Criterion to evaluate the stability of Nd sintered magnets for refrigerant compressor motors

摘要

This paper concerns the stability of Nd (neodymium) sintered magnets used for high-efficiency DC motors in refrigerant compressors. Many kinds of Nd sintered magnets with and without surface treatment were subjected to the aging test of 140 °C and 1440 hours under three different atmospheric conditions of refrigerant, oil, moisture content and vacuum level. Mechanical and magnetic properties of the magnet were examined, and chemical characteristics of the oil and refrigerant were also analyzed As a result, most of the tested magnets retained the satisfactory properties after the aging test, but some magnets without surface treatment showed deterioration in magnetic properties. The deterioration was larger under the condition with higher moisture content. Concerning the oils and refrigerants, no remarkable change in their chemical characteristics was observed after the aging test. The test conditions employed in this study become one of the evaluation criteria of the Nd sintered magnets.