GB2379558A

GB2379558A - Electromagnetic component and its method of manufacture

Info

Publication number: GB2379558A
Application number: GB0121902A
Authority: GB
Inventors: Robert Baker
Original assignee: Rbaker
Current assignee: Rbaker
Priority date: 2001-09-11
Filing date: 2001-09-11
Publication date: 2003-03-12
Also published as: GB0121902D0

Abstract

An electromagnetic component and a method of its manufacture comprises forming a winding 51 and moulding it within a ferromagnetic material 60, in a mould 58, such that the winding 51 is surrounded by a core 60 formed by the said ferromagnetic material. The winding 51 may be formed on a bobbin 54 with a central cavity 56 such that it can receive ferromagnetic material during the moulding process. The ferromagnetic material 60 may comprise iron particles coated with an insulating layer of dielectric material and a resin binder which may be consolidated using heat or pressure treatments. The component may include electrical connections 52 which project from the said moulded ferromagnetic core 60. The component may be a transformer, an inductor or an electromagnet.

Description

DESCRIPTION ELECTROMAGNETIC COMPONENT The present invention relates to electromagnetic components including transformers, inductors and electromagnets.

Applications of the present invention to components in the form of transformers are considered particularly important.

The construction of a conventional power transformer is well known. An example 10 is illustrated in Fig. 1 and comprises primary 12 and secondary 14 copper windings which are"double-wound"-ie co-axial and overlapping-and arranged on a ferromagnetic core 16, most typically fabricated from laminae of cold rolled silicon steel, each of which is separated from its neighbour by a dielectric layer. The core is sometimes referred to as an"E"as it has three parallel limbs 18,20, 22, the windings being on the middle limb 20. In fact a bar 24 serves to link the ends of these three limbs, forming two loops within which magnetic flux, indicated by arrows 26, is thereby increased. Note however that while the windings-and the pattern of magnetic flux created thereby-are generally annular, the core is rectangular in side view.

It is important in many circuits to maximise transformer efficiency-that is to minimise energy losses. These arise from: i."copper losses"-joule heating of the coils by the currents passing through them; ii"iron losses"-energy losses in the ferromagnetic core. These can be

broken down between (1) eddy current losses, which are due to eddy currents induced in the core, causing heating thereof, and are reduced by the laminated structure of the conventional transformer core and (2) hysteresis losses, reducing of which requires appropriate choice of core material; and iii flux leakage, due to so-called"fringing flux"not contained within the transformer core.

It is also desirable to manufacture transformers rapidly and economically.

In accordance with a first aspect of the present invention, there is a method of manufacture of an electromagnetic component, comprising; forming at least one electrical winding, positioning the winding in a mould, introducing mouldable ferromagnetic material into the mould around the winding, and consolidation of the ferromagnetic material to form a monolithic structure in which the winding is surrounded by a core formed by the ferromagnetic material.

In accordance with a second aspect of the present invention, there is an electromagnetic component formed as a monolithic structure comprising at least one electrical winding disposed in and surrounded on all sides by a moulded core of ferromagnetic material.

The component in question is preferably a transformer. However it may be an inductor or indeed an electromagnet.

Specific embodiments of the present invention will now be described, by way

of example only, with reference to the accompanying drawings in which :- Fig. I is a section through a conventional transformer; Fig. 2 is a side view of bobbin and windings for use in an embodiment of the present invention; Fig. 3 shows the bobbin and windings in a mould during the process of fabrication of a transformer embodying the present invention, half of the drawing being a section through the bobbin, windings and mould; Fig. 4 is a view from one side of a transformer embodying the present invention; and Fig. 5 is a view from another side of the same transformer.

The bobbin 50 of Fig. 2 is double wound with insulated copper wire to form windings at 51. Projecting wire ends 52 enable formation of connections to the two windings and end plates 54 confine the windings axially. An axial bore or cavity 56 is formed through the bobbin, within the windings.

The windings are sealed against impregnation by magnetic material and then positioned in a mould 58 (Fig. 3) typically formed of metal. Powdered core material 60 is introduced into the mould, surrounding the bobbin and filling the cavity 56. The moulding process typically then involves exerting pressure upon the core material, eg by mechanically sealing the mould 58 and pressing until bonding of the powdered core material 60 has been achieved. The core and windings are then removed from the mould and subjected to heat treatment to consolidate the powder form and achieve target parameters and electrical characteristics.

