Apparatus for drying a web

Abstract: A dryer apparatus for drying alternate sides of a web of paper comprises first and second single tier dryer sections (16,22). The first single tier dryer section (16) includes drying cylinders for drying one side of the web, and the second section (22) includes drying cylinders for drying an opposite side of the web. Means for transferring the web from said first single tier to said second single tier dryer sections are adapted to transfer a web in an open draw defined between first and second gaps. Said first gap is a divergent gap which is defined between the surface of a last drying cylinder (63) of said first single tier of drying cylinders and a first felt (72) and said second gap is a convergent gap which is defined between the surface of a first drying cylinder (94) of said second single tier of drying cylinders and a second felt (110). The divergent gap is located opposite to the convergent gap.

Description: This invention relates to a dryer apparatus for drying both sides of a web of paper emerging from a press section of a paper making machine, the dryer apparatus being of the kind defined in the preamble of claim 1. With the ever increasing operational speed of paper making machines a serious problem has existed in that there is a tendency for the paper web or sheet to flutter as the sheet progresses through the dryer section. Such sheet flutter has been minimized by the use of single felting configurations in which the web and felt run jointly between respective top and bottom cylinders. However, the single felt configuration, although reducing the aforementioned problem of sheet flutter, introduces several disadvantages. Included amongst these disadvantages are, first, the heat transfer from the bottom cylinders is substantially reduced because the wet web is no longer in direct contact with the bottom cylinders, the felt being interposed between the web and the drying surface of the respective bottom cylinder. Second, the web has a tendency to separate from the felt as the web travels towards and around and then away from the bottom cylinders. Third, the initial threading of the web is not particularly easy. A partial solution to the aforementioned problems of the single felt configuration has been provided by the application of the so-called Bel Run dryer section. Bel Run is a registered trademark of Beloit Corporation. With the Bel Run system, the bottom ineffective dryers are replaced by vacuum rolls which positively convey the web from one cylinder to the next. Recent installations of this type of dryer section have shown that the Bel Run concept can be extended to include a large number of dryers without any adverse effect on the web runability. The web runability is not affected because the vacuum rolls are capable of conveying the web along the felt supported spans without the need for sheet tension or section draw points. With the implementation of the Bel Run dryer section there exists a tendency to have a generation of stresses which develop in the web as the web dries. Such stresses impart a tendency for the dried paper to curl. Such adverse curling effect can be minimized or eliminated by drying the web from both sides, but two sided drying requires a transfer point in which the web is transferred from one felt to another felt. A dryer apparatus of the kind defined in the preamble of claim 1 is disclosed in Fig. 10 and the corresponding description on page 628 of an article by J. Linderot: "10 Jahre Erfahrung mit Geschlossener Bahnführung in der Trockenpartie", published in "Wochenblatt für Papierfabrikation", No. 16 of 1986, pages 623-628. The known dryer apparatus includes a first dryer section ("erste Trockengruppe, Bel-Run") which is a single-tier dryer section having a plurality of drying cylinders arranged in a horizontally extending single-tier, and a plurality of vacuum rolls each of which is disposed in spaced close proximity to and between adjacent drying cylinders. The vacuum rolls are lesser in diameter than the drying cylinders of the first dryer section and are disposed below the drying cylinders of the first dryer section. A second dryer section is disposed horizontally adjacent to and downstream of the first dryer section. The second dryer section constituting the fourth group of drying cylinders is of the type having two rows of drying cylinders arranged one above the other, and a single felt extending alternately around a top drying cylinder and a bottom drying cylinder, with the felt being sandwiched between the web and the surface of the bottom drying cylinders. At the top drying cylinders of the second dryer section of the known apparatus, the web is sandwiched between the felt and the surface of the top drying cylinders. The known dryer apparatus further includes a third and a fourth dryer section constituting a fifth and a sixth group of drying cylinders respectively. The third and fourth dryer sections each are of the type having top and bottom drying cylinders and top and bottom felts. In such a dryer section type the web is transferred respectively from each top cylinder to a respective one of the bottom cylinders and from each bottom cylinder to a respective one of the top cylinders in an open draw. In operation of the known dryer apparatus, the web is transferred without open draw from the last dryer of the first dryer section to the first dryer of the second dryer section by means of the single felt associated with the second dryer section. The single felt associated with the second dryer section supports the web at one side as it travels from the last drying cylinder of the first dryer section to the first drying cylinder of the second dryer section. The transfer of a web