Apparatus for drying a web

Abstract: An apparatus for drying a web (12) comprises first dryer section means (16) for drying the web from one side (18) only, and second dryer section means (22) disposed downstream relative to the first dryer section means (16) for continuing the drying of the web (12). To permit the apparatus to be threaded without ropes it is a single tier drying section which extends from a press section (14) to a calender section (230). Each dryer section means (16, 22) includes a plurality of vacuum rolls (64 - 70; 100 - 106) each of which is disposed in spaced close proximity to a respective one of the dryers (58 - 63; 94 -99) of each dryer section means (22). Dryer transfer means (25) for transferring the web (12) from the last dryer (63) of the first dryer section means (16) to the first dryer (94) of the second dryer section means (22) include a joint run of a felt (72) and a further felt (110) such that the web (12) is disposed between said felt (72) and said further felt (110) during passage through said joint run, an upstream vacuum roll (100) of said second dryer section means (22), and a downstream vacuum roll (70) of said first dryer section means (16), said downstream vacuum roll (70) being disposed upstream relative to said joint run.

Description: This invention relates to an apparatus for and a method of drying a web of paper emerging from a press section of a papermaking machine. With the ever increasing operational speed of papermaking 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 is particularly evident when the sheet is transferred between successive sections of the dryer section as the web is transferred between these adjacent sections in an open draw. 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 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 configurations 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. Modern paper drying machines are contemplated in which web speeds of 10,000 or more feet per minute (3048 m/min) are invisaged. Consequently, the introduction of open draws would lead to serious problems of sheet flutter and numerous web breakages. The present invention seeks to overcome the aforementioned inadequacies of the prior art apparatus and to provide a drying apparatus which contributes a significant and non-obvious contribution to the paper drying art. In an article published in WOCHENBLATT FUR PAPIERFABRIKATION No. 16 of 1986, J. Linderot: "10 Jahre Erfahrung mit Geschlossener Bahnführung in der Trockenpartie", pages 623-628, reference is made, on page 628, to a drying apparatus having press-to-dryer transfer means and a substantially horizontally extending drying section which includes three successive, substantially horizontally extending BEL RUN single-tier dryer sections and a fourth, single-felted two-tier dryer section disposed downstream relative to the BEL RUN sections. Each BEL RUN section comprises a plurality of top-felted dryers for drying the bottom side of the web and a plurality of vacuum rolls each being disposed below and between and in spaced close proximity to adjacent dryers. The fourth dryer section has top and bottom dryers and a single felt which is sandwiched between the web and the bottom dryers so that only the top dryers can contact the web. A two-tier two-felt section for continuing the drying process by drying the web directly from alternate sides is disposed downstream relative to the fourth dryer section. The web is unsupported as it extends between the top and bottom dryers of the two-tier two-felt section. Therefore, threading of a tail of the web without the aid of threading ropes would be possible only in the BEL RUN section whereas threading ropes are required for threading the tail through the fourth, single-felted two-tier dryer section and the subsequent two-tier two-felt section. Moreover, there is a tendency for the web to separate from the felt in the fourth, single-felted two-tier dryer section and a tendency for the web to flutter in the subsequent two-tier two-felt section. The drying apparatus disclosed in the afore-mentioned article is considered to be the closest prior art. The above article also indicates that, in the future, when operating speeds may be above 1300 m/min, single felting may be necessary in all dryer sections of a drying apparatus, and that for certain paper grades, this may necessitate installing single felting alternately above and below in order to avoid twosidedness. WO-A-88/04206 (not pre-published) of prior European patent application 88901398 discloses an apparatus for and a method of drying a web, said apparatus comprising a series of single-tier dryer sections for drying alternate sides of the web. Transfer of the web between consecutive single-tier dryer sections is effected without open draw, positively and with an alternate reversal of the web. The single-tier dryer sections are arranged only over a part of the entire length of the drying section, said part including the wet end of the drying section. WO-A-82/02937 discloses a drying apparatus which has a two-tier configuration throughout its entire length. The web is supported by felts only until it has attained sufficient strength to be self-supporting. Each of the dryer groups in which the web is supported by felts, is served by a respective single felt. One of the single-felted two-tier dryer groups has the felt return run arranged above the top row of drying cylinders. Another dryer group which is located immediately downstream of said one dryer group has its felt return run arranged below the bottom row of drying cylinders. Therefore, the bottom side of the web is brought in direct contact with the drying cylinders of the top row of drying cylinders of said one dryer group, and its top side is brought in indirect contact with the drying