Extrusion Drying Defects and Moisture Requirements for Ceramic

Excessively rapid drying of the extruded material. The drying step must be slow enough not to cause crack formation due to uneven shrinkage. Generally this defect is controlled by correcting the velocity or geometry by swirling jets of hot air.

In traditional ceramics mixtures, water is added in order to obtain a material sufficiently plastic to allow extrusion, the amount varying between 15 and 20–22% by weight. This quantity may be subject to change due to the particular characteristics of raw materials. It must be underlined that if this water quantity is compatible with that required for the geopolymerization, then extrusion can be used provided that the extruder is constructed with materials that can withstand the conditions of mechanical and chemical stress generated by the geopolymer paste