How to clean windings of small 3-phase motor, and what bearing type to use

ballen · Feb 1, 2020

I want to refurb and use a small 220/380V 3-phase motor. It's Swiss, 1/2 HP (=400 Watt) and was made for driving an internal grinding spindle via pulleys. The motor dates from the 1960, I would guess.

I opened it up and discovered two things that need attention. First, someone pumped far too much grease into the bearings. The windings and a lot of the other internal components are covered with a mix of grease and grit.

Is there a good way to clean out the motor windings? I suspect this is from the days before epoxy was used for potting windings.

Second topic: the bearings are both toast. They are GMN 6202 without shields. meant to get grease from external grease nipples. Should I replace them with the same type of open bearings? Or metal shield ones? Or rubber seal ones? C0 or C3 clearance? (This motor drives a 250mm/10" diameter flat belt pulley, and does not have belleville washes or some other way to preload the bearings.

Thank you!

tdmidget · Feb 1, 2020

As you can see, many more bearings are ruined by too much grease than not enough. I would clean the windings with mineral spirits after gently removing what you can by hand. I would not use any stronger solvent than mineral spirits. I would replace the bearings with sealed ones. Tell them it is for an electric motor, supposedly they are better than cheapest crap they are used to peddling on a price basis.

priitm · Feb 1, 2020

I was in the same situation except dust in windings.
Swiss motor 50 years old,from tool grinder, without axial preload spring washer. I installed C3 metal shield bearings. The grinder has rather strong belt to spindle. Not sure if I did right, but it works.

redlee · Feb 1, 2020

Years ago I had a 3 Ph. motor that was full of grease.
Pressure washed it, sat the parts in front of the wood stove for a few days, brought it to a mototr shop once assembled and they tested it and it was fine. Been using it for years now with no troubles.

Mark Rand · Feb 1, 2020

As the others have said. The insulation is probably varnish (class B) instead of bitumen (class A). Use kerosene/paraffin/mineral spirits to clean the windings. Then use C3 bearings. A good solution is to use metal shielded bearings and to remove the shield on the side where the grease port is.

Limy Sami · Feb 1, 2020

Like others have said - a bucket of kerosene or mineral spirits (NOTHING STRONGER !!) and a paint brush, plenty of soaking and gentle brushing, leave to drain then gently blow off with air and leave to dry.

Joe Gwinn · Feb 1, 2020

ballen said:
I want to refurb and use a small 220/380V 3-phase motor. It's Swiss, 1/2 HP (=400 Watt) and was made for driving an internal grinding spindle via pulleys. The motor dates from the 1960, I would guess.

I opened it up and discovered two things that need attention. First, someone pumped far too much grease into the bearings. The windings and a lot of the other internal components are covered with a mix of grease and grit.

Is there a good way to clean out the motor windings? I suspect this is from the days before epoxy was used for potting windings.

Insulation is very likely glyptal, which is pretty robust stuff.

Bob-J-H · Feb 1, 2020

I have cleaned many a motor with engine cleaner. Never had a problem>

tdmidget · Feb 1, 2020

Mark Rand said:
As the others have said. The insulation is probably varnish (class B) instead of bitumen (class A). Use kerosene/paraffin/mineral spirits to clean the windings. Then use C3 bearings. A good solution is to use metal shielded bearings and to remove the shield on the side where the grease port is.

Why remove the shield? You shouldn't be greasing it. Remove the grease fitting.

dana gear · Feb 1, 2020

We operate more electric motors in our business then most people would believe, that said more then not when we replace motor shaft bearing that had previously been greaseable we go sealed and use best available sealed bearings.
We have motors out there with sealed bearings pushing 25,000 hours operational time on large motor compressors.

Deerehauler · Feb 1, 2020

I have a 30 hp 3600 rpm motor I use for a rotary phase converter. It runs a 1750 rpm 20 hp motor driving a hydraulic pump for a 60+ ton press.

It was overgreased and VERY dirty when I got it, so I used Gunk Engine cleaner several times to get the old grease out of the windings. The last time I used Dawn dishsoap and hot water, and rinsed with hot water. I blew out everything I could and left the motor sit in the July sun for a couple days with a small fan blowing through the windings. I checked all the windings with a megger and they all passed easily.

I replaced the open bearings with sealed bearings and removed the grease zerks. I use this almost every day for the past two years and have had NO issues.

ballen · Feb 2, 2020

tdmidget said:
Why remove the shield? You shouldn't be greasing it. Remove the grease fitting.

