ISO balancing grades, what are they?

The two primary factors to determine the permissible unbalance (also called the balancing tolerance) are the mass of the rotating part and the maximum operational speed.

Calculating a balancing tolerance based on these parameters is realtively simple. However, these calculated tolerances are for the journal planes, and need to be transposed into correction planes.

Based on experimental data, the potential for damage is proportional to the Balancing Quality Grade. Larger G numbers cause more structural stress.

The EasyBalance software has a built-in balancing quality calculator for ISO, MIL, API and special standards, like 4W/n and such.

Enter rotor mass, service speed and desired quality grade, and click CALCULATE. The correct unbalance tolerance will be calculated, and automatically transposed from journal planes into correction planes.

ISO 1940 is obsolete and has been replaced with ISO 21940-11, edition 2016-11-15. The EasyBalance software Tolerance Calculator has been updated to this new ISO standard.

Balancing Quality Grade
G number
Vibration velocity in mm/s Rotor types
General examples
G100 100 Crankshaft drives of large Diesel engines
Complete engines for trucks and locomotives
G40 40 Crankshaft drives for engines of trucks and locomotives
G16 16 Parts of crushing machinery
Parts of agricultural machinery
G6.3 6.3 Fly-wheels
Aircraft gas turbine rotors
Electrical armatures
Process plant machinery
Pump impellers
G2.5 2.5 Machine-tool drives
Turbo compressors
Small electric armatures
Turbine-driven pumps
G1 1 Grinding machine drives
Textile bobbins
Automotive turbochargers
G0.4 0.4 Gyroscopes
Spindles for high-precision applications