Polyamide Dimensional Shrinkage Differential under Varied Cavity Pressure Conditions
Cavity pressure directly controls polyamide crystallization and volumetric shrink, requiring precise transducer monitoring to hold DIN 16742 tolerances.
Pressure Decay
Meaning
Gradual reduction in pressure within a sealed cavity or system over time is used to detect leaks or evaluate material shrinkage during cooling. Measuring this pressure decay provides a non-destructive way to verify the seal integrity of parts or the closure of valves in processing equipment. The rate of the pressure drop indicates the size of any leaks or the speed of polymer solidification.
This technique is applied in both part testing and injection moulding process control.
Testing Application
Leak testers pressurize the internal volume of a moulded part and monitor the pressure change. When using pressure decay testing, a steady drop in pressure indicates a leak through a crack or a poorly sealed joint. The system compares the leak rate against a pass/fail limit to accept or reject the part.
This method is highly sensitive and can detect very small defects that would not be visible. It is widely used for medical devices and automotive components. The test is fast and can be automated.
Moulding Diagnostic
Cavity pressure sensors record the pressure drop as the polymer cools and shrinks inside the mould. This pressure decay occurs because the polymer occupies less volume as it changes from a liquid to a solid. If the pressure drops too quickly, it suggests that the gate has frozen off before the part is fully packed.
This analysis helps moulders optimize the hold time and gate size. Understanding this rate allows for better cycle time management. This diagnostic is essential for high-precision moulding.
Quality Assurance
Automatic rejection of parts that fail the decay limit ensures that only good parts are shipped. This testing prevents field failures of components that must hold pressure, such as fuel tanks or fluid connectors. Maintaining this quality standard is critical for safety-critical applications.
This test provides a reliable record for trace audits.