ABSTRACT
Forming by pressing consists of granulation of the powder, filling of the mold, pressing to a compact, and ejection of the compact from the mold. When the mold is filled, the granules are compacted by the application of pressure. The pressure can be applied by a die or by an iso-static pressure. Particle-particle lubrication facilitates flow during pressing. Consequently, the adsorption behavior of the dispersants, binders, and lubricants is important to their behavior during pressing. Prior to spray drying, the powder has to be dispersed in a well-concentrated slurry, usually containing some pressing additives. The pressing additives function as a binder for the granules and often as a lubricant during pressing. Organic binders used as pressing additives will migrate during drying, especially if they are water soluble. Binder migration might cause hollow granules, due to the mechanisms mentioned above. Binder migration also results in a binder-rich outer layer of the granule.
