Shear Heating and Melt Degradation Analysis in Thin Wall Tooling
Thin wall injection velocity must balance viscous dissipation heat spikes against gate clearance geometry to prevent local polymer backbone degradation.
Pin Gate
Meaning
Narrow entry ports used in injection molding to feed plastic into a cavity from a runner system are designed to shear off cleanly when the mold opens. A typical pin gate is less than one millimeter in diameter and is located on the non-visible side of the part. This design minimizes the need for manual trimming or finishing of the component.
Shear Heating
High flow resistance occurs when molten material is forced through such a small opening. In systems utilizing a pin gate, this resistance creates localized heat that temporarily lowers polymer viscosity. This effect helps the material flow into the cavity, but can also degrade sensitive resins if the flow rate is too high.
Cycle Economy
Automatic degating reduces labor costs by separating the runner from the part during the ejection phase.
Production Scale
Transitioning a multi-cavity mold to full production requires precise balancing of the flow to each cavity. When using a pin gate, minor differences in gate size can lead to uneven filling and structural variation across the molded parts. If these variations are not identified during initial tool tuning, they can cause high rejection rates and inconsistent part weights once the automated line runs at full speed.