US2664361A

US2664361A - Method and apparatus for applying electron emission material

Info

Publication number: US2664361A
Application number: US66642A
Authority: US
Inventors: William P Zabel
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1948-12-22
Filing date: 1948-12-22
Publication date: 1953-12-29
Anticipated expiration: 1970-12-29
Also published as: NL77446C; FR1006991A; GB692479A; BE492888A; DE959574C

Description

Dec. 29, 1953 w. P. ZABEL 2,664,361 METHOD AND APPARATUS FOR APPLYING ELECTRON EMISSION MATERIAL Filed Dec. 22, 1948 2 Sheets-Sheet l WiLLiam P. ZabeL, by MC His Airlror-ne3 Dec. 29, 1953 I w. P. A'BEL 2,664,361

METHOD AND APPARATUS FOR APPLYING ELECTRON EMISSION MATERIAL --'Filed Dec. 22, 1948 I 2 Shee ts-Sheet 2 Inventor:

M V WiLLiam-PZabet, \i, )7 5 6/ is His A bi-orneg.

Patented Dec. 29, 1953 2,664,361 METHOD AND APPARATUS FOR APPLYING ELECTRON EMISSI William P. Zabel, Cleveland Electric signor to General ration of New York Application December 22, 1948, Serial No.

12 Claims.

of the cathode.

One object of somewhat thin and more tightly adhering sur- ON MATERIAL Heights, Ohio, as- Company, a corpomethod and apparatus for applying an ample amount of electron emission material to a cathode of so-called coiled-coil or doubly coiled form, and variations thereof, in a manner which causes said emission material to be retained tenaciously by said cathode. To efiect this object, in accordance with my invention, the cathode coil is in a linearly stretched condition at the time the emission material is applied or, more specifically, at the time the cathode is separated from the ap plicator and Withdrawn from the source of supply of said emission material. The efiect of the stretching operation on the cathode is to space the larger and, therefore, more resilient secondary coils thereof very widely so that the emission material does not bridge these larger coils, and so that all emission material not contained within the smaller interstices and wetting the surface of said cathode can be withdrawn therefrom. The proper carrying out of the complete method requires that the emission material be applied in suspension in a vehicle, and the viscosity of the liquid so formed be less than that producing an excess thickness of the surface coat of said emission material and only partial filling of the smaller interstices of the cathode, and, more than that, producing an unnecessarily thin surface coat and excessive travelling within the smaller interstices of said cathode. The stretching operation is restricted to an amount within the elastic limit of the cathode inasmuch as said cathode is contracted to substantially its former length after the liquid has been applied thereto. It is preferable that contraction of said cathode liquid has partially dried. must be efiected while stretching operation; however, all of said interstices are completely filled with the emission material.

The application of the emission material in accordance with my invention can be practiced with equal success on unmounted cathodes or on cathodes which have been mounted on or attached to the leading-in wires of a mount, parcombination with larger coils or configurations,

as said method prevents the parts of the cathode least adapted to retain the emission material from gathering large bodies thereof and assists in the filling of the smaller interstices of the cathode best able to hold said emission material. A discharge lamp containing a cathode manufactured according to my method is particularly well adapted to withstand rough handling and to have a long life because said cathode is best adapted to retain a ver generous quantity of the emission material.

Other objects and advantages of my invention will appear from the following detailed description of species thereof and from the drawing.

In the drawing, Fig. 1 is a plan view of apparatus comprising my invention and occup ng the four work stations along a mount conveyor; Figs. 2, 3 and 4 are corresponding perspective views of the mount midway in the course of the essential operations occurring at said work stations; Figs. 5 and 6 are plan and side views, respectively, of the mount spreading, emission material applying, air drying. and mount closing portions of the apparatus located at said work stations: Fig. 7 is a vertical section through the spreading device along line 'l--! of Fig. 6; Fig. 8 is a side elevation of a modified manually operated apparatus for holding and stretching an unmounted cathode for manual application of the electron emissive material according to my invention; and Fig. 9 is a perspective view of modified automatically operating apparatus combining at one station the operations of spreading the coil and applying the emission material. No claims are made herein to the apparatus shown in Fig. 9 s nce it constitutes the subiect matter of an application of Lee E. Dilts, Serial No. 66.798. filed of even date herewith, now Patent No. 2.611335, and assigned to the assignee of this a plication The method and apparatus of my invention associated with Figs. 1 to 7, inclusive, is a form thereof particularly suited to the division of the operations between a grou of work stations A to D. inclusive, and to the application of the electron emissive material to a coiled tungsten wire cathode I attached to the leading-in

