US2727168A - Electronic rectifier tube and ignitor assembly - Google Patents

Description

Dec. 13, 1955 D, E, MARSHALL ETAL ELECTRONIC RECTIFIER TUBE AND IGNITOR ASSEMBLY Filed Feb. 27, 1952 2 Sheets-Sheet l INVENTORS D. E. M/nz/MLL ase/MPP zw/N v :nl i Infini alla. 5,, W, W ll 5./7- GOLD/mvv BY 9 'ATTORNE Dec. 13, 1955 D. E. MARSHALL Erm. 2,727,168

ELECTRONIC RECTIFIER TUBE AND IGNITOR ASSEMBLY Filed Feb. 27, 1952 2 Sheets-Sheet 2 60 50 E V Z INVENTORS D. E. MAPS/WL saw/Pp nw/v E. fi. Gaz MMV ATTORNEY United States Patent @thee 2,727,168 Patented Dec. 13, 1955 ELECTRONIC RECTFHZR TUBE AND GNITOR ASSEMBLY Donald E. Marshall, Clifton, Gerhard Lewin, Maplewood, and Ernest Arthur Goldman, leomiieid, N. .1., :isu signors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsyivania Application February 27, 1952, Serial No. 273,603

10 Claims. (Cl. 313-13) This invention relates to electronic rectifier tubes and more especially to a gas-filled power rectier tube having a eld emission cathode. Commercially, rectier tubes of the general category specilied, are exemplified in the mercury arc rectier in its various forms, such as the ignitron, the excitron, and the like which utilize a pool vof mercury as the cathode.

Objectively, the invention proposes an improved structure and combination of parts to overcome previous defects and diihculties in power rectiiier tubes and to provide a tube having more universal utility, one solving the problems of suitable eld arc, instigation of the arc and utilization thereof, and one which will function irrespective of vibration, roll and pitch on impact shock of the vehicle in or on which the device is mounted.

Other objects of the invention will appear to persons skilled in the art to which it appertains as the description proceeds, both by direct recitation thereof and by implication from the context,

Referring to the accompanying drawings in which like numerals of reference indicate similar parts throughout the several views:

Figure l is a longitudinal section of an ignitron arbitrarily selected for illustrating the invention in one practical embodiment;

Figure 2 is a cross-section on line II-II of Fig. 1;

Figure 3 is a sectional elevation of the cathode-ignitor assembly on increased scale over the showing in Fig. l;

Figure 4 is another elevation of the cathode-ignitor assembly, looking toward the side of Fig. 3;

Figure 5 is a sectional plan of the cathode-ignitor assembly as on line V-V of Fig. 3; and

Figure 6 is a further enlarged sectional elevation of a portion of said assembly of Fig. 3.

ln the specic embodiment of the invention illustrated in said drawings, the general organization of parts comprises a cylindrical metal envelope 10 surrounded by a water jacket 11 and closed at its ends by top and bottom headers 12 and 13. The bottom header is constituted as part of a cathode-ignitor assembly shown in Figure 5, and described below in greater detail. The top header is sealed to an anode lead-in post 14 which passes through the header and carries an anode 15 in depending position coaxially within the envelope. The headers are applied by appropriate technique to render the envelope vacuum tight and adapted to retain the desired vapor, such as mercury, therein.

The upper end of the water jacket wall is extended above the cylindrical envelope wall, and transversely within that extension is a strong insulating disc 16, which may conveniently be made from a material obtainable on the market under the name of Mycalex and said to be a compressed mixture of mica and fused glass. This disc has a central hole to pass the lead-in 14 therethrough and preferably the surface of said hole is lined with an aluminum bushing 17 the ends of which overlap the margins around the hole. The outer edge and adjacent margins of the disc are similarly covered with an aluminum rim 18. These aluminum bushings or coverings provide um'- form pressure distribution on the Mycalex which s somewhat brittle. The marginal portion of the disc, where protected by the aluminum covering, are held between two rings 19 welded to the inside circumference of the water jacket extension with adequate clamping engagement of the rings with the disc to x the disc immovably in place.

The lead-in 14 has a shoulder 20 beneath the disc 16, and between said shoulder and the disc is a metal sealing ring 21 which can be tightly clamped against the rim of the aluminum bushing 17 by a nut 22 screw threaded onto the lead-in above said disc. Said sealing ring 21 is preferably welded, brazed or soldered on said shoulder for obtaining a vacuum-tight joint therewith. Said sealing ring 21 has a greater diameter than said shoulder and accordingly projects outward beyond the shoulder and there receives and is secured with a vacuum-tight joint, to a ilexible or resilient annular band or bellows 23 substantially coaxial with and around the lead-in post 14. The lower end of said band or bellows is attached vacuum-tight to the upper margin of a sealing collar 24 the lower margin of which is sealed in a glass ring 25. The lower edge of the glass ring 2S is sealed upon an upwardly projecting rim of a flexible or resilient eyelet 26 the lower part of which is secured, vacuum-tight, to the aforementioned top header 12. Said ring 2S and eyelet 26 are of appropriate metal to seal to, and to have substantially the same coeiticient of expansion as the glass ring, such as those described in U. S. Patent 2,062,335 of December l, 1936, to Howard Scott.

