On jaw crushers, hammer crushers and mills, the motor must accelerate a heavy flywheel or rotor from standstill. Starting can take long; during this time the motor draws high starting current and the winding heats quickly. If material remains in the crushing chamber, the motor also starts against load.

What selection looks at:

  • Starting and breakdown torque: given in the catalogue as Ts/Tn and Tmax/Tn; a breakdown torque margin matters so the motor does not stall on momentary shocks.
  • Inertia and starting time: send flywheel data or the starting time expected by the machine maker.
  • Frame: cast iron is preferred because of vibration and shock.
  • Speed: the catalogue favours 4, 6 or 8 poles for crushers, screens and mills.
  • Belt drive: most crushers are pulley-driven; pulley diameter and belt tension determine the load on the shaft and bearing.

Repeatedly trying to start a full machine is the hardest case for the motor; where possible, restart after clearing the crushing chamber. Dedicated range: stone crushing plant motors; for the data needed for loaded starts see our starting under load article.