wires

2 and 3 of a mount 4. The work stat ons are preferably those taken successively by the mount 4 in the regular order of movement of a conveyor in part supporting said mount 4 by the engagement of the jaws 5 and 6 with the exhaust tube 1 thereof, and are preferably associated with an automatically operated mount making machine such as that disclosed in U. S. Patent 2,380,742, Flaws, issued July 31, 1945.

In the first step in the operation with which this invention is concerned, the mount 4 is advanced to a position above the spreading device 8 at work station A and is reshaped by having the relatively short, and therefore relatively rigid, ends of the leading-in

wires

2 and 3 bent apart so that the springy or resilient cathode coil l is stretched linearly. The spreading device 8 (Figs. 5 and 6) effects the reshaping operation by an upward movement of the fingers 9 and Hi to a position between the laterally extending ends I l and 12 of the leading-in

wires

2 and 3, a movement which forces an oppositely sloping outer face 9' or ill of each fin er 9 or against a respective end II or L? of the leading-in

wires

2 and 3 to spread them apart. The fingers 9 and Hi, which are mounted at fixed positions on the bracket l3 on the upper end of the slide M, are arranged so as to pass to respective sides of the vertical portions of the leading-in

wires

2 and 3 and to opposite sides of the ends of the cathode l which is located at a slight angular relation to the plane of the leading-in

wires

2 and 3. The spreading operation is the only function of the device 8 and is initiated at the proper interval with respect to the arrangement of the mount 1 in operative relation thereto by operating means controlling the upward travel of the slide I l which is located behind the cover plate 15 in ways in the stationary support bracket I6.

As shown in Fig. 7, the contraction force of the spring H, which extends between a post 18 in the plate l5 and a second post [3 in the lower end of the slide it, urges said slide is upward and is controlled by the presence of the bar 20, which is fastened to the vertically movable rod 2! by the clamp 22, in the path of motion of the post is. The bar 29, clamp 22 and rod 2i are elements of the common actuating means for the entire apparatus and have a vertical motion shifting the rod 2! within the arms of support bracket 23 in each cycle of operation which is determined by common driving means (not shown) also advancing the mount conveyor. A driving means of this type is shown in the cam-actuated means in the mount making apparatus disclosed in Patent 1,907,532,Flaws, issued May 9, 1933; however, said means may be any of the well-known means commonly used for synchronizing such operations.

The upward movement of the spreading fingers 9 and i0, and the consequent spreading operation, is completed when the stud 24 extending from the back of slide Hi in a slot in support bracket 16 butts against the end of the stop screw 25, at which time the larger secondary coils 26 of said cathode are spread out greatly as shown. The spreading is restricted to the larger secondary coils 25 of the coiled-coil cathode I because of their relative flexibility and is restricted to an amount which stretches the cathode 1 within the elastic limit thereof so that it does not take a permanent set and is therefore capable of returning to its original form. One particular cathode having nine turns of secondary coils 71 mm. in diameter and having a length of 5.3 mm. is stretched to a length of 13 mm. without permanent set in the above operation.

The cycle of operation of the stretching device 8 is completed by a returning downward movement of the spreading fingers 9 and iii, the leading-in

wires

2 and 3 having been bent to such an extent that they remain in their spread position. The relatively small increase in tension in the cathode l in its stretched condition is not of sufficient magnitude to disturb the position of the leading-in

wires

2 and 3 after the spreading

fingers

2 and 3 withdraw.

