Cooling Circuit Design Deciding the Cycle a Quote Assumes
Cooling circuit design dictates actual injection cycle time; quotes assuming unrealistically fast cooling cause part warpage or forced piece-price increases.
Latent Heat of Fusion
Meaning
Quantity of thermal energy required to change a substance from a solid to a liquid state at a constant temperature defines the energy demand of the phase transition. Latent heat of fusion is a critical property for semicrystalline resins like polyethylene or polypropylene which must absorb significant energy to melt.
Energy Demand
Barrel heaters in the injection moulding machine provide the calories needed to break the crystalline lattice of the polymer pellets. The latent heat of fusion represents a large portion of the total heat load, often exceeding the energy required to simply raise the temperature of the solid plastic.
Cooling Requirement
Solidification of the melt inside the mould releases the same amount of energy back into the tool. A high latent heat of fusion means the cooling system must remove more energy to solidify the part, which can lead to longer cycle times compared to amorphous materials.
Process Stability
Variations in the crystallinity of the incoming resin can alter the melt behaviour in the screw. If the latent heat of fusion varies between batches, the melt temperature may drift, affecting the viscosity and the final dimensions of the moulded parts. Monitoring heat input ensures the material is fully melted.