What is Dynamic Balance?

Dynamic balancing is a critical process used to prevent unwanted vibrations and mechanical stresses in rotating machinery. Simply put, it's the process of aligning the center of mass of a rotating part with the axis of rotation. Imbalances in the mass distribution of a rotating part create centrifugal forces at high speeds. This force can overload bearings, shafts, and other machine components, leading to serious damage, energy loss, and, most importantly, operational noise. Therefore, dynamic balancing is essential for extending machine life, improving work safety, and maximizing productivity.

This balancing process not only aligns the part's center of mass at a single point but also eliminates imbalances in two different planes. This balances the moments and coupled forces generated during rotation, ensuring more stable and quiet machine operation. At MBS Balance, we perform this process precisely with our state-of-the-art balancing machines, helping our customers' machines operate at maximum performance and with minimal risk of failure. Correct dynamic balancing reduces wear on machine components, lowers maintenance costs, and improves production quality.

From an engineering standpoint, dynamic unbalance is divided into three components: static unbalance (the offset of the center of mass from the axis), couple unbalance (the principal inertia axis forming an angle with the axis of rotation), and their resultant, which is true dynamic unbalance. Because correction performed in two planes eliminates these three components in a single operation, it comes into play precisely where single-plane static balancing falls short on long rotors.

Residual Unbalance and Tolerance

How precisely a rotor must be balanced is defined by the G quality grades in the ISO 21940-11 standard (formerly ISO 1940-1). The permissible specific unbalance is calculated with the formula e_per = (G × 1000) / w, where w is the angular operating speed of the rotor. For example, while grade G6.3 is sufficient for general-purpose fan and pump rotors, critical parts such as a jet engine shaft require much tighter grades like G1 or even G0.4. As the operating speed increases, the permissible gram-millimeter value for the same G grade decreases; this explains why balancing is far more critical for high-speed parts.

At MBS Balance, we build our dynamic balancing processes on these standard calculations, predetermining the target G grade and correction planes for each rotor to reduce centrifugal force to levels that will not threaten bearing life.