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Abstract

This dissertation deals with increasing the recyclability of NdFeB-containing electric machines by design. Design for Recycling is re-defined in this work to comprise product design, process design and policy design to develop a coherent strategy for achieving high yields of good-quality material of recycled NdFeB at reasonable effort. Recycling of NdFeB is essential for three major reasons: To avoid the negative environmental effects of mining, to increase the resilience of the European rare earth permanent magnet supply chain and to utilize a source of material which is much closer to the desired composition than the mined minerals.
In the theoretical foundations and state of the art, NdFeB magnets are characterized in detail with an emphasis on sintered permanent magnets and the mechanisms of how the magnetic properties emerge to allow a better understanding of the effects of recycling-related changes in the material. Secondly, the recycling of NdFeB permanent magnets, with an emphasis on the short-loop route is explained, starting at the sorting and preprocessing and ending at resintering and postprocessing. Third, electric machines containing NdFeB are discussed to understand their variations and functions. The advantages and limitations of the use of NdFeB in electric machines are discussed. In the last sub-chapter, design for recycling is explained and defined. General and specific research on design for recycling and disassembly are presented and complemented by extensive patent research to show current recycling-friendly solutions.
In the practical investigations, three major studies are presented. The first study deals with in situ processing of electric machines, skipping the demounting and demagnetization and clarifies the possibilities and limitations by machine design. Furthermore, mechanical separation of contaminants like coating residues is discussed. The second study deals with another simplified processing route, using demagnetization to safely demount magnets and to combust adhesives and organic coatings, investigating the effects on the magnet materials and how to mitigate them. The third study complements the other two, investigating quantitatively what effects contaminants have on the magnetic properties at what level of contamination.
Finally, for implementation, a thorough analysis of the electric machine design from the housing down to the detailed magnet alloy is given. To make use of the work, a design for recycling guideline using a questionnaire and a conditional logic algorithm is designed and programmed to offer machine designers direct support to promote recycling-friendly design decisions. Finally, the creation of a technical specification within CEN/TC 472 on behalf of supporting the Critical Raw Material Act's Article 28 on labelling of magnet containing products is addressed. Leading this project allowed the partial implementation of the findings of this work at policy level, as the contents and technicalities of the label are defined there, which is meant to transfer the recycling-relevant knowledge from designers to recyclers.