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Oct. 29, 1946. L. <;. GOODALE 2,410,060 L ‘METHOD OF PRODUCING VACUUM TUBE ELECTRODES Filed March” 11, 1942 g h‘“ .> BY Zrxwv INVENTOR . . 000,445 ATTORNEY Patented Oct. 29, 1946 ' 2,410,000 UNITED STATES PATENTOFFICE 2,410,060 METHOD OF PRODUCING VACUUM TUBE" ELECTRODES ‘ > 0 Lynn C. Goodale, Newark, N. J., assignor to Federal Telephone and Radio Corporation, a, corporation of Delaware Application March 11, 1942, Serial No.- 434,269 9 Claims. (Cl. 148-115) 1 This invention'relates to vacuum tube ?la ments and more particularly to the method of making spiral vacuum tube ?laments and the ?laments so made. In vacuum tube ?laments, particularly ?la entary cathodes for tubes designed to operate at high frequencies, the spacing requirements of . 2 Turning ?rst to Fig. 1, l0 and II represent two‘ spiral‘?lament wires connected together in series at one end to provide a known form of bi-?lar ?lament winding. These wires are gen erally supported by a supporting member 12 ex tending inside of the spiral and fastened atone end to the connected ends ‘of the ?lament. In the ?lament may be very critical. For example, many power tubes the ?lament Wires are made of in a certain type of tube the spacing between tungsten and often they are thoriated for the, the ?lament and grid is in the order of 0.040 inch. 10 purpose of‘increasing their electron emission.‘ In'such‘ tubes the ?lament is generally of rela > The wires may be in ductile form as originally tively ?ne wire and may warp or sag during car wound, and'iit is then desirable to have them‘ burizing or setting thereof. Such warping or set before incorporating them in the Vacuum sagging may upset‘ the’ entire characteristics of tube to preventdistortion or warping of the wires the tube. ’ 1 15 due to strains that may exist therein. This so ;:‘It is Fan‘object of my invention to overcome - called 'setting of the wires-is accomplished by the‘ above dii?culties by use of a new method of heating the wires to a temperature near the producing spiral ?laments. ‘ ' ‘ melting point-of the wires or at least to incan Furthermorapractice of mynew methodmay de'scense. After such a heat treatment, tung-v produce a ?lament which is ca'rburized only on, 20 sten wires in particular, are found to be more the outside and a further object of my invention rigid than previously although they are also is the production, of spiral ?lamentscarburized morev brittle. Furthermore, in the case of thori only on‘ the outer surface of the spiral. , ated tungsten ?laments it is often desired to treat _ According to a feature of my invention, spiral these ?laments to produce carburization.‘ This ?laments, single or multispiral, areformed and 25 treatment also calls for heating at a relatively are then screwed into a sleeve made of :carbon high temperature after the wire has been cov or of other material if setting alone is desired, ered with a, carbon composition. During such threaded to’ receive the ?lament: The whole; heat treatment the ?lament may sag or deform, assembly is then heated .to a high, temperature. thus producing errors in the spacing of the ?la This heating serves to set the ?lament/land if 30 ment ‘with respect to other electrodes in the vac a carbon sleeve is used alsov carburizes for, par uum tubes. Since, in many tubes these spacings tially ‘carburizes the ?lament. Preferably, for between electrodes are relatively small and very carburizing, the spiral ?lament is lubricated with critical, this variation in spacing tends to pro colloidal graphite while screwing into the sleeve.. duce errors in the characteristics of the tubes. ‘, Since the spiral ?lament is held ?rmly in 35 ‘ ‘In accordance with my invention in order to place by the grooved sleeve, the ?lament has no prevent these faults in ?laments, the spiral ?la opportunity to sag‘ or warp, during theiheatingl ment consisting of coils l0 and l I, is screwed into thermore, since only the outer surface of the; a previously prepared block or sleeve I 3, which ?lament spiral is inrcontactiwith the, block or is provided with an internal threaded groove I 4 sleeve, this outer surfaceis carburized to a greater 40 of the proper,‘ dimension and pitch to receive the extent than the inner surface when a carbon spiral and hold it in place during heating. The block is used. ‘ ‘ entire unit is then inserted into a heater I5, which may be for example, a coil supplied with heating energy ‘over leads