ISO 21940 Balance G Grades – Universal Balancing

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ISO 21940 Balance Quality G Grades are used to calculate balance tolerances in conjunction with the rotor weight and service speed (RPM).

Guidance for balance quality grades for rotors with rigid behaviour.

BALANCE QUALITY GRADE GMAGNITUDE e per Ω
mm/s		MACHINERY TYPES – GENERAL EXAMPLES
G 40004 000Crankshaft drives for large, slow marine diesel engines
(piston speed below 9 m/s), inherently unbalanced
G 16001 600Crankshaft drives for large, slow marine diesel engines
(piston speed below 9 m/s), inherently unbalanced
G 630630Crankshaft drives, inherently unbalanced, elastically mounted
G 250250Crankshaft drives, inherently unbalanced, rigidly mounted
G 100100Complete reciprocating engines for cars, trucks and locomotives
G 4040Cars: wheels, wheel rims, wheel sets, drive shaftsCrankshaft drives, inherently balanced, elastically mounted
G 1616Agricultural machineryCrankshaft drive, inherently balanced, rigidly mountedCrushing machinesDrive shafts (cardan shafts, propeller shafts)
G 6,36,3Aircraft gas turbinesCentrifuges (separators, decanters)Electric motors and generators (of at least 80 mm shaft height), of maximum rated speeds up to 950 r/minElectric motors of shaft heights smaller than 80 mmFansGearsMachinery, generalMachine toolsPaper machinesProcess plant machinesPumpsTurbo chargersWater turbines
G 2,52,5CompressorsComputer drivesElectric motors and generators (of at least 80 mm shaft height), of maximum rated speeds up 950 r/minGas turbines and steam turbinesMachine-tool drivesTextile machines
G 11Audio and video drivesGrinding machine drives
G 0,40,4GyroscopesSpindles and drives of high-precision systems
NOTE 1    Typically, completely assembled rotors are classified here. Depending on the particular application, the next higher or lower grade may be used instead. For components, see clause 9.

NOTE 2   All items are rotating if not otherwise mentioned (reciprocating) or self-evident (e.g. crankshaft drives).

NOTE 3   For some additional information on the chosen balance quality grade, see Figure 2 which contains generally used areas (service speed and balance quality grade G) based on common experience.

NOTE 4    For some machines, specific International Standards stating unbalance tolerances exist.

NOTE 5   The selection of a balance quality grade G for a machine type requires due consideration of the expected duty of the rotor when installed in situ which typically reduces the grade to a lower level if lower vibration magnitudes are required in service.

NOTE 6   The shaft height of a machine without feet, or a machine with raised feet, or any vertical machine, is to be taken as the shaft height of a machine in the same basic frame, but of the horizontal shaft foot-mounting type. When the frame is unknown, half of the machine diameter should be used.