A MAGNETIC CIRCUIT OR PART OF A MAGNETIC CIRCUIT AND A METHOD FOR PREPARATION THEREOF

Abstract: A magnetic circuit or part of a magnetic circuit and a method for the preparation thereof. Said magnetic circuit comprises a sheet pack assembled from sheet pieces. In order that a crystal-oriented armature sheet could be used without the need of termal treatment, the sheet pieces are pre-designed with bending points (k) and the matching bending points of adjacent sheets are set on the same line (1) about which the sheets of a sheet pack are bent.

Description: A magnetic circuit or part of a magnetic circuit and a method .or preparation thereof. The present invention relates to a magnetic circuit or part of a magnetic circuit, consisting of a sheet pack built up by sheet pieces. The invention is also directed to a method for the preparation of a magnetic circuit of part of a magnetic circuit by building a sheet pack from sheet pieces. A magnetic circuit of the invention or a part thereof is intended for use as magnetic cores of ballasts or transformers but it can also be incorporated in other machines which employ magnetic circuits. It is known in the art that, when using a crystal- oriented transformer sheet, the core packs must be prepared by making the magnetic flux in a core parallel to the sheet rolling direction. This can be effected e.g. by laying the sheet pieces into a sheet pack, as shown in fig. 1. In an O-ring, this leads to four sheet pieces. Manufacturing of such sheet pieces to precision measurements generally leads to material losses and, furthermore, a great number of sheet pieces results in high manufacturing costs. This has limited the use of such sheet cores especially in light-duty transformers or ballasts. Another prior art approach is to prepare a magnetic core from a band of sheet by winding (fig. 2). uring the winding of a core, the iron losses of a crystal- oriented sheet material increase and, therefore, it is virtually always necessary to subject them to thermal treatment. If the core of a ballast is manufactured by employing this method, the ring core must be sawn open to form an air gap. These factors add considerably to the manufacturing costs of such cores. An object of the invention is to provide a magnetic circuit or a part thereof by means of which a magnetic core can be manufactured from few sheet pieces, so that the cold working of sheets is as little as possible, whereby the sheet packs need not be heat treated thus resulting in considerably lower manufacturing costs. This object is achieved on the basis of the inventive characteristic features set out in the annexed claims. The invention will now be described with reference made to the accompanying drawings, in which fig. 1 shows an O-core assembled from four individual sheet packs and figs. 2a and 2b show ring cores assembled from a sheet band by winding in order to illustrate the prior art, Fig. 3 shows a variety of alternatives a - j for providing the sheets with a bending point k. Fig. 4a shows a sheet pack assembled from sheet pieces accord ing to the invention prior to the bending and fig. 4b shows a sheet pack after the bending. Fig. 5 is a plan view of a sheet piece provided with three bending points k. Fig. 6 shows a ring core according to one embodiment of the invention. Figs. 7a - d illustrate a variety of alternatives for assembling a ring core by the method of the invention. Figs. 8a - f, 9a and 9b as well as 1Oa - f illustrate a variety of further alternatives for assembling a ring core by the method of the invention. Fig. 11 shows one embodiment of a ring core assembled by the method of the invention. Fig. 12 shows a ballast or transformer core which is assembled from ring cores prepared by the method of the invention. A method of the invention is used to manufacture or prepare the magnetic circuit of a ballast or a transformer by producing sheet pieces of suitable length and by providing them with bending points k, as shown in fig. 5. Each sheet piece is provided with a necessary number of bending points so as to obtain a magnetic circuit of desired shape by bending at these points. Said bending points can be made as continuous grooves (figs. 3a, 3c, 3d, 3e, 3f, 3g and 3j) or discontinuously by leaving some intact sheet between (3b, 3i). When the bending points of adjacent sheets are located on the same line 1 (fig. 4), such a sheet bundle can be readily bent all at once to a desired angle. In a preferred embodiment of the invention, the bending point comprises a V-groove (fig. 3c) or an obtuse V-groove (fig. 3j), the sheets being laid as shown in fig. 4a on top of each other in a manner that one side of the V-grooves sets on line 1 which forms with the normal of said sheets an angle b which is half of an angle a1 between the sides of V-grooves. In other words, a 1 = 2 x ss . Thus, said angle a1 between the sides of V-grooves facilitates the bending of sheets or the entire sheet pack to an angle a2 (fig. 4b) so that, for a good magnetic joint, angle a2 is equal to or greater than al. A tight joint ensures quite slight additional losses and it should further be noted that working of the sheets only effected within a small area at the bending point, so ending of a sheet does not lead to the increase of iron losses elsewhere. The bending can also be left unfinished, i.e. a 2 1S smaller than a if the magnetic resistance of a circuit is to be increased. The sheets can also be bent one by one or as smaller bundles prior to stacking them into a finished sheet pack. The magnetic resistance of a bending point can also be increased by other suitable bending point designs, e.g. by making holes in the bending point of the sheets (fig. 3i). The bending point can also be designed by cutting a sheet to form partially cut-off tongues (fig. 3h). In view of the above it is possible to understand how the ring cores shown in figs. 6, 7, 8 and 9 are prepared by bending the sheet packs at one or more bending points k designed according to the invention. The opposite end faces of a sheet pack have been designated with reference p. In fig. 9, the ring core is closed by means of a separate sheet bundle R positioned at the end of a U-pack. In the embodiment of fig. 8, the annular magnetic cores have been made of two U-shaped sheet packs which, in turn, are prepared by utilizing bending points k designed according to the invention. The ends p of U-packs have been designed to fit each other and are positioned against each other. The embodiment shown in fig. 10 only differs from that of fig. 8 in the sense that the arms of U-packs are of different length and their oppositely fitted faces p are located symmetrically relative to center 0. In the embodiment shown in fig. 11, the annular magnetic core consists of two L-shaped sheet packs, each of those having been made by utilizing the bending points k made according to the invention. The sheet lengths have been selected so that the opposite faces p fit against each other. The above designs of ring cores are characterized in that, prior to the final closing of a ring, a winding can be fitted around the ring arm. The ring cores designed according to the invention can be placed parallel to each other in order to form the magnetic core of a ballast or a transformer, as shown in fig. 12.

