A cone-shaped washer that acts as a very stiff spring when squeezed toward flat. Stacked in series for more travel or in parallel for more force, Belleville washers hold clamp load on joints that relax through embedment, gasket creep or thermal cycling, such as bus bar connections, flange bolting and aluminum assemblies. Because their force depends on deflection, they are often tightened to a set amount short of flat rather than to torque alone.
Bus bar joints get a Belleville washer under every nut, snug them till they're almost flat and stop there.
Also heard as
- disc spring
- conical spring washer
- cupped spring washer
Related terms
Embedment
Preload lost soon after tightening as surface roughness under the head, nut and threads flattens out.
Clamp load
The compressive force a tightened fastener puts on the joint members, holding them together in service.
Split lock washer
A split, helical spring washer sold to stop loosening, though it does little once a joint is properly tightened.
Preload
The tension created in a bolt by tightening it, which clamps the joint and keeps it from slipping or opening.