Title:
Lamp expaust method
United States Patent 2313788


Abstract:
This invention relates to electric discharge devices and more particularly to those containing a quantity of mercury therein. , An object of this invention is to provide a means for preventing the mercury from being I drawn off from the device during the evacuation process. Another object...



Inventors:
Dyke, Walter Van H.
Application Number:
US41837541A
Publication Date:
03/16/1943
Filing Date:
11/08/1941
Assignee:
SYLVANIA ELECTRIC PROD
Primary Class:
Other Classes:
141/8, 445/56
International Classes:
C03C3/072; H01J9/38
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Description:

This invention relates to electric discharge devices and more particularly to those containing a quantity of mercury therein. , An object of this invention is to provide a means for preventing the mercury from being I drawn off from the device during the evacuation process.

Another object is to accomplish the first mentioned object in such a manner that not only will the evacuation process not be deleteriously 11 affected but will actually be aided and its efficiency increased thereby.

Further objects, advantages and features will be apparent from the following specification taken In conjunction with the accompanying drawing in 11 which: The figure is a side elevational view of a lamp, in which it is desired to seal a quantity of mercury, connected to a vacuum pump and a supply of an inert gas such as argon. 2( In the manufacture of electric gaseous discharge devices and more particularly fluorescent lamps, it has been found desirable to introduce a quantity of mercury into the lamp at some point during the manufacturing process. This may 21 well be done when the elongated glass envelope, with a pair of filamentary electrodes sealed at each end thereof, Is heated and evacuated, the evacuation taking place through an exhaust tubulation projecting from an end of the elongated glass tube. The mercury may be introduced in any one of several ways, but it may be enclosed in a small metallic tube or bomb and Joined to one of the lead-in wires on which one of the filamentary electrodes is mounted when the mounts which are sealed in the elongated glass tube are first assembled and then exploded during the evacuation process thereby releasing the mercury as disclosed in my Patent Number 2,283,189 of May 19, 1942. In the accompanying figure, the elongated tubular glass envelope I, has a coating of luminescent material 2 on the inner walls thereof and the mounts 3 sealed at each end thereof. The leadin wires 4 sealed in the mounts 3 and projecting upwardly therefrom support the filamentary electrodes 5. The metallic tube 6 suspended from one of the lead-in wires 4 contains a quantity of mercury. The exhaust tubulation 7 extends from one end of the elongated tubular glass envelope o5 and is projected up into a rubber washer 8 on which sufficient pressure Is exerted to hold the bulb suspended through the exhaust tube.

The rubber washer 8 is connected through a line s to a vacuum pump 10 and a supply chamber 6S of an inert gas, such as argon, with which It may be desirable to fill the lamp after evacuation and before the lamp-is finally sealed off. Control over the establishment of connections between the line 9 and the pump 10 and the inert gas supply chamber II may be exercised through the valves 12 and 13 respectively.

In the evacuation of the tubular glass envelope according to my invention, the envelope is located 0 in an oven in which it is heated, a quantity of mercury is vaporized in said envelope, it is subjected to a series of evacuating and flushing steps, the filamentary electrodes are subjected to a series of heating steps, and a final filling of an inert gas at the desired pressure is introduced therein before it is finally sealed and severed from the exhaust tubulation.

This oven assembly consists of a pair of walls 14, a roof 15 and a floor IS. The roof 15 is pro0 vided with a small aperture therein through which the exhaust tubulation 1 may extend. The heating elements 17 are suspended within the area bounded by the walls 14 and may be energized by connecting them to a source of electrical energy I through the insulating sleeves 18 which project through the walls 14. The filamentary electrode may be heated by connecting the metallic plates 19, on the floor of the oven, and with which the lead-in wires 20 of the electrodes are in contact, Swith a source of electrical energy.

When a mercury bomb 6 of the type disclosed in the co-pending application referred to above is located on the mount which is sealed in the end of lamp opposite to the end from which the exhaust tubulation 7 extends, it has been found desirable to locate it in such a manner that the free end thereof is directed downwardly towards the adjacent end of the lamp as shown in the accompanying drawing. This metallic bomb containing mercury will be heated by heat from the oven and by heat conducted thereto from the lead-in wire to which it is attached during the electrode heating period. The combination of the heat from these two sources will cause the bomb to explode and release the mercury, held therein. By having the bomb directed downwardly, that mercury which does not vaporize immediately will collect or condense on the mount and not on the coating of fluorescent material on the walls of the lamp. Thus the smooth even coating is neither removed nor discolored by the condensation of mercury thereon.

