In order to reduce the amplitudes of deflection, one could try and reduce the eccentricity or the unbalanced forces (known as the problem of “balancing”) or design the system such that the frequencies  and  do not match. Our present discussion will be focusing on the techniques of balancing out the unbalanced forces.
The “balance grade” suitable for an application is typically prescribed in Indian or International Standards (for example ISO-1940). The balancing grade is usually specified as “G n”, where “n” is a number representing the permissible peripheral velocity in mm/s. Thus G100 implies, for a rotational speed of 1000 RPM, a permissible eccentricity of the center of mass from the axis of rotation within 0.1mm. This can be readily obtained from the following formula:
(Eccentricity permitted “e” mm)(speed of rotation rad/s) < 100 mm/s (in general "n" in Gn)
Typical balancing grades for a few applications are listed in the Table below to give you an idea of the task of balancing.
Balance Quality Grade “G” |
Rotor Type (application) |
G 4000 |
Crankshaft-drives of rigidly mounted slow marine diesel engines |
G 100 - 250 |
Crankshaft drives of rigidly mounted fast diesel or gasoline engines for cars, trucks, locomotives |
G 16 |
Rotating parts of agricultural or crushing machinery |
G 2.5 |
Gas and steam turbine rotors |
G 0.4 |
Spindles of precision grinders and gyroscopes |
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