US2056665A - Vapor electric discharge device - Google Patents

Description

Oct. 6, 1936. 'r. w. FRECH VAPOR ELECTRIC DISCHARGE DEVICE Filed Aug. 18, 1934 lnvhtov: Theodore W. Frech, b w 88W 9 fi/flfi i5 Attorney.

Patented Oct. 6, 1936 UNITED STATES PATENT OFFICE Theodore W. Frech, Shaker Heights, Ohio, assignor to General Electric Company, a corporation of New York Application August 18, 1934, Serial No. 740,508

10 Claim.

This invention relates to gaseous or vapor electric discharge devices of a general type exemplifled by metal vapor lamps, and particularly to devices containing a substance (like sodium, potassium, or other alkali metal) which while gaseous or vaporous during operation of the device is readily condensible,in part, at least,and which may tend to attack some part of the device at temperatures attained during its operation. Examples of susceptible lamp parts are lead wire seals, a glass stem, or an area of glass envelope wall which is unresistant, as where a protective glaze on the inner surface has been destroyed by local fusion of the envelope in lamp manufacture. In such cases as these, it is desirable to exclude the hot substance from the susceptible parts, or from the internal region of the device where they are located. Other cases may also aoccur where it is desirable to exclude alkali metal vapor or other vaporous working substance or material more or less completely from certain regions of the device, irrespective of possible attack of metal vapor on any part. My invention is less expensive than means hitherto employed for similar purposes in metal vapor lamps, and allows the lamp to be made shorter than usual heretofore. It is especially adaptable and advantageous for tubular lamps, where an ordinary bulb neck is usually not desired.

In accordance with my invention, I arrange that the portion or region of the device (or of its envelope) from which for any reason it is desired to exclude the hot substance shall be kept cool enough to condense the substance, or even to solidify it. I may specially construct the device with one or more recesses opening oil from its main internal space, to include the susceptible part or area, and to be cooled sumciently below the general temperature of the device to assure condensation, etc. Ordinarily, the usual exter-- nal cooling of the envelope wall surrounding a suitable recess will suflice, without any special cooling provisions,even when the device is enclosed in a heat-conserving vacuum jacket, as is customary with sodium vapor lamps. (As sodium, for example, boils at about 877 C., as against temperature around 220-275 C. for the envelope walls of a sodium lamp, only a relative coolness of, the recess is required, because the sodium is'continually condensing all over the inner envelope surface and vaporizing again, with a tendency to accumulate and remain in any region that is especially cool, owing to the slower vaporization there.) By the coolness. and in other ways, if desired, I provide in the cool region an occluding shut-oil, formed (in an alkali metal lamp) of sodium, potassium, or other alkali metal. Accordingly, I prefer a recess comparatively narrow and deep, not only to assure coolness, but to minimize the amount of material required in it, and to cause the material to stay in the recess even when molten. Sodium melts as low as 98 C., and potassium at about 62 C.; but at such temperatures these molten materials are quite viscous, and readily remain in a narrow, deep recess. At such temperatures moreover, these metals do not readily attack glass, nor other materials which are quite susceptible to attack at the normal sodium lamp temperatures of around 220 to 250 C. Preferably, Iprovide in the device an excess of the material as compared with what is used in ordinary practice, to assure plenty for the shut-oil.

When the thus shut-off cool region or recess of a vapor glow discharge device is traversed by a part (like a lead wire) that tends to conduct heat into the recess, I preferably arrange for dissipating this heat in the main internal space of the device, or otherwise impeding and minimizing its transmission into the cool region or recess.

Various other features and advantages of the invention will appear from the following description of species thereof, and from the drawing.

In the drawing, Fig. 1 is a side view of a tubular lamp (suitable for operation on alternating current) embodying my invention in one simple form.

Fig. 2 is a similar view showing a different form of construction.

Fig. 3 is a similar view showing yet another form of construction.

Fig. 4 is a similar view of a lamp having a neck and stem construction at one end.

Fig. 5 is a similar view of a lamp having a neck and stem construction at one end, and a construction like that of Fig. 1 at its other end.