The anode 15 is mounted, as by threaded attachment, to the lower end of the lead-in post 14, and is preferably graphite and constructed to afford maximum surface area and minimum weight compatible with suiiicient mechanical strength. As shown, said anode is cylindrical with a plurality of longitudinal holes 27 therein for weight reduction purposes, the holes extending from the top toward the bottom but with reduced size at the bottom sufficient only for draining any mercury that may condense in said holes.

For cooling purposes, the water jacket extension may be provided with a plurality of vent openings 2S in the region above the header 12 and below the insulating disc 16. The region between the water jacket and cylindrical envelope 1i) constitutes the cooling chamber 29 and may be provided with a spiral guide 3l) therein `for desired distribution of the coolinfr medium. There are preferably three water connections, namely, an inlet 31, shown at the lower part of the water chamber, and two outlets 32, 33, of which one, referred to as the intermediate outlet, is in the region between the cathode and anode, and the other, 33, is next the upper end of the water chamber and above the location of the anode. The purpose of the intermediate outlet is to make possible the colder operation of the lower part of the tube, thereby concentrating the mercury condensation in the cathode region ofthe tube, thus reducing the amount of mercury outside the sponge, hereinafter described, and the danger or" arcing back caused by mercury droplets striking the anode under shock or otherwise. Furthermore, the higher temperature in the anode region reduces the average vapor density there, which also helps to avoid arcing back. By means of a throttle valve 341 in the upper outlet line, the temperature distribution along the tube wall can be controlled.

The cathode assembly includes the bottom header i? on the upper face of which, Within the envelope, is secured, as by welding or otherwise, a cathode body 35 composed or' a porous material which has t. e property of a sponge sorptive to mercury or other reconstructing liquid cathode material, and while metal is preferred for this sponge, the present invention is not restricted thereto. Siutered iron is an acceptable material for the .Said sponge.. Sintericd molybdenum likewise makes an excellent porous body for the purpose and is in some respects superior to sintered iron. Said' body or sponge35` is flat and substantially lls the bottom of the envelope 10. Mercury or other recon,- structing, liquid cathode material is applied to the sponge body to extent that said body willabsorb the mercury orl the like without any excess remaining onV the surface. As a speciiicexample, a sponge cathode having a diameter of three and a quarter inches andthickness of at least tive sixteenths of an inch, will be filled for such dimensions by approximately one hundred titty grams4 of mercury. At the rate current of one hundred amperes, direct current average, this amount of mercury is vaporiZed in about four minutes. The porosity of the iron body used in this instance was measured to be 35%, or having a density of 65%,-

Material having the best characteristics for an arcstriking surface' for a sponge cathode is ruthenium, and, except for the expense, would be advantageous for the sponge body 35. However, the beneficial characteristics of this material may be utilized by providing a surface disc or raised portion 36- of ruthenium centralized on the top face of the iron or other body 35'. In the specific example gvenabove, the ruthenium disc was one end three eighths inches in diameter for the portion exposed and approximately twelve thousandths of an inch thick. The are is limited to the exposed areaof saiddisc by an arc-retaining ring 37 of a refractory material, such as molybdenum having an angle cross-section with one flange flatwise against avmarginal portion of the. disc surface and the other flange projecting upright from the cathode body. This ring 37 is held in place by a plurality of molybdenum strips bent over the upright ange and each providing a foot portion ilatwise on the cathode body and secured thereto by bent-over pins 38 the lower ends of which are sintered into the said body outside of the ring and arc region.

At a midfpart of the header 1'3 is a downwardly extending bar 39 which serves as an electrical connection to the cathode and ground, and may be made integral with the header by welding, brazing or otherwise. Within the cylinder 1t), coaxial therewith is a support rod 40 the lower end portion of which passes through the cathode body 35 and its surface disc 36 as well as the header, and screws into the upper end of said bar 39 (see Fig. 3) and may also be brazed in said bar, thereby affording desired rigidity of the support rod in place in the device. At its upper or inner end, said support rod carries a molybdenum or other` battle disc 41, for which purpose said rod is shown with a shoulder at its upper end receiving two clamping washers 42y with the disc therebetween and a securing pin 43 through the rod above the top washer. Above this rodsupported bafe disc 41 is an annular baille 44 secured to the inside surface of the cylinder wall. These two baiiles serve to reduce the probability of arcing back.

