Chuck Yung
EASA Senior Technical Support Specialist
Rapid changes in technology can mean better ways of doing things. In the EASA spirit of cooperation, we’re asking for proven tips from members. Do you have a shortcut or tip for doing a job better? Is there a new tool that works particularly well for some motor-shop task? Share your knowledge! To kick things off, here are a few “Quick Tips” using technology that has been around for as long as I can remember.
Tired of wiping out sleeve bearings when testing 2-pole machines? Use your vibration analyzer to monitor the axial vibration reading. If a sleeve bearing starts to wipe, the velocity reading will climb before the temperature does. If you wait to see smoke from vaporizing oil, the bearing may be damaged beyond repair.
Immediate action when the velocity starts to climb lets you stop the motor before the babbitt bearing is damaged. If your analyzer is set up for two probes, monitor both ends.
Want to reduce labor costs? Use a vibratory tumbler to polish brushholders and breaker contacts. Corn grit works best, and the labor saved will pay for the tumbler within a few jobs. Place the parts in the tumbler a few hours before you need them and they will look brand new.
Dissect ball bearings on incoming work to catch problems like preloading or shaft currents. Predictive maintenance tools let customers remove motors from service before they fail. Something caused that noisy bearing — find out what! Be sure to mark each bearing to identify which way it was mounted on the shaft. That makes it easy to pinpoint the source when you find a problem.
Use a die grinder with a thin wafer disc to cut cleanly through the outer race. Wear tracks that appear to be off-center indicate thrusting or a preload condition. The frame may be bolt-bound, or the coupling may need to be adjusted. Diagonal tracking indicates misalignment, possibly of the bearing housing. Striations/fluting are a sure sign of shaft currents.
Identify these problems early, before the job is quoted. Additional billing is always better than an unhappy customer!
You weekend racers know all about Plastigage! Use it when inspecting sleeve bearing machines to check bearing-housing and bearing-shaft clearance during disassembly. It really improves the quality of inspections when working with spherical sleeve bearings. Not to mention field service jobs, when complete disassembly is not an option.
Silicone is available with a curing agent that does not attack copper. Tell your supplier when the application involves copper, to be sure you use the best product. Avoid using the wrong silicone in or near a DC machine. The out-gassing that occurs during curing will inhibit proper commutation. It only takes a few parts per million to prevent a commutator film from forming. Never use a latex product to pot electrical components — latex is semi-conductive. Using latex to seal diodes will result in some unusual performance problems!
Having a hard time convincing an old-time millwright that laser alignment is better? Next time he pulls out that dial indicator, show him this check for indicator sag. Attach the indicator to a shaft, and zero the indicator at 12:00. Now rotate the shaft so the indicator is at 6:00. The difference is due to indicator sag. Don’t let him choke it up close. Extend the indicator arm just like on a real alignment job. Light doesn’t sag!
Most of you have little tricks devised to make the job easier. Please write down your tips, and send them to me so that I can share them with fellow EASA members. You can write to me in care of EASA Headquarters, fax to 314-993-2998 or email to cyung@easa.com.
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