High-pressure agglomeration

Figure 179. Schematic representation of high pressure agglomeration equipment, (a) Reciprocating piston and die (eccenter) press, (b) rotary tabletting machine, (c) ram extrusion or plunger press, (d) roller compacting machine, (e) roller briquetting machine...

High pressure agglomeration methods compact essentially dry particulate solids. 

The most commonly used contemporary high pressure agglomeration method for fertilizers applies roller presses (see Section 4.2.2.4.3). 

High pressure agglomeration uses two fundamentally different principles confined volume compaction (Section 4.2.2.3) and roll pressing (Section 4.2.2.4). 

In high-pressure agglomeration, another interlocking mechanism may occur if a mixture of rigid and plastic materials is compacted. In this situation, the plastic component flows into recesses and, more generally, envelopes the exterior structure of harder particles, thus producing a strong structural bond that resembles the effect of a matrix binder (see also Section 8.1). 

Fig, 6.5 Schematic representation of equipment for high-pressure agglomeration, Ram press (upper left), punch and die press (upper right), roller presses for compaction (lower left) and briquetting (lower right). 

Fig. 8.4 Structures of compacts from high-pressure agglomeration after processing equal feed materials (recrystallized KCI, Potash) at low (left, brittle disintegration) and elevated (right, plastic deformation) feed temperatures in identical roller presses with the same operating parameters. (For more information see text.).

For example, Fig. 8.4 illustrates the influence of feed temperature on the structure of specific compacts. These scanning electron microscope (SEM) photographs depict microstructures of recrystallized (upgraded/concentrated) fertilizer grade potassium chloride (potash) after high-pressure agglomeration in a roller press (see also Section... 

Although, the structure obtained from either brittle or plastic behavior of feed materials during high-pressure agglomeration is quite different, as demonstrated in Fig. 

An important post-treatment method for many parts obtained from powders by high-pressure agglomeration is sintering (see Chapter 9). This technology produces final strength and structure in most ceramic and powdermetallurgical parts. 

Finally, because during high-pressure agglomeration porosity is often reduced to very low levels, post-treatment methods may be required to regain a more open pore structure and larger voids (see Section 5.3.2). 

Smaller machines are employed in many fields, including the pharmaceutical, confectionary, and fine chemicals industries, if only a limited output is required and, to a certain extent, for development work in all areas of high-pressure agglomeration (see Section 11.2). Larger ejection type presses are mainly used in the powder metal and ceramic industries. However, even there, the applications are in most cases limited to compacts that feature no or little change in cross section. 

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