Papermaking machine employing an impermeable transfer belt, and associated methods
A papermaking machine for making paper includes a forming section, a press section, and a drying section. The paper web is pressed between two press members while enclosed between a press felt and a transfer belt having non-uniformly distributed microscopic depressions in its surface, the web following the transfer belt from the press to a transfer point at which the web is transferred via a suction transfer device onto a structuring fabric, the web then being dried on a drying cylinder. The transfer point is spaced a distance D from the press nip selected based on machine speed, a basis weight of the web, and the surface characteristics of the transfer belt, such that within the distance D a thin water film between the web and the transfer belt at least partially dissipates to allow the web to be separated from the transfer belt.
1. An apparatus for transferring a wet paper web from a press nip defined between two press members in a press section to a drying section of a papermaking machine, comprising:
an impermeable transfer belt arranged in a loop such that the transfer belt passes through the press nip and a wet paper web passes through the press nip enclosed between a press felt and the transfer belt; and
a permeable structuring fabric having a structured surface and being arranged in a loop within which a suction transfer device is disposed,
the suction transfer device having a suction zone in which suction is exerted through the structuring fabric, the suction zone including a transfer point spaced a distance D from the press nip in a machine direction along which the transfer belt runs, the transfer belt being arranged to bring the paper web into contact with the structuring fabric in the suction zone for a length L in the machine direction, such that suction is exerted on the paper web to transfer the paper web from the transfer belt onto the structuring fabric at the transfer point,
the transfer belt having a surface in contact with the wet paper web characterized by a non-uniform distribution of microscopic-scale depressions.
2. The apparatus of claim 1 , wherein the structuring fabric runs at a linear speed that is from about 3% higher to about 10% lower than a linear speed of the transfer belt.
3. The apparatus of claim 1 , further comprising an adjustable guide roll for the transfer belt disposed upstream of the suction transfer device, the adjustable guide roll being adjustable in position with respect to the suction transfer device for adjusting the length L between a first value and a second value.