Scientific papers
Capping is a common manufacturing issue observed in tablets, with a tendency to affect biconvex tablets more than their flat-faced counterparts. One contributing factor may be the generation of higher residual die-wall pressure during the unloading phase. However, conflicting findings have been reported on this matter. In this study, we investigated the variation of die-wall pressure during the compaction of biconvex tablets through experimental methods and finite element method (FEM) modeling, comparing the results with those of flat-faced tablets. Both experimental and numerical findings revealed that the compression of biconvex tablets led to a lower maximum die-wall pressure and a higher residual die-wall pressure compared to flat-faced tablets. Additionally, both approaches demonstrated a temporary rise in die-wall pressure towards the end of the unloading phase for biconvex tablets. FEM analysis indicated that this phenomenon resulted from a gradual loss of contact between the punch and the tablet, starting from the sides towards the center. This intricate unloading behavior contributes to the temporary increase in die-wall pressure and the emergence of shear stress between the convex part and the land of the tablet, potentially explaining the capping susceptibility of biconvex tablets.
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