Rotating Mold Core Improves Part Quality

A new patented process turns the core of the tool during injection molding as a means to reduce the effects of knit lines and improve burst strength and dimensional stability of cylindrical or conical parts.

A new patented process turns the core of the tool during injection molding as a means to reduce the effects of knit lines and improve burst strength and dimensional stability of cylindrical or conical parts. This new development from Solvay Advanced Polymers LLC, Alpharetta, Ga., is said to at least double the burst strength of parts molded of semi-crystalline engineering polymers reinforced with glass and/or minerals. The effect has been demonstrated with Solvay’s Amodel PPA (nylon 6T) and Ixef polyarylamide (MXD6 nylon). By rotating the core during injection, the polymer chains are arranged around the circumference of a cylindrical or conical part rather than along the flow path of the injected plastic. Reinforcing fibers in the melt are also arranged in this direction, which increases the part’s ability to withstand internal pressure. Rotating the core helps decrease knit lines by distributing them around the entire circumference of the part. Parts are also said to show improved dimensional stability over a wide range of temperature and humidity. Solvay is building a developmental tool to evaluate additional benefits, such as controlling initial dimensions and improving surface finish.