Meaning
Mechanical tension loss occurs when the compressive forces of a battery header assembly diminish through material cold flow. Over the service life of a cylindrical cell, crimp relaxation reduces the pressure applied to the polymer gasket that separates the positive terminal from the can. This process is driven by the internal stress of the deformed metal and the plastic deformation of the insulating ring.
Even a minor decrease in force allows microscopic pathways to form.
Polymer Deformation
Polymers used for sealing often undergo permanent shape changes under constant load. This crimp relaxation happens faster when cells are stored at elevated temperatures. The molecular chains in the gasket material slide past one another to relieve the stress imposed during the assembly process.
Once the gasket thins, the original seal diameter is no longer tight.
Seal Performance
Leakage of electrolyte becomes a risk when the interface pressure falls below a specific threshold. Manufacturers measure crimp relaxation by monitoring the force required to move the top cap over time. If the compression drops by more than twenty percent, the likelihood of moisture entering the cell increases.
This moisture reacts with lithium salts to form hydrofluoric acid.
Storage Duration
Long term stability depends on the material properties of both the steel can and the polypropylene seal. While crimp relaxation is inevitable, choosing materials with low creep rates extends the shelf life of the battery. Testing protocols involve accelerated aging at sixty degrees Celsius to predict behavior over several years of operation.
Reliable cells maintain enough tension to pass vacuum leak tests even after extended storage periods. The metallurgical properties of the nickel plated steel also influence the rate of force decay. When the metal spring back is insufficient, the seal fails early.
An effective design accounts for these changes during the initial engineering phase.
