US 2956312 A
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H. NAIMER Oct. 18, 1960 PROCESS OF MANUFACTURING INSULATED MAGNET COILS Filed Aug. 26, 1957 O00. O00. ZQXQXQXQQQ.
R E M. mr m A I.
United, States Patent PROCESS OF MANUFACTURING INSULATED MAGNET COILS Hubert Naimer, Schumanngasse 35,
Vienna XVIII, A
This invention relates to the problem of the inexpensive mass production of magnet coils for electrical equipment, e.g. for switchgear such as contractors and the like, which coils are surrounded on all sides with an insulating covering. It is an object of the invention to provide a process whereby a coil which is stable in shape, absolutely tight and preferably suitable for tropical conditions can be obtained with smaller expense than by previously known methods.
In order to produce coil bodies which are enclosed on all sides and are stable in shape it has already been proposed to embed the coil bodies in thermosetting synthetic resins or in cast resins. In most cases the covering material should not penetrate between the several turns because this would adversely alrect the electrical properties of the coil. In order reliably to prevent such penetration of the winding the covering must not be applied by dipping processes whereby the coil is impregnated with insulating material. Whereas thermosetting synthetic resins of the phenolic type give a covering which is very rigid in shape it is very difficult to form a thin-walled casing from this material while preserving the winding unless a composite housing is accepted; in the latter case the sealing of the joints between the several housing parts involves difliculties.
It has also been proposed to provide windings with a covering of rubber, which is vulcanized on the winding. The coils thus obtained, however, are not sufficiently stable in shape for many purposes and the process of manufacture is complicated.
Processes are also known for injection-molding fusible materials around wound capacitors. Whereas these processes provide complete enclosures for protection against atmospheric influences, the bituminous materials used for this purpose do not provide particularly high strength. It has also been proposed to enclose small electric components such as resistors in a bipartite plastic housing and then tightly to seal the joints between the housing parts with a similar plastic material. This process is also complicated. Where these known processes are applied to coils, a coil former is wound first and the resulting structure is then covered as a whole with insulating material or the former is removed from the coil and the latter is covered alone. In both cases the interstices between the turns may or may not be filled with insulating material. If the coil former is embedded in the covering the insulating material may accumulate at points where this is undesirable. The provision of a covering on former-less coils by dipping or other methods is less suitable for rational mass production because special precautions must be taken to preclude a deformation during the covering step.
The invention avoids these disadvantages by winding a coil former which consists of thermoplastic material and injection-molding a covering which consists also of thermoplastic material around the resulting coil to enclose the previously exposed portions of the winding and to cause said coil former and covering to fuse together in their areas of mutual contact.
This affords the following advantages: Where modern commercial thermoplastics are employed which are particularly suitable for the present purpose the practice of the invention provides a coil body which is very stable in shape, having high strength, and which has a covering that is actually homogenous in the sense that it does not differ from a covering obtained in a single operation. Examples of such thermoplastics will be mentioned hereinafter. Because the coil former becomes a part of the covering which encloses the coil the covering of the resulting coil may be relatively thin, particularly where it engages the iron core, whereas the coil has nevertheless high strength and can be produced by a simple method which lends itself to mass production.
The accompanying diagrammatic drawing serves to illustrate the present process of manufacture. The upper half of the drawing shows the wound, but uncovered coil former; the lower half shows the finished coil. Both halves of the coil are shown in section.
The coil former consists of a tubular portion 2 and a single flange 3 integral therewith. This shape is distinguished by simplicity. The coil former 2, 3 consists preferably of a polyamide-base plastic, particularly of a superpolyamide-base plastic. This thermoplastic material has very desirable mechanical properties, is absolutely moisture-proof and may be considered suitable for tropical conditions. This former is wound in the usual manner. For this purpose the fiangeless end of the inner part 2 may be mounted on a disc 4, which either remains permanently in the finished coil body or is removed before the subsequent injection molding of the outer covering. The resulting coil consisting of the parts 2, 3, optionally disc 4, and the magnet winding 5 is then placed in an injection mold where it is provided with the covering 6; this covering is shown in the lower half of the drawing and consists of the second flange and an outer shell. The temperature of the molten plastic entering the mold is so high, as a rule, that the solid portions of the coil former become readily fused at the points where they are contacted by the molten material. This is desirable for a good joint between the covering parts. According to another feature of the invention, grooves or recesses 7 or undercuts 8 may be formed at the previously existing covering portions 2, 3 in order to obtain a joint which has also suflicient mechanical strength even if adjoining housing parts should only superficially fuse together. In this way a seamless transition between the previously existing parts of the covering and those parts of the covering which are formed only in the mold can be ensured.
Another advantage of the process according to the invention resides in the fact that the outer covering may be injection-molded with projections or embedded parts. For instance, an extension can be provided which may subsequently serve for fixing the coil in the electrical equipment. It is also possible, for example, to embed the terminals 10 connected to the winding ends in the resulting covering portion, e.g., in the flange 6. Such embed ding steps are known per se.
It has already been stated that superpolyamide type plastics are highly suitable for the present purpose although the invention is not restricted to the use of plastics of this type. If supporting projections like the projection 9, wherein other parts such as fixing screws or the like may be embedded, are not desired, it is possible to use thermoplastics which do not have the strength of superpolyamides but have satisfactory electrical properties and are resistant to moisture or suitable for tropical conditions. Such thermoplastics could be based, e.g., on polyvinyls. A coil body obtained with such a covering,
Patented Oct. 18, 1960 however, will not have that stability of shape which can be achieved where superpolyamides are employed.
It should be noted that the parts 2, 3 and 6 need not be made of the same material. For some applications it will be suflicient to make a part which provides the rigid shape, e.g. the portions 2 and 3, from harder and stronger material Whereas the complementary other part of the covering, eg the part 6, has only the function of an envelope. It is essential, however, that these different materials can be fused together to form a housing having integrally merged portions. In this connection the above-mentioned profiled portions 7, 8 have also proved desirable.
1. A process for manufacturing an insulated magnet coil, comprising the steps of molding a tubular thermoplastic coil former with a single flange at one end and with an annular recess on the outer face of said flange, placing on said former a coil winding in contact with said flange, and molding a second flange and a peripheral covering of thermoplastic material around said winding and around portions of said coil former including the circumference of the first-mentioned flange so as to fill said recess and thus result in interlocking engagement therewith and at a temperature sufficient to soften said 4 portions whereby said covering, said flanges and said coil former are fused into a unitary housing.
2. A process for manufacturing an insulated magnet coil, comprising the steps of molding a tubular coil former of polyamide-base plastic material with a single flange at one end and with an annular recess on the outer face of said flange, placing on said former a coil winding in contact with said flange, and molding a second flange and a peripheral covering of like polyamide-base plastic material around said winding and around portions of said coil former including the circumference of the first-mentioned flange so as to fill said recess and thus result in interlocking engagement therewith whereby, through a softening of said portions in the molding step, said covering, said flanges and said coil former are fused into a unitary housing.
References Cited in the file of this patent UNITED STATES PATENTS 2,624,526 Green Jan. 6, 1953 2,683,572 Morin July 13, 1954 2,773,657 Morin Dec. 11, 1956 FOREIGN PATENTS 578,024 Great Britain June 12, 1946