EFFECTS ON PAPER PROPERTIES AND RETENTION OF THE PROPORTION OF ROLL DEWATERING DURING TWIN-WIRE ROLL-BLADE FORMING OF TMP

In a previous pilot machine investigation of twin-wire roll-blade form ing, it was concluded that the effect on formation of a final blade de watering is a balance between improving and impairing mechanisms, diff erent in different scale size ranges. A shift in the balance as a resu lt of the blade pulse force and the headbox jet quality was then demon strated. This is generalized further in the present investigation, sho wing that the balance is influenced by the distribution between roll a nd blade dewatering. The potential improvement in the large-scale form ation (3-30 mm wavelength) owing to the final blade dewatering is best exploited with a sufficiently large proportion of roll dewatering. Un expectedly, the retention showed no significant increase with increasi ng proportion of roll dewatering, the major difference being between r oll-blade and pure roll dewatering. This indicated that fines initiall y retained during roll dewatering were loosened during blade dewaterin g. Sheet density, fibre orientation anisotropy, tensile stiffness, fra cture toughness and Z-toughness were also evaluated.