The operations of the conveyor now advance the mount 4 from work station A to work station B, and in so doing place the mount 4 directly above and in operative relation to the device 21. which device 21 is the immediate means of applying the electron emission materials to the cathode I. At that time, the applicator receptacle 28, which is an element of the dipper 2S and which is located directly below the mount 4, is located within the cup 38 and is completely flooded by the liquid containing the electron emission material. Subsequent operations of the device 27 provide for the upward movement of the dipper 29, causing a small quantity of the liquid carried by the applicator 28 to be brought into engagement with the Cathode l, and then provide for a lowertached to the upper end of the rod ill by. means of the arm ti and the rod 32, is moved correspondingly and functions both. as an agitator for the main supply of liquid contained in the cup 39 and as a means of moving the applicator 28, which is an integral part of a partition 33 bridging the ring 34 within the interior of the dipper 29. The upward movement of the dipper 29 carries it clear of every portion of the supply of the liquid and in so doing causes the liquid contained within the dipper 29 to drain through the bottom opening 35 to the cup .39, effecting a thorough washingof the liquid over the applicator 28. This method of operation causes the main supply of liquid :contained in the cup til (which is mounted upon thestud 36 extending from bracket 23) to be agitated continuously, both by the upward movement of the dipper 29 and again by the return of said dipper 29, so that the emission material in suspension therein is thoroughly mixed with the other igredients of the liquid.

The "upward movement of the dipper 29 continues until the secondary coils 2d of the cathode I are within the open-ended trough 3i running the full length of the applicator 2a and are seated upon andpushed upwardly slightly out of their normal'position (as shown in detail in Fig. 3) by the ridge 38 along the bottom thereof. This operation has the effect of aligning all portions of the cathode l within the trough 31 along the bottom thereof and causing said portions to be immersed to an equal depth in the liquid retained by the capillary attraction thereof. As the trough .31 is only slightly larger than the coils 26 of the cathode I, it is so small that the attending capillary attraction thereof causes a sufficient quantity of said liquid to be retained thereby, although both ends thereof are open and allow the greater portion of said liquid to flow back into the main supply thereof. In the present instance it is desired to restrict the liquid to that portion of the length of the cathode l which becomes heated in use in the discharge device because the emission material placed upon said cathode i must be converted to oxides of suitable character and emissivity by heating the cathode in subsequent manufacturing steps. To this end it is preferred that the applicator 28 he only long enough to accommodate the largersecondary coils 25 of the oathode I and therefore bathe those coils 25 directly .in the liquid. The distribution of the liquid over the length of the cathode l is also dependent upon the viscosity of said liquid in that the fluidity thereof must be such as to cause it to flow into the closely coiled primary coils thereof and to be drawn by capillary attraction into the open core of the ends to within a few turns of the lead- .ing-in

wires

2 and 3. Distribution of the emission material over the full periphery of the cathode "i depends in a like manner on both the size of the applicator 2i; and the viscosity of the liquid in that the depth of the fillet developed over the bottom of the applicator it should be suificient to almost completely cover the secondary coils 2 6 of the cathode l. The liquid may, however, be of lesser depth as the capillary attraction of the secondary coils causes said liquid to be drawn upand compietelyicover the cathode .I when such conditions prevail. The final upward motion of the applicator 28 after the secondary coils 26 of the'cathode l first engage the ridge 38 across the bottom thereof causes every secondary coil to be 5 forced thereagainst and, accordingly, to be sim ilarly bathed in the liquid even though certain of said secondary coils may be slightly out of proper alignment with the others.