During the series of evacuating and flushing steps, a quantity of an inert gas such as argon is introduced therein to mix with the volatilized foreign gases which it is desired to remove from the lamp before it is finally sealed. This series of alternate evacuating and flushing steps has been found to enable the attainment of a relatively high vacuum. However, I have found that an even higher degree of vacuum may be obtained by using an exhaust tubulation, the inner walls of which are roughened, for example, one that has been etched. When this is done, that mercury which vaporizes when released from the bomb in which it is held diffuses with the volatile gases in the elongated tube and acts like a diffusion pump.

As this mercury vapor aids in sweeping the volatile gases the entire length of the elongated tube, it actually passes out of the tube and into the exhaust tubulation. There is a sharp difference in the temperature of that portion of the exhaust tube which has been firmly held within the rubber washer 8, throughout the exhausting process as compared to the temperature of that portion of the exhaust tube below the rubber. The lower portion of the exhaust tube has been exposed to all the heat to which the elongated tube itself was exposed in the heating oven, whereas the portion within the rubber 8 has been protected so that it remains relatively quite cool. I have found that when an exhaust tube, the inner walls of which have been roughened, is used, the vaporized mercury, sweeping the volatile gases from the elongated tube, will condense .on that portion of the exhaust tube which is kept cool by the rubber washer 8.

When a quantity of an inert gas is introduced into the elongated tube I, the force exerted by the inrushing gas will be greater than the surface tension between the condensed mercury and the roughened walls of the exhaust tube 7 and the mercury will be driven back into the lamp and perform the same function during the next evacuation step as just described.

Since the elongated tube receives a final filling of an inert gas before it is finally sealed, this final introduction of gas will dislodge the condensed mercury 21 and cause it to trickle down the exhaust tube walls as shown in the accompanying drawing and thus locate itself within the tube I before the exhaust tubulation is severed therefrom.

Not only does the utilization of this combination enable the accomplishment of a higher degree of vacuum in the lamp but it also accomplishes the re-distillation of the mercury which is to be finally sealed into the lamp. This is also highly desirable because the purity of the mercury in the lamp may well be a vital factor in lamp operation. When the mercury vapor, diffused with the volatile gases in the elongated tube, passes through the exhaust tubulation, the mercury will condense and the foreign gases will be carried off. This re-distillation may well take place once, twice or several times depending on the number of times flushing and evacuating takes-place after the mercury bomb 6 has exploded and released the mercury.

What I claim is: 1. The method of evacuation and gas-filling an elongated glass envelope having an exhaust '15 tubulation projecting from an end thereof, said method comprising: vaporizing a quantity of mercury at the bottom of said envelope; exhausting the glass envelope; condensing said vaporized mercury on the walls of said tubulation; and introducing a filling of an inert gas into said elongated glass envelope.

2. The method of evacuating and gas-filling an elongated glass envelope having one or more filamentary electrodes and a mercury bomb sealed therein, and a tubulation projecting from an end thereof, said method comprising: heating said mercury bomb sufficiently to free the mercury enclosed therein; heating the envelope to diffuse the mercury; exhausting the glass envelope; condensing said vaporized mercury on the walls of said tubulation; and introducing a filling of an inert gas into said elongated glass envelope to sweep the condensed mercury back into the glass envelope therewith.

3. The method of evacuating and gas-filling an elongated glass envelope having one or more filamentary electrodes sealed therein, an exhaust tubulation projecting from an end thereof, and a mercury bomb electrically connected to the electrode located at the end further removed from the exhaust tubulation, said method comprising: reducing to a gaseous state the moisture and volatile foreign substances within said envelope; heating said mercury bomb sufficiently to free the mercury enclosed therein; flushing said elongated glass envelope with an inert gas and such of said freed mercury as has vaporized; drawing off the foreign gases and the flushing gas; condensing said vaporized mercury on said exhaust tubulation; and introducing a final filling of an inert gas into said elongated glass envelope, sweeping the condensed mercury back into the glass envelope therewith.

WALTER H. VAN DYKE.

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