As shown in Figure 2, as the screw speed increases the head pressure increases. The die , when attached acts as a restriction to the flow of the material, which results into an increase in the head pressure. As the take up speed increases for a no-die extruder, the head pressure remains constant. The effect of screw speed on the residence time. As shown in Figure 3, as the screw speed increases the residence time decreases.
Barrel is generally completely full in case of single-screw extruder with the material.
As the screw speed is increased, more material is pumped out of the extruder. To maintain the material in the barrel, the rate at which material enters the extruder also increases, and therefore, the residence time decreases. When the die is attached to the extruder, the decrease in the residence time is less as compared to the attached die extruder. The die offers a restriction to the flow of material, hence the residence time decreases. As the screw speed is increased, the head pressure increases and the residence time decreases.