Industry: Paper Mill

Area: Tissue Machine - third level

Assets: Hood circulation fans

Comments: Centrifugal fan, catiliver arrangement, grid coupling, 800 hp - 1780 rpm electric motor

Problem: High vibration (20 mm / s) 1xrpm in horizontal direction in a higher percentage in the free side bearing, this high vibration occurs with the burners at full load, with which temperatures of up to 500 oC are reached.

The fans are operated at very close speeds, usually with a difference below 100 rpm. Therefore Beat is presented

When the burners are off, the vibratory amplitudes register maximum 5 mm / s in the horizontal direction.

What do you think of this case?

“Rotor Mass Unbalance:Exposure to high air stream temperatures can cause uneven growth of the fan rotor.”   ...???

Thank you

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Original Post

Yes on your assumption, as the fan heats up it grows and in some cases creates imbalance, I have seen this on smaller applications, had to balance hot to achieve acceptable levels.

If this fan has been is service for sometime, and the vibration is now starting to change, other faults/problems could be present

Dave

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RAAL posted:

Industry: Paper Mill

Area: Tissue Machine - third level

Assets: Hood circulation fans

Comments: Centrifugal fan, catiliver arrangement, grid coupling, 800 hp - 1780 rpm electric motor

Problem: High vibration (20 mm / s) 1xrpm in horizontal direction in a higher percentage in the free side bearing, this high vibration occurs with the burners at full load, with which temperatures of up to 500 oC are reached.

The fans are operated at very close speeds, usually with a difference below 100 rpm. Therefore Beat is presented

When the burners are off, the vibratory amplitudes register maximum 5 mm / s in the horizontal direction.

What do you think of this case?

“Rotor Mass Unbalance:Exposure to high air stream temperatures can cause uneven growth of the fan rotor.”   ...???

Thank you

Dear RAAL

How about vertical vibration?

Do u get phase difference between H&V?

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You state that motor is rated 1780 rpm, and it has grid coupling. The fan is direct drive, and the measured fan speed from vibration is 1316 rpm, so motor-fan must have speed control; correct? If yes, then there may be a resonant structure that changes vibration amplitude when speed changes. I suggest you check for resonant structure (fan wheel on shaft or support structure) by impact test or by variable speed test.

Walt

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