Page 351 - Biosystems Engineering

328 Cha pte r Ele v e n

Input hopper for
resin pellets

Rotating feeder screw

Motor Heated barrel Extrusion die
FIGURE 11.1 Single-screw extruder. (Adapted from Ref. 2.)

the polymer melt is pumped through a slit die and film is passed over
chilled rollers and wound into rolls. In the blown film process, a thin
tube is extruded through an annular slit die in a vertically upward
direction, followed by air blown through the die head to inflate into a
thin tube. The tube of film is cooled and then passed through nip rolls
where the tube is flattened and then wound up (Fig. 11.2). The

Nip rollers
Guide frame

Blown tube Compressed
air

Screw extruder

Wind-up roll
FIGURE 11.2 Extrusion-blown tubular fi lm. (Adapted from Ref. 2.)