without open draw between adjacent dryer sections makes it difficult for an operator to inspect the web during its movement from one dryer section to the next dryer section. Furthermore, a transfer of the web without open draw impedes broke removal. Since the first dryer section of the known apparatus is a single-tier dryer section, the web is dried from only one side as it is passed through the first dryer section. In the second, third and fourth dryer sections the web is dried from both sides as it passes alternately around sequential top and bottom cylinders. However, the heat transfer from the bottom cylinders of the second dryer section to the web is less efficient than the heat transfer from the top cylinders of the second dryer section to the web because the felt is interposed between the web and the bottom cylinders whereas the top cylinders of the second dryer section are in direct contact with the web. During drying the web normally shrinks both in the machine direction and in the cross machine direction as it travels from the last drying cylinder of the first dryer section to the first drying cylinder of the second dryer section and around the bottom cylinders of the second dryer section of the known apparatus. The dried paper tends to curl if it is allowed to shrink during drying and also if the two sides of the web are dried unevenly. In dryer sections having top and bottom cylinders, uneven drying of both sides of the web can be avoided by suitably adjusting the steam pressures of the top and bottom drying cylinders separately. However, the web is permitted to shrink in the known apparatus whenever it is not held between the felt and the surface of a drying cylinder. FR-A-2 386 638 discloses a dryer apparatus comprising first and second dryer sections each having two rows of heated drying cylinders disposed one above the other and a single felt wrapped around the top and bottom cylinders in a serpentine configuration. The web is transferred with open draw from the first dryer section to the second dryer section. The arrangement is such that that side of the web which is in direct heat transfer contact with the drying cylinders is reversed as the web is transferred from the first dryer section to the second dryer section. The bottom drying cylinders of the first dryer section and the top drying cylinders of the second dryer section are grooved. The grooves defined in the surface of these drying cylinders are evacuated by means of external vacuum boxes disposed in the pockets between adjacent drying cylinders. The felt supported draws between top and bottom cylinders of each section are large, thereby permitting the web to shrink as it is moved through these felt supported draws. Shrinkage of the web during drying, however, is one cause of curl of the dried paper as stated above. An object of the invention is to modify the dryer apparatus of the kind defined in the preamble of claim 1 so that the web can be readily inspected during its transfer from the single-tier dryer section to the further dryer section. Moreover, the removal of broke is to be facilitated. Furthermore, the tendency of the dried paper to curl is to be minimized. The object of the invention is achieved by the implementation of the features recited in the characterizing portion of claim 1. Another object of the present invention is the provision of an apparatus for drying a web of paper in which blow boxes would be redundant. Another object of the present invention is the provision of an apparatus for drying a web of paper in which ventilation of the pockets defined by the cylinders and the vacuum rolls is improved, thereby improving the drying rate of the web. Another object of the present invention is the provision of an apparatus for drying a web of paper in which gear case leaks are inhibited and removal of broke is facilitated. Another object of the present invention is the provision of an apparatus for drying a web of paper in which fewer steamfits are required and none of the dryers is redundant, thereby reducing the blow through rate. Another object of the present invention is the provision of an apparatus for drying a web of paper in which the frame is symmetrical and in which the base frame is subjected to equal loading forces, thereby resulting in a sturdy low-profile frame which reduces vibration and its attendant noise level. Another object of the present invention is the provision of an apparatus for drying a web of paper in which the power required to drive the cylinders is reduced and due to the layout and configuration of the dryers, such arrangement lends itself to the provision of a low-profile hood. Another object of the present invention is the provision of an apparatus for drying a web of paper in which runability of the drying apparatus is increased and in which doctors can be applied to each dryer. Another object of the present invention is the provision of an apparatus for drying a web in which open access to the dryers and vacuum rolls is provided and a supply of air can be fed uniformly through each of the vacuum rolls. Another object of the present invention is the provision of an apparatus for drying a web of paper in which hoods are provided over and adjacent the vacuum rolls for handling the humid exhaust and possibly eliminating the need for large scale exhaust hood construction. Another object of the present invention is the provision of an apparatus for drying a web of paper in which such vacuum roll hoods can be provided for profiling the web by removing exhaust air from selected transfer sections of these hoods. Another object of the present invention is the provision of an apparatus for drying a web ranging from tissue to fine paper. Another object of