Gerd Hüffmann presents an ideal tool for the compression of heat-sensitive products
Some pharmaceutical and nutritional products are adversely affected by heat exposure during compression.
Vitamins and antibiotics can deteriorate when exposed to high temperature, compromising the effectiveness of the finished drug. In other cases, products or product ingredients (e.g. Ibuprofen) may melt, leaving sticky deposits on die plates and punch tips, causing compression force and thus weight variations, product losses and reducing the effective operations speed (and thus output) of a tablet press.
Especially critical are the temperatures of product contact parts exceeding 30°C. A tablet press that is ‘cool by design’ therefore creates a multitude of advantages for its user and the products being compressed on it.
There are a number of measures that can be effectively taken to reduce the heat that is generated by and within a tablet press. Replacing a typical drive assembly – consisting of an inverter driven main drive, gear box and transmission belt –with a water-cooled torque drive system is one measure.
Eliminating the gear box not only cuts out an unnecessary source of heat generation but also helps to reduce energy losses and the need for gear-box maintenance, e.g. regular oil changes, or cleaning out of grime caused by fine dust abrasion from a transmission belt. As an added advantage, torque drive systems offer an excellent dynamic behaviour due to the availability of constant torque through a wide speed range.
A closed-circuit liquid cooling circuit for the actual (torque) drive unit, ensures that there is virtually no heat transfer to the main shaft of the press and thus the die plate. If ‘active cooling’ is desired, the cooling system can be connected via a heat exchanger to chilled water, providing a noticeable cooling effect. In an ideal situation, as for instance on a Romaco Kilian KTP series press, even the dynamic seal between the die table and the base of the compressing chamber is integrated in such a cooling circuit.
Using closed punch bellows (which requires the use of an appropriately designed tablet) is another method to reduce heat. The use of closed punch bellows, which do not have air-vents/air exchange with the compression chamber allows for generous oil lubrication settings without any risk of tablet contamination (black spots). The increased lubrication effectively reduces friction of the punches within the punch guides (cams) thus minimising heat and as a side effect considerably reducing wear.
Low friction compression rollers Where there is friction, there is heat. Therefore the aim is to compose the compression rollers of such materials and design as to prevent or at least reduce friction in the roller movement, while at the same time ensuring that there is sufficient friction between the roller surface and the punch head to make the roller turn.
This requires the use of low inertia, low friction bearings, limiting punch slip and heat generation. This is aided in effect by roller materials that are lightweight and extremely durable at the same time.
One last way to reduce heat is via air circulation and/or dust extraction. Allowing for large air volumes to circulate through the technical area of the machine not only transfers unwanted heat from the technical compartment, but also provides effective cooling for components within the airflow. This is assisted by effective dust extraction system, removing dust (and warm air) from the compression chamber.
Where there is a tablet press used that effectively combines all the above measures, it is almost guaranteed that that there will be no detrimental heat influence on any product compressed, resulting in superb product quality and the highest possible yields.
For more information, visit www.scientistlive.com/eurolab
Gerd Hüffmann is with Romaco Kilian.