ISO 21940 Balance Quality 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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We provide static and dynamic balancing services to repairers and large companies across UK and Europe who require crankshaft balancing, fan balancing, shaft balancing, and much more. We have the equipment and experience to balance almost any rotating component quickly and to a high standard.

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