the present invention is the provision of an apparatus for drying a web of paper in which the felt wrap is increased relative to the felt wrap of a two felt type drying section, particularly by decreasing the space between adjacent dryers. Another object of the present invention is the provision of an apparatus for drying a web of paper in which the humidity is decreased by eliminating the closed pockets associated with a typical two felt type drying section. Another object of the present invention is the provision of an apparatus for drying a web of paper in which the apparatus is no longer than a conventional dryer section but requires less equipment. Another object of the present invention is the provision of an apparatus for drying a web of paper in which the felt supported draw is reduced to a minimum. Another object of the present invention is the provision of an apparatus for drying a web of paper in which sheet control is provided by the direct application of vacuum. Another object of the present invention is the provision of an apparatus for drying a web of paper in which there is no need for residual sheet tension to hold the sheet against the felt since the sheet is entirely supported by vacuum as it wraps the transfer roll. Another object of the present invention which is a less obvious factor relative to the runability of the dryer section is the uniformity of dryer surface speeds. Such uniformity is obtained because the dryers are driven by the felt instead of by a gear train. Dryers which are geared together are forced to run at equal rotational speeds. In the case of dryers which have slightly different diameters, perhaps due to manufacturing tolerances or differences in steam pressure, such differences result in unequal dryer surface speeds. These unequal surface speeds not only increase the drive load but also cause problems with sheet runability. With the open symmetrical framing according to the present invention, broke removal, dryer access, and dryer visibility are greatly improved. Additionally, although not a requirement of the present invention, each of the dryers can be easily fitted with a doctor, such doctors being unloaded automatically with air cylinders if required. The apparatus according to the present invention permits a significant reduction in the amount of paper machinery which is required to meet the design production. In addition to reducing the number of dryers, felt rolls and guides, there is also a corresponding reduction in the number of steamfits, the elimination of blow boxes and pocket ventilation ducts. Also, the present invention enables simplification of the dryer framing. With the application of the "Silent Drive" dryer system (Silent Drive is a registered trademark of Beloit Corporation) and additionally with the low profile afforded by the framing layout of apparatus according to the present invention, dryer section noise and vibration will be reduced to a minimum. Furthermore, smaller drive motors can be installed due to the fact that the section inertia is reduced in view of the elimination of the bottom dryers utilized in a typical Uno-Run system. Additionally, the dryer hood can have a low profile construction, and hood door lifts can be installed on the back as well as the front of the machine. Another object of the present invention is the provision of an apparatus for drying a web of paper in which the energy efficiency of the apparatus is improved. More specifically, the dryer section of the present invention provides improved energy efficiency in the following three areas. First, the drive load is reduced by having fewer dryers and less steamfit drag. Second, the amount of blowthrough steam is reduced by minimizing the number of dryers. Third, the large blowthrough quantities associated with the bottom dryers of Uno-Run type sections are entirely eliminated. Another object of the present invention is the provision of an apparatus for drying a web of paper in which the quality of the sheet is improved. More specifically, the dryer section according to the present invention has the capability of influencing the sheet properties as follows. First, the tensile strength and stretch of the web in the machine direction is improved. Second, the tensile strength and stretch of the web in the cross machine direction is improved. Third, the tendency for the sheet to curl is reduced and fourth, the tendency to generate edge cockles is reduced. Once the sheet leaves the press section, the machine direction tensile and stretch are influenced primarily by the press section draw and somewhat less by the draw between dryer sections. In conventional drying sections, these dryer draws are usually set as low as possible but the minimum draw is dictated by runability and sheet control. However, in the drying section according to the present invention, there is no minimum draw requirement for runability. Nevertheless, the machine direction properties can still be influenced in the usual way by pulling a draw between sections if such is deemed desirable. In a somewhat similar manner, the cross machine direction tensile and stretch are influenced by the cross machine direction sheet restraint. In an open draw, there is no restraint, so the sheet freely shrinks (although this shrinkage is greatest at the edges). In operation of a Uno-Run type drying section, there is a degree of web restraint as evidenced by the increase in trim and the decrease in edge cockles. In the drying section according to the present invention, the sheet restraint is more positive than that provided by a Uno-Run system and this further reduces any tendency for edge cockles to develop. With the improved restraint provided by the present invention, a slight