Note: Descriptions are shown in the official language in which they were submitted.
METHOD OF PROVIDING INSULATION SUPPORT
FOR ELECTRICAL CONDUCTORS, ESPECIALLY
IN ELECTRIC COILS
This invention relates generally to the art of
providing insulation support for electrical conductors
and, more particularly, to a method of making electric
coils.
In many conventional coils, such as transformer
coils, the various conductor or winding layers are sup-
ported an~ insulated from each other by means of cellu-
losic insula~ion, such as oil-paper or car~board, for
example. Other conventional coil structures employ non-
cellulosic insulating material, such as cast-resin, to
provide conductor support and insulation, and these
cellulose-free coils have certain advantages over the
others insofar as they are more resistant to short cir-
cuits, moisture degradation, mechanical vibration, and
fire, and less susceptible of out~gassing and thermal
aging. Unfortunately, cellulose-free coils of conven
tional design also have certain drawbacks, chief among
them relatively high cost in terms of both manufacture and
loadability, and a diffieulty of ridding them of shrinkage
voids.
It is the principal object of the invention to
provide a method which will alleviate these problems
heretofore encountered with cellulose-free structures, and
the invention, from a broad aspect thereof, accordingly
resides in a method of providing insulating support for an
electrical conduc-tor, characterlzed by the steps o~ apply-
ing a liquid coating of an electrical insulati~g material
upon a substrate, gelling the liquid coating to a firmness
sufficient to support an electrical conductor, and apply-
ing a conductor upon the gelled insulation.
The above-stated sequence of steps can be re-
peated as often as required to provide a desired number o
conductor layers, in which event a mandrel, an insulated
supporting member or a first conductor layer applied upon
the insulated supporting member will form the substrate
for the first liquid coating of insulating material to be
applied and gelled, and each subseguent conductor layer
supported by such gelled insulation coating will form the
substrate for the next liquid coating of insulation to be
applied and gelled.
The term "gelling", as used herein in context
with the invention, is intended to mean partially polymer-
lzing to an extent rendering the li~uid insulation su~fi-
ciently consistent to provide mechanical support for the
conductor applied thereupon, but leaving it plastic enough
for the conductor to somewhat nest in it and thereby to be
held against sliding. Moreover, as li~uid insulation
coating is applied upon conductor layer and conductor
layer is applied upon gelled insula~ion coating, the
conductor layers as well as all conductor portions in each
layer become completely insulation-bound and any polymeri-
zation shrinkage is accommodated as the insulated struc-
ture is being formed, all of which contributes to produc-
ing a coil the insulation of which is a homogeneous and
3Q essentially void-free mass in intimate physical contact
with essentially all surfaces of the winding or windings
embedded therein.
The liquid insulatinq material preferably is
gelled through irradiation from a suitable source, such as
an infrared or ultraviolet radiation unit or an elec-tron
beam unit. At present, ultraviolet radiation is believed
to be the most practical and, accordinyly, is preferred.
The insulating material may be any suitable
cross-linkable liquid resin, such as acrylic epoxy, and
preferably is a substantially unfilled resin capable of
being instantly gelled through irradiation.
Depending upon such factors as the viscosity of
the liquid insulation before gelling, the desired thick-
ness of each finished coating, and the like, the insula-
tion coating upon each substrate (i.e. mandrel, insulating
support member or previously applied conductor layer) may
be applied as a single-layer coating or it may be formed
by applying several thin layers of liquid insulation one
upon the other and gelling each such layer before the next
one is applied. The viscosity of the liquid insulation
should be as low as possible in order to minimize the
chance for pockets or voids to develop as the coating is
being formed, but it also should be sufficient to mi~imize
undesirable flow of the applied liquid insulation before
gelllng.
In addition to ofering the advantages mentioned
hereinbefore, as well as others still to become apparent
as the description proceeds, the method according to the
invention lends itself admirably well to being applied to
the art of coil forming since it permits layer insulation
to be formed in situ while the coil structure being built
is on a mandrel or coil forme-r and the latter is rotating
at commercial winding speeds.
When so employed, the method preerably com~
prises the step of forming an i~sulating coating upon the
rotating mandrel or coil former by applying thereon liquid
insulation in one or several layers and ins~antly gelling
each layer thus applied, and it includes further the steps
of winding upon the above-mentioned insulating coating an
electric conductor layer, forming upon the latter another
gelled insulation coating in the manner set forth above,
winding thereon another conductor layer, and so forth
until the coil forming operation is completed. A~ter
completion of the coil forming operation, the finished
product is subjected to a suitable curing process causing
the gelled i~sulation to set. If desired, provision for
cooling ducts can be made during the coil forming opera-
tion by introducing, in the liquid insulation, s~.rips of a
material which can be subseq~lently removed from the fin-
ished coil, such as polyethylene, for example, which can
be melted out with heat suitably applied.
