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ISO 21940 Balance G Grades

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

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Guidance for balance quality grades for rotors with rigid behaviour.

BALANCE QUALITY GRADE G MAGNITUDE e per Ω
mm/s		 MACHINERY TYPES – GENERAL EXAMPLES
G 4000 4 000
  • Crankshaft drives for large, slow marine diesel engines
    (piston speed below 9 m/s), inherently unbalanced
G 1600 1 600
  • Crankshaft drives for large, slow marine diesel engines
    (piston speed below 9 m/s), inherently unbalanced
G 630 630
  • Crankshaft drives, inherently unbalanced, elastically mounted
G 250 250
  • Crankshaft drives, inherently unbalanced, rigidly mounted
G 100 100
  • Complete reciprocating engines for cars, trucks and locomotives
G 40 40
  • Cars: wheels, wheel rims, wheel sets, drive shafts
  • Crankshaft drives, inherently balanced, elastically mounted
G 16 16
  • Agricultural machinery
  • Crankshaft drive, inherently balanced, rigidly mounted
  • Crushing machines
  • Drive shafts (cardan shafts, propeller shafts)
G 6,3 6,3
  • Aircraft gas turbines
  • Centrifuges (separators, decanters)
  • Electric motors and generators (of at least 80 mm shaft height), of maximum rated speeds up to 950 r/min
  • Electric motors of shaft heights smaller than 80 mm
  • Fans
  • Gears
  • Machinery, general
  • Machine tools
  • Paper machines
  • Process plant machines
  • Pumps
  • Turbo chargers
  • Water turbines
G 2,5 2,5
  • Compressors
  • Computer drives
  • Electric motors and generators (of at least 80 mm shaft height), of maximum rated speeds up 950 r/min
  • Gas turbines and steam turbines
  • Machine-tool drives
  • Textile machines
G 1 1
  • Audio and video drives
  • Grinding machine drives
G 0,4 0,4
  • Gyroscopes
  • Spindles 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.

 

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