Patent Publication Number: US-2004050517-A1

Title: Method and device in a paper or board machine

Description:
[0001] The invention relates to a method in a paper or board machine according to the preamble of claim 1.  
       [0002] The invention also relates to a device in a paper or board machine according to the preamble of claim 12.  
       [0003] As known from the prior art, in multi-cylinder dryers of paper machines, twin-wire draw and/or single-wire draw is/are employed. In twin-wire draw, the groups of drying cylinders comprise two wires which press the web, one from above and the other one from below, against the heated cylinder surfaces. Between the rows of drying cylinders, which are usually horizontal rows, the web has free and unsupported draws which are susceptible to fluttering, which may cause web breaks, in particular as the web is still relatively moist and, therefore, has a low strength. Therefore, in recent years, ever increasing use has been made of said single-wire draw in which each group of drying cylinders comprises only one drying wire on whose support the web runs through the entire group so that the drying wire presses the web against the heated cylinder surfaces of the drying cylinders and the web remains at the side of the outside curve of the reversing cylinders or rolls situated between the drying cylinders. Thus, in single wire draw, the drying cylinders are arranged outside the wire loop, and the reversing cylinders or rolls are arranged inside the loop.  
       [0004] With increasing speeds of paper machines, the runnability of a paper machine is, of course, also affected by the dryer section, whose length with the prior art multi-cylinder dryers would, at high speeds, also become very long. If it is imagined that a present-day multi-cylinder dryer were used at a web speed of 40 m/s, it would include about 40-80 drying cylinders, and its length in the machine direction would be about 180 m. In such a case, the dryer would comprise several wire groups and a corresponding number of draws over the group gaps. It is to be assumed that, in a speed range of 30 to 40 m/s, the runnability of the normal prior art multi-cylinder dryers would no longer be even nearly satisfactory, but web breaks would be frequent, which lowers the efficiency of the paper machine. Open draws in particular are problematic, the web moving in them without support of a fabric or a roll or a cylinder or equivalent. To enhance runnability, attempts have been made to find arrangements in which free draws are minimized.  
       [0005] In a speed range of 30-40 m/s and at higher speeds, the prior art multi-cylinder dryers would also become uneconomical because the cost of investment of an excessively long paper machine hall would be unduly high. It can be estimated that, at present, the cost of a paper machine hall is typically about one million FIM per metre in the machine direction.  
       [0006] Thus, the dryer sections of paper machines known today are formed of dozens of drying cylinders and reversing rolls or reversing cylinders associated with them. In a modern high-speed newsprint machine there are in total about 60-80 such rolls and cylinders.  
       [0007] Moreover, in the applications known from the state of the art, it has been necessary to accomplish threading at least partly by using a lead-in strip, and the strip has been conveyed from one position to another before it is spread to the width of the web, which lowers the production capacity which is achieved.  
       [0008] The wet strength and the elastic properties of a paper web depend on the solids content of the web and, directly after the press section, it has been problematic to make the web sufficiently tight because the web has not been sufficiently dry. For this reason, in single-wire draw groups, which are often placed at the beginning of the dryer section, i.e. in so-called slalom-draw groups, problems have been encountered in runnability, in particular in high-speed paper machines. As one solution, short groups including just a few cylinders have been employed at the beginning of the dryer section, so that by means of a positive difference in speed between the groups, it has been possible to maintain web tightness. The solution, however, increases the costs of investment and operation because of the increased number of wire circulations.  
       [0009] When attempting to achieve high speed and good runnability, a web with a high solids content has been needed from the press section and a high difference in draw has been required between the press section and the dryer section, in which connection certain properties of the paper web may, however, be destroyed. A high draw difference can, for example, have an adverse effect on the porosity of the paper web. Since it has been necessary to restrict the temperature of the drying cylinders of the dryer section at the beginning of the dryer section for runnability reasons, it has led to poor operating efficiency. In addition, for runnability reasons, between the press section and the dryer section it has been necessary to use a high draw difference, which also mainly has an adverse effect on the elongation and strength properties of the web, in which connection it has not been possible to control the quality of the paper web in a desired manner as runnability has determined the situation.  
       [0010] Moreover, when tightening of the paper by means of differences in speed between support fabrics has been employed, the paper web may be constricted unevenly, and high differences in tension applied to the web may cause problems in achievement of a sufficiently uniform quality, in particular in relation to the cross-direction profile of the paper.  
