Method of making a self-supporting wire coil

A wire is wound on a coil body form about a removable mandrel in a first layer in which the turns abut one another. A guide ring reverses the direction of lead of the wire to form a second, overlying layer in which the turns are spaced a short distance apart from one another. The final turns of the outer layer engage about the coil form. A casting agent applied to the coil penetrates the turns of the second and first layers and is hardened. The mandrel is removed and the coil is self-supporting, for use as in a moving-coil motor. A fiberglass sheet may optionally be applied about the first layer before the second layer is wound thereover to increase the strength of the coil.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method and apparatus for the production 
of a coil which is self-supporting over its principal length. 
2. The Prior Art 
Coils which are self-supporting in the winding area have various uses, as 
in moving coils in moving-coil motors. In such applications the mass in 
motion and the size of the permanent magnet in the motor should be as 
small as possible. Where the air gap about the moving coil is in such 
cases to be small, the winding zone of the coil must be built to close 
tolerances, yet it is expedient to dispense with a coil-supporting body in 
the winding area. Thus, it is desirable to provide a method and an 
apparatus for constructing a self-supporting coil which is both simple and 
inexpensive to produce. Once the coil is wound, the well-known drip method 
is employed for casting together the layers of the coil, for instance 
using a resinous material as a drip or casting agent. 
SUMMARY OF THE INVENTION 
A method and an apparatus are disclosed for producing a wire coil which is 
self-supporting over at least a principal part of its length. Either a 
single or a double strand of wire in parallel is wound in a first annular 
layer of abutting turns about a mandrel form with a uniform lead in a 
first direction. The first layer of turns extends from an edge of a coil 
body, the edge being adapted to the diameter of the wire and hence the 
lead of the turns. At the end of the first layer, a guide ring is employed 
to abut the last turn in the inner layer and to redirect the wire upwardly 
in a reverse lead direction. A spacing roller with peripheral channels is 
employed to wind the wire turns tightly upon the inner layer and to space 
them slightly apart axially of the coil. The outer layer is wound onto a 
collar on the coil body to form a strong mechanical bond. 
A casting agent is applied to the outside of the second layer, the agent 
penetrating about and between the turns of the second and first layers of 
the coil, apparently by suction or capillary action, before hardening. The 
spacing of the turns of the outer layer permits penetration of the drip 
agent through the outer layer, while the abutting wires of the inner layer 
permit resin flow just beyond the lines of contact between the turns of 
wire. 
The leads of the inner and outer layers of wire are established 
respectively by an edge of a collar or ledge on the coil body and by a 
guide ring pressed axially onto the last turn of the inner layer and which 
guides the wire into a reverse lead at a radially outward point at the 
opposite end of the coil from the coil body. A mandrel employed to support 
the windings of the coil before the casting step is removable from within 
the coil, to leave the coil self-supporting.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows in partly schematic form a coil body 10 which carries a coil 
or winding 12 which is, aside from some coil body support, 
self-supporting. As shown in FIGS. 1 and 2, the coil 12 comprises two 
layers of wires supported from a collar 16 on one side of the coil body 
10. Wires from the coils 12 connect to voltage and current sources through 
a groove 14 formed on one side of the coil body 10. In FIG. 1, the coil is 
wound in pairs of wires, as shown by the leads running through the groove 
14. 
FIG. 2 is an enlarged, sectional view of the area Z in FIG. 1. The ledge or 
collar 16 extends from the coil body 10 in the axial direction. The first 
turn of an inner or first layer 18 of the winding 12 abuts a rightward 
edge of the collar 16. As shown in FIG. 2, the turns of the inner layer 18 
are wound to lie tightly together. An outer layer 20 overlies the inner 
layer 18, having the individual turns thereof spaced slightly apart from 
one another. A woven glass fiber sheet 22 is preferably laid between the 
outer layer 20 and the inner layer 18 to stiffen the coil. The woven glass 
fiber 22 preferably also is cemented firmly directly onto the collar 16, 
as shown. The outer layer 20 is then wound onto and about the collar or 
ledge 16 for increased strength of the winding 12. 
The individual turns of the outer layer 20 have a fixed spacing from one 
another, so that a casting agent shown in finished form at 24 in FIG. 2 
can penetrate therebetween. The agent is preferably an epoxy resin which 
can be dripped in liquid form onto the windings 12 as at 40 in FIG. 1. The 
drip or castng agent 24 reaches the inner layer 18 between the turns and 
by a capillary or suction action between the turns of the layer 18 
penetrates just beyond the contact points between the turns of the inner 
layer 18. In this way the inner and outer layers 18, 20 are bonded 
together by the agent 24 with the added stengthening of the woven glass 
fiber sheet 22 therebetween. 
Production of the coil employs, as shown in FIG. 3, an internal winding 
mandrel 26 which may consist of separable segments fixed in place during 
winding and casting of the coil but readily removable thereafter. The 
mandrel permits production of a precisely cylindrical coil or, where 
required, a coil of any other convex annular shape. The coil body 10 is 
received on the mandrel 26 at one side thereof. A guide ring 28 is 
received over the mandrel at an opposite end. Segments of the mandrel 26 
are spread radially to engage the interior surface of the coil body 10 and 
the guide ring 28 as by means of a cone plate assembly 30. The cone plate 
30 permits removal of the coil, when completed, from the winding mandrel 
26. 
