JPS5836810B2 - How to regenerate the arc tube of a high-pressure alkali metal vapor discharge lamp - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention utilizes a light-transmitting polycrystal or a light-transmitting single-crystal oxide crystal (hereinafter referred to as a light-transmitting oxide crystal) such as a light-transmitting alumina ceramic or single-crystal sapphire. This invention relates to a method for regenerating an arc tube that has become unusable in a high-pressure alkali metal vapor discharge lamp used as a tube.

High-pressure alkali metal vapor discharge lamps that have become popular in recent years, such as high-pressure sodium lamps as shown in Figure 1, emit light of 110 to 120 1 m7W due to the emission of sodium metal.
It is possible to obtain high efficiency, and has recently been applied in many fields.

As shown in FIG. 1, the structure of the high-pressure sodium lamp is such that an arc tube 2 made of a translucent oxide crystal is mounted inside a vacuum outer tube 1 made of hard glass.

Furthermore, the arc tube 2 is coated with Nd (
There are caps 3 made of metal such as niobium (niobium), tantalum (Ta), and molybdenum (molybdenum), which are hermetically sealed, and caps 3 made of ceramic material as shown in FIG.
′ is hermetically sealed.

Here, 4 is the electrode, 5 is the glass frit for airtight sealing, and 6 is the electrode.
is an exhaust pipe made of metal such as Nb or Ta.

An example of glass frit No. 5 is Al203 (alumina),
It is a high melting point glass that has Cab (calcia) as its main component and MgO (magnesia), Bad (barrier), etc. as its main component.

The reason why a translucent oxide crystal such as alumina ceramic or sapphire is used as the material for the arc tube 2 in the above-mentioned high-pressure alkali metal vapor discharge lamp is because of the resistance of such a translucent oxide crystal. Because it is highly alkaline, it is ideal as an arc tube for lamps filled with alkali metals such as sodium.

Since the above-mentioned transparent oxide crystals are very expensive, the production cost of the lamp is high, and there is a drawback that damage due to defects occurring during the manufacturing process is increased.

In order to reduce the above-mentioned damage as much as possible, we cut off both ends of the defective arc tube 2 and replaced it with the electrode 4, exhaust pipe 6, metal cap 3 (or ceramic cap) shown in FIGS. 2 and 3. Attempts have been made to use light-transmitting oxide crystal tubes, such as light-transmitting alumina ceramic tubes that have been shortened by removing 30 mm, as arc tubes for lower-wattage lamps.

However, in this method, the diameter of the arc tube remains unchanged, making it difficult to design an appropriate lamp.

In other words, the appropriate design values for the diameter and length of the arc tube vary depending on the rated power of the lamp, for example 400.
It is not desirable in terms of lamp design to shorten a W arc tube and use it as a 250 W arc tube.

In addition, this method requires a considerable number of steps to finish the end face of the cut short arc tube so as not to interfere with hermetic sealing, which is troublesome.

The present invention was conceived in view of the above circumstances, and mainly involves recycling defective arc tubes that occur during the manufacturing process and reusing them as arc tubes with the same rated power. This article relates to a method for recycling defective arc tubes.

That is, a translucent oxide crystal, such as a translucent alumina ceramic tube, used in the arc tube 2 of a high-pressure alkali metal vapor discharge lamp such as the above-mentioned high-pressure sodium lamp is shown in FIG.
As shown in FIG. 3, a metal cap 3 or a ceramic cap 3l is attached to the end of the tube by using a glass frit 5 with a high melting point, such as one mainly composed of alumina or calcia.
Usually, the exhaust pipe 6 is sealed to maintain airtightness.

Therefore, it is possible to regenerate a defective tube by melting the glass frit 5.

For example, the glass frit 5 mainly composed of alumina and calcia is soluble in acids such as nitric acid and phosphoric acid, but nitric acid with a concentration of 30% by weight is most suitable.

When using nitric acid at a concentration of 30% by weight, the glass frit is completely dissolved in 2 to 3 hours.

A strong acid such as hydrofluoric acid dissolves the glass frit 5 in a short time, but it is not preferable because it also corrodes the arc tube 2 itself, such as a translucent alumina ceramic tube.

