Determination of a Relationship Between Force-Displacement and Force-Time Compression Curves

Abstract

A series of experiments were conducted to evaluate and compare force-displacement and force-time compression curves. A Stokes B-2 sixteen station rotary tablet press was instrumented with piezoelectric transducers to monitor compression and ejection forces (in addition to punch proximity) and interfaced with a microcomputer. Processing and material variables were examined for their effects on the direct parameters (ie. height and area) and derived parameters (ie. area:height ratio and maximum s1ope:height ratio) of the force-time compression curve. Upper punch displacement was estimated and force-displacement curves were plotted. The force-time curve was then divided into three segments pertaining to the three stages of upper punch movement: compression, relaxation, and decompression. The “relaxation” stage was defined as the portion of the compression force-time curve corresponding to the interval when the upper punch displacement was held constant. The total, net and elastic works of compaction were calculated and their relationships with the areas of the individual phases of the force-time compression curve were examined. It appears that the area under the cornpression force-time curve can be related satisfactorily to the work of compaction.