Method for manufacturing a fiber-reinforced push or pull rod

A process for manufacturing a fiber-reinforced push or pull rod formed of electrically insulating plastic material having flange fittings fastened to respective ends thereof. The push or pull rod is formed preferably as a hollow cylinder, and the flange fittings are adapted for transmitting compression or tension forces. A plurality of threads are arranged in parallel with each other and an axis of the rod; which threads are then impregnated with a hardenable plastic material. In accordance with the invention, the tensile strength of the rod is improved by wrapping the threads about at least one pair of wires which are arranged substantially parallel and at a distance with respect to each other so as to form a tape wherein the wires form the edges of the tape. The wires, as tape edges, are inserted into helical external recesses of the flange fittings and are secured therein in a form-locking manner.

BACKGROUND OF THE INVENTION 
This invention relates generally to methods for manufacturing rods formed 
of electrically insulating plastic material, and more particularly, to a 
method for manufacturing a fiber-reinforced, hollow-cylindrical push or 
pull rod formed of electrically insulating material and having flange 
fittings fastened at end faces thereof for transmitting compression or 
tension forces; the fibers being formed of threads which are oriented 
parallel to the axis of the rod and are impregnated with hardenable 
plastic material. 
Push or pull rods formed of insulating material are used as 
force-transmitting members in high voltage circuit breakers. In such 
circuit breakers, the contacts across the switching gaps are at high 
voltage potentials, and are actuated by a drive at ground potential. One 
particular hollow, cylindrical push or pull rod which is known is 
described in DE-AS No. 24 29 475. In this known rod, sleeves are provided 
in the vicinity of the end faces as force transmitting members which cover 
the areas of the tube wall of the rod at the end faces. The sleeves are 
connected by a close fit to the rod by elements of structure which are 
inserted into the outer layer of the rod, project radially beyond the tube 
wall, and engage in recesses in the sleeves. This known push or pull rod 
is made by a process essentially in which a fabric having threads oriented 
parallel and transversely to the axis of the rod is impregnated with 
electrically insulating plastic material of the type which is hardenable. 
The wrapping process may be of a wet type, or a dry wrapping process 
wherein the wrap is subsequently impregnated. 
It is a problem with such known rods that even if high tensile strength 
threads are used, the rod can be stressed in compression or tension only 
to the extent that the form-locking connection between the sleeve and the 
outer layer of the rod can be stressed in shear. It is, therefore, an 
object of this invention to provide a method for manufacturing a 
fiber-reinforced push or pull rod wherein the tensile strength of the rod 
is relatively large and limited essentially by the tensile strength of the 
threads which are oriented parallel with the axis of the rod. 
SUMMARY OF THE INVENTION 
The foregoing and other objects are achieved by this invention which 
provides a method for manufacturing a fiber-reinforced push or pull rod 
wherein the threads are wound on at least one pair of wires which are 
arranged to be substantially parallel and at a predetermined distance from 
each other. The method further includes the forming of a tape wherein the 
wires form the edges of the tape, placing the wires in helical external 
recesses contained in conical fittings, and securing the wires therein in 
a form-locking manner. 
It is evident that since the threads are connected directly to the conical 
fittings in a form-locking manner, the combination of the conical fittings 
and the multiplicity of threads which extend therefrom in a substantially 
parallel relationship with the axis of the rod, form a composite body 
after the plastic material has hardened. The threads cooperate primarily 
in the transmission of force between the push or pull rod and the fitting, 
while the impregnating or shaping plastic material participates only 
indirectly. The push or pull wire which results from the inventive method 
is substantially less susceptible of having its fittings torn-off under 
high tensile strength than known rods. 
In accordance with a further embodiment of the invention, the recesses in 
the fittings can be rolled closed or beaded-over in the direction of the 
tension of the thread after the wires which form the edges of the tape are 
placed therein. In a simple mechanism, the projecting portions of the 
helical recesses, or their boundaries, which are rolled-over in accordance 
with the present inventive process, constitute a particularly advantageous 
and simply locking arrangement wherein the transmission of the pulling 
forces can be selected independently of the tensile strength of the wires. 