increase in cross machine direction tensile and a decrease in cross machine direction stretch is evident. The decrease in cross machine direction stretch is most pronounced at the edges where the sheet normally has the least restraint. Accordingly, the net effect according to the present invention, will be a sheet with more uniform properties in the cross machine direction. The propensity to curl is caused by three factors as follows. First, fiber orientation, second fines and filler (bonding) distribution, and third, residual fiber stress. The dryer section influences only the fiber stress. Curl is normally controlled by adjusting the drying from each side of the sheet by separate control of the top and bottom dryer steam pressures. Accordingly, in the drying section according to the present invention, such control is provided by adjusting the steam pressures in subsequent sections. Another particularly important object of the present invention is the provision of an apparatus for drying fine paper grades where directionality is important. More particularly, restrained drying of the web is an important feature of the present invention in that it will not permit the edges of the sheet to shrink more than the center portion of the sheet. The key to restraining the sheet while it is not held between the felt and the dryer drum is the vacuum in the transfer, or turning roll, below adjacent drums. The sheet is restrained by the application of a vacuum within the range of 1.49 to 2.49 kPa (6-10 inches wc). Other objects and advantages of the present invention will be apparent to those skilled in the art by a consideration of the following detailed description taken in conjunction with the annexed drawings. The present invention relates to a single tier drying section for drying a web. The drying section includes a dryer and a felt guided about the dryer such that the web is disposed between the dryer and the felt for drying a first side of the web. A further dryer is disposed downstream relative to the dryer and a further felt is guided about the further dryer such that the web is disposed between the further dryer and the further felt for drying a second side of the web. A dryer transfer means transfers the web from the dryer to the further dryer. Preferably, the single tier drying section extends from a press section to a calender section and includes a multiplicity of single tier subsections. The arrangement is such that alternate sides of the web are sequentially dried as the web progresses through the subsections and each of the subsections is disposed at a different height relative to each other with preferably every other subsection disposed at the same height relative to each other. The dryer transfer means includes means for transferring the web with open draw from the dryer to the further dryer. Additionally, the present invention relates to an apparatus for drying a web of paper emerging from the press section of a papermaking machine. The apparatus includes a first dryer section means for initiating the drying of the first side of the web. The first transfer means transfers the web from the press section to the first dryer section means. A second dryer section means is disposed downstream relative to the first dryer section means for initiating the drying of the second side of the web. The second side of the web is opposite to the first side of the web. A first dryer transfer means transfers the web between the first and the second dryer section means such that the drying of both sides of the web is permitted. More particularly, the first dryer section means also includes a first dryer section for initiating the drying of the first side of the web and a second section disposed downstream relative to the first dryer section for continuing the drying of the first side of the web. A second dryer transfer means transfers the web without open draw between the first and the second dryer sections. The first dryer section includes a first plurality of dryers and a first plurality of vacuum rolls with each of the vacuum rolls being disposed adjacent to a corresponding dryer of the first plurality of dryers such that the web extends alternately past each vacuum roll and a dryer in serpentine configuration. The first felt extends around the first plurality of dryers and the first plurality of vacuum rolls in close conformity with the web. The second dryer section includes a second plurality of dryers and a second plurality of vacuum rolls with each vacuum roll of the second plurality of vacuum rolls being disposed adjacent to a corresponding dryer of the second plurality of dryers, such that the web extends alternately past each vacuum roll and dryer in serpentine configuration. A second felt extends around the second plurality of dryers and vacuum rolls respectively such that the second felt is disposed in close conformity with the web. The second felt and an unfelted portion of a downstream dryer of the first dryer section defines a first pick-up section for transferring the web from the unfelted portion onto the second felt so that the web is transferred without open draw from the first dryer section to the second dryer section. Each of the vacuum rolls of the first and the second dryer sections is disposed in spaced close proximity to its adjacent corresponding dryer such that the felt draw between each of the vacuum rolls and the corresponding dryer is minimal, thereby inhibiting any tendency of the web to flutter relative to the supporting felts. The apparatus also includes a base frame for rotatably supporting the first and the second plurality of dryers such that the axes of the first and the second plurality of dryers are disposed in a first plane. The frame also