Large Machine Resonance base Repair
Large Machine Resonance base Repair
(OP)
This follows the thread "large machine resonance".
Here is where we stand: The base of the machine appears to be resonant because it is not firmly mounted on its concrete and grout base.
At first glance, this could be easily corrected by simply bolting the base in more locations. However, the concern is that if the grouting is not uniformly flat, the addition of more bolts might end up distorting the gearbox case, leading to possible gear or bearing damage.
How can quality of the grout application be determined without removing the entire gearbox for inspection?
Here is where we stand: The base of the machine appears to be resonant because it is not firmly mounted on its concrete and grout base.
At first glance, this could be easily corrected by simply bolting the base in more locations. However, the concern is that if the grouting is not uniformly flat, the addition of more bolts might end up distorting the gearbox case, leading to possible gear or bearing damage.
How can quality of the grout application be determined without removing the entire gearbox for inspection?





RE: Large Machine Resonance base Repair
Cheers
Greg Locock
RE: Large Machine Resonance base Repair
A good suggestion. However, I suspect it will reveal low impedance at the points where the ODS study showed greatest movement. SO the question remains--if the grout application is faulty, is there any way to add rigidity to the structure (such as adding bolts through the base) that will not distort the gearbox case and will avoid lifting the entire gearbox up to repour the grout?
RE: Large Machine Resonance base Repair
But I have a suspicion that it will be more difficult than that. Oh, longer, thicker, bolts would always help, of course.
Cheers
Greg Locock
RE: Large Machine Resonance base Repair
I would clean out the grout and re-level the machine by ensuring that there are steel packers and shims extending from the concrete foundation to the machine base. These should be close on either side of each holding down bolt and must be shimmed so that the packer stack at every location is under pressure when the machine is level (otherwise you get a condition known as a soft foot). For added security and despite my comment above I would then apply a good quality, non-shrinking (epoxy) grout to finish the job.
When there is a problem with stiffness that is not related to the above issue it is more likely to be associated with the stiffeness of the base flange on the machine. On a fabricated base there should be stiffening gussets close either side of each HD bolt.
RE: Large Machine Resonance base Repair
I think one of the poster child applications for this in power plants is the GE stator cooling pump skid. Two 2-pole motors on large shared baseplates with double suction overhung pumps. Not only was 1X near natural frequencies, but so was twice line freq. for these notoriously susceptable motors. Other applications included IR air compressors, Condensate Booster pumps, and Control Rod MG sets.