Tablets & Capsules


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32B January 2017 Tablets & Capsules M tabletting Rough going? Tips for fighting abrasive wear of punches and dies Michael Oxford I Holland Compressing abrasive nutraceuticals can wear tooling prema- turely and cause other problems. This article discusses how wear-resistant tooling steel, anti-abrasive coatings, and good tablet design extend the service life of punches and dies. anufacturers face several challenges when compressing nutraceutical tablets, many of which are unrefined natural ingredients that are abrasive, corrosive, and/or coarse. It's thus important to determine which material will prolong the service life of compression tooling. As the components most in contact with the product, tablet punches and dies require robust metallurgy and design. While sticking—the adherence of granules to the punch tip face—can be difficult for pharmaceutical manufacturers to overcome, the ingredients they use are often formulated to improve tablet compression and binding without much physical impact on the tooling. In the nutraceutical indus- try, it is not so simple. Nutraceutical formulations can contain tens of active ingredients that tend to be bulkier than those used in pharmaceuticals, which makes production problematic. Formulation characteristics like wide variation in particle size, poor compressibility, incompatible ingredients, and moisture sensitivity can also lead to production and tool- ing issues. To avoid replacing your tooling prematurely and to minimize tablet defects, use punches and dies made from a suitable steel. Also consider adding a coating to the punch tips. Wear-resistant steel and coatings In their natural states, vitamins and minerals can be hard and thus difficult to compress. In fact, some ingredients are just as hard as low-chromium steel and can wear punch faces and dies quickly. That can lead to weight variation, sticking, and other problems and cause you to scrap punches too soon. Wear also degrades embossing on the punch face, leading to poorly defined if not illegible tablet lettering. Most suppliers of tooling offer a variety of steels that resist abrasion, corrosion, and impregnation by hard gran- ules. Deciding which to use can be overwhelming, but your supplier should offer guidance. One option is electro slag re-melted premium steel [1], which is refined to reduce non-metallic inclusions and make it more homogenous. Its high chromium content also improves wear resistance. Tungsten carbide [2] extends the life of tooling by reducing premature die wear and die bore deformation. It also offers high compressive strength. But tungsten carbide is also very brittle and using it to tablet nutraceuticals can lead to premature punch tip fractures. In addition, certain formulations react with tungsten carbide, and when it's used in dies, it can leave black spots on the tablet walls. When tabletting especially abrasive formulations, a powder metal- lurgy grade of steel may be a better choice for punches and dies [3]. If wear-resistant steel alone can't withstand the rigors of nutraceutical tablet production, consider adding a wear- resistant coating to the punch tip. One resilient surface coating [4] is approximately five times harder (about 3,000 on the Vickers scale) than standard tablet tooling steels and can extend punch service life by more than 900 percent. It also boosts corrosion protection and helps prevent sticking. Because of its hardness, the coating is only applied to the punch tip to prevent excessive wear of the compression rollers, which are much softer than the coating.

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