The arc tube, such as a translucent alumina ceramic tube, whose glass frit 5 has been dissolved and separated from the end metal cap 3 or ceramic material cap 3/ is cleaned depending on the degree of contamination.

For example, if the electrode material is scattered on the inner wall of the arc tube, it can be cleaned with nitric acid.

The sealed portions at both ends of the arc tube 2 after melting undergo some devitrification due to reaction with the glass frit 5, but this only causes a loss of surface smoothness and does not pose a practical problem.

After dissolution, the arc tube that has been cleaned with nitric acid or the like is washed with water and then burnt in air, hydrogen, inert gas, or vacuum for about an hour at a minimum temperature of about 800°C to remove distortion.

In lamps made from recycled arc tubes that are not subjected to such burning, the incidence of cracks at the ends increases.

This is thought to be because when there is a minute crack at the end of the arc tube, the crack lengthens due to distortion.

Distortion occurs mainly at the ends of the arc tube because stress is concentrated at the ends when the arc tube is exposed to high temperatures during the sealing process during lamp manufacturing.

If the firing temperature is below 800°C, the distortion will not be removed and the crack occurrence rate will not be much different from the case where there is no firing.

Burning atmosphere means burning or removing impurities, in hydrogen,
Either in an inert gas or a vacuum is preferable.

The firing temperature should be scheduled so that there is no sudden heating or cooling.

For example, raise the temperature to 800°C at 30°C/min, and at 800°C
A pattern is used in which the sample is held for a period of time and then cooled to room temperature at a rate of 30° C./min.

Specific examples of the present invention will be shown below.

(1) Place the defective arc tube to be recycled into a plastic beaker, fill it with nitric acid at a concentration of 30% by weight, and leave it for 3 hours to dissolve the glass frit.

(2) Wash the arc tube whose glass frit has melted and separated from the cap with running water.

(3) Remove any deposits on the inner surface with a brush and wash again with running water.

(4) After boiling and cleaning with nitric acid at a concentration of 30% by weight for 10 minutes, cleaning with running water and acetone.

(5) Place in a clean alumina tray and incinerate at 1,200°C for 1 hour in an argon atmosphere.

The firing temperature schedule was to increase to 1,200°C at 30°C/min, hold at 1,200°C for 1 hour, then increase to 30°C.
/ minute to cool to room temperature.

(6) After soaking in 30% by weight nitric acid for 5 minutes, wash with running water, pure water, and acetone in this order, and dry.

400W using a recycled arc tube with the specifications above
When we manufactured 20 high-pressure sodium lamps and conducted a lighting test, we found that overload (10% overvoltage) lighting resulted in 6,000 yen.
There were no abnormalities in all cases even after 0 hours had elapsed.

As described above, according to the present invention, an arc tube of a lamp that becomes defective during the manufacturing process can be reused, so that damage caused by defects can be minimized.

It goes without saying that the present invention can be applied not only to defects occurring during the manufacturing process but also to arc tubes of lamps that have reached the end of their service life.

[Brief explanation of drawings]

FIG. 1 shows the external shape of a high-pressure sodium lamp, and FIGS. 2 and 3 show arc tubes for high-pressure sodium lamps of metal cap type and ceramic cap type, respectively. 1 is an outer tube, 2 is an arc tube, 3 is a metal cap, 3' is a ceramic cap, 4 is an electrode, 5 is a glass frit, and 6 is an exhaust pipe.

Claims (1)

[Claims] 1 Use of a high-pressure alkali metal vapor discharge lamp having a light-transmitting polycrystalline or light-transmitting single-crystalline oxide crystal arc tube with a metal cap or ceramic material cap hermetically sealed at both ends using a high-melting-point glass frit. After the failed arc tube is cleaned (1) by dissolving the glass frit with acid and removing the metal cap or ceramic cap, (2) in air or inert gas at a high temperature of 800°C or higher, A method for regenerating an arc tube of a high-pressure alkali metal vapor discharge lamp, the method comprising firing it in hydrogen or vacuum to remove distortion and impurities at the end of the tube so that it can be used again as an arc tube.