• - In terms of the eccentricity of the mass: μm, mm, cm, ...; μin, thousand, in, ...

• - In terms of the mass at a given radius: μg, mg, g, kg, ...; moz, oz, ...

• - In terms of mass × radius moment (mR): mg-mm, g-mm, mg-cm, g-cm, kg-mm, ...; oz-in, g-in, ...

Static rotation imbalance

Static rotational unbalance (sometimes called inertial force unbalance[3]​[4]​) occurs when the axis of inertia of a rotating mass is offset from, but parallel to, the axis of rotation. Static imbalances may occur more frequently in disc-shaped rotors, because the thin geometric profile of the disc allows for an uneven distribution of mass with an axis of inertia that is nearly parallel to the axis of rotation.[5]​.

where U = balance, m = mass, r = distance between the imbalance and the center of the object.

Torque rotation imbalance

Torque rotational imbalance occurs when a rotating mass is subjected to a set of inertial forces whose moments do not cancel each other out, and the axis of rotation and the axis of inertia intersect each other. A system that is statically balanced may have a torque imbalance. Torque imbalance frequently occurs in elongated cylindrical rotors.

where d = distance between the two unbalance forces with respect to the axis of rotation.

Dynamic rotational imbalance

In rotation, when the mass/inertia axis does not intersect with the rotation axis, a situation called dynamic unbalance is generated. The combination of static unbalance and torque unbalance gives rise to dynamic unbalance. It occurs in virtually all rotors and is the most common type of imbalance. It can be solved by correcting the weight distribution in at least two planes.[6]​.

• - Addition of mass.

• - Elimination of mass.

• - Mass displacement.

• - Mass centering.

Measuring the existing vibration and calculating the required mass change is normally carried out using some form of balancing machine.

ISO 21940[7]​ classifies vibration in terms of G codes. Unfortunately, it is the theoretical value assuming the rotor rotates in free space, so it does not relate to actual operating conditions. Rotors of the same type have the same allowable residual specific unbalance value e, which varies inversely with the rotor speed.

where ω = angular velocity (radians per second; e = admissible residual specific imbalance.

This constant is the quality grade G. Balance grades are used to specify the allowable residual imbalance for rotating machinery. The ISO 1940 standard defines the degrees of balance for different classes of machinery. A rotor balanced at G2.5 will vibrate at 2.5 mm/s at operating speed if it rotates in a suspended state without external influences.

where U = balance tolerance (or) residual imbalance.

where F = force due to imbalance; U = imbalance; ω = angular velocity; e = specific imbalance; m = mass; r = distance between the imbalance and the axis of rotation of the object.

• - Vibration.

• - Noise.

• - Decrease in the useful life of the bearings.

• - Unsafe working conditions.

• - Reduction in the useful life of the machine.

• - Greater maintenance.

• - In terms of the eccentricity of the mass: μm, mm, cm, ...; μin, thousand, in, ...

• - In terms of the mass at a given radius: μg, mg, g, kg, ...; moz, oz, ...

• - In terms of mass × radius moment (mR): mg-mm, g-mm, mg-cm, g-cm, kg-mm, ...; oz-in, g-in, ...

Static rotation imbalance

Static rotational unbalance (sometimes called inertial force unbalance[3]​[4]​) occurs when the axis of inertia of a rotating mass is offset from, but parallel to, the axis of rotation. Static imbalances may occur more frequently in disc-shaped rotors, because the thin geometric profile of the disc allows for an uneven distribution of mass with an axis of inertia that is nearly parallel to the axis of rotation.[5]​.

where U = balance, m = mass, r = distance between the imbalance and the center of the object.

Torque rotation imbalance

Torque rotational imbalance occurs when a rotating mass is subjected to a set of inertial forces whose moments do not cancel each other out, and the axis of rotation and the axis of inertia intersect each other. A system that is statically balanced may have a torque imbalance. Torque imbalance frequently occurs in elongated cylindrical rotors.

where d = distance between the two unbalance forces with respect to the axis of rotation.

Dynamic rotational imbalance

In rotation, when the mass/inertia axis does not intersect with the rotation axis, a situation called dynamic unbalance is generated. The combination of static unbalance and torque unbalance gives rise to dynamic unbalance. It occurs in virtually all rotors and is the most common type of imbalance. It can be solved by correcting the weight distribution in at least two planes.[6]​.

• - Addition of mass.

• - Elimination of mass.

• - Mass displacement.

• - Mass centering.

Measuring the existing vibration and calculating the required mass change is normally carried out using some form of balancing machine.

ISO 21940[7]​ classifies vibration in terms of G codes. Unfortunately, it is the theoretical value assuming the rotor rotates in free space, so it does not relate to actual operating conditions. Rotors of the same type have the same allowable residual specific unbalance value e, which varies inversely with the rotor speed.

where ω = angular velocity (radians per second; e = admissible residual specific imbalance.

This constant is the quality grade G. Balance grades are used to specify the allowable residual imbalance for rotating machinery. The ISO 1940 standard defines the degrees of balance for different classes of machinery. A rotor balanced at G2.5 will vibrate at 2.5 mm/s at operating speed if it rotates in a suspended state without external influences.

where U = balance tolerance (or) residual imbalance.

where F = force due to imbalance; U = imbalance; ω = angular velocity; e = specific imbalance; m = mass; r = distance between the imbalance and the axis of rotation of the object.