Combined DEM and Johanson model for ribbon density prediction in a roller compactor

Abstract

Johanson (1965) developed a one-dimensional model for the stress acting on the powder in between the rolls of a roller compactor. Limited work has been performed regarding estimation of inlet stress; a parameter required for the estimation of ribbon density in a roller compactor. Due to the difficulty in the design and implementation of stress measurement systems, measurement of inlet stress is difficult experimentally. Therefore, a Discrete Element Method (DEM) based approach is proposed to get the inlet conditions which are used in the Johanson model to predict the ribbon density. The results indicate that the inlet stress and the corresponding pre-consolidated density obtained from DEM simulations were different for different process parameters. The combined methodology of using output from DEM simulations as an input condition for Johanson model yields a good prediction of the ribbon density with the inclusion of elastic expansion ratio (ribbon thickness/roll gap).

Roller compactor geometry

A roller compactor (FP90x30S, Freund Turbo Corporation, Japan) was used in this study. Fig. 1a shows the roller compactor as visualized in Rocky DEM v 4.2 with the respective parts: the hopper, which stores the material, the screw that conveys and consolidates the material and the counter rotating rolls, which apply pressure in the compaction zone. The roller compactor had rolls designed with a roll diameter of 90 mm and a width of 30 mm. Along the screw conveying length, there are degassing

Results and discussion

The results and discussion are split into three main parts. The first one is the compressibility constant estimation, the second one is the DEM simulations and the third one is the ribbon density prediction. The DEM simulations were performed to evaluate the influence of process conditions, such as (1) roll speed, (2) screw speed and the (3) roll gap on the flow behavior and output values. The output values analyzed are the mass flow rate, the packing fraction, stress values, the ribbon density

Conclusions

From this study, it can be concluded that the proposed methodology of utilizing DEM simulations to extract the data for the Johanson’s compaction model is a better approach as compared to previous studies. The various other outcomes are:

The variability of the compressibility constant for different punch speeds and masses of the sample investigated using the Texture Analyzer showed that there is insignificant influence on K (for a limited range of punch speeds and masses of the sample).

 

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Shubhangini Awasthi, Srikanth R. Gopireddy, Daiki Kako, Shuichi Tanabe, Hiroshi Nakagawa, Makoto Miyajima, Thomas Profitlich, Regina Scherließ, Nora A. Urbanetz, Combined DEM and Johanson model for ribbon density prediction in a roller compactor, Powder Technology, 2023, 118296, ISSN 0032-5910,
https://doi.org/10.1016/j.powtec.2023.118296.