Extrusion Strategies Tackle Temperature Overshoot for Better Control

Extrusion, the backbone of plastic manufacturing, faces a persistent challenge: barrel temperature overshoot. This phenomenon, where actual temperatures exceed preset values despite cooling efforts, plagues production lines worldwide, compromising efficiency, product quality, and energy consumption.

Barrel temperature overshoot manifests in several ways:

• Global overshoot: All heating zones exceed target temperatures
• Localized overshoot: Specific zones (particularly near the die) run hot
• Fluctuating overshoot: Temperatures oscillate above setpoints
• Sustained overshoot: Persistent temperature elevation resistant to cooling

Multiple factors contribute to temperature overshoot:

• Shear heating: Mechanical energy converts to heat during polymer processing
• Poor thermal conductivity: Polymers resist heat transfer, creating internal hotspots
• Cooling inefficiencies: Inadequate heat dissipation from barrel surfaces
• Screw design flaws: Improper compression or mixing sections concentrate heat
• Process parameters: Excessive screw speeds or feed rates generate excess heat

Standard cooling approaches often exacerbate the problem:

• Extruder drive systems typically overpower cooling capacity by 4-20 times
• Polymer's insulating properties prevent effective internal cooling
• Overcooling increases viscosity, requiring more energy input

This creates a vicious cycle: cooling increases viscosity, demanding higher torque, which generates more shear heat.

The extrusion process converts electrical energy to mechanical energy to thermal energy:

• Drive torque depends on melt viscosity
• Lower viscosity polymers require less torque but transfer less energy
• Cooling affects viscosity, altering energy requirements

Temperature-viscosity relationships vary by polymer:

• The consistency coefficient quantifies viscosity-temperature dependence
• Power law models describe most polymers' flow behavior
• Viscosity changes range from 10 to 1,080 poise per °C across polymers

• Moderate screw speeds to balance output and heat generation
• Optimize feed rates to maintain stable flow
• Adjust backpressure to minimize resistance heating

• Upgrade cooling systems with proper maintenance
• Implement screw designs that distribute shear heating
• Consider barrel insulation for thermal stability

• Choose polymers with favorable thermal properties
• Consider viscosity-temperature profiles when selecting resins

A manufacturing facility addressed chronic temperature overshoot by:

• Reducing screw speed by 15%
• Cleaning and optimizing cooling channels
• Installing a screw with extended compression zone
• Improving workshop ventilation

These changes reduced temperature fluctuations by 60% and improved product consistency.

Effective temperature control requires understanding energy dynamics, material properties, and process interactions. Rather than relying on aggressive cooling, manufacturers should adopt comprehensive strategies that address root causes while maintaining process stability and energy efficiency.