Die-Cast Copper Motor Rotors: Motor Test Results, Copper Compared to Aluminum
Motor manufacturers have long realized that because the electrical conductivity of copper is nearly 60% higher than that of aluminum, substituting copper for aluminum in the squirrel cage of the induction motor would markedly increase the electrical energy efficiency of the machine. Most motors larger than about 200 kW and a few special purpose smaller motors are built with copper squirrel cage structures manufactured by a time consuming and costly fabrication process. The intricate squirrel cage of smaller motors is produced by pressure die casting aluminum. Alternative cost-effective manufacturing methods have not been devised. A major barrier to adoption of copper for the rotor has been the high cost resulting from the short die life of the ordinary die steels experienced in die casting copper with its high melting temperature (1083°C compared to 660°C for aluminum).
Copper die-cast rotor efficiency improvement and economic consideration
Significant motor efficiency improvement can be achieved by substituting aluminum with copper die-cast rotor in a squirrel cage induction motor. This paper summarizes the experiments conducted by Westinghouse Motor Company Canada Ltd. in our copper die-cast rotor induction motors project. >
Efficacy of Biodentine as an Apical Plug in Nonvital Permanent Teeth with Open Apices: An In Vitro Study
The aim of this study was to evaluate the apical microleakage of Biodentine and MTA orthograde apical plugs and to compare the effect of thickness of these biomaterials on their sealing ability. A total of eighty maxillary anterior teeth were used. The apices were removed by cutting with a diamond disc (Jota, Germany) 2 mm from the apical root end in an attempt to standardize the working length of all specimens to 15 ± 1 mm. Both materials were placed in 1–4 mm thickness as apical plugs root canal. Root canal leakage was evaluated by the fluid filtration technique. One-way ANOVA was used in order to determine normality of dispersal distribution of parameters; thereafter, results were analyzed by Kolmogorov-Smirnov test. Overall, between microleakage values of MTA and Biodentine regardless of apical plug thickness, no difference was observed. In terms of plug thickness, a statistically significant difference was observed between the subgroups of MTA and Biodentine (p < 0.05). The apical sealing ability of Biodentine was comparable to MTA at any apical plug thickness.