Meaning
Optical technique designed to measure internal stress in transparent polymers by analyzing light polarization. Inline polarimetry monitors the birefringence of a moving web or a moulded part as it exits the tool. Sensitivity decreases when the resin opacity exceeds the penetration depth of the light source.
Birefringence Measurement
Detection of molecular orientation occurs as polarized light passes through the strained polymer structure. Inline polarimetry quantifies the difference in the refractive index along the principal axes of the material. This measurement correlates directly to the level of frozen-in stress caused by high shear during the injection phase.
Stress Distribution
Mapping the internal tension across a part helps in predicting where cracks or failures might occur under load. Inline polarimetry identifies areas of high stress near the gate or in regions with thin walls. Correcting these issues involves adjusting the hold pressure or the melt temperature to allow for better relaxation.
Quality Control
Automated inspection systems use this technique to reject parts that exceed a predefined stress limit. Inline polarimetry provides real-time feedback to the moulding machine, allowing for immediate adjustments to the process parameters. This proactive approach reduces the amount of scrap and ensures that every part meets the mechanical specifications.
The technology is essential for producing high-quality optical components and medical devices.
