GB2057194A - A method of producing a permanent anisotropic magnet - Google Patents

Abstract

In a method of producing a magnet with a convergent magnetic orientation to raise to magnetic induction by concentrating the magnetic flux into a reduced cross-section, anisotropic permanent magnetic material where the magnetic orientations converge to each other is combined, magnetisation being effected either before or after combination. The magnet may be pressed with a binder, sintered, cast in a mould or built up from separate, machined parts. <IMAGE>

Description

SPECIFICATION A method of producing a permanent anisotropic magnet The invention relates to a method of manufacturing an anisotropic permanent magnet, having a convergent controlled orientation throughout at least part of the magnet body.

Anisotropic permanent magnets have many uses where one desires rapid magnetic induction into an air gap or other portion of a magnetic circuit. The anisotropic magnets used at present are of the type where the directions of easy magnetization of the elementary magnet constituents (such as powder particles with pulverized materials or crystals with cast materials) are co-extensively oriented into the overall direction in which the complete permanent magnet is magnetized. In this way considerably higher values of remanence and (BH)max product are obtained, compared with isotropic non-oriented magnets.

In many cases it is preferable to apply magnets in the entire volume or in a part having an orientation of easy magnetization axes. This orientation is convergent at at least one pole surface. Thus, it is possible to raise substantially the magnetic induction value in the pole region, compared with existing homogeneously oriented magnets. The increase in magnetic induction present in the surrounding space is achieved over a smaller cross-section than that of the magnet itself. This effect is caused by the fact that the convergent orientation concentrates the magnetic flux, raises its density and reduces the flux of magnetic leakage.

Various processes can be used to achieve an homogeneous anisotropic structure with existing magnets, depending upon the material typeorientation of powder particles by a magnetic field, crystallization resulting from a directed temperature gradient, extrusion, rolling and other properties.

Present technology enables a series production of magnets, the homogeneous orientation of which is almost ideal.

To produce a convergent oriented structure that would raise the magnetic induction in a desired region is, as a rule, more difficult than to produce an orthodox homogeneous orientation, since specific processes for manufacturing permanent magnets with controlled convergent structure have not yet been developed. As a result, wide use of this type of magnet is impossible, in spite of the fact that in many applications, it would substantially improve the parameters of magnetic circuitry.

We have developed a magnet which can eliminate or reduce these drawbacks of the prior art.

Thus, the present invention consists in a method of producing a permanent anisotropic magnet having a convergent magnetic orientation throughout at least part of its body which raises magnetic induction by concentrating the magnetic flux into a reduced cross-section, which comprises combining anisotropic parts of magnetic material, to give a magnetic orientation comprising two or more con vergentconfigurations, magnetism being induced in the material either before or after combination.

The invention also consists in the magnet itself.

Forthe manufacture of conventional homogeneously oriented parts of the final magnet, it is possible to employ known processes for manufacturing anisotropic magnets. As an example there can be named processes for manufacturing an isotropic powdered magnets pressed in combination with a binder, or sintered, or cast anisotropic magnets. The desired shapes of the parts can be obtained either directly by using suitable press dies, casting moulds and like devices, or by dividing into parts, or by machining homogeneously oriented magnets of other forms as, e.g., by cutting and grinding. The parts can be fixed to one another to produce a final magnet having a convergent magnetic orientation; this can be effected by various mounting methods, such as encasing, screwing, framing, cementing and soldering.

It is to be understood that the parts can be combined together at different stages of the overall method. The parts can be either ready-to-use permanent magnets, orsemi-finished products. Thus, for instance, in the manufacture of sintered powder magnets, one can combine parts made of the final sintered material, or powder pressed pieces that are not sintered until they are fused into a complex.

Alternatively, one may use cast magnets wherein the parts can be combined with one another before or after heat treatment. Furthermore, the parts can be combined in the magnetized or unmagnetized state.

In the former case, repulsive forces have to be coped with, whereas in the latter it should be ensured that the final magnet be magnetised in accordance with a convergent orientation.

According to the invention, permanent magnets with convergent orientation can be made, preferably, from any of the known magnetically hard materials, such as magnetically hard ferrites, rare earth based materials, AlNiCo, PtCo, MnAI and MnBi. The final magnets can be made in various forms, such as prisms, pyramids, cones, cylinders, annuli, rods, U-, C-, E-shapes, and in intricate or irregular forms with apertures, notches or projections.