The result (Figs 4 and 5) once the transformer 62 has been removed from the mould is a monolithic structure in which the windings are surrounded by, and encased in, the solid transformer core formed by the core material 60. The projecting wire ends 52 emerge from the core to enable connection to the windings. Due to the material within the cavity 56, the core has a limb passing through the windings, in similar manner to limb 20 of the known transformer.

Despite the fact that the core material 60 is typically not as physically strong as the laminated steel core of a conventional unit, the transformer 62, due to its monolithic structure, can be highly robust.

Energy efficiency in use can also be high due in part to the fact that by surrounding the windings with the core material all flux (up to a chosen design parameter) can be captured by the core. That is, fringing flux can be reduced as compared with a conventional transformer.

The core material 60 itself is in current embodiments a ferromagnetic composite iron material. Such materials are known in the art and comprise powdered ferromagnetic material-specifically iron-combined with a resin binder. Iron of high purity provides desirable magnetic characteristics.

A paper by J. Mark Battison and Claude Gelinas, entitled"Imminent Changes in Soft Magnetic Devices"and presented at the PM2TEC conference in Las Vegas in May 1998 describes a suitable material comprising high purity wateratomized iron particles insulated by dielectric material, typically organic. The particles may be pre-coated (and this can be by formation of an oxide layer) or may

be insulated in situ during the moulding process. The particles are bound together in a plastics material which may be thermoplastic or thermosetting. Depending on the plastics material chosen, the heat treatment step referred to above may be omitted. The plastics may be a resin, so that the material 60 is initially a pourable mixture of ferromagnetic particles and resin.

An epoxy resin-a thermosetting, catalysed, resin-may be used. Preferably the material chosen has high thermal conductivity, to allow heat due to exothermic setting to be dissipated during manufacture and to conduct away heat produced in operation The electrical insulation of the particles from each other serves to reduce eddy currents in the core and so to increase efficiency.

It is to be understood that the design and appearance of the transformers embodying the present invention may be adapted to particular applications. For example the core shape and winding pattern may take various forms. The core may be shaped to correspond to the field pattern produced by the windings. Furthermore, while the above discussion has concerned transformers, inductors using a single winding may, as will be apparent, also be constructed in accordance with the present invention. Electromagnets may also be so constructed.

Transformers embodying the present invention are well suited to low frequency applications eg at 50Hz.

Claims

1. A method of manufacture of an electromagnetic component, comprising forming at least one electrical winding, positioning the winding in a mould, introducing mouldable ferromagnetic material into the mould around the winding, and consolidation of the ferromagnetic material to form a monolithic structure in which the winding is surrounded by a core formed by the ferromagnetic material.

2. A method as claimed in claim 1, comprising the further step of arranging electrical connections to the winding such that they project from the mould and are thus exposed at the exterior of the completed transformer or inductor.

3. A method as claimed in claim 1 or claim 2 wherein the winding is formed around a bobbin defining a cavity which receives the ferromagnetic material during the moulding process.

4. A method as claimed in any preceding claim wherein the ferromagnetic material comprises iron particles.

5. A method as claimed in claim 4, comprising the further step of forming a dielectric layer around the particles thereby to electrically insulate one particle from another.

6. A method as claimed in claim 5 wherein the material further comprises a binder in the form of a resin which is solidified during the consolidation step.

7. A method as claimed in any preceding claim wherein the consolidation

step comprises pressure treatment.

8. A method as claimed in any preceding claim wherein the consolidation step comprises heat treatment.

9. An electromagnetic component formed as a monolithic structure comprising at least one electrical winding disposed in and surrounded on all sides by a moulded core of ferromagnetic material.

10. An electromagnetic component as claimed in claim 9 wherein the core has an integrally formed limb extending through the winding.

11. An electromagnetic component as claimed in claim 9 or claim 10 having electrical connections to the winding projecting from the core.

12. An electromagnetic component as claimed in any of claims 9 to 11 wherein the ferromagnetic material comprises iron particles.

13. An electromagnetic component as claimed in claim 12 wherein the iron particles are surrounded by dielectric material and thereby electrically insulated from one another.

14. An electromagnetic component as claimed in claim 12 or claim 13 wherein the ferromagnetic material further comprises a plastic material containing the particles.

15. A method of an electromagnetic component substantially as herein described with reference to, and as illustrated in accompanying Figs. 2 onward.

16. An electromagnetic component substantially as herein described with reference to, and as illustrated in accompanying Figs. 2 onward.