350 kW motor impacts

[berryc]

I have a large Beloit double disc refiner driven by a Seimens 350kW 8 pole motor. Recently there has been a change in the motor vibration readings. TWF of the DE of the motor shows what looks to be a beat frequency type TWF with impacts of motor speed phasing in and out at ~16 x motor speed (1.37 Seconds). I have checked the gear coupling and it looks to be in good condition and the refiner plates have been changed recently (after the impacts started) resulting in no change. This is a large motor (for our site) and is critical to production. We have 10 of these refiners all in the same room running at the same speed, but his is the only one with the irregularity. Any feedback would be greatly appreciated.

Craig

 

[jkftl]

Wow! That's a tiny difference. I'd look to the process, not the drive. Sorry I don't know what a refiner is.

 

[ronfrend]

I am a little confused about just what the frequency of concern is. Is the beat frequency at 1.37 seconds (0.73 Hz)? Or is ther a vibration at 16x run speed or is it both?

How about emailing me the signatures as picture (jpg) or wav files and I'll have a look.

Usually, beats occur when you have two similar machines running close together but I really need to look at the data before giving you advice.

ron.frend@predicon.net

 

[electricpete]

You said impacts at motor speed beating (modulating) at approx 16 times motor speed.

That description in itself seems contradictory since how do you know that anything is modulating at 16 times per machine revolution when you only get an impact at one time per machine revolution.

What is much easier to imagine would be impacts at approx 16 times per machine revolution modulated at once per machine revolution. If a bearing defect frequency corresponds to approx 16x, then you might be seeing an impact every time the defect strikes (or possibly at 2 times ball spin frequency) which is modulated by running speed of the machine. This is typical for inner race defects where defect moves with respect to the stationary load zone at 1x running speed. Also occurs for all types of defects during the later stages when clearances open up and the rotor starts wandering around within those enlarged clearances creating a moving load zone.