In winding the coil, a single or double strand of wire is brought through 
the groove 14 of the coil body 10, as shown in FIG. 4, and is led 
downwardly about the coil body 10 in the orientation of FIG. 4 abutting 
the edge thereof. The collar or ledge 16 is machined so that a complete 
revolution of the wire about the coil body 10 will result in an axial 
displacement thereof by the axial width of the wire or wires being 
wrapped. In this manner the turns of the wire will closely abut one 
another while maintaining a uniform lead in accordance with the principles 
of the invention. That is, the lead of the collar 16 is dependent upon the 
diameter of the winding wire in the axial direction, as shown by the two 
arrows of FIG. 4. Where two wires are employed, winding time is halved and 
a greater angle of intersection between the inner and the outer layers is 
obtained, simplifying production of the uniform lead in the outer layer. 
Once winding is completed, two ends of the wires can be connected in 
series to form a single coil. 
The inner or first layer 18 of the coil 12 starts from the edge of the 
collar 16. The turns of the inner layer 18 are pressed firmly against one 
another so that no spacing occurs between the turns. Winding continues 
with a uniform lead in the first direction, for example right-handedly, 
until a desired coil length is formed. To ensure that the windings of the 
inner layer do not expand axially, a guide ring 28 is fitted onto the 
mandrel 26 and pressed firmly, axially against the final turn of the inner 
layer 18. 
The guide ring 28 is shown in FIGS. 5, 6, and 7. The guide ring 28 has a 
collar 32 having a radially inward portion with corresponding parts 
arranged parallel to, for instance, the right-handed lead of the inner 
layer 18 and the edge of the collar 16. The guide ring 28 thus will mate 
precisely with the inner layer 18 of the turns of the winding 12. The wire 
is then led to a gap 34 in the collar 32 to pass outwardly to begin 
forming the outer layer 20 of the winding 12. The desired lead direction 
for the outer winding 20 is also machined into the collar 32 of the guide 
ring 28, so that the first turn of the outer layer 20 is wound with a lead 
having a desired angle to the underlying turns of the layer 18. In FIG. 7, 
the track of the lead for the last turn of the inner layer 18 is shown in 
a dot-and-dash line and the path of the lead of the first turn of the 
outer layer is shown in a broken line. 
Once the inner layer is secured between the coil body 10 and the guide ring 
28, the woven glass fiber sheet 22 is placed in position about the inner 
layer 18 and is cemented to the flange or collar 16 of the coil body 10. 
Then winding of the outer layer 20 commences, with a constant spacing of 
0.03 to 0.06 mm between the adjacent turns. These spaces are selected to 
allow for penetration of the casting agent 24 into the windings. 
A spacing roller 36 as shown in FIG. 8 is conveniently employed to affect 
the desired spacing. Channels 38 are formed in the periphery of the 
spacing roller 36, centers of the individual channels being spaced apart 
by the wire diameter plus the desired space between the individual turns. 
More channels than wires being wound are provided, to wind the wire 
according to the preceding turns to maintain uniformity of the lead and 
the spacing of the wires. The spacing roller 36 is pressed against the 
outer winding with a force of about 10N. In the orientation of FIGS. 1 and 
8, the winding wire(s) will run into the left-most channels and be pressed 
between the spacing roller 36 and the fiber mat 22 and/or the inner 
winding 18. Turns of the outer layer 20 already wound lie in the remaining 
channels of the spacing roller 36. The outerlayer 20 is wound in this way 
until the left end of the collar 16 of the coil body 10 is reached, as 
shown in FIG. 1. The wires are then routed through the groove 14 to the 
appropriate connections. 
Casting of the coil is then accomplished, as by the well-known drip method. 
The winding mandrel with the finished, wound coil is heated to about 
120.degree. C. With the winding mandrel stationary the agent is dripped 
along an upper-most line 40, as shown in FIG. 1, parallel to the axis of 
the coil. The agent flows freely under the heat of the winding and so 
penetrates into the winding very quickly. Application of the casting agent 
all over the periphery of the coil coats and bonds the windings of the 
coil. If a uniform surface is desired, excess casting agent may be wiped 
off the surface while rotating the winding mandrel. Jelling of the drip 
agent in and about the coil is accelerated by further heating of the coil 
and the casting agent, with hardening occurring in an oven at about 
120.degree. C. 
After casting and hardening of the material 24, the winding mandrel and 
coil are cooled to room temperature. The mandrel 26 is then taken apart by 
loosening the cone plate 30. The guide ring 28 is released and removed 
from the end of the coil 12, and then the segments of the mandrel 26 are 
removed from the interior of the coil. The coil 12 is left cantilevered 
from the coil body 10 as shown in FIG. 1. 
Although the drawings illustrate production of a cylindrical coil, is also 
possible for coils with other annular shapes to be produced according to 
the principles disclosed. Although these and various other minor 
modifications may be suggested by those versed in the art, it should be 
understood that we wish to embody within the scope of the patent warranted 
hereon all such modifications as reasonably and properly come within the 
scope of our contribution of the art.