US2738435A - Electrode arrangement - Google Patents

Description

M r 1956 P. LEMAlGRE-VOREAUX 2,738,435

ELECTRODE ARRANGEMENT Filed Dec. 14, 1950 .nvenm- United States Patent ELEC'IRDE ARRANGEMENT Pierre Lemaigre-Voreaux, Paris, France, assigner to Societe Anonyme pour les Applications de lElectricite et des Gaz Rares-tablissements Claude-Fez & Silva, Paris, France, a company of France Application December 14, 1950, Serial No. 200,7 68

Claims priority, application France December 20, 1949 3 Claims. (Cl. 313-40) This invention relates to an electrode arrangement for electrical discharge apparatus.

One object of this invention is to provide an electrode arrangement for electrical discharge apparatus wherein a metal wire, wound and coated with emissive materials, is attached to an electrically conducting support, which may be a current connection for the electrode, at least at one point, said one point being located at one end of the wire or in the immediate vicinity of said end.

Another object is to provide a support for the coated wire of an emissive electrode, which support is in contact, locally at least, with a fin of heat conducting materiai, which may form a portion of the support.

One feature of the invention consists in providing the support of the electrode wire with a fin, the distance between the support and the fin being not more than 1 millimeter along the support from the penetration place of the support into the inner atmosphere of the discharge apparatus up to at least one contact point of said fin with said support and to the attachment point of said electrode wire to said support.

One advantage of the invention is to avoid that the electrode be put out of use prematurely in some cases, said putting out of use being caused by the fact that either the small wire portions which connect the wound portion with the supports, or the supports themselves, happen to break. This may happen, particularly, when the electrode is mounted in a discharge apparatus subjected, at the time of its starting, to a relatively high voltage, higher than 500 volts, for instance. The putting out of use is said to be premature, when it occurs before an almost total exhaustion of the emissive materials on the electrode. These breakings should probably be attributed to an excessive heating of the parts in question, due to a higher density of the cathode glow on said parts than on the rest of the electrode, or even to cathode spots forming on said parts during the starting period which lasts for the time of the voltage application to the time when a discharge with a low cathode drop is normall initiated on the winding coated with emissive materials.

Other objects, features and advantages of the invention will in part be obvious, and will in part be explained hereinafter.

In drawings which illustrate embodiments of the in vention,

Figure 1 is a side elevation of a wound-wire-support assembly,

Figure 2 is an end view of the assembly shown in Figure 1.

Figure 3 is a side elevation of another woundwire support assembly.

Figure 4 is an end view of the assembly shown in Fig. 3.

Figure 5 is a side elevation of yet another wound-wire support assembly and,

Figure 6 is an end view of the assembly shown in Figure 5.

In the assembly shown in Figures 1 and 2 the wire,

wound and coated with emissive oxides, is secured by pinching, to the ends 2 and 3 of two supports, constituted by current leads 4 and 5. Fins 6, 7 are secured to the current leads 4 and 5 respectively by welded spots 8 and 9 located between the stem 10 in which the current leads are secured, and the point of attachment of the winding 1.

The electrode proper consists, as known, of,a double wound refractory metal wire, coated with emissive mate rials composed of alkaline earth oxides partly reduced at the time of the formation of said electrode. The ends 12, 11, of winding 1 are secured, respectively, to the lead-in wires 4, 5 by pinching said ends in the hooks 2, 3 terminating said lead-in wires. These pinchings are efiected as close as possible to the ends of the winding, so as to decrease as much as possible the lengths of the wire por tions placed between each lead-in wire and the wound portion, saidportions being most fiable to break under the action of startings; the precaution is taken, after the winding has been secured to the supports 4 and 5, of mov ing the ends 2 and 3 of the current leads slightly closer together so as to move the end turns of winding 1 doser together, since these turns loosen slightly during the winding of the wire. The winding is coated with the emissive alkaline earth compounds after it has been secured on the current connections.

The fins 6, 7 may be made, for instance, of nickel sheet 0.2 mm. thick. In the case shown, each of them has the shape of an approximately isoceles triangle, the case of which, 14, 18 or 13, l7, is very close the lead 4 or 5; the fins are located at little distance from the plane containing the current leads 4 and 5. The apices 13 and 14 of these triangles protrude, in the direction of the discharge (i. e. towarcls the upper portion of the figure), and extend in this direction, beyond the winding. The apices 13 and 14 point approximately in the directions et the discharge at the ends of the winding; in the presentcase, since nothing is acting as a screen in the vicinity of the electrode, these directions are close to each other and are in the general direction of the arrow 20. The points of the fins at 13 and 14 facilitate the initiation of the discharge when the apparatus having the electrode has a voltage applied thereto.