       [0011] Since the profile properties must be in order after the press section and in today&#39;s paper machines the web must most often be conveyed through the entire paper machine before its properties are measured, the delay becomes very long, with the result that regulation is slow.  
       [0012] Accordingly, it is an object of the present invention to provide novel solutions for the problems mentioned above so that said drawbacks in the prior art and drawbacks that will come out later are substantially avoided.  
       [0013] It is an object of the invention to propose a solution that enables full-width threading from the press to the dryer section and through the dryer section.  
       [0014] It is known in the prior art to use various impingement/through drying units for evaporation drying of a paper web, which units have been used for drying paper. With respect to the prior art related to this, reference is made, for example, to the documents FI 931263 (corresponding to U.S. Pat. No. 5,495,678) and SE 9502570.  
       [0015] From the prior art applications are also known in which threading has been accomplished as of full-width from the press to the dryer section. With respect to the prior art relating to these, reference is made to the document FI 905798 (corresponding to U.S. Pat. No. 5,389,205).  
       [0016] With a view to achieving the objects described above as well as those which will come out later, the method according to the invention is mainly characterized in that which is stated in the characterizing part of claim 1.  
       [0017] In addition, the device in a paper or board machine according to the invention is mainly characterized in that which is stated in the characterizing part of claim 12.  
       [0018] In the present invention and in its different embodiments, the inventors have succeeded in combining some partial solutions in a new and inventive manner, some of them prior known in themselves from paper machine technology, such that it has been possible to get the above-mentioned problems, different by nature, under control and solved by a new overall concept.  
       [0019] In accordance with one advantageous exemplifying embodiment, the concept according to the invention comprises a large-diameter impingement roll, an impingement arrangement associated therewith, a measuring beam, a profiling unit, a curl control apparatus located on the impingement roll, a suction roll located after the large impingement roll, and a belt calender located before a reel. After the belt calender, there is also a measuring beam, when needed, two measuring beams can also be used.  
       [0020] In an advantageous embodiment of the invention, the web is transferred from a press section onto the large impingement roll as a supported draw and as of full width. By means of devices located inside a transfer roll, a vacuum is provided through a perforated roll shell to the surface of the roll, and the web is transferred by means of said vacuum onto the surface of a transfer fabric on the surface of the roll. The web is transferred from the transfer fabric onto the fabric of the impingement roll (large vacuum roll) by means of the vacuum of the large vacuum roll. The impingement or vacuum roll represents prior art known in itself as applied in the invention to a larger size. Depending on the application, the roll can thus be of the type known under the applicant&#39;s trademark VacRoll, in which the vacuum prevailing inside the roll acts to the same extent over the entire length of the circumference of the roll, and the interior of the roll has not been divided into separate chambers. It is also possible to use a conventional suction roll type, in which connection one or more boxes are arranged in the interior of the roll to divide the roll in the circumferential direction into chambers, sectors, in which vacuums of different magnitude can be used. The diameter of the roll is over 2.5 m, even over 10 m, most appropriately 3-6 m. There may be one or more impingement drying groups one after the other. In applications in which one large-diameter roll is employed for drying the web substantially dry, the diameter of the roll is typically over 10 m. When several rolls are used in succession, their diameter is typically 3-6 m. The web is dried on the large roll by the impingement technique, and a first measuring beam is located after the impingement proper, said measuring beam measuring moisture, basis weight, ash and the like from one side while the paper is against a wire. After the measuring beam, these is an impingement portion in which the moisture profile of the web is corrected and this is followed by correction of curl by moisturizing. A moisturizing beam is advantageously provided with a housing and a suction blowing in order that moist water mist shall not escape into the surroundings. When the paper has been dried, its moisture profile has been corrected and curl is under control, the next step is to treat the surface of the paper. In the arrangement in accordance with the invention, the web is passed from the wire of the large impingement roll by means of a suction roll to a calender, which is formed by, for example, a smooth heated roll and a belt roll placed against it. The web is brought as of full width to the calender roll, from the doctor of which it can be run down into a pulper. The tail is passed from here to a reel as of full width or as a strip. The device used for cutting the lead-in strip, for instance, a spray cross cutter, is placed, when needed, for example, in connection with a transfer wire.  
