Technical Foundation
What Is a Conical Washer?
A conical (Belleville) washer is a cone-shaped disc spring that, when compressed flat under a bolted joint, stores spring force and maintains preload tension on the fastener even as the joint experiences thermal expansion, vibration, or gasket relaxation that would otherwise let a standard flat washer's clamp load drop off. As the disc flattens under load, it follows a load-deflection curve defined by DIN 2093 (metric) or similar standards, with the exact spring rate determined by the washer's thickness, cone height, and material.
Belleville washers can be stacked in series (increasing total deflection at the same load) or parallel (increasing total load capacity at the same deflection) to tune the spring characteristic to a specific application — a series stack of several washers gives a softer, longer-travel spring, while a parallel stack of washers nested cone-to-cone gives a stiffer, higher-load spring in the same axial space. Orientation matters: stacking direction determines whether the assembly behaves in series or parallel.
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| Spec | What It Means | Why It Matters |
|---|---|---|
| Inside/Outside Diameter | Sized to the bolt/stud and seating surface | ID must clear the fastener shank; OD must fit within the available seating area |
| Load Rating | Force at specified deflection, per DIN 2093 curve | Determines how much preload the washer maintains as the joint relaxes or expands |
| Material | Spring steel, 17-7 PH stainless, Inconel | Stainless and Inconel variants hold spring rate at higher temperatures and resist corrosion |
| Stacking Configuration | Series (more deflection) vs. parallel (more load) | Determines whether the assembly behaves as a soft, long-travel spring or a stiff, high-load spring |
| Flatness/Cone Height | Ratio of free height to thickness (DIN classification) | Determines whether the washer behaves linearly or with a snap-through (non-linear) load curve |
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Applications
Where Conical Washers Get Used
Conical washers are specified anywhere a bolted joint needs to maintain clamp force despite vibration, thermal cycling, or material relaxation.
Bolted Joint Preload Maintenance
Belleville washers maintaining clamp force in flanged joints subject to thermal cycling and vibration.
Electrical & Busbar Connections
Disc spring washers maintaining consistent contact pressure on busbar and electrical lug connections as temperature cycles.
Valve & Pump Assemblies
Belleville washer stacks compensating for gasket creep and thermal expansion in bolted valve bonnets and pump housings.
Heavy Machinery & Structural Bolting
High-load Belleville washers maintaining preload on critical structural and machine-mounting bolts.
Aerospace & High-Temperature Applications
Inconel and 17-7 PH stainless Belleville washers holding spring characteristics at elevated operating temperatures.
General Industrial Assembly
Conical spring washers used as a compact alternative to coil springs for load compensation in tight axial space.
FAQ
Conical Washers Questions, Answered
What's the difference between a conical washer and a standard split lock washer?
A split lock washer resists loosening primarily through its sharp edges biting into the mating surfaces and a small amount of spring action, which is limited and can be defeated by vibration or a smooth surface. A Belleville (conical) washer stores a much larger, engineered spring force over a defined deflection range, actively maintaining clamp load as the joint relaxes — a fundamentally different and generally more reliable mechanism for preload retention.
How do I stack Belleville washers for more load vs. more deflection?
Stacking washers in parallel — nested with cones facing the same direction, cup inside cup — increases total load capacity at the same deflection as a single washer. Stacking in series — alternating cone direction so each washer flattens independently — increases total deflection (travel) at the same load as a single washer. Combinations of series and parallel groups let you tune both load and travel.
Why does the orientation of a Belleville washer matter during installation?
The washer must be installed with the correct cone orientation relative to the joint and any adjacent washers in a stack, since installing it backward or misaligning a stack's series/parallel orientation changes the resulting spring rate and load capacity from what was calculated for the joint. Always follow the specified stacking diagram for multi-washer assemblies.
What material should I use for a high-temperature application?
Standard spring steel Belleville washers lose spring rate (relax) at elevated temperatures, so applications above roughly 250-300°F typically call for 17-7 PH stainless steel, and Inconel is used for the highest-temperature or most corrosion-demanding applications. Match the material to both the operating temperature and the corrosion environment, not just the load requirement.
Can Belleville washers be used instead of a coil spring?
Yes, in applications where axial space is limited — a stack of Belleville washers can deliver a comparable spring force and load-deflection characteristic to a coil spring in a much shorter axial length, which is a common reason they're chosen for bolted joint applications where a coil spring wouldn't fit under the bolt head or nut.
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