US2550658A - Exhaust tubulation - Google Patents

Description

April 24, 195l w. H. VAN DYKE EXHAUST TUBULATION Filed March 29, 1947 Mercury Dfspenser l2 Walter H..

Y E N R 0 T T Patented Apr. 24, 1951 EXHAUST TUBULATION Walter H. Van Dyke, Peabody, Mass., assignor to Sylvania Electric Products Inc., Salem, Mass., a corporation of Massachusetts Application March 29, 1947, Serial No. 738,158

1 claim. 1

This invention relates to electric discharge devices and more particularly to those containing aquantity of mercury therein.

An object of this invention is to provide a means for preventing the mercury from being 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 deleterously affected but will actually be aided and its einciency increased thereby.

Further objects, advantagesvand features will be apparent from the following specification taken in conjunction with the accompanying .drawing in 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, a supply of an inert gas such as argon, and a mercury dispenser.

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 well be done when the elongated glass envelope, with a pair of lilamentary electrodes sealed at each end thereof, is heated and evacuated, the evacuation taking Vplace through an exhaust tubulation projecting from an end of the elongated glass envelope. The mercury may be introduced in any one of several Ways. For example, it may be introduced in the form of a mercury bomb of the type shown in U. S. Patent 2,283,189 issued May 19, 1942. It may also be introduced from an external source, such as a dispenser of the type shown in U. S. Patent 2,203,612 issued June 4, 1940, for example.

In the accompanying figure, the lamp comprises an elongated tubular glass envelope I which has a coating of luminescent material 2 on the inner Wall thereof and the mounts 3 and 4 sealed in the ends thereof. The lead-in wires 5 sealed in the mounts 3 and 4 and projecting upwardly therefrom support the filamentary electrodes 6. The exhaust tubulation 1 extends from one end of the elongated tubular glass envelope and is projected up into the lower end of a rubber washer 8 on which sufficient pressure is exerted to hold the envelope I suspended by its exhaust tube. v

One end of a manifold 9 is connected to the upper end of the rubber washer 8. To this manifold 9 there `is connected a vacuum pump II), a.V

supply II of an inert gas such as argon, and a mercury dispenser I2. Control over the establishment of connections between the manifold 9 and the vacuum pump I0, the inert gas supply I I, and the mercury dispenser I2 may be exercised through valves I3, I4, and I5 respectively.

In the evacuation of the tubular glass envelope according to my invention, the envelope is located in an oven in which it is heated, a quantity of.

the filamentary electrodes are subjected to a series of heating steps, and a nal filling of an inert gas at the desired pressure is introduced therein before it is finally sealedand severed from the exhaust tubulation. This oven ZI comprises a pair of Walls I6, a roof I'I, and a licor I8. The roof Il is provided with a small aperture therein,through which the exhaust tubulation 1 may extend. Heating elements I9 are suspended within the area dened by the walls I6 and may be energized by connecting them to a source of electrical energy through the insulating sleeves 20 which project through the walls I6.

During the series of evacuating and flushing steps which comprise the exhaust cycle, a quantity of an inert gas such as argon is introduced into the envelope to mix with the volatilized foreign gases which it is desired to remove from the envelope before itis 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 attained during the evacuation process by introducing into the envelope I a quantity of mercury 22. The heat of the oven is sufficient to vaporize the mercury which then diffuses with the volatile gases and acts like a diffusion pump.

As this mercury vapor aids in sweeping the volatile gases the entire length of the elongated envelope, it' actually passes out of the envelope 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 envelope itself was exposed in the heating oven, whereas the portion Within the rubber 8 has been protected so that it remains relatively quite cool. The vaporized mercury willl V3 therefore, condense on the cool portion of the Wall of the exhaust tube.

Since the mercury is introduced into the envelope not only to aid in the evacuation thereof but also to be permanently sealed therein, it is necessary to either drive the condensed mercury 23 back intovtheenvelope or introduce an' additional quantity thereof so that a ypredetermined amount will'be finally sealed therein. Normally, the force exerted by the inert gas, usually argon, which is used to ush the envelope and to pro Vide a nal filling thereof which is sealed therein, is not sufficient to overcome the surface tension between the condensed mercury 'and the Wall of the exhaust tubulation. Therefore Some means must be employed to effect the dislodging of the condensed mercury.

In my Patent 2,313,788 I pointed out that etching of the exhaust tabulation will rou'ghn the inner wall thereof enough to reduce the surface tension toa point wher-'e the force `"exerted by the inriishing gas will be great encg-h to'drive the mercury `back into theenvelope. However, I have vfound that etching weakens the exhaust tubilation `and causes higher vspoilage of lamps at this stage of theinanufacturing process.

I'have, therefore, `developed a means of effecting the dislodging of the condensed mercury without weakening the Vexhaust tubulation. I accorn'plish this by coating the clear glass, normally used in lamp manufacturing practice for exhaust tubulations, witha-n anti-*wetting substance, such as monoethyl chlorosilane, which remains stable chemically when subjected to the heat of a lamp exhaust machine. This coating of an anti-wettingsubstance'causes themer'cury to condense in the form of ydroplets rather than Vin theA formv of a mist or fog as is the case when the exhaust tubulation is uncoated or unetched. The reduction of the surface tension which is thereby effected is suicient to enable the inrushng inert gas to drive the condensed mercury back into the lamp and perform the same diffusion pump action described above.

Since, as was mentionedabokve the lamp recives a final filling of an inert gas 'before it is finally sealed, this nal introduction of gas will dislodge the condensed mercury on the wall of the exhaust tubulation and force it back into the lamp before the exhaust tubulation is severed therefrom.

Although I 'haveV mentioned above the use of monoethylchlorosilane as an exhaust tubulation coating material which has proven advantageous, any anti-wetting substance, which will withstand theA lamp exhaust temperatures, may be used Without departing from the spirit of my invention.

WhatI claim is: 4 A

electric gaseous discharge lamp comprising a glass enveiope, electrodes mounted within said envelope, a filling of'inert gas within said envelope, va quantity of mercury within said venvelope, an exhaust tubulationl extending from said envelope, and a 'coating of monoethyl'chlorosilane on the inner wall of said tubulation. i n ,K

WALTER H. VVAN DYKE.

REFERENCES GITED The renewing refrencs are f regard in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,306,222 panique Dec. 22,1942 2,313,788 vannyke Ma'r. 16, 1943 2,408,822 'rams 0013.8, 1946

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