Up Time Magazine - December 2008/January 2009 - (Page 58) defects. All clearances and run-outs were within acceptable tolerances. There were no rub marks or evidence of any shorting on the rotor or in the winding. The bearings had only normal wear and the journals were in good shape. The motor was steam cleaned, and the winding dipped and baked. The rotor went through the balance machine before reassembly. The motor was test run on a test pad at full voltage. The vibration amplitude exceeded acceptance standards. Trim balancing was attempted and the test run repeated without improvement. At this point, there was a pause to take another look at the data and develop a new plan of action. Not only were the overall levels too high, there was a significant 2x component with some 3x in the spectrum. Looseness was an immediate speculation. The carrier bearing in the outboard of the motor is a critical fit, and any taper in the journal or looseness in this fit will cause excessive vibration in the top of the motor. The carrier bearing had not been removed during disassembly due to the meticulous effort required to maintain this critical fit. Figure 6 – A bump test showed natural frequencies occurring at running speed and 2x running speed. We decided to pull the rotor and remove the carrier, but the journal and bearing were well within tolerances. All clearances and run-outs were re-checked and found to be acceptable. We found nothing to explain the high vibration. The motor was carefully reassembled and test run. Vibrations were still high, with a 2x running speed frequency that was higher than the running speed component and there was still some 3x. Knowing that the motor had been scrutinized with a fine tooth comb twice, suspicion shifted to the shaft. Since the pump had suffered such a catastrophic failure, perhaps some of the energy transferred through 58 december/january 2009 http://www.mobiusinstitute.com http://www.mobiusinstitute.com
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