CA1126013A - Air impingement web drying apparatus - Google Patents

Abstract

S P E C I F I C A T I O N
TO ALL WHOM IT MAY CONCERN;
BE IT KNOWN that we, GEORGE H. WONG, LAMAR EMBRY, DONALD A. ELY, PETER F. PANTALEO, RONALD D. COOKE. JAMES
LARRY CHANCE AND EDWARD D. BEACHLER, citizens of the United States and residents of the City of Roscoe, in the County of Winnebago and State of Illinois; the City of Tacoma, in the County of Pierce and State of Washington, the City of Roscoe, in the County of Winnebago and State of Illinois; the City of Beloit in the County of Rock and State of Wisconsin; the City of Beloit, in the County of Rock and State of Wisconsin;
and the City of Rockton, in the County of Winnebago and State of Illinois; the City of Beloit, in the County of Rock and State of Wisconsin respectively, have invented certain new and useful improvements in "AIR IMPINGEMENT WEB DRYING APPARATUS"
and we do hereby declare that the following is a full, clear and exact description of the same; reference being had to the accompanying drawings and to the numerals of reference marked thereon, which form a part of this specification.

ABSTRACT OF THE DISCLOSURE

A method and mechanism for dewatering a web in a paper making machine having press means, a first thermal dryer section having a long continuous support looped belt carrying the web along a first drying run with rolls and suction zones beneath the web and a hot air generating means for directing a flow of air onto the web in the first thermal run with the web being received substantially 40% bone dry at the beginning of the first thermal run and being delivered substantially 50% bone dry at the end of the run onto a heated drum dryer section.

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Description

'rl~e inven~i.on relates to improvement:s in paper makinK
macllines, and n~ore pa]. ticularly to improvemellts in dewaterillg a web by thermal nleans wllich permits tlle ~achine to be run at high speeds.
In the continual striving for increased speed of operation in paper malcing machines, speeds above 3000 eet per nninute in exlsting,mncllines hclve enco-lntered d:ifficulty in the occurrence o~
~lu~ter alld breaks in the clryer section One of the reasons is that the ~eb is insufficiently drled and cloes not have sufficient strength to carry across the open draws necessary in a standard dryer where the web is threaded,in a serpentine path back and forth between dryer drums. It has been discovered,that'if the web is-dried to on t:lle order of 50% bone dry, it will have the strength and stability to witllstand an open draw between the dryer rolls.
It is'impractical to attain this dryness in a press section.
. It ls accordingly an object o~ the present invention.to : provide,a high speed paper malcing machine for the production of fibrous paper web. particularly such as newsprint, which can oper-ate at higll speeds on the order of above 3000 feet per minute with-out enco~mtering breaks or other damage to the web at the beginning of the dryer section.
In accomplishing the foregoing objective in accoLdance with the principles of the present invention, the web is carried on a first dryer run between the press and standard dryer section being continuously supported so that no,flutter or'wrinkling can ' ' 'occur. During this first dryer run, the web is dxied from about .
,' 40% bone dry as it is received from the press section and leaves this run on the order of about 50~/O bone dry at which time it will llave strengtll and s~a~-ility to withstand an open dràw in passing through the rc,~gular clryer drum sectlon. The long continuous .. ~ . ~ .` .

support o~l ~lle run is ~rovide(~ in ~he .~orrn o.~ an endless l~elt.
Difficulties have been encountered in such support in providin~
stability to the belt, accommodating evaporation of the moisture from tlle web on the belt, imparting thermal energy at a sufficient temperature to cause meaningful evaporation from the web during the time it is supported and providing engagement between the web and tlle ~elt without generating air pockets or 10ating of the web such as causecl by inaclvertently cap~urin~, air between the.web and the belt at hi~,h operating speeds.
It is accordingly a further object of the present inven-tion to provide a mechanism which drives'the web between the press section and dryer dru~ section by providing a long continuous support ~or the web and providing for heated air impingement on the we~b during its term of long continuous support.
~ further.object of the invention is to provide a support means for the belt whic~h provides a long continuous support for the web which is capable of stable operation or l.ong periods of time which eliminates poclcets of alr beneatll the web, permits imparting themlal energy to tlle web without damage to the ~elt and accommo-dates satisactory high speed transfer to the belt from the press section and from the belt to the dryer drums at the end of the long continuous supported run.
.The invention provides' a continuous looped belt of porous material capable of wi'thstanding the high temperatures o the heated air, either i.nherently or by being provided with'a heat .
- resistant coating on the upper surace and a roll with a suction gland-on the lead end for transer of the we~ onto the belt without inducing a cushion of air beneath the web, and a heated air gener-a~ing means Eor d:irecL-ing a blanket of heated drying air continuously onto tlle upper surfacF of the web T..Thile it is carried on the belt , . _ . . ... .... _ _ . . . . .. _ . . , . ~

