Binding for winding overhangs of rotors of electric machines, and method of producing bindings for winding overhangs

In a binding (19) for winding overhangs (20) of rotors (1) of electric machines, essentially comprising a plastic matrix with fibrous material embedded therein, the binding (19) is formed by winding a fiber tape (15) onto the winding overhang (20). The plastic matrix is composed of a thermoplastic. Furthermore, a method is described for applying the fiber tape to the winding overhang of an electric machine.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a binding for winding overhangs of rotors of 
electric machines in accordance with the preamble of the first claim. It 
likewise relates to a method of producing a binding in accordance with the 
preamble of the independent method claim. 
2. Discussion of Background 
Such bindings for winding overhangs of rotors of electric machines are 
known from "Herstellung der Wicklung elektrischer Maschinen" Production 
of the winding of electric machines!, edited by H. Sequenz, Springer 
Verlag, page 236 f. There, the windings of winding overhangs of the rotors 
of electric machines are retained by bindings made of steel wire or glass 
fibers impregnated with resin. A further mounting and supporting of 
winding overhangs, not described in that document, are cap rings. The wire 
bindings are formed from as far as possible only one layer of wire turns 
lying closely adjacent to one another. An insulating layer is placed 
between binding and winding. Bronze or nonmagnetic steel is used as 
winding wire material. 
The thermosetting glass fiber bindings are composed of glass fiber tapes 
preimpregnated with resin, which are wound in multiple layers around the 
winding overhang. Advantages in terms of construction and production 
result from the use of thermosetting glass bindings. On the market, the 
widest possible range of glass fiber tapes with a thermosetting matrix can 
be obtained, for example glass fibers which are impregnated with a 
solvent-free resin. During the binding, operations are carried out with a 
pretension which is as high as possible, the maximum applicable pretension 
being dependent on the tensile strength of the glass fiber tape. The 
thermosetting binding material is heated so intensively by a heat source 
that the resin becomes liquid. As a result of the pretension, outer layers 
already penetrate into the lower layers during the binding, which results 
in a certain proportion of the pretension being lost before the resin has 
hardened. The pretension must be applied during the processing in such a 
way that the pretension remaining in the hardened material is sufficient 
to compensate for the centrifugal forces in the winding overhangs during 
operation. The advantages of glass bindings over wire bindings are, inter 
alia, the reduction in cost of the final product, special insulating 
layers are dispensed with, the specific elasticity is higher, lower 
loading by the centrifugal force as a result of lower weight, and so on. 
However, the thickness of the binding needed is decisive as the selection 
criterion for the application of glass bindings or steel bindings for 
winding overhangs. Starting at a thickness of the thermosetting glass 
binding of over 8 mm, further turns of thermosetting fibrous material 
which are applied no longer have any effect on the strength of the glass 
binding. Therefore, when greater strength is needed, the glass bindings 
are replaced by steel bindings. 
SUMMARY OF THE INVENTION 
Accordingly, one object of the invention is to provide novel bindings with 
a higher pretension and hence a higher strength at as low a thickness as 
possible in the case of a binding for winding overhangs of rotors of 
electric machines of the type mentioned at the beginning. 
According to the invention, this is achieved by the features of the first 
claim. 
The core of the invention is therefore that the plastic matrix of the fiber 
tapes is composed of a thermoplastic. 
The advantages of the invention can be seen, inter alia, in the fact that 
during the application of the thermoplastic fiber tapes, no losses in 
pretension arise as a result of relaxation. As a result, more pretension 
can be applied per turn of the thermoplastic fiber tapes, which results in 
fewer layers of fiber tapes being needed in order to achieve a specific 
pretension and strength. This means that the thickness of the 
thermoplastic bindings can be reduced over thermosetting bindings, by 
which means the heat occurring during the operation of the rotor can be 
dissipated better. Furthermore, previously used steel bindings can be 
replaced by the thermoplastic bindings because of the low thickness needed 
of the thermoplastic bindings. A further advantage is the short time which 
is needed for the production of a thermoplastic binding and the low 
production costs, resulting therefrom, of such bindings. 
