Meaning
Physical phenomena occurring when mechanical shear forces in a moving fluid generate heat internally can raise the temperature of the material without any external heat source. During the extrusion of high-viscosity polymers, thermal viscous heating is caused by the friction between the polymer molecules as they are forced through the narrow die. This effect is especially pronounced in high-speed extrusion lines where shear rates are high, representing a major challenge for operators trying to maintain uniform product quality across long production runs.
Material Impact
The sudden increase in temperature can lead to localized thermal degradation of the polymer melt. This thermal viscous heating often causes defects like discoloration or bubbling of the extruded part. Recognizing the onset of this degradation is critical for maintaining the structural integrity of the finished plastic profile.
Temperature Control
Processing engineers use specialized barrel cooling systems and optimized screw designs to dissipate the excess thermal energy. To counteract thermal viscous heating, the extruder’s cooling zones must be adjusted dynamically based on the shear rate of the melt. This control strategy is essential for preventing run-away heating that can ruin the entire batch of resin.
Process Limit
Operational constraints set a practical limit on the speed at which the extruder can be run without damaging the material. When attempting to increase production throughput, thermal viscous heating must be carefully balanced against the cooling capacity of the machinery. This limitation dictates the maximum output rate of the production line for high-viscosity materials.