It will be appreciated that a coil formed in
accordance with the invention will have a much better
conductor space factor than a conventional paper wound
coil, for example. Moreover, the novel coil winding
method makes possible a reduction of the conductor mean
turn and of the overall coil dimensions (determining the
size of the core needed for the coil), it do~s away with
costly coil bonding and drying operations, and it obviates
oil impregnation problems since, contrary to conventional
insulation systems employing cellulosic material, such as
paper, a coil formed in accordance with the invention
needs no oil for insulation purposas, all of which tends
to lower cost significantly with respect to coil struc-
tures of the prior art.
Still another significant advantage derived from
the invention in connection with coil winding has to do
with insulation grading. It is known that when an elec
trical winding is formed from wire wound helically about
the coil axis alternately back and forth between the
opposite coil ends so as to form consecutive layers of
conductor turns, the dlelectric ~tress from layer to layer
is relatively low at the mutually connected ends of any
two adjacent turns layers and gradually increases toward
the mutually non-connected ends of such turns layers.
With conventional coil structures having winding or turns
layers spaced apart uniformly for the whole length, i.e.
axial dimension, of the coil, the overall coil siæe is
determined by the thickness which the insulation between
turns layers must have in order to withstand the highest
dielectric stress therebetween, that is, it is determined
by the thickness of insulation needed at the non-connected
ends of the turns layers.
The method according to the invention allows the
total volume of the insula~ion and, hence, the total coil
size to be considerably reduced in a facile manner by
grading the insulation during coil winding, that is, by
varying the thickness of insulation between adjacent
winding layers in accordance with the changing dielectric
stress therebetween.
In a preferred embodiment of the invention, such
graded insulating coating is formed upon a conductor turns
layer, or winding portion, of the coil structure by apply-
ing and instantly gelling, as the coil structure is being
rotated, layer upon layer of liquid insulation in a manner
such that the width of the various layers, as measured
across the underlying winding portion from the end thereof
which will be the high-stress end with respect to the
conductor-turns layer or winding portion to be formed
next, changes incrementally from insulation layer to
successive insulation layer so that the resulting insulat-
ing coating will have a wedge-like or tapered cross-
section, that is, will be graded, its thickness being
maximal at the high-stress end and decreasing gradually
toward the low-stress end of the underlying winding por-
tion thus coated.
The incremental change in the width of succes-
sively applied insulation layers is achieved through axial
relative displacement effected between the insulation
applicator and the coil structure as the latter is being
rotated.
In another embodiment of the invention, a graded
insulating coating is formed on a conductor-~urns layer of
the coil structure by applying, and gelling, a single
layer or coak of liquid insulation exkruded through a
nozæle shaped to impart to the extruded layer of insula-
tion either the desired wedge-shaped cross-section or a
rectangular cross-section which then is re-shaped, e.g. by
Z~59~
means of a wiper, such as a rubber blade or the like, ~o
assume the desired wedge-like cross-sectional configura-
tion.
Preferred embodiments of the invention will now
S be described, by way of example, with reference to the
accompanying drawings, in which:
Figure 1 is a cross-sectional partial view of an
electric coil made in accordance with the prior art;
Fig. 2 is an isometric view schematically illus-
trating a manner of making an electric coil in accordancewith a preferred embodiment of the invention;
Fig. 3 is a sectional view taken along line
II-II of Fig. 4;
Fig. 4 is an isometric view of the nearly fin-
ished coil;
Fig. 5 is a cross-sectional partial view of an
electric coil having graded insulation formed in accord-
ance with the invention;
Eig. 6 is an isometric view schematically illus-
trating one manner of forming layer insulation in a coil
such as shown in Fig. 5;
Fig. 7 ls an enlarged, fragmentary sectional
view illustrating in greater detail how insulation grading
is achieved by the method of Fig. 6;
Fig. 8 is a cross sectional partial view similar
to Fig. 5 and showing an electric coil with graded insula-
tion formed in a manner as illustrated in Figs. 9 to 15 or
Figs~ 16 to 20;
Figs. 9, 10 and 11 are fragmentary end views
illustrating successive stages of applying insulation in
forming the coil of Fig. 8;
Figs. 12, 13 and 14 are cross-sectional views
taken along lines XII-XII, XIII-XIII and XIV-XIV of Eigs.