I6, l1. During the the particular description thereof made with ref 45 heating process the spiral grooves I4 hold the erence to the accompanying drawing, in ‘which wires ?rmly‘in place so that after the wire has ‘ Fig.’ 1 illustrates an‘arrangement for practic been set it, will be shaped properly and not de _ A better understanding, of my inventionhand thev objects andrfeatures thereofmay be had from ingv the process andproducing ?laments inac-I cordance‘with‘ my invention; , ‘ H formed. Fig. 2 is an illustration of a single spiral ?la ment; Figs, 3 and 4 are elevations and end views re spectively of quadra-?lar ?lament, and outer surface. ' , ' desired the wire ?laments, are preferably lubri ‘ ‘ ‘ ‘Fig. 5 is a cross-sectional View of a ?lament wire indicating the earburization‘ effect ‘on’ the‘. ‘ ‘If sleeve [3 is made of carbon then the ?la ment Ill, II is carburized at the same time that the setting takes place. When carburization is V cated-with a colloidal graphite suspension at the time ‘they are’ threaded into the blocks I 4. 55 It is further to be noted that a ?lament treated ‘ in accordance with my invention will generally 2,410,060 3 4 emission which in some cases is equivalent to be carburized primarily on the outer surface of almost twice that of the emission from a ?lament formed and carburized in the ordinary way. It should, of course, be understood that the the cylindrical spiral. In Fig. 5 is shown a cross seetional view of a ?lament wire greatly en larged to illustrate this feature. In this ?gure it is shown that the ?lament wire 50 will be above description merely described a preferred manner inmaking and using my invention. Also, carburized on a section 5| corresponding to the. outer edge of the spiral coil. Of course, a cer tain degree of carburization may take place on it should be understood‘ that in most cases the ?lament wires will not be made of as heavy ma quantity of carbon and for this reason the car-y ing the ?lament on a central mandrel of carbon or some other material such as ceramics which terial as shown in the drawing and will generallyv the inner surface of the coil as‘ well, due to the graphite lubrication. However, the greatest in, be of a, smaller size. The carburization may be achieved by support heat is on the outside as well as the greatest , burization will be largely on the‘. outer- surface will‘ withstand the necessary heat. The unit may then be painted with colloidal graphite or im bedded, in granulated carbon and heated to car carburizing the ?lament may be reused for treat burizing temperature. Threads or other depres ment of a plurality of individual ?laments and sions in the mandrel may be provided and the need not be replaced newior each ?lament to be ?lament thus held in position during the simul treated. It should be noted. that in many cases the wire 20 taneous heating and carburization. It should, also, be distinctly understood that ?laments might tend to. expand upon attempt to my invention includes not only treatment of: screw them into thesleeve in the. manner of cer-v spiral ?laments in this manner, butthe simulta tainforms-of spring clutches. In order to avoid neous carburization and setting of ?laments by this di?icultyshould the wires be sufficiently flex ible to tend to expand in this manner, it is advis-. 25 insertion in any properly formed‘. carbon block and subsequent heat treatment or by other treat-. able that the threading action be. taken at the ments as explained above regardless of the ?la-v leading. edge of the spiral so that instead of pro ment form. ducing a tendency to expand the tendency will . While the speci?c description ‘has beendirected be to. contract the ?lament as it is screwedinto place. In many cases the supporting rods [2 will 30 to ?lamentary cathodes, it, should be understoodv that the invention applies to. any form of ?la have su?icient rigidity to serve this purpose. mentary electrodes, for example to ?lamentary However, in. event the supporting rods are not of the spiral ?lament. ' ' It is clear that the blocks or sleeves used for su?iciently rigid, for this purpose, a special tool grid electrodes. the sleeve. art. Many other modi?cations and examples’ ofi my. may be provided. which will befastened to the invention will be apparent to thoseskilled in .the 35 ?lament at the leading’ edge for inserting it into 7 What is claimed is: , Fig. Zillustrates asingle spiral ?lament. It is 1. The method of producing. spiral ?lamentary clear