Two Common Wurster Coating Challenges- Resolved!
urster coating can be tricky, even in small-scale R&D batches. Larger-scale batches must be monitored carefully, as any mistake could result in costly product waste. Production size Wurster coaters with multiple coating partitions have two very critical process challenges to overcome: balancing the air flow to each coating zone, and the potential for clogged spray nozzles.
Process air entering the system’s inlet plenum below the multi-partition coating bowl will naturally seek the route of least resistance in moving up through the screens, product in the bowl, and out the exhaust. Some partitions will see an abundance of process air while others will be starved unless corrective measures are taken.
An air-starved partition will quickly fill with particles from the active partitions. The product will come in direct contact with the nozzle, resulting in over-wet product and potentially the loss of an entire batch. We’ve overcome the potential for poor air distribution by inserting a special plate assembly with adjustable shutters beneath each coating zone.
This allows the user to adjust the air flow to each zone and lock down the shutter once proper equalization has been achieved and before any coating activity commences. Balancing occurs during set-up and can be repeated for the same product as part of a batch record set-up.
Our fluid bed systems can also be outfitted with optional self-clearing spray nozzles. Self-clearing spray nozzles are equipped with a pin in the nozzle tip which fires when high liquid pressure is detected, clearing the nozzle of debris. Self-clearing nozzles are ideal for solutions that have solids which can accumulate in the nozzle tip.