Meaning
Mold temperature regulation requires highly efficient heat transfer between the molten polymer and the circulating fluid within the cooling channels. This optimal thermal state, known as turbulent cooling flow, is achieved when the velocity of the cooling medium is high enough to generate chaotic fluid motion with a Reynolds number exceeding four thousand. It increases the heat extraction rate by up to ten times compared to laminar flow, which results in faster cycle times.
Processors design their cooling circuits to maintain this condition throughout the production run. It ensures consistent part quality and reduces moulding cycle times.
Thermal Transfer
Laminar flow creates a slow-moving boundary layer of fluid along the channel walls that acts as an insulating barrier to heat. When the system transitions to turbulent cooling flow, this boundary layer is disrupted, allowing rapid thermal exchange between the mold steel and the coolant. This rapid exchange ensures that the heat from the injected plastic is drawn away quickly and evenly.
It prevents localized hot spots that can cause part warping.
Flow Management
Maintaining the correct flow rate through the cooling channels requires careful selection of pump capacity and channel diameter to overcome the hydraulic resistance of the circuit. To achieve turbulent cooling flow, the fluid must be pumped with enough pressure to maintain high velocities through all cooling passages, especially in deep-core areas. Incorporating baffles, bubblers or conformal cooling lines helps to direct this high-velocity flow to the areas that need it most.
Moulders monitor the Reynolds number using flowmeters to ensure that the system remains in this high-efficiency regime, preventing any drop in cooling performance that could lead to dimensionally unstable parts or cosmetic defects.
Moulding Efficiency
Optimizing the cooling cycle has a direct effect on the profitability of the molding operation by reducing the time required for the plastic to solidify. Achieving turbulent cooling flow allows the press to run at its fastest stable cycle time while minimizing internal stresses in the moulded parts. This thermal consistency also reduces the variation in part shrinkage across different cavities.
It keeps the production run within tight dimensional tolerances.
