GB2075273A - Magnetic cores, methods of and components for making them and electromagnetic apparatus incorporating the cores - Google Patents

Abstract

A magnetic core comprises at least two sub-units 1, 2 built up of substantially rectangular laminations 3, 4, 5, in which the laminations are secured together in such relative positions that at least at one end of each said sub-unit, the ends of the laminations lie in two distinct zones such as the planes P and Q or R and S spaced apart in the direction of length of the rectangles and in which the laminations at the cooperating ends of two sub- units are interdigitated. Identical laminations have notches spaced along one edge, so that by displacing alternate laminations by the notch spacing correct alignment is achieved. Stacks of laminations are secured by heat shrinkable bands 19, and a jig 16 facilitates the assembly. <IMAGE>

Description

SPECIFICATION Magnetic cores, methods of and components for making them and electromagnetic apparatus incorporating the cores This invention relates to magnetic cores for transfor meres, inductors, and other electromagnetic apparatus which comprise a number of laminations assembled together.

It is well known to assemble the magnetic cores from laminations stamped into E- and I-shapes. The tooling for manufacturing these laminations is becoming very expensive. Rectangular laminations assembled individually are sometimes used, but this is expensive in labour utilisation.

It has been proposed that magnetic cores might be made from blocks of rectangular laminations secured together which are assembled together so as to form butt joints between the blocks. This requires machined joint faces if a low reluctance is to be achieved.

According to the invention a magnetic core comprises at least two sub-units built up of substantially rectangular laminations, in which the laminations are secured together in such relative positions that at least at one end of each said sub-unit the ends of the laminations lie in two distinct zones spaced part in the direction of length of the rectangles and in which the laminations at the said end of two said sub-units are interdigitated.

Preferably at said end of said sub-units, the ends of the laminations lie some in one and some in the other of two different planes each substantially perpendicular to the length of the rectangles.

Usually these two sub-units will be at right angles to one another in the assembly.

In most cases, the sides of the laminations in each one of the sub-units will be aligned, though this is not essential in every case, and for example a sub-unit with a cross-section differing from a rectangle could be made with rectangular laminations of different widths.

The arrangement of the lamination ends in the sub-units may be such that the ends of no two contiguous laminations coincide, or the ends of small groups of neighbouring laminations (two's or three's for instance) may coincide.

A sub-unit may be built up of substantially identical laminations such that at each end of the sub-unit the ends of the laminations lie in two distinct zones, spaced apart in the direction of length of the rectangles. Alternatively, the same result can be achieved using laminations of two different lengths for assembling a sub-unit.

Preferably the laminations of a sub-unit are secured together by at least one sleeve, for example a sleeve of heat-shrink material which is shrunk into position, which passes around the laminations. In this case, each lamination of the sub-unit preferably has at least one indentation in one side so that the assembled sub-unit has at least one row (and preferably at least two rows) of aligned indentations in one side in which a sleeve is positioned to restrict its movement relative to the length of the sub-unit. In the case where the laminations of a sub-unit are substantially identical, each lamination preferably has two or more indentations in one side forming at least one row of aligned indentations in the assembled sub-unit. Where a narrow sleeve (or narrow sleeves) is used to secure the laminations, the sleeve fits within the, or one of the, rows of aligned indentations.Where a long sleeve (or long sleeves) is used, the sleeve is depressed into the or each row of aligned indentations. In this latter case the long sleeve or sleeves may also serve as an insulating covering for the sub-unit.

Alternatively the laminations may be secured together by adhesive, rivets or any other suitable alternative.

Preferably each lamination has a closed slot at each end. The slots are preferably rectangular with their longitudinal axis parallel to the ends of the lamination. The slots help to reduce volt-amps consumpfion by stemming the leakage flux at the corners of the magnetic core.

This invention has an advantage over cores assembled from stamped E- and I- laminations when made from grain oriented material in that the cores can be assembled with the rolling direction of the strip in the longitudinal direction in both the limbs and the yokes of the core, whereas with an Elamination either the limb or the yoke must be at 90 to the rolling direction. The cores of this invention can therefore operate at a higher flux density than conventional interleaved E-i cores, and offer a more efficient and smaller bulk design for the same output. Other advantages include easier assembly and cheaper tooling.

The invention also includes electromagnetic apparatus comprising at least one magnetic core as herein described.