, _, _,, _ _ _ . _ A ~ _ . _ ~ ~ . _ . _ . _-- . ' -- ' ., . ..... _ _ support. 'll~e l)elt i5 SUp~)Or~"~ over a long sliglll:ly arclJ;1te path on successive porous rolls with suctlon hoxes therebetween. l'hese suction "bo~.es" Ir,ight more appropria~ely be characterized as suction zones ~ltllin a single SUCtiOIl box e~tend;ng the length of the first dryer run ~Inder the support ~)elt. The porous rolls themselves define the sicles of tllese zones ~ith the ends ~eing constructed of sheet nletal. '.I'Ilere are no tops since the belt is supported be-tween successive poro~s roll.s over each zone. The rolls are per-foratc and have suction ventilati:ng glands therein ~so that alr is removed beneath the porous belt. Between the spaced parallel rolls are the suction zones wi~h curved edge surfaces. At the end of the long continuous run is a roll within the belt, preferably an ordinary heated dryer drum roll, over which the belt and web pass immedi.ately beEore the ~eb is tllreaded onto a felt to pass throu~h the dryer drum section.
Other objects, advantages and features as well as equiv-alent structures and methods which are intended to be covered here-in, will become more apparent with the teaching of the principles of the invention in connection with the disclosure of the preferred embodiments in the specification, claims, and drawings, in which:
DI~AII~IGS
- FIGURE 1 is a side elevational view in somewhat schematic form of a dewatering section of a paper making machine constructed and operating in accordance with the principles of the present invention; ~ - :
~ I~UR~ 2 is an enlarged detailed side elevational view, partially in section, of a portion of the first thermal drying run;
FIGURE 3 is a fragmentary schematic view o~ a suction arrangement for the rolls and suction box;
~ IGUR~ i.s a ~ragmentary detailed view of the suction box structure;