In accordance with the inventive method, the wrapping can be performed 
rapidly if the wires are wrapped with groups of parallel threads. It is 
therefore advantageous that the threads be drawn from a revolving 
transporting device, illustratively a carousel with a spool, and that they 
be wound about the spaced wires through a wire guide arranged at a point 
on the circumference of the transporting device. 
It is a feature of the present invention that the threads are stretched to 
extend between conical fittings in an arrangement which is concentric 
about the rods axis of reciprocating motion. Thus, the threads are secured 
in a form-locking manner in recesses of the fittings which extend 
transversely with respect to the axis of the rod. Each such stroke has a 
length which corresponds to the length of the rod. By this method, the 
conical fittings and the multiplicity of threads stretched substantially 
parallel to the axis of the rod form a composite body after the plastic 
material has set and threads have been connected directly to the fittings 
in a form-locking manner. 
It is a further feature of this invention that the threads participate 
primarily and directly in the transmission of force between the push or 
pull rod and the fitting, while the impregnating, or shaping, plastic 
material participates only indirectly. Thus, the danger of the fittings 
being torn-off under high pulling forces is substantially eliminated with 
this solution. 
It a particularly advantageous embodiment of the invention, the recesses 
are formed by circular slots into which a spring ring is inserted for 
securing the threads. Alternatively, wires, stranded wires, ribbons, or 
other flexible tying devices can be used to secure the threads. 
In accordance with a further embodiment of the invention, the fitting is 
made of several parts, each of which can have a recess. Such parts of the 
fitting can be stacked successively after each stroke motion and fixation 
of the threads.

DETAILED DESCRIPTION 
FIG. 1 is a schematic representation of a winding arbor 1 which is provided 
to facilitate performance of the present inventive method. Winding arbor 1 
is advantageously adapted to have a length corresponding to that of a 
preferably hollow, cylindrical push or pull rod. The winding arbor is 
rotatably supported on one side thereof in a tail stock 2, and is clamped 
on the other side in a chuck 3 which is rotatable driven by a drive 4. 
Conical fittings 5 and 6 are arranged at respective ends of winding arbor 
1. The conical fittings are provided with helical external recesses 7 such 
that a wire 8 can be inserted into recess 7 of conical fitting 5, while a 
wire 9 is introduced into recess 7 of conical fitting 6. Wires 8 and 9 are 
arranged to be substantially parallel with one another and become spaced 
further apart when they are wound up. 
Threads 10 are wound about wires 8 and 9; such threads being advantageously 
formed of high tensile-strength plastic fibers. The threads are taken from 
a carousel 12 which contains a plurality of spools 11. When the carousel 
is rotated, the threads are wound to form a tape which has edges formed by 
wires 8 and 9. Wires 8 and 9, being thus wrapped by threads 10, are then 
placed in helical external recesses 7 of conical fittings 5 and 6, and 
secured therein in a form-locking manner. After wires 8 and 9 which form 
the tape edges are inserted, recesses 7 can be rolled closed, or at least 
partially closed, in the direction of the tension of the thread. Such 
wrapping of the wires in groups by substantially parallel threads 
facilitates rapid rates of production. 
It is evident from the foregoing and from FIG. 1 that the diameter of 
carousel 12 depends upon the length of the push or pull rod which is to be 
manufactured. It may therefore be advantageous in the production of long 
rods to utilize a different transporting arrangement, illustratively a 
chain or a belt, instead of carousel 12. The use of a chain or belt in the 
production of long push or pull rods saves substantial space. 
FIG. 2 is a cross-sectional representation of the detail of FIG. 1 showing 
wire 8 inserted into helical recesses 7. Three turns of wire 8 are shown 
with looped-around threads 10a and 10b. The detail of FIG. 2 further shows 
that the conical angle of end fitting 5 in this presentation and the pitch 
of the thread-like helical recess 7 are adapted to the diameter of the 
thread, taking into consideration the two parallel threads 10a and 10b of 
each loop, so as to achieve the closest possible packing of the threads. 
