Melt flow rate injection moulding

This rubber has a very high melt viscosity and this was reduced by using a polar flow promoter such as zinc stearate at levels of 9.5 and 19%. This not only reduced the viscosity at low shear rates but also increased the level of pseudoplasticity so that at the high shear rates used in injection moulding flow was even more enhanced. 

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. 

Scaling up, however, a single spiral mould test is not possible. Therefore, Fritch recommends that test should be carried out at three melt temperatures and three injection rates for a total of nine tests, in such a way that they cover melt temperature and mould flow rate in commercial processing. 

In extensional flows, the velocity increases (fibre melt spinning) or decreases (radial flow from the sprue in an injection mould) along the streamlines, but there is no velocity gradient in the perpendicular direction. Figure 5.5 shows fibre melt spinning where the velocity increases with distance x from the spinneret, as the result of a tensile stress along the fibre. The tensile strain rate 6x is defined by... 

Compression moulding, a primitive form of injection moulding, is widely used for elastomers and some thermosets. However, it suffers from the primitive control of melt flow, although tools are simple and production rates high. The features that may become defects are similar to those of injection moulding. Perhaps the most sophisticated method is used in tyre building, where temperature control is crucial to achieving the best properties of the many different parts of the product. 

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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