JPH0215557A - High pressure sodium lamp - Google Patents

Abstract

PURPOSE:To keep an electrode axis at its high temperature so as to raise temperature at the outer end portion of an exhaust pipe where the end portion being the coolest portion by encircling the circumference of the electrode axis with a heat reserving tube made of metal with a space held therebetween. CONSTITUTION:Exhaust pipes 4 made of metal are airtightly attached respectively to both ends of a luminous tube bulb 1 formed of translucent ceramics, an electrode 7 is installed to each of these exhaust pipes 4, and a luminous metal which causes volatilization during the phase of lighting the bulb and also a rare gas are sealed into the luminous tube bulb 1 so that the luminous metal in surplus is condensed within the exhaust pipes 4. The circumference of the electrode axis 8 of the electrode 7 is then encircled with a heat reserving tube 10 made of metal, with a space toward this electrode axis 8. On this account, radiant heat ready to be emitted from the electrode axis 8 is prevented from its emission by the heat reserving tube 10. This makes it possible to raise temperature in the outer end portion of an exhaust pipe where the end portion being the coolest portion with the electrode axis kept at its high temperature and a more quantity of heat transmitted to the exhaust pipe.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Field of Application) The present invention provides an airtight metal exhaust pipe at both ends of an arc tube bulb made of a translucent ceramic with excellent heat resistance and corrosion resistance. This invention relates to a high-pressure sodium lamp that is attached to a lamp, electrodes are attached to these exhaust pipes, and in which excess luminescent metal during lighting is condensed in the exhaust pipe.

(Prior technology) High-pressure sodium lamps are made of a light-transmitting ceramic material with excellent heat resistance and corrosion resistance, such as light-transmitting alumina, and an exhaust pipe made of a metal such as niobium is attached to both ends of the bulb. These exhaust pipes each hold an electrode, and these electrodes are provided so as to face each other within the arc tube bulb. The arc tube bulb is filled with sodium Na amalgam in excess of the amount that evaporates during lighting, and with a starting rare gas such as xenon.

In such lamps, Na amalgam is evaporated during lighting and is excited to emit light, but excess Na amalgam is condensed in the outer end of the exhaust pipe, which is the coldest part during lighting. do.

In such lamps, it is known that increasing the vapor pressure of Na improves the color rendering properties of the lamp;
a The vapor pressure is affected by the amount of evaporation of excess amalgam that condenses in the coldest part. That is, increasing the temperature of the coldest part formed at the outer end of the exhaust pipe during lighting is effective in improving color rendering.

Conventionally, the heat from the electrode, which becomes high during lighting, was conducted to the exhaust pipe via the electrode shaft, thereby raising the temperature at the outer end of the exhaust pipe. This part is supported by a blocking wall that closes off the end of the arc tube bulb, so that the heat that is about to be transferred to the outer end of the exhaust pipe via the electrode shaft is transferred from the blocking wall in the middle to the end of the bulb. There was a limit to how much temperature could be raised at the outer end of the exhaust pipe, that is, the coldest part.

In order to eliminate such problems, conventionally, both ends of the arc tube bulb and the blocking wall that blocks these ends are covered with a heat insulating material made of a heat-resistant metal band, etc. Measures were adopted to prevent heat from being released from the wall to the outside, and to prevent heat from escaping from the middle of the exhaust pipe through the closing wall.

(Issue 8 to be solved by the invention) However, in the structure in which the end of the bulb is covered with the heat insulating material, if the heat retaining effect is to be further enhanced, the area covered by the heat insulating material at the end of the bulb must be increased. must,
If this is done, the light emitted from the bulb will be blocked by the heat insulating material, resulting in a problem that the amount of light will decrease.

The present invention provides a high-pressure sodium lamp that can prevent heat conducted through the electrode shaft from escaping without reducing the amount of light, and increase the temperature of the coldest part formed in the exhaust pipe to improve luminous efficiency. This is what we are trying to provide.

[Structure of the Invention] (Means for Solving the Problems) The present invention airtightly attaches metal exhaust pipes to both ends of an arc tube bulb made of translucent ceramic with excellent heat resistance and corrosion resistance. Electrodes are attached to these exhaust pipes, and luminescent metals and rare gases that evaporate during lighting are sealed in the arc tube bulb, and the excess luminescent metals are condensed in the exhaust pipes. It is characterized in that the electrode axis of the electrode is surrounded by a metallic heat-insulating tube with a gap between the electrode axis and the electrode axis.

