Magnetizing Fixtures

Axial Field Solenoids generate a high magnetic field along the bore of the fixture. As most sintered rare earth magnets are anisotropic, these fixtures are perhaps the most common fixture used in the magnetization industry. The big advantage they can be used for any shape of magnet as long it will fit within the bore of the solenoid with the direction of magnetization in line with the axis of the coil. As the space around the fixture is not limited as with a multipole fixture, very high fields can be generated if necessary, in excess of 5T.

Depending on the length of the solenoid, multiple magnets can be magnetized on one go, or magnets can be fed into the coil using a continuous feed system. Although most fixtures have a round bore, square or rectangular solenoids can be designed for specific shaped magnets.

Internal radial multipole magnetizing fixtures are designed to produce a multipole radial field on the internal diameter of a ring magnet or magnet assembly such as the rotor of an exterior rotor permanent magnet machine, permanent magnet stators or flywheels. They are optimized to produce a sharp a pole transition as possible within the constraints of the magnet size or pole number.

The big advantages are that permanent magnet assemblies can be assembled un-magnetized avoiding safety and issues with the handling high energy magnets, and significantly reducing assembly times. Multipole fixtures can be used on assemblies that are constructed from either anisotropic or isotropic magnets, radial rings or pre-aligned segments. They can also be used to re-magnetize assemblies that have been thermally demagnetized.

Radial or Homopolar magnetizing fixtures are designed to produce a single radial pole on the inner and outer diameters of a ring magnet. They are in essence constructed from two opposing axial field solenoids, such that the opposing flux is forced radially outwards in the region between the two coils.

The consequence of having two opposing coils is that they both generate very high opposing forces which try and force the coils apart. In addition, the magnitude of the field in the centre of each coil is significantly higher than in the magnet region and so the mechanical construction of these fixtures is paramount. It is not surprising that these fixtures have been known to be called ‘bucking coils’ as they can jump around of not mechanical restrained.

Not all magnets are suitable for radial magnetization. The ideal shape is a washer shape magnet where the length to diameter ratio is small. The longer the magnet is, the more distorted the radial field becomes and the higher the higher fields in the centre of the coil need to be to fully saturate the full length of the magnet. Further information on this can be found in the attached technical paper.

Research and development work often requires small numbers of magnets for prototyping or testing at different stages of the development of a new product. Simple 2 pole magnets can always be magnetized in one of our own standard solenoids fixtures but any multipole magnet usually requires a dedicated magnetizing fixture. To avoid the cost of a production magnetizing system, Bunting Magnetics can build prototype fixtures which will be magnetically same as a production unit, but may be manufactured from less hard wearing materials and will be without all the cooling and normal fixture interlocks. These fixtures can only be used at Bunting Magnetics and have a limited lifetime, but will be available for use by the customer for the duration of a project.