Page 291 - Plastics Engineering

274 Processing of Plastics

(driven) Coated
fabric

Fig. 4.26 Extrusion coating process

be coated

Fig. 4.27 Wire Covering Die

to an extruder (see Fig. 4.27). The drawing speed may be anywhere between
1 dmin and lo00 dmin depending on the diameter of the wire. When the
wire emerges from the die it has a coating of plastic, the thickness of which
depends on the speed of the wire and the extrusion conditions. It then passes
into a cooling trough which may extend for a linear distance of several hundred
metres. The coated wire is then wound on to storage drums.
Wire covering can be analysed in a very similar manner to that described
for extrusion. The coating on the wire arises from two effects:
(a) Drug Flow due to the movement of the wire
(b) Pressure Flow due to the pressure difference between the extruder exit
and the die exit.