in Press section, the roll at Tending side is supported by 2 air billows (nearly 70 degree ). bearing housing has 2 pivots one on the billow and one at the machine structure.
i experienced very high vib. at at 1x roll, 7 Hz ( 20 in/s !!), i think it is resonance.
i performed bump test on the air billow construction , relieved 7 Hz natural frequency, we tried to change the pressure and the tension of the felt but did not help.
how to fix such problem, the roll is only one year in operation.
waiting your help