Rigid Rotor : when the component is rotated at low speeds or below the critical operating speeds

  • A rigid rotor has minimal bending or distortion due to its stiffness and rigidity.
  • The shaft deflection is very small, the mass inertia forces are small and the majority of centrifugal force energy is counteracted by bearing deflection.
  • The bearing vibration is usually large and can be rectified by using normal balancing methods

Rigid Rotors & Unbalance

Bearing vibration is large and forces due to unbalance can be measured on bearings. There is minimal shaft deflection due to component rigidity and the machine RPM is significantly lower than the critical speed of that component

Flexible Rotor: when the component is rotated at high speeds or above the critical operating speeds.

  • A flexible rotor machine that has significant bending during operation.
  • These conditions are found in components where the length to diameter ratio is at its extreme and the component is running at critical/operating speed.

Flexible Rotors & Unbalance

Bearing vibrations are small and shaft deflections are large. Forces due to unbalance are better measured at shaft rather than at bearing.