The device shown in Fig. 1 is adapted for use as a glow discharge lamp, and comprises a tubular glass envelope ill with electrodes II, I l axially arranged in its opposite ends, and supported by current lead wires 12, I2 sealed through the end walls l3, 13. The exhaust tip 14 on one end wall I3 is also shown. The electrodes H, l i are here shown as of the so-called cold type,

comprising tubular nickel bases externally coated with electron-emissive material, such as barium oxide. The current leads [2, I2 may be of any suitable kind that will seal into glass satisfactorily, such as tungsten, molybdenum, or a copper-clad wire, all of. which are subject to oxidation in sealing them into glass. The envelope to contains a charge of the working substance, such as sodium or other alkali metal, and may also usually contain a small amount of easily ionized gas like neon, argon, etc., whose partial pressure in the device is around 1 or 2 to 7 mm., to assist in starting the sodium or other vapor discharge. This is the more desirable in lamps using a dimcultly vaporizable working substance like sodium-es contrasted with one that is much more easily vaporized like mercury.

As thus far described, the device and its details of construction are illustrative, and may be widely varied, or even radically changed. Moreover, it is to be understood that in practice the device may be operated with such usual sodium lamp accessories as an enclosing vacuum jacket (not shown), to conserve heat; a ballast (not shown), to control the current rise as the device heats up after starting; a compensating resistance, reactor, or transformer (not shown), to allow the device to be used on ordinary A. C. lighting circuits of 110-120 volts or the like; etc., etc. It is also to be remarked that the oxide layer on the current lead I2 in the seal at each tube end I3 is liable to rapid attack by alkali metal vapor, which causes leakage at the seal; and that in making the seals any protective coating on the glass wall is fused and is often partially destroyed, which allows sodium attack at the fused areaand consequent objectionable blackening of the glass.

In this particular device, there are cool regions consisting of deep, narrow recesses opening into the main interior space of the envelope III at either end, and formed by hollow-projections I5, I5 of the envelope wall, such as short lengths of glass tubing sealed into the end walls I3, I3, coaxially with the cylindrical envelope walls. When the inner surfaces of the envelope II) are protectively coated or glazed against attack bythe working substance, this is preferably done after the tubes I5, I5 have been affixed to the ends I3, I3, rather than before, so that only the subsequently made exhaust seal I4 and lead-wire seals I6, I6 will cause susceptible internal areas. These areas, however, are the very depths of the tubes I5, I5 where they can best be protected. The current leads I2, I2 extend axially through the tubes I5, I5, and are sealed through their closed outer ends by seals I6, I6. Preferably, each lead I2 is provided with heat-radiating means between its electrode II and the tube I5, as by (helically) coiling the lead wire at I! to the extent of a couple of turns, more or less. While it is impossible to interpose heat-insulating material in a lead I2 which must be a good electrical conductor, the length of wire in the coil I1 offers a more or less equivalent resistance to thermal conduction via the lead, and is thus thermo-insulative. The tubes I5, I5 may be as small as is consistent with adequate mechanical strength, or as large as is consistent with retaining the required amount of protective material therein. If the tubes are small enough, they will readily stay quite full of liquid metal. In general, tubes of about in. internal diameter answer very well, being small enough to bring capillarity into play to help hold a molten filling in them. The axial current leads I2, I2 assist in holding liquid material in the tubes I5, I5, excepting insofar as heat transmitted by the leads may tend to vaporize the material.

