Performance Polymers

Anisotropy – It Boils Down to the Right Direction!

In the injection molding process, various flow forms are linked and are produced simultaneously, depending on the component. While elongation flows, for example, tend to orientate the short-glass fibers radially around the injection point (Fig.1), the shear flows produced via the flow cross section result in rotation of the fibers (Fig.2). Depending on the plastic used, the geometry of the component and the process conditions, a three-layer distribution of the fibers occurs. On the edge of the component, the fibers tend to lie in the direction of molding, while in the center the orientation is transverse (Fig.3).

Fig. 1

Fig. 2

Fig. 3

Here, the layer thicknesses depend very much on the rheological properties of the melt. Different layer thickness distributions occur in the component depending on the flow geometry and the degree of structure viscosity. The mechanical properties are greatly influenced by the anisotropic fiber distribution (Fig.4). Depending on the fiber content, both the stiffness and the stress that can be withstood can differ by a factor of up to 2 depending on the direction.

Fig. 4

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