The downward movement of the dipper 29 re- 1:) turning it to the cup 30 and separating the applicator 28 from the cathode I drains most of the liquid away from said cathode I, leaving thereon only that liquid completely filling the primary coils thereof and that liquid clinging to the sur- 5 face thereof. In this connection, it is desired that the liquid drain completely out of the core of the secondary coils 25 to avoid having the emission material bridging said coils 25 and that little free running liquid be allowed to remain on the suro face of the coils is. The draining function of the applicator 23 is also assisted by the ridge 38 along the bottom thereof. The V-shaped channels formed by the ridge also cooperate in causing circulation of the liquid throughout the trough is 37 and the separation of any solid particles within the liquid from the portion thereof contacted by the cathode i. The proper draining, etc., of the cathode i is also dependent upon the viscosity of the liquid which must be such as to cause so only a relatively thin, uniform, coating thereof to cover the surface of the cathode l, and a complete filling thereof to remain in the primary coils of said cathode l. None of the liquid should bridge the secondary coils 26 of the said cathode 35 l because such large accumulations are not as securely held by the cathode l and readily separate therefrom early in normal use, and particularly under conditions of vibration. Inasmuch as the liquid containing the emission material is 40 comprised of a very fluid vehicle which is driven off the cathode l in the course of the manufacture of the electrical device, the viscosity of said liquid is readily controllable without consideration as to its effect on the final composition of 15 the emission material. The particular applicator apparatus disclosed herein is separately claimed in my applicationserial No. 66,643, filed of even date herewith, new Patent No.2,545,909,.

The next step in the manufacture associated with Figs. 1 to 7, inclusive, occurs at work: station C and consists in a partial drying operation causing the emission material to contract slightly and change to a state Where it does not recirculate over the cathode I. Although the drying operation can occur during an interval in which the cathode l is only exposed to it is accelerated in the present instance by the circulation of a low pressure jet of warm air directed againstsaid cathode l by the nozzle 39. This operation prevents any recirculation of the emission material over the cathode i possible bridging of the secondary coils 25 thereof in the subsequently occurring operations or the apparatus when the cathode l is contracted.

The next step in the course or operation cccurs at work station D into which the mount 4 now indexed and consists in the reshaping of said mount 4 by the r unt closing devic 4-3 to cause he leading-in

wu es

2 and 3 and the cath ode i to take substantially the form they prior to the coating operation.- The index carries the ends of the leading-in

wires

2 and 3 clamped to the cathode l to positions opposite the bending fingers ll and d2 of the closing device til, which bending fingers ti and :42 are caused to close on the mount 4 from opposite sides as shown in Fig. 4 and rebend said ends of the leading-in

wires

2 and 3 so that they and the secondary coils 26 of the cathode I take substantially their former arrangement. The change in length of the cathode I results in a closing of the pitch of the secondary coils 26 thereof, and the relieving of most of the tension therein, and has no appreciable effect on the emission material thereon, although said emission material is partially dry and incapable of flexing greatly without separating from said cathode i.

The bending fingers 4| and 42 of the closing device MI, which are pivoted upon portions of corresponding vertical shafts 43 retained by the arm 44 extending from the support standard 45, are actuated in the course of movement to and from engagement with the mount 4 by movement of the fixed collars 46 clamped to the upper ends of the shafts 33. This manner of construction permits the extent of the movement of the bending fingers GI and 42, which are positioned by the cooperative function of springs ti and the screws 48 on the respective arms of the collars to be set independently as said screws 48 can be adjusted to change the relation of said bending fingers AI and 2 with respect to said collars 6.

The other members of the operating means for the mount closing device 46 consist of the intermeshing spur gears 49 on the lower ends of the shafts 43, the arm 59 attached to one of said shafts 43, and the link joining the arm Ell the operating lever 52. The hereinbefore described vertical movements of the rod ZI are also the initiating force for the closing device at in that one arm of the operating lever 52 constantly bears against the roller 53 on a stud extending from the clamp 22 on said rod 2I during the operating interval. The operating lever 5'2 is pivoted upon the pin 54 extending from the support bracket 55, which is also the means of holding the support standard at, and is biased toward the roller 53 by the helical spring 56. The movements of the operating rod 2I and the roller 53 are more than that required to close the bending fingers II and 42, which are interrupted in their motion at the time the collars 46 butt against the stop post 51 extending from arm 44, and separate the roller 53 from the operating lever 52 after motion of said operating lever 52 stops. This operation completes one preferred manner of applying the electron emission material to the cathode I.

In certain other instances it may be desirable to apply the electron emission material to a cathode in a manner according to my invention prior to the assembly of said cathode with other parts of the discharge device. One such manner of operation is shown in part in Fig. 8 where the cathode i, which has the same form as that previously described, is comprised of a continuous coiling of wire referred to as the primary coils, and a second coiling of the primary coils at the middle of the cathode I referred to as the secondary coils 25. In the present instance, the operator places one end of the cathode I between the fixed jaws 66 and Si and then, after the

jaws

62 and 63 are moved along the bed 66 to operative relation to the opposite end of said cathode i,

places said end between said

jaws

62 and 63.

