Mold filling imbalances in geometrically balanced runner systems

This paper presents the results of a study which reveals a significant shear induced flow imbalance developed in multi-cavity molds which use the most commonly accepted naturally balanced runner designs. The flow imbalance exists in all standard "H" patterned runners with eight or more cavities and results in as much as 95% flow to the inner cavities. This paper also reveals a solution to this imbalance through a means of flipping the melt in the runner. The "melt flipper" in the runner creates a thermal and flow balance to all cavities, thereby improving product quality and productivity.