Plain bearing lubrication

[chrisr]

Hi all.
I thought someone here might know about these, though the application won't be normal forum fodder.

A typical one that I come across has a 5mm steel shaft running through, is about 12mm and not quite spherical. There's a pocket of yellow grease around it. They dry up.

I'm a boiler engineer (sorry gas, not steam!) and these bearings are in pairs, in the flue fans, which are about 50W, shaded pole motors. They operate in the flue gas, which could could be say 200°. Some of the fans cost £150+ while almost identical ones are £35. The variations make swapping things impossible.

I assume the bearings are sintered metal, originally oil impregnated, but I'm not sure. A squirt of WD40 gets them going again for a day or so, car engine oil a couple more days, but they seize again and have to be binned.

Can anyone suggest what might be successful in getting these fans going again? The one's I mean aren't worn significantly, it seems nuts to chuck them out and have to charge so much.

[ron]

Hi
Have you investigated hi-temp lubricants like 'Thread Guard' which is a molly based lubricant that doesn't dry out even under VERY high temperatures, it isn't meant for something that is moving all the time but it would suggest there are specialist lubricants that would suit your purpose.
Ron

[chrisr]

Hi Ron
No, I haven't yet. I imagine the "yellow grease" must be a high temerature product, but I'm wondering how the bearing is supposed to work. I mean, would the part I've drawn speckly be porous as I suggested, or just a solid piece? It's sort of grey...
There was plenty of yellow stuff in the one I just took apart.
Thanks for your thoughts.

[Malcolm]

A silicone grease might work. Worth a try.

[David Thompson]

You could try re-impregnating the bushes by soaking them in warm oil for some time. It would have to be an oil suitable for the service temperature. Perhaps synthetic engine oil would work.

[jackrae]

Also make sure that you fully clean the shaft of all old hard gunge before you re-assemble. There is usually a hard black residue builds up on the shafts and this seems to be the root of most "seizing" problems.
jack

[mackintosh]

Hello Chrisr I think you are right about the sintered bearing and assume they are spherical as a self centering action, the lubrication needs to be soft enough to be absorbed into the porous bearing a silicon based grease may be the best bet.
Bob

[chrisr]

Thanks chaps. Plenty to think on.
I might try carburettor cleaner to wash the hard black stuff out, which is probably clogging the bush. Or methylene chloride, which dissolves most hard oil based things (eg paint!)

Yes the ball shape is to centre and allow misalignment of angle - I've left out some detail in the sketch.

[spurley]

Hi Chris

I wonder if a sonic cleaner might shift the stuff out of the sintered bearing? When I worked in the Instrument shop at BCAL we used one filled with solvent, MEK, to clean sintered oxygen filters.

Might help if you can get one? My wife has a plastic one for jewellry but I don't think that would stand the solvent!

Cheers

Brian

[havoc]

I don't know how large those bearings are, but if you could find a syringe large enough to put them in, then put one in the syringe, add the oil you want to impregnate it. Don't fill to the top, just enough to cover it. Then put in the plunger and squirt out all the air. Close the tip and pull on the plunger. The vacuum you create will let the air escape and the oil enter the bearing.