Convergently oriented structures of magnets manufactured by the method of the invention can have various configurations. Particular structures may be designed according to the desired spatial distribution of magnetic induction to be supplied by the magnet into the surrounding space. The standard forms, dimensions and magnetic characteristics of materials used for manufacturing permanent magnets may be taken into consideration. Thus, for example, convergently oriented structures concentrate the magnetic flux into a larger or smaller region in the centre of area of one, two or more poles. The modification of the directions of orientation in the convergent structure in the magnet body can take place either continuously, or discretely.The anisotropic convergent structure can be produced in one or more parts, or throughout the entire magnet body, it can be linear, curvilinear, continuous, or stepwise, and it can be produced in two orthree dimensions. The shapes and dimensions of the individual parts will be selected so as to give, after the combination, a magnet having a desired form and size. The parts can have various forms, such as prisms, pyramids, cones, annuli, and other solids. To achieve a convergent magnetic structure which comprises two or more convergently oriented configurations, the parts should be oriented so that the orientations of adjacent pa rts are inclined towards each other, and are magnetized so thattheir like polarities point to the same pole.The inclination angles and the number of parts with convergent orientations will be chDsen according to the required degree of convergency and to the number of various orientation configurations in the convergent structure of the final magnet.

The invention is now further illustrated by the following example, with reference to the accompanying drawings, each of which depicts a magnet.

Example A sintered ferrite magnet of convergent structure was made in theform of a right parallelepiped having the dimensions 2525,12 mm. The convergent structure raised the value of magnetic induction discharged by the 2 & 25 mm area of the S pole in the region of the axis passing through the centre of this area.

Figure 7a shows this anisotropic structure in a sectional view taken parallel to the magnet axis pointing to the pole, while Figure ib is a view perpendicular to the pole area.

The magnet was made by combining three pieces of sintered, homogeneously oriented parts, shown separated in Figure 2 which also shows their orientation.

Figure 3 shows the final magnet manufactured by combining these parts.

In this way a substantial increase in induction was achieved in the central part of the pole area, compared with conventional anisotropicpermanent magnets. By way of example, it is possible to refer to the value of magnetic induction present adjacent to the pole surface, measured by a Hall probe applied close to the centre of the pole area. The comparison was carried out by measuring reference magnet specimens made of the same material and having the same dimensions. A conventional homogenously oriented magnet in the central area region gave an induction of 0.125 T, and the magnet manufactured from parts as shown in Figures 2 and 3 gave an aimost double induction of 0.249 T.

The process of manufacturing magnets according to the invention has many advantages. It is particularly advantageous that various configurations of convergently oriented structures can be produced, according to the required characteristics of the final rnagnet. Among such structures there may also be some extreme cases, the manufacture of which in other ways would be very difficult, if not impossible.

An example of this is convergent orientations which concentrate the magnetic flux as much as possible into a narrow region, orto magnets having complicated shapes, or a plurality of poles.

As starting materials it is possible to use currently available anisotropic, magnetically hard materials, or final magnets. Also the techniques for manufac ture are relatively simple and inexpensive. For these reasons, the method of the invention can be used by the magnet users themselves who are not equipped, as a rule, with means for series production of magnetically hard materials.

The magnets ofthe invention have many uses. An increase in the magnetic induction at an air gap or at any other parts of the magnetic circuit, compared to that of the conventional magnets, improves the operation of, for example, motors, engines, drive units and generators having permanent magnets, microwave appliances, measuring apparatuses, electroacoustictransducers, magnetic pick-ups, re lays, bearings, clutches, separators and clamping elements. The improvement can result from lower power demand, higher efficiency, output, torque, attractive or repulsive force effects, sensitiveness and accuracy, depending on the application. Another merit of the present invention is the various possibi lities of miniaturization of magnetic circuitry, reduction of material costs, longer lifetime and simplified structure.

Claims (10)

1. A method of producing a permanent anisotropic magnet having a convergent magneticorientation throughout at least part of its body which raises the magnetic induction by concentrating the magnetic flux, which comprises combining anisotropic magnetic material to give a magnetic orientation comprising two or more convergent configurations, magnetism being induced in the material either before or after combination.

2. A method according to Claim 1, in which the magnet is a sintered powdered magnet.

3. A method according to Claim 2, in which sintered anisotropic magnetic material is combined.

4. A method according to Claim 2, in which unsintered powder pressed an isotropic magnetic material is combined, and the combination sintered.

5. A method according to Claim 1, in which cast anisotropic magnetic material is heat treated and then combined.

6. A method according to Claim 1, in which combined anisotropic magnetic material is heattreated.

7. A method of producing a permanent anisotropic magnet substantially as herein described with reference to any one of the accompanying drawings.

8. A permanent anisotropic magnet produced by a method according to any one of the preceding claims.

9. A permanent anisotropic magnet, comprising at least two pieces of magnetic material aligned to give a convergent magnetic orientation which raises magnetic induction by concentrating magnetic flux.

10. A method of manufacturing anisotropic permanent magnets with a convergent magnetic orientation in a part of or in the entire magnet body to raise the magnetic induction by concentrating the magnetic flux into a reduced cross-section, the method comprising manufacturing a final magnet by combining together anisotropic parts made of a permanent magnet material and complementing said parts, according to their shapes and dimensions, so as to give the final magnet of the desired shape and dimensions, the magnetic orientation which comprises two or more various convergent configurations, being produced in such a manner that at least with two adjacent parts, the magnetic orientations converge to each other, and their magnetization polarities point toward one and the same pole.