Active Core Micro Moulding Resonator Dimensional Control
Active core micro moulding controls resonator dimensions by displacing sub-micron pins during fill, suppressing volumetric sink and frequency drift.
Runner Shear Heating
Meaning
Frictional heat generation occurs within a moving polymer melt as a result of high velocity gradients near the cold walls of a flow channel. This phenomenon, known as runner shear heating, raises the melt temperature as it travels from the nozzle to the gate.
Viscosity Reduction
High shear rates in the runner system reduce the viscosity of the polymer, allowing it to flow more easily into the cavity. The runner shear heating effect can be utilized to fill thin-walled parts without requiring excessive injection pressures or high barrel temperatures. However, this localized heating must be carefully managed to prevent the melt from becoming too fluid, which can lead to flashing at the parting line.
Processors must balance runner dimensions and injection speed to optimize this behavior.
Melt Degradation
Excessive friction in narrow channels can raise the polymer temperature beyond its safe processing window. If runner shear heating is too intense, the material may undergo thermal degradation, resulting in outgassing and reduced mechanical strength in the moulded part. Heat-sensitive resins like polyvinyl chloride or polyoxymethylene are highly susceptible to this type of damage.
Monitoring the screw recovery time and melt appearance helps detect and prevent degradation issues.
Tool Balance
Multi-cavity moulds require identical thermal histories for the melt entering each cavity to ensure dimensional uniformity. Uneven runner shear heating in unbalanced runners can cause some cavities to fill faster or hotter than others, leading to weight variations and warp. Designers utilize geometrically balanced runner systems to distribute the heated melt evenly.
This configuration ensures that every cavity produces parts with identical properties.