Reed Frequency

[mottto]

Hi there , im wondering what is the difference between critical speed and reed frequency of a shaft.I believe both are defined as 187.7/sqrt(deflection).
Thanks

 

[electricpete]

I'm not postive but here's what I think:

If we restrict our discussion to shafts and rotors - Reed frequency refers to overhung rotors while critical speed refers to any rotor.

If we talk about entire machines

Reed frequency can also refer to resonant frequency of entire machine such as vertical pump/motor. In that case, the critical speed would likely be close to the reed frequency of the rotor alone but reed frequency of the whole machine is different based on stator, support etc.

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[vanstoja]

The critical speed of a rotating shaft generally refers to the frequency at the first bending mode of the shaft which is approximated by the "beam-loading" frequency of a stationary shaft in its support bearings. There are two lower frequency rigid-body(non-bending) rotorshaft vibration modes called "cylindrical" and "conical" with the latter being the non-bending version of a "reed" (ie. cantilevered)response.
Generally, the reed frequency is used to designate the cantilevered bending mode about a fixed base of a vertically mounted pump assembly with its drivemotor.