(Function) According to the present invention, since the electrode shaft is surrounded by a metallic heat-insulating tube with a gap, the heat-insulating tube prevents radiant heat that is about to be released from the electrode shaft, thereby increasing the temperature of the electrode shaft. by keeping it high and increasing the amount of heat transferred to the exhaust pipe.
The temperature of the outer end of the exhaust pipe, which is the coldest part, can be increased.

(Example) The present invention will be described below based on an example shown in FIGS. 1 to 4.

FIG. 4 is a sectional view of the entire arc tube of a high-pressure sodium lamp, and numeral 1 indicates an arc tube bulb made of a translucent alumina ceramic tube.

The openings at both ends of the valve 1 are hermetically closed by a closing body 2.2 made of, for example, an alumina ceramic disk via a solder 3.

Note that the closing base 2 may be made of a metal cap such as niobium or tantalum, which has a coefficient of thermal expansion similar to that of alumina.

Exhaust pipes 4, 4 are passed through the centers of these closing bodies 2, 2. The exhaust pipes 4, 4 are made of metal pipes such as niobium or tantalum, and are hermetically joined via solder 6 to the through holes 5.5 formed in the closure body 2.2.

An electrode 7.7 is attached to the exhaust pipe 4.4.

The electrode 7.7 is constructed by attaching an electrode coil 9, which is a double-wound tungsten wire, to an electrode shaft 8 made of tungsten, and the electrode coil 9 holds an electron emitting substance such as barium.

The electrode 7.7 has its electrode shaft 8 supported by the exhaust pipe 4, but in this case, as shown in FIG. 1, the exhaust pipe 4 is open at its tip facing the electrode 7. The electrode shaft 8 is inserted from this open end. The electrode shaft 8 is guided inside the exhaust pipe 4 to the vicinity of the outer end of the exhaust pipe 4, and by crushing the vicinity of the outer end of the exhaust pipe 4 as shown in FIG. It is clamped. For this reason, the exhaust pipes 4, 4 also serve as power feeders to the electrodes 7, 7.

After exhausting the inside of the valve 1, the outer tip of the exhaust pipe 4.4 is filled with a predetermined luminescent metal and a starting rare gas, and then crushed and closed airtight. The above-mentioned luminescent metals are sodium Na and mercury Hg, and the luminescent metals are sealed in an amount in excess of the amount that evaporates during lamp lighting, making it a so-called saturated high-pressure sodium lamp. For example, xenon Xe gas is used as the gas.

A heat-retaining tube 10.10 is inserted into the exhaust pipe 4.4. The heat insulation tube 10 is made of a heat-resistant and corrosion-resistant metal tube such as niobium, tantalum, or molybdenum, and as shown in FIG. 2, the outer diameter d1 of the heat insulation tube 10 is smaller than the inner diameter of the exhaust pipe 4. , inner diameter d
2 is formed larger than the outer diameter dO of the electrode shaft 8 (D>dl
>d2>dO). Therefore, heat insulation tube 1
0 surrounds the electrode shaft 8 with a gap therebetween, and is also disposed on the inner surface of the exhaust pipe 4 with a gap therebetween.

One end of the heat insulating tube 10 is in contact with the back surface of the electrode coil 9, and the other end is in contact with the constricted portion of the exhaust pipe 4.

Note that the arc tube bulb 1 is covered from both ends to the closing body 2°2 with a heat insulating material 11 made of a heat-resistant metal band or the like.

The operation of the lamp having such a configuration will be explained.

When the lamp is lit, an electric discharge is generated between the electrodes 7.7 which are spaced and opposed to each other in the arc tube bulb 1, and the coldest part is at the outer end of the exhaust pipe 4.4 located behind these electrodes 7.7. Occur. In particular, as shown in FIG. 1, when the arc tube bulb 1 is supported and lit so that the tube axis is vertical, the coldest part of the arc tube is the lower end of the exhaust pipe 4 located below. occurs in In this case, surplus sodium Na amalgam that does not evaporate during lighting condenses at the lower end inside the exhaust pipe 4 located on the lower side.

During lighting, the electrodes 7 generate heat, and the heat from the electrodes is transmitted to the exhaust pipe 4 through the electrode shaft 8, raising the temperature at the lower end of the exhaust pipe 4, heating the condensed Na amalgam, and evaporating it. encourage.

In this case, the electrode shaft 8 is guided inside the exhaust pipe 4 to near the outer end of the exhaust pipe 4, and the electrode shaft 8 is clamped by crushing the exhaust pipe 4 near the outer end of the exhaust pipe 4. Therefore, the heat conducted through the electrode shaft 8 is transmitted to the vicinity of the outer end of the exhaust pipe 4 with which the base end of the electrode shaft 8 is in contact, thus heating the vicinity of the outer end of the exhaust pipe 4.