cylinders of the bottom row of drying cylinders whereas, in the other dryer group, the bottom side of the web is brought in indirect contact with the drying cylinders of the top row of drying cylinders and the top side of the web is brought in direct contact with the drying cylinders of the bottom row of drying cylinders. Thus the web is transferred from said one dryer group to said other dryer group with a reversal of the web. Moreover the web is transferred without open draw and positively between said one single-felted two-tier dryer group and said other single-felted two-tier dryer group. An object of the invention is to provide an apparatus for and a method of drying a web of paper emerging from a press section of a papermaking machine such that threading of a tail of the web and the subsequent full width web through the entire drying section can be accomplished without the assistance of threading ropes, the apparatus is capable of operating at extremely high speeds, and any ineffective dryers with which the web is not in direct contact are eliminated, while two-sided drying of the web is maintained. According to one aspect of the invention, there is provided an apparatus for drying a web of paper emerging from a press section of a papermaking machine, said apparatus comprising a substantially horizontally extending drying section which has a single-tier configuration throughout its entire length, said drying section comprising a plurality of successive, substantially horizontally extending single-tier dryer section means, a plurality of felts for supporting the web in said dryer section means, a plurality of dryer-to-dryer transfer means for positively transferring the web between adjacent dryer section means without open draw and with an alternate reversing of the web; each dryer section means comprising a plurality of dryers and a plurality of vacuum rolls each of which is disposed between and in spaced close proximity to adjacent dryers such that the web extends alternately past each vacuum roll and dryer in serpentine configuration, with only one side of the web contacting each dryer of the respective dryer section means. According to another aspect of the invention, there is provided a method of drying a web of paper emerging from a press section of a papermaking machine, the method comprising the steps of: transferring the web from the press section to a first substantially horizontally extending single-tier dryer section means of a substantially horizontally extending drying section having a single-tier configuration throughout its entire length, passing the web through said drying section by passing it successively through said first, a second and subsequent single-tier dryer section means in close conformity with a respective one of a plurality of felts, each dryer section means comprising a plurality of dryers and a plurality of vacuum rolls each of which is disposed between and in spaced close proximity to adjacent dryers such that the web extends alternately past each vacuum roll and dryer in serpentine configuration, with only one side of the web contacting each dryer of the respective dryer section means, and positively transferring the web between adjacent dryer section means without open draw and with an alternate reversing of the web such that the first and second sides of the web are alternately exposed to the drying effect of said first, second and subsequent dryer section means in sequence. Another object of the present invention is the provision of an apparatus for drying a web of paper which completely eliminates the need of open draws. Another object of the present invention is the provision of an apparatus for drying a web of paper in which open draws for the sheet or web is eliminated. 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 of paper which permits automatic threading of a tail and subsequent web therethrough. 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 runnability is improved by eliminating open draws. 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. In a conventional Uno-Run dryer section, a draw is required in order to induce a tension in the sheet to hold the sheet as it wraps the bottom dryer. Although blow boxes can be used to prevent the sheet from leaving the felt, the vacuum produced by these boxes is quite low -- in the order of .05 to .1 inches (1.27 to 2.54 mm) wc (water column). Furthermore, the vacuum does not extend around the bottom dryer and it is generally not sufficient to hold the sheet against centrifugal forces and residual sheet tension is required to hold the sheet against the felt. In an embodiment of the present invention, the transfer roll vacuum is not so limited and typically, 4 inches (101.6 mm) wc is applied to the web which is more than four times the level needed for sheet support. Another object of the present invention which is a less obvious factor relative to the runnability 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 runnability. Another object of the present invention is the provision of an apparatus for drying a web of paper in which threading of the apparatus is simplified. More specifically, in a conventional Uno-Run system, the tail tends to separate from the felt on the bottom dryers and wander in the cross machine direction as it moves down the machine. In an embodiment of the present invention, the vacuum transfer rolls are equipped with internal dampers for concentrating the vacuum in front side threading chambers. When these dampers are closed, the vacuum in the threading chambers is increased from 4 inches (101.6 mm) wc to 10-12 inches (254 - 304.8 mm) wc. Such vacuum holds the tail tightly to the felt and prevents the tail from wandering and stabilizes the entire threading operation. Additionally, since the apparatus according