TABLETING 73
wear to the upper punches can be easily identifi ed through the ‘fi ngernail method’- this is done by picking at the inner edge of the cup and feeling for the curled edge that is indicative of J-hook.
A technician can repair the J-hook and return the tool to service by lightly polishing the surface of the punch cup and performing a quick blended polish on an un-sewn buff wheel. T is repair cannot be achieved by using a drag fi nisher. Die bore wear occurs during
compression of product and ejection of the tablet from the die. T is wear pattern is exacerbated when compressing abrasive products such as nutraceutical tablets. Die bore wear cannot be completely eliminated but may be drastically reduced through implementation of a complementary steel type, die bore taper, or the use of a carbide or ceramic lining in the die. (Contact your tooling vendor for their
recommendations on combating troublesome products). T ese options can also help reduce ejection forces of the tablet from the die, which in turn will reduce friction, premature cam wear, and most importantly tablet quality issues such as sticking to the lower cup, chipping at take- off and laminating.
Inspection procedures Inspection of die wear can be done visually for the obvious appearance of wear rings, a pattern within the die that allows prominent wear to be visible to the naked eye. Although this method is common, it does not indicate how much wear is present. Other inspection procedures include using a split ball bore gauge on an indicator or digital handheld gauge to physically measure deviations within a die bore. T e amount of allowable deviation within a die bore is determined by the characteristics of the powder, this can vary
from product to product. For example: if it’s known that with a wear ring of .004 you are still manufacturing a quality tablet with light fl ashing and no negative reaction to the tablet press, this measurement could be acceptable. However, if it’s determined through the use of a split ball bore gauge that the tolerance is exceeded, then the best option is to replace the dies. Often, if the wear occurs high enough in the die, it can be fl ipped over to compress tablets in the other half of the die. T is would not work if the die has a one-way taper as it may not achieve the same fi nished product results and can cause production issues. Monitoring punch and die
wear can bring decreased cost and fewer tableting production issues. For best results, implement inspection procedures into SOPs wherever possible.
For more information ✔ at
www.scientistlive.com/eurolab
Stephen Natoli is with Natoli Engineering.
www.natoli.com
For more information ✔ at
www.scientistlive.com/eurolab
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