The Misconception of Eddy Current Separator Belt Speed

2nd of 5 Misconceptions about Eddy Current Separators

This is the 2nd in a series of blogs discussing misconceptions about Eddy Current Separation.  Eddy Current Separators are used extensively throughout the recycling industry to separate non-ferrous metal (e.g. aluminium beverage cans, shredded aluminium and copper etc) from non-metallic materials. A recent case history details the installation at Recapture Plastics in Kent.

The belt needs to run as fast as possible.

Many users of Eddy Current Separators are focused solely on how far the item of non-ferrous metal will be thrown.  By increasing the speed of the conveyor belt of the Eddy Current Separator it is possible to produce a further throw, but does this actually aid separation?

The forces on a particle as it enters the rotating magnetic field of the Eddy Current Separator are:

A – Eddy Current repulsion from the Magnetic Rotor

B – Forward force from being conveyed along the conveyor belt

C – Gravity

D – Resultant force

Bunting Eddy Current Separator-14

All the material on the conveyor belt will be affected by B and C, but only non-ferrous metals will be affected by A, the Eddy Current repulsion.  Therefore, if the size, shape and weights were the same and there was no Magnetic Rotor, the throw would be the same.  Adding in the Eddy Current repulsion changes the trajectory of the non-ferrous particle, sending it more in an upward direction.  When setting up an Eddy Current Separator, it is best to first run non-metallic material over the unit and check the material trajectory for positioning of the splitter.  Then introduce the non-ferrous metal to check that this different trajectory enables it to throw past the splitter.  The extra force from the Eddy Current affect, should result in greater throw and hence a longer trajectory.

However, if Force B (the forward force from the conveyor) is increased and all the other forces remain constant, the resultant force vector flattens to a point where the trajectories of the non-ferrous metal particle and non-metallic material cross or are nearly the same.  At this point no separation will be achieved.

As Eddy Current Separators have different designs of magnetic rotor and the variety of shapes, sizes and characteristics of non-ferrous metal particles is extensive, there is not one belt speed that suits all and each time the application needs to be studied and understood to enable the best level of separation.

Previous blogs looking at the misconceptions of Eddy Current Separators include:

For further details on the Bunting range of Eddy Current Separators, Magnetic Separators and Metal Detectors please contact Carlton Hicks (carltonhicks@buntingeurope.com) or our technical sales team on:

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