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Published: 1961

Total Pages: 68

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Earlier work on the ultrasonic extrusion of lead and aluminum has been extended to the cold extrusion of plasticized ceramic compositions, resulting in significant improvements in increased extrusion rate (more than 100-fold), decreased extrusion pressure (2 to 10 fold), and in extruded specimen properties. It has also been found possible to extrude materials which are normally nonextrudable because of their low plasticizer or water content. Fused, ground alumina could be ultrasonically extruded with 15% less water than the minimum content without ultrasonics, and only 40 to 60% of that used in normal commercial practice. Significant improvement in the strength of as-extruded shapes, as well as reduced shrinkage and deformation in drying and firing, resulted. Compositions normally using 3 w/o ammonium alginate as a plasticizer can be extruded with 0.2 w/o plastizer when ultrasonically activated. It has been postulated that the ultrasonic effects observed are derived from reduction of surface friction, shear thinning of the thixotropic systems, particle orientation, surface-film rupture, and wetting phenomena. As-extruded specimen improvement was evidenced by a smoother surface and freedom from cracks, tearing, and peeling. When steel dies were used, abrasion of the die surface sometimes caused a superficially discolored surface in nonultrasonic extrusions. The comparable ultrasonic extrusions showed little or no discoloration as the ultrasonic power level was increased. Ultrasonically extruded specimens which were fired in the same kiln loading as their corresponding controls show small but consistent increases in fired density. Water absorption was approximately 75% of the control. The highest moduli of rupture in the fired specimens were found in the ultrasonic specimens even though these required only 25% of the extrusion pressure of the controls.