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the formulation is ‘damaged’, and results in additional fines within the material. Minimising the amount of product that gets recirculated is crucial. Proper press set-up plays a vital role in preventing dark specks
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from occurring in tablets. Confirm that the feed frame is positioned at the correct distance above the highest point on the die table. If not properly set, particles can become lodged in-between the feeder and die table, leading to scorched material on the
tablets. Also, setting the feeder clearance at the correct location prevents contact between the feeder and the die table during press operation. Small amounts of ferrous metal from these components could scrape off when contact is made and end up on your tablets as dark spots. Metal detectors should be utilised to detect foreign material. 4: LESS COMMON FACTORS There are instances where dark spots are a result of
something far less common, but should be considered during the troubleshooting process. Poorly maintained or worn processing equipment can result in contamination. For example, sieves utilise mesh screens to control particle size distribution. The screens may deteriorate leading to contamination of the formulation, and must be inspected regularly. Blenders, used for processing powder, require bearings for general mechanical operation. If a bearing or seal is damaged, its lubricant may leak into the formulation, thus resulting in a contaminant that may be seen throughout the tablet. Ensure that all processing equipment is in good mechanical order prior to use to significantly reduce the likelihood of dark spots. If you’re unable to ascertain the source of the problem, contact your tooling vendor for further assistance. In some cases, sending sample tablets and/or tooling for further analysis is an option as well. Dark spots are a tabletting defect that no manufacturer wants to encounter. Understanding the primary causes of dark spots, whether as a result of lubrication in the powder, scorched material, or improper set-up, can help you to implement proactive solutions to produce high quality tablets and reduce production downtime.
Image 3: Depicts the differences between a standard tip vs. a narrow tip width with a double-deep relief. It is required that all lower punches have a sharp relief for consistent, quality operation.
Image 4: Damaged feed frame.