New trends in CD weight control for multi-ply applications

CD weight control on multi-ply board machines presents challenges which are quite different to those on single-ply grades - the selection of an actuator controlling, for example, the stiff throat cross section of a cylinder vat machine, or the more easily deformed slice of a Kobayashi type former. Other issues include : ply on which to apply CD control ; obtaining the narrowest CD weight resolution ; and consistency profiling (CP) headbox technology. This paper reviews conventional and consistency profiling on several types of multi-ply formers. Strategies to optimise CD weight control with a minimal number of actuators are discussed, and non-scanning measurement of the individual CD weight profiles on a multi-Fourdrinier machine is described. Typical improvement in CD weight from selected technology is reviewed.