A recent change from perforations to slots using Conn-Weld Inc., Wedge Wire slotted baskets has debunked two long held beliefs about slots in Approach Flow Screening. In fine slots, .012” and smaller, passing velocities with long fiber furnishes generate strings, and centripetal flow baskets cannot produce flows equivalent to centrifugal flow designs. In this application, a set of .012” slotted baskets were installed in a dual basked approach flow screen. A screen with an inner (centripetal flow) basket and outer (centrifugal flow) basket. This application is on a bleached fine paper machine making a variety of grades with furnishes ranging from 40% SW up to 80% SW. Flow ranges produced calculated passing velocities of 2.1 m/s at the low end and 2.9 at the high end. The high flow equated to 85% of the original max design flow for that machine, equipped with perforated (holed) baskets with 12% open area.
What this means is that any AF screen currently operating with perforated baskets, with one or two baskets, can now operate with fine slots (.012”) with No Stringing, No Modifications Required, and No loss of capacity or run ability, Guaranteed.