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I'ICUK1' S is a fragmentary schematic side elevational vie~
somewllat en3.ar~e~1 lrom ~igurc l illustra~ing the entering end o~
the first dryer section;
~ IGI]RE 6 is a fragmentary dia~ram~atic side elevational view slightly enlar~ed ~rom ~igure l showing the discharge end of the ~irst dryer section; and FIGURE 7 is a ~ragtnentary side e].evational view similar to Fi~ure 2 showing an alternate form of tlle invention.
DI~SCNPTION -' As illustrated in Fi~ure l, a we~ web 1~ which has been formed in a forrning section, is passed through a press section lO.
Therea~ter the web is thermally driecl in a first drying run ll while being continual].y supported to avoid fluttering and wrinlcling.
Followin~ the n1n ll, t11e web is transferred to the second thermal run 12 w11ic1~ comprises standard dryer drums. In the first or intermediate run ll, the web enters rom t1~e press section at a dryness o~ about ~0~/0 bone dry, and in that condition does not have su~icient strength to stand the ~lutterin~, to which it will be subjected i~ it is passed directly to a dryer drum section. The web, therefore, receives full support in such a manner that air currents cannot cause flutter when it is drled to a bone dryness on the order of 50% at which time it has sufficient strength to be handled by a standard dryer section and can withstand the flutter-ing which occurs.
The web is i.llustrated leaving the press section, pas~ing through a last press nip between press rolls 13 and l4 having a felt 15 passing theough the nip. The elt passes upwardly over Ielt roll 9 ~or its returll run. The web passes downwardly over a roll l4a and is laid onto a long continual support belt 16. The belt ex~ends ~or a suls~ant:ial run beln~ supported in a sli~htly arcuate path as illustrated so that the bPlt can be tensioned and held ~ithout any up and down movement or flutter itself.
At the lead end of the long continuous support run of the belt 16 is a belt support roll 17 having a small suction gland 18 therein to flrmly transfer the web onto the belt. The web passes over a roll 19 which is adjustable in position as shown by the dotted lines l9a so as to control the location where the web is laid onto the belt relative to the suction gland 18, for threading.
The web is carried on the upper surface of the belt, and the belt is formed of a porous material and has a surface extending across the full width of the web and providing full and complete support therefor. While on the belt, the web is subjected to a flow of drying air from above from a mechanism of the type known in the art as an air cap. Inasmuch as the web is supported only from below, the possibility of scuffing which could occur if the web is carried between two belts is avoided. The porous belt is preferably coated on its upper surface with a heat resistant material of a type which can withstand air drying temperatures up to 500F, 245C. The belt is preferably maintained at a tension to reduce the possibility of wrinkling or ~luttering, and tensions up to 30 pli are preferred. These tensions are maintained by stretch rolls, not shown, within the looped belt. By training the belt over an arcuate surface, this tension is readily maintained in such a manner so that the web receives continual nonfluttering support. It will be noted that with the effect of training the belt over an arcuate path, that is, over an upwardly curved convex path, the web is maintained taut or under a slight tension as it is bowed upwardly on the belt to thereby help insure that no wrinkles or fluttering occur in the web~
Above the belt are arranged air caps 22. These are supplied with a flow of heated air to be able to deliver air of a temper-ature o~ a ~uficient degree that can be~withstood by the belt and and temperatures of up to 500F have been utilized successfully, , ;~, "~
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and it is believed under certain conditions that temperatures up to 900F, 480C may be used.
The air caps are constructed as enclosures with perforate lower surfaces 24 as illustrated in Figure 2. The air caps are arranged to extend the full width of the belt and web, and arrange-ments can be provided so that cooling air may be directed against the belt surface at the exposed edge of the beltno-t covered by the web to prevent its being damaged by being directly exposed to the heated air.
Support for the continuous belt is provided by a series of spaced horizontal support rolls 20. These rolls have a hollow construction as shown in Figure 2 with a compartment 26 therein extending for the length of the roll, and the roll has a perforate outer shell surface. Suction is applied to the compartment 26 through a suction line 27 so that a continual slight vacuum will be applied to the lower surface of the belt preventing any build up of air therebeneath due to the induced flow of air with rotat-ion of the rolls 20 or to the layer of air carried by the travel-ing belt.
Between each of the rolls is a suction box 21 with the first box meeting the oncoming web being tilted toward the oncoming direction of the belt. Inasmuch as the belt is under tension, it will tend to be stretched tangentially between its points of contact with the upper surface rolls butwill depend slightly in a catenary curve. The top edges 28 of the sides of suction boxes 21 are curved to conform substantially to the curvature o~ the belt between the rolls~ The end walls of the suction box are made of sheet metal, and at the upper edges 28 of the end walls are plastic t shoes 29 for nonwearing engagement with the belt.
Suction is applied to the compartment 26 within the rolls and into the interior of the suction box 21 provided by separate suction pumps 30, 30a, Figure 3, wHich connects through suitable lines 31, 31a to the rolls and suction boxes. Control of the , .
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applied suction is accomplished by a valving axrangement shown somwhat schematically at 32 and 37. The suction which is applied beneath the belt is rela-tively light an on the order of 1" - 2"
H2O, although at threading a higher suction is applied. When threading a web through the machine, the web will have a leading tail which will be less width than the full width web and to in-sure retention of the tail and threading of the web, a higher suction on the order 4" H2O is applied. This is done by setting of the valves 32 and 37 to the higher suction during threading and then shifting to a position of the regular suction during normal operation. The web is dewatered and begins at 35% to 45%
bone dry at the beginning of a run and is dried to 45% to 55% bone dry at the end of a run.
With this arrangement, two important objectives are provided in that the web is being dried from about 40% bone dry at the run beginning to about 50% bone dry at the end of the run while simultaneously being continually supported without any possibility of flutter or wrinkle. The other objective which is served is the support of the web on a belt with the spoiling of any induced air cushion which might tend to form between the web and supporting belt and between the belt and supporting rolls 20. This is achiev-ed by the fact that there is no open draw which supports the objective of continuous support and avoids the inducement of air, and the spoiling of air layers is additionally achieved by the application of suction beneath the porous belt.
Preferably, the suction compartments 26 in rolls 20 are slightly tilted toward the oncoming felt so this additionally functions to spoil any wedge of induced air which tends to be carried between the felt and pass up to cushion the web on the belt.
The air caps have a perforated plate on the bottom, as shown at 24 in Figure 2, and the holes in this plate are on the ~ ~ 2 ~
order oF al)proximl~tely 3/3" in diame~er. ~ir -is blown throu~h the distribution of holes onto tlle web at a velocity o~ about 24,000 feet per minute at the temperature of abo~ 500F. This temper-ature, oE course, will be increased in accordance with the-ability of the bel~ ~o witlls~and hea~. At the downstream or terminal end of the Eirs~ run where the web is supported on the belt, inside tlle belt is a heated roll 33 ~hich provides additional drying heat, but pri.marily ~unctions as a driving roll for the belt. For heatin~ the roll, a steam li.ne 34 is connected to a gland at the end of the hollow roll. At the location of the roll 33, an upper felt 35 comes down onto the web and the web is transferred onto the felt to pass down with the felt over a roll 36. A lower felt 37 receives the web and the ~elts pass over dryer rolls 38 and 39 in serpentine fashion in a normal manner. At this point the web ~ill have heen dried to substantially 50% bone dry so it will have the strength to be carried through the dryer.drums.
. With thls arrangement, speeds on the order o 4,000 feet per minute and higher can be accomplished without damage to the web. The drying o the web in the irst or intermediate run be-tween the press and tlle dryer drums does no~ only dry the web to a degree where it has strength because o~ its dryness, but has dried it in a fashion while under continuous suppor~ without ~lex-ure which increases its strength.
Figure S shows in greater detail the manner in which the paper web i5 ~ed from the press section onto the ~irst dryer: -secti.on. In initial threading, tbe web is run through the press section by feeding a tail (a narrow strip of web) as ~ed through the press xection and passed directly downwardly following the last press nip orF o~ the pre.ss roll 14 A doctor blade 41 against tlle surEace oF thc press roll 1.4 de1ects the web tail 40 ,t..

