Emergency Brake of an Offshore Winch Uses Rare Earth Magnetic Assembly

The Bunting Magnet design team were contacted and asked to manufacture a Magnetic Assembly that would act as an emergency brake on an offshore winch.

The original design called up bespoke Neodymium Rare Earth Magnets with a strength of 50MGOe (megaGauss oersted)  Such an assembly had an ten-week lead time.  This was too long for the customer.

The design teams of Bunting and the customer worked together on a new magnet configuration.  The magnet shape in their original design was modified to accommodate a standard Bunting Magnet that is held in stock.  The Magnets selected are commonly used in the manufacture of large Plate Magnets which are used to separate ferrous metal contamination from free-flowing materials.

However, the new Magnet Configuration meant that there was a slight reduction in magnetic energy.  In order to produce a similar performance, a thicker magnet block was used.  This produced the necessary magnetic force.

The final design reduced the lead time from 10 to 2 weeks. In addition, the design lowered the total cost of the Magnet Assembly.bunting_magnets_eddy_current_brake

The magnet array design is a 10-pole alternating pattern that is mirrored across the aluminium disk. The alternating polarity allows the re-circulation of magnetic field in the back iron plate.  The back iron plate is sized to fully saturate magnetically, thus preventing stray leakage from the rear of the assembly. The magnetic field projected from the exposed side is designed to link up with the opposite structure.  This creates a region of high intensity magnetic field that interacts with the moving aluminium to generate the braking eddy currents.  An ‘Eddy Current’ is a localized electric current induced in a conductor by a varying magnetic field.

The finished Magnetic Assembly is commonly know as an ‘Eddy Current Brake‘, similar to the technology used to safely stop roller coasters. This is a passive, fail safe technology that slows in proportion to the differential in speed of the static magnet assembly and the rotating aluminium part.

The Bunting Magnet engineering team, based at Berkhamsted in the UK, regularly design special Magnet Assemblies for customers.  For further information or to discuss as specific Magnetic Assembly requirement, please contact us on: