Method for conditioning paper and paperboard webs
First Claim
1. A method for treating an elongate moving web which comprises conditioning the web by applying a flow of moistened gas to a surface of the moving web across its width and along at least a portion of its length from a plurality of substantially overlapping flow zones wherein the flow in each zone is sufficient to create a combination of suction and pressure forces on the surface of the web to promote convective heat transfer and thereby decrease its surface temperature.
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Abstract
The specification discloses embodiments of a process and related apparatus for conditioning a fibrous web in order to improve the efficiency of drying and calendering thereof. In the process, a moving fibrous web is conditioned after the drier unit of a papermaking machine by applying a flow of moistened gas through one or more arrays of radial jet reattachment nozzles placed in close proximity to the web surface prior to a calendering unit or prior to a steaming unit placed between the nozzles and the calender unit to cool the web and/or increase its moisture content. Webs treated according to the invention exhibit improved properties including less moisture streaking, enhanced smoothness and avoidance of optical property loss.
26 Citations
52 Claims
- 1. A method for treating an elongate moving web which comprises conditioning the web by applying a flow of moistened gas to a surface of the moving web across its width and along at least a portion of its length from a plurality of substantially overlapping flow zones wherein the flow in each zone is sufficient to create a combination of suction and pressure forces on the surface of the web to promote convective heat transfer and thereby decrease its surface temperature.
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15. A method for treating a fibrous web proceeding from a dryer unit of a papermaking machine, the web having a temperature of at least about 80°
- C., which comprises conditioning the web by applying a flow of moistened gas to a surface of the moving web across its width and along at least a portion of its length from a plurality of substantially overlapping flow zones wherein the flow is sufficient to create a combination of suction and pressure forces on the surface of the web to enhance convective heat transfer and thereby decrease its surface temperature, and thereafter calendering the web.
- View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
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27. A method for treating a moving cellulosic web proceeding from a dryer unit of a papermaking machine, the web having a moisture content below about 8 wt. % and a temperature of above about 80°
- C., which comprises conditioning the web by applying a flow of moistened gas having a temperature in the range of from about 10°
to about 65°
C. to a surface of the moving web across its width and along at least a portion of its length from a plurality of spaced apart radial jet reattachment nozzles to thereby increase the moisture content of the web by at least about 0.2% and decrease its temperature, and thereafter calendering the web. - View Dependent Claims (28, 29, 30, 31, 32, 33, 34)
- C., which comprises conditioning the web by applying a flow of moistened gas having a temperature in the range of from about 10°
- 35. A papermaking process which comprises depositing an aqueous slurry of cellulosic and/or synthetic fibers at a consistency of from about 0.2 to about 1.5% by weight on a moving web former screen thereby forming a layer of slurry on the screen, dewatering the slurry on the moving screen to form a fibrous web, pressing the thus formed fibrous web with one or more wet press nips to provide a pressed web having a solids content in the range of from about 32 to about 45% by weight, drying the pressed web to provide a dried web having a moisture content of from about 0.2 to about 6% by weight, conditioning the dried web by applying a flow of moistened gas to the web from a plurality of radial jet reattachment nozzles placed in close proximity to the web to provide a conditioned web having a moisture content which is substantially uniformly increased across its width by at least about 0.2% relative to the moisture content prior to conditioning, and calendering the conditioned web in a calendering unit.
- 42. An apparatus for conditioning an elongate moving web which comprises a means for producing a moisturized gas and moisturized gas application means for applying a flow of the moisturized gas onto a surface of the moving web such that the web is urged toward the gas application means while providing a cushion of air between the gas application means and the web to thereby limit contact between the application means and the web and cause moisture in the gas to contact the web.
Specification