Optimizing Hopper Airflow and Temperature Controls in Plastic Processing
Hopper airflow rates of 0.8 to 1.2 m3/hr per kg/hr combined with a dew point below -40 C prevent hydrolytic degradation and guarantee uniform drying.
Dynamic Heat Capacity
Meaning
Thermal energy absorption variables describe how much heat a polymer takes in or releases during temperature fluctuations. Dynamic heat capacity changes as the resin undergoes phase transitions from a melt to a solid. It differs from static measurements because it accounts for the speed of heating or cooling within the injection cycle.
High values require longer dwell times in the tool.
Cooling Behavior
Rapid heat removal through the mould walls depends on the thermal conductivity of the tool steel and the resin properties. During the solidification phase, dynamic heat capacity determines the slope of the temperature curve. A sudden spike in heat release occurs as semi-crystalline polymers begin to crystallize.
This exothermic event must be managed to prevent internal stresses.
Processing Variable
Cycle times are optimized by balancing the melt temperature against the required ejection temperature. If the dynamic heat capacity of a new resin grade is higher than the previous material, the existing cooling circuit might prove insufficient. Moulders adjust the water flow rates or lower the chiller setpoint to compensate.
Thermal Measurement
Laboratory testing using differential scanning calorimetry provides the data needed for simulation software. Precise knowledge of dynamic heat capacity improves the accuracy of fill and pack predictions.