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The majority of polymer films are manufactured by film blowing (blown film extrusion). A single screw extruder is used to melt the polymer and pump it into a tubular die, as shown in cross-section at right. Air is blown into the center of the extruded tube and causes it to expand in the radial direction. Extension of the melt in both the radial and down-stream direction stops at the freeze line (frost line) due to crystallization of the melt. The nip rolls collect the film, as well as sealing the top of the bubble to maintain the air pressure inside. This process is used extensively with polyethylene and polypropylene.

Process Schematic

film blower


A good textbook treatment of film blowing can be found in:
J.F. Agassant, P. Avenas, J.Ph. Sergent, P.J. Carreau,
Polymer Processing Principles and Modeling, Hanser, New York (1986). ISBN 0-19-520864-1, pages 252-262.

Suppliers of Film Blowing Lines

Wayne Machine and Die Company

Copyright 2000, 2001