Characterising the Shoe Press Nip to Enhance Dewatering, 2000 Papermakers Conference Proceedings

Peter F. Slater--The introduction of shoe presses and the relative design needs of commercial machines brought many challenges with respect to shoe press belts design. Definite water removal and runnability benefits can be obtained by the correct application of a grooved belt. Operating Shoe Presses and the key factors relating to shoe press design and running conditions are discussed with reference to improvements in configurations and operation over the years. This leads to a discussion of Shoe Press Development. Machine and press parameters critical to the design of a shoe press belt and efficient running with extended life times are discussed. Also, the fact that we must consider not just static but also an active void volume and material properties for efficient operation of vented belts. The advent of single felted presses and the application of shoe pressing on fine paper grades which has stimulated the development of grooved belts and innovative press fabrics is discussed. Pilot machine work comparing different vented structures and their relative merits is seen to prove evidence of a difference in behaviour in the nip. Grooved nips using belts are seen to provide certain advantages and the reduction of hydraulic pressure in the nip, relieving pressure in felts thus giving efficient water removal and runnability over a long life. This work is confirmed via an extensive series of case histories from commercial production machines. These histories demonstrate improvements in machine speed and sheet dryness over a range of speeds and weights after grooved belt installation. Measurement of advantages is also discussed, as are methods of characterising the shoe press nip to enable optimum design of belt and Press fabric systems for the shoe press nip. In order to continue the development of true high-speed shoe presses at 2000 m/min and above it is clear that innovative belt and press fabric structures are needed to optimise dryness and sheet control. These concepts are discussed with the conclusion that machine speeds in excess of 2000 m/min with more cost effective press section operation is possible with technology available today.