INSTRUMENTATION AND CALIBRATION OF A SINGLE-PUNCH PRESS FOR MEASURING THE RADIAL FORCE DURING TABLETING

A single-punch tablet press was instrumented for radial force measurement during tableting by cutting out segments from the die, leaving 5.0 mm of die wall, and by applying strain gauges to these thinner parts. Active horizontal gauges were connected to temperature-compensating vertical gauges to Torm a Wheatstone bridge with two fixed resistors in the bridge amplifiers. The instrumentation was dynamically calibrated at tableting speed (30 rpm) with rubber-like materials lubricated with molybdenum disulphide (Molykote). The die wall signals were reproducible and increased linearly with the applied pressure. The signals increased with increasing height of the compact. The position of the lower punch had a marked influence on the response. When the lower punch was in a position 10.2 mm below the upper surface of the die, the signal at constant pressure was proportional to the cross-sectional area of the compact. At this position the die wall pressure could be calculated from the regression line of signal/cross-sectional area vs applied pressure. This regression was the same for all tested rubber materials and the estimated relative standard deviation of single determinations at 100 MPa was about 3%. © 1979.