Cleaning rust from motor laminations
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  1. #1
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    Default Cleaning rust from motor laminations

    Does anyone have any advice for cleaning rust from motor laminations?

    For background, a few years ago a friend gave me a really nice Baldor bench grinder (maybe 1980's vintage) that had been submerged (briefly) in a flood. It worked well, but the bearings didn't last long - I soon had to wear hearing protection just to be near it when running. When I took it apart to replace the bearings I was dismayed by the rust encrusted on the rotor, so I took a brass brush and (lightly) brushed it off by hand. I probably didn't have to, except that I was mentally incapable of leaving it there, and I figured having rust powder coming loose inside the motor wasn't actually a good thing.

    When I put it back together it ran very slow - probably a few hundred RPMs, very weakly, and very hot.

    So I have three questions:

    (1) What exactly was wrong? I assume that the laminations had shorted, either magnetically or electrically (those seem to be very similar things when magnets are concerned). Some of the insulated coating must have come off the outside edge of the laminations for the metal underneath to rust. I didn't brush it vigorously, so I don't think I could have removed enough of the insulation to allow the laminations to actually come into contact. Did the rust stick inside the exposed edges of the laminations, making contact with metal on each side, and cause a short?

    (2) Was there some way to fix it without going back in time and not screwing with it? I don't remember what I did to clean it afterwards, although I'm generally fond of WD40, brake cleaner, and naptha, so I certainly would have rinsed it with at least one of those. Assuming the problem was the rust in between the laminations, would it have been possible to wash it out? I guess I could have dropped the whole thing in evaporust, since it was toast anyway, but I was pissed off at myself for not being able to stop while I was ahead so I gave it away.

    (3) Is there a way to clean it that wouldn't risk making it worse, and, if I can clean it, is there anything wrong with a light coat of clear coat to cover the exposed metal? I now have another motor on the bench with rust on the rotor. My temptation is to hold it with a silk cloth, clean it with a chinchilla hair brush, and clean it by gently whispering "solvent" at it (like the way one puts vermouth in a martini). It's a vintage windshield wiper, however, and lives under the bonnet of an old British car that can't keep the rain out on a dry day let alone a wet one, so I'd like to give it a fresh clear coat to keep future rust at bay, which means some amount of cleaning.

    I didn't see another forum covering motors and there seem to be plenty of people here who have spruced up old motors. Sadly the couple of local motor shops I've dealt with in the past are long gone.

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    I'll start by saying that I'm not a motor repair person by trade, but my first thought is doesn't have anything to do with your rust removal of the rotor. The rotor to field clearance is small, but if it ran with the fungus on it, and you removed the fungus, it should run fine. Are you sure you didn't 'short stack' it..put the rotor in backwards! This would be obvious as the L-R hand nuts on the arbor would be bass-ackwards to the way they should be.

    Is it possible you assembled the bearings incorrectly and that may be the cause of the problem. Is there a centrifugal switch in the motor for a start cap that may have been damaged when you took the motor apart.

    Is there a start cap hidden in the base that failed or was broken or disconnected when you did the work?

    What I'm hinting at is that the rust removal probably isn't the cause and you should look elsewhere.

    Stuart

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    if you can turn it by hand and you don't feel any drag by the rotor hitting the stator [laminations ] if so you can lightly wire wheel the roror and use a small wire brush to remove any scale from the stator [keeping away from the windings as you don't want to rub the coating off and short things out and if its a bearings new will fix that . if that's all ok and its a 120 or 240 volt 1 ph. then it may have a start winding and if that's the case i would be looking at the centrifugal switch that powers up that winding when it starts [you know that click you hear ] and more then likely it dose not have a start cap but it may . just some thing you may try . good luck its a baldor so its worth putting some time in to.

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    Leaving the diagnosis to the pro motor guys here, I don't feel knowledgeable enough to contribute there.