to the present invention has a single-tier configuration through the entire dryer section, the tail can be threaded without the use of ropes. Special air nozzles are located near the edges of each dryer to insure that the tail follows the felt and is transferred by the vacuum rolls. These air nozzles eliminate the need for threading ropes, threading equipment and maintenance. Furthermore, the aforementioned threading arrangement helps to insure safe operation of the apparatus. Also, when the ropes are removed, a wider felt can be used which tends to further stabilize the edges of the sheet on the felt. With the open symmetrical framing in an embodiment of 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, 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 conventional 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 affecting 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 affected 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 runnability and sheet control. However, in the drying section according to the present invention, there is no minimum draw requirement for runnability. Nevertheless, the machine direction properties can still be affected 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 affected 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 typical 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 typical 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 affects 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 may be restrained as stated hereinbefore by application of a vacuum within the range 1-10 inches (25.4 - 254 mm) wc and preferably approximately 4 inches (101.6 mm) 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 provides 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-to dryer transfer means transfers the web from the dryer to the further dryer. More particularly, the dryer-to-dryer transfer means transfers the web without open draw from the dryer to the further dryer. Additionally, the dryer-to-dryer transfer means includes a joint run of the felt and the further felt such that the web is disposed between the felt and the further felt during passage through the joint run. In one embodiment of the present invention, the dryer-to-dryer transfer means further includes vacuum means disposed downstream relative to the joint run for positively maintaining the web in close conformity with the further felt when the felt and further felt diverge relative to each other downstream relative to the joint run. More specifically, the vacuum means is a vacuum roll. Preferably, the single tier drying section extends from a press section to a calender section and includes a multiplicity of single tier subsections and a plurality of dryer-to-dryer transfer means with each dryer-to-dryer transfer means being disposed between adjacent subsections such that as the web progresses through consecutive subsections, alternate sides of the web are dried. 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-to-dryer transfer means also includes air nozzle means for assisting guidance of a tail of the web from the dryer to the further dryer. Additionally, the present invention provides an apparatus for drying a web of paper emerging from the press section of a papermaking machine, which apparatus includes a first dryer section means for initiating the drying of the first side of the web. A press-to-dryer 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-to-dryer transfer means transfers the web without open draw between the first and the second dryer section means such that the first dryer-to-dryer transfer means permits both threading of the web without the assistance of threading ropes and the drying of both sides of the web. 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 dryer section disposed downstream relative to the first dryer section for continuing the drying of the first side of the web. A 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 press-to-dryer 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 press-to-dryer 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. The first dryer-to-dryer transfer means also includes a downstream vacuum roll of the first dryer section means. A downstream felt roll of the first dryer section means, a second felt of the first dryer section means extends between the downstream vacuum roll and the downstream felt roll with the second felt supporting the web such that the web is conveyed and disposed between the second felt and the second dryer section means. The first dryer-to-dryer transfer means also includes an upstream vacuum roll of the second dryer section means and an upstream felt roll. A third felt extends between the upstream felt roll and the upstream vacuum roll of the second dryer section means such that the third felt and the second felt define therebetween a first dryer transfer means section for transferring the web without open draw from the second to the third felt. Subsequent dryer section means are provided such that the first, second, third and fourth dryer-to-dryer transfer means permit the transfer of the web between adjacent dryer section means without open draw and 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. The invention also includes a method of drying a web of paper emerging from a press section of a papermaking machine, the method comprising the steps of transferring the web from the press section to a first dryer section means of the apparatus, initiating the drying of a first side of the web during passage of the web through the first dryer section means and transferring the web without open draw between the first dryer section means and a downstream second dryer section means, the web transfer being such that the web is reversed so that drying of a second side of the web is initiated during