Extrusion Blow Molding Basics

Extrusion means that material is forced out. In this case, melted and molten plastic is forced out of a container into a hollow tube which forms a parison. The parison is then placed in a cool metal form that represents a bottle or hollow shape. This parison is like a very small bottle, but it has a tube in the middle which blows air into the parison. It inflates the parison much like a balloon being inflated. The outside edge inflates to the shape of the bottle and then is ejected when it is cooled enough to be stiff.

A screw (1) rotates to push (extrude) material from the hopper (3) in green through the barrel (5) where the heater bands (6-7). This liquifies the resin. A tube fills with resin with a smaller tube in the center (8), which blows air (10) into a form tool below and “blows”  the material into the shape as it cools.

Cdang, Brendan Rockey, University of Alberta Industrial Design, Christophe Poret – Own work, from http://en.wikipedia.org/wiki/File:Injection_molding.png Extrusion-blow molding of polymers: reciprocating screw compressed air; hopper; granules; barrel; heaters; grinding, mixing; actuator’s hydraulic generator; draw plate; core/punch.


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