Investigation of the Effect of Runner Inlet Diameters on Flow Length in Plastic Injection Molding

The injection molding method, which is widely used in shaping polymer materials, is the process of melting the plastic material into the mold, filling the mold cavity, solidifying during the cooling process, and then separating it from the mold with the help of pushers. In this process, the complete filling of the mold cavity is extremely important for the product to come out flawlessly. There are many factors such as the diameter of the designed runner inlet, wall thickness and injection parameters in the complete filling of the mold cavity by the plastic fluid. One of the most important components of mold design is flow analysis. Plastics have a wide range of viscosity changes that determine the nature of the flow in the mold cavity. This flow behavior feature should be analyzed and examined to determine the optimum operating conditions during production. In this study, polypropylene (PP) and low density polyethylene (LDPE) polymers, which are widely used in the plastics industry, were preferred. Flow analysis was performed with the SolidWorks Plastics Program by determining the runner inlet diameters as $0.25 \mathrm{~mm}, 0.50 \mathrm{~mm}$ and 0.75 mm, respectively, and the injection parameters were kept constant in the analysis and the injection pressure was selected as 10 MPa. As a result of the analysis, the spiral flow lengths for inlet diameters of $0.25 \mathrm{~mm}, 0.50 \mathrm{~mm}$ and 0.75 mm were determined as $215 \mathrm{~mm}, 255 \mathrm{~mm}, 280 \mathrm{~mm}$ for PP, and $135 \mathrm{~mm}, 180 \mathrm{~mm}, 210$ mm for LDPE, respectively. Although there was a $100 \%$ increase in flow length in the transition from 0.25 mm to 0.50 mm, this rate was $18.6 \%$ for PP, and despite a $50 \%$ increase in flow length in the transition from 0.50 mm to 0.75 mm, a $9.8 \%$ increase in flow length was observed for PP. For LDPE, an increase of ${3 3 . 3 \%}$ and ${1 8 . 6 \%}$ was determined, respectively.