Critical or Whirling Speed in Mechanical Engineering

Critical or whirling speed is an important concept in mechanical engineering, especially when dealing with rotating shafts. Let's understand what it means and how it affects the machinery.

Definition of Critical or Whirling Speed

Critical or whirling speed is the speed at which the shaft tends to vibrate violently in the transverse direction. In other words, it is the rotational speed at which the natural frequency of the shaft coincides with the frequency of the external force, causing resonance and vibration.

Effect of Critical or Whirling Speed

When the critical or whirling speed is reached, the centrifugal force acting on the shaft increases significantly, causing the shaft to bend in the transverse direction. This bending motion leads to an increase in stress and strain in the shaft, which can eventually lead to failure.

Therefore, it is important to avoid operating the machinery at or near the critical or whirling speed. This can be achieved by designing the machinery in such a way that the natural frequency of the shaft is significantly higher than the operating speed.

Factors Affecting Critical or Whirling Speed

The critical or whirling speed of a shaft depends on several factors, such as:

- Length and diameter of the shaft
- Material properties of the shaft
- Boundary conditions (fixed or free)
- Mass distribution along the shaft

Conclusion

In summary, critical or whirling speed is the speed at which the shaft tends to vibrate violently in the transverse direction, leading to an increase in stress and strain in the shaft. It is important to avoid operating the machinery at or near the critical or whirling speed by designing the machinery in such a way that the natural frequency of the shaft is significantly higher than the operating speed.