KEVOS® MAKEOS · Springs
Spring Clamp Hydraulic Release Check (Clamp Force, Release Pressure, Spring Stress)
For a clamp or brake held on by springs and released by a hydraulic piston, is the spring clamping force enough, what pressure releases it, and are the springs stressed within limits when released?
Check of a spring-applied, hydraulically released clamp, brake or tool holder: the rate, load and stress of each coil spring at the clamped length (as the compression spring tool), the total clamping force of the springs in parallel, the extra compression and load at the release stroke, the hydraulic pressure on the annular release piston needed with an allowance for seal friction, the spring stress at release and the clearance to solid, against the clamping force needed, the pressure available and the allowable stress.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Clamping force needed | N | Clamping or braking force the springs must give when clamped. |
| Number of springs | springs | Number of identical springs working in parallel. |
| Release stroke | mm | Extra compression of the springs to release the clamp. |
| Each spring | ||
| Wire diameter | mm | Wire diameter of each spring. |
| Mean coil diameter | mm | Mean coil diameter. |
| Active coils | coils | Active coils. |
| End type | choice | End type. |
| Shear modulus | GPa | Shear modulus. |
| Unloaded length | mm | Length of each spring unloaded. |
| Length when clamped | mm | Length of each spring when clamped. |
| Allowable shear stress | MPa | Allowable shear stress. |
| Release piston | ||
| Piston outside diameter | mm | Outside diameter of the release piston. |
| Piston inside diameter (0 = full piston) | mm | Inside diameter of an annular piston (0 for a solid piston). |
| Seal friction allowance | % | Extra pressure for seal friction as a share of the spring load. |
| Pressure available to release | bar | Hydraulic pressure available. |
Method and formulas
- k = G d⁴ ÷ (8 D³ N_a); load = k (L₀ − L); Wahl-corrected stress (as the compression spring tool).
- Clamping force = springs × clamped load; load at release = springs × k (L₀ − L_w + stroke).
- Release pressure = load at release × (1 + friction) ÷ piston area.
- Example: 3,177.6 N of clamping; 11.01 bar releases it with 422.29 MPa in the springs.
Limitations
- Springs share the load equally; uneven spring lengths load some springs more.
- Clamping force falls as linings or pads wear and the springs lengthen.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a fail-safe brake or clamp
- Find the release pressure of a spring clamp
- Choose the number of springs for a clamping force
Who it is for
- Hydraulic engineers
- Machine designers
- Toolmakers
What you get
- Spring rate, clamped load and stress
- Total clamping force
- Release pressure and stress at release
Interpreting the result
- A softer spring with more compression keeps the clamping force steadier as the pads wear, at the cost of a higher release pressure.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 304–324, 281–286. Topic reference; no source tables or recommended settings are reproduced.
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