9, 10 and 11, respectively;
Fig. 15 is an isometric and partly sectional
view showing how a graded coating of liquid insulation is
applied upon a layer of conductor turns in making the coil
of Fig. 8;
Fig. 16 is a sectional view illustrating a
somewhat different manner of forming graded insulation;
~ig. 17 is a cross-sectional view taken along
line XVII-XVII of Fig. 16;
Fig. 18 is a sectional view showing a modifica-
tion of the method of Fiy. 16;
Fig. 19 is a cross-sec-tional view taken along
the line XIX-XIX of Fig. 18; and
Fig. 20 is a view similar ~o Fig. 19 but showing
the coil in a more advanced coil forming sta~e.
Referring now to Fig. 1 of the drawings, it
shows part of a conventional transformer coil, still on a
coil forming mandrel 4, in which layers 3a, 3b and 3c of
conductor turns, forming part of a winding of the coil,
are supported and insulated from each other by cellulosic
insulation in the form of paper wraps or cardboard tubes
2a, 2b and 2c. Typically, such coil is formed in succes-
sive steps by applying the first wrap or tube of cellu-
losic insulation 2a upon the mandrel 4, then winding
thereon the first layer 3a of turns from one end of the
coil to the other, as indicated by the lowermost arrow in
Fig. l, thereafter applying the second wrap or tube 2b of
insulation upon ~he turns layer 3a, then winding thereon
the second layer 3b of turns in the opposite direction,
and so forth until the coil is finished.
As distinct therefrom, Fig. ~ schematically
illustrates a method of making a cellulose-free coil, such
as shown in Eigs. 3 and 4, in accordance with the inven-
tion. In Eig. 2, reference numeral 4 again designates a
mandrel, numeral 5 refers to an applicator, such as a
paint roller, numeral 6 designates a winding station,
numeral 7 indicates a conductor, such as enamelled copper
wire, numeral 9 designates a gelling station, numeral 10
indicates the direction in which the mandrel 4 with the
coil structure thereon is rotated during a coil forming
operation, and numeral 17 indicates an insulating coating
applied by means of the applicator 5. As mentioned here-
inbefore, the gelling station 9 may comprise any suitable
radlation source, such as an infra-red or ul~raviolet or
electron beam unit, but preferably comprises an ultra-
violet radiation source.
Fig. 2 shows the coil forming operation at an
advanced stage. From Fig. 3 it is seen that the whole
coil forming operation of this embodiment comprises the
steps of providing an insulatiny substrate 13 upon the
mandrel 4; forming upon the substrate 13 a first, e.g.
low-voltage, winding by applying, as the mandrel is turn
ing, several layers 15 of insulated, e.g. enamelled,
conductor strip first upon the insulating substrate 13 and
then one upon the other; forming a gelled insulating
coating 17 upon the winding 15; helically winding, as
shown in Fig. 2, preferably insulated, e.g. enamelled,
conductor wire 7 upon the gelled coating 17 from one coil
end to the other so as to form a layer of conductor turns
19 as part of a second, e.g. high-voLtage, winding; forrn-
ing a gelled insulating coating 21 upon this turns layer
19; helically winding upon the coating 21 a layer of turns
23 rom the same wire as above but proceeding in the
opposite axial direction; and covering the turns layer 23
with an insulating coating 25, preferably likewise gelled.
The insulating coatings 17, 21 and 25 are shown in Fig. 3
25 as forming overlaps 17', 21' and 25', respectively, which
cover the edges of the respective underlying winding 15
and winding layers 19, 23 at both ends of the coil so as
to provide maximum protection xom arc-overs between the
edges of adjacent windings or winding portions.
The substrate 13 on the mandrel 4 may be a
tubular member preformed from a suitable resinous material
and slipped onto the mandrel or it may be an insulating
coating formed in the same manner as the coatings 17 and
21 and, preferably, also the coating 25, namely by apply-
ing the insulating material as a viscous liquid by means
of the applicator 5 (Fig. 2), and instantly gelling the
applied liquid insulation through irradiation received as
~2~ 7
it is being carried past the gelling station 9 by the
mandrel 4 rotating in the direction of the arrow 10.