Further advantageous embodiments of the invention emerge from the 
subclaims. 
Moreover, a method of producing a binding of the generic type is further 
specified.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings, wherein like reference numerals designate 
identical or corresponding parts throughout the several views, in FIG. 1 a 
rotor 1 of an electric machine is rotatably supported with its shaft ends 
2a, 2b on two bearing blocks 3, 4. Integrated in the bearing block 3 is a 
rotary device, not shown, by means of which the rotor 1 can be rotated 
about its rotor axis of rotation 30. Arranged above the rotor 1 is a 
portal frame 5, which runs parallel to the rotor axis of rotation 30. 
Arranged essentially vertically on the portal frame 5 is a support arm 7, 
the support arm 7 being able to be displaced horizontally over the 
transverse support 6 of the portal frame 5. Arranged on the lower end of 
the support arm 7, located opposite to the rotor 1, is a pressure cylinder 
8. By means of the pressure cylinder 8 and a mounting 9, a head piece 10 
can be moved vertically and pressed with an adjustable force against a 
winding overhang 20 of the rotor 1. The head piece 10 in this case serves 
to apply a thermoplastic fiber composite material tape 15 to the winding 
overhang 20. 
According to FIG. 2 and FIG. 3, the head piece 10 comprises a press roller 
11, a guide roller 12 and a heating device 14. The elements 11, 12, 14 of 
the head piece 10 are connected to one another via mountings which are not 
shown. The thermoplastic fiber tape 15 is unwound from a binding material 
reel 13 via an unwind device 16. The thermoplastic fiber tape 15 is then 
led over the guide roller 12 to the heating device 14. There, the 
thermoplastic fiber tape 15 is heated by means of a heating element 18, at 
least on that surface facing the heating device 14, to at least the 
melting point of the thermoplastic matrix of the thermoplastic fiber tape 
15. By means of the press roller 11, the thermoplastic fiber tape 15 is 
pressed onto the winding overhang 20 and is cooled, so that it bonds 
firmly on the winding overhang 20. The rotational speed of the unwind 
device 16 is in this case less than that of the rotor 1, by which means 
the unwind device 16 exerts an adjustable tensile force on the 
thermoplastic fiber tape 15. The fiber tape 15 is thus applied to the 
winding overhang under a specific pretension. Once a first web of the 
thermoplastic fiber tape 15 has been applied to the winding overhang 20, 
the outer surface, facing away from the winding overhang, of the 
thermoplastic fiber tape 15 which is located on the winding overhang is 
heated by a heating element 17 of the heating device 14, likewise to at 
least the melting point of the thermoplastic matrix. This results in the 
two mutually facing surfaces of the thermoplastic fiber tape 15 being 
melted, and optimum welding is produced at the press roller 11. As a 
result of the application of the thermoplastic fiber tape 15, an at least 
one-layer binding 19 is thus produced which has an appropriate pretension. 
The heating elements 17, 18 are supplied with hot air via an air supply, 
for example. 
According to the invention, the binding material is composed of 
thermoplastic fiber composite material tapes. These tapes comprise a 
thermoplastic matrix with fibers embedded therein, the fiber content being 
able to amount to over 60%. Any thermoplastics which satisfy the 
corresponding requirements can be used as the thermoplastic matrix, 
preferably aromatic plastics, in particular polyetherether ketone or 
polyether imide. Any desired fibrous materials which have a 
correspondingly desired tensile strength can be used as fibers, preferably 
carbon fibers or glass fibers. 
TABLE 1 
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Modulus 
Tensile 
of 
Fiber Density 
strength 
elasticity 
Ex. Material type Matrix (g/cm.sup.3) 
(MPa) (GPa) 
______________________________________ 
a QLG4068 Glass PPS 1.65 1110 44 
b QLC4160 Carbon PPS 1.5 1837 114 
c QLC4064 Carbon PPS 1.5 1950 121 
d PEI-S2 Glass PEI 1.6 1170 55 
e APC2-S2 Glass PEEK 1.6 1170 55 
f APC2-AS4 Carbon PEEK 1.5 2070 140 
g Polyglass Glass Polyester 
1.6 800-1200 
40-60 
______________________________________ 
The material properties of some selected examples of thermoplastic fiber 
composite material tapes are illustrated in Table 1. The tapes illustrated 
in the table comprise glass or carbon fibers and a matrix made of 
polyphenylenesulfide (PPS), polyether imide (PEI) or polyetherether ketone 
(PEEK). The tapes with the designations a, b, c are produced by the 
Quadrax company, the tapes with the designations d, e, f are produced by 
the ICI Fiberite company. Example g serves as a comparative example having 
a thermosetting matrix, which is produced by the Isola von Roll company. 
