Attrition characteristics relating

The values of the HGI usually range from 15 to 140. The higher the HGI, the higher is the grindability of the material. The HGI has been found to correlate with the attrition characteristics of the particles in fluidized beds and in pneumatic transport lines (Davuluri and Knowlton, 1998). The HGI does not directly relate to hardness. For example, some materials such as plastics are difficult to grind. 

Particle behavior is a function of particle size, density, surface area, and shape. These interact in a complex manner to give the total particle behavior pattern [28], The shape of a particle is probably the most difficult characteristic to be determined because there is such diversity in relation to particle shape. However, particle shape is a fundamental factor in powder characterization that will influence important properties such as bulk density, permeability, flowability, coatablility, particle packing arrangements, attrition, and cohesion [33-36], Consequently it is pertinent to the successful manipulation of pharmaceutical powders that an accurate definition of particle shape is obtained prior to powder processing. 

A related property, which is also an important factor, is the ability of the individual coal particles to retain their initial size during handling and processing. In fluidized-bed processes, attrition and decrepitation of the feed coal may result in unacceptable tines carryover losses. For processes that must withstand high temperatures and blast velocities, only hard and resistant coals are satisfactory feed materials. In addition, the fusibility and caking characteristics are properties of importance to moving bed or fluidized-bed processes. 

It is very important to understand key elements of the hydrodynamic behavior of gas-fluidized beds before planning new applications or undertaking design, since the flow characteristics affect gas-soUd contacting, heat and mass transfer, dispersion of the gas as it passes through the bed, entrainment, attrition, wear, and so on, all of which are related to overall process and reactor performance. 

Attributes. Qualitative characteristics of products, whose presence or absence is subject to inspection to assess the acceptance quality level of a sample. (Inspection by variables involves numerical measurement) BS 1902 Pt 3.13 relates to the attributive properties of corner, edge and surface defects in refractories. See acceptance testing. Attrition. Particle-size reduction by a process depending mainly on impact and/or a rubbing action. 

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