Bearing Housing Repair

[TugboatEng]

Is there any reason not to use hard chrome to build up a bearing housing after a bearing has spun in the housing? It saves on machining vs. welding as there is no distortion. I have seen it used on shafts where the bearing has a slight interference. This particular case is a housing with an axially free fit, ISO H7.

 

[MikeHalloran]

To the limited extent to which I understand this stuff:

When a hardened bearing spins in a softer cast steel or cast iron housing, it leaves a hole that is slightly larger than the original, and centered on whatever axis around which the bearing had been spinning. If that axis is not colinear with the original bearing bore, the result may be two half-holes, making the 'bore' egg-shaped.

Applying hard chrome to that 'bore' gives you a smaller 'bore', also egg-shaped.

It would be ideal to then grind a circular bore centered on the original axis. ... if you can find the original axis, e.g. by using whatever portion of the original bore has not been abraded away, or by measuring from the mounting surfaces. But if you actually do that, when you grind to size, you'll grind away the chrome from the original bore, or maybe leave a very thin layer of chrome, or maybe a discontinuous very thin layer of chrome.

To prevent that happening, you might pre-bore around the theoretical center before plating. ... but you need to plate on a lot of chrome to get the bore down to where it should be.

It might be easier to bore quite a bit larger than the original bore, around the theoretical center, then make and fit a sleeve from material similar to the housing, and pin the sleeve in place, without any chrome at all.

Have you got an old,cranky machinist on site with whom to discuss the possible repair options?
Mine has re-retired and is out riding his Harley, somewhere.





Mike Halloran
Pembroke Pines, FL, USA

 

[TugboatEng]

That is exactly what is happening. As the axis shifts we start getting uneven tension on the belts this bearing is supporting. Fortunately, we have been catching the wear while it is small, about 0.010". The chromers want the bore oversized by 0.010-0.015" so we do quick lathe cut or grind to clean it up, plate it up, then finish grind the bore diameter to the correct dimensions. I have already had one repaired and placed in service. I was thinking about the long term, though. Is the bearing going to be fine riding in the hard chrome, is there a big risk of flaking or failure of the chrome? It's expensive to do it this way, nearly the cost of a new part but I am hoping the chrome gives an improvement in life.

The housing is thin walled which makes me leary of sleeving it and is also why I don't want to weld it.

 

[Tmoose]

I'd expect a bearing subjected to ~ one directional loading, like a belt drive, to be pretty tolerant of outer race fit. With the one directional load the outer race is pressed hard against the bore, with limited tendency to creep.

Is this the fixed or thrust bearing too?

Have you qualified the shaft bearing seats, especially the shoulders, for accurate geometry?

 

[MikeHalloran]

Ah. And of course, the housing is a special shape, not a generic industrial bearing housing, etc.

I think the chrome will be okay, assuming that your chromer knows what he is doing.

I'd be concerned about preventing the bearing race from spinning in the housing.
... as in, assuring that it gets lubricated as often as it needs,
and maybe installing it into the housing with some Loctite Pipe Sealant with Teflon, which will at least provide a little drag against spinning, but will not bond the bearing and housing to the same extent that neat Loctite does.



Mike Halloran
Pembroke Pines, FL, USA