Single Plane Balancing
Why can single-plane balancing not correct dynamic unbalance?
Dynamic unbalance involves a couple moment where unequal forces act in two planes; single-plane balancing only corrects a net force offset (static unbalance) and cannot eliminate the moment.
How is the correction mass calculated in vector terms?
Correction weight = Trial weight × |O|/|T|, where |O| is the original vibration vector magnitude and |T| is the trial response vector magnitude derived from the difference between original and new vectors.
What ISO standard guides rotor balancing criteria?
ISO 1940-1 provides guidance on balancing quality grades and the L/D threshold for selecting single-plane vs. two-plane balancing.
Single-plane balancing corrects static unbalance by adding or removing mass in one radial plane, suitable for thin rotors with a length-to-diameter ratio (L/D) typically less than 0.5. It is a rotor balancing procedure that addresses unbalance where the principal axis is displaced parallel to the rotation axis, common in fans, impellers, and pulleys.
On the shop floor, single-plane balancing is applied to thin rotors like fans, impellers, pulleys, and small motors. Technicians measure initial 1× rpm vibration amplitude and phase, stop the machine to attach a known trial weight at a specific angle, restart to record the new vector, then calculate the correction mass and angular position using vector analysis or influence coefficients to cancel the original unbalance vector. This procedure is efficient for static unbalance correction in maintenance environments.
Applying single-plane balancing to long rotors (L/D > 0.5) experiencing dynamic (couple) unbalance, which fails to correct wobbling and leaves high vibration.
Neglecting phase reference marking (e.g., no optical probe target or encoder), causing incorrect angular placement of the correction weight and worsening imbalance.
Using inadequate trial weight mass (too small to produce measurable vector change) or ignoring the rule of thumb for 30° phase change or 30% amplitude change, leading to inaccurate correction calculations.