The maximum temperature of use of the tapes from Example a, b, c, d and g 
is about 200.degree. C., that of Examples e and f is approximately 
240.degree. C. PEEK is normally processed at about 400.degree. C. and PPS 
at about 340.degree. C. 
In FIG. 4, a pretension 31 which is applied during the processing of fiber 
tapes is plotted against a distribution of the remaining pretension 32. 
For a distribution curve 33 of a thermoplastic fiber tape 15, a mean value 
35 lies higher than that mean value 36 for a distribution curve 34 of a 
thermosetting fiber tape. A safety margin 37 for the thermoplastic fiber 
tape 15 is smaller than a safety margin 38 of the thermosetting tape, that 
is to say the variance of the curve 33 of the thermoplastic fiber tape is 
smaller than that of the curve 34. This can be explained by the fact that 
during the processing of the thermoplastic fiber tapes, only very low 
losses of pretension are produced as a result of relaxations. Experiments 
have shown that the remaining pretension for thermoplastic bindings is at 
least between 70-100% of the original pretension. As a result, in order to 
produce a binding having a specific pretension, fewer turns of the 
thermoplastic fiber tape are needed in comparison with thermosetting fiber 
tape, as emerges from the following Table 2. 
TABLE 2 
______________________________________ 
Fiber type Glass fibers 
Carbon fibers 
______________________________________ 
Number of turns of thermo- 
&lt;0.7 &lt;0.4 
plastic fiber tape as a ratio 
of the number of turns of 
thermosetting fiber tape with 
glass fibers 
______________________________________ 
It can be seen from Table 2 that, for example when thermosetting bindings 
with glass fibers are replaced by thermoplastic bindings with carbon 
fibers, the thickness of the binding can be reduced by more than the 
factor 2.5. As a result, steel bindings which were previously used can be 
replaced by thermoplastic bindings. 
According to FIG. 5, the thermoplastic fiber tape 15 can be applied by 
means of a connecting force F without a press roller 11, in particular in 
the case of relatively small winding overhangs 20, that is to say in the 
case of winding overhangs having small radii. The connecting force F is in 
this case proportional to the tension applied to the tape 15 and inversely 
proportional to the radius of the winding overhang 20. In this case it 
must be taken into account that the radius of the winding overhang is 
predetermined by the parameters of the electric machine, and that the 
maximum tension which can be applied to the tape 15 is determined by the 
tensile strengths in accordance with Table 1. Wherever the radius of the 
winding overhang is sufficiently small and the applicable tension is 
sufficiently large, it is thus possible to dispense with the press roller 
according to FIGS. 2 and 3. As a result, the application process has fewer 
process variables and is greatly simplified thereby, which also saves 
investment costs. A further advantage is that the method is less dependent 
on the geometry and topology of the conductor bars of the winding 
overhang. 
Cap rings of generators and motors, which serve to retain and support the 
winding overhang, can also be replaced by bindings made of thermoplastic 
fiber tapes. This is made possible by the excellent mechanical properties 
of the thermoplastic fiber tapes, and by the low thickness of the bindings 
produced therefrom. 
The invention is of course not restricted to the exemplary embodiment shown 
and described. By means of the thermoplastic fiber tapes, the bindings can 
also be constructed from individual rings. This has the advantage that the 
heat produced in the rotor can be dissipated via the interspaces between 
the rings. 
Obviously, numerous modifications and variations of the present invention 
are possible in light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims, the invention may 
be practiced otherwise than as specifically described herein.