Article

How flexible rotors are balanced at speed: the vacuum facilities that run them to service speed, correction planes chosen for the modes, the sequence of a job from setup to acceptance, and the influence coefficient method, plane by plane or in plane sets for modal balancing.

Why a low-speed balance can be necessary but not sufficient: critical speeds and mode shapes, amplitude and phase through resonance, the line between rigid and flexible rotors, and the distributed unbalance that excites bending modes beyond the reach of two correction planes.

The shop balancing procedure from setup through correction: the measure-and-correct cycle, correction methods, splitting a correction between available angular positions, and the residual unbalance verification test that proves a balance independent of the machine’s calibration.

How a low speed balancing machine works: the hard-bearing and soft-bearing architectures, the hardware that supports and drives the rotor, how measured amplitude and phase become unbalance vectors, and how to assess whether a machine is adequate for a particular rotor.

The taxonomy of unbalance — static, couple, dynamic, and quasi-static — why couple unbalance is invisible to a single-plane measurement, why two correction planes are sufficient for any rigid rotor, and where the terms static balancing and dynamic balancing come from.

What unbalance is physically, the units and conventions that quantify it, which rotors qualify for single-plane treatment, and how the ISO and API balance tolerance criteria are constructed and compare — the fundamentals behind one of the most common jobs in a rotating equipment repair shop.