Laboratory Study of Shoe Pressing for Low Basis Weight Paper Applications, 2000 Engineering Conference Proceedings

P. Phelan, F. Ahrens, G. Worry--Results of laboratory-simulated shoe pressing experiments on low basis weight handsheets are presented. Five different pressure pulse shapes, two dwell times (20 and 40ms), two average pressure levels (106 and 250 psi, simulating 4.7 inch and 2 inch shoes, respectively, at a press load of 500 pli)1 , and two basis weights (13.4 and 24.4 g/m 2 ) were investigated. In general, the expected water removal results were obtained, with the shoe press pulses better than the haversine control pulse, and high-pressure, short nip (narrow shoe) pulses better than low-pressure, long nip pulses. Short, high impulse shoes were significantly better than long, low impulse shoes for water removal. However, the high dewatering led to lower caliper (bulk) with higher tensile strength. For low basis weights, rewet is a major concern. This concern may be supported by the water removal data, which indicate that slight changes in the rate of depressurization (i.e., location of the peak pressure within the nip) appears to have a significant effect on outgoing solids. When the depressurization was steeper than average, higher solids were obtained than expected, and vice versa.