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.
Frozen Layer Kinetics
Meaning
Melt solidification along the cold mould wall governs the effective flow cross-section and the resulting shear rate in the filling cavity. Understanding frozen layer kinetics helps processors predict the growth of this solidified skin.
Flow Channeling
During the injection phase, the polymer melt that touches the cold mould surface freezes instantly, forming a stationary layer that restricts the flow of the remaining molten core. The frozen layer kinetics determine the rate at which this layer grows, directly impacting the pressure required to fill the mould. A rapid increase in the frozen layer thickness can lead to premature freeze-off, causing short shots in thin-walled sections.
Molders balance this growth by increasing melt temperature or injection speed.
Surface Finish
Initial contact of the polymer melt with the steel determines the replication of the mould surface texture and the presence of cosmetic defects. Slow frozen layer kinetics can allow the polymer to record the details of the tool before solidifying, improving gloss and reducing gate blush. Conversely, if the skin freezes too quickly, the polymer cannot fully adapt to the tool surface, resulting in dull areas and visible weld lines.
Adjusting the mould temperature is the primary method used to control this phenomenon.
Solidification Process
Shear forces are concentrated at the boundary between the moving melt core and the stationary frozen layer. These localized forces orient the polymer chains parallel to the flow direction, which creates anisotropic mechanical properties in the finished part. The frozen layer kinetics determine the thickness of this highly oriented skin layer relative to the unoriented core.
A thicker skin increases the part’s flexural modulus but can also increase the tendency to warp.