Twin-wire blade forming versus roll forming of a linerboard furnish―effects on tensile strength and formation

摘要

There is presently a trend from fourdrinier to twin-wire forming for packaging paper grades. As in the printing paper area, twin-wire formers in the sense of roll-blade formers are being installed in the packaging area. Blade dewater-ing induces a pulsating pressure, whereas roll dewatering involves a nearly constant pressure after an initial rise in pressure. The use of blade dewatering for grades whose mechanical properties are of primary importance was questioned in this work. In a pilot machine investigation, blade forming was evaluated against roll forming of linerboard furnishes concerning effects on formation and tensile strength. Roll-blade forming was also evaluated. Under the conditions used in this study, blade forming and roll-blade forming gave better formation than roll forming. Part one of this study investigates blade forming versus roll forming of semi-kraftliner roll stock over a range of speed differences between fiber suspension and wires. Roll forming gave about 10% better tensile strength (geometric mean) than blade forming. The effect concerned primarily the MD-component. Part two is similar to part one but with kraftliner roll stock. Roll forming showed better tensile strength than blade forming also in this case. Part three concerns roll-blade forming versus roll forming of a kraftliner roll stock over a wide range of speed differences. Roll forming showed a similar advantage over roll-blade forming concerning the tensile strength as in the comparison against blade forming. The results obtained here for linerboard furnishes agree with earlier results for TMP. The adverse effect of a pulsating dewatering pressure may be interpreted as being due to deterioration of the deposited fiber mats by shear stresses imposed during sudden accelerations and decelerations of the remaining fiber suspension. It is concluded that pure roll forming is the preferred variant of twin-wire forming for grades whose mechanical properties are of primary importance.