Page 282 - Plastics Engineering

Processing of Plastics 265

Feedstock
Cutter haul - ,Laces,

Water bath

Fig. 4.17 Use of extruder to produce granules

Fig. 4.18 (a) Extruded panel sections (b) Extruded window profile

longer baths are needed for crystalline plastics since the recrystallisation is
exothermic.
The storage facilities at the end of the profile production line depend on the
type of product (see Fig. 4.19). If it is rigid then the cooled extrudate may be
cut to size on a guillotine for stacking. If the extrudate is flexible then it can
be stored on drums.

(c) Film Blowing
Although plastic sheet and film may be produced using a slit die, by far
the most common method nowadays is the film blowing process illustrated in
Fig. 4.20. The molten plastic from the extruder passes through an annular die
and emerges as a thin tube. A supply of air to the inside of the tube prevents
it from collapsing and indeed may be used to inflate it to a larger diameter.