US 5,849,156 AGranted

Press section with an equalizing nip in a paper machine

AssigneeValmet Corporation

InventorOiva Vallius

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Abstract

A press section of a paper machine through which a paper web has a substantially closed and supported draw including an extended-nip zone and an equalizing-nip zone following the extended-nip zone in the running direction of the web. In the equalizing-nip zone, the asymmetry of roughness is equalized that was formed in the web to be pressed in the preceding press nip or nips, while not dewatering the web to a substantial extent. The extended-nip zone and the equalizing-nip zone are formed between three press components which are interconnected in a compact way so that the extended nip is formed by a press component provided with a flexible mantle together with a press roll provided with a rigid mantle. The press roll with the rigid mantle also forms the equalizing-nip zone together with a smooth-faced equalizing-press roll. After the equalizing-nip zone, the web has at least one free draw or runs on a transfer fabric, on which draw(s) or run, by a difference in speed, the stretch of the web in the machine direction, taking place in the equalizing-press nip is compensated for and the web is kept appropriately tensioned.

Claims15

Dependent claims

In a paper machine having a forming section in which a paper web is formed, a press section in which the web is pressed and a dryer section in which the web is dried, the press section including extended-nip means for forming an extended nip, said extended-nip means comprising a first press roll having a flexible mantle and a second press roll having a rigid mantle arranged in nip-defining relationship with said first press roll, a press felt or fabric for carrying the web through said extended nip whereby the web is dewatered in said extended nip, the improvement comprising:

an equalizing nip arranged after said extended nip for equalizing asymmetry of roughness of the web formed in said extended nip, said equalizing nip being defined by a third press roll and said second press roll, the web contacting an outer surface of said second press roll as it passes through said equalizing nip,
a smooth-faced, substantially non-water-receiving, elastic transfer belt arranged to run in a loop over said third press roll through said equalizing nip and in direct contact with the web, said transfer belt being stretchable in a running direction thereof, the asymmetry of roughness of the web being equalized in said equalizing nip by virtue of the pressing contact of said transfer belt with the web and the web being elongated as a result of the equalization of the asymmetry of roughness, the web being carried on said transfer belt after said equalizing nip and transferred therefrom to the dryer section of the paper machine, and
stretching means arranged after said equalizing nip for stretching said transfer belt in the running direction thereof after said transfer belt separates from said third press roll and before the web is transferred from said transfer belt to the dryer section, the stretching of said transfer belt causing the web to run at a different running speed after said transfer belt separates from said third press roll than before said equalizing nip and thereby tension the web and compensate for the elongation of the web taking place in said equalizing nip.

passing the web through an equalizing nip after said extended nip in order to equalize asymmetry of roughness of the web formed in said extended nip, said equalizing nip being defined by a third press roll and said second press roll, the web contacting an outer surface of said second press roll as it passes through said equalizing nip,
transferring the web to a smooth-faced, substantially non-water-receiving, elastic transfer belt in said equalizing nip, said transfer belt running in a loop over said third press roll through said equalizing nip and in direct contact with the web, said transfer belt being stretchable in a running direction thereof, the asymmetry of roughness of the web being equalized in said equalizing nip by virtue of the pressing contact of said transfer belt with the web and the web being elongated as a result of the equalization of the asymmetry of roughness,
rotating a drive roll arranged in the loop of said transfer belt to stretch said transfer belt in the running direction thereof after said transfer belt separates from said third press roll in order to cause the web to run at a different running speed after said transfer belt separates from said third press roll than before said equalizing nip and thereby tension the web and compensate for the elongation of the web taking place in said equalizing nip and then
transferring the web from said transfer belt after said transfer belt has been stretched to the dryer section of the paper machine.

1 more element

Dependencies are inferred from the claim text.