Low Frequency Shear Rheology Metrics for Assessing Extrudate Swell in Bimodal Pipe Resins
Low frequency storage modulus G prime below 0.1 rad/s isolates high molecular weight elastic recovery to predict bimodal pipe swell and prevent over-extrusion.
ISO 1167
Meaning
Determination of the resistance of thermoplastics to internal pressure relies on defined testing parameters. The standard iso 1167 provides a framework for evaluating the long term hydrostatic strength of plastic pipes and components through pressurized water exposure at constant temperatures. Pipe manufacturers use these procedures to establish minimum required strength values, ensuring that fluid transportation networks maintain integrity under specified load conditions.
Pressure Protocol
Applying internal stress to a pipe segment requires a controlled hydraulic environment where temperatures remain stable within set tolerances. This protocol within iso 1167 dictates how samples are submerged in water or air while subject to constant hoop stress to monitor the time until failure occurs. Moulders and extruders rely on this data to predict the longevity of finished parts, since premature rupture indicates poor fusion or suboptimal material density.
Material Specification
Resin performance often varies depending on the processing history and whether a manufacturer employs virgin pellets or recycled regrind. The testing defined by iso 1167 focuses on the inherent capability of the polymer matrix to withstand persistent forces rather than the quality of a specific finished part. Datasheets typically report these values under optimized laboratory conditions, yet a production run might exhibit drift if thermal degradation occurs during the extrusion phase.
Failure Mechanism
Creep rupture happens when the molecular chains of the polymer gradually slide past one another under the influence of continuous internal loading. If the iso 1167 testing reveals an unexpected drop in hours to failure, the variance points to excessive internal voids or improper cooling rates during the manufacturing process. Consistent adherence to these hydrostatic benchmarks proves the structural reliability of a thermoplastic pipe system over its intended service life.