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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 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 shaftsCrankshaft drives, inherently balanced, elastically mounted |
| G 16 | 16 | Agricultural machineryCrankshaft drive, inherently balanced, rigidly mountedCrushing machinesDrive shafts (cardan shafts, propeller shafts) |
| G 6,3 | 6,3 | Aircraft 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 2,5 | 2,5 | CompressorsComputer 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 1 | 1 | Audio and video drivesGrinding machine drives |
| G 0,4 | 0,4 | GyroscopesSpindles 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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