Abstract:
A web dryer structure for thermal removal of liquid from a traveling web such as a web of paper coming from the press section of a papermaking machine including a row of upper dryer drums and a row of lower dryer drums with the drums positioned to carry the web in a sinuous path successively between upper and lower drums and the web wrapping the upper and lower surfaces of the drums respectively with upper and lower looped felts wrapping the web on the upper and lower surfaces of the drums with the felt guided by felt rolls which for the upper felt is beneath lower drums and for the lower felts are between the upper drums with the felt rolls being hollow roll shells and having glands therein divided so that a first portion of the felt roll faces the onrunning web and a second portion faces the offrunning web with the vacuum means and pressure means connected to the interior of the felt rolls so that one portion is subjected to a vacuum, and the other portion is subjected to a pressure, and the arrangement accommodates running the web in either direction without the necessity to have any open unsupported travel of the web.

Description:
BACKGROUND OF THE INVENTION 
     The present application is a continuation-in-part of my copending application, Ser. No. 426,609, filed in the Patent and Trademark Office on Sept. 29, 1982, Entitled &#34;Dryer Felt Run&#34; now U.S. Pat. No. 4,485,567. 
    
    
     The invention relate to improvements in dryer drum structures for drying a traveling web, and more particularly to a structure which is used for thermally drying a web such as a continuous run of paper which is received at high speed from the press section of a papermaking machine. 
     More particularly, the invention relates to a particular arrangement and guidance for the web and felts which are threaded over the dryer drums with means for subjecting the web to zones in the felt or pressure and vacuum rolls for improved control of the web and improved removal of moisture to enhance the operation of the dryer, without open unsupported travel of the web. 
     In the dryer section of a thermal dryer such as for a paper machine, the liquid or moisture carrying web is received from the press section of the machine and is directed along a serpentine path in wrapped relation with a plurality of steam heated dryer drums. These drums are usually arranged in upper and lower rows with the drums staggered so that the paper web can pass back and forth in a serpentine path and wrap the upper and lower drums with the moisture evaporating from the web. To aid in the heat transfer from the drum to the web and to support the web in travel between the drums, upper and lower looped felts are provided which wrap the outer surface of the web while on the drum surface. 
     In relatively high speed papermaking machines, disadvantages have been encountered that the web is not controlled in transfer between the upper and lower felts and is sometimes lost. Further, other disadvantages are encountered in that moisture which is removed by heating is not carried away as fast as possible. 
     It is accordingly an object of the present invention to provide an improved dryer section arrangement which improves the handling and transfer of the web and which also improves the removal of moisture therefrom. This objective generally is desired and sought after because with the increase in speed of papermaking machines, it is necessary for the dryer section to be able to accommodate such increase in speed, without increasing the sheet strength and consequent increased cost and with a minimum of sheet wrinkles and paper breaks, plus lost production. 
     A further object of the invention is to provide a web handling arrangement for a dryer section of a papermaking machine which achieves and accommodates more uniform drying across the width of the sheet and which helps avoid the complications of buildup of air flow or windage and buildup of moisture in the pockets formed between the felts, the dryer drums, and the felt rolls. 
     A feature of the invention is the provision of felt rolls for the felts which are constructed as perforated roll shells with glands within the roll shells that divide the areas into a pressure and vacuum chamber or vacuum and pressure so that the web is alternately subjected to vacuum and pressure as it travels over the roll. This unique arrangement has been discovered to avoid damages in web handling and drying in both arrangements. 
