Plastic and nonmetallic article shaping or treating: processes – With step of making mold or mold shaping – per se
Reexamination Certificate
1999-09-27
2001-04-24
Ortiz, Angela (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With step of making mold or mold shaping, per se
C264S272190, C029S605000
Reexamination Certificate
active
06221297
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method of manufacturing transformer windings embedded in casting resin and more particularly to a method of manufacturing a transformer coil encapsulated in casting resin wherein the disposable mold acts both as a winding mandrel and as an inner mold shell for resin encapsulation. The invention is particularly suited to the manufacture of low voltage non-standard oval shaped or circular shaped epoxy encapsulated coils for dry type distribution transformers.
2. Description of the Prior Art
Currently the state of the art is precision made standard sized re-usable round shaped mandrels and molds in fixed size increments. Examples of prior art methods of encapsulating transformer coils are disclosed in U.S. Pat. Nos. 4,337,219, 4,540,536, 5,036,580 and 5,633,019.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a method of manufacturing a low voltage transformer coil utilizing a molding process with an integrated winding mandrel for producing a non-standard oval or circular shaped epoxy encapsulated low voltage coil for dry type distribution transformers. The process includes winding a circular or oval coil over a disposable mold which acts as both a winding mandrel and as an inner mold shell for epoxy encapsulation. It is an object of the invention to make the inner and outer molds of low cost sheet metal. The invention process has many advantages over conventional fixed size standard winding mandrels and casting molds. Among the features and advantages of the present invention are the use of low cost sheet metal in a “wrap and band” process to form a flexible sized oval or round mandrel and mold. The complete winding and molding processes can all be conducted on a standard winding machine. The invention process provides the advantages of flexible oval or round dimensional sizes, flexible and incremental oval or round shapes providing substantially reduced mandrel and molding costs, elimination of costly standard mold storage, elimination of the need for standard winding mandrels, controlled epoxy thickness for increased dielectric strength and reliability, improved manufacturer ability, reduction in epoxy cost, and facilitates the opportunity to manufacture transformer coils in a round to oval configuration.
In accordance with the foregoing objects and advantages, the present invention provides a method of manufacturing a transformer coil encapsulated in a casting resin utilizing a disposable casting mold comprising the steps of forming an annular mandrel by applying to a mandrel shaft, a plurality of annular shaped support plates spaced on the shaft. The method further includes the step of forming a disposable inner mold by wrapping sheet metal over the annular shaped support plates during the winding set up process to produce an integrated winding form/mandrel/inner mold for use in the winding process and placing the integrated winding form/mandrel/inner mold in a winding machine. The method further includes the step of winding a coil around the inner mold while in the winding machine and forming an outer mold by wrapping a plurality of sheet metal layers over the finished coil and mechanically attaching the layers to the finished coil with glass adhesive tape to hold the sheet metal in its starting position. The method further includes the step of spirally wrapping non-adhesive glass tape over the outer mold to secure it in position and completing the outer mold by banding the outer mold with banding strip in a plurality of spaced positions and removing the manufactured coil and mold assembly from the winding machine. The method further includes the steps of up righting of the coil and mold assembly and attaching a base thereto, providing a seal between the base and the coil and mold assembly to prevent epoxy leaks during the encapsulation process, and filling the mold with epoxy to encapsulate the coil with casting resin.
In accordance with a further aspect of the invention the disposable inner mold is formed by three overlapping layers of sheet metal attached to the inner mold support plates so that the sheet metal can be tightly wrapped around the inner mold support plates thereby eliminating and metal slippage during the wrapping process, securing the wrapped sheet metal in place with non-adhesive tape temporarily, wrapping plastic tape over the entire length of the wrapped inner mold to provide sealing of the wrapped inner mold for the subsequent epoxy encapsulation process, and applying a mold release agent over the plastic tape to eliminate epoxy adhesion thereby simplifying the mold removal process thus completing the integrated form/mandrel/inner mold so that it is ready for the winding process.
For a more detailed disclosure of the invention and for further objects and advantages thereof, reference is to be had to the following description taken in conjunction with the accompanying drawings.
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Lambert Wayne
Lanoue Thomas J.
Sarver Charles
ABB Power T&D Company Inc.
Ortiz Angela
Woodcock Washburn Kurtz Mackiewicz & Norris
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