GB2266626A - A Magnetiser - Google Patents

Abstract

The magnetiser comprises a coil 1 and a magnetically permeable member 7, 9, 11. The magnetically permeable member provides a return path for flux emanating from the coil and includes a substructure 7 for supporting a sample 3 to be magnetised in a position adjacent to an end of the central core 2 of the coil. The support substructure includes a block 9 with a void 10 for redistributing flux in the sample so that the sample will only be magnetised in that part which directly faces the coil. The magnetiser is able to magnetise rare earth permanent magnets with 2, 4, 6 or more poles, for example in the manufacture of the rotor of a motor. <IMAGE>

Description

TITLE: A Magnetiser DESCRIPTION The invention relates to a magnetiser, that is equipment for the energising of magnets.

Conventional magnetisers put a large, uniform field across a sample to be magnetised in such a way and of such strength that it becomes magnetised. The magnet is then assembled with other components, possibly including other magnetised components, to form the finished product. The assembly of premagnetised components can be quite difficult and expensive, so it would be preferable to magnetise the finished assembly rather than the separate components. However, the size of the magnetising field required often precludes this approach, especially where rare earth permanent magnets are used in a magnetic circuit more complex than a simple 2-pole arrangement. The task becomes even more difficult where non-magnetic materials are included in the magnetic circuit.

One type of conventional magnetiser, as shown in Figure 9 of the accompanying drawings, is similar to an air cored solenoid. The sample is placed in the hollow centre of the coil which is then pulsed with a very large current, often by capacitor discharge. This method is suitable for small components that have a simple 2-pole magnetic circuit.

Another conventional type of magnetiser, as shown in Figure 10 of the accompanying drawings, is a form of magnetic C-core. The sample is placed between the jaws of an iron ring that has a coil fitted to it. The coil is then pulsed, either by capacitor discharge or by DC, and the sample is magnetised. The magnetic core of this machine affords greater control of the magnetic flux paths, so that relatively complex circuits can be magnetised as shown in Figure 11.

As the known magnetisers are not able to magnetise the sample in a multipole configuration, plural magnetisers are necessitated for this purpose. Furthermore, since many magnetic leakages are generated, in particular in the case of the magnetiser shown in Figure 11, magnetisation of the sample is not conducted efficiently.

The invention provides a magnetiser comprising: an energisable coil having a central core, a magnetically permeable member which provides a return path for flux emanating from the coil when energised and which includes a substructure for supporting a sample to be magnetised in a position adjacent to an end of the core, and means in the substructure for redistributing flux in the sample such that only the part of the sample adjacent to the said end of the core is effectively magnetised.

The invention is illustrated with reference to Figures 1 to 8 of the accompanying drawings. Figures 9 to 11 of the accompanying drawings illustrate prior art magnetisers. In the drawings: Figure 1 is a transverse sectional view of a magnetiser according to the invention; Figure 2 is a longitudinal sectional viewWfff' the magnetiser of Figure 1; Figure 3 is a partly enlarged transverse sectional view which shows the magnetic field lines in the x-y plane of the magnetiser of Figure 1; Figure 4 is a partly enlarged longitudinal sectional view which shows the magnetic field lines in the x-z plane of the mag'netiser of Figure 1; Figure 5 is a partly enlarged transverse sectional view which shows the changing flux density in the x-y plane of the magnetiser of Figure 1;; Figure 6 is a partly enlarged longitudinal sectional view which shows the changing flux density in the x-z plane of the magnetiser of Figure 1; Figure 7 is a partly enlarged transverse sectional view of the magnetiser of Figure 1 and shows a carriage arrangement for axially locating a sample to be magnetised; Figure 8 is a partly enlarged longitudinal sectional view of the magnetiser of Figure 1; and shows an arrangement for rotationally locating the sample to be magnetised; and Figures 9 to 11 are schematic illustrations of known magnetisers.

Referring first to Figures 1 to 4, a magnetiser according to the invention comprises a coil 1, a magnetic core 2, on which the coil 1 is wound, a sliding support 7, a block 9 and a frame 11. The coil 1 is connected to an electrical power source (not shown). The core 2, the sliding support 7, the block 9 and the frame 11 form a magnetic circuit for passing flux which is generated by the coil 1. In the illustrated embodiment, the frame 11 is constituted by four metallic plates (such as steel plates). The coil 1, the core 2, the support 7 and the block 9 are accommodated in an area which is formed by the frame 11. The core 2 is fixed to a centre portion of the lower plate of the frame 11 and the block 9 is fixed to a centre portion of the upper plate of the frame 11 so as to be opposite to the core 2. The support 7 is movably installed to the block 9.A sample 3 to be magnetised is attached to the support 7 by clamps 5 and 6 so as to be adjacent to the coil 1 and the core 2.

It is also possible to. form the frame 11 from three metallic plates so as to be in the form of a magnetic G -core (namely, for example, a form which the right hand as shown in Figure 1 - half of the frame 11 is eliminated.

The arrangement of the invention allows the coil 1 to be of the optimum shape to minimise magnetic leakage and maximise the flux density in the sample 3 for a given supply current as discussed later.

The magnetic core 2 is optional and may be omitted in other embodIments. If it is included, it may have a flat, pointed, rounded or otherwise shaped tip, the choice being made dependent upon the shape of the sample 3 so as to optimise performance.

In the illustrated embodiment, the sample 3 forms part of a sub-assembly 4, for example the rotor of a motor, which is attached by clamps 5 and 6 to the support 7. The support 7 is designed so that the area of the support 7 adjacent to the sub-assembly 4 is substantially larger than that of the core 2 adjacent to the sub-assembly 4.