Said support rod also carries a welded frame for holding two ignitors, said frame being here shown asvcomf prising two parallel cross members 45 perpendicular to said rod and having holes through which the rod passes midway of the lengths of said members. Said cross members are of channel cross section and arrangedso that the open sides of the channels look toward each other. Said cross members are secured in their parallel spaced relation by two face plates 46 parallel to each other and 'to the rod on opposite sides of said members and rod. These plates extend above the upper one of the two cross members and are secured by a dowel 47 through both of said plates and diametn'cally through the rod. It will be. seen that the cross members 45 project each at opposite sides of the support rod, and are utilized in pairs as slidable mounting means for the ignitors. Description of the mounting for a single ignitor will therefore suice for both.

Each of the portions of the two cross members45 projecting from the rod 40 is provided with a bushingreceiving hole .in each of which is an iusulative bushing, 48 and the bushings at each side of the rod are aligned with one another on an axis parallel to said rod. These bushings 48 are appropriately shouldered and located so as to be insertable from the inside of the channel formation of the members 45 and prevented from passing entirely through the holes. A slidfable shaft or stem 49, preferably of molybdenum extends through the two aligned bushings projecting above the upper member and below the lower member of the frame. A compression spring 5@ surrounds said shaft between the cross members, said spring having pressure collars 51 at opposite ends thereof which are partly within the spring and partly opposite the end of the spring. The upper one of these collars seats against the upper bushing whereas the lower one has a transverse pin 52 locking it upon the shaft so that the spring pressure tends to slide the shaft downward. Said ,shaft is in a location overlying the arc-striking region provided by the ruthenium disc 36.

On the lower end of said shaft is an ignitor 53V the` lower end of which is shown as rounded and in contact' with the upper face of the ruthenium disc 36`under pressure or" said spring 50; The particular ignitor shown isindicated as having a graphite core or insert 54 having adherent engagement with the' molybdenum shaft 49 to obtain goed mechanical and electrical contact. This; graphite core is part of the'plunger used in hot-pressingV the ignitor during fabrication thereof and to assure a bond` between it and the ignitor body, an intermediate coating of an admixture of 30% boron powder and 70% of the ignitor mix may be advantageously used on the' junction face of the core'with the body prior to hot pressi ing. During the hot pressing of the ignitor, the boron combines with the graphite forming boron carbide and integrating the core with the body. It isl deemed' feasible, however, to omit the core and tit the shaft in the ignitor body if so desired.

We have found that an ignitor operating in contact with a sponge cathode develops a very high cur-rentk density at the tip and that a much smaller firing energy is required for operating the same ignitor than when immersed in a mercury pool. The life of a common com mercial ignitor is very short when used with a sponge cathode, and for example a commercial Welder ignitor lasted only a few' minutes and a commercial rectifier ignitorv only a few hours, namely about ten hours'. In view of this diiiiculty, it has been necessary tov devise an ignitor adapted more especially for use with the sponge cathode. For this purpose, we provide a mixture of aVv stable refractory insulator and a refractory conductor, such as alumina andA 30% boron carbide to comprise the ignitor as more fully described in copending sole application of Gerhard Lewin S. N. 244,455 tiled August 30, 1951, assigned to the same assignee as the present case. v

Heat shielding may be provided where deemed desirable, as for instance provision of a cylindrical molybdenumsleeve 55? around the support bar 40 between the sponge cathode and lower cross member 45 of the ignitor-moumf ing frame, and also a molybdenum covering or shield 56 under said lower cross member for its protection. Shielding caps 67 are also shown on the upper ends of shafts. Also at the underside of bottom member 45 and aroundy the lower bushing 48 is another shield 68', of refractory material, such as molybdenum. Shields 67 and 68 are primarily forv protection of the bushings to keep` them free of sputtered material in use, since sputtered material on the bushings would render the surfaces thereof conductive. The lower shield is shown as madein the form of an eyelet for convenience in mounting. Sinceit isv affected by a considerable temperature range and welding thereof to thecross member, which is` preferably of stain. lessl steel, would be` inadvisable, the shield is mounted to said member by an offsetisteel. Washer. 69 which is welded to said member and overlaps the. flange ofy the eyelet.

Aforementioned shield covering 56 underlies the washer and member. It may also be found desirable to include stainless steel mesh or other washers 57 between the ceramic insulators or bushings 48 and the opposing faces of the frame members and pressure collars 51 absorb shock and distribute and equalize pressures applied in use to the more frangible bushings.

