Bultmann's Roll Compaction-site
on Dry Granulation


[Expert system] [Mechanical malfunctions] [Trouble in processing powder to ribbon] [Problems with the final tablets]

Expert System

Many questions regarding supposed or real hardware malfunctions are answered by the MAX Expert System, which is exclusively available for Gerteis machines (including supposed mechanical malfunctions of the machine, process malfunctions, process control, etc.).

Mechanical malfunctions

Most mechanical malfunctions are based either on user handling or on poor process conditions.
Some examples for errors caused by the operator: Most of these problems can easily be solved by reading the last alarm message or by inspecting the alarms window (Gerteis machines) on the display.

Some examples for poor process conditions:

More mechanical malfunctions and how to solve them can be found in the above mentioned program.

Trouble in processing powder to ribbon

Flakes instead of ribbons in rim roll systems

If flakes are produced instead of ribbons or larger ribbon like parts, the cause is often the shape of the stripper. Because of elastic recovery, the ribbons stick between the rims. It is the stripper’s task to remove the ribbon. If the ribbon meets the stripper in a right angle, the ribbon is crushed to pieces, while a stripper that reaches behind the ribbon gently pulls out the ribbon without doing major harm to the ribbon shape. The ribbon parts produced this way are usually 1-2 cm in length.


Figure: Conventional stripper (left) causes the ribbon to break into small flakes while the flat stripper reaches behind the ribbon (middle) and produces ribbon pieces of ca. 1cm in length (right).

Roll adhesions

Roll adhesions should be avoided for several reasons:
· The powder which adheres to the roll is compacted many times while the actual number of recompression cycles is unknown and irreproducible. Thus the process would not be validable.
· In addition to this, repeated compression is unfavourable because of poor recompactibility.
· Third, adhering plaques disturb gap control algorithm, which should be avoided. The use of a small amount of lubrication agent solves this problem efficiently. Of course, recompactability slightly decreases and dissolution might be prolonged. The latter two topics are only minor problems since the amount of lubricant, which is necessary for tabletting can be decreased . This usually compensates for the mentioned effects. One might also consider the reduction of compaction pressure to decrease plaque forming.

Problems with the final dosage form (tablet)

Tablets are too weak

Powder should be compacted as gently as possible in order to obtain granules of the desired size, distribution and flow. Ther ususally is no need to produce the strongest ribbon possible.
Porous (but therefore somewhat weak) ribbons usually result in harder tablets than hard ribbons when the same pressure is applied at the tablet press.

Tablets rapidly desintegrate to granules but those granular particles do not desintegrate/dissolve

The cause for this is the same as above: Very hard ribbons result in hard granules. If they are compressed to tablets, those tablets are weak and easily desintegrate to granular particles, they were made from. Those hard granules do not easily desintegrate, however.

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