Journal bearing wiped, l/h liner found loose!! Problem??

[Ayden]

We just wiped a journal bearing at our Turbo-Generator.
We bumped the rotor to verify speed indication on the panel but the machine stopped rapidly.
We decided to slow roll the machine to 500 RPM and monitor for noises, rubs etc... after 3 min. into slow roll at 500 RPM the Bearing RTD went of the chart at > 300.deg. F
Yes we wiped the bearing but why?
We opened up the bearing #1 where we got the alarm from and found upper half wiped, when lower half was removed we noticed the liner was loose!!! Could this be an assembly problem or was this caused by the heat generated from wiping. I really doubt that the liner came loose because of liner heating up.

What do you think??

 

[Ayden]

Yes, we checked everything with the liner and bearing shells out of the turbine pedestal. We took bottom and top half to the shop.
What we didn't check was installing the bearing shell back in the pedestal and installing the last cover, the top cover at the turbine it self.

 

[diamondjim]

Why did it happen only at low speed?

 

[Ayden]

diamondjim:

I'm not sure but having the machine running at very low speed there is the posibility that the hydrodynamic film doesn't generate enough pressure to support the load, and solid contact takes place between the surfaces (shaft and liner)

Ayden

 

[JJPellin]

Very interesting result. In the example that I mentioned above, there was a liner with a slight interference fit in a bearing retainer. The retainer was in a spherical seat within the housing. Once the housing was closed up, a large jam bolt in the top cover would clamp down the retainer to lock it in place. It is a good practice to check the lift on a shaft within the assembled bearing housing at the very end of the assembly process. This can often catch problems with crush, installation, clearance, bearing defects, etc. Even with a 15,000 lb rotor in our compressor, we always do a lift check at the end.