     Other objects and advantages and features wi11 become more apparent with the teaching of the principles of the invention in connection with the disclosure of the preferred embodiments thereof in the specification, claims and drawings, in which: 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a somewhat schematic side elevational view of a dryer section of a papermaking machine constructed and arranged to embody the principles of the present invention; 
     FIG. 2 is another somewhat schematic elevational view similar to FIG. 1, but showing an alternate arrangement; 
     FIG. 3 is a sectional view taken through a felt roll generally along line III--III of FIG. 4; and 
     FIG. 4 is a sectional view taken generally along line IV--IV of FIG. 3. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As illustrated in FIG. 1, a web W is received from a press section, not shown, in a papermaking machine to pass into a dryer section shown in FIG. 1. As the web W passes over a roll 10, it is received by an upper felt F-U threaded down onto the web over a guide roll 11. The web then becomes sandwiched between the upper felt F-U and a lower felt F-L guided up over guide rolls 10a and 10b. 
     In the dryer section, the web is threaded over dryer drums alternately carried by the felts F-U and F-L, and the felts are threaded by felt rolls to wrap the web on the drums. 
     Generally the dryer drums are steam heated cylindrical cast iron drums as will be known to those versed in the art, arranged in an upper row as illustrated by the drums 12 and 13 and arranged in a lower row as illustrated by the drums 14 and 15. 
     In the travel of the felts through the dryer drum system, the felts are guided by two types of rolls. One type of roll will be referred to as felt rolls including numbers 16, 17, 18, 21, 37, 38, 39 and 40, and these rolls comprise perforate rotatable roll shells with glands therein which expose the perforations of the roll shells to either pressure or vacuum to thereby subject the felt and the web carried thereby to a pressure or vacuum as will be more fully described. The other type of rolls will be referred to as guide rolls, and these are solid rolls which are positioned to help guide the path of travel of the felts, and the guide rolls are numbers 10a, 10b, 11, 11a, 11b, 19, 23, 24, 31, 32, 42 and 43. 
     The upper felt F-U is threaded over upper felt rolls such as 16 and 17 which are positioned beneath the upper drums 12 and 13 respectively. The lower felt F-L is guided over lower guide rolls such as 18 and 19 with the felt roll 18 positioned above the lower drum 15. In the construction embodying the principles of the present invention, each of the felt rolls are constructed as hollow roll shells with glands within the shells so that a portion can be subjected to a vacuum and a portion subjected to pressure as will be described in further detail in connection with FIGS. 3 and 4. As illustrated therein, the hollow roll shells 45 are supported on end bearings 46 to be either driven in rotation or to rotate due to frictional contact with the felts. The hollow roll shells are perforate having openings 47 therethrough so as to expose the felt and the web carried on the surface to the pressure or vacuum within the felt roll. 
     As illustrated in FIG. 4, a gland or gland walls 49 and 50 are positioned within the hollow roll shell to divide the roll shell into first and second portions, with one portion being subjected to a vacuum, and the other portion being subjected to a pressure. As illustrated in FIG. 4, the portion 51 is subjected to a vacuum, and the portion 52 subjected to a pressure, and the arrowed lines in FIG. 4 illustrate the direction of flow of air relative to the roll shell. 
     As illustrated in FIG. 3, a conduit 48 connects to the portion 52 to pressurize that portion. Similarly, a conduit 49 connects to a vacuum to subject the portion 51 to a vacuum. Suitable pressure and vacuum means are provided shown schematically by the arrowed lines in FIG. 3, and pumps or fans of known construction will be arranged to provide the pressure and vacuum. 
     Returning to the arrangement shown in FIG. 1, the upper felt F-U is led away from the web by a grooved guide roll 11a before the web reaches the dryer drum 14. The felt F-U passes up over a further guide roll 11b and then is threaded down onto a felt roll 16 to pick up the web which has been carried up to the felt roll 16 on the felt F-L. 
     Just prior to where the upper felt F-U leaves the web, the web is picked up by a lower felt F-L and the guide rolls 10b and 11a form a nip to transfer the web from the upper felt F-U to the lower felt F-L. The lower felt carries the web down into direct contact with the dryer drum 14. After the web leaves the lower dryer drum 14, it is first subjected to a pressure from the portion 16a of the guide roll 16 in the area 14a. As it leaves the bottom felt F-L, the sheet is subjected to a vacuum in the portion 16b of the felt roll. The glands within the felt rolls are arranged so that the web on its onrunning side is subjected to a pressure and on the offrunning side, is subjected to a vacuum. The pressure on the onrunning side helps force a flow of air out of the pocket 14a and holds the web on the felt F-L. The pressure may also cause a flow of air into the area on the onrunning side of roll 16 which helps carry away the moisture vapor which is present in the zone 14a following the drum 14. 
