Extrusion of ceramic tubes with complex structures of non-uniform curvatures made from nano-powders

A computer-controlled extrusion technique was introduced for making ceramic tubes (with a wall thickness of 2 mm and external diameter of 8.0 mm) with tightly controlled bends from ceramic pastes prepared from nano-size boehmite powders. Firstly, the rheological flow behaviour of the paste and related flow parameters were calculated in order to show their effect on the curvature of the tubes. Secondly, an extrusion die with three adjustable pins set 120° apart, an extrusion device and a computer program were developed. The bending of the tube is adjusted automatically through stepper motor-driven pins and 2-D or near 3-D shapes are produced by altering the geometrical flow conditions during the paste extrusion. The computer program developed allows the extrusion time to be controlled for any desired die configuration, i.e. the time between the movement of the pins in any direction, therefore, this adjustment alters the geometrical configuration for flow, inducing bending in the tube. Finally, the effects of the extrusion speed and geometrical flow conditions on the curvature and shape of the tubes were reported. It is also shown that complicated shapes, such as near helical tubes or spiral ceramic tubes can be produced by moving the pins in an appropriate manner.