The magnetising fixture is the mechanical interface between the component to be magnetised and the magnetiser. The fixture produces the specific magnetic field pattern that is required for that particular application. Hirst Magnetic Instruments Ltd. have a wealth of experience in the design and manufacture of magnetising fixtures.
In its simplest form the magnetising fixture is a simple coil with the required field along the axis of the coil. The required components to be magnetised are placed in the coil while the magnetising pulse is applied.
Complex multipole fields are often required for magnetising of competed assemblies, such as motors. The fixture may contain several individual coils with appropriate pole pieces to complete the magnetic circuit when the component is fitted to the fixture.
A J2A fixture with interchangeable pole pieces.
Another common fixture (J2A) consists of a U shaped iron core with interchangeable pole pieces which are secured to the top of the iron core. The required magnetic field is produced between the adjustable pole pieces.
For magnetising of rare earth magnets, air cored fixtures are usually provided as the fields required are above the saturation level of iron cores and therefore the field cannot be "directed" to an area away from the centre of the coil.
Many applications require individual magnets, or a final assembly with magnets fitted, to be calibrated to a specific parameter. This could be performed by applying demagnetising pulses in the opposite direction to the original magnetising pulse, or using a second coil to apply a field at right angles to the magnetising pulse. This is particularly suitable where the component uses the strength of the magnet field in a single direction. The MCSD range of Hirst magnetisers are often supplied as dual output units for this application.
Dependent upon the frequency of operation and energy used, the fixture may require external cooling to prevent overheating of the coil. This can be achieved using compressed air, water or oil circulating through the fixture. Hirst can supply complete cooling systems to compliment our fixtures as a complete turnkey solution.
Special fixture for skewed pole magnetising.
Custom fixtures may also contain embedded search coils to be connected to a Hirst Integrating Fluxmeter as part of a quality control or magnet calibration system.
Our fixtures are usually supplied with the windings of the coils fully encapsulated in epoxy resin. This provides a good mechanical support for the windings and provides operator safety by insulating the windings, which can see voltages of up to 3,000 volts.
Hirst Magnetic Instruments Ltd. can also manufacture coils to suit a customer's particular application or to interface with 3rd party magnetiser.