Resolving Inline Wall Thickness Drift to Eliminate Conversion Mass Variances in Profile Extrusion
Inline mass drift is resolved by closed-loop gravimetric control and downstream ultrasonic wall tracking adjusting haul-off speed in real time.
Barrel Zone Temperature
Meaning
Thermal regulation in plastic extrusion and injection moulding utilizes independent heating and cooling bands along the processing cylinder to establish localized thermodynamic conditions. Each discrete region has its own setpoint, known as a barrel zone temperature, which collectively determines the heat transition from the feed throat to the nozzle. These setpoints establish the boundaries where polymer transition occurs from a solid particulate bed to a homogeneous fluid melt.
Thermal Gradient
Progression along the extruder screw requires a specific temperature profile to ensure stable conveying and melting. Adjusting each individual barrel zone temperature creates a temperature profile that accommodates the progressive flight depth reduction of the screw. Rear zones are maintained lower to prevent premature melting and bridging at the feed throat, whereas forward zones are set higher to assist the mechanical shearing of the polymer matrix.
If the feed zone is set too high, the polymer melts on the screw root rather than the barrel wall, which stops the forward transport of the material. This forward transport is the foundation of pressure development in the extrusion system.
Process Impact
Insufficient thermal energy input results in incomplete melting and high mechanical torque. This condition leads to unmelted solid polymer entering the die or mould cavity, creating cosmetic blemishes and mechanical weaknesses. Operating at an excessive barrel zone temperature causes thermal degradation, which reduces molecular weight and diminishes the tensile strength of the finished part.
Viscosity Control
Rheological behavior of the melt depends directly on the localized energy input during transit. The pressure drop across the die or the flow front velocity in the mould is stabilized by holding the final barrel zone temperature to a tight tolerance. Steady melt viscosity reduces part weight variation and prevents flash or short shots during production.