Polymer_4

Question 1

Describe Blow Moulding.

Answer 1

Molten or softened plastic tube or ‘parison’ is blown from inside into a two-part mould.

Limited to hollow parts (bottles, containers etc.)

Relatively thin wall thickness.

Relatively little scrap.

Higher melt strength thermoplastics (PE, PET etc).

Distinct from film blowing/ blown film extrusion.

Question 2

Describe Extrusion Blow Moulding (EBM).

Answer 2

Process:
Extrude molten 'parison'.
Close Mould.
Insert blowing pin.
Inflate and cool.
Eject.

Limited biaxial polymer orientation.

Vary parison thickness to ensure constant wall thickness.

Vary parison thickness by raising/lowering the die mandrel.
Die swell.

Creates ‘pinch off’.
Scrap.
Weak point.

Various container sizes from small (a few ml) to large containers (~200 L).

Question 3

What are the characteristics of Extrusion Blow Moulding (EBM)?

Answer 3

Extrusion phase is quicker than inflate/cool/eject.
Shuttle extruder between two moulds.

Higher efficiency attained using more than one extruder and a multiple cavity mould.

Highest efficiency attained by extruding into moulds on a rotating wheel.

For large moulds, parison can sag under it’s own weight and tear.
Need to use an accumulator arrangement (cf. injection moulding) to manage sag.

Question 4

Describe Injection Blow Moulding (IBM).

Answer 4

Two step process:
Injection mould a pre-form.
Soften pre-form and blow mould into final shape.