The invention further includes a sub-unit built up of substantially rectangular laminations for use in a magnetic core, in which the laminations are secured together in such relative positions that at least at one end of the sub-unit the ends of the laminations lie in two distinct zones spaced apart in the direction of length of the rectangles such that the laminations at the said end of the sub-unit can interdigitate with another similar sub-unit.

Preferably at said end of the sub-unit the ends of the laminations lie some in one and some in the other of two different planes each substantially perpendicular to the length of the ractangles. In this case the spacing of the planes is preferably equal to, or half of, the maximum width of the laminations of the sub-unit to which it interdigitates; or is of the order of magnitude of the maximum width of the laminations of the sub-unit itself.

The invention further includes a method of forming a sub-unit of laminations for use in a magnetic core by positioning the laminations end-on in a jig comprising a number of spaced parallel walls defining slots, the slots being blocked at one end by stops lying in a first zone, and the ends of the walls (defining the openings of the slots) lying in a second zone, the two zones being spaced part in the direction of height of the walls; some of the laminations sliding into the slots to engage the stops so that the ends of these laminations lie in said first zone, the ends of the other laminations engaging the said ends of the walls to lie in said second zone; securing the laminations together to form the subunit; and removing the sub-unit from the jig.

The invention is further illustrated in the accompanying drawings in which: Figure 1 is an isometric sketch of part of a magnetic core in accordance with the invention; Figures 2 to 4 are diagrams illustrating the alignment of rectangular laminations; Figure 5 is an isometric sketch of laminations assembled in a jig, and Figure 6 is an isometric sketch of a jig.

Referring to Figure 1, the magnetic core includes three sub-units 1, 2 (at least one other sub-unit is omitted for clarity of illustration). The sub-units 1 are assembled from identical rectangular laminations 3 such that at each end of the sub-units the ends of the laminations lie some in one plane P and some in another plane 0, the two planes being spaced apart.

The sub-unit 2 is assembled from short rectangular laminations 4 and long rectangular laminations 5 such that at each end of the sub-unit the ends of the short laminations lie in plane Rand the ends of the long laminations lie in plane S, the two planes being spaced apart. The widths of the short laminations 4 and the long laminations 5 are the same, and the width equals the distance between plans P and Q.

Similarly, the width of laminations 3 equals the distance between planes R and S. All the laminations 3, 4, 5 of each sub-unit 1, 2 are secured together by a suitable adhesive. The ends of the sub-units 1,2 are assembled together by interdigitation of the lamina tions3,4,5.

Figure 2 shows a rectangular lamination 6 which has four indentations 7 in one side. A similar lamination 61 shown in dotted outline illustrates how such laminations in a sub-unit can be off-set from one another to form two rows of aligned indentations 8. Similarls Figure 3 shows how laminations 9, 91 having two indentations 10 can be off-set to form one row 11 of aligned indentations, and Figure 4 shows how laminations 12, 121 having three indentations 13 can be offset to form two rows 14 of aligned indentations. The laminations 6, 61 shown in Figure 2 also have closed rectangular slots 24, 241 at each end, which help stem the flux leakage at the corners of a magnetic core assembled from these laminations.

Figure 5 shows identical rectangular laminations 15 assembled in a jig 16 (similar to that shown more clearly in Figure 6). Each lamination 15 has three indentations 17 (as shown in Figure 4) in one side so that when the laminations are off-set from one another as shown two rows 18 of aligned indentations are formed. The laminations 15 are positioned endon in the jig 16 and vibrated so as to finish in the assembly shown, after which two short heatshrinkable sleeves (shown in part) 19 are positioned around the laminations 15 and shrunk so that one shrinks into one of the rows 18, and the other shrinks into the other row. In this way the sleeves 19 are restricted from moving relative to the length of the laminations 15 and the laminations 15 are secured together to form a sub-unit 20. The sub-unit 20 is then removed from the jig 16.

The jig 21 shown in Figure 6 comprises a number of spaced parallel walls 22 defining slots 23. The slots are blocked at the bottom by a base plate (not shown) fitted to the jig 21. The upper surface of the base plate defines a plane for one end of some of the laminations of a sub-unit assembled in the jig 21.

