Dual Slide Bearings

[gearcutter]

I'm in the middle of a gearbox failure investigation and have come across a type of plain journal bearing that I've never seen or heard of before.
The OEM calls it a 'Dual Slide' or 'Double Sliding' Plain Bearing. Rather than the bearing element being fixed (like the mains or big ends on a crankshaft) the bearings I'm looking at have elements that are free to rotate, they are not fixed by either pins/tabs or by the use of an interference fit.
Has anyone heard of such a bearing?

I'm having trouble understanding how a hydrodynamic oil film can be developed or even maintained if no relative motion is possible due to the fact that one of the members is not fixed as is normally the case.

These bearings, by the way, are the focus of the investigation due to a series of catastrophic failures.

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181

 

[tbuelna]

gearcutter-

The most common example of this type of journal bearing are the "floating" journal bearings used on turbocharger spools. These journal bearings are designed with clearance at both the inner and outer surfaces. The hydrodynamic oil film created at the inner interface between the bearing ID and shaft is the primary bearing, while the oil film between the bearing OD and housing bore provides for some damping of the shaft dynamics.

Sometimes plain bearings are designed to allow rotation at both the ID and OD surfaces for reasons of reliability. By allowing rotation at both the ID and OD bearing interfaces, the bearing would be able to continue to function if there were a seizure between the shaft and bearing.

Regards,
Terry

 

[MikeHalloran]

Didn't they used to make turbocharger shaft bearings like that? I think the theory was that the intermediate ring would be dragged into rotation at ~half the turbo rpm, and develop a hydrodynamic film on both inside and outside surfaces. I have no idea to what extent or how it _really_ worked, but it was in serious mass production for a while starting around 1960 or a little earlier.


Are you allowed to provide a photo, or reference to a patent drawing, or some such?



Mike Halloran
Pembroke Pines, FL, USA

 

[gearcutter]

Thanks for the replies.

I've been able to find more information via the link below.
All the examples that I've been able to find so far are in high speed, low load applications, such as turbo chargers.
The bearings I'm looking at are within a set of planetary gears that are operating at very, very low speed and are lubricated under pressure so they are more like hydrostatic bearings rather than hydrodynamic.
Inner diameter of the bearings is around 275mm so they are quite large.
I've never seen anything like them before and am questioning how it is they can operate under high radial loads.
Would the elements stop rotating with high enough radial load?
Motor power is around 4,500Kw.
Application is a vertical cement mill gearbox.

http://naca.central.cranfield.ac.uk/reports/1947/naca-report-866.pdf

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181

 

[MikeHalloran]

Since planetary drives are often built with controlled elasticity in planet carriers, or costly measures like planets selected for tooth thickness, I am failing to see how doubling the radial clearance of any bearing in the system is a good thing.

I'm guessing maybe the double bearing is some kind of "hopeful engineering" scheme intended to promote or allow proper load sharing among the planets.

The catastrophic failures are experiment reports.



Mike Halloran
Pembroke Pines, FL, USA

 

[tbuelna]

I've never seen a hydrostatic journal bearing with dual rotation surfaces like you describe. I suppose it might be possible in theory, but in practice it would present quite a difficult design problem. Hydrostatic journal bearings typically use recesses in the bearing surface where pressurized fluid is delivered to, and the bearing surface surrounding these recesses must maintain a close fit to the journal to minimize fluid leakage from the load bearing recess locations. For this reason hydrostatic journal bearings are often constructed in segments, with each segment being allowed to pivot so that its bearing surface can maintain a tight fit to the journal surface.

Based on your description of how the bearing is used, it may be that the planet bearing is operating mostly in boundary conditions. The radial loads on this bearing are fixed with respect to the pin. The benefit to using a floating bearing in this application is that the rotation would equalize wear over the bearing surface.