The thickness of each insulation coating 13, 17,
21 or 25 may vary, depending upon such parameters as the
required insulating or dielectric strength of the coating,
its mechanical strength, and the like; and the various
coatings may be formed as single-layer coatings or as
multi-layer coatings, depending upon overall coating
thickness desired, the viscosity of the liquid insulation
to be applied, coil winding speed, and the like.
A multi-layer coating is formed, as the mandrel
4 is turning, by applying several relatively thin layers
of liquid insulation one upon the other by means of the
applicator 5, and instantly gelling them at the gelling
station 9, one such liquid layer of insulation being
applied and gelled during each revolution of the mandrel.
For instance, there may be 5 to 10 liquid layers, each
about 40 mils (l.0 mm) thick, wound upon each other and
resulting in a coating having a thickness of about from
0.2 to 0.4 inch ~5.0 to 10.0 mm), or there may be 30 to 50
liquid layers, each about 4 mils (0.1 mm) thick, wound
upon each other and resulting in a coating having a thick-
ness of from 0.1 to 0.2 inch (3.0 to 5.0 mm).
3uilding up such insulating coating from thin
layers of liquid insulation each wound upon the other and
instantly gelled offers a significant advantage insofar as
the liquid insulation thus applied in thin layers will
readily flow into and thus eliminate any spaces between
adjacent conductor portions, and any holes and voids, and
will completely cover and effectively isolate small co~
taminants such as might be present and as would reduce the
breakdown strength of the finished coating. 0 course,
even though the insulation is applied layer upon layer, it
will be understood that applying it as a liquid and just
gelling, instead of curing, the latter before the next
layer is applied will yield a coating that is not strati-
fied but is dense and homogeneous. Thus, the term "multi-
layer" used herein as part of the expression "multi~layer
coating" is to be construed as referring to the manner of
applying the coatiny and not to the structure of the
finished coating.
If desired, extra insulation can be provided
between the conductor-strip layers lS of the first winding
by applying to the pre-insulated conductor strip, as it is
being wound in place, a liquid layer of insulation by
means of the applicator 5 (Fig. 2), and instantly gelling
the liquid layer, thus applied, through irradiation re-
ceived at the gelling station 9.
It should be noted also that even though the
first winding is shown in the embodiment of Fig. 3 as
wound spirally, i.e., as layer-wound, from conductor
strip, it could be formed from a conductor wire wound
helically in a similar manner as shown in Fig. 2; and
that, furthermore, the second winding, although shown
herein as helically wound from wire, could be formed from
conductive strip material layer-wound in a similar manner
as the first winding 15 of the illustrated embodiment. Of
course, the particular number of conductor layers 15 and
turns layers 19, ~3 employed in this embodiment likewise
must not be considered as limiting, having regard to the
scope o the invention.
The insulation overlaps 17', 21' and 25' may be
formed independently of the respective coatings 17, 21, 25
by applying insulation to the opposite edges of the wind-
ing lS and each turns layer 19 or 23 as the winding or
turns layer is formed, and instantly gelling the applied
edge insulation in a similar manner as explained in con-
nection with the insulating coatings.
As an alternative which may be preferred, the
overlaps, such as 17', 21' and 25' can be formed concur-
rently with the respective insulating coatings 17, 21 and
25, simply by applying an excess of insulation beyond the
opposite edges of the associated winding or turns layer
and lapping it, the overlaps thus formed being gelled, of
course, together with the remaining part of the coatin~.
~Z~Z~
As seen from Fig . 3 and 4, provision ~or cool-
ing ducts can be readily made by winding into the outer
insulating coating 25 a strip or strips 35 of a suitable
material which can be removed when the coil structure is
complete. Thus, with the coatiny 25 formed to part of its
desired thickness, the strips 35 are put in place thereon
at the desired locations and then are covered with more
insulation as the mandrel 11 continues to rotate. When
the coil winding operation is finished and the coil struc
ture is complete, the strips 35 are removed to leave ducts
for cooling liquid, such as transformer-oil, to pass
therethrough. A suitable material of which the strips 35
may be made is polyethylene which can be melted out,
subsequently, e.g., by electrically energizing the fin-
ished coiL prior to immersing it in a coolant.