rotatably supports the first and the second plurality of vacuum rolls such that the axes of the first and second plurality of vacuum rolls are disposed in a second plane with the first plane being disposed above the second plane. An upstream vacuum roll of the second plurality of vacuum rolls is disposed in close proximity to the unfelted portion of the downstream dryer of the first dryer section. A first felt roll is rotatably supported by the base frame for guiding the second felt past and in conformity with the unfelted portion of the downstream dryer and thereafter around the upstream vacuum roll of the second dryer section such that the web is transferred from the unfelted portion to the second felt without open draw. The first transfer means for transferring the web from the press section to the first dryer section means also includes a lead in roll which is disposed in spaced close proximity relative to the press section. The first felt extends around the lead in roll for transferring the web from the press section to the first dryer section means. A guide roll is disposed between the lead in roll and the first dryer section means for assisting the transfer of the web from the press section towards the first dryer section means. A transfer felt extends around the guide roll such that the transfer felt and the first felt define therebetween a transfer section for transferring the web from the press section towards the first dryer section means. The first transfer means also includes an upstream vacuum roll of the first dryer section means. This upstream vacuum roll cooperates with the first felt and the transfer felt such that the transfer section extends from the guide roll to the upstream vacuum roll so that the web emerging from the transfer section is guided around the upstream vacuum roll into the first dryer section means. The second dryer section means also includes a third plurality of dryers with each of the dryers of this third plurality of dryers being disposed downstream relative to the first dryer section means. A third plurality of vacuum rolls are each disposed in spaced close proximity relative to a corresponding dryer of the third plurality of dryers such that the web extends alternately past each vacuum roll and dryer of the second dryer section means in serpentine configuration. The third plurality of dryers and vacuum rolls are rotatably secured to the base frame such that the third plurality of dryers are disposed in a third plane and the third plurality of vacuum rolls are disposed in a fourth plane with the fourth plane being disposed above the third plane. A third felt extends past the third plurality of dryers and vacuum rolls such that the third felt supports the web through the second dryer section means with the second side of the web being urged by the third felt into close conformity with each dryer of the third plurality of dryers. Subsequent dryer section means are provided such that the third, fourth and fifth dryer transfer means each permits the transfer of the web between adjacent dryer section means with an alternate reversing of the web such that the first and second side of the web are alternately dried as the web extends through the apparatus and past consecutive dryer section means. Although the following detailed description exemplifies a single tier drying section and a particular embodiment of the present invention, it should be understood by those skilled in the art that the present invention is not limited to such an arrangement. Rather the present invention as defined by the appending claims invisages a multitude of variations thereof, including a single felt extending around the dryers of the first and second dryer sections rather than using a first and second felt as shown in the drawings. In the drawings: Figure 1 is a side elevational view of a single tier drying section extending from a press section to a calender section, said side elevational view showing the press section, the first transfer means, a multiplicity of single tier subsections, the calender section and a first, second, third, fourth and fifth dryer transfer means for transferring the web without open draw between consecutive single tier subsections; Figure 2 is an enlarged fragmentary view of Figure 1 showing the press section, and more particularly, the first transfer means for transferring the web from the press section to the first dryer section; Figure 3 is an enlarged fragmentary view of Figure 1 showing the first dryer section means, including the first dryer section and the second dryer section; Figure 4 is an enlarged fragmentary view of Figure 1 showing the second dryer section means; Figure 5 is an enlarged fragmentary view of the third dryer section means; Figure 6 is an enlarged fragmentary view of Figure 1 showing the fourth dryer section means; Figure 7 is an enlarged fragmentary view of Figure 1 showing the fifth dryer section means; Figure 8 is an enlarged fragmentary view of Fig 1 showing two of the vacuum rolls between adjacent dryers of the first dryer section; and Figure 9 is a side elevational view of a dryer transfer means according to the present invention showing an open draw transfer of the web from the last drying cylinder of the first dryer section means to the first drying cylinder of the second dryer section means. Figure 1 is a side elevational view showing the apparatus generally designated 10 for drying a web 12 of paper emerging from a press section, generally designated 14 of a paper making machine. The apparatus 10 includes a first dryer section means, generally designated 16 for initiating the drying of a first side 18 of the web 12. A first transfer means generally designated 20 transfers the web 12 from the