Claims
- 1. A method in a dryer section of a paper or board machine for controlling curl of a web being dried therein to an ultimate dry solids content, the web being worked in a finishing device after the dryer section, comprising the steps of:
- while the web has a dry solids content in a range from K1 to K2 wherein K1 is the ultimate dry solids content -7% and K2 is the ultimate dry solids content +3%, guiding the web through a plurality of curl control stages in which steam is directed at the web or the web is moistened, and
- constructing the dryer section such that during at least one of said curl control stages, the temperature of the web is lower than 85.degree. C.
- 2. The method of claim 1, wherein the dryer section is constructed such that during said at least one curl control stage, the temperature of the web is lower than 75.degree. C.
- 3. The method of claim 1, wherein the finishing device is a coating/surface-sizing device, further comprising the steps of:
- drying the web in a forward dryer section including drying cylinders and a drying wire for pressing the web over heated faces of said drying cylinders,
- passing the web from the forward dryer section into a finishing section in which said coating/surface-sizing is situated,
- coating/surface-sizing the web in the finishing section by means of said coating/surface-sizing device,
- drying the web in an after-dryer arranged after said coating/surface-sizing device,
- calendering the web in a calender arranged after the after-dryer, and then
- reeling the web into a machine reel.
- 4. The method of claim 3, wherein said forward dryer section includes only normal single-wire draw dryer groups such that the web is dried in the forward dryer section from the side of its bottom face.
- 5. The method of claim 3, wherein said after-dryer includes normal single-wire draw dryer groups such that the web is dried in the after-dryer from the side of its bottom face, each of said normal single-wire draw dryer groups including drying cylinders arranged in a first row, reversing cylinders arranged in a second row below said first row, and a drying wire for carrying the web over said drying cylinders and said reversing cylinders.
- 6. The method of claim 5, further comprising the step of:
- selecting the diameter of said drying cylinders and said reversing cylinders in a last one of said normal dryer groups in said after-dryer in a running direction of the web such that the ratio of the diameter of said drying cylinders to the diameter of said reversing cylinders in said last normal dryer group in said after-dryer is from about 0.75 to about 2.5.
- 7. The method of claim 5, wherein at least one of said drying cylinders in a last one of said normal dryer groups in said after-dryer in a running direction of the web is structured and arranged to provide an adjustable temperature of an outer surface thereof over which the web runs.
- 8. The method of claim 7, wherein said at least one drying cylinder providing an adjustable temperature is structured and arranged to be cooled.
- 9. The method of claim 7, wherein said last normal dryer group is structured and arranged such that said drying wire which carries the web over said at least one drying cylinder providing an adjustable temperature carries the web over only said at least one drying cylinder providing an adjustable temperature.
- 10. The method of claim 9, further comprising the step of:
- separating said at least one drying cylinder providing an adjustable temperature in a hood of the dryer section by means of a partition wall arranged in said hood.
- 11. The method of claim 9, further comprising the step of:
- cooling said drying wire which carries the web over only said at least one drying cylinder providing an adjustable temperature.
- 12. The method of claim 3, wherein said after-dryer includes dryer groups each having drying cylinders, reversing cylinders and a drying wire for carrying the web over said drying cylinders and said reversing cylinders,
- said step of guiding the web through a plurality of curl control stages comprising the steps of:
- arranging a moistening device in a last one of said dryer groups in said after-dryer in a running direction of the web,
- passing the web in front of said moistening device such that the web is moistened, the moistening of the web constituting a first one of said curl control stages,
- thereafter passing the web along a cylinder face of a first one of said drying cylinders, said first drying cylinder being arranged to provide an adjustable temperature of said cylinder face thereof along which the web runs,
- passing the web from said first drying cylinder to one of said reversing cylinders,
- arranging a steam box or a moistening device in connection with said one of said reversing cylinders such that the web is steam-treated or moistened as it passes over said one of said reversing cylinders, the steam-treatment or moistening of the web constituting a second one of said curl control stages, and
- thereafter passing the web along a cylinder face of a second one of said drying cylinders, said second drying cylinder being arranged to provide an adjustable temperature of said cylinder face thereof along which the web runs.
- 13. The method of claim 12, further comprising the steps of:
- arranging a steam box or a moistening device after said second cylinder to steam-treat or moisten the web, and then
- passing the web to the calender.
- 14. The method of claim 12, further comprising the step of:
- drying the web prior to said first curl control stage to a dry solids content between about 96% and about 99%.
- 15. The method of claim 1, further comprising the step of:
- during said curl control stages, supporting the web or directing the web in a draw in the machine direction.
- 16. The method of claim 1, further comprising the step of
- subjecting the web to a spreading effect during or directly after said curl control stages.
