Bottom spraying

Bottom-fermenting yeasts, 26 465 Bottom-pressure casting method, 23 269 Bottom-spray fluidized-bed units, 16 448-449... 

Bottom Spray Wurster 2. Top Spray [Granulator) S.Tangenlial Spray (Rotor- processor)... 

The bottom-spray process, commonly called the Wurster process and the only one specifically designed as a coating process... 

Bottom spray Moderate batch Poor nozzle access Application of ... 

Fig. 4. Diagram of a Bottom Spray (Wurster) Coater. (Courtesy Glatt Air Techniques, Inc.)...

Bottom Spray (Wurster) Coating Applications/Characteristics... 

The Wurster bottom spray system has also been used successfully to coat particles as small as 100 microns. Attempting to coat smaller particles may result in the same difficulties as discussed in the previous segment. Batch capacities range from a few hundred grams to approximately 600 kg. Because fluidization quality is affected by batch size, at least 50% of the volume outside of the partition should be occupied by the uncoated product. Finished product batch size (for fine and intermediate particles) can be determined by the following equation . 

Fig. 9. A bottom spray (Wurster) film coating, surface and...

Spraying. The coating or aggregative solution can be sprayed from the top (top spray, Figure 8a) or bottom (bottom spray or Wurster when a tube is inserted in the reactor, Figure 8b) or in the particle bed itself. 

The principle and possible applications of the three basic processing options (top-spray, bottom-spray or tangential-spray) of the batch-fluidised bed are discussed below (Jones 1994). Both the top- and bottom-spray methods are characterised by a conical product container and expansion chamber, resulting in a more vigorous fluidisation pattern and a decrease in velocity as the particles move upward in the expansion chamber. 

Bottom-spray film coating is accomplished by means of the Wurster system, originally developed by Dr. D.E. Wurster (Wurster 1959). A scheme of the bottom-spray fluid bed is given in Figure 16.4. 

In a top-spray fluidised bed, air is introduced through a uniform air distribution plate. Compared to the particle motion in the bottom-spray fluidised bed, the fluidisation pattern is less controlled. Particular to the top-spray method, the nozzle is positioned above the particle bed, and coating liquid is sprayed coimtercurrently, or down, into the fluidising core particles. Compared to a Wurster fluid bed, it is more... 

Parameter Top-spray Bottom-spray T angential-spray... 

In contrast to the coating pans, small particles such as beads, pellets, granules, and powders are generally coated using the fluidized bed or air suspension method, which utilizes a carrier gas to keep the cores in motion. The high air current makes this technique more efficient at water removal. The bottom spray technique is one of the most common fluidized bed application methods and a schematic of this process is shown in Fig. 4A. A perforated distribution base plate allows sufficient air into the product container to force the particles up into a cylindrical or slightly conical coating chamber, known as a Wurster insert. These inserts have been recently improved to keep... 

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