Correct coupling selection guide under abnormal operating conditions, e.g. drive blockage, short circuit or supply deviations, as well as under normal operating conditions, e.g. during starting or breaking. Particularly in the case of high mass moments of inertia of the driven machine, torques that are amultiple of themotor starting torquemay become effective during direct starting or star-delta starting. Overload conditions may damage not only the coupling but also the entire drive train. Overload conditions can frequently be prevented with special design measures. SIRIUS soft starters or SINAMICS frequency converters are suitable for considerably reducing starting torques of asynchronous motors. If drive blockages and overloads of the drivenmachine cannot be ruled out, torque limiting SECUREX couplings can prevent damage to the drive train. CouplingBehaviour Under Overload Conditions Coupling behaviour under overload where the torque is considerably above the limits of use of the coupling concerned is determined by the engineering design of the coupling series. The ZAPEX, ARPEX, N-ARPEX, N-EUPEX, RUPEX and N-BIPEX coupling series can withstand overloads until the breakage of metal parts. These coupling series are designated as fail-safe. Coupling types which can withstand overload, i.e. fail-safe types, are used e.g. in crane systems. In case of coupling breakage due to overloads, the splintering metall parts may cause injury to persons and property damages. The N-EUPEX DS, ELPEX-B, ELPEX-S and ELPEX coupling series throw overload. The elastomer element of these couplings are irreparably damaged without damage to the metal parts when subjected to excessive overload. These coupling series are designated as non-fail-safe. The types that fail can be fitted with a failsafe device. This component enables emergency operation, even after the rubber element of the coupling has been irreparably damaged. The fluid couplings of the FLUDEX series withstand a load for a short time. Persistent overload causes the FLUDEX coupling to heat up beyond limits, causing the fuse to operate and so emptying the coupling and interrupting the torque transmission. Torsional and bending vibrations On drives which are prone to torsional and bending vibrations, measurements or calculations such as natural frequency calculations, torsional vibration simulations or bending vibration calculations are necessary. The drive train may, depending on complexity, be regarded as a two-mass vibration-generating system or N-mass vibrationgenerating system. The vibration-generating masses are defined by the rotating bodies and the couplings by the coupling stiffness and shaft stiffness. The effect of torsional vibration excitations on the behaviour of the system is calculated. Torsional vibration excitations may occur during the starting of an asynchronous motor, during a motor short circuit or in diesel engine drives. Bending vibrations may be critical if the coupling is insufficiently balanced and/or at an operating speed close to the critical speed. The details needed for calculating torsional vibration are specified in the coupling catalogue: » Dynamic torsional stiffness » Damping (specification of the damping coefficient ψ or Lehr's damping D = ψ/4π). » Mass moment of inertia of the coupling halves. 23 #DriveLineHarmony Environmental Conditions & ATEX Mechanical Power Transmission Couplings