What are the two types of unbalance?

Unbalance in a rotating machine can be categorized into two primary types: static and dynamic.

Static unbalance occurs when the center of mass of the rotating assembly is not aligned with the axis of rotation. This misalignment leads to a condition where the machine experiences a noticeable amount of vibration when it rotates, usually at low speeds. Static unbalance is often addressed by adding weights to the rotor to bring the center of mass in line with the axis of rotation.

Dynamic unbalance, on the other hand, is a more complex condition where the center of mass is located away from the axis of rotation, resulting not just in vibration but also in a resultant force that creates an imbalance as the rotor spins. This type of unbalance manifests even at higher speeds and can lead to more severe operational problems than static unbalance. Correction usually involves modifying the mass distribution around the rotor to ensure it rotates evenly.

This twofold classification is critical for diagnosing and fixing issues in machinery and helps ensure smoother operation, minimized wear, and extended equipment life.