Characterization of Tablet Attritional Forces in a Friability Tester and Film Coating Pan Using DEM
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The objective of this work was to better understand the forces generated on tablets in the friability tester and pan coater using discrete element method (DEM) simulations. Such systems are used in the pharmaceutical industry for measuring the strength and hardness of tablets. The operation of a standard friability tester was simulated using the discrete element method (EDEM™ from DEM Solutions). Simulations of a tablet coating pan at different pan speeds, pan loading and pan sizes were also performed using DEM. The predicted forces from the DEM simulations of both the systems were compared for various tablet shapes. It was observed that the average normal forces experienced by the tablets in the friability tester were 3 times larger than the average tangential forces. Moreover, the number of tablet/tablet collisions are fewer than the tablet/drum collisions for the standard number of tablets used in the tester (n=20). However, for large number of tablets (n=100), the number of tablet/tablet collisions are larger than the tablet/drum collisions. This situation is more representative of conditions in a large scale tablet coating pan. The forces in the coating pan generally showed the following trend: impact zone > shear layer > rotating layer. The force magnitudes were similar for all the tablet shapes that were investigated. The forces increased with pan speed, pan loading and pan size. The large scale pan showed ~ 1.5 to 4 times increase in the forces. Moreover, it was observed that the maximum normal force in the friability test was ~ 2 times greater than the maximum normal force in the large scale coating pan (pan diameter ~ 24”). However, the maximum tangential forces were similar. The results lead to a better understanding of the tester.