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26 July/August 2021 Tablets & Capsules • Reduce the paddle speed in the tablet press feeder. High paddle speeds result in better mixing and reduced weight variations but greater friability and overlubrication. • Reduce the press speed for highly strain rate sensi- tive products. • Consider using a Teflon coating in the tablet press' discharge chute for reduced friction to decrease tablet damage. Also, regarding tablet ejection, the tablet stripper's proper height and placement is more critical with tablets of marginal strength. • Optimize weight control set points as described in my article, "Minitablets and microtip tooling" in the September 2020 issue of Tablets & Capsules [6]. T&C References 1. Gabaude CM, Guillot M, Gautier JC, Saudemon P, Chulia D. "Effects of true density, compacted mass, compression speed, and punch deformation on the mean yield pressure." J Pharm Sci. 1999 Jul; 88(7);725-30 doi: 10.1021/js9803050, page 725. 2. Ohwoavworhua FO. "A comparative evaluation of the flow and compaction characteristics of a-cellulose obtained from wastepaper." University of Benin. Topical Journal of Pharmaceutical Research. March 2007; 6(1):646-649. 3. Baserinia R. "Flow of fine and cohesive powders under controlled air pressure conditions." Department of Engineering, University of Leicester, PhD dissertation, page 14, 40. 4. Santl M, Ilic I, Vrecer F, Baumgartner S. "A com- pressibility and compactibility study of real tableting mixtures: The effect of granule particle size." Acta Pharm. 2012 Nov; 62(3):325-40. 5. Mahmoodi F. "Compression mechanics of powders and granular materials probed by force distributions and a micromechanically based compaction equation." Uppsala University, digital comprehensive summaries of Uppsala dissertations from the faculty of pharmacy 159, p 13. ISBN 978-91-554-8319-7. 6. Available at www.tabletscapsules.com. Todd D. Martin is a senior tooling engineer at Wilson Tool International, White Bear Lake, MN (866 752 6531, www. wilsontool.com). Wilson Tool's tableting division provides compression tooling, including standard punches and dies, accessories, and custom-designed tool solutions, to the pharma- ceutical, nutraceutical, industrial compression, confectionary, and other industries. Tablet press operation. For poorly compactible for- mulations, you should: • Set precompression to remove entrained air and allow for some plastic deformation to take place. Typically, precompression should make a tablet that is approximately 125 percent of the tablet's final thickness. The precompression force should be less than main compression force; 20 percent is common. You may need to adjust from this initial value to optimize the tablet's final hardness. One exception—a slightly higher precompression force than that of the main compression—is applicable to heat-sensitive formulations, such as ibuprofen, which can benefit from internal friction between particles at precompression to bond the material together by melting. • Set main compression values to reach target hard- ness and thickness values. To establish the optimum value, take hardness and thickness measurements at increasing force values, then plot the results. Every formulation has an elastic limit where further increases in pressure can cause a breakdown. Beyond the elastic limit, tablet thickness can increase with higher force, with tablet strength being substantially reduced. Around the elastic limit value, performance values can be erratic. Sign up now by emailing kmyers@cscpub.com your name, company, and email address. To see a sample, please visit our website.