| μ | W (N) | Ri (mm) | Ro (mm) | Model | n | Capacity (N·m) |
|---|---|---|---|---|---|---|
| 0.30 | 4500 | 60 | 110 | Wear | 2 | 229.50 |
| 0.35 | 8000 | 75 | 140 | Wear | 2 | 602.00 |
| 0.28 | 12000 | 80 | 160 | Pressure | 4 | 1,673.33 |
| 0.40 | 6000 | 55 | 120 | Wear | 2 | 420.00 |
| 0.25 | 15000 | 90 | 180 | Pressure | 6 | 3,150.00 |
This calculator estimates the static torque capacity of a friction clutch using:
- T = torque capacity
- n = number of friction surfaces
- μ = coefficient of friction
- W = axial clamping force
- Ri, Ro = inner/outer friction radii
- Rm = mean effective radius
When you provide power and speed, required torque is computed as:
- Enter μ, clamp force W, radii Ri and Ro, and friction surfaces n.
- Select a mean radius model: uniform wear or uniform pressure.
- Optionally add demand using power & speed, or direct torque.
- Set a service factor to cover shocks and uncertainties.
- Press Calculate to view capacity, pressure, and safety factor.
Export buttons download your saved history. PDF includes the latest result; CSV includes up to 50 recent calculations.
Torque Capacity Drivers
Torque capacity scales linearly with friction coefficient, clamp force, surface count, and mean radius. For dry linings, μ commonly falls near 0.25–0.45, while wet systems can be lower with oil and material. Increasing n from 2 to 4 doubles the interfaces, so capacity doubles if W and μ stay constant. In practice, W comes from springs or hydraulic actuation. Keep units consistent: convert lbf to newtons and inches to meters before comparing designs.
Choosing Uniform Wear vs Uniform Pressure
Uniform wear is often used for clutches that have run-in, because the pressure profile tends to adjust with lining wear. Uniform pressure is a conservative choice for new or lightly used surfaces, where pressure is closer to constant across the face. The model only changes Rm, so it directly affects torque through T = n·μ·W·Rm. If unsure, compute both and bracket your design for reviews.
Interpreting Mean Radius and Geometry
Mean radius rises with larger outer radius and smaller inner radius, but geometry also impacts heat and pressure. A narrow annulus (Ro close to Ri) can concentrate contact and reduce robustness even if Rm looks acceptable. Typical friction faces use Ro/Ri ratios around 1.4–2.2 to balance packaging and area. Use radii at the effective contact band, not the full plate diameter. Consider hub clearances that shrink usable Ri.
Using Power, Speed, and Service Factor
When you select power-and-speed mode, required torque is derived from T = P/ω with ω = 2πN/60. For example, 5.5 kW at 1500 rpm corresponds to about 35 N·m before factors. Apply a service factor to cover shocks and duty cycle; light steady duty may be 1.1–1.3, while heavy shock can exceed 2.0. Safety factor compares capacity to demand after the service factor. Add margin for engagement heating.
Checking Pressure and Design Limits
Average pressure is computed as W divided by the annular contact area π(Ro²−Ri²). Use it to spot unrealistic inputs: high pressure can imply rapid wear, overheating, or actuation limits. Many designs aim for moderate average pressure and manage temperature with ventilation or wet cooling. Verify allowable pressure, temperature, and PV limits with supplier data, then iterate W, area, and n accordingly.
1) What does “friction surfaces (n)” mean?
n is the number of active friction interfaces. A single plate clutch typically has two interfaces (n=2). Multi-plate packs can have many more. Torque capacity increases roughly in direct proportion to n.
2) Which mean radius model should I choose?
Use uniform wear for run-in linings and many design handbooks. Use uniform pressure for new faces or when you want a conservative radius estimate. If uncertain, calculate both and design to the lower capacity case.
3) Why is my safety factor showing “—”?
Safety factor is only computed when a required torque is provided. Select a demand mode and enter power plus rpm, or a direct torque value. The calculator then divides capacity by required torque multiplied by service factor.
4) Can I use this for wet clutches?
Yes for a first estimate, but wet friction coefficients can vary strongly with oil, groove pattern, temperature, and speed. Use realistic μ from testing or supplier data, then validate with thermal capacity and engagement energy limits.
5) How is required torque computed from power and speed?
The calculator converts power to watts, then uses ω = 2πN/60 and T = P/ω. Ensure rpm is the shaft speed at the clutch. Apply service factor to reflect shocks, start-stop duty, and uncertainty.
6) Is average pressure the same as peak contact pressure?
No. Average pressure is W divided by total contact area. Local pressure can be higher due to misalignment, waviness, or thermal distortion. Use average pressure to sanity-check inputs, then confirm allowable peak limits separately.