CRITICAL PRESSURE CONTROL OF DELAMINATION IN IMPULSE DRYING

Different methods of preventing delamination in impulse drying are dis cussed, and a new method to avoid delamination is presented. The metho d is based on maintaining a low hydraulic pressure in the paper web. T his gives a low temperature in the web, and the corresponding vapor pr essure is not sufficient to delaminate the paper web. Experiments were made on a nip simulator to determine the critical pressure, the peak pressure above which delamination occurs. The critical pressure was de termined as the pressure where the Scott bond value suddenly decreases . Experiments were made at 300 degrees C and a swell time of 40 ms for three basis weights: 54, 84, and 155 g/m(2). For the 54-g/m(2) basis weight, no delamination could be determined. For the 84- and 155-g/m(2 ) basis weights, the critical pressure was determined as 1.6 and 1.4 M Pa respectively. For the 54-g/m(2) basis weight, an increase of the pe ak pressure did not affect the moisture ratio change, but for the 84- and 155-g/m(2) basis weights, the moisture ratio change increased with increasing peak pressure.