JPS6145552A - Metal vapor discharge lamp - Google Patents

Abstract

PURPOSE:To surely prevent damage to the end part of a luminous tube by an arc spot when starting by providing a rod-shaped arc back preventive needle made of tungsten in the rear of an electrode of the inner end part of a ceramic luminous tube. CONSTITUTION:A rod-shaped arc back preventive needle 7 made of tungsten is welded en bloc on an electrode lead-in wire 4 so as to be positioned in the rear of an electrode 3 inside a luminous tube 1 made of ceramics. For instance, projection ends 7a, toward the central part side of the luminous tube 1, of an arc back preventive needle 7 made of tungsten provided in the rear of the electrode is made to extend about to the central part of the electrode 3 so as to hold the electrode core 11 between the flat part 4a provided on the electrode lead-in wire 4 and the arc back preventive needle 7 made of tungsten while welding them en bloc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a metal vapor discharge lamp in which a rod-shaped arc prevention needle made of tungsten is provided behind an electrode in a ceramic arc tube.

[Prior art]

Conventionally, in a metal vapor discharge lamp using a ceramic arc tube, an arc spot is not formed on the electrode at the start of discharge, but is formed by moving to the end of the arc tube. It is known that a so-called arcing phenomenon occurs, and in some cases, the end of the arc tube may be damaged due to thermal shock.

In order to prevent such arcing phenomenon, for example,
In publications such as No.-2903, as shown in Figure 1,
Behind each electrode (3) is a circular arc prevention plate (5
) is attached to cover the end of the two arc tubes (1) from the inside to prevent the arc spot from moving to the end of the arc tube.

However, with the arc prevention plate as described above.

Due to its heat reflection effect, the temperature at the end of the arc tube drops too much, making it difficult to obtain appropriate lamp characteristics.Also, since the arc prevention plate is plate-shaped, its material is easy to work with. Limited to molybdenum (MO), tankard (Ta), etc. However, these materials have the disadvantage that when a spot is formed, it easily evaporates and adheres to the inner wall of the two arc tubes, resulting in deterioration of the luminous flux.

[Summary of the invention]

In view of the above-mentioned drawbacks of the conventional ones, this invention uses a rod-shaped arc-preventing needle made of tungsten (W), which has low evaporation, and is easy to process, behind the electrode at the inner end of the ceramic arc tube. This is a replacement for the conventional arc prevention plate.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be explained regarding a high-pressure sodium lamp.
This type of arc prevention phenomenon disclosed in Publication No. 6 will be explained.

That is, the electrodes (3) at both ends of the arc tube (1) shown in FIG.
When a starting voltage is applied to the starting voltage, the starting gas sealed inside is ionized and arc discharge is started.

After that, the heat of this arc discharge causes the inclusions in the two arc tubes (1) to become ? For example, it is known that sodium and mercury evaporate and are ultimately generated. Generally each electrode (3) just before starting
, inclusions such as sodium and mercury adhere to the surface of the electrode, reducing the electron emitting ability of the single pole itself. By the way, the phenomenon of the above-mentioned inclusions adhering to the electrode surface can be summarized as the inclusions inside the lamp that evaporated immediately after the lamp was turned off.

This is due to dew condensation on each electrode where the cooling rate is high.

Specifically, the ceramic arc tube (1) has a lower thermal conductivity than each electrode (3), so its cooling rate is low.
Therefore, the evaporated inclusions were removed from the ceramic arc tube (1
), the condensation is captured by the colder electrodes (3), resulting in dew condensation on the electrode surfaces.

Under these conditions, when discharge starts, each electrode (3)
As the temperature rises, the sealing substance on the electrode surface immediately evaporates,
It adheres to the inner wall of the ceramic arc tube (1) in the vicinity of one pole, and this is the cause of arc tube glaucoma due to movement of the arc spot.

By the way, the enclosed substance evaporated from each electrode (3).

As shown in Figure 3, starting from the tip of the electrode, it spreads in all directions as indicated by the arrows in the figure, and although the temperature of each electrode (3) at this time has risen to some extent, the position of the arc spot is Since the temperature is not high enough to determine the arc spot (9), the arc spot (9) is located in front of the electrode.
(Moves toward point 81 as shown in the figure. After that, the temperature of each electrode (3) gradually increases, so the arc spot does not move from each electrode (3) to the deposit layer on the inner wall of the pipe. Even if there is, it cannot move to the end deposit layer behind each electrode (3).

As a result of detailed study by the inventors, the reason why the arc spot moves to the end of the arc tube behind each 'rTL pole (3) is mainly because the temperature of each electrode (3) is low after the start of discharge. ,
It has been found that this phenomenon tends to occur when inclusions remain on the surface of the electrode without being evaporated. This is because the temperature of each electrode (3) is extremely low, so there is almost no so-called thermionic emission, and as mentioned earlier, each electrode (3)
This is thought to be due to the fact that electron emission due to an electric field is difficult to occur due to the inclusions attached to the surface of the electrode.

Therefore, one of the specific reasons why the arc spot moves beyond the electrodes to the end of the arc tube is due to the contact resistance at the connection Ql between each electrode (3) and the electrode lead-in wire (4).
Immediately after the start of discharge, the temperature of this connection part Q (I rises instantaneously, and therefore the electron emission property from this connection part < 11 is improved. Another reason is that the above-mentioned electrode introduction There is often a gap between the wire (4) and its cap (2) 9. Furthermore, there is a sealant (6) at the base of these lines, and this sealant (6) is generally electron-radioactive. This may also be due to the fact that it is good.