Sodium or other alkali metal 'mayvbe distilled into the envelope Ill through the usual exhaust tube at I4 (not shown), after exhaustion of the device, but before sealing off; or it may be introduced in a hermetic (glass) capsule which is afterward ruptured, or in other ways. By holding the device upright, first one end up and then the other, and externally heating the envelope walls II) while or after the material is introduced, a considerable amount of it can be gotten into the tubular recesses I5, I5 at the outset, before the device is ever operated. If the tubes l5, I5 are externally chilled while being thus charged, the initial metal charges may coat them internally and there solidify,even covering the Junetion between the leads I2, I2 and the glass before or without actually filling the entire cross-section of the tubes. Or the material may initially fill the sealed-up ends of the tubes I5, I5 throughout their cross-section. In either case, the metal in the tubes I5, I5 embeds the leads l2, I2 adjacent the glass and forms an effective shut-off to protect the lead seals (and any susceptible adjacent areas of glass) against vapor attack when the device is first operated. Whether the tubes I5, I5 contain much, little, or no metal initially, they gradually fill up completely (about as shown at I8 in Fig. 1) as more and more material condenses in them during operation. The heat of the leads I2, I2 tends to cause the metal surface around them to be hollowed more than would otherwise be the case, but less than without the heat-dissipating lead coils l1, l1. Solid or liquid, the material in the tubes l5, I5 does not attack the parts; at ordinary temperatures, solid sodium and potassium are of a yielding, wax-like consistency, and so offer no danger of bursting the tubes I 5, I5 as a result of thermal expansion or contraction when the-device is thrown out of operation and allowed to cool,or 'vice-versa.

In the device of Fig. 2, the axially tubular projections I5a, I5a and the axial current leads l2, I2 in them are bent upward (in the position of the device shown), at right angles to the axis of the envelope II). This makes the device shorter over-all than that ofFig. 1. The exhaust tip Ila is shown on one of these tubes I5a, where it will be protected by the shut-off materiaL-instead of exposed on the tube end l3 as in Fig. l.

In the device of Fig. 3, the tubular projections I51), I52) do not open through the end walls I3b, I3b, but through the side walls of the envelope I0 adjacent the ends; and the tubes I51), I51) are sharply bent toward oneanother, into parallelism with the axis of the envelope. Thus the device is even shorter over-all than that of Fig. 2. The

current leads I2b, I2b extend radially of the envelope II) from their coils I1, I! into the-tubes I527, I51), and are there bent at right angles so as to extend axially in the tubes.

The device of Fig. 4 is of a more ordinary tubular lamp type,'with both current leads I2c, I2c introduced at the same end I30 of the envelope Iilc, through an ordinary tubular stem 20 with the usual seal press 2| and tipless" stem exhaust tube 22. The stem 20 is sealed as usual into a reduced neck I5c on one envelope end I3c, while the other envelope end I 30 is spherically rounded. The current leads I20, I20 carry the electrodes II, II in the opposite ends of the envelope I00; and one of the leads extends the whole length-of the envelope in an insulative cover-tube 23 (of glass, or of refractory material like alumina), which is sealed into the stem press 2I, and is offset to one side of the envelope axis. This insulative cover 23 prevents electrical discharge between this long lead Ilc and the adjacent short lead I2c as well as short circuiting between these leads by the metal in the neck I50. Only the short lead I20 has a coil I'Ic, since the length of the long lead serves to dissipat heat.

Here the neck I5e forms the cool recess for the sodium or other shut-off. The stem 20 is preferably made as small as possible (e. g., of standard automobile headlight size), and the neck I50 correspondingly small, though necessarily larger than in Fig. 1. However, the narrowness of the annular space around the stem 20 in the neck I50 helps to hold the material in the neck to its very junction with the rest of the envelope Inc. The whole neck I5e is initially or eventually filled with condensed material (as shown at I80), embedding the whole stem 20 and the portions of the leads I20, I20 within the neck I50, and protecting the stem 20 if made of glass that does not resist alkali metal attack. This is advantageous because a stem of resistant glass would be difilcult to make and seal properly. Operating this device upright and neck-down, there is no difficulty in maintaining a body of molten material completely filling the neck I5e.

The device of Fig. 5 is like that of Fig. 4 at its left-hand end, where it has a neck I5d, etc., and like that of Fig. 1 at its right-hand end, where it has a tube I5e. Preferably, it is operated upright with neck I5d down. Its electrodes IId, ii are of an indirectly heated type such as known in the art, and their internal (tungsten coil) heating resistances 24, 24 are interconnected in series between the leads I2d, In by a (molybdenum) lead 25 extending axially of the envelope IIid. Thus the serially connected heating resistances 24, 24 are in parallel with the glow discharge between the electrodes IId, IId during the operation of the device.