passage of the web through the second dryer section means, the second side of the web being opposite to the first side of the web. The method also includes the step of transferring the web without open draw between subsequent dryer section means such that the first and second side of the web are alternately exposed to the drying effect of the subsecuent dryer section means in sequence. Although the following detailed description exemplifies 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 the apparatus according to the present invention showing the press section, the press-to-dryer transfer means, the first dryer section means, the second dryer section means, and the first dryer-to-dryer transfer means; Figure 2 is an enlarged fragmentary view of Figure 1 showing the press section, and more particularly, the press-to-dryer 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 Figure 1 showing two of the vacuum rolls between adjacent dryers of the first dryer section; Figure 9 is a side elevational view of one embodiment of the present invention showing the air nozzle means for assisting guidance of the tail of the web from the dryer to the further dryer; and Figure 10 is a side elevational view of another embodiment of the present invention showing a transfer box. 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 press-to-dryer 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-to-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. The first dryer-to-dryer transfer means 25 permits both threading of the web 12 without the assistance of threading ropes and the drying of both sides 18 and 24 of the web 12. Figure 2 shows in more detail the press-to-dryer 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 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 44, 46, 48, 50, 52 and 54 respectively. Each of the first plurality of vacuum rolls 44 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 44 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 44 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, 69 and 70. Each of the vacuum rolls 64 to 70 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 70 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 70 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 plurality of 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 open 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 press-to-dryer transfer means 20 for transferring the web 12 from the press section 14 to the first dryer section means 16. This press-to-dryer 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 press-to-dryer 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 100, 101, 102, 103, 104, 105 and 106 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 axis 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 106 such that the axis of each of the vacuum rolls of the third plurality of vacuum rolls 101 to 106 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 106 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-to-dryer transfer means 25 includes the downstream vacuum roll 70 of the first dryer section means 16 and a downstream felt roll 112 of the first dryer section means 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-to-dryer transfer means 25 also includes the upstream vacuum roll 100 and an 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 second, third and fourth dryer-to-dryer transfer means 124,126 and 128 for transferring and reversing the web as the web progresses through the drying apparatus. The first second, third, and fourth dryer-to-dryer transfer means 25, 124, 126 and 128 permit the transfer of the web between the respective dryer section means 16, 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 16,22,118,120 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 first dryer-to-dryer transfer means 25 includes a joint run of the felt 72 and the further felt 110 such that the web is disposed between the felt 72 and the further felt 110 during passage through the joint run. Also, the first dryer-to-dryer transfer means 25 further includes vacuum means disposed downstream relative to the joint run for positively maintaining the web in close conformity with the further felt 110 when the felt 72 and further felt 110 diverge relative to each other downstream relative to the joint run. In a specific embodiment of the present invention, the vacuum means is the vacuum roll 100. The single tier drying section 10 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 10 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 dried sequentially. 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. As shown particularly in figure 9, the first dryer-to-dryer transfer means 25 also includes air nozzle means 132 for assisting guidance of the web from the dryer 63 to the further dryer 94. In a further embodiment of the present invention as shown in figure 10, the first dryer-to-dryer transfer means 25' includes a transfer box 134 adjacent to a turning roll 100B which may be grooved. The transfer box 134 may be a vacuum box or a blow box having a Coanda effect nozzle for transferring the web so that it follows roll 100B. In operation of the apparatus, the web is transferred from the press section 14 to the first dryer section means 16 of the apparatus. 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 without open draw 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. In operation of the apparatus the web is also transferred without open draw 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. The present invention provides a drying section which is capable of operating at extremely high speeds as no open draws exist between the various sections thereof. Furthermore, the present invention enables threading of the drying section without the use of threading ropes.

