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.
Thermal Spikes
Meaning
Transient temperature anomalies represent rapid localized rises in fluid temperature during high speed shear or improper heater zone control. Process technicians track thermal spikes during mold filling and screw plasticating to prevent localized polymer degradation. The phenomenon alters localized melt viscosity, causes material burning and induces severe internal stress concentrations.
The scope includes localized temperature surges occurring inside barrel zones, nozzle tips, hot runner channels and restrictive gate geometries.
Shear Dissipation
Rapid fluid acceleration through small channels generates intense internal friction, converting mechanical energy directly into heat. Uncontrolled viscous dissipation causes severe thermal spikes that elevate local melt temperatures far above barrel controller setpoints. High speed injection phases magnify shear heating at restrictive gates, degrading sensitive additives and colorants while leaving wall thermocouple readings unaffected.
Slow cycle pilot trials often conceal localized shear spikes that appear only when production ramps to high speed automated filling. Demonstrating process safety requires continuous high frequency thermal logging at critical channel constrictions.
Detection Audit
Fast response thermocouple probes and inline infrared sensors capture rapid thermal transients during injection and plasticating steps. Undetected temperature surges create cosmetic black specks and mold deposit buildup that compromise long term tool operations. Process readiness demands mapping localized temperature excursions under maximum injection velocity conditions to verify material safety margins.
Degradation Impact
Exceeding resin degradation temperatures causes immediate polymer chain breakdown, gas generation and surface defects. Gate dimensions or injection speed profiles must be modified to keep peak fluid temperatures within material limits.