       [0021] The arrangement in accordance with the invention provides a fully closed draw all the way to the calender, even through the paper machine, and full-width threading can be accomplished through the dryer section, even as far as the calender and the reel. Since the web is supported from the press section to impingement drying and advantageously further to the calender, the solids content of the paper need not be raised in the press section for runnability, but, instead, it is possible to run the desired solids content. Moreover, quality values can be selected as the determining factors in treatment once runnability problems have been solved.  
       [0022] In addition, control of paper quality is possible thanks to the measurement devices most appropriately placed at various locations.  
       [0023] When the arrangement in accordance with the invention is applied and when a measurement device is advantageously placed in connection with the impingement roll, it is also possible to utilize a web possibly of poor quality produced in the starting stage, which web can be run and the values can be adjusted to a correct level.  
       [0024] Moreover, when using impingement drying in accordance with the invention, steam is not needed, but impingement is most appropriately accomplished with gas, for example, natural gas.  
       [0025] The invention also allows a draw difference according to the desired quality to be used because runnability is not a decisive factor.  
       [0026] When using the arrangement in accordance with the invention, the moisture profile also need not be as precise when coming from the press section as in the prior art arrangements because, when using impingement, the web can be made dry at one go, in which connection no transfers are needed from one cylinder to the next, during which transfer the web having an uneven moisture profile adheres unevenly to the cylinder and causes runnability problems.  
       [0027] In accordance with an advantageous feature of the invention, impingement drying and a calender have been integrated, whereby the resultant length of the paper machine is considerably shorter than that of the prior art dryer sections. 
     
    
    
     [0028] In the following, the invention will be described in more detail with reference to the figures in the appended drawing, to the details of which the invention is, however, not by any means meant to be narrowly confined.  
     [0029]FIG. 1 is a schematic view of a prior art paper machine.  
     [0030]FIG. 2 is a schematic view of an advantageous application of the invention.  
     [0031]FIG. 3 is a schematic view of a second advantageous application of the invention, in which, as compared with the one shown in FIG. 2, the draw between a calender and a reel is closed and a support fabric does not run through the nip of the calender.  
     [0032]FIG. 4 is a schematic view of another advantageous application of the invention, in which, as compared with the application shown in FIG. 2, the draw of the web from a press to a dryer section is different.  
     [0033]FIG. 5 is a schematic view of an application of the invention which mainly corresponds to the one shown in FIG. 2 but a multi-nip calender is used as the calender.  
     [0034]FIG. 6 is a schematic view of an application of the invention in which a paper web is surface-sized, after-dried, calendered and reeled after a dryer section.  
     [0035]FIG. 7 is a schematic view of an application of the invention in which several impingement units are used and the web is passed from impingement drying through a multi-nip calender to a reel.  
     [0036]FIG. 8 is a schematic view of an application of the invention which mainly corresponds to the application shown in FIG. 7 but the draw from the calender to the reel is closed.  
     [0037]FIG. 9 is a schematic view of an application of the invention which mainly corresponds to the application shown in FIG. 6 but the draw from one drying unit to the next is closed. 
    
    
     [0038]FIG. 1 schematically shows one prior art application in which stock is fed from a headbox  100  to a wire section  200 , in which a gap former  250  is located and which is followed by a press section  300  having two press nips  350 . A web W is passed from the press section  300  to a dryer section  400  to a first drying group  410 , which is arranged to be a so-called short group for runnability reasons, and which is followed by single-wire draw groups  450  in the application shown in the figure. The web W is passed via a measuring beam  500  to be surface-sized on a sizer  600 , after which the web W is dried in an after-dryer section  700  in single-wire draw groups  750 . After that, the web W is calendered in a calender  800  and, finally, the web W is passed to a reel  900 , in which the web is reeled into rolls  950 .  
     [0039] Some advantageous exemplifying embodiments of the invention are illustrated in FIGS.  2 - 8 , and the same reference signs have been used of the corresponding parts, and the applications shown in them correspond to one another unless otherwise stated.  
     [0040] As shown in FIG. 2, the basic concept of the invention comprises a large-diameter impingement roll  45 , impingement units  46  associated therewith, and a measuring beam  47 , a profiling unit  42  and a curl control apparatus  43  placed on the impingement roll  45 , a suction roll  51  placed after the large impingement roll  45 , and a belt calender  60  placed before a reel  70 . After the belt calender  60  there is also a measuring beam  69 .  
