PURPOSE: To provide a method of checking a protective film of a rare earth iron permanent magnet, where the 100% inspection of the magnets can be quickly carried out without overlooking rust gathered on the permanent magnet.
CONSTITUTION: A rare earth iron permanent magnet coated with a protective film is exposed to an atmosphere of H2 for a certain time, and if a protective film has defects such as pinholes or the like, a rare earth iron permanent magnet main body is disintegrated by hydrogen which penetrates through defects such as pinholes or the like produced in the protective film in an inspection tank. Therefore, if a protective film is defective, a permanent magnet is disintegrated by hydrogen after a certain time elapses, so that it can be visually, surely, and quickly discriminated that a protective film is defective or not. A non-defective magnet is kept constant in magnetic characteristics, and a protective film is free from damage.
MIZUHARA TAKESHI
KOBAYASHI KOJI
