What is the Load-Retention Benefit of Preset Belleville Washers?
Technical White Paper Download
What Is Preset (Scragging)?
As a Belleville washer is loaded, stresses build throughout its cross section, and on first loading that stress can drive localized yielding, permanently reducing the spring's free height. Presetting, also called scragging, compresses the spring to or slightly past flat before it ships, taking that plastic deformation out at the factory instead of in the field. The result is a spring whose free height is stable from the very first load cycle.
In a bolted joint, any loss of spring free height behaves exactly like joint relaxation: it removes elasticity from the system and reduces preload. Whether that loss actually happens depends entirely on whether service conditions push the spring into its plastic range, which is exactly what this white paper quantifies.
Worked Example
In a worked example of a hot, differential-thermal-expansion (DTE) loaded joint, adding Belleville washers alone, preset or not, cuts preload loss from 50% down to roughly 11%. Preset recovers an additional 790 lbf on top of that, lifting retention from 89.1% to 93.5%, meaning a non-preset stack loses 1.67× as much preload as a preset stack under identical joint conditions.
Download the White Paper: Quantifying the Load-Retention Benefit of Preset Belleville Washers
Download the technical white paper, Quantifying the Load-Retention Benefit of Preset Belleville Washers, to see the full derivation, the worked example, and the four service regimes that determine whether preset is actually worth specifying on your next joint.
Additional Resources
Technical Service Bulletin: D73321.20 Elimination of Preset From Some Belleville Designs
Technical White Paper: Maintain Bolt Preload on Electrical Connections Using Belleville Springs
Technical White Paper: Using Belleville Springs to Maintain Bolt Preload
Technical White Paper: Why Bolts Work (and why some don't)
Technical White Paper: Why Do Gasketed Joints Leak?
Technical White Paper: Combatting Embedment Relaxation in Bolted Joints
Case Study: Reliable Bolted Connections in LNG and Refinery Operations
Case Study: Heat Exchanger Leaks at Indonesian Refinery
Case Study: Enhancing Pipe Support Reliability with Belleville Washers
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