Stress and input energy analyses of shearing a particle bed under a centrifugal field

Sadegh Nadimi,Mojtaba Ghadiri

doi:10.1016/j.powtec.2021.08.086

Sadegh Nadimi, Mojtaba Ghadiri

Open Access

https://doi.org/10.1016/j.powtec.2021.08.086

Copy DOI

Abstract

Effective shearing of fine powders for surface modification and dry coating requires a compressed powder bed to prevent aeration. A device known as Mechanofusion® provides the necessary conditions using a centrifugal field, under which submicron particles are coated onto coarser host particles by shearing under great compressive forces at very high strain rates. This creates composite powders with enhanced properties, such as good flowability, surface functional effects, etc. Understanding the dynamics of particle motion, required level of shear stresses and input energy is a prerequisite for process optimisation. Here, numerical simulation by the Discrete Element Method is carried out, analysing features which are otherwise difficult to obtain by experimental work, e.g. the determination of the thickness of the zone in which particles experience shearing strains, as necessary for functional effect, compressive forces on particles, and input energy. Correlations are proposed for the energy input requirement and stresses experienced by the device as a function of rotational speed.

Highlights

Dry coating and surface modification of fine powders are challenging as the bulk powder readily aerates, making it difficult to shear the particles under large stresses to smear the surfaces with other powders of interest
Yokoyama et al [1] developed a device called the Angmill Mechanofusion system, employing a centrifugal field to compress the fine powder, making it possible to shear the bulk powder for surface modification and dry coating of micrometre size powder with finer powders for fusion or dry lubrication
Particles accumulate in front of the push arm, caused by the constricting gap, the extent of which is increased as the rotational speed is reduced

Summary

Introduction

Dry coating and surface modification of fine powders are challenging as the bulk powder readily aerates, making it difficult to shear the particles under large stresses to smear the surfaces with other powders of interest. Yokoyama et al [1] developed a device called the Angmill Mechanofusion system, employing a centrifugal field to compress the fine powder, making it possible to shear the bulk powder for surface modification and dry coating of micrometre size powder with finer powders for fusion or dry lubrication. Several new versions of this device are available commercially, known as Mechanofusion®. This device consists of a rotating cylindrical chamber, in which a fixed rounded inner-piece, called push-arm, and a fixed scraper blade are placed. When the chamber is rotated, high centrifugal forces are exerted on the particle bed, causing it to undergo compression against the chamber wall.

Methods

Results

Conclusion