     [0041] As shown in FIG. 2, a web W is passed from a press section  30  onto the large impingement roll  45  as a supported draw and as of full width. On the large roll  45 , the web W is dried by the impingement technique by means of the impingement units  46 , and the measuring beam  47  is located after the impingement proper, said measuring beam measuring moisture, basis weight, ash, etc. from one side while the paper W is against a wire  41 . The measuring beam  47  is followed by the profiling unit, for example, an impingement device  42  or a steam box or equivalent, by means of which the moisture profile of the web W is corrected. After that, there is curl correction by moisturizing with the curl control apparatus  43 , for example, a moisturizing beam with a housing and air blowing (not shown) closely connected therewith in order that moist water mist shall not escape into the surroundings. As shown in the figure, after the impingement roll  45  there is a transfer wire  50  on which the web W is passed to a first roll  61  of the calender  60 , a belt roll  62  constituting the backup roll of the first roll  61  and having its own belt loop  63 . After that, the web W is passed further as a closed draw to the reel  70 .  
     [0042] When the paper has been dried, the moisture profile has been corrected and curl is under control, surface treatment of the paper is carried out. In accordance with the invention, the web W is passed from the wire  41  of the large impingement roll  45  by means of a suction roll  51  and the transfer fabric  50  to the calender  60 , which, in the application shown in FIG. 2, is formed by the smooth heated roll  61  and the belt roll  62  placed against it. The web is brought as of full width to the heatable calender roll  61 , from whose doctor  64  it can be run, when needed, down into a pulper  65 . From here, the web is passed to the reel  70  as of full width or as a strip. A doctor  71  is arranged in connection with a reel drum of the reel  70 .  
     [0043] In the application of the invention shown in FIG. 2, a fully closed draw has been provided through the paper machine and full-width threading can be accomplished all the way to the calender  60  and as far as the reel  70 . In addition, the quality of paper is controlled in each treatment phase. In connection with the transfer fabric  50 , it is possible to arrange, when needed, a diagonal cutter apparatus  59  for cutting a lead-in strip.  
     [0044] In the paper machine in accordance with one application of the invention shown in FIG. 2, the run of the paper web W is as follows. Stock is supplied from a headbox  10  into a gap between forming rolls  21 ,  22  of a gap former  25  in a wire section  20 , from which gap it is passed between wires past dewatering devices of the gap former  25  further on support of a wire to a press section  30 . The press section  30  comprises two presses  35  and  36 , and the web W is passed on an upper fabric of the first press  35  between the press rolls of the press  35  while supported by a lower fabric. From the lower fabric the web W is passed onto an upper fabric of the next press  36  and further between the upper fabric and a lower fabric between the press rolls of the press  36 . From the press section  30  the web W is passed from the lower fabric of the latter press  36  on a transfer fabric  39  and via a transfer suction roll  38  arranged in connection therewith as a supported draw without a free draw to the dryer section  40  onto the drying wire  41 , on whose support the web W is passed onto the large-diameter impingement drying cylinder  45 . The impingement units  46  are arranged in connection with the impingement drying cylinder  45 .  
     [0045] In the exemplifying embodiment shown in FIG. 2, the transfer fabric  39  is arranged before the impingement roll above the lower fabric  36 A of the last press nip  36  of the press section  30 , the web W being detached from the fabric  36 A of the press and transferred onto the surface of the transfer fabric  39  by means of the transfer suction roll  38  arranged in connection with the transfer fabric  39 . From the transfer fabric the web W is transferred by means of the vacuum of the impingement roll  45  onto the wire  41  and further so as to run around the impingement roll  45 , which is a large-diameter vacuum roll provided with devices for producing a vacuum to the surface of the roll  45 .  
