Effects of melt rotation on resulting localized material properties throughout injection molded polymeric products

For some time now the effects of runner-based shear imbalances on melt flows during polymer molding processes have been studied and found to be problematic, even in cases where mold cavities are naturally balanced as traditionally defined. In such instances, melt rotation technology has been applied on many occasions to accommodate resulting cavity filling imbalances as well as shrinkage and warpage issues. In the present study, this approach was taken a step further with the goal of exploring affiliated product quality variations that exist as an extension of the imbalanced polymer melt flow problem. Molding trials were conducted with and without melt rotation using several types of polymers, and the resultant effects on final product physical, thermal and mechanical properties were explored. When this was done, it was found that important product quality parameters such as crystallinity and tensile modulus can vary significantly throughout conventionally molded products and be dramatically altered by the implementation of melt rotation technology. Specimens taken from product regions associated with higher melt flow shear levels exhibited higher crystallinity levels as well as higher tensile moduli. This supports the concept of melt rotation adoption for a broader range of problems extending far beyond cavity fill balancing alone.