Analysis of particle dynamics in a pin mill by Discrete Element Method

Wei Pin Goh,Mojtaba Ghadiri,M.A Aguirre,L.A Pugnaloni,R Soto,S Luding

doi:10.1051/epjconf/202124907010

Abstract

Milling is an important process for tailoring the particle size distribution for enhanced attributes, such as dissolution, content uniformity, tableting, etc., especially for active pharmaceutical ingredients and excipients in pharmaceutical industries. Milling performance of particulate solids depends on the equipment operating conditions (geometry, process conditions and input energy etc.) as well as material properties (particle size, shape, and mechanical properties, such as Young’s modulus, hardness and fracture toughness). In this paper the particle dynamics in a pin mill is analysed using Discrete Element Method (DEM), combined with a novel approach for assessing particle breakability by single particle impact testing. A sensitivity analysis is carried out addressing the effect of the milling conditions (rotational speed and feed particle flow rate), accounting for feed mechanical properties on the breakage behaviour of the particles. Particle collision energy spectra are calculated and shown to have a distribution with the upper tail end being close to the maximum energy associated with the collision with the rings. Breakage is primarily due to collisions with the rings, except for large particles that are comparable in size with the gap between the rings, nipping is also a contributory breakage mechanism.

Highlights

Milling is commonly used in a wide range of manufacturing operations to tailor desired product specifications and quality attributes [1]
The milling performance of particulates is dictated by the mechanical properties of the material and the operating conditions of the chosen mill such as the geometry, process conditions, input energy, etc
The effect of rotational speed on the average number of particle collisions before they leave the mill is shown in Fig. 2 (327 μm particles fed at 0.2 g/s)

Summary

Introduction

Milling is commonly used in a wide range of manufacturing operations to tailor desired product specifications and quality attributes [1]. The milling performance of particulates is dictated by the mechanical properties of the material (hardness, fracture toughness and Young’s modulus) and the operating conditions of the chosen mill such as the geometry, process conditions, input energy, etc. The working principle of a pin mill is similar to that of a hammer mill, where the size reduction is due to the impacts between the particles and the pins but generally at higher tip speed configuration. At the early stages of product and process development, adequate test material is not generally available. For materials that exhibit semi-brittle behaviour, the case under consideration here, their breakage propensity can be described as a function of their mechanical and physical properties and incident impact energy [2]. Several experimental approaches have been developed to assess particle breakability using various equipment, such as the single particle impact tester. Bonakdar et al [4, 5] proposed a new approach, where the extent of particle breakage can be determined experimentally in a commerciallyavailable particle size analyser

Methods

Results

Conclusion