Increasing Dwell Time without Decreasing Output

Q. We have several tablet formulations that are dwell-sensitive—they require more time under compression than other formulations. Given increasing demand, we do not have the luxury of slowing the tablet presses down in an effort to increase that dwell time. How can we maximize dwell time and maintain or increase output in our tablet presses?

A. The issue of dwell time (i.e., the brief time that the flat top surface of a punch remains in contact with a compression roll) has always been of great importance for compressing granules or powders that are not easy to form into tablets. Generally, the longer a product can remain under peak compression, the better the chances of compressing it to the required hardness. Making small changes to the size of the compression roll does not extend dwell time. An effective system recently developed by some press manufacturers allows operators to add another pair of compression rolls to the press easily. Not only does this system increase dwell time by 50%, but it also provides the user with the option of running bilayer tablets on a single-sided press, where the additional station acts as a tamping station for the first layer.

Some of the same press manufacturers have also developed technologies for dramatically increasing the number of stations on a single-sided press without increasing the overall size of the machine. The result is a single-sided press that occupies the footprint of a single-sided machine, although its output begins to approach that of a double-sided machine. The end user therefore enjoys maximized efficiency in the footprint-to-output ratio of the machine, which permits the best use of available real estate within the manufacturing area.

—Matt Bundenthal, technical writer for Fette Compacting America

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