Both pairs of jaws 60, El and 62, 63 are similarly constructed, the

jaws

66 and 62 of the pairs being pivoted upon the pins 65 and influenced toward the opposite jaws GI and 63, respectively, 'so as to grip the end or the cathode I by the expansion force of the springs 66 located therebetween. The cathode I is retained without tension therein at this position of the jaws 60, 6| and 62, 63.

The next step in the manufacture consists in expanding the cathode I lengthwise by manually moving the

jaws

62 and 63 along the bed 64 in a direction away from jaws 60 and 6| until stop 64 on said bed 6 3 is engaged. By prior adjustment of the position of the stop 64', it has been determined that this movement of the

jaws

62 and 63 spreads the larger secondary coils 26 an amount such as to permit the proper application of a liquid containing an emission material, but does not bend the cathode I beyond its elastic limit whereby it will not spring back to its former shape on being released. A 50 per cent expansion of the secondary coils 26 of the cathode I is normally possible in this step in my method, which expansion is sufficient to separate said secondary coils 25 very widely.

The next step associated with Fig. 8 occurs as the liquid containing the electron emission material is applied to the cathode I, an operation which, in the present instance, is preferably performed manually by manipulation of suitable brush, spoon, dip rod, or other applicator not shown. Because of the large spacing of the secondary coils 26 of the cathode I, the distribution of the liquid to the various parts of said cathode I automatically restricts itself to the core of the primary coils thereof and to a uniform covering of the surface thereof and does not bridge the larger secondary coils 26. The viscosity of the liquid is in part responsible for the ease with which the liquid is applied to the cathode I in this manner and is controlled by varying the vehicle content thereof to produce the desired coating conditions. After application of the liquid, an interval of time is allowed to lapse to permit the vehicle to evaporate therefrom and the emission material to become relatively dry, whereupon the cathode I is allowed to contract and is removed from the apparatus. It is preferred that the

jaws

62 and 63 be moved toward jaws 60 and 6| before the cathode i is released to cause the contraction thereof to occur without a snap which could possibly dislodge the emission material. Cathodes I manufactured. according to the above method retain the electron emission material very tenaciously and can be handled in bulk form and mounted in the usual commercial manner without injury.

The modified apparatus appearing in Fig. 9 is an automatic apparatus for effecting the application of electron emission material accord ing to the broad aspect of my invention to a cathode I of a mount 4 having sufficient resiliency to permit said cathode I to be stretched linearly during the application of the emission material. Such a mount is usually one having leading-in wires 2' and 3, as shown, of a size and extent beyond the vitreous stem 61 such that they can be sprungfrom their normal position to efiect the stretch in the cathode I' without being bent beyond their elastic limit so that they will spring back to their original position upon being released. As in the prior instance, the apparatus is preferably located at a work station taken by the mount 4' in the course of its manufacture and is associated with means for supporting the mount 4 at said work station and means for effecting operation of said apparatus at proper intervals. The particular apparatus disclosed is the subject of the aforesaid co-pending application of L. E. Dilts, Serial No. 66,798, now Patent No. 2,611,335.

The course of operation of the modified apparatus in Fig. 9 is initiated immediately upon arrangement of the mount 4' opposite the fingers 68 and 69 when said

