Mill reversal

A reversing mill hands back its flywheel energy at every pass. See how much, how fast, and why no resistor could take it.

Lesson: Mills, furnaces, kilns and drilling rigs

Try it: energy at every mill reversal

Inertia J_eq (at the motor)4,200 kg·m²

Rolling speed ω60 rad/s

Reversal time (each ramp)2.5 s

Time at speed per pass3.0 s

Speed
Inertial power

Energy per reversal: 7.56 MJ
Mean power while slowing: 3.02 MW
Peak regenerated power: 6.05 MW
Average over the cycle: 0.95 MW

At 7.5 reversals a minute, a resistor would have to dissipate 0.95 MW continuously, on top of the peaks. That is why reversing mills are always specified with a fully regenerative supply.

E_rev = ½ J_eq (ω₁² − ω₂²) ; P_mean = E_rev / t_r ; P_peak = J ω α