What is the Difference Between Dynamic Balancing and Static Balancing?

Static balancing and dynamic balancing are two different methods for correcting a part's unbalance, and their fundamental difference is based on whether the part is stationary or in motion. Static balancing ensures the part's weight is evenly distributed around its axis of rotation while it's at rest. This process is done by placing the part on a knife edge or bearings, with the goal of making the center of gravity coincide with the geometric center. Static balancing can be sufficient for disc-shaped parts that are short in length relative to their diameter and rotate at slow speeds. This single-plane balancing prevents the heavy spot of the part from settling at the bottom when it's at rest, but it doesn't correct dynamic unbalances that occur during rotation.

On the other hand, dynamic balancing aims to eliminate the vibrations and forces a part generates while rotating. In a high-speed rotating part, an unbalance in mass distribution creates unbalanced forces (centrifugal force and couple force) in at least two different planes. These forces cause the part to wobble and vibrate excessively during rotation. Dynamic balancing requires corrections to be made in at least two different planes to eliminate these forces. For this reason, dynamic balancing is critically important for high-speed parts like spindles, shafts, and long rotors. At MBS Balance, we perform these complex balancing procedures with the highest precision using our dynamic balancing machines, ensuring parts have a long and efficient service life.

From an engineering standpoint, unbalance is divided into three types in ISO 21940-11, and these types clarify the difference between static and dynamic balancing. Static unbalance is the parallel offset of the center of mass from the axis of rotation, and it pulls the heavy point downward even when the part is stationary. Couple unbalance is the principal inertia axis forming an angle with the axis of rotation even though the center of mass is on the axis; it appears only during rotation, as opposite-direction forces in two planes, and is not seen on a static stand. The combination of the two is true dynamic unbalance.

The selection rule is based on this distinction: while static (single-plane) balancing is sufficient for disc-like parts with a small length/diameter ratio and low speed, couple unbalance becomes significant on parts whose length is close to their diameter or which are large and high-speed, and dynamic (two-plane) balancing becomes mandatory. MBS Balance evaluates the part's geometry and speed to determine which type of unbalance is dominant and applies the appropriate balancing method.