Injection moulding angles

Control of fibre orientation with short fibres, such as those sometimes used in injection moulding or reaction injection moulding (RIM) is also important. The flow in the mould may be constrained in two directions such as width and thickness, giving linear flow only in one direction. Or, the flow can instead be radial, that is, constrained in just one direction, for example the thickness, in which case the usual shear forces due to the mould walls will operate, but there will be an additional extensional force, caused by the expanding flow front. This results in fibre orientation being normal to the flow direction. The orientation angle is usually very small at the surface, but it can be almost 90° at the mid-plane [7]. 

However, angled injection moulding machines, and especially large ones, make up only a tiny fraction of the injection machines in use. 

Wide-angle XRD patterns of injection-moulded nanocomposites. 

The rubber mix is extruded by a screw through a non-retum valve into a separate chamber from which it is injected into a mould by a simple ram set at an angle to the screw. The tight fitting separate piston gives accurate delivery of the rubber mix allowing more efficient application of ram pressures up to 160 MPa. This pressure can inject even unusually high viscosity natural rubber mixes of Mooney viscosity (ML1+3, 120 °C) up to 100. 

The mixture should enter the mould in a laminar flow at a velocity not greater than 2 5m s for a thin part (<6mm) and l 2m s" for thicker parts. The mixture should also enter the mould in such a way that it is guided on to the bottom mould surface and not merely injected at random. The mould is usually tilted at an angle (15-45°) such that the cavity can be filled from the bottom to the top. 

Figure 9.9 Stack mould with HR manifold adapted to work with angle injection machine Reproduced with permission from Arburg)...

Orientation based on the flow direction from injection point of the mould Par, parallel to flow RA, at right-angles to flow. 

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