3. Origin of extrusion defects

3.1 Study of extrusion defects

Readers are invited to consult the article Rheological properties of thermoplastics. in the same treatise, in particular paragraph 2.2.3.

Capillary rheometers (commonly used in industry, this device enables flow curves to be obtained over a wide range of velocity gradients ) are simplified extruders that enable extrusion faults to be studied systematically. The complexity of industrial extrusion processes is thus reduced to a well-mastered and modeled experimental set-up.

The main assumptions of this model are :

• a fully developed and isothermal steady shear flow;

• negligible transient effects...