The fins thusarranged form good heat conducting surfaces, which are in contact with or in the vicinity of the supports and the non-wound portions of the electrode; they decrease the temperature rise of these parts. These parts, where they do not touch the adjacent fin, are cooled, since the gas layer separating them from the adjacent fin is very thin. In Figures 2, 4 and 6, the spacing between the current lead shown and its fin has been exaggerated so as to make it visible, but, in practice, it can be decreased to a fraction of a millimeter without any dif ficulty. Experience has shown that for distances greater than 1 mm. between the fin and current lead, the effect of the fin is inSufiicie-nt; the result obtained becornes botter as these distances become smaller. For reasons of convenience in manufacture, the lower portions 2), 21, of the current leads are not completely covered by the fins. T his olers no drawback since these portions of the current leads, having no point less than 1 mm. from the closest point of the corresponding fin, are cooled by the latter; further, they are also cooled by thermal conductivity through the portions 22, 23 inside the stem.

Figures 3 and 4 show a modification in which the ends of the winding are pinched in lugs such as 24, cut out in the fins. To pass from one support-lead to winding 1, the current must fiow though the corresponding fin itself which may thus be considered as part of the support and as supporting the winding. The lugs may also be out from nickel strip and welded to the fin.

Figures 5 and 6 show another type of embodiment in which the winding is attached by welding to the current leads and at points intermediate betwen those where the leads corne out of the stem and those where the fins are attached. Each fin is very close to the current lead, from the stem, or nearly from the stem, to the point 25 where the fin is welded to the lead closest to the stem; thus protection is provided for all points of the current lead on which the discharge would have a tendency to concentrate during the starting period.

The following numerical example gives dimensions which gave good results in one particular case; an order of magnitude of the dimensions to be adopted in other cases can easily be derived therefrom.

The electrode, of the type shown in Figures 1 and 2, is designed for a fluorescent lamp 2.5 mm. long and 25 mm. in diameter, of an usual type except as regards the electrodes. This lamp, which comprises two similar electrodes, is supplied with an alternating current of 0.3 ampere; its operating voltage is approximately 300 volts. When the lamp is in position in its sockets, the two current leads to each electrode are connected together outside the lamp so as to be at the same potential; the starting without any preheating is ensured by the open circuit voltage of the power supply apparatus, said voltage reaching about 650 volts.

Winding l, neglecting its activating coating, is formed as a helix 3 mm. long and 1 mm. outside diameter; it is obtained by winding on a mandrel a molybdenum wire, 0.1 mm. in diameter, on which a molybdenum wire 0.05 mm. in diameter has been previously wound, and thereafter removing the mandrel. The current leads, inside the lamp, are nickel wires, 0.6 mm. in diameter, about 8 mm. long, from the point where they corne out of the stem to the point where the ends of the Winding are se cured thereto. Each fin forms a triangle With an approximate area of 31 mrnfl, and it has been eut out of a nickel strip 0.2 mm. thick. The lamp provided with electrodes thus protected can start more than 100,000 times before it is put out of use, which then coeurs by an exhaustion of the emissive material coating the Winding 1.

Numerous modifications may be made in the above described electrodes. The Windings coated with thermoemssive materials may be of a variety of types and may be attached to one support only or to three or more; one or more of these supports may not be used as a current lead. In case there is more than one support, it is often unnecessary that all supports be provided with fins. For instance, in the case of usual fluorescent larnps, with bipolar electrodes and starting by pre-heating, it is generally unnecessary for the supports which connect the activated Winding with the preheating interrupter to carry fins; it is preferable, however, that all the supports carry fins so that special bases and sockets are not required for preventing connection of the lamp in a manner which connects the current source to the supports not provided with fins. The latter may have varied shapes and orientations, they may receive a coating facilitating their thermal radiation, for instance by superficially carburizing the metal they are made of; several fins may of course be used on the same support.

What I claim is:

1. An electrode mount for an electric discharge lamp having an inner space, comprising a stem, a metal wire and an assembly formed of electrically conducting supports extending from said stem into said space and a fin in contact with each of said supports at least at one point and each spaced from its respective support at other points, said fins being made of heat conducting material, said metal wire being wound, coated with emissive matcrials and electrically connected to said supports, the distance between each support and its correspondin g fin being not more than one millimeter along that portion of the support extending from said stem to the point of contact of the support with the fin, said fins lying in a plane close and parallel to said metal wire.

2. An electrode mount as set forth in claim 1, wherein the ends of the wire are attached directly to the fins.

3. An electrode mount as set forth in claim 1, wherein each fin is substantially triangular in shape and is secured to its corresponding supports at its base.

References Cited in the file of this patent UNITED STATES PATENTS 1,388,793 Birdsall Aug. 23, 1921 2,366,292 Smith Jan. 2, 1945 2,462,837 Braunsdorfi Mar. 1, 1949

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