Referring now to Figs. 5, 6 and 7 of the draw-
ings which are partial views of an electric coil ormed
with graded insulation in accordance with the invention,
Fig. 5 shows the coil, mounted on a mandrel 4, as compris-
ing conductor turns layers 29a, 29b and 29c forming por
tions of an electric winding, an insulating substrate or
base coating 27a on the mandrel, graded insulating coat-
ings 27b and 27c, and an insulating coating 34. The
conductor-turns layers 29a-c, wound from a single conduc-
tor 7 (Fig. 6), such as copper wire, are interconnected at
the thinner ends of the graded insulating coatings 27b and
27c therebetween to fcrm a complete winding. It will be
appreciated, of course, that the invention is not limited
to the three winding portions and four insulating coatings
shown in this embodiment, the number of windings and
winding portions, and consequently the number of insulat-
ing coatings, depending in each case upon the kind of coil
desired.
Eig. 6 illustrates a method of forming a coil
such as shown in Fig. 5. Except for the step of insula-
tion grading, this method is similar to the one previously
described herein in connection with orming insulation
A ~fll~ol-W
12
coatings from several gelled liquid layers of insulation
applied one upon the other, and the same reference num-
erals are used in Fig. 6 as in Fig. 2 to indicate similar
elements performing corresponding functions, such as the
coil former or mandrel ~, the insulation applicator 5, and
the gelling station 9. The inner and outer insulating
coatings 27a and 34 of the coil shown in Fig. 5 are of
substantially uniform thickness throughout, and they can
be formed in the same manner as hereinbefore set forth in
connection with the previously described embodiment. The
following description will be limited to the manner of
forming graded insulation coatings, such as the coatings
27b and 27c.
Referring in this context to Fig. 5 which shows
the coil forming operation at a stage where the turns
layer 29a is wound in place upon the insulating coating
27a and the insulating coating 27b is applied upon the
turns layer 29a, it will be seen therefrom that provision
i~ made in this embodiment for axial relative displacement
to occur between the insulation applicator 5 and the coil
structure as the liquid insulation is being applied. More
specifically, the applicator 5 is seen as advancing in the
same axial direction as the conductor-turns winding opera-
tion, with the result that, during each revolution of the
coil former 4, the applicator 5 applies a liquid layer of
insulation (instantly gelled at 9) to cover the whole of
the previously applied and gelled layer and, in addition,
at least one still exposed conductor turn of the turns
layer 29a. This procedure is graphically illustrated in
Fig. 7 wherein the llnes, such as lines 27b1 and 27b2,
represent the various layers of liquid insulation applied
and gelled individually, albeit preferably in one continu-
ous operation. Of course, it will be appreciated that,
even though the width of the successively applied layers
in this embodiment is shown as incrementally incraasing
~because the applicator 5 is assumed to advance from left
to right, as viewed in Figs. 6 and 7 ), it would incremen-
tally decrease if the applicator 5 first applied liquid
insulation -to cover the whole width of the underlying
conductor-turns layer, and then advanced toward the left.
Upon the insulating coating 27b thus formed, the
wire 7 is wound, starting at the thin end and proceeding
towards the thick end of the coating, to form ~he turns
iayer 29b, upon which the graded insulating coating 27c
then is formed in the same manner as described with
respect to the coating 27b, but with the axial relative
motion between the applicator 5 and the coil structure
reversed in order to form the coating 27c with a reverse
taper, having regard to the previously formed coating 27b.
Next, the conductor-turns layer 29c is wound in
place upon the gelled coating 27c, and then the insulating
coating 34 is formed on the turns layer 29c, preferably by
means of the same applicator 5, however arrested in its
axial movement and applying several layers of liquid
insulation one upon the other and all of them over the
full width of the coil, as the latter is turning.
It will be appreciated that alternate insulating
coatings, such as coatings 27a-c and 34, and conductor-
turns layers, such as layers 29a-c, can be formed, accord-
ing to the invention, in one substantially continuous
winding operation. Furthermore, it will be clear from the
above that the volume of insulation in a coil formed as
described above will be only about half the volume of a
similarly rated coil formed in accordance with conven-
tional practice, such as shown in Fig. 1, and in which the
insulating layers between conductor-turns layers are of
uniform thickness determined by the region of maximum
dielectric stress.
Turning now to the next embodiment of the inven-
tion, Fig. 8 shows, as mounted on a mandrel or coil former
4 having end flanges 60 and 62, a coil structure which is
similar to the one of Fig. 5 in that it, too, comprises
conductor-turns layers 44a, 44b, 44c, an insulating base
coating or substrate 42a, an insulating outer coating 50,
14
and graded insulating coatings 42b and 42c which are
relatively thick at one end, such as at 68 or 76, respec-
tively, and relatively thin at the other end, such as at
70 or 78, respectively.
