Numerical simulations of partially‐filled rubber mixing in a 2‐wing rotor‐equipped chamber

Abstract

Partially filled internal batch mixers are used for mixing of rubber compounds in the polymer industry. The use of mixing in such mixers equipped with a rotor is critical to the process itself, and hence, understanding of mixing is important in terms of evaluating how various operating parameters such as rpm, fill factor, and ram pressure affect distribution and dispersion of materials. The objective of the current study is to gain valuable insights on the influence of fill factor, which is the volume of the material relative to the volume of the chamber. Two‐dimensional (2D) computational fluid dynamics (CFD) simulations of rubber mixing in a 2‐wing rotor‐equipped chamber are presented here, for the first time, for fully‐filled/100% and partially‐filled/75% chambers. The volume‐of‐fluid (VOF) technique is employed to capture the interface between the rubber and air in partially filled isothermal simulations. Flow patterns are visualized to analyze the material movement. Massless particles are injected and various statistics are calculated from their positions in order to compare dispersive and distributive mixing characteristics between the fully‐filled and partially‐filled cases. Specifically, quantities such as mixing index and the maximum shear stress distribution history of particles are analyzed to obtain information about dispersive mixing, while length of stretch and cluster distribution index, also calculated from particles, are presented to investigate distributive mixing capabilities. All the results consistently demonstrated the superior effectiveness of partially‐filled mixing chambers in terms of their dispersive and distributive mixing characteristics in comparison to fully‐filled chambers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44250.

3D numerical investigations of the effect of fill factor on dispersive and distributive mixing of rubber under non‐isothermal conditions

“…Statistical quantities, such as SOS, LOS, and CDI were evaluated in to assess the effectiveness of mixing. Dhakal et al developed a model to investigate the effect of different fill factors on distributive and dispersive mixing using a finite volume method assuming isothermal conditions. Das et al also developed a 3D model using a finite volume method to analyze the effect of rotor phase angle and speed ratio of rotors on distributive and dispersive mixing.…”

Friction and Wear between Polymer and Metal in the Mixing Process

“…The calculation of the contact force is based on the contact model. Due to the viscoelasticity of the rubber particles themselves, the particle model adopted is the soft ball model, while the Hertz-Mindlin model with the JKR (Johnson-Kendall-Roberts) cohesion model was used between rubber and rubber particles [11][12][13][14][15][16]. In the mixing process, carbon black itself does not have viscosity, but under the action of the rotor, the rubber was constantly deformed and carbon was covered by rubber, so that the carbon black particles can move with the rubber and finally disperse evenly.…”

A CFD‐DEM approach to study the breakup of fractal agglomerates in an internal mixer

“…[2,3] Several studies have investigated the flow dynamics in such a mixing equipment for different rotor designs and operative conditions, such as rotor speed ratio, fill factor, and batch temperature, by using flow visualization techniques, [4][5][6] or computational fluid dynamics simulation. [7][8][9][10][11][12][13] However, the studies of the effect of the flow field on the filler breakup has been so far limited to a generic analysis of the flow characteristics, in terms of shear rate and mixing index, or were based on simplified approaches for the agglomerate breakup mechanism. [14] It is well known that the breakup of agglomerates occurs when the internal stresses, induced by the viscous forces due to the flow, exceed a certain threshold value.…”