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Optical monitoring of polypropylene injection molding
Author(s) -
Thomas Charles L.,
Bur Anthony J.
Publication year - 1999
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.11516
Subject(s) - materials science , molding (decorative) , polypropylene , crystallinity , optical fiber , composite material , backlight , core (optical fiber) , intensity (physics) , optics , scattering , light scattering , light intensity , light guide , optoelectronics , liquid crystal display , light source , physics
We have constructed an optical fiber sensor for monitoring injection molding and we have developed a model to describe sensor behavior. The sensor consists of a sapphire window at the end of a sleeved ejector pin into which an optical fiber is inserted. The optical view with this sensor is through the thickness of the molded product. The measured optical signal was light that transmitted through the resin, reflected off the back wall of the mold, and retraced its path through the resin to the optical sensor, i.e., light transmitted through twice the thickness of the resin. While monitoring polypropylene during the packing and cooling phase of the molding cycle, we observed a decrease in light intensity due to scattering of light by the growing microcrystals. A characteristic minimum in the transmitted light intensity versus time curve is attributed to scattering by growing crystalling spherulites at the core of the molded product. Cavity pressure was also measured and was found to be an essential parameter in the process model. The model illustrates how temperature, pressure, and crystallinity affect the detected light intensity and clarifies the roles that temperature and pressure play in the crystallization process.