Claims: Apparatus for drying a web (12) of paper emerging from a press section (14) of a papermaking machine, said apparatus comprising: a substantially horizontally extending drying section which has a single-tier configuration throughout its entire length, said drying section comprising a plurality of successive, substantially horizontally extending single-tier dryer section means (16, 22, 118, 120, 122), a plurality of felts (56, 72, 110) for supporting the web (12) in said dryer section means (16, 22, 118, 120, 122), a plurality of dryer-to-dryer transfer means (25, 124, 126, 128) for positively transferring the web (12) between adjacent dryer section means (16, 22, 118, 120, 122) without open draw and with an alternate reversing of the web (12) ; each dryer section means (16, 22, 118, 120, 122) comprising a plurality of dryers (32, 34, 36, 38, 40, 42, 58, 59, 60, 61, 62, 63; 94, 95, 96, 97, 98, 99) and a plurality of vacuum rolls (46, 48, 50, 52, 54, 64, 65, 66, 67, 68, 69; 101, 102, 103, 104, 105) each of which is disposed between and in spaced close proximity to adjacent dryers such that the web (12) extends alternately past each vacuum roll and dryer in serpentine configuration, with only one side (18; 24) of the web (12) contacting each dryer of the respective dryer section means. Apparatus as set forth in claim 1, characterized in that said dryer section means (16, 22, 118, 120, 122) are disposed at different heights relative to each other. Apparatus as set forth in claim 2, characterized in that every other dryer section means is disposed at the same height relative to each other. Apparatus as set forth in claim 1, characterized in that a first dryer section means (16) includes: a first dryer section (26) for initiating the drying of one side (18) of the web; a second dryer section (28) disposed downstream relative to said first dryer section (26) for continuing the drying of said one side (18) of the web; dryer transfer means (30) for transferring the web without open draw between said first and said second dryer sections (26, 28). Apparatus as set forth in claim 4, characterized in that said first dryer section (26) includes: a first plurality of dryers (32 - 42); a first plurality of vacuum rolls (46 - 54) each vacuum roll of said first plurality of vacuum rolls being disposed adjacent to a corresponding dryer of said first plurality of dryers (32 - 42) such that the web extends alternately past each vacuum roll and dryer in serpentine configuration; and a first felt (56) which extends around said first plurality of dryers (32 - 42) and said first plurality of vacuum rolls (46 - 54) in close conformity with the web; said second dryer section (28) includes: a second plurality of dryers (58 - 63); a second plurality of vacuum rolls (64 - 69), each vacuum roll of said second plurality of vacuum rolls (64 - 69) being disposed adjacent to a corresponding dryer of said second plurality of dryers (58 - 63) such that the web extends alternately past each vacuum roll and dryer in serpentine configuration; a second felt (72) extending around said second plurality of dryers (58 - 63) and vacuum rolls (64 - 69) respectively such that said second felt (72) is disposed in close conformity with the web; said second felt (72) and an unfelted portion (74) of a downstream dryer (42) of said first plurality of dryers defining a first pick-up section (76) for transferring the web from said unfelted portion (74) onto said second felt (72) so that the web is transferred without open draw from said first dryer section (26) to said second dryer section (28). Apparatus as set forth in claim 5, characterized in that it includes: a base frame (78) for rotatably supporting said first and said second plurality of dryers such that the axes of said first and second plurality of dryers are disposed in a first plane (80); said frame (78) rotatably supporting said first and said second plurality of vacuum rolls such that the axes of said first and second plurality of vacuum rolls (46 - 54, 64 - 69) are disposed in a second plane (82). Apparatus as set forth in claim 6, characterized in that said first plane (80) is disposed above said second plane (82). Apparatus as set forth in claim 7, characterized in that an upstream vacuum roll (64) of said second plurality of vacuum rolls (64 - 69) is disposed in spaced close proximity to said unfelted portion (74) of said downstream dryer (42) of said first dryer section (26); a first felt roll (84) is rotatably supported by said base frame (78) for guiding said second felt (72) past and in conformity with said unfelted