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Thread: How to clean motor armature ?
12-05-2008, 02:46 PM #1
How to clean motor armature ?
DC perm magnet (German CNC axis) motor that has internal short. Slight possilbity if cleaned and baked to remove all oil traces it might be ok... so how do professional facilities do this..ultrasonic or ?
12-05-2008, 08:15 PM #2
I have a '91 HAAS that alarmed out 3 or 4 years ago because of brush dust buildup. The dealer said the only solution was to replace the motor. I had nothing to lose so I took the motor apart and put the whole armature in the ultrasonic for about 10 minutes. I put in new brushes and it's been working fine ever since.
12-05-2008, 10:33 PM #3
Wash and stove.
Wash with a solvent (gen clean) or hot soapy water forced into windings. Place in stove at about 110 deg C with a temp probe on the armature (Don't over cook it) for several hours. Remove and megger, plot result over time on a graph, repeat until reading stabilises. As armature cools, insulation reading may fall.
Ultrasonic tank would be quicker? (don't have the luxury)
If and when readings improve to a satisfactory value, re insulate.
12-06-2008, 05:08 PM #4
Only thing I'd add would be clean out the armature slots if they need it. The comm may need to be re-cut and undercut but all that is obvious.
Trink is to get the armature out without buggering up the magnets.
12-06-2008, 05:40 PM #5
I used to reclaim locomotive fuel pump armatures on a regular basis. The advice so far has been good. Avoid any sort of caustic or otherwise harsh solvent. Soapy water and a good rinse is fine. I then would heat them up to just over boiling, 110C is fine, then put them in a vacuum chamber overnight. That almost always brought the megger reading up to infinity. Then I would vacuum impregnate them with transformer varnish in the vacuum chamber, pumping it down, then letting varnish in to cover the armature. The vacuum in crevices pulls varnish into them when you let atmospheric pressure back in, really sealing them. For some jobs, people pressurize the chamber, but that mostly just speeds things up. Then they got a couple of hours bake at 265F to cure the varnish. They almost always needed the commutator turned and the slots undercut, so getting varnish on it didn't matter. About the only failures we had were when someone used a strong caustic solution. Those usually had to be rewound. Of course, if the breakdown has carbonized a track, none of this will help.
If you want, I can do yours, but there probably is a local motor shop that would save shipping. Don't settle for just dunking it in varnish, which is what some of them do. They may give you a song and dance about how it doesn't matter. Don't listen. Insist on vacuum impregnation.
12-28-2008, 01:34 PM #6
If your cure works, I will have numerous "bow down" emoticons thrown your way and you will be hailed here on PM as the Armature King, posthaste, forthwith and forthwright !
12-28-2008, 02:50 PM #7
On inspection, the state of the armature looks "as new", except for dirt, doesn't it? If one winding has been overheated (darker brown), but not black, I would try and figure out what could be the most likely cause. As far as I know windings are wound on a former, extricated like a hank of wool, they are then taped to hold the turns in place then "crushed" into a pair of straight sides with rounded ends. The straight sides are put in the pre-lined (with insulation) slots with a strip of insulation pushed in to hold them in the slot. The rounded ended are then dressed neatly (with a hammer?). So it is most likely that any damage is in the rounded ends if it were there to start of with but its the slots where the windings will over heat. The other factor is if the leadout wires were stretched as tight as a bowstring before being crimped at the communtator segements, the tension (+vibration) could have caused the leadout to rub through another turns insulation.
We had a range of motors that failed after a couple of years age in service because the windings slowly moved with heat cycling and stressed an added component (temperature detector).
If I could not figure out any potential fault with a strong eyeglass and fix it. I would just go for ultrasonic cleaning if that clears the fault, then a bakeout and vacuum impregnation, to try and hold the wires in this position while its spinning at 10k RPM.
I am thinking if over heating caused the wires to touch each other, what would happen if you put it in a deep freeze for a couple of hours. In my simple mind, if the expansion due to heat pushed the wires together, then contraction due to cold. . .?
12-28-2008, 04:58 PM #8
Ah, you do have a megger, right?
12-29-2008, 03:05 AM #9
9100 has got it right.