press section 14 to the first dryer section means 16. A second dryer section means generally designated 22 is disposed downstream relative to the first dryer section means 16. This second dryer section means 22 initiates the drying of a second side 24 of the web 12. The second side 24 of the web 12 being opposite to the first side 18 thereof. A first dryer transfer means generally designated 25 transfers the web 12 without open draw between the first and second dryer section means 16 and 22 respectively. In contrast to the present invention, the first dryer transfer means 25 transfers the web 12 without open draw between the first and second dryer section means 16 and 22, whereas the dryer transfer means 116A shown in Fig. 9 transfers the web with open draw between the first and second dryer section means 16 and 22 in accordance with the invention. Figure 2 shows in more detail the first transfer means 20 and will be described in more detail hereinafter. Figure 3 shows in detail the first dryer section means 16. This first dryer section means 16 includes a first dryer section generally designated 26 for initiating the drying of the first side 18 of the web 12. A second dryer section generally designated 28 is disposed downstream realtive to the first dryer section 26 for continuing the drying of the first side 18 of the web 12. A second dryer transfer means generally designated 30 transfers the web 12 without open draw between the first and the second dryer sections 26 and 28 respectively. More particularly, with reference to Figure 3, the first dryer section also includes a first plurality of dryers 32, 34, 36, 38, 40 and 42 respectively. The first dryer section 26 also includes a first plurality of vacuum rolls 46, 48, 50, 52 and 54 respectively. Each of the first plurality of vacuum rolls 46 to 54 is disposed adjacent to a corresponding dryer of the first plurality of dryers 32 to 42 such that the web 12 extends alternately past each vacuum roll 46 to 54 and dryer 32 to 42 in serpentine configuration. A first felt 56 extends around the first plurality of dryers 32 to 42 and the first plurality of vacuum rolls 46 to 54 in close conformity with the web 12. The second dryer section 28 also includes a second plurality of dryers 58, 59, 60, 61, 62 and 63. The second dryer section 28 also includes a second plurality of vacuum rolls 64, 65, 66, 67, 68 and 69. Each of the vacuum rolls 64 to 69 is disposed adjacent to a corresponding dryer of the second plurality of dryers 58 to 63 such that the web 12 extends alternately past each vacuum roll 64 to 69 and dryer 58 to 63 in serpentine configuration. A second felt 72 extends around the second plurality of dryers 58 to 63 and the vacuum rolls 64 to 69 respectively such that the second felt 72 is disposed in close conformity with the web 12. The second felt 72 and an unfelted portion 74 of the downstream dryer 42 of said first dryers 32 to 42 defines a first pick-up section generally designated 76 for transferring the web 12 from the unfelted portion 74 onto the second felt 72 so that the web 12 is transferred without draw from the first dryer section 26 to the second dryer section 28. Each of the vacuum rolls of the first and the second dryer sections 26 and 28 is disposed in spaced close proximity to its adjacent corresponding dryer such that the felt draw between each of the vacuum rolls and its corresponding dryer is minimal, thereby inhibiting any tendency of the web to flutter relative to the supporting felts 56 and 72 respectively. As shown in Figure 3 the apparatus 10 also includes a base frame 78 for rotatably supporting both the first and the second plurality of dryers such that the axes of the first and second plurality of dryers are disposed in a first plane 80 as shown in Figure 3. Additionally, the frame 78 rotatably supports the first and second plurality of vacuum rolls such that the axes of the first and the second plurality of vacuum rolls are disposed in a second plane 82 shown in Figure 3. The first plane 80 is disposed above the second plane 82 as shown in Figure 3. As shown in Figure 3 the apparatus 10 includes an upstream vacuum roll 64 of the second plurality of vacuum rolls and this vacuum roll 64 is disposed in spaced close proximity to the unfelted portion 74 of the downstream dryer 42 of the first dryer section 26. A first felt roll 84 is rotatably supported by the base frame 78 for guiding the second felt 72 past and in conformity with the unfelted portion 74 of the downstream dryer 42 and thereafter around the upstream vacuum roll 64 of the second dryer section 28 such that the web 12 is transferred from the unfelted portion 74 to the second felt 72 without open draw. As shown in Figure 2 referred to hereinbefore the apparatus 10 includes a first transfer means 20 for transferring the web 12 from the press section 14 to the first dryer section means 16. This first transfer means 20 further includes a lead in roll 86 which is disposed in spaced close proximity relative to the press section 14. The first felt 56 extends around this lead in roll 86 for transferring the web 12 from the press section 14 to the first dryer section means 16. A guide roll 88 is disposed between the lead in roll 86 and the first dryer section means 16 for assisting the transfer of the web 12 from the press section 14 towards the first dryer section means 16. A transfer felt 90 extends around the guide roll 88 such that the transfer felt 90 and the first felt 56 define therebetween a transfer section 92 for transferring the web 12 from the press section 14 toward the first dryer section means 16. With further reference to Figure 2, the first transfer means 20 further includes an upstream vacuum roll 44 of said first dryer