Testing has shown that the rate of cooling after removal of the copper rotor from the die-casting die is unimportant and does not impact electrical performance.
It has been suggested that water quenching of the rotors after removal from the die might help break any bonding between the die-cast copper and the lamination steel, thereby minimizing electrical losses. Therefore, a series of test rotors were die-cast where half of the rotors were water quenched and the remainder air-cooled. Testing showed that there was no difference in the electrical performance of the two sets of copper rotors.