Issue link: https://www.e-digitaleditions.com/i/1163217
Tablets & Capsules September 2019 11 • Wear on the flight-control cam or punch-holding plug or improper setup can increase tablet weight variations. • Scraper-blade wear can increase weight variations. • Tail-over-die wear can increase weight variations. • The feeder platform's height and wear on the feed- er's bottom surface can increase weight variations. Tablet weight variation is directly proportional to force variation as is the pressure applied during com- paction. Tablets compressed under higher than average pressure can exhibit more flashing. Generally speaking, batch runs with higher weight variations require a higher average compression force to help the low- weight tablets meet the targeted hardness values. Flashing is worse when you run the tablet press at high compression forces. All of the above issues can impact the tablet compres- sion process, potentially causing non-uniform or exces- sive wear to punch tips and die bores. In contrast, a well-maintained press can reduce the number of vari- ances, minimizing flashing and tool wear as well as the need for extra downstream processing. Tool loading. If your tablet press is well maintained and in good working order, the next factor to consider is how you are loading the tools into the tablet press. The clearance between an upper, shaped (not round) punch tip and die bore when made to TSM standards can be as much as 0.003 inch (0.076 millimeter), providing room for manual manipulation. The manual manipulation occurs when the setup oper- ator inserts the upper punch of a shaped tool into the die. Best practice includes manually turning the punch in the direction that the press rotates, clockwise or count- er-clockwise, to align the die before locking it down. This human involvement in alignment has some inherent error associated with it, such as the lack of consistent torque from one punch to the next. regardless of the tablet shape and is most common when compressing materials that undergo plastic deformation under high pressure. The particle size of the formulation and the amount of pressure applied during compaction are also factors. In this article, I'll discuss the impacts and causes of flashing and suggest some preventive measures to help minimize it. Impacts of flashing Flashing occurs in the production of every tablet to some extent, due to the clearance between the punch tip and the wall of the die bore. When a punch tip's outside edge becomes worn, the clearance increases, which increases the propensity for flashing to occur during compression. Flashing is one way some tablet manufac- turers determine that their tooling is nearing the end of its useful life. I would not recommend this method, how- ever, because of flashing's impacts on product quality, customer experience, and process efficiency, including: • Excess dust in bottles; • Raised sharp edges around the tablet band, inhibit- ing swallowability; • Aesthetically unappealing tablets; • Reduced yield, which increases manufacturing costs; and • More downstream processing to remove the flash- ing, which also increases manufacturing costs. Causes of flashing Tablet press. The tablet press can introduce variations in the compression process that may contribute to increased flashing. For example: • Worn guideways can cause excessive punch deflec- tion and nonuniform clearances. • Turret misalignment can cause uneven wear on punch tips and nonuniform clearances. • Die-table runout can affect fill depth and cause tab- let weight variations. Photo 1: Flashing occurs in the production of every tablet to some extent, due to the clearance between the punch tip and the wall of the die bore, but it can become more pronounced and problematic when a punch tip's outside edge becomes worn. Photo 2: Stoning the punch tip with a 600-grit polishing stone is a quick way to restore a land that has become too thin, remove J-hooks, and maintain a sharp outside edge.