Air drying is also called instant drying, from easy to dehydration of the small particles, powder wet material quickly remove water ( mainly surface water ), in a dry, due to short staying time of material in drying, so that the quality of the finished product to get the best control. Air drying for powder or granular materials, its particle size generally below 0.5~0.7mm, not more than 1mm, for the block, paste and paste material, selection of mill and dispersing device and air drying series process, so that the wet material drying and crushing surface at the same time, constantly updated, in order to facilitate the drying process continuously, or use a partial drying of qualified products return feed port and wet materials are mixed, so that the wet paste material, sludge-like material dispersed into the powdery material after drying.