Inner gliding surfaces

Another type of lamination is that caused by inner gliding surfaces due to the relative movement of the ceramic body and auger respectively extruder barrel. Segregation occurs in the boundary layer between metal and ceramic body. The coarser material particles in particular are pressed inside the body whilst the liquid phase and the very fine particles concentrate in the boundary layer (Fig. 5). 

Similar to the inner gliding surfaces certain areas of the column will have a reduced strength. Sometimes the resulting laminations are already apparent at the extruded product in the form of cracks, and if this is the case such columns and/or products can easily be pulled apart, even by hand. 

Contrary to inner gliding surfaces, cutting laminations are usually a-ligned in the direction of extrusion. As they are created exclusively in the die or pressure head, these cutting laminations can be found with ill types of extruders, i.e. with piston extrusion presses as well as auger extrusion units. 

Flow laminations, laminations caused by inner gliding surfaces, and cutting laminations, all can be distinguished to varying degrees in the extrusion of plastic bodies, independent of the extrusion method employed, e.g. piston extrusion presses, single-shaft extruders, twin-shaft extrusion machines or rotory-type extruders. 

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