GB2129622A - Magnetic cores - Google Patents

Abstract

A magnetic core for a transformer, inductor, etc. is separable into two parts for assembly with an electrical winding and after assembly is secured together by a clip (for example, an EK-core or an EI-core). The clip comprises two interfitting parts 2 that together encircle the core, and at least one of the parts is resilient and is deformed when the parts are assembled to provide a biasing force urging the parts of the core together; e.g. in the case of a sheet metal clip, the base may be bowed inwardly. Each of the parts of the clip is shaped to engage and hold the corresponding part 1 of the core, independently of any other parts, and this provides the sole means by which the laminations of the core part are held together. <IMAGE>

Description

SPECIFICATION Magnetic cores This invention relates to magnetic cores for transformers, inductors, and other electrical apparatus. More specifically it relates to cores of the kind that are separable into two parts for assembly with an electrical winding and after assembly are secured together with a clip. The invention is primarily, but not exclusively, directed to the cores known as "Ecores" or "EK-cores" and "El-cores" in which at least one of the parts is formed by a stack of laminations of magnetic material that are generally E-shaped, the laminations of the other part being either also generally E-shaped or else generally I-shaped so that the parts, when assembled, form a core of generally rectangular shape with three parallel limbs spaced by two windows.

The preferred current practice is for this type of core to be securely bonded together with suitable adhesive, though formerly loose laminations were used and were held in position only by the coil bobbin and the external clip applied after final assembly; a cost-cutting expedient that has sometimes been used is to secure loose laminations temporarily using sticky tape.

Clips for use with this type of core are usually made of nickel-silver or other suitable resilient sheet metal bent to a general channel shape corresponding to three sides of the rectangular core shape and with inturned flanges on the free ends of the limbs to engage the fourth side. The base of the channel is bowed inwardly to provide a spring force urging the parts of the core together, and inturned tabs may be placed round the periphery to ensure lateral registration with the core.

The clips are normally applied by hand, and it is not easy to do so without risk of hurt to the fingers as the deflection needed to bring the flanges of the clip round the corners of the core is quite considerable. Proposals have been made to use two-part clips, each part having a bowed base and two side limbs without inturned flanges but with means for securing the limbs of the two parts together; but as hitherto known these two-part clips have not been sufficiently effective to displace the conventional single-part clip.

In accordance with the present invention, a magnetic core of the kind that is separable into two parts for assembly with an electrical winding and after assembly is secured together by a clip is distinguished by the facts that: (a) the clip comprises two interfitting parts that together encircle the core, at least one of the parts of the clip being resilient and deformed when the parts are assembled to provide a biasing force urging the parts of the core together; (b) each of the parts of the clip is shaped to engage and hold one of the parts of the core, independently of the other part of the clip or the other part of the core; and (c) the laminations of the core are not bonded together but are held solely by the clip.

In some cases, especially when the clip part concerned does not provide biasing force, it may be sufficient for the core part to be gripped by formations (such as tabs or a continuous flange) that engage the exposed faces of the outer laminations only, but in most cases the laminations should be shaped to provide a formation that interlocks with a mating formation on the clip part. A small notch in the side of the lamination engaging a rib on the clip part is effective and need not significantly affect the magnetic properties of the core.

Preferably the clip parts are identical even if the core parts are not.

The clip parts can be secured together in any appropriate manner; when the clip parts are made of sheet metal, a simple arrangement of tabs and apertures, or tabs and notches, is satisfactory; alternatively a snap fitting can be provided in either sheet-metal or plastics material.

In the accompanying drawings: Figure 1 is a perspective sketch of one particular form of core in accordance with the invention, seen in its unassembled condition; Figure 2 is a similar view of the clip forming part of the core in Fig. 1; Figure 3 is a corresponding view of one of the core parts of the same core; Figure 4 is a view, corresponding to Fig. 2, showing an alternative form of clip; Figure 5 is a view, corresponding to Fig. 2, of another alternative form of clip; Figures 6 and 7 are enlarged details of the clip of Fig. 5; Figures 8 and 9 are views, corresponding to Figs. 6 and 7 respectively, illustrating another modification; Figures 10-11 are views, corresponding to Figs. 1 and 2 respectively, showing another modified form of clip; Figures 12 and 13 are views corresponding to Figs. 8 and 9, showing another modifications;; Figures 14 and 15 are mutually perpendicular views of yet another modified from of clip; and Figure 16 is a sketch of a portion of the clip shown in Figs. 14-15.

