Page 304 - BOLA Catalogue
P. 304

 Stirrer shafts - Maximum Revolutions per Minute
We would like to give advice on the appropriate RPMs, but unfortunately this question is not easy to answer. 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 called resonance. At a certain speed, a superposition of the oscillations takes place and the resonance becomes visible as vibrations. 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
Diameter of the stirrer shaft incl PTFE coating in mm
Ø 6x L 350
Ø 6x L 450
Ø 8 x L 350
Ø 8 x L 450
Ø 8 x L 600
Ø 10 x L 450
Ø 10 x L 600
Ø 10 x L 800
Ø 10 x L 1000
Ø 16 x L 1000
Ø 16 x L 1200
of liquids as medium can reduce vibrations, worn out agitator bearings or insufficient stability of the agitator support increase vibrations.
In practice, these “critical RPMs” 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.
                      0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 Stirrer shaft revolution speed in U/min
The chart
shall help you to choose the right stirrer shaft respectively to determine the maximum RPM. As many different parameters affect the quiet running of a stirrer shaft, it is recommended that the user will test it under his own conditions.
Please note that for double impulse stirrer shafts the critical RPM range lies 200 rpm below the stated values.
» GreenArea– » RedArea–
» BlueArea–
indicates up to which rpm the shaft will not be affected by vibration
marks the critical RPM range. These rpms should be avoided whenever possible.
is reached after quick skipping of the critical RPM range, vibration seldom occurs, however, agitators and stirrer shafts are extremely stressed by high RPMs. Therefore we recommend to use stirrer shafts only in the green range – if possible.
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