The wheel carries Z buckets around diameter D at n rpm. As the wheel slews sideways into the bench at the advance rate, each bucket shaves a thin layer ("chip") off the face before the next one arrives at the same spot:
s = (v_adv / n) / Z chip thickness per bucket (m)
a = s · w chip cross-section (m²), w = bucket width
F = k_s · a · K cutting force, K buckets engaged at once (kN)
M = F · D/2 cutting torque on the wheel shaft (kN·m)
P = M · ω, ω = 2πn/60 drive power (kW)
Q_th = Z · n · 60 · V_bucket theoretical volumetric output (m³/h)
Q_act = Q_th · fill(s) actual output after bucket fill efficiency
ṁ = Q_act · ρ_lignite mass throughput fed to the conveyor (t/h)
Bucket fill efficiency rises with chip thickness up to the bucket's own capacity, then saturates at 100%: a slow advance under-fills the buckets (wasted rotor power), while too fast an advance overloads the cutting force and can exceed what the discharge conveyor can carry — watch the conveyor-load readout turn red.
- Bench face — the material profile the wheel is cutting into; it visibly recedes as material is removed.
- Buckets — fill color darkens with lignite as each passes through the cutting arc, then empties into the chute at the top of the wheel.
- Boom conveyor — carries the discharged material off at a rate that must match ṁ; the moving-dot density is proportional to actual mass throughput.