72 TABLETING
TABLET MANUFACTURING tool guidance
Stephen Natoli on tool inspection procedures for die wear
M
ost tablet manufacturers focus their inspection
procedures for both new and in-process tools on the punch. Written procedure usually dictates the age-old method of using a digital indicator on an extension pole affixed to a granite stand. With this equipment, they measure the overall length minus the cup depth to determine the working length for that punch. However, this method is flawed because the tolerance of the overall length and cup depth are greater than that of the working length, so they cannot be used to calculate the working length with its much tighter tolerance. A better method of
measurement prescribes using a datum (reference punch) from the set. One can then measure the rest of the tools against that one punch to ensure all tools are within .002in from the shortest to the longest, across either the lowers or the uppers, using a “pass/fail method”.
While this method is best for measuring working length, there are additional critical wear patterns that can affect tablet production. For example, punch tip wear is a common issue
www.scientistlive.com
that can be identified through inspection of a couple of areas. Causes of punch tip wear are: die pockets leading to misaligned dies; worn punch guides and keyways; and running new punches with worn dies. When an old set of dies is used with a new set of punches, it’s nearly impossible to realise a proper clearance between the punch tips and the die wall as there will be a gap. It’s within this void that excess powder begins ‘flashing’ or slipping around the edges during compression. Tis travelling powder creates a tight space for the upper punch that generates
friction and heat, and results in premature wear to the punch tip, upper punch binding and can lead to premature wear to the upper raising cam as well.
A common deformity Tip wear, which can occur from worn die pockets (especially on tools with deep cups and little land), includes ‘J-hook’, which appears when the edge of the punch tip curls in to create a burr. Tis common deformity can create tablet capping and lamination (where the upper cup of the tablet is removed partially or completely from the remainder of the tablet.) J-hook
Smart inspection procedures help reduce wear on both punch tips and the die
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84