US2609590A

US2609590A - Method of manufacturing a

Info

Publication number: US2609590A
Authority: US
Publication date: 1952-09-09
Anticipated expiration: 1969-09-09

Description

INVENTORS Harry Bender Wlll M nflw rws ATTORNEYS mm B. Voorhis 2 SHEETS-SHEET 1 Fig H BENDER ET AL METHOD OF MANUFACTURING A FILAMENT UNIT Sept. 9, 1952 Original Filed Aug. 4, 1945 P 9, 1952 H. BENDER ET AL METHOD OF MANUFACTURING A FILAMENT UNIT 2 SHEETS-SHEET 2 Original Filed Aug. 4, 1945 INVENTORS Hurry Bender William B. Voorhis ATTORNEYS Fig.lO

Patented Sept. 9, 1952 Harry Bender, Princeton, and William B. Voorhis, East Orange, N. J assignors to Tung-Sol Lamp Works, Inc., Newark, N. J a corporation of Delaware Original application August 4, 1945, Serial No.

608,960, now Patent No. 2,482,826, dated September 27, 1949. Divided and this application October 30, 1948, Serial No. 57,482

This invention relates to thermionic tubes and particularly to heating filaments and mounts therefor, although certain features of theinvention'have other applications.- 1

Heating filaments and mounts-in cathode assemblies of the conventional practice are not entirely satisfactory and particularly assemblies One object of the invention is a filament mounting structure and cathode assembly whereby -the above difficulties and others are minimized or avoided.

A further object of the invention is aheating filament and cathode assembly of the above indicated character which is characterized by the firm and stable support of the elongated coil-filament inside the cathode against collapse and by the ease of welding the filament terminals to the lead wires to form both a firm support and electrical connection and by the ease of forming the filament and assembling it to the mount.

A further object of the invention is a coiled filamentary element of the above indicated character having a novel and improved end connector or terminal and support.

A further object of the invention is a novel and improved method of making heating filament units for thermionic tubes and particularly elongated high voltage filaments which is characterized by marked economy'in the use of raw materials, by a substantial reduction in the number of manufacturing steps or operations, by the ready adaptabilityof the method to the making of filamentary units embodying filaments of the fineness required for high voltage heaters and by a substantial. decrease in material loss.

Further objects of the invention will hereinafter appear.

For a better understanding of the invention reference may be had to the accompanying drawings forming a part of this application, wherein Fig. 1 is a side view ofa therminoic tube embodying the invention;

Fig. 2 is a side view on an enlarged scale of a filament mount and cathode assembly embodying the invention;

2 Claims. (Cl. 29-2518) Fig. 3 is a sun further enlarged view of a part of the mount shown in Fig. 2;

' Fig. 4 is a view similar to Fig.3 but disposed at right angles thereto; I

Figs. 5 and 6 are sectional views along the lines 5-5 and 6-6 of Fig. 3;.

Fig. '7 is a view similar to Fig. 3 showing a modification; Y

Fig. Bis a diagrammatic view'illustrating steps in making of the filamentary units according to the invention; and Y v Figs. 9 and 10 illustrate further steps in the method of manufacture.

The invention is illustrated as embodied in a thermionic tube I having two cathode elements, only one being shown and this one being indicated at'2 and being suitably mounted between the upper and lower

insulating plates

3 and 4. This cathode 2 is hollow and of conventional make. It

may be circular in cross sectionor of other conventional section. In the embodiment illustrated the cathode element 2 is tubular and circular I in cross section. The filament element of the of the insulating materials used for that purpose so as to prevent short-circuiting of adjacent coilsv or the short-circuiting of any part of the filament by coming in contact with the interior surface of the metallic cathode 2. At I are shown the lead or support wires extending from the press of the tube with their ends I turned over at an angle and fastened to the end structure '6 of the filament 5 as, for example, by welding.

