Pharmaceutical Manufacturing Handbook: Production and

1144 TABLET COMPRESSION
speed of the paddles is adjustable and should be synchronized with the die table in
order to prevent tablet weight variation. Better adjustment of the paddle speed
could be achieved when keeping the lowest standard deviation of the compression
force. The feeder system height above the die table is usually kept between 0.05 and
0.10 mm. When the product to be compressed is of very fi ne particles, this height
should be kept at 0.025 mm.
Presses are commonly equipped with a powder aspiration system which is connected
to a vacuum source in order to remove excess powder from the die table.
This assembly is essential for a high - speed press working for extended periods of
time. Special attention must be taken when the powder product comprises an active
ingredient of fi ne particle size. In this case, aspiration should be minimal in order
to prevent loss of the active ingredient.
The compression subsets comprise the upper roller assembly and the lower roller
assembly. The upper roller assembly is located on the roof plate of the press and
utilizes an adjustment system for the regulation of the insertion depth. The lower
roller assembly is located on the underside of the die table and utilizes a device for
the regulation of the tablet edge thickness.
The turret head is fi xed to the main shaft of the gear box. It is manufactured in
two pieces (upper and lower) which guarantee the alignment between punches and
dies. The gear box is mounted on the lower section under the die table and is responsible
for transmitting the draft movement of the motor toward the turret head.
The upper cams are responsible for guiding the upper punches around the circumference
of the turret head. It comprises the fi lling stage track, which guides the
upper punches in an up position during its passage over the feeder system; the upper
lowering cam, which guides the upper punches down in order to keep their tips
covering the cavities (precompression position) and directs the upper punches to
their compression stage; the upper compression roller, which guides the upper
punches to their compression position; and the upper fi lling cam, which guides
the upper punches back to the fi lling track.
The weight control assembly, which comprises the weight adjustment cam, is
located in the lower section of the press and is regulated by an adjustment system.
The lower cams are also located in the lower section of the press and comprise the
preweight control (or fi ll cam), the weight adjustment cam, the lower lowering cam,
and the ejection cam. The preweight control guides the lower punches to the full - fi ll
position. The weight adjustment cam guides the lower punches up to the desired
fi ll position. The lower lowering cam guides the lower punches to the precompression
position. The ejection cam guides the lower punches and the formed tablets to
the discharge position. It is recommended to operate the weight adjustment cam in
the approximate center of the fi ll cam and because of this the fi ll cam is removable
and available in different sizes having a range of approximately 10 mm with an
increment range of 4 mm. The choice of the adequate fi ll cam for the operation of
a tablet press with a particular product should be based on the density of the
product. According to Figure 3 , the fi ll cam can be adequately chosen when taking
into account the density of the material to be compressed and thus the material
column height in the die cavity.
Rotary tablet presses could be designed to be single, double, or triple sided. A
single - sided press comprises one hopper, one set of compression rolls, and one take -
off chute unit whereas double - and triple - sided presses comprise two and three each