Research ArticlesThe effect of punch tilting in evaluating powder densification in a rotary tablet machine
Section snippets
INTRODUCTION
Tablets are the most common pharmaceutical dosage form, but while the compression of powdered or granular material into a cohesive mass may seem simple, it is actually a complex and irreversible dynamic process.
Mechanically, the process consists of imposing a progressive strain on the powder, confining it to a certain final volume and porosity.
The dimensional constraints imposed by the punches and die are then removed and the compact is allowed to relax.
The compacted material exerts a certain
Punch Displacement Device
One of the eight stations of a Ronchi FA rotary tablet machine was equipped with four LVDT transducers. They were symmetrically installed beside the punches (one preceding and one succeeding) in either the upper or the lower turrets, according to the chart in Figure 1. Punches were equipped immediately below their head, with two symmetrical narrow flat steel arms that ended just above the transducer. The remaining seven stations were blinded.
Displacement Transducer Set Up
Transducer calibration and validation were performed
Powder Bed Reduction and Punch Tilting
Figure 2 shows a plot of bed reduction inside the die without any material in it.
As can be noted, there is a small difference between the preceding and succeeding curves and this, of course, depends on the signals retrieved from the preceding and succeeding transducers. As expected because of the mechanism of punch tilting, both signals are incorrect. Values of punch penetration from the preceding transducers are underestimated, whilst values from the succeeding transducers are overestimated.
CONCLUSION
Punch tilting always occurs in a rotary tablet machine during the compression cycle and should be taken into account together with the machine deformation. The correct values of punch penetration in the die depend on both phenomena.
Like machine deformation, punch tilting also depends in practice on the compression force used, regardless of the type of material under study. This means that if the device installed in the rotary machine for monitoring punch penetration fails to assess the tilting
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2014, International Journal of PharmaceuticsCitation Excerpt :The blend for all the formulations was prepared using a v-shape mixer in two consecutive steps, the first mixing all the active ingredient and the excipients without MgST for 5 min at 48 rpm and the second adding the MgSt on the pre-blend and mixing at the same condition at 48 rpm for one additional minute. All the formulations prepared were compacted using an eight station rotary tablet press (FA/8, Ronchi, Cinisello Balsamo, Italy) instrumented to measure both force and displacement (two transducers for each punch in order to remove the effect of tilting) of upper and lower punches (Cespi et al., 2008; Palmieri et al., 2005). The tableting machine was equipped with 6 mm diameter, round, flat-faced punches and the rotation speed of the turret was set at 25 rpm.
Effect of temperature increase during the tableting of pharmaceutical materials
2013, International Journal of PharmaceuticsCitation Excerpt :The tableting machine was also instrumented with load cells for the force measurement and 4 LVDT trasducers (2 for the upper punches and 2 for the lower punches) for the punches displacement recording. More details on force and displacement devices set-up and calibration procedure were previously described (Cespi et al., 2008; Palmieri et al., 2005). Preliminary test performed without the materials at 50% UR and temperature of 25, 35 and 50 °C did not highlight any effect of the environmental conditions, inside the working area of the tableting machine, on the transducers and load cells transmission apparatus (Figure SF1 in supplementary data).
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