Meaning
High-speed polymer melt flow through branching runner systems generates uneven shear heating across the cross section of a fluid stream. Frictional energy accumulation creates the Beaumont Effect, where molten material at channel margins retains higher thermal energy than the central core. The resulting viscosity variation splits homogenous resin into laminas of differing temperature before entering cavity gates.
Coverage applies strictly to multi-cavity injection molds with geometric branching, terminating at single-cavity tools or unbranched delivery channels. Mold designers calculate shear distribution to prevent part variance across multi-cavity layouts.
Shear Distribution
Frictional forces along channel walls generate high shear rates in moving polymer melts. The Beaumont Effect redistributes hot outer laminas into inner runner branches at secondary intersections. Consequently, cavity positions receiving outer shear layers fill faster than those fed by core material.
Melt temperature differences reach several degrees Celsius between inner and outer cavities.
Thermal Asymmetry
Viscosity drops sharply in regions subjected to elevated shear heating inside runner channels. The Beaumont Effect promotes unbalanced filling rates despite geometrically symmetrical runner layouts. Mold cavities receiving hotter, less viscous polymer experience higher peak packing pressures and lower volumetric shrinkage.
Warpage and dimensional discrepancies develop between parts produced in the same moulding cycle.
Mold Correction
Melt rotation devices reposition high-shear polymer layers evenly before entering gate locations. The Beaumont Effect requires specialized runner geometry or melt flip technology to homogenize fluid temperature profiles across all cavities. Standard geometric runner sizing fails to correct thermal imbalances because symmetric channels preserve shear separation.
Corrective insert installation eliminates filling disparities without altering overall cycle time.