In the core shown in Fig. 1, the core parts 1 are identical and the clip parts 2 are also indentical. As best seen in Fig. 3, the core part is made up of an appropriate number of identical stamped E laminations 3, and is entirely conventional in form except for the absence of any bonding and for the provision of a shallow recess 4 in one of the side limbs.

The core part 1 is assembled by the lamination manufacturer with a clip part 2 (best seen in Fig. 2), which provides lateral tabs 5 for resilient engagement with the exposed faces 6 of the end laminations. One of the limbs of the clip part 2 is formed with a rib 7 which engages in the notch 4 to hold the core part in the clip part, notwithstanding the tendency of the bowed base 8 of the clip part to expel the core part in an upward direction as seen in Figs. 2 and 3.

After assembly with an appropriate electrical coil (not shown) the two clip parts are secured together by springing the longer limb 9 of each clip part over the shorter limb 10 of the other clip part until tabs 11 pass through apertures 12, after which, if desired, the tabs may be flattened outwardly for extra security.

The modified clip shown in Fig. 4 differs in having notches 1 3 instead of the aperture 1 2 to engage the tabs 10; in this case, the tabs would of course be flattened inwards.

In the modified clip of Figs. 5-7, a snap fitting is provided by a resilient latching tab 14 which snaps into the aperture 1 2 when the parts are assembled; and in the clip of Figs. 8-9 a similar effect is achieved using a substantially rigid abutment member 1 5 and relying on the resilience of the main members of the clip to urge it into the aperture 1 2.

The clips of Figs. 10-16 are made of a suitable plastics material; the greater resilience of the clip material allows the interlock of groove 4 and ribs 7 (preceding figures) to be dispensed with.

In the clip of Figs. 10-11, the clip parts interengage by a system based on ribs 1 6 entering grooves 1 7.

In the modification of Figs. 12-13, this interengagement is provided by a plastics equivalent of the arrangement of Figs. 8 and 9, whereas the plastics clip of Figs. 14-16 uses an interengagement substantially equivalent to that of the metal clip of Figs. 5-7.

Claims (17)

1. A magnetic core of the kind that is separable into two parts for assembling with an electrical winding and after assembly is secured together by a clip, distinguished by the facts that: (a) the clip comprises two interfitting parts that together encircle the core, at least one of the parts of the clip being resilient and deformed when the parts are assembled to provide a biasing force, so urging the parts of the core together; (b) each of the parts of the clip is shaped to engage and hold one of the parts of the core, independently of the other part of the clip or the other part of the core; and (c) the laminations of the core are not bonded together but are held solely by the clip.

2. A core as claimed in Claim 1 in which the laminations are shaped to provide a formation that interlocks with a mating formation on the clip part.

3. A core as claimed in Claim 2 in which each lamination is formed with a notch and the mating formation on the clip part is a rib.

4. A core as claimed in any one of the preceding Claims in which the two clip parts are identical.

5. A core as claimed in any one of the preceding Claims in which the clip parts are made of sheet metal and are secured together by an arrangement of tabs and apertures, or tabs and notches.

6. A core as claimed in any one of Claims 1-4 in which the clip parts are secured together by a snap fitting.

7. A magnetic core substantially as described with reference and as shown in Figs.

1-3.

8. A magnetic core substantially as described with reference to the drawings and including a clip substantially as shown in Fig.

4.

9. A magnetic core substantially as described with reference to the drawings and including a clip substantially as shown in Figs.

5-7.

10. A magnetic core substantially as described with reference to the drawings and including a clip substantially as shown in Figs.

8-9.

11. A magnetic core substantially as described with reference and as shown in Figs.

1 O- 1 1.

1 2. A magnetic core substantially as described with reference to the drawings and including a clip substantially as shown in Figs.

12-

13.

1 3. A magnetic core substantially as described with reference to the drawings and including a clip substantially as shown in Figs.

14-16.

1 4. A sub-assembly of a core part and a clip part for making, with an identical subassembly, the core claimed in any one of the preceding Claims.

1 5. A clip substantially as described with reference to and as shown in Fig. 2 or Fig. 4 or Figs. 5-7 or Figs. 8-9.

16. A clip substantially as described with reference to and as shown in Fig. 11 or Figs.

12-13 or Figs. 14-16.

17. A clip substantially as described with reference to and as shown in Figs. 8, 9, 1 2 and 13.

1 8. A clip substantially as described with reference to and as shown in Figs. 5-7 and 14-16.