BIZOMAT MAKEOS · Power Transmission
Caliper Disc Brake Design (Clamp Force, Pad Pressure, Heat)
What clamp force does this caliper disc brake need to stop the inertia in time, is the pad pressure acceptable, and how hot does the disc get per stop?
Design check of a caliper disc brake: the braking torque to stop an inertia in the required time against a load that drives through the stop or helps it, the effective friction radius for uniform wear or uniform pressure, the clamp force for the number of friction faces, pad pressure, friction energy per stop, the disc temperature rise if the disc absorbs the heat, and the stopping angle.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Inertia at the brake disc | kg·m² | Inertia of everything that stops, referred to the brake disc. |
| Speed at the start of braking | rpm | Speed of the disc when braking starts. |
| Required stop time | s | Time within which the load must stop. |
| Load torque at the disc | N·m | Load torque at the disc (friction or gravity). |
| Load during the stop | choice | Whether the load helps the brake or drives through it. |
| Pad outer radius | mm | Outer radius of the pad contact. |
| Pad inner radius | mm | Inner radius of the pad contact. |
| Friction radius basis | choice | Uniform wear (the usual design case) or uniform pressure (new pads). |
| Friction coefficient | Friction coefficient of the pad material. | |
| Friction faces | Number of friction faces (2 for a single disc with a caliper on both sides). | |
| Pad area per face | cm² | Contact area of the pad on one face. |
| Largest pad pressure | MPa | Largest pad pressure for the lining (your value from the maker). |
| Clamp force available | N | Clamp force the caliper can apply. |
| Disc mass | kg | Mass of the disc that takes up the heat. |
| Disc specific heat | kJ/kg·K | Specific heat of the disc (about 0.46 steel, 0.5 cast iron). |
| Largest disc temperature rise per stop | K | Largest temperature rise you accept in one stop. |
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: Inertia at the brake disc
- What it is
- The rotating inertia of everything the brake must stop (load, shafts, couplings, gears), all referred to the brake disc shaft.
- Units and format
- Enter a number in kg·m²: kilogram square metres (mass moment of inertia). The form accepts 0.000001 kg·m² to 1000000 kg·m². Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2 kg·m² as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- More inertia raises the braking torque, clamp force and heat per stop.
- Get it right
- For inertia on a shaft turning at another speed, multiply it by (that shaft’s speed ÷ disc speed)² before adding it.
What this means: Speed at the start of braking
- What it is
- The speed of the brake disc at the moment braking starts, usually the full running speed.
- Units and format
- Enter a number in rpm: revolutions per minute. The form accepts 0.000001 rpm to 100000 rpm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1000 rpm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Required stop time
- What it is
- The longest time allowed from the start of braking until the load stands still.
- Units and format
- Enter a number in s: seconds. The form accepts 0.000001 s to 600 s. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2 s as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A shorter stop time raises the braking torque and clamp force needed.
What this means: Load torque at the disc
- What it is
- The steady torque at the disc from friction or gravity during the stop. The next field says whether it helps the brake or drives against it.
- Units and format
- Enter a number in N·m: newton-metres. The form accepts 0 N·m to 10000000 N·m. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0 N·m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Enter it as a positive value at the disc shaft; choose its direction in “Load during the stop”.
What this means: Load during the stop
- What it is
- Whether the load torque helps stop the disc (friction) or keeps driving it through the stop (for example a load being lowered).
- Units and format
- Choose one of 2 options from the list: Load helps the stop (friction); Load drives through the stop (lowering).
- Example
- The form opens with “Load helps the stop (friction)” selected as a worked example. Choose the option that matches your case.
- Effect on the result
- A load that drives through the stop adds to the braking torque; a helping load subtracts from it.
What this means: Pad outer radius
- What it is
- The radius from the disc centre to the outer edge of the pad’s contact on the disc.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 2000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 120 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Radius from the disc centre, not the pad width or the disc diameter.
What this means: Pad inner radius
- What it is
- The radius from the disc centre to the inner edge of the pad’s contact on the disc.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 2000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 80 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- It must be smaller than the outer radius, or the tool stops.
What this means: Friction radius basis
- What it is
- Which model sets the effective friction radius: uniform wear, for bedded-in pads, or uniform pressure, for new pads.
- Units and format
- Choose one of 2 options from the list: Uniform wear (worn pads); Uniform pressure (new pads).
