode is used as the electrode of the metal halide lamp or the high-pressure mercury lamp.

[0012]

As is apparent from the above description, the present invention prevents the scattering of electron emissive substances from the sintered body due to electron impact during the operation of the metal vapor discharge lamp by defining the electrode dimensions. be able to. As a result, it is possible to obtain a metal vapor discharge lamp using a sintered electrode having a good luminous flux maintenance factor and a long life.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a sintered electrode according to the present invention.

[Explanation of symbols]

 1 Sintered body composed of refractory metal and electron emitting substance 2 Tungsten rod 3 Tip projection of tungsten rod

Claims (1)

[Claims] 1. A sinter type having a protruding portion at the tip used for a metal vapor discharge lamp, which is obtained by heating and sintering a mixed powder of a refractory metal powder such as tungsten and an electron emitting substance such as barium calcium tungstate. In the electrode, when the diameter of the sintered body is R, the diameter of the protrusion is r, and the length of the protrusion is 1,
A sintered electrode for a metal vapor discharge lamp, wherein a protrusion is formed so that l ≧ (R−r) / 2.