Melt flow rate mould design

The flow ratio is the flow length in the mould divided by the wall thickness of the moulding. A number of factors can affect the flow ratio such as melt flow rate, the processing conditions and the features of the mould. Thick sections enable higher flow ratios to be achieved while very thin sections have the opposite effect. The flow length of the material provides tire mould designer with a guide to the minimum number or position of feed points which will be advisable. 

However, for the high strain rates appropriate for the analysis of typical extrusion and injection moulding situations it is often found that the simple Power Law is perfectly adequate. Thus equations (5.22), (5.23) and (5.27) are important for most design situations relating to polymer melt flow. 

Die swell is important in the design of gates for injection moulds too little swell can lead to jetting of the melt stream across the mould cavity instead of a smooth filling of the mould. The primary variables may be taken to be the gate dimensions t, w, and I (see Figure 7.32), melt temperature T, injection volume flow rate Q, and polymer... 

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