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TABLETING


Fig. 5. Compressibility profile


Fig. 6. Rotary


press strain rate data


ejected from the die. Te ejection force is a product of the residual radial die wall force and coefficient of friction between the compact and die wall. High ejection forces can cause premature wear to the punches, press cams, and cause tablet quality issues. Te most common remedy for high ejection forces is increased levels of powdered lubricant in the blend (e.g. magnesium stearate). Te lubricant level should be optimised as an excessive amount can cause tablet capping, friability issues, and higher disintegration times. Tis study can be achieved by recording the ejection forces with incrementally increased compression forces. To perform this study with accurate data, the ejection transducer must be a “full-travel” design especially if the lower compression roller is adjusted to change tablet thickness and compression force. A full-travel ejection design will provide an accurate millivolt signal across the full range of the ejection sensor. It is common for some press manufacturers to use a button load cell that only captures the data in one small area and a compaction profile study will report incorrect data.


Te last phase of the tablet cycle is the tablet take-off or removal from the lower punch face. Take-off is the phase where tablet picking or sticking may occur. An instrumented take-off bar permits measurement of this force and detects early signs of sticking. Te force required to release the tablet from the lower punch face is normally in the order of a few Newtons and will require a very sensitive sensor. Tis sensor is typically manufactured with a material that exhibits a very low elastic modulus (e.g. aluminium). Additionally, semiconductor strain gauges allow more than 20 times the sensitivity output of a standard foil strain gauge. Tablets are regarded as complex drug


Fig. 7. Instrumented single station press data - compaction/displacement profiles


compression forces, ejection, and take-off sticking forces. Te pre-compression and main


compression readings play a significant role in analysing the product consolidation and compaction phase where air is removed from the product, particles are deformed,


48 www.scientistlive.com


and interparticulate bonding occurs. At this stage, it is critical to understand the product’s failure limits with tablet strength, capping, and lamination, friability, disintegration, and dissolution times. After the compression and


decompression stages, the tablet is


delivery systems and to underestimate the importance of their design, development, and manufacture will certainly invite significant issues at some stage of development or product life. Instrumented tablet presses and data collecting software packages are crucial in the success of the tablet manufacturing process.


Robert Sedlock is with Natoli Engineering. www.natoli.com


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