Extrusion and Extruders

In nearly all applications of piastics in packaging, the first step is to convert the soiid piastic, usuaiiy in peiiet form, into a meit. This meit can then be shaped using heat and pressure into a usefui form. The equipment used to do this is an extruder. An extruder is used for him and sheet, and is part of a blow molder for bottles. An extruder is also part of an injection molding machine for injection molded or injection blow molded packaging. The extruders used in all of these applications work in a similar manner, but they deliver the melt to the shaping operation differently. We will explore these differences as we proceed. 

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Extrusion and extruder design are apparently almost entirely empirical at present. This field might well defy rigorous theoretical analyses until the simpler problems of flow in annular spaces and rectangular ducts and of nonisothermal fluid flow are understood. 

Fielden K . Newton JM. Extrusion and extruders. In Swarbrick J. Boylan. JC, eds. Encyclopaedia of Pharmaceutical Technology. Vol. 5. New York Marcel Dckker Inc., 1992 395-442. 

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