    I can however vouch for Evapo Rust. I had a simple Starrett height gage that came I by for $10 had lite surface rust.
    Disassembled it, put it in a small Tupperware, submerged all parts for ~10 hrs. Pulled them out and man they looked good. A little flat surface finish.

    I would like to blue it some how, but I am not the sharpest tool in shed when bluing. Does anyone have suggestions?

    Back to the motor, just spit balling but this product may help you in some manner. Being the density of H20 you get it in places by capillary action.

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    Rust on the laminations is a sign to me that their insulation has been compromised. Disturbing the rust may have established electrical shorts between the weakly insulated laminations.

    It's also possible you disturbed a corroded electrical connection somewhere and the motor is now single-phasing or the start/run winding is open.

    Best bet is to leave rotor/stator rust alone and lightly oil the laminations to prevent further damage. Check for weak connections.

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    A few shorted lams generally should not slow the motor. They do not mess up the magnetic field that much. And I doubt they got shorted.

    Running slow is reason enough for heating. And that generally comes from not starting right, or miswired coils.

    Baldor grinders are generally PSC motors with no start switch, and a single always-connected capacitor. If that is not connected, or is not connected to the correct winding, the thing will not start well, or possibly not at all.

    If dual voltage, be sure it is connected correctly for the voltage you are using, and that the capacitor is good.

    They are usually symmetrical, so reversal may get the wheel nuts on the wrong ends, but will not generally mis-position the rotor. There may be exceptions, but I'd think they would be obvious as soon as assembly is attempted.

    Brake cleaner is bad stuff for motors.... it can dissolve insulation and short wires. If that was used, and got on the windings in any quantity, there may be a real problem. Most solvents are bad for motor windings. There are safe ones available.

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    What JST said is right on. The laminations in the rotor are largely low carbon steel and probably don't have core plate. Core plate is a coating of inorganics such a paint that are used to insulated the laminations one from another to cut down on eddy currents. The reason being that the is little in the way of eddy currents in the rotor. In the stator, often just a light coating of rust on the laminations is enough core plate. The stator laminations are of better quality steel, having aluminum or silicon added to inhibit magnetic aging. In other words look to something other than rusty laminations, just make sure that rust does not bridge the rotor-stator air gap.

    Tom

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    In fact, the rotor only sees 60 Hz on starting. The molten aluminum that is injection molded around the laminations to form the bars, end connections, and maybe fan blades, likely shorts the laminations anyhow.

    But the rotor sees only the slip frequency when the motor is running, so no great efforts are needed to make the rotor laminations insulated. That's maybe 4 to 5 Hz at most.

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    Within the craft of Electric Motor Repair, rusty laminations are cleaned using blasting media.

    The sequential steps in a complete rebuilding of an apparatus is outside the scope of a little ole Internet forum.

    Any motor subjected to being submerged in water should be dealt with in a timely fashion after the event occurs,
    or the internal parts will quickly be degraded beyond being economically repaired. Obviously, that time has long past.

    There is a lot of false or inaccurate information in this thread which is reflective of what the Internet has evolved into (especially on public forums).

    The short simplified answer to the OP's question is, rust is removed from stator and rotor laminations when the motor's components
    have been stripped of all other parts making up its assembly.

    The letters "PSC" stand for Permanent Split Capacitor run. It's a single phase AC motor typically used in fan and blower applications.

    A single phase bench grinder from the era noted by the OP incorporates either a Split Phase, or a Capacitor Start motor.

    I'll second what the OP wrote regarding the decline and disappearence of motor repair shops.
    It is as with everything else in the world... the transition of chasing more economical methods of keeping a business afloat.
    I was surprised one day on the shop floor when learning a 1000 horsepower motor was not going to be rebuilt because of all the costs
    making it not worth repair. Simply, open up the "catalog", and buy a new one. Yes, a thousand horsepower.

    John

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    brushing off the windings could have created a short. pull it apart and check the resistance to ground and the windings.

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    Quote Originally Posted by d'Arsonval View Post
    .....................................There is a lot of false or inaccurate information in this thread which is reflective of what the Internet has evolved into (especially on public forums).

