How to calculate the critical speed of fan rotor?
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The rigid integral bearing seat of the original fan was seriously damaged and had to be replaced with two split bearing seats. A new shaft was also installed according to the size of the new bearing seat, which caused high vibration. Factors such as dynamic unbalance/shaft misalignment have been ruled out, and it is now suspected whether the critical speed changes due to changes in rotor size/support form, approaching the operating speed. Asking for help from seniors/students: How to calculate the critical speed of fan rotor?
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It is always not safe to calculate the critical speed, and the calculated critical speed given by the manufacturer is often incorrect. It is best to do a speed-increasing test and measure the changes in vibration as the speed increases, which is a Bode plot. It is safest to conduct an actual measurement. I have encountered cases where the actual critical speed was more than twice the value given by the manufacturer, and was close to the operating speed, so the machine was forced to return to the factory.
The critical speed has been measured by installing the frequency converter to be 2900RPM.
The calculation software on the second floor is not easy to use.
The fan manual has detailed formulas and examples on page 181