- Example
- The form opens with “Uniform wear (worn pads)” selected as a worked example. Choose the option that matches your case.
- Effect on the result
- Uniform wear gives a slightly smaller radius and so a slightly larger clamp force.
What this means: Friction coefficient
- What it is
- The friction coefficient between the pad lining and the disc, from the lining maker for the working temperature range.
- Units and format
- Enter a plain number with no unit. The form accepts 0.05 to 1. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.35 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The clamp force needed is inversely proportional to friction.
- Get it right
- Use a value for hot linings too; friction can fall as the lining heats (fade).
What this means: Friction faces
- What it is
- The number of pad-to-disc contact faces that carry the braking torque. A single disc gripped from both sides has two.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 20. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The clamp force needed is inversely proportional to the number of faces.
What this means: Pad area per face
- What it is
- The contact area of one pad on one face of the disc, from the pad drawing or caliper data.
- Units and format
- Enter a number in cm²: square centimetres. The form accepts 0.000001 cm² to 10000 cm². Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 30 cm² as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Pad pressure is inversely proportional to pad area.
- Get it right
- cm², not mm²: 1 cm² = 100 mm².
What this means: Largest pad pressure
- What it is
- The highest contact pressure the pad lining may carry, from the lining maker. The calculated pad pressure is compared with it.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 20 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Clamp force available
- What it is
- The clamping force the caliper can press each pad onto the disc with, from the caliper maker’s data at the available actuating pressure or spring force.
- Units and format
- Enter a number in N: newtons. The form accepts 0.000001 N to 10000000 N. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10000 N as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Disc mass
- What it is
- The mass of the disc that soaks up the heat of one stop. The tool assumes all the braking energy goes into it.
- Units and format
- Enter a number in kg: kilograms. The form accepts 0.000001 kg to 10000 kg. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 5 kg as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The temperature rise per stop is inversely proportional to disc mass.
What this means: Disc specific heat
- What it is
- The heat one kilogram of the disc material absorbs per degree of temperature rise, from material data.
- Units and format
- Enter a number in kJ/kg·K: kilojoules per kilogram per kelvin. The form accepts 0.000001 kJ/kg·K to 2 kJ/kg·K. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.46 kJ/kg·K as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The temperature rise per stop is inversely proportional to specific heat.
- Get it right
- kJ/kg·K, not J/kg·K.
What this means: Largest disc temperature rise per stop
- What it is
- The largest rise in disc temperature you accept from a single stop, compared with the calculated rise.
- Units and format
- Enter a number in K: kelvin (a difference of 1 K equals 1 °C). The form accepts 0.000001 K to 600 K. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 150 K as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- This is a rise in kelvin, not a final disc temperature.
Method and formulas
- ω = 2π n ÷ 60; brake torque T_b = J ω ÷ t_s − T_L (load helps) or + T_L (load drives through).
- Effective radius r_e = (r_o + r_i) ÷ 2 (uniform wear) or 2(r_o³ − r_i³) ÷ [3(r_o² − r_i²)] (uniform pressure).
- Clamp force F = T_b ÷ (μ r_e × faces); pad pressure = F ÷ pad area.
- Energy per stop = T_b ω t_s ÷ 2; disc temperature rise = energy ÷ (m c).
- Example: stopping 2 kg·m² from 1000 rpm in 2 s needs 104.72 N·m and 1,496 N of clamp; the disc warms 4.7679 K.
Limitations
- All the heat is taken by the disc mass; pads and hub take some, cooling runs between stops.
- Constant friction coefficient; it falls as the lining heats (fade).
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size a caliper brake for a machine spindle, winch or conveyor
- Check pad pressure and disc heating
- Compare uniform-wear and uniform-pressure assumptions
Who it is for
- Design engineers
- Maintenance engineers
- Power transmission engineers
What you get
- Braking torque and clamp force
- Pad pressure
- Energy, disc temperature rise and stopping angle
Interpreting the result
- Repeated stops add up: check the cooling time between stops as well as the single-stop rise.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2455–2459. 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
Disc brakes
In Clutches and Brakes by the Numbers
What it covers: How to size a caliper disc brake to stop a load that drives through the stop or helps it: braking torque, friction radius, clamp force, pad pressure, energy and stopping angle.
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Open the Caliper Disc Brake Design (Clamp Force, Pad Pressure, Heat) calculator