• Gonzalez-Gutierrez, Joamin
• Burkhardt, Carlo
• Schlauf, Thomas
• Holzer, Clemens
• Kukla, Christian
• Krispin, Michael
• Walton, Allan

Abstract

Rare earth magnets are very useful in today’s life. For example, they are present in electrical motors, turbines, speakers, microphones, and computer hard drives. Finding ways to recycle these magnets is important to maintain an adequate supply of these materials, since most rare earths are mined outside Europe. One way to recycle rare earth magnets is to expose magnets to hydrogen, which cause the magnets to crumble, in a process called hydrogen decrepitation [2]. The powder is then sieved to remove coatings and milled into finer particles. In order to make magnets with complex shape metal injection moulding (MIM) can be used. In MIM, the powder is mixed with a polymeric binder system that can be shaped in an injection moulding machine. After shaping, the binder is removed, followed by sintering and magnetisation to obtain magnets with complex shape. In this paper, an example is shown how MIM can be used to produce sintered mag-nets from recycled rare earth magnets. Neodymium-iron-boron (NdFeB) magnets were recycled by hydrogen decrepitation, burr-milled and sieved. The recycled powder was then mixed with a polyolefin-based binder system in an inert atmosphere. The volume of powder in the feedstock accounted for 55 % of the feedstock volume. The feedstock material was then injected moulded into the shape of rotors. The rotors were then debound in cyclohexane for 24 h and subjected to a sintering profile to obtain solid parts of NdFeB. The sintered parts were then analysed for oxygen, nitrogen and carbon content, as well as density and magnetic characterisation coercivity. Results indicate that the used method can yields magnets with promising magnetic properties.

Topics

• density
• impedance spectroscopy
• Carbon
• Oxygen
• Nitrogen
• Hydrogen
• Boron
• iron
• sintering
• Neodymium
• coercivity
• carbon content