Meaning
Thermal instability in injection moulding represents a rapid, transient escalation in resin temperature that exceeds the established set point of the heater bands or the barrel interface. melt temperature surge occurs when viscous dissipation or barrel friction generates heat faster than the control system can dissipate or compensate for the energy gain. This condition risks polymer degradation, loss of molecular weight, and sudden changes in the final product density. Accurate monitoring of this phenomenon relies on thermocouples positioned near the internal wall of the barrel rather than external heater sensors.
Thermal Dynamics
Extreme pressure gradients within the screw flight generate shear stress that converts mechanical energy into internal heat. melt temperature surge often follows a change in screw speed or back pressure where the plastic reaches its flow limit. High viscosity resins suffer more frequently from these spikes because the material retains internal heat longer than low viscosity alternatives.
Material Impact
Structural properties in the finished part weaken when thermal spikes trigger chemical chain scission. melt temperature surge alters the flow length and crystalline structure of commodity polymers which leads to inconsistent shrinkage rates across different batches. Regrind usage amplifies this risk because the material has already undergone a previous thermal cycle and possess a lower tolerance for additional heat exposure.
Operational Boundaries
Production equipment manufacturers define safe operating ranges for barrel temperature control through PID loops that counteract minor fluctuations. melt temperature surge signals that the process has moved outside the effective compensation range of the controller hardware. Constant deviation from the nominal temperature target indicates either a mechanical blockage in the nozzle or an undersized screw design for the current throughput volume. A stable melt stream requires strict adherence to documented screw recovery times.
