Page 290 - Plastics Engineering

Processing of Plastics 273
(b) producing a preform ‘bottle’ in one mould and then stretching this longi-
tudinally prior to inflation in the full size bottle mould. This is illustrated
in Fig. 4.25.

(11 Extruscon (111 Inflation of preform
la) Manufacture of prefwm

(I ) Stretching (ii) Inflation (iiil Ejection
Ib) Manufacture of bottle
Fig. 4.25 Extrusion stretch blow moulding

Injection Stretch Blow Moulding
This is another method which is used to produce biaxially oriented blow
moulded containers. However, as it involves injection moulding, the description
of this process will be considered in more detail later (Section 4.3.9).

(e) Extrusion Coating Processes
There are many applications in which it is necessary to put a plastic coating
on to paper or metal sheets and the extruder provides an ideal way of doing this.
Normally a thin film of plastic is extruded from a slit die and is immediately
brought into contact with the medium to be coated. The composite is then
passed between rollers to ensure proper adhesion at the interface and to control
the thickness of the coating (see Fig. 4.26).
Another major type of coating process is wire covering. The tremendous
demand for insulated cables in the electrical industry means that large tonnages
of plastic are used in this application. Basically a bare wire, which may be
heated or have its surface primed, is drawn through a special die attached