fingers

68 and 63, Whichare mounted upon the block 1e, are turned down into the horizontal position shown from an oblique position out of the field ofmovement of the mount 4. This operation is the result of a partial rotation in the block it, which is attached to a shaft l'l carried by the stationary support bracket 12, and occurs when the down ward pressure of the cam 73 against the opposite ends of the fingers t3 and 69 from the mount 4 is relieved by the upward movement of said cam 13 and a consequent turning movement in the shaft H. The initiating force for the rota tion of the block "Hi is created by the contraction force of the spring it engaging the arm 15 on the opposite end of shaft H and a post extending' from support bracket 72. This rotative movement of the fingers 68 and 59 only arranges them at operative relation to the leading-in wires 2 and 3' inasmuch as the ends of said fingers adjacent thereto are relatively close together at such times and pass between the wires during said movement. The lateral separating movemerit of the fingers 68 and 69 eiiecting the oper ative function thereof occurs when the rotation of the block it is interrupted by the engagement of the arm 75 with the stationary stop screw 75 on the support bracket 72 and the wider portion of the'cam 73 is moved out from between said fingers 68 and 69 by the continuing upward motion of said cam 13. The lateral motion in the fingers 68 and ES turns them about the screws 77 by which they are held on the block 10 and progresses at a rate determined by the change in shape of the portion of the cam 73 located between the ends of said fingers 68 and 69 which are constantly being drawn thereagainst by the contraction force of the helical spring 78 joining posts therein. The extent to which the fingers 68 and 69 are separated is such as to bring them against the leading-in wires 2' and 3' and to spread said leading-in wires 2' and 3 sufiiciently to efiect the desired stretch in the cathode attached thereto and is complete when the lower end portion 79 of the'cam 13 is located therebetween.

The spreading function of the presently considered apparatus is for the purpose of spacing the larger coils 26 of the cathode I so that said coils 26' are not bridged by the liquid contain-'- ing the emission material, and to this end it is preferred that the spread given the leading-in wires 2' and 3' be as much as practical under the conditions of operation. In the present instance the spreading function is limited both by the ability of the secondary coils 26' of the catho'de I to return to form after the application of the emission material and by the ability of the leading-in wires 2' and 3, which are flexed only beyond the rigid vitreous stem 67, to spring back to position. These properties in the cathode 'l" and the leading-in wires 2' and 3' depend upon the particular construction thereof which can vary greatly: the cathode I for instance can be made of various diameters of wire, one, two or more Wires and one, two or various complex ceilings thereof; and the leading-in wires 2' and 3', for instance, can be of various sizes and lengths and be restrained by various mount elements. The spreading function of the apparatus is applicable in every instance where the cathode has one or more sections of relatively large and, therefore, flexible coils, etc., since said sections are readily stretched, and is of particular advantage to cathodes of this character in that the emission material would otherwise bridge these sections which are least adapted to retain the emission material; I

The vertical movements of the earn it effecting the positioning and spreading movements of the ringers as and 55 originate in the arm 20 located thereabove, to which said cam 13 is attached by the rod iii, and correspond to operative movements of the emission material applying means 2? associated therewith which is simie larly attached to the arm 80.

The next occurring operations of those effecting the cathode l are those having to do with the application of the emission material to said cathode l' and relate to the applying means 27, which is a substantial duplicate of that previously described and which accordingly bears primed reference numerals corresponding to said means 27. The interconnection of the operating elements of the spreading and emission mate: rial applying means by the arm 80 on the upper end of the operating rod 25' causes the applica tor 28 bridging the dipper 29 of the latter to be moved upabout the cathode I at the moment a further extent of the lower end of the cam 13, which is of uniformly narrow width, passes between the fingers BB and t9, and causes said cathode i to be immersed in the liquid carried in the trough 31 of said applicator 28' when it is fully stretched. As previously described, the liquid contained in the applicator 28 enters the interstices of the center portion of the cathode I, located within the applicator 23 and the oppositely extending portions, to approximately the clamped portions held by the leading-in wires 2' and .3.

The following downward movement of the arm 80 and operating rod 25 separates the applicator 28' from the cathode i and in so doing withdraws the excess emission material which is present in a coating over the surface thereof, and in a filling in the closely held turns of the primary coils and other portions thereof. The

, applicator 28' and the dipper 29' move downward into the main supply of the emission material within the cup 30, thereby flooding them with a fresh supply thereof in preparation to a succeeding cycle of operation. During the downward movement of the arm 80, the wider portion of the cam '53 is again forced between the end of the fingers 68 and 69, causing the opposite ends thereof to be brought closer together and allowing the leading-in

wires

2 and 3 to spring back to their former relation. The still further movement of the cam 13 carries the flanged top end 82 thereof against the upper surface of the fingers 63 and B9 and thereby forces said fingers 63 and Stand the supporting block 10 therefor to a tilted position. This movement of the fingers $8 and 169 withdraws the ends thereof from between the leading-in wires 2' and 3', permitting the mount 4' to be readily indexed out of operative relation of my apparatus by movement of its supporting means, or taken from said supporting means, whichever is required, without in- Jury.

