BIZOMAT MAKEOS · Power Transmission
Plate Clutch and Disc Brake Torque
How much torque can this plate clutch or disc brake transmit?
Torque capacity of a plate clutch or disc brake by the uniform-wear and uniform-pressure assumptions, with the peak lining pressure, against a required torque.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Outer diameter of lining | mm | Outside diameter of the friction lining. |
| Inner diameter of lining | mm | Inside diameter of the friction lining. |
| Friction surfaces | surfaces | Number of friction interfaces (a single plate between a flywheel and pressure plate has 2). |
| Coefficient of friction | Dynamic friction coefficient of the lining from its maker (use a conservative value). | |
| Clamping (axial) force | N | Spring or actuator clamping force. |
| Required torque (with service factor) | N·m | Torque to be transmitted, multiplied by your service factor. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Outer diameter of lining
- What it is
- The outside diameter of the annular friction lining or pad contact area.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 250 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger outer diameter raises the mean radius and the torque capacity.
- Get it right
- Use the lining diameter, not the plate or disc outer diameter if the lining is smaller.
What this means: Inner diameter of lining
- What it is
- The inside diameter of the annular friction lining, which must be smaller than the outer diameter.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 150 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use the inner edge of the friction material, not the hub or spline diameter.
What this means: Friction surfaces
- What it is
- The number of friction interfaces that carry torque. A single plate clamped between a flywheel and a pressure plate has two.
- Units and format
- Enter a number in surfaces: surfaces. The form accepts 1 surfaces to 100 surfaces. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2 surfaces as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Torque capacity rises in proportion.
- Get it right
- Count interfaces, not plates; each plate faced on both sides gives two.
What this means: Coefficient of friction
- What it is
- The dynamic friction coefficient of the lining against its mating surface, from the lining maker.
- Units and format
- Enter a plain number with no unit. The form accepts 0.000001 to 2. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.3 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Torque capacity rises in proportion.
- Get it right
- Use a conservative value; friction falls with heat, wear and contamination.
What this means: Clamping (axial) force
- What it is
- The axial force pressing the friction surfaces together, from the springs or the actuator.
- Units and format
- Enter a number in N: newtons. The form accepts 0.000001 N or more. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 4000 N as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Torque capacity and peak lining pressure rise in proportion.
- Get it right
- Use the force with a worn lining if spring force falls with wear.
What this means: Required torque (with service factor)
- What it is
- The torque the clutch or brake must transmit, already multiplied by your service factor.
- Units and format
- Enter a number in N·m: newton-metres. The form accepts 0 N·m or more. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 200 N·m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Moves the pass or fail line only; the torque capacity does not change.
- Get it right
- Apply the service factor before entering the value; the tool compares capacity with it directly.
Method and formulas
- Uniform wear: T = μ F n (Rₒ + Rᵢ) ÷ 2.
- Uniform pressure: T = (2/3) μ F n (Rₒ³ − Rᵢ³) ÷ (Rₒ² − Rᵢ²).
- Peak pressure (uniform wear) p_max = F ÷ (2π Rᵢ (Rₒ − Rᵢ)).
- Example: 4000 N on 2 surfaces of a 250/150 mm lining with μ 0.3 carries 240 N·m (uniform wear).
Limitations
- Flat, annular linings; heat capacity and wear rate are not checked.
- Friction coefficient changes with temperature, speed and contamination.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size a friction clutch or brake
- Check torque capacity after a lining change
- Find the clamp force needed
Who it is for
- Design engineers
- Maintenance engineers
- Automation engineers
What you get
- Torque by uniform wear (normal design basis)
- Torque by uniform pressure (new lining)
- Peak lining pressure
- Margin over the required torque
Interpreting the result
- Design on the uniform-wear torque, which is the lower and more realistic value after bedding in.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2446–2458. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Method explained here · BIZOMAT original book
Plate clutch capacity
In Clutches and Brakes by the Numbers
What it covers: How a plate clutch carries torque: the uniform-wear and uniform-pressure models, friction radius, faces, spring force and lining pressure, checked against the torque the drive needs.
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