Recycling of additively printed rare-earth bonded magnets

Abstract

In this work, we describe an efficient and environmentally benign method of recycling of additive printed Nd-Fe-B polymer bonded magnets. Rapid pulverization of bonded magnets into composite powder containing Nd-Fe-B particles and polymer binder was achieved by milling at cryogenic temperatures. The recycled bonded magnets fabricated by warm compaction of ground cryomilled coarse composite powders and nylon particles showed improved magnetic properties and density. Remanent magnetization and saturation magnetization increased by 4% and 6.5% respectively, due to enhanced density while coercivity and energy product were retained from the original additive printed bonded magnets. This study presents a facile method that enables the direct reuse of end-of-life bonded magnets for remaking new bonded magnets. In addition to magnetic properties, mechanical properties comparable to commercial products have been achieved. This research advances efforts to ensure sustainability in critical materials by forming close loop supply chain.

Manufacturing Processes for Permanent Magnets: Part II—Bonding and Emerging Methods

“…Big area additive manufacturing (BAAM) is a system developed by Cincinnati Inc. to fabricate large parts via a material extrusion method which has produced bonded Nd-Fe-B magnets with attractive properties. [16][17][18][19][20][21][22] BAAM deposits layers of molten thermoplastics with magnet particles by extruding the material through a nozzle. The thermoplastic solidifies rapidly after deposition, allowing a large magnet to be built quickly.…”

“…They found that the powders recycled via the hydrogen decrepitation performed better than the powder recycled via mechanical milling, although the remanence and coercivity degraded for both methods-with coercivity degrading the most. Gandha et al 18 reported on recycling waste bonded magnets by pulverizing thermoplastic bonded magnets in liquid nitrogen and then warm- compacting the powders to remake bonded magnets. The approach used by the authors yielded magnets having B r , H c , and (BH) max in the range 96-104%, 90-96% and 86-100%, respectively, compared to the waste bonded magnet being recycled.…”

Dismantling of Printed Circuit Boards Enabling Electronic Components Sorting and Their Subsequent Treatment Open Improved Elemental Sustainability Opportunities

“…This is, however, more difficult here, as these alloys oxidize easily in air, hence their covering with a protective coating. Various groups have therefore reported a general process that first performs a hydrogen exposure, which creates a volume expansion of the magnet as metal hydrides are formed [205][206][207][208][209][210]. This allows the casing to break, and the alloy to turn easily into fine powder.…”

“…This process also has the advantage that, if carefully performed, it protects the alloy from oxidation [211]. Additional milling, sometimes at cryogenic temperatures, has also been reported [205]. Once hydrogen is removed, by heating in neutral atmosphere (~200 • C), one can then reprocess the powder via compaction (with additives, binder, reducing agents, etc.)…”

“…then follow with a sintering step to produce new permanent magnets with the best performances possible (Figure 7). Many reports and patents can be found on this last portion of the process [205][206][207]209,[212][213][214][215][216][217][218][219], which most likely only represents the tip of the iceberg when compared to the unpublished trade secrets from the permanent magnet industry.…”