Onsite Dynamic Balancing

Onsite Dynamic Balancing

Unbalance is the most common source of vibration in rotating equipment, and it is frequently left alone because conventional balancing means stripping the machine down, lifting the rotor out and returning it to a workshop. The plant then stays down for days, and a single hour of vibration is judged not worth that cost.

Onsite dynamic balancing removes both problems. The machine is balanced in place, at speed, with the rotor still fitted, using a portable analyser and a set of trial weights. Correction is normally reached within a single outage, and the machine is verified across its full speed range, through any critical speeds, before the guards go back on.

Dynamic balancing corrects:

• Single-plane unbalance of rigid rotors, most commonly at the shaft end or a balance weight ring
• Two-plane and multi-plane unbalance of flexible rotors, impellers, fans and long rotors
• Imbalance introduced by a coupling, sprocket, chain drive, sheave or pulley
• Buildup on impellers, fans and blades, and the correction of damaged or missing blades
• Severely out-of-balance machines and rotors that have been repaired or reassembled

Balancing Method

The as-found condition is measured at both bearing housings across the machine''s operating speed range, and the rotor is confirmed clean, undamaged and secure before any correction is attempted. An initial phase reading on each plane establishes the direction and size of the unbalance vector, from which a trial weight and angular position are calculated. The weights are fitted and the machine re-measured, and the process is iterated until the vibration is inside the target tolerance at every speed.

Every job is recorded with the as-found levels at each bearing and speed, the unbalance vector for each plane, every trial weight used with its position, mass and angle, the final permanent weights and their clocking positions, and the as-left vibration across the full speed range confirming the machine is inside the specified tolerance.