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Fundamentals of melt rheology, heat generation, and heat transfer as applied to polymer processing
Author(s) -
Carley James F.
Publication year - 1966
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.760060213
Subject(s) - materials science , laminar flow , heat transfer , rheology , plastics extrusion , die swell , mechanics , thermodynamics , shear thinning , thermal conduction , flow (mathematics) , composite material , polymer , physics
The flow of polymer melts is normally laminar, but pseudoplastic in character. That is, flow rate increases in proportion to a power higher then 1, usually between 1.5 and 4, of the applied pressure difference. Viscosities are extremely high—more then a mollion times that of water—so considerable heat is generated in the flowing melt by viscous dissipation of flow energy. This mode of heat generation is put to good practial use in the screw extruder, a device that converts plastic pellets into hot melt for shaping into pipe, sheets, coatings and molded products. Equations are given for computing flow rates and viscous dissipation rates. Heating (except by viscous working) and cooling of polymers are slow processes because all these materials are poor heat conducts nad their extreme viscosities make convection impracticable. The princliples of heat transfer are reviewed, and the solutions are given for some transient‐conduction problems frequenlty encountered in processing. Equations are given for judging the operation of extruders.