Patent GB-742413-A (GB)
Title: Improvements relating to methods of manufacturing insulated electrical apparatus
IPC: H01F27/32
Filed: 1953-05-22
Abstract: 742,413. Electric coils; transformers. REYROLLE & CO., Ltd., A., and MOSERGLASER & CO., AKT.-GES. May 22, 1953 [May 23, 1952], No. 14510/53. Classes 35 and 38 (2). [Also in Groups V and XXXVI] An article of electrical equipment is made by centrifugally casting an insulating moulding of thermosetting synthetic resin around one or more electrical components supported in a rotating mould so that the components become embedded in the insulating moulding, the resin solidifying by polymerization or condensation in the rotating mould during the centrifugal casting operation. The material may be cast in a mould and then removed from the mould with the embedded component(s); or a part of the finished article may be used as a part or the whole of the mould, and this part of the article may be either a conducting part or a part of insulating material, e.g. porcelain or synthetic resin. Fig. 1 shows a rotary mould 1 to the interior of which is secured an electrical coil 2 which during casting is embedded in a synthetic resin cylinder 3. The resin may be fed into the mould as a thermosetting liquid which will later be polymerized, or a thermosetting condensation type resin may be used. The mould is spun, the required amount of resin is fed in and rotation is continued whilst the resin is solidified by polymerizing or condensation. In the case of a polymerizable resin heat may be applied to the material and the mould, or the material itself may contain catalysts which favour the polymerization process; or a special gas atmosphere may be used for this purpose. In the case of a condensation resin the mould and the material are heated. In a modification (Fig. 2, not shown) the coil 2 is embedded in the interior surface of the cylinder. In a second modification the mould of Fig. 2 is replaced by a pre-cast synthetic resin tube which forms part of the finished article. In a third modification (Fig. 3, not shown) two coils are embedded coaxially in the cylinder; curing may be completed outside the mould. Fig. 4 illustrates another modification, in which two separate cylinders 3, 6 are made, each cylinder incorporating a coil 9, 10. The cylinders are cast with an intervening layer 11 of wax or soluble material, which is removed after casting. Fig. 6 shows the high-voltage winding 20 of a transformer embedded in a cylinder having cupshaped projections 19 through which pass conducting leads 21. Balancing cups 19a are cut away after moulding; or the balancing cups may be dispensed with. Fig. 7 shows a high-voltage transformer comprising a test-tube like body 27 having a tapered wall in the outside of which is embedded a coil 25. The variation in the wall thickness of the body 27 (due to the vortex formed in the vertically-rotating liquid material before it solidifies) corresponds closely to the voltage distribution along the length of the coil 25, so that the insulation stress remains constant. After moulding, the inner and outer surfaces 26, 28 of the body 27 are coated with conducting material and an iron core 29 carrying a low-voltage winding 30 is inserted into body 27 to complete the transformer, which in use is inverted from the position shown. Fig. 8 shows a bus-bar support comprising an insulator 35 having a metal insert 32 embedded therein, made in a mould 31, the top of which is closed by a base plate 34 which will form the base of the finished support. The interior of the mould may be kept under a vacuum, or inert atmosphere, to inhibit bubbles and prevent oxidation, or, when a condensation type of resin is used, under pressure to remove volatiles. The fluid moulding material may comprise a mixture of different materials of equal or differing specific gravities; e.g. a mixture of liquid and solid particles. Thus, if the dielectric constant of a completed article is to be greater in the outer layers than in the inner, the fluid material may contain solid particles having a higher dielectric constant and a higher specific gravity than the liquid, these particles being flung to the outside of the article; such an article may be a high-voltage component having a condenser plate embedded therein. Cavities may be formed in the components by removable filling pieces. Pre-solidified packing pieces of insulating material may be used to fill holes in components before casting, e.g. the space within the windings of an electrical coil. Several articles may be embedded simultaneously in one mould, varnished or other spacing members non-adherent to the resin being used to keep them separate.