GB2181379A - Soldering fixture, particularly for sealing electric gas discharge tubes having a ceramic envelope - Google Patents

Abstract

The invention relates to a soldering fixture, particularly for sealing electric gas discharge tubes having a ceramic envelope, comprising carrying means for receiving an envelope (1) of a gas discharge tube and soldering means equipped with at least one heating body (10). The carrying means consist of a cooled container (4) arranged underneath the heating body (10) for receiving the lower part of the envelope (1) and in the container (4) there is an opening (13) with inner surface shaped according to the cross-section of the envelope (1) and being in connection therewith and it contains a unit for pressing the envelope (1) to the inner surface of the opening (13). The fixture is capable of limiting the vaporization of active materials introduced into the envelope of the gas discharge tube. <IMAGE>

Description

SPECIFICATION Soldering fixture, particularly for sealing electric gas discharge tubes having a ceramic envelope The invention relates to a soldering fixture, particularly for sealing electric gas discharge tubes having ceramic envelopes, comprising carrying means for receiving an envelope of a gas discharge tube and soldering means equipped with at least one heating body.

Certain gas discharge lamps, mainly of the ceramic envelope type, e.g. high-pressure sodium vapour lamps, require no exhaust tubes in their manufacture. Such discharge lamps are manufactured so that in the first step of closing the gas discharge tube one end of the usually tubular-shaped ceramic envelope is sealed, this half-sealed tube is brought into vertical position, the discharge material comprising components taking part in the discharge process is placed into the tube through its still open end and, then, this latter end is also sealed in a second step of closing.

An apparatus, an electrically heated fixture for making soldered seals on gas discharge tubes of this kind, i.e. without exhaust tubes is disclosed in FRG patent specification No.

2005630.

The disadvantage of manufacturing to be carried out by the apparatus shown in this specification lies in the tendency of the introduced discharge material to evaporate under the effect of the heat applied while the upper end of the tube is sealed at a temperature of about 1 4000C range, though said material is located at the bottom of the tube due to the vertical position of the latter. The evaporated components leave the inner volume of the tube and the composition of the remaining mixture shows changes. The risk of said evaporation is the higher, the shorter the tube, i.e. the lower is the light output of the manufactured discharge tube. E.g., the length of a 400-watt high-pressure sodium vapour discharge lamp is about 100 mm, whereas the tube of a 35-watt lamp is only 30 mm long.

In both cases, the discharge material is a sodium amalgam which must not be permitted to heat up substantially above room temperature because of the risk of considerable rate of evaporation, while a temperature of 1 4000C prevails at a distance of scarcely 30 mm away from it.

In the case of known kinds of apparatus used in the manufacture of gas discharge lamps provided with especially short tubes, the procedure adopted for reducing evaporation of the discharge material is to let the lower half of the tube/i.e. the half containing the discharge material/hang out into the free air of the environment. This is accomplished by applying a rubber seal at the middle portion of the tube to separate the free air from an atmosphere necessary for preparing the sealing at the second tube end.Thus in the case of a discharge tube of 35 watt light output, this rubber seal is separated by a distance of a mere 15 millimetres from the hot soldered seal of temperature range 1400 C. If, now, it is considered that, because of its compactness equal to that of crystals, the thermal conductivity of the transparent ceramic tube applied here lies in the order of magnitude of that of some metals, an idea may be formed of the great difficulties associated with making sealings of this kind.

Another methods for solving this problem have been also proposed. The specification of the Hungarian patent No. 188.893 discloses a method essentially consisting of applying intense cooling, together with said rubber sealing, to the part of the ceramic tube protruding from the sealing apparatus/electric furnace/by placing said part into an outer cooling chamber during the sealing process.

The subject of the present invention is a soldering fixture which effectively protects the thrown-in discharge material from evaporation mainly even in the case of especially short tubes, during the second sealing operation, beside being of simple construction. The setup of the fixture is based on the recognition that the discharge material is jeopardized by the heat generated during the second sealing opertion, passing partly by radiation and conduction through the tube wall, but to provide protection against this effect, it is sufficient to press resiliently the ceramic tube against the wall of a preferably water-cooled holder proposed by the present invention.

With such arrangement, however, hazardous conditions may arise in the tube by sudden cooling, leading to fractures. Therefore, also according to the invention, the boring of the water-cooled holder surrounding the ceramic tube during the sealing operation is made with varying diameter along its length.

Summing up the above, the subject of the invention is a soldering fixture, mainly for manufacturing ceramic gas discharge tubes. In the soldering fixture, comprising carrying means for receiving an envelope of a gas discharge tube and soldering means equipped with at least one heating body as specified by the invention, it is essential that the carrying means comprise a preferably water-cooled holder, an opening of boring provided in said holder for receiving the envelope of the discharge tube and a unit for pressing the envelope of the discharge tube against the wall of the opening.