Claims: Claims 1. A magnetic circuit or part of a magnetic circuit, comprising a sheet pack assembled from sheet pieces, c h a r a c t e r 1 z e d in that the sheet pieces are provided with predesigned bending points (k) and the corresponding bending points of the adjacent sheets of a magnetic circuit or a part thereof lie on the same line (1), the sheets of a sheet pack being bent about said line. 2. A magnetic circuit or part of a magnetic circuit as set out in claim 1, c h a r a c t e r i z e d in that the sheets of a sheet pack are made of crystal oriented armature sheet. 3. A method for the preparation of a magnetic circuit or part of a magnetic circuit as set forth in claim 1 or 2 by assembling a sheet pack from sheet pieces, c h a r a c t e r i z e d in that for making a sheet pack said sheet pieces are pre-provided with bending points (k) and the matching bending points of the adjacent sheets of a magnetic circuit or its part are set on the same line (1) (figs. 5 and 4a), the sheets of said sheet pack being bent about that line. 4. A method as set forth in claim 3, c h a r a c t e r i z e d in that said pre-designed bending point (k) is made by providing each sheet with a groove. 5. A method as set forth in claim 4, c h a r a c t e r i z e d in that each sheet is pre-designed with a V-groove or an obtuse V-groove, with an angle (a1) between the sides thereof substantially corresponding to that angle (a2) to which the sheets of a sheet pack are bent. 6. A method as set forth in claim 3, 4 or 5, c h a r a c t e ri z e d in that an annular magnetic core is so prepared that a ring-forming sheet pack is provided with one or more bending points (k) and that some of the pre-designed bending points of a sheet pack are bent for closing said ring only after fitting on a winding, so that the contacting faces (p) of a sheet pack set against each other or at a desired distance from each other (fig. 6; figs. 7a and 7b; figs. 7c and 7d). 7. A method as set forth in claim 3, 4 or 5, c h a r a c t e ri z e d in that an annular magnetic core is assembled from two U-shaped sheet packs in a manner that each U-pack is provided with two or more bending points (k) and that the ends (p) of U-packs are designed so as to fit against each other (figs. 8a-f). 8. A method as set forth in claim 3, 4 or 5, c h a r a c t e ri z e d in that an annular magnetic core is assembled from one U-pack provided with two or more bending points (k) and that for closing the ring the end of a U-pack is fitted with a separate sheet bundle (R) (figs. 9a and b). 9. A method as set forth in claim 3, 4 or 5, c h a r a c t e ri z e d in that an annular magnetic core is assembled from two identical U-packs whose faces (p) to be fitted against each other are of identical shape and positioned symmetrically relative to the center (0) (figs. 10a - f). 10. A method as set forth in claim 3, 4 or 5, c h a r a c t e ri z e d in that an annular magnetic core is assembled from two L-shaped sheet packs provided with one or more bending points and whose faces (p) are designed so as to fit against each other (fig. 11). 11. A magnetic core for a ballast or a transformer, wherein use is made of a magnetic circuit as set forth in claim 1 or 2, said circuit being assembled by method as set forth in any of the preceding claims 6 - 10, c h a r a c t e r i z e d in that two annular cores are positioned adjacent to each other (fig. 12).

Inventors: LILJA, PERTTI
Applicants: OY HELVAR
Application year: 1983
Main classification: H01F41
IPC codes: H01F27, H01F41