FIELD OF THE INVENTION This invention relates to continuous extrusion manufacturing of ring magnets.

SUMMARY OF THE INVENTION Magnetic material in powder form, such as neodymium iron boron, Nd2Fel4B, is continuously forced through an extruder and compressed, preferably to about 1/9 its original diameter. In a preferred embodiment, the extrusion process is accompanied by heating. The continuously extruded product possesses magnetic domains that are surprisingly uniform and elongated, parallel to the axis of extrusion. This permits easy high-energy magnetization in the radial direction (perpendicular to the axis of extrusion). The invention is very useful for making ring magnet rotors for generators and electric motors.

DESCRIPTION OF THE DRAWINGS Figure 1 is a diagram of an embodiment of an extrusion apparatus of the continuous process of the invention.

Figure 2 is a comparison between prior art product and the product of the continuous process of the invention.

DETAILED DESCRIPTION OF THE INVENTION Referring to Figure 1 there is shown an extruding apparatus 1, into which is introduced a magnetic material in the powder form. A preferred magnetic material is Nd2Fel4B. The magnetic powder is introduced into a hopper 2 or other suitable receiving device that introduces the magnetic powder into a first chamber 7. The walls 5 of the extruder 1 define a first chamber 7 in which a compression means 3, such as a continuously reciprocating piston, or rotating screw, or other suitable means forces the magnetic powder through a successive series of ever narrowing chambers 8,9 until the compacted material extrudes through an outlet 10 as an elongate compacted product. The path of the material is depicted by flow arrows labeled 11 in the Figure 1. The compacting process is preferably aided by ball bearing rollers 6 arranged at the junctions between chambers of changing cross-section.

The extrusion process can be executed cold, but it is also preferred in an alternative embodiment that heating means 4 be provided. The advantage of heating means is, among others, to (a) soften the magnetic powder, by partially melting, and make it easier to compress and (b) and to force out gas pockets, also making compression easier and the final product denser.

It is preferred that the magnetic powder be heated to about750°C to about 1,000°C, preferably from about 750°C to about 800°C, and that the material be compacted by a factor of from about one-eighth to one-tenth its original volume (i. e., eight to ten times its original density). Keeping the temperature at or below 800°C prevents undesirable grain growth. It is also preferred that the process be carried out under an inert atmosphere, such as nitrogen or argon, so as to prevent oxidation during heating.

The resultant magnet exudes from the extruder as a continuous worm through an outlet. The outlet may be any shape, but will usually simply be circular for most applications. When any granular or powdered material is extruded under pressure, the grains of material will elongate in the direction of

extrusion flow. The magnetic material will be forced through the outlet at pressures of from about 5,000 psi to about 15,000 psi, so as to obtain grain elongations of from about 50% to about 80%, more preferably about 10,000 psi to obtain from about 65% to about 70% grain elongation.

A slicer 12 or equivalent means known in the art is required to cut individual magnets 13. The slicer 12 may be as simple as a mechanical blade or as sophisticated as a water jet.

The outlet will preferably have a central wire or cylinder mounted thereat so as to form product with an axial cylindrical cavity, such as shown in Figure 2, so that the ring magnet product 13 may be mounted on a shaft.

After production, the ring magnet 13 may be easily magnetized by subjecting it to a magnetic field.

Referring to Figure 2, there is depicted a prior art ring magnet formed by a step-by-step (or"batch") process, such as that disclosed in commonly assigned U. S. Application Serial No. 09/567,110, filed May 8,2000, Attorney Docket No. DP-300626, entitled Manufacturing Technique for Multi-Layered Structure with Magnet Using an Extrusion Process, the disclosures of which are incorporated by reference herein in their entirety. The methods of either the batch process or the continuous process both result in ring magnets with magnetic domains aligned with the longitudinal axis (i. e., the direction of extrusion flow, labeled 11 in Figure 1). The result is that each magnet can be magnetized with the magnetic poles arranged radially. This makes the process particularly useful for making components for electrodynamic machines such as generators and electric motors. Simply mount the ring magnet on a shaft and magnetize alternating poles around the circumference and you have a rotor. Moreover, this process can be carried out at any scale, from miniscule micromagnets less than a centimeter in diameter to megamagnets several feet across.

Figure 2 shows that the continuous process produces a product with more homogeneous magnetic domains than can be achieved with a batch process.

This permits more and stronger magnetic poles to be created in the radial direction (perpendicular to the extrusion flow). This means better and smaller high-energy

performance for electrodynamic machines. The availability of stronger magnets allows the production of smaller components meeting the same performance requirements.

More sophisticated variations are possible by extrusion technologies known in the art, such as extruding multiple layers or even extruding with a shaft already in place by continuous running through shaft material. By these variations, layered ring magnets may be manufactured, such as those made by the batch process of U. S. Application Serial No. 09/567,110, filed May 8,2000, Attorney Docket No. DP-300626, entitled Ring Magnet Manufacturing by Extrusion Method.

While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration only, and such illustrations and embodiments as have been disclosed herein are not to be construed as limiting to the claims.