Flow path ratio

Some typical data for this mouldability index are given in Figure 8.8. One limitation of these data is that they do not explicitly show whether or not a mould will fill in an injection moulding operation. This will clearly depend on the thickness of the moulding, the flow distances required and operational parameters such as melt and mould temperatures. One very crude estimate that is widely used is the flow path ratio, the ratio of flow distance to section thickness. The assumption is that if this is greater than the ratio (distance from gate to furthest point from gate)/section thickness, then the mould will fill. Whilst... 

Table 8.2 Some collected values for the flow path ratio of injection moulding materials...

The melts, unlike unmodified PPO, are very pseudoplastic. At 280°C one standard grade (Noryl 110) has a viscosity of 675Ns m" at 100 s but a value of only 7 N s m at 100 000 s The flow depends considerably on the grade but flow path ratios tend to be in the same range as for ABS materials... 

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