portion (74) of said downstream dryer (42) and thereafter around said upstream vacuum roll (64) of said second dryer section (78) such that the web is transferred from said unfelted portion (74) to said second felt (72) without open draw. Apparatus as set forth in claim 1, characterized in that it includes a press-to-dryer transfer means (20) for transferring the web from the press section (14) to the first dryer section means (16); said press-to-dryer transfer means (20) including a lead-in roll (86) disposed in spaced close proximity relative to the press section (14); a first felt (56) extending around said lead-in roll (86) for transferring the web from the press section (14) to said first dryer section means (16); a guide roll (88) disposed between said lead-in roll (86) and said first dryer section means (16) for assisting the transfer of the web from the press section (14) towards said first dryer section means (16); a transfer felt (90) extending around said guide roll (88) such that said transfer felt (90) and said first felt (56) define therebetween a transfer section (92) for transferring the web from the press section (14) towards said first dryer section means (16). Apparatus as set forth in claim 9, characterized in that said press-to-dryer transfer means (20) further includes an upstream vacuum roll (44) of said first dryer section means (16), said upstream vacuum roll (44) cooperating with said first felt (56) and said transfer felt (90) such that said transfer section (92) extends from said guide roll (88) to said upstream vacuum roll (44) so that the web emerging from said transfer section (92) is guided around said upstream vacuum roll (44) into said first dryer section means (16). Apparatus as set forth in claim 1, characterized in that it includes a base frame (78); said base frame (78) rotatably supporting each dryer (94 - 99) of a second dryer section means (22) such that the axes of said dryers (94 - 99) of said second dryer section means (22) are disposed in a third plane (107); said base frame (78) rotatably supporting each vacuum roll (101 - 105) of said second dryer section means such that the axes of said vacuum rolls (101 - 105) of said second dryer section means (22) are disposed in a fourth plane (108). Apparatus as set forth in claim 11, characterized in that said fourth plane (108) is disposed above said third plane (107). Apparatus as set forth in claim 1, characterized in that it includes: a first, second, third, fourth and fifth dryer section means (16,22,118,120,122); and a first, second, third and fourth dryer-to-dryer transfer means (25,124,126,128); said first, second, third and fourth dryer-to-dryer transfer means (25, 124, 126, 128) permitting the transfer of the web between said respective dryer section means without open draw and with an alternate reversing of the web such that the top and bottom sides (18, 24) of the web (12) are alternately dried as the web extends through the apparatus and past consecutive dryer section means. A method of drying a web (12) of paper emerging from a press section (14) of a papermaking machine, the method comprising the steps of: transferring the web (12) from the press section, (14) to a first substantially horizontally extending single-tier dryer section means (16) of a substantially horizontally extending drying section having a single-tier configuration throughout its entire length, passing the web (12) through said drying section by passing it successively through said first (16), a second (22) and subsequent single-tier dryer section means (118, 120, 122) in close conformity with a respective one of a plurality of felts (56, 72, 110), each dryer section means comprising a plurality of dryers (32, 34, 36, 38, 40, 42, 58, 59, 60, 61, 62, 63; 94, 95, 96, 97, 98, 99) and a plurality of vacuum rolls (46, 48, 50, 52, 54, 64, 65, 66, 67, 68, 69; 101, 102, 103, 104, 105) each of which is disposed between and in spaced close proximity to adjacent dryers such that the web (12) extends alternately past each vacuum roll and dryer in serpentine configuration, with only one side (18; 24) of the web (12) contacting each dryer of the respective dryer section means, and positively transferring the web (12) between adjacent dryer section means (16, 22, 118, 120, 122) without open draw and with an alternate reversing of the web (12) such that the first and second sides (18, 24) of the web (12) are alternately exposed to the drying effect of said first, second and subsequent dryer section means (16, 22, 118, 122) in sequence.

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