A superconducting solenoid and press for permanent magnet fabrication

For the first time, a superconducting solenoid (SCM) was used to increase the remnant magnetization of sintered NdFeB permanent magnets (PMs). In particular, magnetic alignment of commercial-grade PM powder was improved by axial-die pressing the powder into 12.7-mm diameter cylindrical compacts in the 76.2-mm warm bore of a 9-T SCM. The press used to compact the powder is unique and was specifically designed for use with the SCM. Although the press was operated in the batch mode for this proof-of-concept study, its design is intended to enable automated production. In operation, a simple die and punch set made of nonmagnetic materials was filled with powder and loaded into a nonmagnetic press tube. The cantilevered press tube was inserted horizontally, on a carrier manually advanced along a track, into the SCM. The mechanical components and the SCM, in its liquid helium dewar, were specifically designed to allow for insertion and extraction of the magnetic powder and compacts, while operating the solenoid at 9 T. Compaction was achieved by pressing the punches between the closed end of the press tube and the hydraulic cylinder mounted on the opposite end. Improvements up to 10% in magnetization and 20% in energy products of the permanent magnets were obtained, as the alignment fields were increased above the 2-T maximum field of the electromagnets used in industry. For comparison, increases in magnetization of 3% are significant in the mature sintered magnet industry.