Also my thinking, unless someone can convince me otherwise. I think both grease and bearings have improved a lot in 60 years.

ballen · Feb 2, 2020

dana gear said:
When we replace motor shaft bearing that had previously been greaseable we go sealed and use best available sealed bearings.

Do you mean rubber full seals or metal shields? I just checked and decent bearings (SKF) with 2RS (rubber shields both sides) are rated over 10k rpm continuous duty. In my case the motor is running at 2800 rpm, so well below that speed.

Frankly I don't see any decent reason not to close the grease ports and use rubber sealed bearings. It seems like the sensible choice, no?

metalmagpie · Feb 2, 2020

Many motors have grease ports whose only purpose is to lubricate the bearing races so that they can slide when the rotor gets longer from heat. These motors should never have grease or oil pumped in post-assembly.

Rubber sealed bearings have some drag, which wastes energy as heat. Buy shielded, not sealed. If you want one side open buy 6202-Z; else buy 6202-ZZ.

C3 is a good choice.

metalmagpie

rons · Feb 2, 2020

Remove end bells. Set the motor on end with wood blocks. Then use some Mineral Spirits and brush the inside. Let the solution drain into a pan.
Reverse orientation of motor and brush down again. Keep doing this until clean.

If you really must use those grease fittings buy rubber sealed bearings and remove the seals on the end bell side. Nothing will leak into the winding compartment again. But it's better to use sealed bearings as is and forget about the grease fittings.

tdmidget · Feb 2, 2020

When a motor is actually intended to be greased due to severe service (automobile shredder comes to mind) the end bells will have 2 plugs or one on the bottom and a fitting on top. To grease this properly the bottom plug is removed and clean grease pumped the top WHILE IT IS TURNING. The dirty grease will come out the bottom. When clean grease comes out the bottom replace both plugs. It will have the correct amount of clean grease. Any normal service will be better off with sealed bearings.

ballen · Feb 2, 2020

Thanks everyone for the advice and experience. It's been very helpful.

I washed out the windings today with white spirit. I used a paintbrush, a toothbrush and an acid flux brush. Afterwards I let it drain for a while then blew it off gently with some compressed air. Right now it's sitting with a 40W light bulb inside it, just a bit too hot to touch comfortably. I'll leave it like that for a few days to dry out.

I've pulled out the brass grease nipples and will turn a couple of brass plugs to block the ports. I've also ordered a pair of SKF explorer 6202 2RS C3 bearings. With the use this will get (tens of hours a year) and the nasty environment (coolant, grinding grit) I think that makes more sense than metal shields. I don't care if a few watts of power are lost to heat in the seals. (The literature I have seen only cautions against this for shaft sizes larger than 30mm or rotation speeds about 3600 rpm. Neither is true here.)

The front bearing is captured both sides. The rear bearing is a snug sliding fit and the designers left enough clearance that it can move back and forth as the motor warms and cools. I'll be sure to leave a bit of grease in there to help it move back and forth. I think it'll be another sixty years before the next guy has to swap the bearings again.

Cheers,
Bruce

rons · Feb 2, 2020

ballen said:
The rear bearing is a snug sliding fit and the designers left enough clearance that it can move back and forth as the motor warms and cools. I'll be sure to leave a bit of grease in there to help it move back and forth.

That shouldn't be done. The fit is supposed to be a little tight. When the motor is to be taken apart a little heat from a torch will allow the bearing fit to loosen
just enough so that it slides away from the housing.

ballen · Feb 3, 2020

rons said:
That shouldn't be done. The fit is supposed to be a little tight. When the motor is to be taken apart a little heat from a torch will allow the bearing fit to loosen just enough so that it slides away from the housing.

In this motor design, the bearings inner races are a snug interference fit on the shaft. (When I put on the replacements, I will put the motor rotor in the deep freeze and heat the bearings to 120C so that they slide together.) On the other hand the bearing outer races are a transition fit in the housing. I was able to pull them out of the housing with hand force. Not heating was/is needed.

Within the category of transition fit they are somewhere in between a "tight fit" and a "similar fit". This means that the outer races will not rotate in the housing, but with moderate hand force they can be moved back and forth. I don't think that wiping a bit of extreme pressure grease inside the gear housing will change that, and it should help prevent corrosion and fretting damage.

How to clean windings of small 3-phase motor, and what bearing type to use

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