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

l. The method of applying electron emission se n material to a closely wound coiled-coil filamentary cathode which comprises stretching the filament linearly by pulling apart its ends to widely separate the secondary turns thereof, immersing the filament in a liquid suspension of the emission material which substantially fills the turns of the filament, removing the supply of emission material while the filament is still stretched to such an extent that the material drains out from between the secondary turns, and then causing the filament to contract to approximately its original length, before the suspension of emission material has completely dried and hardened.

2. The method of applying electron emission material to a closely WOlll'lCl coiled-coil filamentary cathode which comprises stretching the filament linearly by pulling apart its ends to widely separate the secondary turns thereof and subsequently causing the filament to contract to approximately its original length, and prior to contraction of the filament momentarily flooding the filament with a liquid suspension of the emission material which substantially fills the turns of the filament and removing the supply of emission material while the 'nlament is still stretched to such an extent that the material drains out from between the secondary turns thereof, the contraction of the filament being effected before the suspension of emission material has completely dried and hardened.

3. The method of applying electron emission material to a closely wound coiled-coil filamentary cathode which comprises stretching the filament linearly by pulling apart its ends to widely separate the secondary turns thereof, coating the filament with a liquid suspension of the emission material which substantially fills the turns of the filament, removing the supply of emission material while the filament is still stretched to such an extent that the material drains out from between the secondary turns, partially drying the coating, and then causing the filament to contract to approximately its original length, before the suspension of emission material has completely dried and hardened.

4. The method of applying electron emission material to a closely wound coiled-coil filamentary cathode secured at opposite ends to the leading-in wires of a mount which comprises contacting the leading-in wires to spread them apart and stretch the filament linearly so as to widely separate the secondary turns thereof, applying to the filament a liquid suspension of the emission material which substantially fills the turns of the filament, removing the supply of emission material while the filament is still stretched to such an extent that the material drains out from between the secondary turns thereof, and then effecting a return of the leading-in wires to approximately their original position to contract the filament, before the suspension of emission material has completely dried and hardened.

5. The method of applying electron emission material to a closely wound coiled-cil filamentary cathode secured at opposite ends to the relatively rigid leading-in wires of a mount which comprises contacting and bending the leading-in wires to a spread position to stretch the filament linearly so as to widely separate the secondary turns thereof, applying to the filament a liquid suspension of the emission material which substantially fills the turns of the filament, removing the supply of emission material while the filament is still stretched to such an extent that the material drains out from between the secondary turns thereof, and then rebending the leading-in wires to allow the filament to contract, before the suspension of emission material has completely dried and hardened.

6. The method of applying electron emission material to a closely wound coiled-coil filamentary cathode secured at opposite ends to the leadingin wires of a mount which comprises contacting the leading-in wires to spread them apart and stretch the filament linearly so as to widely separate the secondary turns thereof, coating the filament with a liquid suspension of the emission material which substantially fills the turns of the filament, removing the supply of emission material while the filament is still stretched to such an extent that the material drains out from between the secondary turns thereof, directing a stream of air against the filament to partially dry the coating, and then effecting a return of the leading-in wires to approximately their original separation to contract the filament, before the suspension of emission material has completel dried and hardened.

7. Apparatus for applying electron emission material to a closely wound coiled-coil filament comprising means for stretching the filament linearly by pulling apart its ends to widely separate the secondary turns thereof and for thereafter effecting a contraction of the filament to approximately its original length, coating means in cooperative association with the first-mentioned means for immersing the filament in a supply of liquid suspension of the emission ma terial which substantially fills the turns of the filament, and means for effecting operation of said stretching and contracting means and said coating means in proper time relation to cause said coating means to coat the filament during an interval prior to the contracting operation of the first-mentioned means, the last-named means including means to remove the supply of coating material from the filament while the latter is stretched to such an extent that the secondary turns thereof are not bridged by the material.

