Yankee machine, a bit larger having 1st and 2nd presses vibrating in machine direction (horiz) in the range of 24Hz..... at 1600 m/min machine speed. Horiz vibe is like 15-17 mm/s and in vert 4 mm/s (on motor free end) so it´s a clear resonance candidate regarding the press drive mounts that sit on a vert. T shape concrete thingy.
Could not stop to make knock test or run up/down. But where does the impulse come from? This about 24 Hz is also found on the Yankee drive motor as dominating but only 2-3mm/s compared to next peak at 0.5mm/s. When increasing speed 100 m/min the freq. increased 1.5Hz, so it´s connected in some way.
Problem existed for some time but got worse in last few week(s). To make things complicated the machine has "flexible clothing" if it makes any sense, eg. the material they put btw. the cylinders/rollers is not fixed but flexible like a pretty big rubber band. So ideas I have, part from advice on stiffening press drives mount to avoid resonance,: Is the 24Hz from interaction btw. control system and rubber band effect in "clothing" and cylinders? Would it be from friction somewhere that excite all undamped resonances?, normally btw. yankee and presses then, (why would it change with speed?). Final abnormal is that there is virtually no 6xLF (300Hz)that is always found in DC drives. Anybody seen a DC drive lately that has no 6xLF? and as last, the 1ress tacho assy sound like there is a squirrel being beat inside.... Olov

Oli,

Have you eliminated barring?

Olov,

I'd blame the damn squirrel!

I can't help on the details, but is it possible to have a stick-slip friction process that excites the resonance? Perhaps you need a very accurate comparison of roll speeds. You are the right man for this job!

Walt

Danny,
Well it goes away, they say when slowing down, if that is an effect of not exciting the resonance or the exciting impulse drops off, hard to say as all they have is vibrometer. So no, I can´t eliminate barring or clothing disturbance. They didn´t like to lift the press(es) either.
Walt, I agree, the squirrel is the culprit.
I will advice on replacing the tacho to one that have a fresh squirrel inside that don´t argue like that.
They did fiddle with the tuning of the load distribution btw. 1:st and 2:nd and it made no difference. I could not stop or get any tacho from the different drives at least not now. So why would a squirrel make 24Hz? Is that normal for that animal?
They will have drive specialist and hopefully a squirrel chaser in next week, and they will prop up the drive mount by 4 props of 4"x4" of pine.
Have a nice weekend. Olov

Olov,

I worked on a steel rolling mill driven by DC motors. It had product quality issues and unusual noise and vibrations. A controls technician thought that there was a control issue but could not find anthing after changing all of the circuit boards. I found a faulty tachometer using ultrasound meter. It was outputing a noisy speed signal to controller. Try a new squirrel (tachometer) just for fun and see what happens.

Walt