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Stress birefringence patterns in molten polymers during the mold‐filling and cooling process
Author(s) -
Han Chang Dae
Publication year - 1974
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1974.070181208
Subject(s) - mold , materials science , birefringence , composite material , molding (decorative) , isothermal process , photoelasticity , stress (linguistics) , optics , linguistics , thermodynamics , solid mechanics , philosophy , physics
An experimental study has been carried out to better understand the phenomenon of stress buildup during the mold‐filling process in the injection molding operation. For the study, a rectangular mold with two glass windows was constructed, so that stress birefringence patterns of molten polymers flowing into the mold could be photographed with the aid of a polariscope. As a feeding system, a 1‐in. extruder was used attached to the mold with a 2‐ft length of stainless steel tubing having a relief valve. In this way, the injection pressure (and injection velocity) was carefully controlled to ensure that the glass windows would not be damaged. The development of stress birefringence patterns during the mold‐filling process was recorded on a movie film. It was observed that, in isothermal operation, when flow stopped after the mold was filled, stresses relaxed immediately because of the very slow cooling of the mold by ambient air. However, it was observed that, as cooling proceeded, stresses were gradually built up again in the mold. It was possible, therefore, to determine the residual stress in the mold, which originates from the cooling process alone.