Production & Quality
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PA6 Water Absorption Dimensional Expansion
Problem Phenomenon
Product dimensions became larger and assembly became tighter after being placed or used for a period of time, and rigidity declined.
Cause Analysis
PA6 absorbs about 2.8% water in equilibrium in a 50%RH environment, with dimensional expansion of 0.5%~1.0% and rigidity decline of 50%~60%; dimensions change with humidity, which is the material nature of PA6 and cannot be eliminated by process.
Solution
①Indicate the measurement state on the drawing (dry state/conditioned state);②correct the mold according to equilibrium water absorption expansion;③consider measuring precision parts after conditioning treatment;④evaluate low-water-absorption grades for humid and hot environment applications;⑤make products with sealed moisture-proof design to control moisture absorption.
Key Takeaway
PA6 dimensions 'must indicate dry state or wet state': water absorption expansion is the material nature; precision nylon parts must be designed according to wet state and measured after conditioning, otherwise the dimensions will never match.
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