Meaning
The specific distribution of heat applied across the zones of an injection moulding barrel ensures the progressive and uniform melting of plastic resin. Establishing a melt temperature profile is necessary to transition solid polymer pellets from the hopper to a homogeneous molten state as they are moved forward by the rotating screw. This profile is divided into multiple heating zones, typically ranging from the coolest zone at the feed throat to the hottest at the nozzle.
Viscosity Control
Temperature settings directly influence the viscosity of the molten polymer, which determines how easily the material flows into the mould cavities. If the profile is too low, the resin remains too viscous, requiring high injection pressures and risking short shots or high internal stress in the parts. Adjusting the profile to have a gradual rise across the transition and metering zones ensures the polymer is fully melted without overheating the outer layers.
This progressive heating minimizes the mechanical energy required from the screw, reducing screw wear and saving electricity.
Thermal Degradation
Setting the profile too high can cause thermal degradation of the polymer chains, leading to a loss of mechanical properties, discoloration, and outgassing. Degraded material often shows as silver streaks or splay on the surface of the finished parts. To prevent this, the profile must stay within the resin manufacturer’s recommended processing window.
Process Startup
This temperature profile must be stabilized before production begins to ensure consistency in the initial parts. Technicians monitor the actual melt temperature during startup using a purge-melt pyrometer to verify the barrel heaters are accurate. This step establishes a stable processing baseline.