The risk of fracture of the discharge tube due to the high temperature gradient can be avoided or limited essentially by providing an opening having an upper area of enlarged cross-section.

The cooling of the container can be realised in many ways, however, water cooling seems to be the most advantageous. For this purpose channels can be provided in the container. Surface cooling of the container can be effective in certain conditions, too, or other cooling liquid can be applied, if required.

The unit for pressing the envelope of the discharge tube against the wall of the opening comprises advantageously resilient members whereby the envelope can be introduced into the opening without difficulties. The unit is equipped e.g. with a spring and a pin resting on this spring. The latter is connected to an inner surface of the container wherein on the outer surface thereof a plate spring can be fixed for pressing the pin and holding it in the opening.

The proposed soldering fixture ensures very effective and intense cooling of the received part of the envelope introduced into the opening and thereby the risk of evaporation of the discharge material is highly limited.

The soldering fixture according to the invention will be now described in more detail with reference to the accompanying drawing wherein the only Figure, Figure 1 is a cross-section of an advantageous embodiment of the proposed soldering fixture.

As shown in this Figure a discharge tube consisting of a tubular ceramic envelope 1 and ceramic plugs 2 closing the end parts of the envelope 1, either of the two plugs 2 being provided with electrodes 3 also serving as current inlet terminal, is placed into an opening 13 of a cooled container 4, with its previously sealed and looking downwards end. The cooling medium, e.g. water is kept advantageously circulating in channels 5 of the container 4. For cooling the outer surface of the container can be applied, too. Discharge material 6 previously thrown into the tube lies on the bottom of the vertically positioned envelope 1 of the discharge tube. The ceramic tube is pressed against the wall of the holder by a plate spring 7 through a pin 8, whereby the temperature of the tube closely follows that of holder.A helical spring 9 around the pin 8 serves for facilitating insertion of the ceramic tube, after slightly displacing plate spring 7.

For the second sealing operation mainly radiant heat of a heater 10 located around the upper tube end is utilized, causing the melting of annular solder 11 placed to the top of ceramic plug 2 and of a similar-shape largerdiameter solder 12 located at the top end surface of the ceramic tube. The shapes assumed by the annular solders after melting can be seen at the bottom end of the tube, the first seal being made similarly.

The opening 13 of the container 4 can be of slightly larger diameter at its upper end, thus in this region there is no direct contact between the cold wall of the container 4 and this part of the ceramic envelope 1. This gap of a few tenths of a millimeter, also in accordance with the invention, serves for providing the required transition of heat from the hot upper half toward the cold bottom half of the tube, whereby fracture is prevented.

The opening 13 should be shaped with cross-section according to the shape of the envelope 1. Advantageously it is also tubular with diameter slightly greater than that of the envelope 1; however, it should be shaped in a manner for ensuring great surface of the contact when pressing the envelope 1 against the wall of the opening 13. This is the basic condition of effective heat transfer between the envelope 1 and the container 4 made of material of high heat conductance.

The method of manufacturing shown above without exhaust tube essentially consists of performing the second sealing operation by the use of the proposed apparatus in a noble gas atmosphere of pressure range about 2 to 14 MPa/20 to 1000 Hg mm/, this gas being kept trapped in the tube after sealing, facilitating subsequent ignitions of the tube. During this operation the discharge material can evaporate in a very low extent and the discharge tubes manufactured by the proposed apparatus can meet in a high number the requirements. Thus, the proposed apparatus improves the output quality of the discharge lamp production.

Claims (6)

1. Soldering fixture, particularly for sealiing electric gas discharge tubes having a ceramic envelope, comprising carrying means for receiving an envelope of a gas discharge tube and soldering means equipped with at least one heating body, characterized in that the carrying means consist of a cooled container arranged underneath the heating body for receiving the lower part of the envelope and in the container there is an opening with inner surface shaped according to the cross-section of the envelope and being in connection therewith and it contains a unit for pressing the envelope to the inner surface of the opening.

2. 4 soldering fixture according to claim 1, characterized in that the opening is shaped in its upper part by a region of enlarged crosssection in comparison to its lower part.

3. A soldering fixture according to claim 1 or 2, characterized in that the container comprises channels for circulating a cooling medium, especially water.

4. A soldering fixture according to any of claims 1 to 3, characterized in that the unit for pressing comprises a pin acting on a resilient member, especially a spring resting on an inner surface of the container.

5. A soldering fixture according to claim 4, characterized in comprising a plate spring fixed on the outer surface of the container and resting on the pin.

6. A soldering fixture substantially as herein described with reference to and as shown in the accompanying drawing.