noisy large rotor seasoning

[Tmoose]

We have a 20 ton motor rotor made with large diameter shrinkfits and hundred or so shrink fitted pinned joints.

During the first few hundred revolutions on the balance machine it emitted some creaks and groans. It has been silent ever since, but has not gone thru any operating cycles.

Have others experienced rotating machinery that requires "seasoning" to run quiet?

 

[GregLocock]

Be afraid. Any clunks groans or creaks imply movement. If your joints were designed not to move, why are they able to move?

So much for the ideal world. I know of several joints that exhibit 'green' clunks. Once they settle down they seem OK. However these are typically bolted joints, of mass produced assemblies. Equally I can think of other joints that never settle down.

Sorry not much help, but I would double check your joint forces and designs.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[MikeHalloran]

Like Greg says. I'd triple check the stresses in, and the hardness of, the pinned elements.

Mike Halloran
Pembroke Pines, FL, USA

 

[Cheddarcaveman]

Before panic sets in, first make sure the noise IS coming from the rotor and not the balance machine. I worked for GE balancing their turbine rotors and the machines often groaned a bit to begin with, during the first few revolutions. That's a huge weight on two small load areas!
If it is the rotor then BE VERY CAREFUL. As has been said, any noise from a rotor, particularly one with shrink fits, would tend to indicate a problem either with a fit or even possibly a shaft fracture within the shrink being held by the shrink.
Put a dial indicator on the shaft either side of the rotor mass and check for any sign of deflection. If there is a crack under there somewhere, you should pick it up. You could also do a bump test on the rotor to see if it "rings" or "thuds" but ideally you should suspend it for this, not have it on rollers.

 

[GregLocock]

Aye, good point about the balance machine. Tapered centres would be a good example of joints that might exhibit green creaks.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[sreid]

If there are any shrink fits slipping, fretting corrosion can set in at an alarming rate.

 

[rmw]

If your rotor had any bow in it due to having sat prior to being loaded on the balance machine, it may have been the bearings complaining while the rotor straightened itself out.

rmw

 

[rmw]

Or it may have been the dry bearing/shaft interface before the oil wedge built up (both on the journals and the thrust pads). The shaft would be contacting the bearing dry at that point and trying to climb the bearing and sliding/falling back as prevented by the bearing clearances. Once the oil wedge forms, it then rides there as it is supposed to.

It may not happen on a restart because there is sufficient residual lubrication on the bearing/shaft surfaces to quickly form the wedge.

rmw

 

[Cheddarcaveman]

Hey RMW - we're on a balance machine here so I guess the rotor is running on a crowned roller, not in a sleeve bearing or am I wrong there Tmoose?

 

[Tmoose]

The motor uses sleeve bearings, but The journal diameters are so big they won't fit on many balance machines' puny roller trunnions, which most likely would have plowed into the bearing journals anyhow. Tooling with integral spherical roller bearings were made to bolt to the rotor.
I can picture those spherical rollers being slightly axially displaced as the rotor was set down and tracking differently and objecting to being dragged a little bit sideways as they rolled.

 

[Cheddarcaveman]

So if your balance machine has "puny roller trunnions" as you call them, then I would suggest that you are possibly exceeding the working load of your balance machine or its rotor support system.

In GE we used primarily Schenck balance machines and in the turbine rotor workshop I ran these were rated at 40 tons with crowned roller bearings to match. Even with a complete Frame 5 single shaft rotor in them, round about 22 tons, we still used the supplied rollers.

I think you've also answered your own question in your last posting by stating "I can picture those spherical rollers being slightly axially displaced as the rotor was set down and tracking differently and objecting to being dragged a little bit sideways as they rolled". With this setup I'm not surprised you heard groaning noises!

 

[Tmoose]

Our balance supplier has an IRD softbearing balancer with curious double stanchions at each end. Not sure of the model number, as he is a pretty secretive guy.

Our hydrodynamic bearing journals are by necessity > 25 inch diameter.

Note IRD standard products are kind of limited to 20 inch journals until capacity of 110,000 lbs.

http://www.irdbalancing.com/softbearing.asp