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Патент USA US2410066

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Oct. 29, 1946.
Filed March” 11, 1942
g h‘“
Patented Oct. 29, 1946
' 2,410,000
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)
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
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
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;
Fig. 2 is an illustration of a single spiral ?la
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
cated-with a colloidal graphite suspension at the
time ‘they are’ threaded into the blocks I 4.
It is further to be noted that a ?lament treated
‘ in accordance with my invention will generally
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
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.
Many other modi?cations and examples’ ofi my.
may be provided. which will befastened to the
will be apparent to thoseskilled in .the
?lament at the leading’ edge for inserting it into
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
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
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
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.
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