In this case, the heat conducted toward the proximal end of the electrode shaft 8 is radiated from the outer surface of the electrode shaft 8, and this radiant heat heats the exhaust pipe 4 surrounding the electrode shaft 8. The heat is transmitted from the exhaust pipe 4 to the closing member 2, but in the case of this embodiment, there is a heat insulating tube 1 between the electrode shaft 8 and the exhaust pipe 4.
Since the heat insulating tube 10 surrounds the electrode shaft 8 with a gap, the heat radiated from the outer surface of the electrode shaft 8 is not received by the heat insulating tube 10, and the heat insulating tube 10 surrounds the electrode shaft 8 with a gap.
In addition to preventing the heat from being transmitted to the closing member 2, the temperature in the gap surrounded by the heat insulating tube 10 is increased.
Therefore, the radiant heat emitted from the outer surface of the electrode shaft 8 is reduced.

Therefore, the heat conducted toward the base end of the electrode shaft 8 is
On the way, it will not be wasted away from the outer surface of the electrode shaft 8, that is, it will not escape wasted, and it will be transmitted well toward the base end of the electrode shaft 80, effectively discharging the vicinity of the outer end of the exhaust pipe 4. It will be heated to.

Therefore, the excess Na amalgam condensed at the outer end of the exhaust pipe 4 is heated and evaporated, thereby increasing the Na vapor pressure within the arc tube and improving the color rendering properties of the lamp.

In this case, there is no need to cover a large area with the heat insulating material 11 from both ends of the arc tube bulb 1 to the closing body 2.2, and therefore the proportion of light blocked can be reduced.

In addition, in the case of this embodiment, the negative end of the heat insulating tube 10 is in contact with the back surface of the electrode coil 9, and the other end is in contact with the constricted portion of the exhaust pipe 4, so that the electrode coil 9 is heated. The heat insulating tube 10 also has the effect of transmitting the heat to the outer end of the exhaust pipe 4.

Note that the present invention is not limited to the above embodiments.

That is, in the above embodiment, one end of the heat insulating tube 10 was brought into contact with the back surface of the electrode coil 9, but in the present invention, as in other embodiments shown in FIGS. 5 and 6, the heat insulating tube 10 One end of the electrode coil 9 may be separated from the electrode coil 9.

In addition, as a support structure for the heat insulation tube 10, the fifth
As shown in the figure, there is a protrusion 20 in the middle of the heat insulation tube 10.
... may be formed, and these protrusions 20 ... may be fitted into the exhaust pipe 4 to fix the heat insulating tube 10.
As shown in the figure, a coil 30 may be inserted between the heat insulating tube 10 and the exhaust pipe 4 to support the heat insulating tube 10.

Furthermore, the heat insulating tube 10 is not limited to a complete tube shape, and may be formed of a dense mesh body or a metal band wound into a spiral cylinder shape.

[Effects of the Invention] As explained above, according to the present invention, since the electrode shaft is surrounded by a metallic heat-insulating tube with a gap, the heat-insulating tube prevents radiant heat that is about to be released from the electrode shaft. As a result, the temperature of the electrode shaft can be kept high, the amount of heat transferred to the exhaust pipe can be increased, and the temperature of the outer end of the exhaust pipe, which is the coldest part, can be increased. Therefore, the vapor pressure of Na can be increased and the color rendering properties of the lamp can be improved.

[Brief explanation of the drawing]

1 to 4 show one embodiment of the present invention, FIG. 1 is a sectional view showing the end of the arc tube of a high-pressure sodium lamp, and FIGS. 2 and 3 are respectively shown in FIG. line and ■
4 is a sectional view showing the entire arc tube of a high-pressure sodium lamp, and FIGS. 5 and 6 are sectional views of an electrode mount showing other embodiments of the present invention. DESCRIPTION OF SYMBOLS 1... Arc tube bulb, 2... Closure body, 4... Exhaust pipe, 7... Electrode, 8... Electrode shaft, 9... Electrode coil part, 10... Heat insulation tube. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 3 Funeral diagram Funeral diagram

Claims (1)

[Scope of Claims] Metal exhaust pipes are airtightly attached to both ends of an arc tube bulb made of translucent ceramic having excellent heat resistance and corrosion resistance, electrodes are attached to these exhaust pipes, and the above arc tube is provided with: In a high-pressure sodium lamp, the bulb is filled with a luminescent metal and a rare gas that evaporate during lighting, and the excess luminescent metal is condensed in the exhaust pipe. A high-pressure sodium lamp characterized in that the lamp contains a metal heat-insulating tube.