KEVOS® MAKEOS · Power Transmission
Friction Clutch Engagement Design
What clamp force does this clutch need to start the load in time, and how much heat does each engagement make?
Sizing a multi-plate or single-plate friction clutch for an inertia start: torque to accelerate the load in the target time plus load torque with a service factor, clamp force for the friction faces (uniform wear), peak lining pressure against the allowable, actual slip time at the design torque, energy dissipated per engagement, temperature rise of the plates and average heat at the engagement rate.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Duty | ||
| Load inertia at the clutch | kg·m² | Inertia of everything being started, referred to the clutch shaft. |
| Driving speed | rpm | Speed of the driving side (assumed constant). |
| Load torque during engagement | N·m | Resisting load torque while starting. |
| Target engagement time | s | Time you want the start to take. |
| Service factor | Factor on the torque for wear and variation. | |
| Clutch | ||
| Friction face outside diameter | mm | Outside diameter of the friction surface. |
| Friction face inside diameter | mm | Inside diameter of the friction surface. |
| Number of friction faces | Number of friction interfaces (2 for a single plate between two faces). | |
| Friction coefficient | Friction coefficient of the lining. | |
| Allowable lining pressure | MPa | Allowable pressure for the lining material. |
| Heat | ||
| Mass of plates absorbing heat | kg | Mass of the parts that soak up the heat of one engagement. |
| Specific heat of plates | J/kg·K | Specific heat of the plates (about 460 J/kg·K for steel). |
| Engagements per hour | How often the clutch engages. | |
Method and formulas
- Torque to start: T = J ω ÷ t + T_L; design torque = SF × T.
- Uniform wear: T = μ F faces (D_o + D_i) ÷ 4, so F = 4T ÷ [μ faces (D_o + D_i)]; peak pressure p = F ÷ [2π r_i (r_o − r_i)].
- Slip time at the design torque = J ω ÷ (T_design − T_L); energy per engagement = T_design ω² J ÷ 2(T_design − T_L).
- Temperature rise = energy ÷ (m c_p); average heat = energy × engagements per hour ÷ 3600.
- Example: starting 2 kg·m² to 1000 rpm in 1 s needs 7.17 kN of clamp force and makes 11.643 kJ per start.
Limitations
- Constant driving speed and constant friction; real engagement curves vary.
- Heat soak assumes the plate mass absorbs each engagement before cooling.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size a clutch or brake for starting a flywheel, conveyor or spindle
- Check clutch heating at a higher cycle rate
- Choose plates and actuator force
Who it is for
- Design engineers
- Maintenance engineers
- Power transmission engineers
What you get
- Design torque and clamp force
- Lining pressure and slip time
- Energy, temperature rise and average heat
Interpreting the result
- Slip energy is set by inertia and speed: a faster start does not reduce it, a lower slip speed does.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2446–2458. Topic reference; no source tables or recommended settings are reproduced.
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