that thefeatures of my invention. may- be. electrodes comprising. forming a spiral of ?la-. applied not only tobi-?lar ?laments of thedoublev spiral,‘ as shown in Fig. 1, but to any spiral ?la 40 ment wire, screwing said spiral into a car» bonaceoussleeve provided with a spiral groove ments regardless otthe. number of spirals there to receive said?lament spiral, and heating the in. In. this ?gurethesingle spiral is shown at assembled?lament and sleeve to a temperature 29,“. provided with. a. supporting rod and return 1 su?iciently high toset said spiral and thusre lead .21. for the ?lament. move internal stresses which might cause defor mationof said ?lament, and to cause carburiza In Figs. 3 and 4 is shown what: is called’ a quadrae?lar. ?lament. In this arrangement there. tion of at least that portion of the ?lament which is incontact with the sleeve. . 34; Spirals 3.1, 3-2, together with a supportingrod 2. The method of simultaneously carburizing 35: form onebi-?lar ?lament winding similar to that shownin Fig. 1. Filaments. 33 and .34, to 50 and setting a vacuum tube ?lamentary electrode Whichcomprises forming the desired‘ shape of? gether with supporting rods 36., form. a second‘ ?lament from ductile ?lament wire, placing the bi-?lar ?lament similar. to that shown in.Fig. 1. shaped ?lament wire in a carbon retaining means The two ?lament elements are. then threaded to a previously formed to retain said ?lament in said gether to form the completebi+?lar unit as shown desired shape, and heating said assembled ?la in Figs. 3 andll. Inpractice, the four. separate ment and retaining means to carburizing tem-‘ ?lament leads of-3I, 32, 33 and 34; and the sepa perature._ rate supporting rod leads areoften brought out is provided four separate spirals 3i, 32‘, 33, and ' 3. The method of'producing carburized' spiral of the tube socket to form ?xed terminals. Usu ally then, the two double spirals whicharepro vided are'then connected in series, for example, by connecting together wires 32 and-33 inthev socket, and .thefenergy issuppliedacross leads 3| and 34. The quadra-?lar ?lament then forms a four-threaded spiralwhich may be screwed'into a sleeve or block. in a-manner-isimilar vto that de scribed previously, and the entire‘ units may be treated in the same manner. I; have found- that spiral-?laments, treated in the manner describedyherein, particularly thori ateditungsten ?laments when treated with-a car bon sleevejso as to produce carburized thoriated tungsten ?laments not only are improved in op ?laments comprising forming a spiral of the desired shape of thoriated ?lament wire, screwing said spiral 'into a previously prepared carbon’ sleeve provided with a-spiral groove to?t said ?lament spiral, and heating the assembled-?lm» merit‘ and sleeve to produce at least a‘partial carburization of said ?lament wire. 4: The method according toclaim 3 further comprising the step of lubricating saidspiral with colloidal graphite as it is‘screwed into said sleeve. 5; The method according to claim 3, wherein 70 said spiral is held at the leading end thereof dur eration, due‘to the-lack of distortion that usually ing the process of screwing said spiral'into, said sleeve. ' ’ 6. Themethod according to claim 3,,wherein accompanies the normal heating" and‘setting of_ said spiral is formed in the shape of a bi-?lar ?la the ?laments, but they produce ment winding. improved‘ 75 ' > 2,410,060 5 7. The method according to claim 3, wherein said spiral is formed in the shape of a quadra ?lar ?lament winding. 8. The method of carburizing ?lamentary vac uum tube electrodes, which comprises forming the ?lamentary electrode in the shape of a spiral, supporting the electrode by engagement of the outer surface of said electrode with interior por tions of a hollow member formed of carbon and subjecting the whole assembly to a, carburizing 10 heat, whereby the outer surface of said electrode is carburized. ‘ 9. In the manufacture of a. vacuum tube elec trode, a, method for producing limited super?cial carburization of a preselected discrete surface area of said electrode that comprises substan tially rigidly supporting the electrode by engage ment with interior parts of a tubular member formed of a carbonaceous substance in a manner such that the surface area to be carburized is in contact with the carbonaceous substance, and heating the electrode while so supported at a temperature suf?cient to effect carburization of said area. . LYNN C. GOODALE.