Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including interlaminar mechanical fastener
Patent
1994-01-05
1995-11-28
Withers, James D.
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including interlaminar mechanical fastener
156162, 156164, 156182, 427116, 427379, 427381, 427386, 4273897, 427402, 42740703, 428251, 428246, 428902, B32B 3108, B32B 700, B05D 512, B05D 136
Patent
active
054706475
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION
The invention concerns a compressible prepreg based on flat substrates impregnated with thermosetting synthetic resins, further a method for its manufacture and its application.
BACKGROUND OF THE INVENTION
Such prepregs are used when making electrical insulation for transformer windings and as a rule consist of a substrate, for instance a fiberglass fabric impregnated with a thermosetting synthetic resin.
When manufacturing said insulation, these prepregs are deposited for instance in tape form on a metal strip and while applying high tension are wound on a mandrel which then is moved into a heated oven. The prepreg synthetic resin in the B stage is then converted at these higher temperatures into the C stage. However, this metal-prepreg compound being under high tension, it may happen, especially where the metal sites are uneven, that the resin will flow out of the fiberglass fabric before curing, as a result of which unimpregnated layers of fiberglass will be present between the metal layers. In that case, shorts will occur at the first use of the transformer windings.
SUMMARY OF THE INVENTION
Accordingly it is the object of the invention to create a compressible prepreg of the initially cited kind which when used as electrical insulation will be free of the above drawbacks.
The prepreg of the invention is characterized in that it comprises a first layer of synthetic resin in the C stage which is directly deposited on the flat substrate and a second layer of synthetic resin in the B stage which is deposited on the first layer of synthetic resin.
The invention offers the further advantage that the flat substrate for the prepreg is an organic-fiber fabric where said fibers are aramide fibers.
In another embodiment of the invention, the flat substrate for the prepreg is a web of inorganic fibers which are glass fibers.
Yet another advantage of the invention is that the prepreg comprises a substrate in the form of organic fibers which are aramide fibers.
Still another advantageous embodiment of the invention is that the flat prepreg support is a web of inorganic fibers, said inorganic fibers being glass fibers.
Yet another advantage of the invention is that the thermosetting synthetic resin is an epoxy resin or a polyester resin.
The prepreg of the invention is manufactured by a method characterized in that the flat substrate is moved into a first bath filled with a solution of curable synthetic resin, in that this impregnated substrate is made to pass over several direction-changing rollers in a heating zone during which the synthetic resin is converted into the C stage and in that thereupon this compound moves through a second bath filled with a solution of curable synthetic resin, in the course of which a second adhesive layer of synthetic resin is formed on the compound, and in that this second layer of synthetic resin then is converted into the B stage.
The invention further concerns the application of a prepreg to insulating coils of electrical machinery, the synthetic resin of the second layer of synthetic resin also being converted into the C stage.
DESCRIPTION OF DRAWINGS
The manufacture of the prepreg of the invention is illustratively carried out using equipment shown in FIGS. 1 and 2.
FIG. 1 shows impregnation apparatus consisting of two baths and an impregnation tower.
FIG. 2 shows a winding device for a metal foil and the prepreg of the invention, where called for followed by an oven.
DETAILED DESCRIPTION OF THE INVENTION
Illustratively impregnation to manufacture the prepreg of the invention can be carried out with the apparatus shown in FIG. 1.
Illustratively a fiberglass fabric 2 is taken off the supply roll 1 and moved over a drive roller 3 to a deposition roller 4. The deposition roller 4 dips into a bath 6 filled with a solution of curable synthetic resin 5. The synthetic-resin solution 5 may consist for instance of epoxy resins dissolved in ketones, their temperature being kept at ambient during impregnation. Thereupon the compound 7 comprise
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patent: 3881978 (1975-05-01), Livingston et al.
patent: 4024305 (1977-05-01), Alpaugh et al.
patent: 4447797 (1984-05-01), Saunders et al.
patent: 4803101 (1989-02-01), Roberts et al.
patent: 5212234 (1993-05-01), Van Gasse et al.
Patent Abstracts of Japan, vol. 11, No. 94 (M-547) (2541), JP 61-246050 dated 1 Nov. 1986, Shin Kobe Electric Mach. Co., Ltd.
Orthofer Willibald
Zimics Bela
Isovolta Osterreichische Isolierstoffwerke Aktiengesellschaft
Withers James D.
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