We have a I.D fan driven by a motor of 2600 kw. Changed its impeller with new bearings and plummer blocks. Before fixing the bearings and plummer blocks, impeller (10 ton weight) was balanced at G 1 (highly precised balancing). Laser alignment carried out and the readings are well within limits. After fixing the assembly we are facing high vibrations from fan side within 15 min of start up. Motor side vibrations are very less (2.0 mm/sec). Kindly advice. Fan is provided by M/s. Reitz GMBH.
Al... delay until vibration exceeds limit could be caused by air temperature-rise through fan.
If you would like a Nomograph that calculates temperature-rise contact me off-forum!
Regards, Phil Corso
Following Phil's comment, can Al indicate what is the operating temperature of the air/gas passing through the fan?
Having said that, you need to check the following:
1. You stated that new plummer blocks have been installed. You need to ensure that one of the plummer blocks (the one away from the motor) allows the bearing to move freely in the axial direction. If both plummer blocks lock the bearings in a fixed position, there is nothing to cater for the expansion of the fan shaft, possibly resulting in fan shaft bow.
2. Do the bearings fitted cater for the axial thrust created by the fan?
3. Did you check the frequency of the vibration? This will tell you what sort of fault you have (eg fundamental - unbalance, 2nd harmonic - misalignment, etc, vibration analysis books have ample data on the matter).
Why was the original fan, bearings, plummer blocks replaced?