     The vacuum in the portion 16b of the felt roll helps transfer the web onto the upper felt F-U on the offrunning side of the felt roll. Also, there may be some air transfer through the web and upper felt to aid in the drying process, and this helps evacuate the zone or pocket 12a ahead of the dryer drum 12. 
     As the web is carried over the upper dryer drum and onto the felt roll 18, it is first met with pressure from the portion 18a. It is next subjected to a vacuum on the offrunning side as it is exposed to the portion 18b of the felt roll 18. This aids in transfer of the web to the lower felt F-L which carries the web down over the lower dryer drum 15. The web is next carried onto the felt roll 17 where it is first subject to pressure on the onrunning side and then subject to a vacuum on the offrunning side to transfer it to the upper felt F-U to be carried up over the upper dryer drum 13. Following the upper dryer drum, the web and upper felt pass over the felt roll 21 whereupon the web is transferred to a second lower felt F-L2 to be carried down over the surface of a lower dryer drum 20. The upper felt is guided away over guide rolls 23 and 24. 
     In the construction of FIG. 2, essentially the same structural elements are employed, but the travel of the web, or in other words, the effect thereon is reversed with the web first being subjected to a vacuum and subsequently to a pressure as it travels over each felt roll. In other words, in the arrangement of FIG. 1, the web sees in sequence a pressure and then a vacuum as it travels over the felt rolls, and in the arrangement of FIG. 2, the web sees a vacuum and then a pressure as it travels over the felt rolls. The web is subjected to advantageous treatment in each arrangement with the same roll construction being used. The papermaker can attain the desired arrangement by merely reversing the pressure and vacuum lines, or a valving arrangement may be used for rapid interchange of these lines and changing the felt run. 
     In the arrangement of FIG. 2, a web W enters a dryer section carried on an upper felt F-U over a roll 30. It is then sandwiched between the felt F-U and a lower felt F-L which is carried up beneath the web over guide rolls 31 and 32. The upper felt is led away from the web on a grooved guide roll 43. 
     The web is carried down over a lower drum 35 on the lower felt F-L. The dryer section is arranged very similar to the arrangement in FIG. 1 with a lower row of drums 35 and 36, and an upper row of drums 33 and 34. The lower drums receive the lower felt F-L which is guided by felt rolls 37 and 38 which are positioned over the lower drums 35 and 36 respectively, and are positioned essentially between the upper drums. 
     The upper felt F-U is guided to wrap the upper drums 33 and 34 by felt rolls 39 and 40 which are positioned beneath the upper drums 33 and 34. Each of the felt rolls are constructed as hollow roll shells, as illustrated in FIGS. 3 and 4, and each are provided with glands therein so that the web is subjected to a vacuum on the onrunning side of the felt roll and to a presure on the offrunning side. 
     As the web is carried over the drum 35 and up over the felt roll 37, it is first subjected to a vacuum which aids in the keeping the sheet on the felt. On the offrunning side, a pressure is directed out through the lower felt to aid in the transfer of the web onto the upper felt F-U. The felt roll 37 has a first portion 37a which is subjected to a vacuum and a second portion 37b which is subjected to a pressure. Thus, with the same construction, a vacuum is used in the arrangement of FIG. 1 for the transfer of the web, and a pressure is used in the arrangement of FIG. 2 for the transfer of the web. In both arrangements, the vacuum and pressure are utilized to carry air from or to the zone between the felt roll and dryer drum to aid in carrying away moisture in the zone. 
