A comparison of pressure screen baskets with different slot widths and profile heights - Selection of the right surface for a groundwood application

The efficiency of pressure screening is greatly affected by the structure o f the screen plate, as any increase in screen aperture size or profile roug hness is known to reduce screening efficiency and increase maximum screen c apacity. The mechanism of this action - why it has this effect - is still u nclear. This paper therefore sets out to discuss the mechanisms connected w ith the screening results achieved using differently designed screen surfac es. In basic research into screen surfaces, attention has so far focused ma inly on the trajectories of individual particles on the surface. We believe that such an approach will not provide solutions to screening problems. In stead, we propose that attention shoud be drawn to the importance of the ro le of flocculation and the flow of water over the screen plate. As a result of this study, the maximum capacity of the pressure screen used for ground wood screening has been found to be determined largely by slot width. On th e other hand, the efficiency of probability screening is more dependent on profile roughness than on slot width. The thinking behind the choice of scr een basket for groundwood is presented as a practical conclusion to this st udy. The best way to select the basket is to take one with a low profile ro ughness and then to find the greatest slot width that still provides the re quired efficiency.