Ceramic Powder Compaction

Abstract

Powder pressing, either uniaxially or isostatically, is the most common method used for high-volume production of ceramic components. The object of a pressing process is to form a net-shaped, homogeneously dense powder compact that is nominally free of defects. A typical pressing operation has three basic steps: (1) filling the mold or die with powder, (2) compacting the powder to a specific size and shape, and (3) ejecting the compact from the die. To optimize a pressing operation, experienced press operators generally understand and control parameters such as die-fill density, die-wall friction, packing density, and expansion on ejection.Die filling/uniformity influences compaction density, which ultimately determines the size, shape, microstructure, and properties of the final sintered product. To optimize die filling and packing uniformity, free-flowing granulated powders are generally used. Spherical granules (i.e., agglomerates or clusters of finer particles) range in size from ~44 to 400 μm with the average size being ~100–200 μm. They are typically produced from 0.5 to 10-μm median particle-size powders by spray drying a ceramic powder slurry. To produce processable powders, various organic additives are typically added to the slurry prior to spray drying. These include binder(s) for strength, plasticizers that produce deformable granules, and lubricants that mitigate frictional effects. Consistent batching and dispersion of the granulated feed are critical for reproducible and uniform die filling. Granule densities that are 45–55% of the theoretical density (TD), and bulk-powder and die-fill densities of 25–35% TD are typical for ceramic powders.

Comparative evaluation of properties of a clay based ceramic shaped via four techniques

“…In the two last sintering temperatures (1300 and 1400 °C), a drop in the densification percentage is observed (Table II). Decay for pressing is the highest, from 32.6% to 1.5%, being this possible due to density gradients generated as the clay is compacted by the distribution of applied load in the pressed samples [18][19][20].…”

Deformation behaviour of aluminium low-micron MMCs and MMNCs at warm working temperatures (0.3-0.5 Tm)

“…Pressure gradients, caused by the friction between the powder and the die walls, lead to non-uniform density distribution in green compacts (Glass and Ewsuk, 1995). The frictional force opposes the applied force and decreases the amount of pressure transmitted to the powder for consolidation (Turenne et al, 1999), so high pressures result in high green densities (Tiwari, Rajput and Srivastava 2012).…”

Influence of the shaping effect on hardness homogeneity by Vickers indentation analysis

“…15,16 Onoda 17 has studied the influence of granule properties by comparing the compaction of 'hard', 'medium' and 'soft' granules. It appears that soft granules produce high-density compacts with large-density gradients.…”