S The coil structure of Fig. ~ differs ~rom the
one of Fig. 5 by the manner in which its insulating coat-
ings are formed or, rather, the kind of applicator em-
ployed in applying them. Referring in this context to
Figs. 9 to 15, Fig. 9 shows the base coating 42a as being
applied upon the mandrel 4 from a nozzle 54 which has a
rectangular cross-section (Fig. 12), and from which liquid
insuLating material 42, preferably a cross linkable vis-
cous resin, is extruded onto the surface of the mandrel 4
as the latter is turning in the direction of the arrow 10.
The insulating material, as extruded, is assumed in this
embodiment to be thick enough to form the coating 42a
having the required thickness with one complete turn of
the mandrel, whereupon the material 42 is severed at the
nozzle so that the leading and trailing ends of the vis-
cous liquid layer thus applied will abut and merge in eachother so as to form a continuous coating 42a. Of course,
here again the viscosity of the resin 42 extruded from the
nozzle 54 is chosen such as to minimize undesirable flow
of the resin until it is gelled at the gelling station
represented by the ultra-violet radiator 58.
Onto the gelled insulating coating 42a, a con-
ductor, e.g., enamelled wire, is wound from left to righ-t,
as viewed in Fig. 8, to ~orm the turns layer 44a upon
which the insulating coating 42b then is applled, as seen
from Fig. 10, in a similar manner as described above in
connection with the coating 42a. However, now a nozzle 64
is being used which has a generally triangular or trape-
zoidal opening 66 (see Fig. 13) which imparts to the
insulating material 42 extruded therethrough the desired
tapered or wedge-like cross~sectional configuration to
grade the coating 42b so that it is relati~ely thick, as
at 68, at one end and relatively thin, as at 70, at the
other. The isometric view of Fig. 15 shows in greater
detail how the dielectric material 42 is extruded from the
nozzle 64 and onto the conductor-turns layer 44a With
which it is shown to be su~stantially coextensive. Of
course, this single-layer insula~ing coating 42b also is
instantly gelled by radiation from the source 58 (Fig. 10)
as the rotating mandrel 4 is carrying it therepast.
With the mandrel 4 continuing to rotate, the
conductor-turns layer 44b is wound upon the graded and
gelled insulating coating 42b from right to left, as
viewed in Fig. 8, whereupon a nozzle 72 (Fig. 11) for
applying the insulating coating 42c is brought into posi-
tion. This noz71e 72 has a generally triangular or trape-
zoidal opening 74 (Fig. 14) just like the opening of the
15 nozzle 64 but 180 displaced relative thereto so that the
coating 42c, when applied, likewise will have its rela-
tively thick end or edge 76 disposed where the dielectric
stress between the turns layers 44b and 44c is greatest,
and wilL have its thin end or edge 78 disposed where the
dielectric stress between is low. The winding operation
continues, with the turns layer 44c being wound in place
upon the gelled coating 42c from left to right, as viewed
in Fig. 8.
It will be understood that additional conductor-
turns layers and graded insulating coatings may be applied,if required, but for the purpose of illustration it is
assumed that the layer 44c completes the electric winding
and is covered with an insulating coating, i.e., coating
50, which is applied in a similar manner as the base
coating 42a, namely, by extruding it from the rectangular
nozzle 54 shown in Fig. 12. Of course, each insulating
coating is gelled as it passes through the gelling station
represented by the ultra-violet radiator 58.
Another method of achieving insulation grading
is shown in Figs. 16 and 17, wherein all insulating coat-
ings are applied by extrusion from the nozzle 54 with the
rectangular openings, and the coatings 42b and 42c are
16
graded by means of a scraper or blade ~0 disposed at an
appropriate angle or having a beveled cutting edge 82 to
trim the extruded viscous material 42 into the desired
triangular or trapezoldal cross-sectional shap~ by remov
ing the excess material, as indicated at 84.
Figs. 18, 19 and 20 show an arrangement which is
very similar to the one in E~igs. 16 and 17, except that
the blade 80 and, consequently, the gelling station 58 are
spaced farther from the nozzle 54 circumferentially about
the coil structure, having regard to the rotational direc-
tion lO of the mandrel 4, and that Fig. 20 shows the
electric winding as comprising only two turns layers 44a
and 44b instead of three, as shown in Fig. 8, and with the
layer 44b sloping and covered with an insulating coating
92 which has a tapered cross-section to adapt to the slope
of the turns layer 44b and to uniform outer coil dimen-
sion.
