MoldMaking Technology

AUG 2018

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Page 27 of 83

Hot Runners 26 MoldMaking Technology —— AUGUST 2018 Assumptions. This research was performed under the assumptions that polypropylene melts at uniform tempera- ture, which is equal to 250°C (plus or minus 30°C) and that the polypropylene had a Newtonian, laminar flow. The pres- sure boundary was at an inlet of 10 kilopounds per square inch, and the research was performed using an isothermal steel manifold. The curved manifold (see Figure 1 on page 24) was designed for equal flow channel length. Other parameters CONTRIBUTOR Dr. William Sames is CEO of HTS International Corp. FOR MORE INFORMATION HTS International Corp. / 865-410-8880 / could be optimized, including pressure drop and residence time. The results of the simulations were significant: resi- dence time (or the time that the polymer spends in the mani- fold channels) was nearly equalized along the different flow paths. The residence time was cut from 400 milliseconds to 200 milliseconds in the outer channels (see the labeled posi- tions 1 and 4 between the graphs in Figure 2 on page 25), while the residence time was increased from 100 milliseconds to 200 milliseconds in the interior channels (see the labeled positions 2 and 3 between the graphs in Figure 2). A look at the normalized, surface-concentration profile further validates the equal filling profiles in the curved manifold compared with the conventional manifold (see Figure 3 on page 25 and Figure 4). While the cases shown represent two extreme ends of the manifold design spec- trum, the benefits of removing constraints on the shape of the manifold channels are clear. For multi-cavity molders, new production capabilities with metal AM can enable the design of higher-density injection gates and can simplify the manifold stack. For single-cavity molders (as in many auto- motive molds), these new capabilities enable the strategic placement of drops in complex arrangements. These benefits occur because patterns are developed without regard for intersecting cross-drill patterns, and curved channels can add path length into a reduced footprint for drops closer to the manifold inlet. Curved channels also reduce the path length for drops located fur- ther from the manifold inlet. Lastly, curving channels in a single manifold body reduce stack height instead of having to stack symmetrically drilled manifolds to achieve uniform channel length in high-volume tools. These images depict surface concentration at 200 millisec- onds simulated time for straight (left) and curved (right) manifold design. The curved design shows completed fill for all drops, while the outer drops of the straight manifold design are still filling. FIGURE 4 maintenance tracking MADE EASY. Drop-down Menus | Standardized Terms | Tech Tips Status Alerts | Powerful Reports | FREE TRIAL Simple-to-use maintenance software that gives you total mold control. NOW OFFERING: Mold maintenance training courses.

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