Permanent magnet d.c. dynamoelectric machine and method of making same

Abstract

A preferred process includes arranging field yoke segments, pole face segments, and one or more pieces of ceramic magnet material so that the yoke segments and pole face segments can be relied upon to establish low reluctance paths for magnetic flux associated with the ceramic magnet material. The process includes holding the ceramic magnet material sandwiched between the yoke pieces and pole pieces within a cavity of a casting fixture; admitting a molten metallic material to the cavity and adjacent to the yoke, pole, and ceramic material pieces; permitting the molten material to solidify; and thereafter removing the field assembly from the cavity with the ceramic pieces completely surrounded and encased by the pole pieces, yoke pieces, and solidified material. In a more preferred form, molten aluminum at a temperature of at least about 660.degree. C is used as the molten metallic material even though the resulting thermal shock causes a fracturing or shattering of the ceramic material. In this form, the process includes fracturing the ceramic material because of the thermal shock caused by exposing it to the molten aluminum. After solidifying, the solidified material, along with the yoke and pole pieces, holds the ceramic material fragments together so that the fragmented ceramic material may be used as a permanent magnet portion of the field assembly.