Attrition of Particulate Solids

Publication Reference: 
Author Last Name: 
M Ghadiri, D Papadopoulos and F Bassam
Report Type: 
Research Area: 
Size Reduction
Publication Year: 
Publication Month: 
United Kingdom

The general aim of the work is to elucidate the mechanisms of attrition of particulate solids. The specific objective of the current work is to investigate various types of damage under impact and sliding conditions. In particular, the transition velocities involved in impact breakage, the relative importance of normal and tangential stresses, the size distribution of the impact product and the effect of load and displacement on the material removal in surface wear have been investgated.

High-speed digital video recording was used to observe fracture patterns of a range of materials with diverse properties and structures as a function of impact velocity. The video recordings clearly show the existence of three identifiable velocity ranges where materials exhibit plastic deformation only, chipping, and a combination of chipping and fragmentation. This information is essential for developing realistic models of particle breakage.

Single particle impact tests of porous silica particles were carried out to investigate the dependence of attrition rate on impact velocity and impact angle. There is a significant increase of the attrition rate with impact velocity, with a maximum level of approximately 4.5% at 20 m s-l, for the size range 2.00-2.36 mm. The attrition behaviour of the samples is relatively insensitive to the impact angle in the range 25”-65’. However, preliminary impact tests with silica particles of different shape and porosities show that there is a dependence of the attrition rate on impact angle, depending on particle structure. Further work is on-going in this area.

A full size analysis of the impact products of PMMA and porous silica particles after a single impact was carried out in order to investigate the change of the size distribution with impact velocity. The Gates-Gaudin-Schumann distribution describes very well the size distributions of the mother particles and debris. The power index of the distribution is nearly constant for PMMA, but it varies significantly for porous silica. The cause of this variation is currently under investigation.

Single particle wear tests were also performed with the aim of elucidating the mechanisms of particle failure under sliding conditions. This occurs by abrasive wear at relatively low loads and long sliding distances, by chipping at slightly higher loads and short sliding distances, and by fragmentation at high loads. The data in the abrasive-wear regime of silica particles with high porosity, and hence low strength, show that the material loss is linearly proportional to the sliding distance and hence corroborate the predictions of the model developed by Ghadiri et al. (1995) for the semi-brittle failure mode. However, the wear test method developed here can provide quantitative information only about the abrasive wear rate, and the impact testing method has to be used for investigating the chipping rate of particulate solids.