     As the web is carried by the upper felt, following the felt roll 37, it is carried over the upper dryer drum 33 and then down over the felt roll 39 where it is first subject to a vacuum from the section 39a of the felt roll and then is subjected to a transfer pressure from the section 39b of the felt roll. The web is then carried by the lower felt F-L over the lower dryer drum 36 and up over the felt roll 38 where it is transferred to the upper felt to be carried over the upper drum 34. Following this, the web passes down over a felt roll 40 where it is transferred to a second lower felt F-L2 which is threaded up over a guide roll 42 to wrap the outer surface of the web on the felt roll 40. The web then is carried by the lower felt F-L2 over a further lower dryer drum 41. 
     The arrangement above described can be repeated throughout the section of the dryer for as many dryer drums as is necessary to attain a drying of the web. 
     It will be noted that in the arrangement of FIG. 1, the web is threaded so that it wraps the lower portion of the upper dryer drums on the oncoming side, and wraps the upper portion of the lower drums on the oncoming side. 
     In the arrangement of FIG. 2, the web wraps the upper portion of the lower drums on the offrunning side and similarly wraps the lower portion of the upper drums on the offrunning side, and this effect is achieved by the arrangement of the felts relative to the felt rolls. Thus, with a given felt run, the mechanism can be arranged to attain the advantages of either subjecting the web first to a vacuum and then to a pressure or in the opposite arrangement, first to a pressure and then to a vacuum. In the first arrangement, the vacuum is used for the web transfer, and in the second arrangement, the pressure is used for the web transfer. Various operating conditions and various types of paper will dictate which arrangement is most advantageous. 
     A preferred arrangement is shown, but the arrangement shown in FIG. 2 could be used with grooved felt rolls on some grades or paper without the vacuum and pressure zones. The felt rolls would be grooved about 3/16 wide×3/16 deep with 3/16 land areas between the grooves. Other groove patterns could also be used, but generally with a surface pattern with 50% open area and 50% land area and about 1/8 to 1/4 inches deep. 
     The drying system shown and described herein is referred to as functioning to remove water vapor or moisture from the web, and it is to be understood that the term moisture is not restrictive in that liquids other than water may be used in the paper making process. For example, U.S. Pat. No. 3,791,044 shows tetrachloroethylene (TCE) used instead of water. Therefore, the features of the invention may be employed to remove wetness of all types from webs including water and TCE. 
     As stated above, the embodiment of FIG. 2 could be modififed from the preferred arrangement shown to provide felt rolls which do not have the pressure and vacuum chambers, but which are grooved rolls inasmuch as the grooves would break the vacuum between the web and grooved roll surface at the points where the web begins wrapping the felt rolls 37, 38 and 39. If these felts rolls are either not grooved nor equipped with the vacuum and pressure glands shown in FIG. 2, air would be trapped between the felt roll surface and the felt which would tend to cause the web to billow off the felt. The use of grooved rolls for the felt rolls is not a preferred structure, but a possible structure. 
     Felt rolls 37, 38 and 39 in FIG. 2 are preferably perforate rolls with the pressure and vacuum chambers therein as illustrated in FIG. 2, but grooved rolls may be employed in some circumstances. In FIG. 1, the felt rolls 16, 17, and 18 each transfer the web off the felt as it comes off the dryer roll and onto the next felt which wraps the felt roll leading to the next dryer drum. By contrast, in FIG. 2, the felt rolls 37, 38 and 39 each transfer the web which is already on the felt wrapping the felt roll off of the felt onto the other felt leading to the next dryer roll. In FIG. 1, the transfer is made from a straight running felt run to the felt which wraps the felt roll. In FIG. 2, the transfer is made from the felt wrapping the felt roll onto the straight run of felt. 
     Thus, it will be seen that I have provided an improved dryer arrangement which meets the objectives and advantages above set forth and which enables better and more uniform drying on higher speed papermaking machines, without any open draws in the sheet travel.