Flow Instabilities (Shark-Skin)

The Shark-Skin effect occurs during the extrusion of plastics, elastomers or food and manifests itself as the stress increases due to increasing shear stress, resulting in a rough or, in this case, shark-skin-like surface in the extrudate.

 

Capillary Rheometers of GOETTFERT, equipped with the Add-on Shark-Skin, offer the possibility to detect these pressure fluctuations by means of high-precision and very fast sensors. On the higher-frequent pressure fluctuation, the maximum shear speed or deformation are determined in the range at which is no shark-skin effect visible and the extrudate surface is still smooth.

This effect can then be detected by the beginning of pressure fluctuations. The exact determination of this maximum shear rate provides possibilities for process optimization or targeted material selection with regard to throughput behaviour as a function of surface quality.

Capillary rheometers from GÖTTFERT offer the possibility to identify the described pressure fluctuations. This gives users the opportunity to sustainably optimize the extrusion, film and coating process.

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