The die-cast copper motor rotor – a new copper market opportunity
Induction motor manufacturers have long known that substitution of copper for diecast aluminum in the rotor squirrel cage would significantly reduce motor losses and improve the electrical energy efficiency. Aluminum is readily die-cast to produce the complex squirrel cage within and around the iron laminations of the rotor. Copper is much more difficult to die-cast due to its high melting temperature which leads to premature die failure. The work reported here addresses the die life problem in die casting electrical grade copper. A number of candidate high temperature die materials were surveyed. Computer simulation of the cyclic thermal and stress gradients in dies provided insight into the “heat checking” failure mechanism and how it could be minimized or avoided. A nickel-base alloy die system preheated to and operated at ~625°C has been developed and shown to greatly extend die life compared to die steels operated conventionally. A die insert heating and insulation system was developed to make extended runs possible. Copper motor rotors were die cast over a range of machine operating parameters in joint effort with several motor manufacturers. Motor test results showing the predicted 15 to 20% reduction in motor losses and reduced motor operating temperatures are presented.
Fault Investigations on Die-Cast Copper Rotors
It has been known for a long time that replacement of aluminum by copper, which has an advantage in high conductivity, can be an economic solution for various applications including electric vehicle in the development of energy efficient motors. In comparison to aluminum, copper die-casting is difficult to perform due to its high density, viscosity, and melting point. Owing to these reasons, the copper die-cast rotors evince several manufacturing problems. The objective of this work is to identify the various defects in the manufacturing of copper die-cast rotor, and identify the lamination coating condition that sustains copper die-cast pressure and temperature. It evaluates the effectiveness of lamination coating on limiting the eddy current loss and the recoating process to improve in case the eddy current loss is in excess due to copper die-casting.
Contractor Failure: Analysis
The possibility exists for any construction contractor to fail to filfill the contract requirements associated with a facility. Contractor failure occurs when a contractor is unable to perform his/her contractual duties, thus requiring the facility owner to invoke the contract's nonperformance clause. This paper provides aggregate contractor business failure statistics and outlines potential causes for failure. A framework to identify and quantify the associated costs is also introduced. Several case studies are presented to examine the cause and cost of failure and the means by which the facilities were completed. Alternatives available for project completion when contractor failure occurs are discussed. Recommendations to identify and monitor contractors at high risk for failure are outlined as well. This paper provides facility owners with a greater awareness of the possibility of contractor failure, how to quantify costs of contractor failure, and avoidance techniques.