A spring-applied electric brake uses spring force to clamp a friction rotor when the coil is off. Energizing the coil attracts the armature toward its housing and releases the friction surfaces. This calculator estimates static holding torque and shows that release sequence.
Electric Brake Interactive Calculator
Compare static holding torque using clamp force, friction, mean radius and active faces. The animation shows a two-face spring-applied brake with an enlarged adjustable magnetic gap.
Equation Used
- Equal load, mean radius and friction coefficient at active faces.
- Applied force entered directly.
- Main drawing illustrates two active faces.
- Release clearance enlarged; sequence assumes successful release.
Static comparison only. No universal air-gap limit, wear penalty or release guarantee.
A rotor clamped between stationary surfaces
The main cutaway shows a fixed reaction plate, a lined rotor that can slide on a shaft hub, an armature, compression springs and a magnet housing with a coil. The rotor has two active friction faces in this illustrative assembly.
In the applied state, the springs push the armature toward the fixed reaction surface. In the release sequence, the armature moves toward the energized magnet housing. Its magnetic gap closes while the friction faces separate. Axial gaps are enlarged for visibility; equal clearance on the two faces is a display assumption.
The lower end view shows a material witness mark rotating only during the fully released part of the inspection cycle. It is not a calculated shaft speed, stopping event or release-time prediction.
Compare static torque and geometry
The inputs are axial clamp force, mean friction radius, friction coefficient, active face count and applied magnetic gap. The torque breakdown below the cutaway shows the selected number of faces; changing it does not claim to redesign the illustrated two-face assembly.
The brake manufacturer specifies the usable air gap, release voltage and application limits for an actual unit. This generic model supplies no such ratings.
Static holding-torque estimate
For clamp force F, friction coefficient μ, effective mean radius r in metres and n active faces, T=nμFr. Each equally loaded face contributes μFr. The sum of tangential friction forces is nμF.
The entered force is the axial clamp load at each active interface, not a force that is divided by n. Radius is supplied directly; the calculator does not infer it from unspecified inner/outer friction diameters.
The fourth result reports the entered gap as the armature travel illustrated to reach the pole face. It is a geometry comparison only. Whether a real coil can complete that motion requires electromagnetic and spring data not entered here.
Default two-face comparison
At F=1000 N, μ=0.4, r=50 mm and two faces, each face contributes 20 N·m. The total static estimate is 40 N·m, corresponding to 800 N summed tangential friction force.
Doubling radius doubles torque without changing tangential force. Changing the gap from 0.3 to 0.6 mm doubles the illustrated travel but leaves the static torque estimate unchanged because the applied clamp force is independently specified.
Limits of the static comparison
Per-face torque, summed friction force and armature travel describe the entered static condition. Permissible air gap and wear limits depend on the actual brake design.
Coil voltage, current, magnetic geometry, spring rate, friction variation, wear thickness, temperature, inertia and speed are not modeled. No stopping distance, release guarantee, thermal capacity, service life or certified holding rating follows from this comparison.
Electric-brake calculator questions
Why is the coil off when the brake is applied?
This page illustrates a spring-applied, electrically released brake. Electrically applied brakes use a different operating principle.
Why does changing air gap not change holding torque?
The entered clamp force is already the applied load. No spring-rate or magnetic-force model links it to gap here.
What does the face slider change?
It multiplies the per-face contribution in the torque calculation. The separate count panel displays those contributions; the cutaway remains a labeled two-face example.
Does the animation verify successful release?
No. It illustrates the assumed sequence and enlarged clearances, not coil capability.
Manufacturer reference
KEB COMBISTOP Type 38 Instruction Manual, page 19 parts illustration and pages 39–40 air-gap and wear dimensions. The manufacturer specifies different gaps by brake size and design; no universal value is used here.
Consult the applicable brake-size instructions for installation and adjustment.
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