Pharmaceutical Manufacturing Handbook: Production and

1150 TABLET COMPRESSION
its low toughness rating typically limits its use to dies only. D2 rates slightly lower in
abrasion resistance than D3 but its increased toughness makes it suitable for punch
use, provided the cup design is not too fragile. A2 is a compromise between the general
purpose S grades and D2 in both toughness and wear. It can be used for punches as
well as dies.
Tungsten carbide, while not actually a steel, is extremely wear resistant and is commonly
used to line dies. Punch tips can be manufactured from tungsten carbide;
however, the cost of tooling is quite high and restricted to applications where tip fracture
due to high compression forces is not likely.
Ceramic materials such as partially stabilized zirconia can also be used as die liners.
Ceramics offer high wear and corrosion resistance and lower tablet ejection forces than
either steel or carbide due to their low coeffi cient of friction.
S1, S7 and 408 provide some protection against mildly corrosive materials. More severe
corrosion problems however, demand the use of stainless steel (440C) tooling. From
the standpoint of wear, 440C falls between the S and D grades of tool steel. Its low
toughness rating (comparable to D3) requires a strong cup design if tip fracture problems
are to be avoided.
One measure of tool steel quality is the rate of inclusions. Inclusion are unwanted
impurities or voids and are present to some degree in all steels. After heat treatment,
inclusions give rise to localized areas of stress concentration where microscopic cracks
can later develop. Remelting of the steel at the foundry will further reduce a tool steel ’ s
level of impurities; therefore improving the quality of the steel and subsequently its
performance in the tooling environment. In cases where punch tip fracture is a problem,
tooling suppliers may recommend a remelted or premium grade of particular steel as
a means of eliminating the problem.
Concerning the confi guration of compression tooling, the most commonly used
are the so - called B (19 mm, or 3/4 in.) and D (21 mm, or 1 in.) tooling types. Additionally,
these two types are classifi ed into three specifi cations: the North American
TSM ( Tableting Specifi cation Manual ) [25] , the European Union (EU) standard,
and the Japan Norm (JN). The North American TSM is used in the United States
and is the only standard offi cially supported by the governing body and published
by the American Pharmacists Association. The EU standard and the JN are generally
used in Europe and the Far East, respectively. In spite of the existence of these
standard specifi cations, there are tablet press manufacturers that use their own
confi gurations for tooling which have the disadvantage of being restricted to a specifi
c tablet press. Figures 6 and 7 depict the three standard confi gurations of compression
tooling. In addition, the International Organization for Standardization
(ISO) standard 18084:2005 [26] comprises specifi cations of the main dimensions,
including tolerances and characteristics of punches and dies.
Regarding the importance of compression tooling to the performance of the
tablet press and the quality of the tablets, it is of paramount importance that
punches and dies are handled with care. The fi rst criterion is the identifi cation
of the tooling; that is, punches and dies should be identifi ed according to the standard
and be designated by “ upper punch without key, ” “ upper punch with key, ”
“ lower punch with key, ” “ lower punch without key, ” or “ die, ” the reference of the
standard (e.g., TSM, EU, JN, ISO), and the punch or die diameter. Punches and
dies should also have a marking that includes at least the manufacturer ’ s identifi cation,
the number of the punch in the series, and/or the identifi cation number. Upon