Pin mixers are frequently used to convert fine particles into larger ones. Powder, liquid (preferably water), and binder are fed into a pin mixer, which consists of an agitator comprised of pins on a horizontal rotating shaft inside an enclosed chamber. The relative rates of coalescence and attrition and the time inside the pin mixer determine the final particle size distribution. The “green” or wet agglomerates that leave the pin mixer must have sufficient strength to withstand the downstream drying process. The strength of a green pellet highly depends on its saturation state, which is the fraction of the void volume of the agglomerates that contain water. Green agglomerates from a pin mixer are the most durable when at their funicular state of saturation, which exists when water begins to accumulate at the contact points between individual particles. At lower moisture contents, dry particles exist, which can turn into dust. Too high a moisture content will reduce the capillary forces that hold the particles together, and if appreciably high, a paste or slurry may be created. Saturation states are illustrated in Figure 1.
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