Meaning
Heat transfer limits occur at the boundary between a solidifying polymer and the metal mould surface due to incomplete contact. This thermal gap resistance is caused by micro-scale air pockets that form as the polymer shrinks away from the steel during cooling. This barrier reduces the rate of thermal exchange.
Interface Behavior
Surface roughness and pressure determine how closely the polymer melt conforms to the metal cavity walls. As thermal gap resistance develops during the packing and cooling phases, the temperature gradient across the polymer-metal boundary changes dynamically. This change complicates the cooling rate calculations.
Cooling Efficiency
Heat removal from the polymer melt dictates the cycle time and the final crystallinity of the part. High thermal gap resistance slows down the cooling process, which increases the time the part must remain in the mould. This delay increases the overall production costs.
Mould Design
Conformal cooling and optimal holding pressures are used to minimize the thermal gap at the boundary. By adjusting the mould surface finish and applying high injection pressure, designers can lower the thermal gap resistance to achieve faster cycles. This optimization is important for thick-walled components where the slow rate of heat conduction through the plastic itself already limits the cooling speed.