In using the lamps of Figs. 1, 2, 4, and 5 in vacuum jackets (not shown), thermoinsulative refractory (asbestos) jacket gaskets 30 will preferably be used around the tubular end projections I5, I50, I5e, I5d, and I5e,--as indicated in dot and dash lines,-to minimize loss of heat by conduction and convection in the air within the jacket around the glow discharge device.

These gaskets 30 may be made of a plurality of superposed sheets of asbestos felt, to make them hug the surfaces of the parts I5, I5d, I5e, I5d, I5e and the internal surface of the vacuum jacket (not shown) more snugly. Care should be taken to place them right against the tube ends I3, I30, IM and on or against the head formed by the merger of the projection I5e with the corresponding spherical envelope end, in order to assist in keeping the parts I5, I50, I5c, I5d, I5e as cool as possible right up to the envelope ends. The lamp of Fig. 3 is also shown with asbestos or other heat-dissipating gaskets 30b, 30b around the bends of its tubular projections I5b, I5b; although here such gaskets cannot coact with the walls of a vacuum jacket to impede air circulation, like those shown in Figs. 1, 2, 4, and 5.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A vapor electric discharge device containing a substance that is vaporous during operation of the device, and comprising an envelope having a relatively cool region in which a portion of said vapor condenses, a part of said region being subject to attack by the hot vapor of the substance, and a shut-off of said substance in said cool region embedding said part and protecting it from the vapor.

2. A vapor electric discharge device containing a substance that is vaporous during operation of the device, and comprising an envelope having a relatively cool region in which a portion of said vapor condenses, an inward extending part attached to the envelope wall in said cool region and including heat-dissipating means substantially to theinside of the point of attachment, and a shut-off of said substance in said cool region traversed by said part between its said heat dissipating means and its said point of attachment.

3. A vapor electric discharge device containing an alkali metal that is vaporous during operation of the device, and comprising an elongated tubular envelope with a relatively cool tubular recess opening laterally from its-end, and a filling of alkali metal in said recess.

4. A vapor electric discharge device containing a substance that is vaporous during operation of the device, and comprising an envelope having a relatively cool, narrow, deep recess adapted to condense said substance therein, and a wire extending into said recess and serving to retain the condensed substance therein.

5. A vapor electric discharge device containing a substance that is vaporous during operation of the device, and comprising an envelope having a relatively cool recess condensing and retaining a portion of said substance therein, and a part in said recess that is subject to attack by the hot vapor of said substance and immune to attack by said substance in a non-vaporous state, said condensed substance covering the non-resistant part of said recess to protect said part from attack by said vapor.

6. A vapor electric discharge device containing a substance that is vaporous during operation of the device, and comprising an envelope having a tubular projection opening into its interior condensing and retaining a portion of said substance therein, and a current lead sealed through the wall of said tubular projection and extending through its bore into the envelope, the joint between said current lead and the wall of said tubular projection being subject to attack by the hot vapor of said substance and immune to attack by said substance in a non-vaporous state.

7. A vapor electric discharge device containing a substance that is vaporous during operating of the device, and comprising an envelope having a relatively cool capillary recess condensing and retaining a portion of said substance therein, and a current lead sealed through the envelope wall in said recess and extending therethrough into the interior of the envelope, the joint between said current lead and said envelope wall being subject to attack by the hot vapor of said substance and immune to attack by said substance in a nonvaporous state.

8. A vapor electric'discharge device containing a substance that is vaporous during operationof a substance that is vaporous during operation of the device, and comprising an envelope having a relatively cool recess condensing and retaining a portion of said substance therein, and a part; attached to the envelope wall in the recess and extending therethrough into the interior of the envelope, and there provided with heat-dissipating means for minimizing heat transmission via said part into the recess.

10 10. A vapor electric discharge device containing aoeaeoe a substance that is vaporous during operation of the device, and comprising an envelope having a relatively cool recess condensing and retaining a portion of said substance therein, and a current lead sealed through the envelope wall in said recess and extending therethrough into the interior of the envelope, and there provided with heatdissipat-ing means for minimizing heat transmission along said lead into the recess.

THEODORE W. FRECH.

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