Flexible Rubber Magnets

During the production of flexible magnets, three different processes are used – Extrusion, Calendering and the third process involves using a combination of the first two.

For magnets with an irregular cross section, the extrusion method is used. This process is also applied during “profile extrusion”. A pelletized compound is rolled between two rollers for the calendering method and this produces a continuous sheet (in thicknesses of 0.020" to over 0.375"or 0.51 mm to over 9.5 mm). During the third process, calendering and extrusion are combined together to produce the magnet in question. Each method has its own strengths and weaknesses and are utilised according to relevant orders.

For Ferrite materials, the energy product can range from 1.0 to 1.6 MGOe (8.0 to 12.7 kJ/m3). Nitrile rubber, Nordel or Natsyn can be used as binders. Although the material can sometimes be used unvulcanised, more often than not it is vulcanised. Higher energy products can be found in rare earth flexible NdFeB magnets.

The sheet material is fairly flexible in that it can be laminated, stamped, slit, punched or indeed sanded in order to profile edges or achieve close thickness tolerance. Magnetised sheet comes in various ppi (pole per inch) configurations and the greater the ppi, the greater the holding strength. The flip side to this is that the higher you go, the more the reach of the magnetic field is reduced. The opposite is also true – reduce the number of ppi and you will see an increase in magnet attraction distance but also a reduction in holding strength. Typically, configurations range between 4 ppi to more than 12 pole per inch. The thickness of the sheets also plays a part - the thicker the sheet, the fewer the ppi. In conjunction with Ferrite, nitrile rubber and polyethylene binders can be used up to a temperature of 120°C. Temperatures up to 150°C have been used in combination with nitrile and Ferrite but the higher the temperature, the more you see a loss in performance, mainly some shrinking and a notable reduction in flexibility.

When rare earth metal powder is present, the temperature capability of the magnets is reduced significantly. Such is the strength of rare earth material that the magnet will self-deform and tear apart – the binder becomes soft when subjected to very high temperatures. For this reason, it is important that the recommended use temperature is not exceeded when flexible rare earth material is present.

With 5 main grades of calendered or extruded product available, in addition to many other variations that are client specific, there is great scope at Bunting Magnetics. Energy products very from 0.6 to 1.4 MGOe (4.8 to 11.1 kJ/m3) and thickness of extruded sheet is from 0.010" to 0.063" (0.25 to 1.60 mm).  There are many different shapes available for extruded profiles. Please contact us for more information.

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