Die-Cast Rotors for Induction Motors

Abstract

There are many problems to solve in connection with the manufacture of diecast rotors that require the co-ordinated efforts of the design and manufacturing engineers. Forcing molten aluminum under high pressures into the rotor slots causes excessive stray load losses unless the laminations are insulated properly and strain relieved, and the slots insulated from the cast aluminum conductors. Heating processes may be necessary after machining the surface. It is also necessary to select the best and most economical die casting methods, equipment, and furnaces. The moulds properly gated, holding pressure, pressure on the die-casting metal, and temperature are all important to the production of homogeneous die cast rotors free from impurities. With proper control, die-cast rotors can be manufactured to relatively close limits of rotor resistance and with the stray load losses reduced to a satisfactory value resulting in satisfactory performance, and generally at a lower cost than copper cage rotors. This paper explains the cause of the stray load losses, processing to reduce them, and suitable test methods. There are curves showing the effect of excessive stray load losses upon performance, results of various processes, and illustrations of die-casting methods and diagrams of equipment for testing die-cast rotors.