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. .. _. _ do~nwardly in~o tlle broke pi~ hen ~he web is established full wicltl~, tlle tail is cut an(l tlrea(led tl.lrou~ll tl~e dryer. For this threadin~,, thc roll 19 is in tl~e ri~hthand dotted line position l9a shown in ~igure 5. ~hen ~lle tail has been established through the drycr, roll ].9 is tllen movecl to lts solid li.ne position and the web i.s expanded to its Eull wi.dtll. The web tension over the rolls in tlle drver is aided by the fact that tlle dryer section is operated at a aster linear speed than the press section.
Fig. 6 illustrates the path of the web and the position . .
oE rolls at the running position an~d threading position at the finishing of the Eirst dryer section where the weo is Eed to thé
second dryer section.
~ s illustrated in Figure G, Eor threading~ the felt roIl 42 is brougl~t into the lower solid line positlon, and the tail led across ~he space to the dryer rolL 36 it~tediately following the felt guide roll 44. The dryer roll 36 is sometimes reerred to as a "baby dryer" and operates to secure the web to the felt 35. A
large dryin~, capacity is not neecled for tllis dryer roll because of the small wrap. The web then continues do~n on the upper felt where it is received by the lower felt ~7. ~fter threaciing, the-roll 42 is moved up to the dotted line positlon which is its normal operating position.
As illustrated in Figure 7, a structure differen~ from .
Figure l t~lay be employed in that instead~of the suction rolls, grooved rolls 46 are employed between each of the suction zones 21 supporting tlle belt 15. The grooved rolls have a plurality of adjacent circumEerential grooves 45 along their surface, and it has been discovered that the.se operate to remove air from beneath tlle belt 16 prevetltin~, any li~ting oE the web carriecl on the upper surface of the belt.

