Runner layout

Example 5.4 Eight polypropylene mouldings, each weighing 10 g are to be moulded using the runner layout shown in Fig. 5.19. If the injection time is 2 seconds and the melt temperature is 210°C, calculate the pressure at each cavity if the injection pressure at the sprue is 80 MN/m. The density of the pwlypropylene is 909 kg/m3 and the volume of the sprue is 5000 mm. Assume that the flow is isothermal and ignore the pressure losses at comers. 

Spme and runners should be as small as possible to avoid rework of the polymeric material. The entrance diameter of the sprue should be larger in diameter than the nozzle diameter. Full round and trapezoidal runners have been used successfully to mold polymeric materials. Runner layout should be balanced and generously radius for smooth and uniform melt flow. Holdup spots can cause resin degradation, color changes, and property loss, especially in the flame-retardant and toughened grades. 

A runner layout of pieces to be demolded by simple ejection should be achieved so that the sprue picker takes the runner easily. A row layout of the mold cavities is more favorable for sprue picking than round or star layout versions. It is often practical to form the upp>er end of the runner with an extra cone which guarantees an easy take-off. 

Runner layouts should be designed to deliver the plastic melt at the same time and at the same temperature, pressure, and velocity to each cavity of a multicavity mold. Such a layout is known as a balanced runner (Fig. 7.15). A balanced runner will usually consume more material than an unbalanced type, but this disadvantage is outweighed by the improvement in the uniformity and quality of the moldings. Balance in a multi-cavity mold with dissimilar cavities (known as a family mold) can be achieved by careful variation of runner diameter in order to produce equal pressure drops in each flow path. Such balancing can only be achieved efficiently by the use of computer flow simu-... 

Figure 4.7 Balanced runner layouts melt has the same length of travel for all impressions...

Figure 4.8 Runner layouts which require balanced gating...

Figure 4.9 Hot runner layout permitting mould to be placed centrally on platen...

To avoid this problem, here we proposed a new methodology to handle this pre-processing issue. In this way, users only need to (fraw lines to represent the runner layout, and set the parameters of the runner geometry. Then, the runner solid mesh can be generated automatically. Indeed, the hybrid mesh is feature of this method shown in Fig.l and Fig.2. Through this way, people can flexibly tune up the resolution of element layer and also retain the quality and quantity of elements. It can further enhance the efficiency of the eomputation and provide more reasonable results. 

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