Current lead-in structure for the ignitors may be appropriately provided, and as here shown, there is a separate lead-in for each ignitor, both being the same, so description of one will suice for both. Au eyelet 58 is Welded to the bottom header and extends downwardly therefrom and has a sleeve 59 secured vacuum tight as an extension thereof and depending still further. The lower end of this sleeve 59 is semed by a glass bead 60 to a graded glass tube 61 coaxially within said sleeve and eyelet, said tube projecting upwardly through the header and sponge cathode. Said bead also makes vacuum tight engagement with a lead-in post 62 which is partly within the glass tube and extends in part to the exterior through said bead. A exible connection 63 of suitable wire, such as molybdenum, is attached at one end to the inner end of the lead-in post, and at its other end to the ignitor or ignitor shaft. lt may be further pointed out that the lead-in post 62, sleeve 59 and glass bead 6i) should be of materials having substantially the same coecient of expansion, and may be comprised of the glass and metal described in the above noted Howard Scott Patent 2,062,335. An exhaust tubulation 64 is also shown on the bottom header and communicates to the interior through a hole 65 in the sponge cathode.

We claim:

l. An ignitron comprising an envelope, a sponge cathode in said envelope, an anode opposed to the cathode, insulative means supporting said anode, an annularly conned arc-striking surface on said sponge cathode, a support rod projecting upwardly through said cathode toward said anode and a pair of spring-loaded ignitors carried by and at dilerent sides of said support rod and pressed into contact with said arc-striking surface.

2. An ignitron comprising an envelope, a sponge cathode in said envelope, an anode opposed to the cathode, a header for said envelope beyond said anode, a supporting lead-in post for said anode projecting through said header, means vacuum sealing the header and post, said means having flexibility, and insulative means beyond said sealing means rigidly supporting said post and anode.

3. An ignitron comprising an envelope, a water jacket around said envelope and extending beyond the upper end thereof, a cathode in said envelope, an anode in said envelope, a rigid insulative disc in the extension of said water jacket mounted rigidly therein, and a supporting lead-in post rigidly carried by said insulative disc and having said anode thereon.

4. An ignitron comprising an envelope, a cathode in the bottom of said envelope, an anode above said cathode and below the top of the envelope, a water jacket around said envelope, said water jacket including a cooling chamber, said cooling chamber having an inlet substantially at the bottom of the envelope and having a plurality of outlets at different water levels above said inlet each for discharge of water admitted by said inlet.

5. An ignitron comprising an envelope, a cathode in the bottom of said envelope, an anode above said cathode and below the top of the envelope, a water jacket around said envelope, said water jacket including a cooling chamber, said cooling chamber having an inlet substantially at the bottom of the envelope and having a plurality of outlets at dierent water levels above said inlet each for discharge of water admitted by said inlet, and flow control means for one of said outlets.

6. An ignitron comprising an envelope, a cathode in the bottom of said envelope, an anode above said cathode and below the top of the envelope, a water jacket around said envelope, said water jacket including a cooling chamber, said cooling chamber having an inlet substantially at the bottom of the envelope and having one outlet at the part of the envelope below the anode and another outlet at the part of the envelope above the anode each for discharge of water admitted by said inlet.

7. An ignitron comprising an envelope, a cathode in the bottom of said envelope, an anode above said cathode and below the top of the envelope, a Water jacket around said envelope, said water jacket including a cooling chamber, said cooling chamber having an inlet substantially at the bottom of the envelope and having one outlet at the part of the envelope below the anode and another outlet at the part of the envelope above the anode each for discharge of water admitted by said inlet, and iow control means for the last said outlet at the part of the envelope above the anode.

8. An ignitron ignitor assembly comprising a sponge cathode, a support rod extending upwardly from said cathode, a frame secured to said rod, a slidable shaft in said frame parallel to said rod, and an ignitor on said shaft having end engagement with said sponge cathode.

9. An ignitron ignitor assembly comprising a sponge cathode, a support rod extending upwardly from said cathode, a frame secured to said rod, a slidable shaft in said frame parallel to said rod, a spring on said shaft having depressive engagement therewith, and an ignitor on said shaft having engagement with said sponge under actuation by said spring.

l0. An ignitron ignitor assembly comprising a sponge cathode, a support rod extending upwardly from said cathode, a frame secured to said rod, said frame having cross members projecting at opposite sides of said support rod, a pair of shafts of which one is carried by the said members at one side of the rod and the other is carried by the said members at the other side of the shaft, and an ignitor on each of said shafts in engagement with the said sponge cathode.

References Cited in the le of this patent UNITED STATES PATENTS 1,991,910 Reid Feb. 19, 1935 1,993,724 Gebhard Mar. 5, 1935 2,362,911 Litton Nov. 14, 1944 2,447,646 Halpine Aug. 24, 1948 2,617,064 Lewin Nov. 4, 1952 2,651,737 Marshall Sept. 8, 1953

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