Multi Cavity Mold Gate Shear Rate Evaluation Methods
Multi cavity mold gate shear rate evaluation requires Rabinowitsch-Mooney corrected velocity gradients matched against real micro-metrology tool dimensions.
Thermal Shear Degradation
Meaning
Irreversible polymer breakdown resulting from the simultaneous action of elevated melt temperatures and high mechanical friction within fluid channels compromises resin integrity. Identifying thermal shear degradation pinpoints the degradation mechanism caused by excessive shear heating combined with prolonged barrel residence times during plasticizing. This material failure alters melt flow index, reduces molecular weight and causes discoloration in processed plastic parts.
The boundary governs heat and shear interactions in polymer processing, ending once the melt solidifies inside the mold cavity.
Chain Scission
Polymer chain scission occurs when high shear stresses break covalent chemical bonds at elevated processing temperatures. Exposure to thermal shear degradation causes severe loss of impact resistance and tensile yield strength in engineered thermoplastics. Automotive under-hood components and structural brackets suffer premature mechanical failure when processed beyond material stability thresholds.
Preventing chemical breakdown requires balancing injection speed against barrel temperature settings.
Viscosity Indicator
Melt flow increases unexpectedly when thermal shear degradation scissors polymer chains, offering less mechanical resistance inside runner channels.
Boundary Determination
Engineers evaluate residence time distribution and shear rate profiles to prevent thermal shear degradation during long molding cycles. Relying on static thermal calculations while ignoring mechanical shear heating leads to localized overheating inside hot runner tips. Supplying parts manufactured near material degradation thresholds results in field stress cracking and customer rejections during commercial distribution.
Spectroscopic analysis during pilot runs verifies chemical stability before scaling up to full production rates.