Running like clockwork
Changeover times on tablet presses now shorter

Rotary tablet presses are not always as user friendly as customers would like. Changeover to a different tablet size is particularly time consuming, but things are now beginning to get better. A drastic reduction in the number of components has significantly shortened changeover times.

Up to this point, the standard solution worldwide for single-sided or multi-sided tablet presses has been a die table on the turret containing a varying number of standardized holes (depending on the turret pitch circle diameter, tablet diameter and punch size). The dies are inserted into the holes, and the geometry of the die determines the geometry of the tablets which are produced. During the compression process, a top and bottom punch in the die compact the powder, forming the tablet. A typical system might look as follows: 36 die stations, which comply with the EU19 standard, are mounted on a turret to produce round tablets with a diameter of 16 mm. Each of the 36 dies is attached with screws which are mounted in radial threaded holes and which are tightened from the outside. There are 72 parts in all, and this configuration carries significant risk of lost production, contamination, mechanical defects, assembly errors and long changeover times. Fette has drastically reduced the part count. Instead of 72, only 9–15 pieces need to be replaced, an 88% reduction.

Shorter changeover times
In practice, pharmaceutical manufacturing is driven by “production on demand” and often by “just in time” as well. Different size batches have to be produced within the constraints of a tight, fixed time schedule, and this makes press utilization a very important issue. Changeover times must be predictable and as short as possible. To give you an idea of the amount of manual intervention which is required, the Fette 2090i had a handling arm which enabled the operator to swivel the exchangeable turret including all of the dies, punches and cam plates out of the press and onto a die cart. The operator then removed the dies and punches, and the individual parts were moved to a washing center. Die table segments have reduced the number of handling steps from 217 to 9. There can be no doubt that despite all of the precautionary measures that are taken, the use of conventional die tables has repeatedly led to some loss of production. The new smooth die table segment eliminates one frequent source of error once and for all, namely dies that are not flush. Integrated die holes (round, oblong or special shapes) eliminate adjustment errors.
With the exception of a few details, the turrets for the die table segments are the same as conventional turrets. Two clamping screws and clamping wedges ensure that the turrets are frictionally engaged and form fitting. An extremely high precision die table with integrated die holes provides the basis for this simple mounting method. The turret and die table are significantly easier to clean than conventional dies and die tables, because there are no holes to hold die screws. It is far more difficult to clean a die screw hole than an entire die table segment, and this is reflected in a significant difference in cleaning times. The greatly simplified design of the die table (no horizontal holes, no threads, no tolerances between the dies and the die insert hole, no dies that are not flush) explains the significant reduction in lost production.
Increased output
The number of press stations per die table is normally limited by the holes for the screws which hold the dies. With die table segment design, the only limiting factor is the amount of material which is needed between the matrix holes to provide stability. This means that the number of stations per die table can be increased significantly (by 25%). The filling characteristics of the die holes remain the same, because the turret runs at the same rotational speed. Stored production data can be used without modification. The only change that you will notice is that your output increases. Following practical testing and production trials (a tablet press using die table segments has now produced considerably more than 200 million hormone tablets at an international pharmaceutical company), Fette is now working on implementation of this successful technology.