In family molds, filling imbalance is hardly avoided in various molding conditions although runner sizes could be optimized by CAE analysis or experiment. For the filling balance, a Variable-Runner System (VRS) utilizing concept of a runner valve proved its balancing capability. In a same family mold, three resins (ABS, LDPE, and PA66) showed different balancing points. In this study, we tried to find the major influencing factor for the phenomenon. We examined whether we could predict the balancing capability of the runner valve with 3D injection molding CAE simulation tool. As the influencing factors, shear heating and shear thinning behaviors of resin are examined by numerical method. Shear heating and shear thinning effects were examined with respect to the temperature increase, and flow rate and pressure drop changes caused by the runner valve, respectively. As the result, shear thinning behavior of a resin is the major factor for the different balancing points, instead of shear heating. With power-law fluid, influence of power index on the balancing capability was examined.
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