Quantifying Shear Degradation and Fiber Breakdown in Mold Tooling
Quantifying shear rates and gate geometry limits prevents fiber length attrition, tool surface erosion, and mechanical strength loss in molded composite parts.
Capillary Rheometry
Meaning
Analytical method used to determine the flow properties of polymer melts under high pressure and shear rates. Such capillary rheometry involves forcing a molten material through a narrow die to simulate the conditions found in injection molding or extrusion. This technique provides data on how a plastic resin behaves during the high speed manufacturing of device enclosures.
The technique stops being effective once the shear rate exceeds the point where the material undergoes melt fracture or degradation.
Melt Viscosity
Measurement of resistance to flow allows engineers to predict how well a resin will fill a complex mold for a smartphone chassis. Data points collected across various temperatures help in selecting the optimal processing window for the production line. When capillary rheometry identifies a narrow processing range, the factory can adjust heater settings to prevent thermal damage to the polymer.
Pressure Drop
Calculation of the energy required to move the melt through the system depends on the geometry of the die. Accurate readings from pressure transducers located before the die entrance allow for the correction of entrance effects. These corrections ensure the resulting viscosity curve represents the actual behavior of the material within the tool.
Material Selection
Technical data sheets often rely on these measurements to compare the processability of different grades of polycarbonate or ABS. Matching the rheological profile of a new batch to a baseline ensures consistency in the mechanical strength of the final housing.