Why is the safety factor not just 1.0?

Because rated motor torque is steady-state. Real braking duty includes inertia, downhill loads, wind on cranes and emergency stops.

What if duty cycle is very high?

Increase disc mass — a larger disc or a ventilated rotor — to absorb the thermal energy without exceeding the pad limit (typically 400–500 °C).

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Resources

Sizing a Disc Brake — Inputs, Formulas, Worked Example

Disc brake sizing reduces to: required torque at the disc, allowable disc temperature rise, and pad wear life. Get these three right and the brake will outlive the gearbox.

Inputs

Motor power, motor speed, gearbox ratio between motor and brake disc, load inertia, required stopping time or duty cycle, ambient temperature.

Torque equation

T_brake = (k × P × 9550) / n_brake, where k is the safety factor (1.5–2.5), P is motor rated power in kW and n_brake is brake-shaft rpm.

Energy per stop

E = ½ × J_total × ω², referred to the brake shaft. This must be within the disc's allowable thermal capacity per cycle.

Worked example

75 kW × 1480 rpm motor, 16:1 gearbox, brake on gearbox input shaft (so n_brake = 1480 rpm), safety factor 2.0: T_brake = (2.0 × 75 × 9550) / 1480 ≈ 968 Nm. Pick the next-larger Pintsch Bubenzer SB-series unit.

FAQs

Why is the safety factor not just 1.0?: Because rated motor torque is steady-state. Real braking duty includes inertia, downhill loads, wind on cranes and emergency stops.
What if duty cycle is very high?: Increase disc mass — a larger disc or a ventilated rotor — to absorb the thermal energy without exceeding the pad limit (typically 400–500 °C).

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