In Figs. 3, 4, 5 and 6 are illustrated thesupporting end structures. or terminals of the coiled filament-.5. Each of the terminalsv B is provided with'a cylindrical supporting part 8 which is of substantially the same diameter as the diameter of the coil into which the filament 5 is formed with that part of the filament 5 being closely wound about the support 8 with the turns of the coil 5' engaging the surface of the cylindrical support 8. This support 8 is of a shape conforming to the coils of the filament 5 and as indicated since the coils are circular the support 8 is circular. The end structure or terminal 6 also embodies another filament supporting part 9 which is formed integrally with the supporting part 8 and this part 9 of the terminal is'fastened as by welding to the lead wire arm 1'. This part 9 of the filament terminal is flattened on one side and the portion of the turns of the filament coil 5' are embedded in the flattened side of the part 9. In the particular embodiment shown the part 9 is flattened on opposite sides to form flat surfaces IE! between which are dis-' posed round surfaces H and'Figs. i and 5 show the opposite portions of the turns of the coils 5 as embedded in the flattened sides 19 of the terminal supporting part 9. The turns of the coils 5 pass around the unfiattened edges H of the supporting part 9 without being embedded therein but these portions of the turns press closely against the rounded edges i I as the turns of the coils 5' closely surround the terminal supporting part 8. By embedding the fine filamentary wire of the filament terminal in the terminal supporting part 9 the filament ends arev thereby firmly anchored to the terminal supporting part 51 a ainst unravelling or dislodgment and the flattened side or sides'lfl where the filament is embedded afford a line contact with the lead arm 7' for-firmly welding the terminals to the lead wires.

As illustrated in Fig. 3 the filament unit and the cathode 2 are preferably assembled with the fila- .ment terminal supports extending up into the cathode a short distance as. for example, a distance of from 1 to 2 millimeters.

)The filamentary unit and cathode assembly have the advantages, among others, of having F a rigid terminal supporting and welding part 9 with the filament turns embedded therein s as v to. prevent any tendency of the filament to become dislodged or removed from the support, and

. so as to present a. solid piece of metal 9 to the lead arm 7' to which it is to be welded and of ,having an adjacent and integral supporting ter- .minal part 8 about which the filament turns are closely wound without-being embedded therein to ;form a. sort of cushioning section for the heating'or body part 5 of the filament. The support- I ing and mounting terminal part 6 of thefilamentend may be of any suitable length but we 'have obtained satisfactory results where this part is around 8 to .9 millimeters and the structure and assembly described render easier and facilitate the mounting of. the filament units on the lead wires, and the assembly in the cathode tubes 2, l the filament terminal forming a rigid integral aligning support for the filament during this mounting and assembly operation. Another advantage of this filament unit is that there is no appreciable tendency for coating material with which the filament body 5 are treated to seep along the terminal 6 to the welding part '9 and there to interfere with the welding and the I the terminal supporting and mounting part 6 is provided with a slightly elongated reduced in diameter portion .or tapered end 8{ and with this structure a substantially reduced tube loss is v obtained as compared with the conventional practice. It is believed that, this reduction in tube loss is due in part to the seepage of coating material on the under sides of the coils of the filament 5 adjacent and along the tapered portion 8 which tends-to strengthen the coatings applied to the part of the coil 5 in that region where the filament 5 tends to form bends and in 4 part to the tendency to form a more gradual bend at the tapered or reduced end but we do not desire to be, restricted to any theory of functioning in this respect.

The method of manufacturing the

filament elements

5, 6 is diagrammatically illustrated in Figs. 8 to 10. A filamentary wire [5 is closely coiled and wound about a metallic wire core Hi from a wire carrying reel l1 somewhat in the conventional manner of forming coil filaments of less fine wire. This step is illustrated at A, Fig. 8. With the filamentary wire it thus wound in closely formed coils and closely about the surface of the wire core or mandrel [6 suitable lengths of this combined filamentary coil and core wire [6 are severed as indicated at B in Fig. 8. The terminal supports for the filamentary part of the filament are formed out of the core or mandrel wire I6 and before or after the severing of the lengths l3, either at one or both Q Q simultaneously, the ends of the lengths-itfcrmed or to be formed are flattened and the filamentary wires are embedded in the fiatsides f the mandrel thus flattened toform the fiat sided welding parts 9 of the terminals. This may be done on any suitablehand or machine press, omittedfor convenience in illustration. In the particular embodiment shown, the lengths I8 are severed at both ends and then flattened and the wires embedded. i

