US2042143A - Enveloe for electric discharge devices - Google Patents

Description

May 26, 1936. H. CHENEY ET AL ENVELOPE FOR ELECTRIC DISCHARGE DEVICES Filed April 11, 1934 INVE NTORS BY 77 8. ljbul'ibw ATTO N EY Patented May 26, 1936 UNITE- STES PAT

ENVELOPE FOR ELECTRIC msc navrc Application April 11, 193%, Serial No. 320,112

In Great Britain April 19, 1933 2 Claims.

This invention relates to envelopes for electric discharge devices, lamps and the like.

In certain types of electric discharge devices particularly those operating with a discharge 5 through a metal vapour such as mercury, sodium or the like it is necessary to design the envelope forming the containing bulb with a simple and smooth contour. The reason for this is that in operation the metal vapour attains a certain vapour pressure which is controlled by the coolest portion of the envelope. The temperature of this is in turn controlled partly at least by the heat liberated inside the envelope when a discharge is taking place. If the containing vessel is not of simple shape and smooth outline, but contains re-entrant or protruding portions, then one or more of these will run at a temperature considerably lower than the main portion of the envelope and will form a pocket in which the 0 metal vapour will condense. This in some types of discharge devices is undesirable, particularly so in those in which it is desired that the vaporizable metal should be at a high temperature. To overcome this difilculty it is necessary to design the envelope symmetrically and simply and to avoid re-entrant stems. An ideal shape would be a sphere with the source of heat (viz: the electrodes and discharge column), located at the center. This is not practicable for several reasons, and the envelope is usually cylindrical with electrodes located on the axis, diametrically opposite to each other and each adjacent to one of the ends of the tube. To avoid pockets the electrodes are not sealed in on the usual type of stems but the tube is closed by pressing the tube around the electrode leads. and shaping the seal by hand so that the closed end is substan tlally hemispherical. Such a method of sealing 'while giving the desired shape is slow, and cannot easily be adapted to normal lamp machine operations.

The object 01' this invention is to overcome this objection and to that end it consists in the 5 provision of a novel type of construction, the fabrication of which can take place on normal lamp making machinery, and yet when finished has' the desired regular shape. *To do this we use an inverted stem or press. Normally a stem is made so that the press remote from the flare carries two or more wires. These extend through the press, and form on the side remote from the flare electrode supports and on the side near to the flare lead in,wires. The stem is,

(or. 176-122) I after the affixing of the electrodes sealed into the bulb so that electrodes protrude inwards.

The accompanying drawing serves to illustrate this invention, Fig. 1 showing an electrode mounted on a stem made by a lamp stem making machine; Fig. 2 illustrates such a stem secured to a tubular envelope suitable for a discharge device; Fig. 3 illustrates our proposed stem and Fig. 4 shows this secured in a discharge tube.

The stem illustrated in Fig. l is usually made from glass tubing which is fed to the stem making machine. The lower end is flared to provide a flange i and the upper end is pressed flat to secure the wires 2 in position. These wires support and lead current to the filament 3. When such a stem is mounted in a discharge tube as shown in Fig. 2 it forms an objectionable annular pocket 4 which is cooler than the remainder of the tube and the mercury or other metal vapour condenses in this pocket. When making use of a machine made stem instead of mounting the electrode on the ends of the wires 2 on the opposite side of the press from the flare we secure it to the wires on the same side as the flare or flange l as shown in Fig. 3. Such a stem can be readily secured to a tubular envelope as shown in Fig. 4 on an ordinary incandescent .lamp sealing in machine.

By suitably shaping the stem for example by shortening the tubular portion, the resulting seal can be made to take the desired form and be substantially hemispherical even when the seal is performed on normal lamp making machines. A further advantage of this method is that it is possible to position the electrodes very close to the sealed off portion 01 the bulb and yet to avoid damage, to them through the heat applied when sealing in. For example, if the electrode consists of an oxide coated cathode it is not advisable to subject it to a high temperatureduring scaling in. If care is not taken to avoid this high temperature, the core or base metal of the cathode may be oxidized and subsequent activation may be diflicult. If, however, the proposed method of stem construction is adopted the uncoated cathode can be attached to the support. wires before the stem is fabricated, the cathode being so positioned that it lies, after the stem is made, in the hollow tubular portion. During the stem making process the cathode core becomes oxidized, but it can be chemically or mechanically cleaned prior to coating with electron emitting materials. During sealing in it is shielded from heat by the portions of the stem that surround it.

What we claimas new and desire to secure by Letters Patent of the United States is:-

1. An envelope for an electric discharge device comprising a tubular portion having electrodes mounted therewithin at each end, tubular flared stems fused to said envelope. each of said stems 2. An envelope for an electric discharge device comprising a tubular portion having thermionic electrodes mounted therewithin at each end, tubular flared stems fused to said envelope, each of said stems having a press at the end thereof opposite the flared part thereof, electrode leads sealed into said press, one of said electrodes being mounted on said leads and being between the flared part of the stem and the press thereof. 10

HORACE CHENEY. LEONARD J. DAVIES.

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