'ri~us, it will be Seetl tllat we llavc provided an improved metho(i an~ mecllanism whicll meets ~le objectives set ~orth and is capable of improved use in a paper making machine or achieving high speeds particularly in the making of newsprint.

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Claims (14)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a paper making machine, a dryer section for thermally drying a wet web between a press section and a dryer drum section, comprising in combination:
a belt having an elongate continuously upwardly facing support surface extending over a dryer run for contin-uously carrying the web and providing continuous support without flutter and wrinkling;
means supporting the belt along said run comprising alternate rolls and suction zones wherein the belt forms a catenary curve between the rolls and the suction zones have belt facing surfaces having a curvature conforming to the curvature of the belt;
hot air generating means positioned above the web on the belt for directing uniform flow of air over the exposed surface along said run;
first transfer means at the lead end of the run for transfer-ring the web onto the belt;
and second transfer means at the terminal end of the run for transferring the web off the run to a dryer drum section;
said hot air generating means thermally drying the sup-ported web continuously along said run without flutter and without wrinkling.

2. In a paper making machine, the combination set forth in claim 1 :
including a heated roll within the belt at the terminal end of said first dryer run immediately before the second thermal dryer section.

3. In a paper making machine, the combination set forth in claim 1:
including a plurality of suction zones within the belt with porous suction surfaces facing the belt and with the belt being formed of porous material.

4. In a paper making machine, a dryer section for thermally drying a wet web between a press section and a dryer drum section constructed in accordance with claim 1:
wherein said supporting means is formed of a plurality of parallel rolls continuously supporting the belt along the run.

5. In a paper making machine, a dryer section for thermally drying a wet web between a press section and a dryer drum section constructed in accordance with claim 1:
wherein said supporting means includes a plurality of suction boxes having porous suction surfaces against the belt and wherein said belt is formed of a porous material.

6. In a paper making machine, a dryer section for thermally drying a wet web between a press section and a dryer drum section constructed in accordance with claim 4:
wherein said belt is formed of a porous material and the rolls are perforate hollow roll sheets with suction means therein.

7. In a paper making machine, a dryer section for thermally drying a wet web between a press section and a dryer drum section constructed in accordance with claim 1:
wherein said supporting means is provided by a plurality of alternate rolls and suction boxes.

8. In a paper making machine, a dryer section for thermally drying a wet web between a press section and a dryer drum section constructed in accordance with claim 5:
including plastic supporting edges at the ends of the suction boxes for engagement with the belt.

9. In a paper making machine, a dryer section for thermally drying a wet web between a press section and a dryer drum section constructed in accordance with claim 8:
wherein the edges of the boxes are curved and have plastic shoes having the curvature of the box.

10. In a paper making machine, a dryer section for thermally drying a wet web between a press section and a dryer drum section constructed in accordance with claim 5:
wherein the first box along the run is tilted toward the oncoming direction of the belt.

11. In a paper making machine, a dryer section for thermally drying a wet web between a press section and a dryer drum section constructed in accordance with claim 1:
wherein the belt is formed of a porous material and has a heat resisting coating on the surface facing the web.

12. The method of dewatering a web in a paper making machine which comprises:
pressing the web for the removal of water therefrom;
thereafter immediately continuously supporting the web over a long run while subjecting the web to a flow of heated air along said run preventing flutter and wrinkling of the web so that the extent of dewatering the web is in the range of from 35% to 45% bone dryness at the beginning of the run and is in the range of 45%
to 55% bone dryness at the end of the run, including supporting the web while subjecting the web to the flow of heated air on a belt formed of a porous material and applying a substantially continuous suction beneath the belt for the run.

13. The method of dewatering a web in a paper making machine in accordance with the steps of claim 12:
wherein the suction applied beneath the belt is in the range of 1" of water to 4" of water.

14. The method of dewatering a web in a paper making machine in accordance with the steps of claim 12:
wherein the web is continuously supported by a belt and the edges of the belt which are exposed beyond the edges of the web are cooled.