section means 16. The upstream vacuum roll 44 cooperates with the first felt 56 and the transfer felt 90 such that the transfer section 92 extends from the guide roll 88 to the upstream vacuum roll 44 so that the web 12 emerging from the transfer section 92 is guided around the upstream vacuum roll 44 into the first dryer section means 16. With reference to Figure 4 the second dryer section means 22 also includes a third plurality of dryers 94, 95, 96, 97, 98 and 99. The third plurality of dryers is disposed downstream relative to the first dryer section means 16. A third plurality of vacuum rolls 101, 102, 103, 104 and 105 each are disposed in spaced close proximity relative to a corresponding dryer of the third plurality of dryers such that the web 12 extends alternately past each vacuum roll and dryer of the second dryer section means 22 in serpentine configuration. As shown in Figure 4 the base frame 78 rotatably supports each of the dryers of the third plurality of dryers such that the axes of the dryers are disposed in the third plane 107. The base frame 78 also rotatably supports each of the vacuum rolls of the third plurality of vacuum rolls 101 to 105 such that the axis of each of the vacuum rolls of the third plurality of vacuum rolls 101 to 105 is disposed in a fourth plane 108 with the fourth plane 108 being disposed above the third plane 107. A third felt 110 extends past the third plurality of dryers 94 to 99 and vacuum rolls 101 to 105 such that the third felt 110 supports the web 12 through the second dryer section means 22 with the second side 24 of the web 12 being urged by the third felt 110 into close conformity with each dryer of the third plurality of dryers 94 to 99. As shown in Figure 4 the first dryer transfer means includes a downstream vacuum roll 70 of the first dryer section means 16 and a downstream felt roll 112 of the first dryer section 16. The second felt 72 of the first dryer section means 16 extends between the downstream vacuum roll 70 and the downstream felt roll 112. The second felt 72 supports the web 12 such that the web is conveyed and disposed between the second felt 72 and the second dryer section means 22. The first dryer transfer means also includes an upstream vacuum roll 100 and and upstream felt roll 114. The third felt 110 extends between the upstream felt roll 114 and the upstream vacuum roll 100 of the second dryer section means 22 such that the third felt 110 and the second felt 72 define therebetween a first dryer transfer means section 116 for transferring the web without open draw from the second to the third felts 72 and 110 respectively. The third felt 110 presses against the web such that the second side 24 of the web is pressed into close conformity with each dryer of the third plurality of dryers 94 to 99 such that the second side 24 of the web 12 is dried. Figures 5, 6, and 7 respectively show third, fourth, and fifth dryer section means 118, 120 and 122 and third, fourth and fifth dryer transfer means 124, 126 and 128 for transferring and reversing the web as the web progresses through the drying apparatus. The third, fourth and fifth dryer transfer means 124, 126 and 128 permit the transfer of the web between the respective dryer section means 22, 118, 120 and 122 without open draw and with an alternate reversing of the web such that the first and second sides of the web are alternately dried as the web extends through the apparatus and past consecutive dryer section means 22, 118, 120 and 122. Figure 8 shows the details of two of the vacuum rolls 46, 48 in which pressure seals 130 may be moved from the position shown with reference to the vacuum roll 46 to that shown relative to vacuum roll 48 for counteracting the tendency of the web 12 to part from the felt 56. The single tier drying section 16 extends from the press section 14 to a calender section 130 or to a size press (not shown) or throughout the entire dryer section. The single tier drying section 16 includes a multiplicity of single tier subsections 16,22,118,120 and 122 and a plurality of dryer transfer means 25,124,126 and 128 each dryer transfer means 25,124,126 and 128 being disposed between adjacent subsections such that as the web progresses through consecutive subsections 16,22,118,120 and 122 alternate sides 18 and 24 of the web 12 are sequentially dried. Additionally, the subsections 16,22,118,120 and 122 are disposed at different heights relative to each other and preferably every other subsection 16,118 and 122 and every other subsection 22 and 120, respectively are disposed at the same height relative to each other. In the embodiment shown in Figure 9, the transfer means 116A includes means 100A and 70A for transferring the web with open draw from the dryer 63A to a further dryer 94A. In operation of the apparatus, the web is transferred from the press section 14 to the first dryer section means 16. Drying of the first side 18 of the web 12 is initiated during passage of the web through the first dryer section means 16. The web 12 is transferred between the first dryer section means 16 and the downstream second dryer section means 22 with the web transfer being such that the web 12 is reversed so that drying of the second side 24 of the web 12 is initiated during passage of the web 12 through the second dryer section means 22. As shown in Figure 9 and in accordance with the invention, the web 12 is transferred between the first and second dryer section means 16 and 22 with open draw. In operation of the apparatus the web is also transferred between subsequent dryer section means such that the first and second sides 18 and 24 of the web 12 are alternately exposed to the drying effect of the subsequent dryer section means in sequence.

