All impeder versions use a material for the ferrite core that meets high standards with regard to its permeability and magnetic flux density saturation. Due to the high energy density at which the impeder works and the heating caused by the eddy currents propagating in a circular fashion close to the surface, a considerable heat develops in the ferrite core.

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This is the reason why the use of cylindrical core materials has proven beneficial since the current can increasingly spread in a longitudinal direction and create additional surfaces to facilitate cooling. Notches and center holes on common core cross sections provide additional cooling opportunities. Although ferrites have a higher electrical resistance they do conduct the electrical current around the circumference.

The highly permeable magnesium-zinc materials used in impeders boast a high conductivity which results in a heating up due to the eddy currents. The additional heating because of the inductor requires adequate uninterrupted cooling of the ferrite in the impeder. Before the welding machine is turned on it is imperative to ensure adequate coolant supply since the high start-up current of the device could otherwise destroy the uncooled ferrite material.

Over time ferrites can lose their magnetic properties, which, however, is not due to wear and tear. Instead, this is caused by an internal fracture of the ferrite core due to mechanical influences from the production tube, for example following the misalignment of the impeders or excess heat. These factors have a negative impact on the life cycle of the tools.