Side Vented Tablet Coating Machines
“ One of the main reasons that side vented coating machines give problems is related to the exhaust plenum seals. The exhaust plenum seals are often overlooked and can mislead the operator, giving problems with over wetting or long process times.
The problem with air is that it will take the easiest path, and if the seals are damaged or worn the air can miss the tablet bed, reducing the drying efficiency. The process time will be extended because of this reduction is drying air, and can also give an inaccurate indication of the tablet bed temperature. The tablet bed can potentially be over wetted if the exhaust temperature is indicated at a higher temperature than the actual tablet bed.
The air within the process path should all pass through the tablet bed, in order to efficiently heat and dry the tablets in the process. Any air which misses the tablet bed is effectively a process loss.
When air is allowed to avoid the tablet bed by leaking into the plenum, due to faulty seals, the air path can be disturbed. This can produce an erratic spray path, which allows the spray pattern to cover incorrect sections of the machine.
An erratic spray pattern can also increase spray drying and additional product loss. The plenum seals are the only regular maintenance areas within a machine and should be checked at least once a year. The access to the seal is often in a service area and consequently the operator is unaware of the need to check them or their impact on the process.”