The top end of the walls 22 define another plane for one end of the other laminations of the sub-unit. The jig 21 can be modified for assembling sub-units in which the ends of the laminations lie in two distinct non-planer zones by placing stops of varying heights in the slots 23 of the jig and by adding blocks of varying heights to the top ends of the walls 22.

Claims (21)

1. A magnetic core comprising at least two sub-units built up of substantially rectangular laminations, in which the laminations are secured together in such relative positions that at least one end of the said sub-unit the ends of the laminations lie in two distinct zones spaced apart in the direction of the length of the rectangles and in which the laminations at the said end of two said sub-units are interdigitated.

2. A magnetic core comprising at least two sub-units built up of substantially rectangular laminations, in which the laminations are secured together in such relative positions that at least at one end of each said sub-unit the ends of the laminations lie in one and some in the other of two different planes each substantially perpendicular to the length of the rectangles and in which the laminations at the said end of two said sub-units are interdigitated.

3. A magnetic core as claimed in Claims 1 or 2 in which the interdigitated sub-units are at right angles to one another.

4. A magnetic core as claimed in any one of the preceding claims, in which the ends of no two continuous laminations coincide.

5. A magnetic core as claimed in any one of Claims 1 to 3, in which the ends of small groups of neighbouring laminations coincide.

6. A magnetic core as claimed in any one of the preceding claims, in which one or more of said sub-units is built up of substantially identical rectangular laminations such that at each end of the or each sub-unit, the ends of the laminations lie in two distinct zones spaced apart in the direction of length' ofthe rectangles.

7. A magnetic core as claimed in any one of the preceding claims, in which one or more of said sub-units is built up of rectangular laminations of two different lengths such that at each end of the or each sub-unit, the ends of the laminations lie in two distinct zones spaced apart in the direction of length of the rectangles.

8. A magnetic core as claimed in any one of the preceding claims, in which the laminations of a sub-unit are secured together by at least one sleeve which passes around the laminations.

9. A magnetic core as claimed in Claim 8, in which each lamination of the sub-unit has at least one indentation in one side so that the assembled sub-unit has at least one row of aligned indentations in one side in which a sleeve is depressed, or within which a sleeve fits, to restrict its movement relative to the length of the sub-unit.

10. A magnetic core as claimed in Claim 9, in which the laminations of a sub-unit are substantially identical, and in which each lamination has two or more indentations in one side forming at least one row of aligned indentations in the assembled subunit.

11. A magnetic core as claimed in any one of the preceding claims, in which each lamination has a closed slot at each end.

12. A magnetic core as claimed in Claim 11, in which each slot is rectangular with its longitudinal axis parallel to the ends of the lamination.

13. Electromagnetic apparatus comprising at least one of the magnetic cores as claimed in any one of the preceding claims.

14. A sub-unit built up of substantially rectangu lar laminations for use in a magnetic core, in which the laminations are secured together in such relative positions that at least at one end of the sub-unit the ends of the laminations lie in two distinct zones spaced apart in the direction of length of the rectangles such that the laminations at the said end of the sub-unit can interdigitate with another similar sub-u nit

15. A sub-unit as claimed in Claim 14, in which at said end of the sub-unit the ends of the laminations lie some in one and some in the other of two different planes each substantially perpendicular to the length ofthe rectangles.

16. A sub-unit as claimed in Claim 15, in which the spacing of the planes is of the order of magnitude of the maximum width of the laminations of the sub-unit.

17. A method of forming a sub-unit of laminations for use in a magnetic core by positioning the laminations end-on in a jig comprising a number of spaced parallel walls defining slots, the slots being blocked at one end by stops lying in a first zone, and the ends of the walls (defining the openings of the slots) lying in a second zone, the two zones being spaced apart in the direction of height of the walls; some of the laminations sliding into the slots to engage the stops so that the ends of these laminations lie in said first zone, the ends of the other laminations engaging the said end of the walls to lie in said second zone; securing the laminations together to form a sub-unit; and removing the sub-unit from the jig.

18. A magnetic core as hereinbefore described, with reference to Figures 1 to 5 of the accompanying drawings.

19. Either of the sub-units shown in Figure 1 of the accompanying drawings.

20. The sub-unit shown in Figure 5 of the accompanying drawings.

21. A method of forming a sub-unit as hereinbefore described, with reference to Figures 5 and 6 of the accompanying drawings.