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:
One of the power switches is in off-position
One of the emergency switches was pressed by accident and nor reset afterwards
One of the security switches is not in position after reassembling the
machine (especially after cleaning)
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:
Blocking roll caused by sticking roll adhesions (-> use lubricant)
Blocking in transfer section between fedding and tamping auger (-> increase
agitator speed)
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.
