Stirrer shaft speed

The following data are based on field experience tests done with BOLA stirrer shafts.

Those tests have shown that it is not possible to state a maximum RPM but the range in which the shafts vibrate heavily. Such vibrations are caused by resonance. Due to those vibrations the bearings of the agitator are exposed to high stresses and in worst case accidents can be caused by tipping over agitators. The use of liquids as medium can reduce vibrations, worn out agitator bearings or insufficient stability of the agitator support increase vibrations.

In practice, the “critical RPM” should simply be avoided by either staying below or skipping quickly this “critical RPM range” to obtain a quiet running stirrer shaft. In general: the longer a stirrer shaft is, the larger its diameter should be.

Green Area: indicates up to which rpm the shaft will not be affected by vibration.

Red Area: marks the critical RPM range. These RPM should be avoided whenever possible.

Blue Area: is reached after quick skipping of the critical RPM range, vibration seldom occurs, however, agitators and stirrer shafts are extremely stressed by high RPM. Therefore we recommend to use stirrer shafts only in the green range