Do Different Balancing Speeds Give Different Unbalance Values?

In dynamic balancing, measurements taken at different speeds are expected to yield the same unbalance value, because unbalance is a vector quantity related to the part's geometry and mass distribution, independent of rotational speed. In other words, the unbalanced mass of the part and its distance from the center of rotation remain constant regardless of rotational speed. Therefore, theoretically, whether you balance a part at 100 rpm or 1000 rpm, you should obtain the same unbalance value. This principle certainly applies to solid rotors, and modern, high-precision balancing machines are designed to operate according to this principle. These machines guarantee that the results remain consistent, within the specified tolerance range, even when measured at different speeds.

However, in practice, small differences can occur during measurement due to factors such as mechanical vibrations within the system, sensor noise, or slight deflections of the rotor at very high speeds. These differences are directly related to the machine's measurement accuracy and quality. High-quality rigid bearing balancing machines can tolerate such small variations and deliver consistent and reliable results, even when measuring at different speeds. At MBS Balancing, we utilize advanced sensor and software technologies to ensure this consistency in our machines. This ensures users can achieve accurate and repeatable results, regardless of the speed at which they balance their parts.

The unbalance measured at different speeds coming out consistent is also an important diagnostic tool. On a rigid rotor, a value changing noticeably with speed (especially the amount increasing and the phase shifting) mostly points to one of three situations: the rotor having a lower critical speed than expected and beginning to behave flexibly, the fixture or connection being loose, or journal runout mixing into the measurement.

Therefore, taking measurements at two different speeds and comparing the results both verifies the machine's linearity and tests whether the rotor's rigid-rotor assumption holds. If the value stays constant, the rigid-rotor assumption and low-speed balancing are safe. MBS Balance machines are equipped with stable drive and digital filtering that keep the repeatability of measurements at different speeds high; thus the user can trust the value obtained regardless of speed.