In particular, the support 7 is provided with a cover portion which largely covers the outer circumferential portion of the sub-assembly 4 and the sample 3. As a result, most of the magnetic flux passes through the sample 3 into the sub-assembly 4 where it divides in such a way that the flux density, as it passes into the support 7, is only a fraction of that in the sample 3.

Figure 3 shows how the flux divides in the x-y plane of the magnetiser. The support 7 has sloping edges 8 intended to minimise magnetic leakage, maximise the flux density in the sample 3 and distribute the flux around the adjacent periphery of the sub-assembly 4. The flux then passes through the block 9 and into the frame 11 before returning through the core 2 and the coil 1 to complete the magnetic circuit. The distribution of the flux can be improved by forming a void 10 in the block 9 directly above the core 2.

Figure 4 shows how the flux divides in the x-z plane of the magnetiser. The clamps 5 and 6 serve the secondary purpose of providing an axial flux path that has no air gap in it- and therefore, especially in low magnetic fields, becomes the main path for the flux after it passes through the sample 3. The void 10 is clearly shown to force the flux away from the axis of the core 2.

Figures 5 and 6 show the same concepts in the form of flux densities. The black shading represents the highest flux densities and white represents the lowest.

Figure 7 shows the arrangement of the support 7. The purpose of this component is to move the sub-assembly 4 axially backwards and forwards in order to position the sample 3 over the core 2. The support 7 is suspended on runners 12 which are fixed to the block 9. The contact between these components is minimal to reduce stiction due to the residual magnetism. The contact area 13 between the support 7 and the block 9 is also reduced to the minimum for the same reason. Furthermore, the support 7 and the runners 12 are provided with plural holes 7a, 12a which are able to overlap each other. The assembly is designed so that, once positioned, it can be fixed firmly by, for example, pins 14 which are fitted into holes 7a and 12a of the support 7 and the runners 12 respectively.

Figure 8 shows the arrangement of the clamps 5 and 6. A pair of fixed clamps 6 are attached to the support 7. The upper half of the fixed clamp 6 is made of a magnetic material and the lower half of a non-magnetic material. A pair of inner, rotating clamps 5 are attached to the end of the sub-assembly 4 and can be rotated so that the sample 3 is positioned over the core 2. Plural holes 5a are formed in at least one of the rotating clamps 5.

Furthermore, a supporting member 16 having a hole 16a is fixed to the support 7. Once in position the rotating clamp 5 can, like the support 7, be fixed with pins 15 which are fitted into the holes 5a and 16a to prevent movement during magnetisation.

The fixing methods depicted in Figures 7 and 8 are not the only possible techiques. In factory production, for example, it would be practicable to automate the positioning process using pneumatic equipment. Similarly there are several ways of pinning the support 7 to the block 9, and several ways of preventing movement of the rotating clamp 5.

As mentioned above, the magnetiser according to the invention is an improvement of the C-core design that allows the magnetisation of a completed sub-assembly, such as the rotor of a motor, to be magnetised in a multipole configuration. This gives it advantages over the solenoid and C-core designs of Figures 9 and 10.

The arrangement of the invention is such that the magnetic leakage is reduced, and thereby the peak flux density increased, compared to the 4-pole C-core arrangement of Figure 11. These improvements are made by shaping the core in the form of 'G', rather than 'C'.

This allows the poles of the core to be arranged opposite each other, thereby reducing the leakage, whilst altering the flux density so that only one pole of the sample is magnetised at a time. This principle allows any number of poles to be magnetised. It is possible to change a magnetic pole by inverting the direction of the current.

The G-core layout of the invention achieves several things. Firstly the point of highest flux density is deliberately kept small so that the volume of the adjacent coil is minimised and the leakage reduced. Most flux passes across the sample and into its centre. The magnetic path then widens considerably so that the flux density rapidly falls to less than one tenth of its peak value before emerging on the other side of the sample so dilute that it is unable to magnetise that side of the sample very much. The ironwork at this point is arranged so that the flux is attracted both axially and rapidly.

The magnetiser is designed so that the item being magnetised can be moved to different positions. Thus the invention allows the magnetisation of 2, 4, 6 or more poles. Another advantage of the layout is that it allows the coils to be their optimum, cylindrical, shape.

Claims (8)

CLAIMS:

1. A magnetiser comprising: an energisable coil having a central core, a magnetically permeable member which provides a return path for flux emanating from the coil when energised and which includes a substructure for supporting a sample to be magnetised in a position adjacent to an end of the core, and means in the substructure for redistributing flux in the sample such that only the part of the sample adjacent to the said end of the core is effectively magnetised.

2. A magnetiser according to claim 1 in which the central core of the energisable coil is formed from a magnetic material.

3. A magnetiser according to claim 1 in which the central core of the energisable coil is an air core.

4. A magnetiser according to any preceding claim in which the area of the support substructure adjacent to the sample is substantially larger than the area of the core adjacent to the sample.

5. A magnetiser according to any preceding claim in which the magnetically permeable member includes a void axially aligned with the core whereby flux is caused to diverge from the axis of the coil.

6. A magnetiser according to any preceding claim in which the support substructure includes means for rotating the sample so as to change the part of the sample adjacent to the said end of the core.

7. A magnetiser according to any preceding claim in which the support substructure includes means for axially translating the sample so as to change the part of the sample adjacent to the said end of the core.

8. A magnetiser substantially as described herein with reference to Figures 1 to 8 of the drawings.