Rigid structure for rotating machine reformation. More mass for a stiffer structure?

[LuisFelipeMS]

Hi all,

I am checking the natural frequency of some rotating machines (electric motors) and for that I have a cast iron slab on the top of a concrete block. The total mass is about 25ton. According to IEC 60034-14 standard, I can use this rigid base to test only machines with less than 2.5 ton (the standard says that the rigid base mass must be at least 10x the heaviest machine mass). However, I was sent some new rotating machines which mass is more than 2.5 ton (about 7 tons). Because of that, I am wondering what should I do to test these motors: should I build another concrete base of about 70 tons (I do have some spacing limitations)? Can I attach some metal ingots to the current concrete block to increase its mass (this may modify its rigidity/stiffness thus natural frequency)? Any other ideas?

Thank you.

 

[GregLocock]

First thing I'd do is measure the inertance of the existing block. You may get a pleasant surprise.

Secondly, using a huge mass as a ground is obviously the ideal, b \ut if you were to monitor the vibration of the ground mass as well as that of the machine then you should be able to correct for your less than optimal mass ratio.



Cheers

Greg Locock


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