Abstract: A method of induction heat treatment of articles having curved outer surfaces, such as differential housings. The method employs a semi-rectangular induction coil that is adapted to provide a plurality of lateral magnetic fields that are used to induce currents in, and thereby provide heat to, a portion of the curved section of the article. The method and induction coil are particularly adapted to provide an induction hardening heat treatment of a curved heat treatment portion of a differential housing. The differential housing was cast from nodular iron. The induction-hardening heat treatment comprised heating the heat treatment portion of the differential housing above the austenite transition temperature and quenching to below the martensite transformation temperature.

Abstract: A method of induction heat treatment of articles having curved outer surfaces, such as differential housings. The method employs a semi-rectangular induction coil that is adapted to provide a plurality of lateral magnetic fields that are used to induce currents in, and thereby provide heat to, a portion of the curved section of the article. The method and induction coil are particularly adapted to provide an induction hardening heat treatment of a curved heat treatment portion of a differential housing. The differential housing was cast from nodular iron. The induction-hardening heat treatment comprised heating the heat treatment portion of the differential housing above the austenite transition temperature and quenching to below the martensite transformation temperature.

Abstract: A method of induction heat-treating certain surfaces of an article comprising a hub and a plurality of trunnions or shafts extending therefrom, wherein the surfaces to be heat-treated comprise the surfaces of the trunnions. The method employs an induction coil that provides a planar magnetic field that is adapted to the irregular shape of the article, such that the induction coil produces magnetic fields that are adapted to induce currents in, and thereby heat, the trunnion surfaces of the article. The method and induction coil are particularly adapted to provide an induction hardening heat treatment for trunnion surfaces of trunnions used in steel spiders of spider or tripod-type constant velocity joints.

Abstract: A method of induction heat treating the outer surface of articles having an irregular surface shape. The method employs an induction coil that provides a non-planar magnetic field that is adapted to the irregular shape of the article, such that distinct sections of the induction coil produce distinct magnetic fields that are adapted to induce currents in, and thereby provide heat to, distinct sections of the outer surface of the article. The method and induction coil are particularly adapted to provide an induction hardening heat treatment for the outer surfaces of the inner races of Rzeppa-type constant velocity joints.