8. Apparatus for applying electron emission material to a coiled-coil filament clamped at opposite ends to the leading-in wires of a mount comprising means for supporting the said mount, means for holding a supply of liquid suspension of the emission material, means for effecting a relative movement of the first-mentioned and secondmentioned means toward and away from each other to momentaril immerse portions of the filament in the liquid, means for engaging and spreading apart the leading-in wires prior to removal of the filament from the liquid to stretch the filament linearly and widely separate the secondary turns thereof, means for eifecting contraction of the leading-in wires and the filament only after removal of the filament from the supply of liquid, and means to eifect operation of the several aforesaid means in proper time relation.

9. Apparatus for applying electron emission material to a coiled-coil filament clamped at opposite ends to the relatively rigid leading-in wires of a mount comprising means for supporting said mount, means for engaging and bending apart the leading-in wires to stretch the filament linearly and widely separate the secondary turns thereof, means for holding a liquid suspension of the emission material, means for effecting a relative movement of the mount support and the liquid holding means toward and away from each other to momentarily immerse portions of the filament in the liquid, means for thereafter engaging and bending the leading-in wires back to approximately their original spacing, and means to eifect operation of the several aforesaid means in proper time relation.

10. Apparatus for applying electron emission material to a coiled-coil filament clamped at opposite ends to the relatively rigid leading-in wires of a mount, comprising means for supporting said mount and carrying it to a succession of work ing fingers for advancement toward and between the leading-in wires of a mount at said work station to engage and bend apart the leading-in wires thereof so as to stretch the filament linearly and widely separate the turns thereof, an applicator receptacle holding a liquid suspension of the emission material and mounted below the path of movement of the mount holder at another of the work stations, means mounting the applicator for movement upward to effect the immersion of portions of the filament in the liquid, bending means at a succeeding work station, means mounting said bending means for engaging and bending the leading-in wires back to approximately their original spacing, and means for actuating said spreading fingers, applicator receptacle and bending means in proper time relation.

11. Apparatus for applying electron emission material to a coiled-coil filament, clamped at opposite ends to the relatively rigid leading-in wires of a moun comprising means for supporting said mount and carrying it to a succession of work stations, a pair of spreading fingers having oppositely sloping outer faces and located at one of the work stations, means mounting the spreading fingers for movement toward and between the leading-in wires of a mount at said work station to engage and bend apart the leading-in wires thereof so as to stretch the filament linearly and widely separate the turns thereof, an applicator receptacle holding a liquid suspension of the emission material and mounted below the path of movement of the mount holder at another of the work stations, means mounting the applicator for movement upward to efiect the immersion of portions of the filament in the liquid, a pair of bending fingers located at a sucoeeding work station, means mounting said fingers for movement toward each other to close on the leading-in wires from opposite sides to bend them back to approximately their original spacing, and means for actuating said spreading fingers, applicator receptacle and bending fingers in proper time relation.

12. Apparatus for applying electron emission material to a coiled-coil filament clamped at opposite ends to the relatively rigid leading-in wires of a mount, comprising means for supporting said mount in an inverted position and carrying it to a succession of work stations, a pair of spreading fingers located at one of the work stations below the path of movement of said mount supporting means, means mounting the spreading fingers for movement upwardly and between the laterally extending ends of the leading-in wires of a mount at said work station to engage and bend apart the said leading-in wires so as to stretch the filament linearly and widely separate the turns thereof, an applicator receptacle holding a liquid suspension of emission material and mounted below the path of movement of said mount supporting means at another work station, means mounting said applicator for movement vertically to and from operative relation to the mount holder at the last-mentioned work station to effect the immersion of portions of the filament in the liquid, a pair of bending fingers located at a succeeding work station to be opposite the filament of the mount at said station,

proximately their original spacing, and means for actuating said spreading fingers, applicator receptacle and bending fingers in proper time Morse Nov. 18, 1947