- 17. In a paper or board machine comprising a headbox for discharging a pulp suspension jet, a former for forming a web from the pulp suspension jet, a press for dewatering the web, a dryer section for drying the web to an ultimate dry solids content while controlling curl of the web and a finishing device arranged after the dryer section for working the web, the improvement comprising:
- at least two curl regulation devices arranged in the dryer section for controlling curl of the web,
- said curl regulation devices being selected from a group consisting of a steam box and a moistening device, at least one of said curl regulation devices being arranged in each of a plurality of curl control stages,
- said curl regulation devices being operative on the web while the web has a dry solids content in a range from K1 to K2 wherein K1 is the ultimate dry solids content -7% and K2 is the ultimate dry solids content +3%,
- said dryer section being structured and arranged such that during at least one of said curl control stages, the temperature of the web is lower than 85.degree. C.
- 18. The paper or board machine of claim 17, wherein the dryer section comprises a forward dryer section, a finishing section arranged after said dryer section, an after-dryer arranged after said finishing section, a calender for calendering the web arranged after said after-dryer and a reeling station for reeling the web arranged after said calender, the finishing device being arranged in said finishing section and being a coating/surface-sizing device.
- 19. The paper or board machine of claim 18, wherein said forward dryer section comprises normal single-wire draw dryer groups.
- 20. The paper or board machine of claim 18, wherein said after-dryer comprises normal-single wire draw dryer groups, each of said normal single-wire draw dryer groups including drying cylinders arranged in a first row, reversing cylinders arranged in a second row below said first row, and a drying wire for carrying the web over said drying cylinders and said reversing cylinders.
- 21. The paper or board machine of claim 20, wherein the diameter of said drying cylinders and said reversing cylinders in a last one of said normal dryer groups in a running direction of the web being such that the ratio of the diameter of said drying cylinders to the diameter of said reversing cylinders in said last normal dryer group in said after-dryer is from about 0.75 to about 2.5.
- 22. The paper or board machine of claim 20, wherein at least a last one of said drying cylinders in a last one of said normal dryer groups in a running direction of the web being structured and arranged to provide an adjustable temperature of an outer surface thereof over which the web runs.
- 23. The paper or board machine of claim 22, wherein said at least one drying cylinder providing an adjustable temperature is structured and arranged to be cooled.
- 24. The paper or board machine of claim 22, wherein said last normal dryer group is structured and arranged such that said drying wire which carries the web over said at least one drying cylinder providing an adjustable temperature carries the web over only said at least one drying cylinder providing an adjustable temperature.
- 25. The paper or board machine of claim 22, wherein said dryer section includes a hood having a partition wall for separating said at least one drying cylinder providing an adjustable temperature.
- 26. The paper or board machine of claim 24, wherein said drying wire which carries the web over only said at least one drying cylinder providing an adjustable temperature is cooled.
- 27. The paper or board machine of claim 18, wherein said after-dryer comprises dryer groups each having drying cylinders, reversing cylinders and a drying wire for carrying the web over said drying cylinders and said reversing cylinders, said curl regulation devices being arranged in a last one of said dryer groups in said after-dryer, said curl regulation device in a first one of said curl control stages being a moistening device arranged before a first one of said drying cylinders, said first drying cylinders being structured and arranged to provide an adjustable temperature of an outer surface thereof over which the web runs, said curl regulation device in a second one of said curl control stages being situated after said first drying cylinder and before a second one of said drying cylinders structured and arranged to provide an adjustable temperature of an outer surface thereof over which the web runs.
- 28. The paper or board machine of claim 27, further comprising a steam box or a moistening device after said second drying cylinder and before said calender for steam-treating or moistening the web before said calender.
- 29. The paper or board machine of claim 17, wherein the web is dried prior to a first one of said curl control stages to a dry solids content between about 96% and about 99%.
- 30. The paper or board machine of claim 17, wherein the web is supported or directed in a draw in the machine direction during said curl control stages.
- 31. The paper or board machine of claim 17, wherein the web is subjected to a spreading effect during or directly after said curl control stages.
- 32. The paper or board machine of claim 17 wherein said range of the dry solid contents is dependent upon a specific final dry solid of said web while said curl regulation devices are operative on said web to moisten said web.
Priority Claims (1)
Number |
Date |
Country |
Kind |
971301 |
Mar 1997 |
FIX |
|
Parent Case Info
This application claims the benefit under 35 USC 119(e) of U.S. provisional application Ser. No. 60/042,421 filed Mar. 27, 1997.
US Referenced Citations (11)
Foreign Referenced Citations (4)
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FIX |
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Aug 1996 |
FIX |
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Jun 1998 |
FIX |