With the ends of the lengths [8 thus flattened, with the filamentary wire l5 at'the ends of the lengths embedded in the fiat sideso'f the fiat portion 9 the lengths 18 are subjected to a suitable acid bath to dissolve out the mandrel '16 within the main heating portion 5'ofthe filament, and the supporting and reinforcing terminals 6 above described are at the sametime formed. In -the particular embodiment shown the filament portion 5 as described above is formed into two substantially parallel branches with the terminals ii welded to the adjacent'l'ead wire supporting arms '5' as desi'zriloed" above, and the next step D of Fig. 8 is the formation of the lengths is into a V 18. With the lengths it thus formed the legs of the V are subjected to a suitable acid bath to dissolve' out the core wire it, leaving the heatmg'filament portion 5 without any core, but leaving a flatagrammatically in Fig. 9 by providing any suitable support 20 for a multiple number of the lengths IS with the support or supports 26 engaging or gripping the flattened ends 9 of the lengths. With the lengths Iii thus supported the support or supports 20 are lowered into an acid bath 2! and the legs of the V lengths 16' are maintainedin the bath 2| until the mandrel it of the legs of thevs is completely dissolved out except for the ends 6 above described consisting'of the flattened parts 9 and the part8.

If it is desired tr.) reduce the diameter of the inner ends of the parts 8 of the terminal$ -,to form the reduced diameter part 3201? Fig. 7, the supports or carriers 20 are first lowered to a depth sufficient to form the terminal. portions 6 of the desired length by whollydissolvin'g out the intermediate partof thecore wireldq The supports or carriers 20 are then lowered slightly,

' as indicated in dotted lines. in Fig. ,9, vto dissolve off a part of the periphery of the inner ends of j the terminal portions 8 thereof to form an inner supporting part or parts at the; extreme end of the portions ii,- which parts are of substantially. lessdiameter than the diameter of the, coils of the filament 5. We have roughly indicated in Fig. '7 the generally tapered shape of such extreme end portions 8' which preferably extend in the mounted position a short distance into the lower nd of the cathode 2, as shownin Fig. 7. f -With the'supporting terminals 6 thus formed,

" maybe of any suitable character so long as the portions intermediate the terminals 6 may be readily dissolved without at the "same time imparing the filam'entary coil. Itm'ay for example be of brass, iron, or molybdenum. The particular 'acid' bath depends on the 'characterof the man-- fldre'l "or core Is and when-molybdenum is useda bath of nitric and sulfuric acid may be used to dissolve it'out. In dissolving the core or mandrel asillustrated in Fig. '9, the level of the'bath should be kept fixed so that with a fixed support coating material of the conventional practice to I insulate the coils of the filament from each other and against short circuiting contact with the cathode 2 against the interior of which the filament branches or legs rest for support. This may be effected by utilizing the same holder or supports 28 for dipping the V filaments in a cataphoretic bath for coating and accordingly after that portion of the mandrel or core 16 between the terminal supports 6 is dissolved, the holder and the filament are withdrawn and washed and the filaments dipped in the cataphoretic bath, as shown in Fig. 10, the bath being diagrammatically indicated at 22.

The filament units thus completed, the filaments are ready for mounting upon the lead wires 1,1 and assembly into the cathode 2. The tendency of the insulating coating material to seep along the filament terminals and there interfere with the forming of a secure weld and electrical connection with the leads I, 1' is minimized or entirely avoided by reason of the particular structure of the supporting terminals 5 wherein the filamentary wire coils are bound about or closely formed about the periphery of the supports with no free spaces on the interior of the coil at the terminals to induce such seepage. Where the terminals 6 are provided with the ends 8 of reduced diameter as compared with the inner diameter of the filamentary coils, the coating material seeps along the turns of the coils about the reduced portion 8' to form a reinforcement of the coating against chipping at this point where the sharper bends of the nonself-supporting filament are likely to occur and in the coating step the filament may be dipped to a point above the tip of the reduced portion 8' of the support, or to a depth co-extensive with the length of this reduced portion 8'. The fiattened and filament embedded ends 9 of the filament units prevent any tendency of the filament coils to ravel, creep or become dislodged, and also forms easily weldable ends for welding to the lead wires 1, 1 while the turns of the closely wound filament about the portions 8 form cushioning means between the portions of the filaments embedded and rigidly fastened to the parts 9 on the one hand, and the heating or body part 5 of the filament. The part 8 also performs an alining function for assisting the operator in assembly with the cathode 2 while the reduced diameter or tapered part 8 of the support imparts the advantages above set forth.

