Plastic article or earthenware shaping or treating: apparatus – Distinct means to feed – support or manipulate preform stock... – Female mold type means
Reexamination Certificate
2002-06-14
2004-07-20
Heitbrink, Tim (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Distinct means to feed, support or manipulate preform stock...
Female mold type means
C425S392000, C425S393000, C425S405200
Reexamination Certificate
active
06764291
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a device for impregnating conductor bars for the stator winding of an electrical machine. The conductor bars are each provided on their surface with an insulation which is produced by wrapping each conductor bar with an insulating tape, preferably with a glass-containing or mica-containing insulating tape, which is impregnated with an insulating agent as impregnating fluid, preferably consisting of curable synthetic resin, in an impregnating tank in conjunction with an autoclave. The conductor bars are pressed to shape and size in a press die before the impregnating fluid cures.
It is conventionally known to provide the conductor bars for the stator winding of electrical machines with insulation before they are inserted into the stator slots provided for this purpose.
The insulation of the conductor bars conventionally consists of a wrapping with mica-containing insulating tape or of a mica tape which is impregnated with an impregnating fluid. The impregnating fluid is preferably a curable synthetic resin. It serves, on the one hand, for fixing the insulating wrapping and, on the other hand, for improving the insulation by preventing the possible absorption of moisture.
The impregnating agent is conventionally applied in a so-called impregnating tank which is arranged in an autoclave. First, a vacuum is thereby set for a short time in the autoclave. The establishment of the vacuum removes possible gas accumulations between the wrapping and the conductor bar which could constitute an obstacle to the absorption of the impregnating fluid.
For impregnation, the impregnating tank is then filled with the impregnating fluid and the respective conductor bar is dipped in. The bar is thereby wetted with the impregnating fluid. An overpressure is subsequently set in the autoclave, ensuring that the impregnating fluid penetrates into the insulating wrapping. Once it is ensured that all the cavities in the insulating wrapping are filled with impregnating fluid, ambient pressure is once more set in the autoclave and any excess impregnating fluid is returned to the supply container.
Due to the fact that the quantity of impregnating fluid necessary for flooding a conductor bar in the impregnating tank is about 10 to 50 times the quantity actually required for impregnating the conductor bar, and due to the fact that the excess which is necessary in each case is, if possible, to be reused, for example for the proper use of resources and in order to reduce the problem of disposing of synthetic resins of this kind, impregnation is to be carried out under defined conditions, for example at an appropriately low temperature which does not impair, or only insignificantly impairs, the stability of the resin, since the renewed processibility of the excess impregnating fluid is otherwise no longer guaranteed.
The viscosity of the impregnating fluid is therefore set in such a way that, on the one hand, thorough impregnation of the wrapping is ensured and, on the other hand, impregnating fluid no longer escapes during curing. After impregnation, that is to say after the wrapping has been impregnated with impregnating fluid, the curing of the impregnating fluid takes place, preferably at increased temperature, in order to reduce the curing time.
In view of the accuracy of contour and the dimensional accuracy required in the ready-to-install conductor bars, they are subjected before or during impregnation to pressing. This ensures that the cross sections of the conductor bars do not lead to fitting problems when they are being installed in the stator. This pressing may be carried out in various ways, specifically locally or totally and both at ambient temperature and at increased temperature, for example in a kiln. Also, if appropriate, pressing may be carried out, before impregnation, as so-called dry pressing, in contrast to so-called wet pressing which is carried out after impregnation has taken place. Before wet pressing, the conductor bar is wrapped in a separating foil which prevent the press die from adhering to the conductor bar.
Another important reason for pressing the insulation is, furthermore, to achieve optimum electrical and mechanical properties which depend essentially on the ratio of the fractions of impregnating fluid to mica or glass.
It follows from the foregoing that the impregnation process described above is highly complicated in manufacturing terms and therefore decidedly time-intensive.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a device for impregnating conductor bars for the stator winding of an electrical machine, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which assures that, while a smaller quantity of impregnating fluid is required, the time necessary for impregnating a conductor bar is reduced.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of impregnating a conductor bar for a stator winding of an electrical machine, which comprises:
providing a surface of a conductor bar with an insulation by wrapping the conductor bar with an insulating tape;
placing a pressure-tight and fluid-tight casing over an entire length of the conductor bar provided with the insulation to form an encased conductor bar;
subjecting the encased conductor bar on all sides to a pressure P
1
in a pressing device and introducing an impregnating fluid into an interspace between the insulated conductor bar and the casing at a pressure P
2
<P
1
; and pressing the conductor bar, loaded with impregnating fluid over the entire length thereof and surrounded by the casing, to shape and size in a press die at a curing temperature of the impregnating fluid.
In accordance with an added feature of the invention, the process is performed in an autoclave, i.e., the encased conductor bar is introduced into an autoclave at least prior to the subjecting step.
In accordance with an additional feature of the invention, the tape is mica-containing insulating tape and the impregnating fluid is a curable synthetic resin.
According to the invention, therefore, each conductor bar having a finished insulating wrapping is provided over its entire length with a pressure-tight and fluid-tight casing. In this context, the encased conductor bar is subjected on all sides to a pressure P
1
in a pressing device, the impregnating fluid being introduced into the interspace between the insulated conductor bar and the casing at a pressure P
2
<P
1
, and the conductor bar, loaded with impregnating resin over its entire length in this way and surrounded by the casing, being pressed to shape and size at the curing temperature.
In comparison with the prior art processes, the method according to the invention improves both the outlay in terms of apparatus and the outlay in terms of process engineering considerably. Instead of impregnation in a bulky impregnating tank, the loading with impregnating fluid which takes place under pressure is now provided only within a casing resting comparatively closely against the conductor bar. This casing also at the same time functions as a separating foil, in order to prevent adhesion to the clamping jaws of a pressing device. In this case, in a development of the invention, the hose-like casing serving as a foil for separation from the pressing device is removed after curing has taken place, that is to say depending on the material used for the casing, being destroyed at the same time or in such a way that it can be reused.
The loading of the conductor bar with clamping jaws of a pressing device serves for ensuring the necessary accuracy of contour and dimensional accuracy during the operation of curing the impregnating fluid, whilst the intended pressing of the conductor bar may be accompanied by thermal action.
Particularly the latter-mentioned aspect has great potential for simplifying the method, since, due to curing in the press mould at increased te
Alstom
Heitbrink Tim
Warnock Russell W.
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