    ......................
    The letters "PSC" stand for Permanent Split Capacitor run. It's a single phase AC motor typically used in fan and blower applications.

    A single phase bench grinder from the era noted by the OP incorporates either a Split Phase, or a Capacitor Start motor.

    .....................

    John
    I'll challenge that...... I have had several single phase Baldor grinders, of various ages, and ALL of them have had PSC motors.

    The cheap hobby grade grinders tend to have motors with start switches. Craftsman, western auto, Buffalo (china), that sort of product. Easily determined because you can hear the click when the centrifugal mechanism resets as the grinder slows down.

    What the OP suggested as the repair technique was fine (done by hand with care, of course) up until the Bra-Kleen etc was mentioned. That is a huge no-no......

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    One further comment, time was that if a motor or transformer got soaked as in a flooded basement, that the first thing to do was to dry the item in a low temperature oven. Completely dry. This was a common fix back in the day when there were large transformers and chokes in tube radios.

    Tom

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    The other option is to apply low voltage DC to the windings and bake it out from internal heat. Start low, and work up, watching the temperature (no cooling with it not spinning).

    Certainly faster than an oven, and does not need one. DC, because DC will provide full current at a low voltage that you can control.

    Some things you cannot use DC on due to special conditions.

    start low, you do not want to boil anything, you just want to drive out moisture. Boiling any trapped water would risk damage to the windings.

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    The thumb in suspender expertise on this thread is hilarious. I work in a pump/motor rewind shop that specializes in submersible pumps, and, except a short 3yr stint in a jydraulic shop, have for 10+yrs.

    Rust on the laminations is no huge deal. Hit it with emory tape on the lathe to keep the crusty from dragging the stator. I see one out of maybe 200 rotors fail core loss, none from getting wet, even to the point of sitting submerged in 20ft of water due to a seal failure. Brake cleaner won't hurt anything. It evaporates in minutes.

    Only big concern with rotors really is damage from dragging on the stator due to catastrophic bearing failure. You have only 10% air gap tolerance before things get bad. On a 30-100hp motor, you are usually looking at .020-.030 air gap. A .003 flat spot on one side or at one end will not stop the motor from running, but it will cause the rotor to be pulled asymmetrically, either radially from the flat spot, or axially from wear on one end. Either will cause higher current draw and short lived bearings.

    Sounds like your start cap, switch, or windings are not right on the slow start. The start switch is obvious when you take the end bells off.

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    Quote Originally Posted by Mike C. View Post
    .................... Brake cleaner won't hurt anything. It evaporates in minutes.

    ..................
    Well......... that depends on what it gets into. You need to keep it off the coils. It is a hellacious good solvent, and may soften or dissolve varnish type wire insulation, with bad results.

    If you use it far away from wires etc, it's OK.... but...........

    There are safe alternatives that won't do damage. Just avoid using Bra-Kleen on electrical stuff.

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    backround in motor repairs.
    Oxide is an electric insulator. we would intentinally rust laminations to increase resistance of rotor as a repair method on old motors with "hot spots" areas in which eddy current was passing through laminations creating heat. please only remove whats needed for clearence to stator.

    as for the slow and hot rotation, is there a chance you have damages one of the phases or coils and the others are working overtime to try and keep up?

    is it single phase? are the start windings damages, start capacitprs toast?
    are you applying the required voltage? low volt=more amps= heat

    does it spin freely by hand when off? if something is dragging it will overload quickly.

    pm me if you like, im poor at following threads some times

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    Quote Originally Posted by tom_boctou View Post
    ...
    I guess I could have dropped the whole thing in evaporust, since it was toast anyway, but I was pissed off at myself for not being able to stop while I was ahead so I gave it away.

    ...
    I guess that the OP got scared away by the replies and by most of us not reading carefully his original post.

    He gave the grider away, no use of asking him to try a few other things on it. The questions he is asking are more targeted on not harming a wiper motor of an old British car.

    Paolo


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