Claims: A dryer apparatus for drying both sides (18, 24) of a web (12) of paper emerging from a press section (14) of a paper making machine, said apparatus comprising: a single-tier dryer section (16) including: a single tier of steam-heated drying cylinders (32-42; 58-63) for drying one side (18) of the web (12), said one side (18) coming into direct surface contact with each drying cylinder (32-42; 58-63) of said single-tier dryer section (16); a plurality of vacuum rolls (46-54; 64-69), each vacuum roll of said plurality of vacuum rolls (46-54; 64-69) being lesser in diameter than, and in close proximity to, and disposed between adjacent drying cylinders of said single tier of drying cylinders (32-42; 58-63), said plurality of vacuum rolls (46-54; 64-69) being connected to a source of partial vacuum; a dryer felt (56; 72) extending alternately around said single tier of drying cylinders (32-42; 58-63) and said plurality of vacuum rolls (46-54; 64-69) in close conformity with the web (12); a further dryer section (22) disposed substantially horizontally adjacent to and downstream of said single-tier dryer section (16) and including: a plurality of steam-heated drying cylinders (94-99) for initiating the drying of the opposite side (24) of the web (12); a further dryer felt (110) extending around said plurality of drying cylinders (94-99) in close conformity with the web (12); and dryer transfer means (116A) for transferring the web (12) from said single-tier dryer section (16) to said further dryer section (22), characterized in that all drying cylinders (94-99) of said further dryer section (22) are disposed in a single tier; said further dryer section (22) includes a further plurality of vacuum rolls (101-105) which are connected to a source of partial vacuum, each vacuum roll (101-105) of said further plurality of vaccum rolls (101-105) being lesser in diameter than, and in close proximity to, and disposed between adjacent drying cylinders (94-99) of said further dryer section (22); said further dryer felt (110) extends alternately around a drying cylinder (94-99) and an adjacent vacuum roll (101-105) of said further dryer section (22) such that the opposite side (24) of the web (12) comes into direct surface contact with each drying cylinder (94-99) of said further dryer section (22); said dryer transfer means (116A) includes means (100A, 70A) for transferring the web (12) with open draw from the last drying cylinder (63) of said single-tier dryer section (16) to the first drying cylinder (94) of said further dryer section (22); a vacuum in the range of 1.49 to 2.49 kPa (6-10 inches WC) is applied in the vacuum rolls (46-54; 64-69; 101-105) of said single-tier dryer section (16) and said further dryer section (22) so as to restrain the web (12) against machine and cross-machine directional shrinkage during movement of the web (12) through said dryer sections (16, 22); and steam pressures supplied to the drying cylinders of said single tier dryer section (16) and said further dryer section (22) are adjustable separately in respect of each dryer section (16, 22) so as to permit additional control of curl of the web (12). A dryer apparatus as set forth in claim 1, wherein each vaccum roll of said plurality of vacuum rolls (46-54; 64-69) is disposed below adjacent drying cylinders of said single tier of drying cylinders (32-42; 58-63); and each vacuum roll of said further plurality of vacuum rolls (101-105) is disposed above adjacent drying cylinders (94-99) of said further dryer section (22). A dryer apparatus as set forth in anyone of the preceding claims, wherein said open draw is defined between first and second gaps, said first gap being a divergent gap which is defined between the surface of said last drying cylinder (63) of said single tier of drying cylinders (32-42; 58-63) and said dryer felt (72), said second gap being a convergent gap which is defined between the surface of said first drying cylinder (94) of said further dryer section (22) and said further dryer felt (110), said divergent gap being located opposite to said convergent gap. A dryer apparatus as set forth in claim 3, wherein said divergent gap is located above said convergent gap.

Inventors: WEDEL GREGORY L, WEDEL, GREGORY L.
Applicants: BELOIT TECHNOLOGIES INC, BELOIT TECHNOLOGIES, INC.
Application year: 1988
Main classification: D21F5
IPC codes: D21F5, D21G9