How does a blow moulding machine work

Blow moulding a shape is a common industrial process. The example shown below is of the production of a plastic bottle. The plastics normally used in this process are; polythene, PVC and polypropylene.

The blow moulding machine is based on a standard extruder barrel and screw assembly to plasticise the polymer. The molten polymer is led through a right angle and through a die to emerge as a hollow (usually circular) pipe section called a parison.

When the parison has reached a sufficient length a hollow mould is closed around it. The mould mates closely at its bottom edge thus forming a seal. The parison is cut at the top by a knife prior to the mould being moved sideways to a second position where air is blown into the parison to inflate it to the shape of the mould.

After a cooling period the mould is opened and the final article is ejected.To speed production several identical moulds may be fed in cycle by the same extruder unit.

The process is similar to injection moulding and extrusion.

1. The plastic is fed in granular form into a 'hopper' that stores it.

2. A large thread is turned by a motor which feeds the granules through a heated section.

3. In this heated section the granules melt and become a liquid and the liquid is fed into a mould.

4. Air is forced into the mould which forces the plastic to the sides, giving the shape of the bottle.

5. The mould is then cooled and is removed.

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How does a blow moulding machine work