Stationary railway clamps, ski lift cable clamps and emergency brakes in elevators are all joints where the clamping force has to survive years of thermal movement, weather and vibration without maintenance. Disc springs for rail applications and lift applications hold that force because a series stack absorbs movement while keeping the load roughly constant, and because the spring provides its force mechanically, with nothing to lose power or pressure.
Infrastructure joints are judged differently from machine joints. Nobody torque checks a rail clamp every month. The design has to assume the next set of hands arrives years later, in bad weather, with a schedule.
Why a spring, and not just a tight bolt
A rail sits on concrete or steel, and everything in that stack moves: thermal expansion in summer, contraction in winter, settlement in the trackbed, wear at the interfaces. A rigid bolted joint responds to that movement by losing preload. A disc spring stack responds by deflecting.
That is the value of series stacking. In series, deflections are additive at the same force, so a taller stack accommodates more movement while the load stays in a usable band. It is how you get constant clamping force out of an assembly that will not stay the same size.
Ski lift cable clamps: grip under a moving load
A ski lift cable clamp has to hold a rope that is loaded and unloaded constantly, in a location where corrosion and ice are permanent conditions. Two decisions dominate. First, the load: parallel stacking makes forces additive at the same deflection, which is how a fixed clamp envelope gets more grip. Second, the environment.
Elevator emergency brakes: force that does not depend on power
An elevator emergency brake spring is a fail-safe element. It has to apply force when everything else has stopped working, which is precisely why a mechanical spring is used rather than a powered actuator. Disc springs suit it because they deliver high load in a short length, are largely self damping, and do not set under static loads once preset, so the brake that has sat unused for a decade still applies the force it was designed to apply.
Outdoors, the material list gets shorter
For outdoor corrosion protection, the corrosion resistant chromium nickel spring steels X10 CrNi 18-8 and X7 CrNiAl 17-7 are available to DIN EN 10151, noting that cold forming makes both magnetic. On washers, X5 CrNiMo 17-12-2 austenitic stainless offers excellent corrosion resistance and lower magnetisability. Coatings add another layer: phosphating with corrosion protection oil, blackened, mechanical zinc, zinc flake, nickel plated and electroless finishes are all available.
Long inspection intervals favour a reusable locking element
When these assemblies are opened, they are usually opened under time pressure. SCHNORR safety washers can be undone and retightened without the securing effect diminishing, and can be used two or more times without restriction. On a maintenance job that means the joint goes back to full specification without a parts chase.
Guidance is the last detail worth insisting on in a drawing: a guide element to prevent lateral movement, inside guidance on a bolt or shaft preferred, guides and abutments hardened to at least 60 HRC with a minimum case depth of 0.8 mm where possible, and a smooth, ideally ground guide surface. Static applications can use unhardened guides.
- SCHNORR components are used in stationary railway clamps, ski lift cable clamps and emergency brakes in elevators.
- In a series stack, deflections are additive at the same force, which lets a joint absorb thermal movement while holding load.
- In a parallel stack, forces are additive at the same deflection, which raises clamping force in a fixed envelope.
- Presetting means disc springs do not set under static loads, so long dormant fail-safe assemblies retain their force.
- Corrosion resistant options include X10 CrNi 18-8, X7 CrNiAl 17-7 and, for washers, X5 CrNiMo 17-12-2. Cold forming makes the chromium nickel grades magnetic.
- Available finishes include phosphating with corrosion protection oil, blackened, mechanical zinc, zinc flake, nickel plated and electroless.
- SCHNORR safety washers can be reused two or more times without loss of securing effect.
Frequently asked questions
Why are disc springs used in rail clamps?
Because the joint has to hold clamping force while the assembly moves with temperature, settlement and wear. A series stack deflects to absorb that movement while keeping the load in a usable band.
How do you increase clamping force without a bigger clamp?
Stack disc springs in parallel. Forces are additive at the same deflection, so load rises with almost no change in installation length.
Why use a spring in an elevator emergency brake?
A spring applies force mechanically, with nothing to lose power or pressure. Disc springs give high load in a short length and, once preset, do not set under static loads, so the force is still there after long periods of inactivity.
Which materials suit outdoor and corrosive installations?
Corrosion resistant chromium nickel spring steels X10 CrNi 18-8 and X7 CrNiAl 17-7, or X5 CrNiMo 17-12-2 austenitic stainless on the washer side, together with a suitable finish such as zinc flake or phosphating with corrosion protection oil.
Do safety washers need replacing at every inspection?
No. The securing effect does not diminish when a joint is undone and retightened, and SCHNORR safety washers can be used two or more times without restriction.