     [0046]FIG. 2 shows a large vacuum roll which is provided with several boxes  101 ,  102 ,  103  for using vacuums of different magnitude over the length of the circumference. The first box  101  is typically a high vacuum zone which serves to eliminate the detrimental effects of the air carried into the closing nip on the surface of the roll and the fabric and to detach the web W efficiently from the surface of the transfer fabric  39  onto the fabric  41 . The vacuum of the second box  102  assures that the web adheres to the surface of the fabric  41  in the area where the fabrics  39  and  41  are separated. The third box  103 , in which vacuum is typically lower than that of the preceding boxes, keeps the web W on the surface of the fabric  41  while the web runs around the large roll  45 . There is no vacuum acting on the circumference of the roll  45  between the transfer suction roll  51  and the first box  101 . The zone  101  typically begins before the point where the fabric  39  and the wire  41  running on the roll  45  meet and ends slightly after this point of meeting. The zone  102  ends when the fabric  39  is substantially separated from the vicinity of the wire  41  and, at the same time, from the vicinity of the roll  45  most appropriately while guided by a wire guide roll, and the zone  103  ends roughly at the point where the wire  41  is detached from the roll  45 .  
     [0047] The exemplifying embodiment shown in FIG. 3 mainly corresponds to the exemplifying embodiment of the invention shown in FIG. 2. In the exemplifying embodiment of the invention shown in FIG. 2, the draw between the calender  60  and the reel  70  is arranged to be closed by means of a support fabric  63 , but differing from the application shown in FIG. 2, the support fabric  63  does not run through the calendering nip formed by calender rolls  61 , 62 , in which connection the calendering nip may be a hard nip or a soft nip. In this application, a measurement device  69  is arranged above the support fabric  63 . FIG. 3 shows an application in which there are no separate chambers inside the large roll but the same vacuum prevails over the entire length of the circumference of the roll in accordance with the principle of the roll marketed by the applicant under the trademark VacRoll.  
     [0048] In the exemplifying embodiment shown in FIG. 4, the web W is kept on the upper fabric  36 Y of the last press nip  36  by means of a transfer suction roll  31 . Vacuum boxes  37  and a suction roll  38 N are placed in connection with the fabric  36 Y to keep the web W in contact therewith. The web W is transferred from the fabric  36 Y onto the impingement roll  45  in the same manner as from the transfer fabric  39  in the applications shown in FIGS. 2 and 3.  
     [0049] In the exemplifying embodiment shown in FIG. 4, the paper web W is passed to the last press nip  36  of the press section  30  on support of the lower fabric  35 A of the press nip  35 , from which fabric the web W is transferred by means of a transfer suction roll  34  onto support of the upper press fabric  36 Y of the latter press nip  36 , the paper web W being passed to the latter press nip  36  while guided by said upper press fabric to remove water from the web W in said nip. The web W is passed from the lower fabric  36 A of the latter nip  36  onto the upper fabric  36 Y by means of the transfer suction roll  31  and, as a closed draw, onto the drying wire  41  of the impingement drying cylinder  45  of the dryer section  40 . The web W is kept on the upper fabric  36 Y by means of the vacuum boxes  37  and the suction roll  38 N, and from this fabric  36 Y the web W is passed further onto the drying wire  41 .  
     [0050] As shown in FIG. 4, the paper web W is thus passed from the last press nip  36  of the press section as a fully closed draw by means of the upper fabric  36 Y onto the drying wire  41  of the dryer section, after which the paper web W is passed on the transfer fabric  50  to the calender  60 .  
     [0051] In FIG. 5, the transfer of the web from the press section  30  to the impingement roll  45  takes place as shown in FIG. 2 and, in the exemplifying embodiment shown in FIG. 5, the web W is passed after the impingement roll  45  from the drying wire  41  as a closed draw on a transfer fabric  50  to the top roll of a multi-nip calender  60  and further through the calender  60  to its bottom roll, in connection with which a doctor  67  is arranged. It is possible to run the web/lead-in strip from the bottom roll of the calender  60  down into a pulper from the doctor  67  placed on the bottom roll. In the application of the invention shown in FIG. 5, the draw between the calender  60  and the reel  70  is open and there is on the web W, for example, a device  77  of the airborne type supporting the run of the web W. A doctor  71  is arranged in connection with the reel drum of the reel  70 .  