For the above-mentioned reasons, it has become clear through studies by the inventors that in order to prevent arcing, it is not necessarily necessary to use the conventional circular arc-preventing plate.

Based on these study results, the inventors have developed a ceramic arc tube (1) equipped with a conventional arc prevention plate (5) as shown in Figure 1, and a circular arc prevention plate (5). On behalf of the fourth
A ceramic arc tube (11) with a tungsten rod-shaped reverse arc prevention needle (7) attached as shown in the figure was prototyped.

The state of arc spot formation after the start of discharge was investigated.

As a result, the arc-prevention plate (5
) also has the same effect as the arcing prevention needle (force) of the present invention. That is, in order to prevent this kind of arcing phenomenon, the needle must have a large area to cover the end of the arc tube. There was no need to use an arc prevention plate, and a rod-shaped arc prevention needle with a small flat area (force was sufficient. In particular, it was possible to reduce the contact resistance between the electrode (3) and the electrode introduction wire (4). Introduced the flat part (
By forming 4a) to increase the electrical contact area at the core, the effect of preventing arcing became even more pronounced.

FIG. 5 shows the center i1i! of the electrode (3) in the present invention.
j! (This is an enlarged cross-sectional view taken along line V-V in Figure 4, in which an arc prevention needle (force) is welded to the welded part between 1υ and the flat part (4a) of the electrode lead-in wire (4) so as to be in contact with both of them. Figure 6 shows another embodiment in which the arc prevention needle (7) of the present invention is welded only to the flat part (4a) of the electrode introduction wire (4). (7) and the flat part (4a) of electrode introduction M (4) hold the electrode core wire αυ in a sandwiched state, so it is more effective than the structure shown in Fig. 6 in increasing the contact area between them. be.

The inventors prototyped 271,610 high-pressure sodium tubes each having a ceramic arc tube (1) having an arc prevention needle (7) with the welded structure shown in FIGS. 5 and 6.

As a result of investigating the discharge start state of each, the above-mentioned arcing phenomenon was observed in 10 and 9L wires with the structure shown in Figure 6, whereas the arcing phenomenon was observed with the structure shown in Figure 5. was not observed at all.

Even with the structure shown in Figure 6, the arc was caught by the arc prevention needle (7) and did not transfer to the end of the two arc tubes (1). In addition, the protruding end (7a) of the arc prevention needle (7) toward the center of the arc tube is preferably extended to the center of the electrode (3), and its material is tungsten (W) that evaporates. I found it to be the most suitable.

In addition, there is a conventional high-pressure sodium lamp having an arc-preventing plate (5) made of Mo as shown in FIG. As a result of making 50 prototypes of each type and conducting lighting tests on each, none of them failed to light up after 9,000 hours.

The luminous flux maintenance rate is 10% for the conventional model shown in Figure 1.

The product of the present invention shown in FIG. 4 maintained 95%.

Although a high-pressure sodium lamp has been described above, other metal vapor discharge lamps using ceramic may be used, and the ceramic material may be alumina or magnesia. Note that the shape of the arc prevention needle of the present invention is not necessarily limited to the U-shape shown in the drawings.

〔Effect of the invention〕

As described above, the metal vapor discharge lamp of the present invention is positioned behind the electrode within the ceramic arc tube.

By integrally welding a tungsten rod-shaped arc prevention needle onto the electrode lead-in wire, it is possible not only to reliably prevent the end of the arc tube from being damaged by the arc spot during startup, but also to reduce the temperature at the end of the arc tube. This has the advantage that a metal vapor discharge lamp with a good luminous flux maintenance rate that can be used for a long period of time and whose lower part is not too υ can be obtained by simply modifying the electrode section.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional high-pressure sodium rung using a circular arc prevention plate, Figure 2 is an enlarged plan view of the arc prevention plate, and Figure 3 is the inner wall of the arc tube containing the luminescent substance sealed inside the arc tube. An explanatory diagram of the state of scattering adhesion to FIG. 4 is a partially enlarged sectional view showing one embodiment of the metal vapor discharge lamp according to the present invention, FIG. 5 is a partially enlarged sectional view showing the welding structure of the arc prevention needle adopted in the present invention, The figure is a similar partially enlarged sectional view showing another embodiment of the welded structure. In Figure 1, (1) is the arc tube, (3) is the electrode, (4) is the electrode lead-in wire, (4a) is its flat part, and (7) is the arc prevention needle. (7a) indicates the protruding end, and Qυ indicates the electrode core wire. In the other nine figures, the same reference numerals indicate the same or corresponding parts. Agent Masuo Oiwa (and 2 others) Figure 1 Figure 3 Figure 5 Figure 6

Claims (3)

[Claims] (1) A metal vapor discharge lamp characterized in that a tungsten rod-shaped back arc prevention needle is integrally welded onto the electrode introduction line so as to be located behind the electrode in the ceramic arc tube. (2) The metal vapor discharge lamp according to claim 1, wherein the electrode core wire is welded together so as to be sandwiched between the flat part provided on the electrode introduction wire and the tungsten back-arc prevention needle. (3) Any one of claims 1 and 2, wherein the protruding end of the tungsten back-arc prevention needle provided at the rear of the electrode toward the center of the arc tube is extended to approximately the center of the electrode. A metal vapor discharge lamp described above.