Friction, interparticle

Powder Mechanics Measurements As opposed to fluids, powders may withstand applied shear stress similar to a bulk solid due to interparticle friction. As the applied shear stress is increased, the powder will reach a maximum sustainable shear stress T, at which point it yields or flows. This limit of shear stress T increases with increasing applied normal load O, with the functional relationship being referred to as a yield locus. A well-known example is the Mohr-Coulomb yield locus, or... 

Pepin, X., Simons, S.J.R., Blanclion, S., Rosstti, D. and Couarraze, G., 2001. Hardness of moist agglomerates in relation to interparticle friction, granule liquid content and nature. Powder Technology, 117, 123-138. 

When the gas velocity in the settler is sufficiently high, the particles deposited on the collection plates can be picked up by the gas stream. This reentrainment can substantially reduce the collection efficiency. By neglecting interparticle friction, the pick-up velocity, f/pp, may be estimated as [Zenz and Othmer, 1960]... 

Polymer processing operations, by and large, are nonisothermal. Plastics pellets are compacted and heated to the melting point by interparticle friction, solid deformation... 

Die fill characteristics depend upon material flow properties that are primarily affected by particle size and shape. Additionally, high interparticle friction can have a detrimental effect on die fill characteristics due to powder bridging and non-uniform flow characteristics. A non-uniform particle size distribution may also lead to material segregation resulting in uniformity problems. Tablet presses employ volumetric filling of the material into the die cavity. Most high-speed tablet presses are equipped with force feeders, which use rotating paddles to promote uniform die fill characteristics. For certain materials, attention must be... 

Second is that the results of Figs. 21-117 and 21-118 do not clearly depict the role of saturation and compact porosity. Decreases in compact porosity generally increase compact strength through increases in interparticle friction, whereas increases in saturation lower strength (e.g.. Figs. 21-112 and 21-113 and Holm et al. [Parts V and VI, Pow-der Technol., 43, 213—233 (1985)]). Hence, the curve of Fig. 21-118 should be expected to shift with these variables, particularly since the viscous force for axial approach is singular in the interparticle gap distance [Eq. 21-111)]. 

The interparticle friction in the slurry can be reduced through the use of surface-active reagents (surfactants). The surfactants, therefore, alter the viscosity and overall rheology of the slurry. It is important to... 

The requirements for coal slurry intended to be used in IGCC are similar to those for pipeline transport, with the added requirement that, as for coal-water fuels, the slurry needs to atomize easily in the reactor. Atomization has been found to be easier (producing smaller-diameter droplets at lower jet pressures) as the size of the coal particles in the slurry increases, because of weaker capillary forces holding the slurry together and decreased interparticle friction. As the capillary forces and interparticle friction are also responsible for increasing the viscosity in coal slurries, it is clear that low-viscosity slurries will atomize more readily than high-viscosity slurries. 

Due to interparticle friction the shear strength r is high in a high vacuum. This explains, for example, the extremely well developed footprints that were visible in the loose dust during the first landing of man on the moon (Apollo II).Interparticle friction is highest in space conditions. 

Because, due to interparticle friction, there is little or no hydrodynamic flow of particulate solids during compaction, each level of more complicated parts must be supported with a separate punch or die member to maintain reasonably uniform density throughout the green pressed part (classes III and IV of P/M Figures 189 and 190). Some additional typical parts obtainable by die pressing are shown in Figure 191. ... 

Due to wall and interparticle friction, the flow of particulate matter is slower near the feeder wall and produces starved conditions at the edges of the rollers, resulting in more or less pronounced zones of less compacted material to overcome this problem, at least partially, the feeder should be wider than the roller, or /[Pg.278]

Freely flowing particulate matter sliding down a vertical chute assumes a flow profile similar to a turbulent velocity distribution. Due to wall and interparticle friction there is a velocity gradient in a material layer close to the chute walls (Figure 288a). The thickness of this layer depends on particle size and cohesiveness of the material (stickiness). When the feed approaches the gripping... 

Friction between the roller, die, and material as well as interparticle friction in the mass to be pelleted are responsible for the pull of feed into the nip region and for densification. Smooth surfaces may result in slip and low interparticle resistance to flow will result in a more or less pronounced tendency of the mass to avoid the squeeze (back-flow), thus reducing densification and potentially choking the machine (see above and Figure 321). While the first problem can... 

Compact density and its distribution is also strongly influenced by interactions between the solid particles and of the particulate mass with equipment features (e.g. die walls, punch surfaces, roller press pockets, etc.). If a perfectly lubricated particulate solid (i.e. featuring no interparticle friction) were compacted in a cylindrical die with frictionless walls, it could be expected that the force exerted by the smooth, flat punch is transmitted through the entire volume of material resulting in uniform pressure and, therefore, uniform density throughout the compact. In reality, the presence of frictional and shear forces leads to a non-uniform pressure distribution and irregular particle movement (displacement) causing variations in compact density. 

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