The filament lengths or forms I8 may be cleaned in any conventional manner before dissolving the mandrel or core I'E out of the lengths as, for example, by subjecting them to caustic or some other conventional cleaning means. After such cleaning the filament lengths or forms I8 may be fired at high temperature to set the filament coils as, for example, in a hydrogen atmosphere furnace. The core or mandrel wire 16 or holder 211 only the part of the mandr'e'l or core 1 between the terminal supports '6is' affected and while the temperature of the dissolving bath may vary with different materials of mandrels or cores, with; a molybdenum mandrel we have found that a'ba'th kept at about 40 C. is hot enough to give a practical rate of solution. One or more of the steps of our method above described may, if desired, be performed automatically or semiautomatically by machine operations and the method facilitates machine operations. For example, the operations A, B, C and D of Fig. 8 may, if desired, be wholly automatically performed on machines either in the exact order of steps A, B, C and D or with a different sequence. It is deemed unnecessary to illustrate apparatus for carrying out these machine operations.

In the particular embodiment shown in Fig. 1, the invention is illustrated as being embodied in that type of radio tube where two heating filament units 5, E are connected in series across ordinary house voltage lines from to volts with each heating filament therefor consuming roughly 55 to 60 volts but one of these identical units together with its cathode 2 is omitted from the drawings for convenience in illustration.

It is understood, however, that the invention is not limited to filament structures of any particular voltage limit and an important advantage of our invention is that within practical limits there is no limit to the fineness of the filamentary wire that can be processed according to this invention to form the highly improved filamentary units of the above described structure and accordingly the invention is particularly adapted to the production of higher voltage filaments than the 50 odd volts of the filament mentioned above. By the structures and practices above described theloss in waste or discarded material is minimized and the filament structures have the advantage above set forth.

For convenience in illustration the coils of the wire l5 are omitted from certain parts of the mandrel Hi as shown in Figs. 8 and 9, and also from certain parts of the terminals 6 as shown in Figs. 4 and 7, and in these and other figures of the drawings the spacing of the filamentary coils from each other is exaggerated for convenience in illustration.

This application is a division of our co-pending application Serial No. 608,960 filed August 4, 1945, now Patent No. 2,482,826, granted September 2'7, 1949.

We claim:

1. The method of making an elongated coiled non-self-supporting cathode heating filament unit for thermionic tubes comprising the steps of flattening the ends of a unit of filament wire closely wound about a mandrel and embedding the adjacent filament turns in the flattened surfaces of the unit, forming the unit into a V and immersing the V unit thus formed into a chemical bath to dissolve out the mandrel up to points spaced from the flattened parts and then lower- "'7 ing; the v unit into the bath forredueing the diameter of. the inner ends of the remaining part of the mandrel. V 2. The method of making an elongated coiled non self-supporting cathode filament comprising the steps of winding filament wire on a mandrel, flattening the ends of the mandrel and at least partially-embedding the filament in the mandrel. torming the mandrel into a V-shape and dissolving out by means of a chemical bath the central part of the mandrel between points spaced from the embedded filament part, and subjecting the remaining mandrel ends to said bath by partially immersing them therein to produce a taper thereon. a I

HARRY BENDER.

B. VOORHIS.

*8 REFERENCES. CITED me of this patent:

5 UNITED STATES PATENTS v Number Name Date 2,075,910 Robinson Apr. 6, 1937 2,287,460 Wagenhals et a1. June 23, 1942 2,359,302 Curtis Oct. 3, 1944