This figure further shows the particularly well formed locking arrangement 
which is achieved by rolling-over the helical recesses 7 or their limiting 
bodies 7a. Such rolling-over securely anchors threads 10a and 10b, and 
wire 8, in recesses 7. In a preferred embodiment, the recess is preferably 
rolled closed in the direction of tension of the thread, as shown in FIG. 
2. 
In a further embodiment of the invention, a plurality of parallel pairs of 
wires can be provided if the end fittings are provided with multiple screw 
threads. Thus, in such an embodiment several parallel wires can be 
inserted simultaneously in respective helical recesses in each conical 
fitting. 
FIGS. 3 to 7 show various stages in the performance of the inventive 
method. As shown in these figures, a receiving arbor 13, which is adapted 
to the length of the preferably hollow cylindrical push or pull rod, is 
rotatably supported and driven by a drive which is not shown in detail in 
these figures. Receiving arbor 13 is provided with conical fittings 14 and 
15 which are mounted on respective ends thereof and which are provided 
with groove-like recesses 17 which extend transversely with respect to an 
axis 16 of the rod. The threads are first anchored at fitting 15 in slot 
17 and are then stretched toward fitting 14 by a ring-shaped thread guide 
19. Thread guide 19 arranges the threads concentrically about axis 16 
between the conical fittings and is supported so as to be movable in a 
reciprocating motion. At fitting 14, the threads 18 are secured in a 
recess 17, whereupon the ring-shaped thread guide 19 executes a stroke 
motion in the direction of arrow 20. The motion of ring-shaped thread 
guide 19 in the direction of arrow 20 is illustrated in FIGS. 3 and 4. 
FIG. 5 shows thread guide 19 arranged beyond conical fitting 14 in the 
direction of arrow 20. While thread guide 19 is at this location, threads 
18 are secured to conical fitting 14. In this embodiment, a flexible tying 
wrap 24, which may be a spring ring, a stranded wire, or any other 
flexible tying wrap which can take tension forces, is wrapped around the 
threads so as to secure them within recess 17. Of course, tying wrap 24 
may be a thread similar to threads 18. 
After threads 18 are secured in recess 17, thread guide 19 is moved in the 
direction of arrow 25 toward conical fitting 15. As shown in FIGS. 5 and 
6, the operation of securing the threads in a recess 17 with a tying wrap 
24 is repeated in the mannner discussed hereinabove. 
FIGS. 8 and 9 are detailed cross-sectional representations of threads 18 
secured by tying wrap 24 in a recess 17 of conical fitting 14. FIG. 8 
shows thread 18 after being secured as shown in FIG. 5. Thus, thread 18 
continues to extend to the right, in the direction of arrow 20. FIG. 9 
shows a limiting body 21 of conical fitting 14 having been bent or rolled 
over to close the recess. 
FIG. 10 is a cross-sectional representation of a concical fitting, such as 
one of fittings 14 and 15, which is formed of several fitting portions, 
such as fitting portions 22a and 22b. In this embodiment, the recesses are 
formed by the coaxially adjacent relationship between fitting portions 22a 
and 22b, respectively. In the specific illustrative embodiment, fitting 
portion 22b is provided with a projecting edge 22c which is bent or rolled 
over to provide the form-locking effect. Thus, in accordance with FIG. 10, 
after threads 18 are secured in slot 17 of fitting portion 22a, fitting 
portion 22b is installed over winding arbor 13 in the direction of an 
arrow 23. In this manner, a selectable number of fitting portions 
corresponding to the number of desired thread layers can be installed. 
Although the invention has been described in terms of specific embodiments 
and applications, persons skilled in the art, in light of this teaching, 
can generate additional embodiments without exceeding the scope or 
departing from the spirit of the claimed invention. For example, the 
present process invention which is described in terms of a continuous 
process cycle and an intermittent process cycle is adaptable for either 
wet wrapping, or for a dry wrapping method with subsequent impregnation. 
Accordingly, it is to be understood that the drawings and descriptions in 
this disclosure are proffered to facilitate comprehension of the invention 
and should not be construed to limit the scope thereof.