5

Project Planning for Gear Units Service factor

Mass acceleration factor The mass acceleration factor is calculated as follows:"All external mass moments of inertia" are the mass moments of inertia of the driven ma-chine and the gear unit, scaled down to the motor speed. The calculation for scalingdown to motor speed is performed using the following formula: "Mass moment of inertia at the motor end" is the mass moment of inertia of the motorand, if installed, the brake and the flywheel fan (Z fan).Service factors f

Mass acceleration factor =All external mass moments of inertiaMass moment of inertia on the motor end

2 J=J nn X

()

M J X = Mass moment of inertia scaled down to the motor shaft= Mass moment of inertia with reference to the output speed of the gear unit= Output speed of the gear unit= Motor speed Jnn M B > 1.8 may occur with large mass acceleration factors (> 10), highlevels of backlash in the transmission elements or large overhung loads. Contact SEW-EURODRIVE in such cases. Service factor: SEW f The method for determining the maximum permitted continuous torque M
a max andusing this value to derive the service factor f
B B = M
a max /M
a is not defined in a standardand varies greatly from manufacturer to manufacturer. Even at a SEW service factor off
B = 1, the gear units afford an extremely high level of safety and reliability in the fatiguestrength range (exception: wearing of the worm wheel in helical-worm pinion units). Theservice factor may differ from specifications of other gear unit manufacturers. If you arein doubt, contact SEW-EURODRIVE for more detailed information on your specificdrive. Example Mass acceleration factor 2.5 (load classification II), 14 hours/day operating time (readoff at 16 h/d) and 300 cycles/hour (Figure 3) result in a service factor f
B = 1.51. Accord-ing to the selection tables, the selected gearmotor must have an SEW f
B value of 1.51or greater.

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Catalog – DR Gearmotors 01/2008