Meaning
A specialized testing methodology measures the flow behavior and viscosity of polymer melts under the extreme deformation rates typical of commercial extrusion or injection molding. Implementing high shear capillary rheometry allows materials engineers to simulate the exact conditions that plastic faces as it passes through narrow die gates. This measurement identifies potential process defects such as melt fracture or die swell before a material is approved for large-scale production.
Running these tests prevent mold filling issues and mechanical failures in the finished parts, ensuring that the production run proceeds without interruption.
Flow Testing
Running high-velocity material through a capillary die requires precision engineering. By utilizing high shear capillary rheometry, technicians record the pressure drop across the die to calculate the shear stress. These calculations generate a flow curve that characterizes the non-Newtonian behavior of the resin.
This testing is crucial for optimizing the temperature profiles of production extruders.
Melt Behavior
Polymer molecules align under high flow rates, which causes the viscosity to drop by several orders of magnitude. The data generated by high shear capillary rheometry maps this shear-thinning region, which is where most industrial processing occurs. Understanding this behavior allows engineers to adjust gate dimensions and cycle times to prevent excessive pressure buildup during the molding cycle.
This knowledge prevents damage to the mold and reduces energy consumption.
Extrusion Run
The transition from lab testing to the factory floor relies on these rheological profiles to configure the processing equipment. High shear capillary rheometry provides the benchmark data that ensures the selected polymer will process smoothly at commercial output rates. If a batch displays a viscosity mismatch during this test, the extrusion run is halted to adjust the plasticizer content of the mix.
This proactive intervention avoids the creation of out-of-spec batches and minimizes machine downtime.
