Ralph,

Attached is an improved sketch.
As far as coastdown test goes, I had similar thoughts, but I still dismissed them based on phase data. The 110 deg lag when cold is weird and different from the rest of the same machines type.

The machine has known HOR shaft misalignment ( bolt bound ) but this should not be affected by the heat. Still, hot-cold situation affects the vibration and possibly occurs due to heat related structural changes. A bump test may confirm this.

Dan,

The sole plate is moving and the grout already detached. The braces were added later and have stabilized the structure.

David

Structure_detailed.doc (28 KB, 19 downloads)

quote:

The 110 deg lag when cold is weird and different from the rest of the same machines type.

So this machine is one of many you have and the only one "showing off" its own unique style of behavior, huh?
Sounds like it is a little different from the rest in some way, like maybe what you told Dan about the braces, grout, Etc.

This may be a little off-point (I've not read this entire thread), but I had a thin rotor in an IRD B50 soft-bearing machine once that really opened my eyes about thin-rotor balance behavior. It was fairly lightweight (aluminum) and only about 3" wide at the outer edge, maybe 5" wide at the hub. I assumed it would balance as a static imbalance since probably 95% of all rotors I've ever balanced (mostly in-place) have. But it wouldn't, and had very pronounced 2-plane behavior. Can't remember exactly how it was configured, but I was using clamp-on weights to balance, about 2" off the centerline. It balanced well (2-plane), but when I bolted on the final weights, about 1.5" off the centerline, vibration went up by 50%. I found it hard to believe that moving the weights in only 1/2" would cause that behavior, but when I added weight, it fell right back in.

I've never seen anything like it before or since, but it did lead me to understand that it is possible for thin rotors to "behave" illogically, as if there is some law of physics that is being violated, or which is perhaps as yet undiscovered.

This thread is interesting.
I recall Ron Eshleman explaining that a rotor bow will cause a "dip" in the coastdown response just below the critical speed since it tends to counteract the unbalance forces for some period of time.
With a slightly bowed rotor (and depending on rotor/mass configuration), typical balancing and phase readings at different speed conditions may cause result in the unusual readings present.
Add on top of that minor rubs (heating?) at various speeds may cause phase to be erratic.
I dont know how this might explain large diffrences in amplitude at each end though.

Jim P