     [0052] In the exemplifying embodiment shown in FIG. 6, the web W is passed after the first impingement roll  45  over the transfer suction roll  51  onto the transfer fabric  50  and from this as a free draw to a sizing/coating unit  80 , in which the web W is surface-sized/coated by means of applicator beams  93 A,  93 B, and after that forwards as a free draw, and the web W is passed on a suction roll  81  and on its transfer fabric  82  to a second impingement drying roll  45 ′, after which the web W is calendered on the calender  60  and passed to the reel  70 , as in FIGS. 2 and 4. In the exemplifying embodiment of FIG. 6, the reference numerals used in the numbering of the latter impingement drying unit correspond to the reference numerals of the first impingement drying unit and the transfer fabric unit arranged in connection therewith, and the reference numerals of the latter unit are provided with an apostrophe for the sake of clarity. In the application shown in FIG. 6, the web W is surface-sized/coated on the sizing/coating unit  80 , which is followed by the drying formed by the impingement roll  45 ′ and impingement units  46 ′ and including a drying wire  41 ′. In addition, a turning device  84  is placed after the coating station  80 . Finally, the web W is passed to the calender  60 . After the calender  60 , the web W is passed to the reel  70 , in which the paper web W is reeled into paper rolls.  
     [0053] In the exemplifying embodiment of the invention shown in FIGS. 7 and 8 there is a closed draw all the way to the calender  60 . In the applications shown in the figures, the web W is passed from the lower fabric  36 A of the latter press nip  36  of the press section  30  as a closed draw all the way to the calender  60 . The exemplifying embodiment shown in FIG. 7 comprises a dryer section  40  which is formed of four impingement drying units, of which the last one corresponds to the impingement drying unit shown in the previous figures also in respect of additional equipment. The first three impingement drying units comprise a large-diameter impingement drying roll  45 , as well as impingement hoods  46  and a drying wire  41  as well as alignment and guide rolls for the drying wire, arranged in connection therewith. The first and the third impingement drying unit is arranged to be a so-called inverted impingement drying group and the second impingement drying unit is situated in the normal direction, and the web W meanders from a lower unit to an upper unit and further back to a lower unit. In the application shown in FIG. 7, the transfer from the impingement drying to the reel  70  corresponds to that described in connection with FIG. 5.  
     [0054]FIG. 8 also shows a multi-nip calender  60 , in which the draw between the calender  60  and the reel  70  is closed, so that in this application it is not possible to run the web down from the calender but it can be done either from the reel drum having a doctor  71  placed in connection therewith or from an auxiliary roll placed before the calender. This exemplifying embodiment shown in FIG. 8 can be combined, for example, with the applications shown in FIGS. 2 and 3, thereby providing an arrangement in which the web can also be doctored from the lowermost or the second lowermost roll of the calender into the pulper  65 .  
     [0055] The application shown in FIG. 9 mainly corresponds to the one shown in FIG. 6 but the transfer from one drying unit to the other is closed. In the application shown in FIG. 9, the transfer from the dryer section  40  through the sizing/coating unit  80  to the calender  60  is closed, and full-width threading is also possible in it. The web W is passed from the transfer fabric  50  through a closed nip  92 , which uses not a high load but a light load, and here the web is transferred from the transfer wire  50  onto a belt  95 . The rolls of the nip may be normal wire guide rolls or they may be specially designed in their structure to withstand the special demands placed by nip operation. The transfer fabric  95  is most appropriately a belt which is impervious to air, gas and liquid and which runs through the nip of the sizing/coating unit  80 . The web is transferred from the transfer belt  95  by means of a transfer suction roll  97  onto a permeable transfer fabric  82 . In this application, one size applicator beam  93 A has been moved into connection with the belt  95  before the transfer nip  92  and a size/coating is applied there to the surface of the belt to form a suitable film. The web is passed from a suction roll  96  onto the drying wire  41 ′ of an after-dryer unit  40 ′.  
     [0056] In the applications shown in the figures in which one large-diameter roll is used in impingement drying to dry the web substantially dry, the diameter of the roll is typically over 10 m. In the applications in which several impingement drying groups are used in succession, the diameter of the large-diameter roll is typically 3-6 m. The large-diameter roll can comprise sectors acting by vacuums of different magnitude, and there may be two or more such sectors, or the same vacuum can act on the circumference of the roll over the entire length of the circumference. Of course, the roll type in the different embodiments of the invention can differ from the examples shown in the figures.  
     [0057] Above, the invention has been described only with reference to some of its advantageous exemplifying embodiments, to the details of which the invention is, however, not by any means meant to be narrowly confined.