CA1336535C - Apparatus and method in a paper machine twin-wire cylinder drier section - Google Patents
Apparatus and method in a paper machine twin-wire cylinder drier sectionInfo
- Publication number
- CA1336535C CA1336535C CA 569636 CA569636A CA1336535C CA 1336535 C CA1336535 C CA 1336535C CA 569636 CA569636 CA 569636 CA 569636 A CA569636 A CA 569636A CA 1336535 C CA1336535 C CA 1336535C
- Authority
- CA
- Canada
- Prior art keywords
- drying
- wire
- cylinders
- situated
- web
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
- D21F5/00—Dryer section of machines for making continuous webs of paper
- D21F5/02—Drying on cylinders
- D21F5/04—Drying on cylinders on two or more drying cylinders
- D21F5/042—Drying on cylinders on two or more drying cylinders in combination with suction or blowing devices
Abstract
A web travelling through a twin-wire cylinder drier of a paper machine is subjected to a suction effect as it separates from a drying cylinder within a negative pressure zone provided at a region of its run at which it is in contact with the drying wire so that the length of the open draw of the web is substantially reduced. The negative pressure zone is produced by a gas jet which is directed through an oblong passage defined by the outer surface of the drying wire situated on the drying cylinder and by the surface of a wall of a blow box. By directing the gas jet through the oblong passage, the boundary-layer flow following the drying wire is substantially reversed in direction to flow in a direction opposite to the run of the drying wire to thereby produce a negative pressure space at the rear side of the passage.
Description
~ 33653~
`_ ~ACKG~OUN~ OF THE INYENTION
This invention relates generally to methods and apparatus in paper ma~ing machines and, more particularly, to methods and apparatus in twin-wire cylinder drier sections of paper machines.
Conventional cylinder driQrs include a line of upper heated drying cylinders and a line of lower heated drying cylinders. such cylinder drier sections can generally be ~ivided into two groups, namely, single-wire draw cylinder driers and twin-wire draw cylinder driers, In single wire draw cylinder driers, the web is passed over the heated drying cylinders running from one line of cylinders to the other whlle supported by a drying wire so that on one line of cylinders, the web is situated between th~ drying wire and the cylinder &urface, while on the other line of cylinders, the web is situated outside of the drying wire with the latter being situated between the cylinder s~rface and the web. Single-wire draw cylinder driers are a~vantageous in tha~ the web is supported at all times by the drying wire and has no open draws o~ any substantial length, whereby the possibilities of web breaka~e and wrinkle formation are substantially reduced.
In twin-wire draw cylinder driers, separate upper and lower wires are used in connection with the upper and lower cylinders respectively. The wires are guided by the surfaçes of the respective drying ~ylinders and by guide rolls situated in spaces between adjacent drying cylinders. In thls manner, the web is pressed by the upper wire in direct drying contact against the surfaces of the upper cylinders, and, ~orrespondingly, is pressed by the lower wire directly against the surfaces of the lower drying cylinders. The we~
passes between the lines of upper and lower cylinders as an open draw.
The present invention is directed to improvemehtS in methods and apparatus in twin~wire draw cylinder drier sections.
In twin-wire draw cylinder drier ~ections, the web usually h~s a substantially long open draw as it passes from one line of cylinders to the other. These open draws have been susceptible to fluttering often re6ulting in breakage and formation of wrinkles in the web.
These draw~acks have been particularly acute in the initial part of the drier section where the web is still relatively moist and, therefore, of low strength and i~s elastic propertles are such as to render the web susceptible to fluttering.
Attempts have been made in ~he past to eli~inate these drawbacks by reducing the length of the open draws of the web in the initlal part of the drying section by moving the cylinder~ of the upper and lower liJles clo~er to each other, i.e., by situating the imaginary planes con~ining the axes of the upper and lower lines of the cylinders at a shorter distance from each other. ~owever, this ~end~
to reduce the drying efficiency of the arrangement.
It has also been suggested to convert the third and fourth groups of drying cylinders in the drier section to single-wire draw arrange~ent~. However, this is considered to be an extreme 601ution since lt results in reduced efficiency of evaporation ~nd increased difficulty in air-conditioning.
Attempts have also been made to reduce fluttering of the paper web in twin-wire draw cylinder drier~ by di~placing the felt or wire guide rolls in a manner such that the unsupported run o~ the web is reduced in leng~h. U.S. pateht 3,753,2~8 dlscloses such an arrangement. Moreover, a Swedish paper machine in which the guide r~lls are positioned in accordance wLth U.S. patent 3,753,298 is described in the paper "Engineering Consideratien for Lightweight Paper Drying in High Speed Machines", Paper Technology In Industry, July/AugUst 1978. This machine ~as reached a running speed of 853 _ 1 ~36535 m/min. However, fluttering of the we~ ha~ continued to be a diffic~lty.
The fluttering of a paper web has also been considered ~n the paper "Paperin valmistus" (Manufacture of paper) (Suomen Paperi-insinoorien Yhdistyksen oppi - ~a kasikirja III osa 1 -Textbook and Manual of the Association of Paper Engineers in Finland, Vol. III, Part 1) on pages 699 to 700. This article suggests that fluttering of the edge of a web ls generally not caused by air flows which had been frequently assumed. Under such circumstances, the fluttering of a web could not be prevented to ~ significant extent by guiding the air flows in the drying section, which has, however, often been attempted.
Web fluttering is today considered to result essentially from excessively strong airflows in the pockets defined inside the cylinder drier by the free surface6 of the drying cyl inders and the wire~ or felts guided by the guide rolls, and ~rom differences in pressure prevailing both in the pockets and in the nips for~ed by the web and the wire and by the cylinder surfaces. The strohg airflows and the differences in pressure that are produced are results of boundary-layer flow~ which are induced by the wires, by the web, and by the cylinder surfaces, as they mov~.
~ he pockets defined by adjacent open draws of the we~, the free surfaces of the corresponding drying cylinders, and the wires or felts guided by the guide rolls, are open at their ends but are otherwise closed. The venti~ation or air-conditioning of such pocketg has been considered an important factor with respect to the ef~iciency and uniformity of ~he drying accomplished in ~he ~ulti-cylinder drier sectiOh.
In recent years, the running speed of paper machines has ~een ~onstantly in~reased and is now approachlng 1500 m/min. As the running ~eeds of paper machines increase, the fluttering of the open draws of the web becomes a more serious problem hampering the running ~uality of the paper machine. Transferring the web from the pres~
section to the drier section and the ~upport of the web within the area of a single-wire draw drier section can be controlled by means of arrangements suggested in earlier patents and patent applications of applicants' assignee. ~owever, in the case of the twin-wire draw cylinder dr~ing groups and, p~rticularly, in the case of the third and fourth dryin~ groups, difficultles often occur at h~gh running speeds. The prior art arrangements are not directed to arrangements which affect the quantities of air pumped into the pocke~s of the drier section so that the web should be suctioned into contact with the drying wire as it separates from a drying cylinder to enter into a pocket.
In prior art twin-wire draw cyllnder driers, the quantity of air pumped into the pocket depends mainly on the speed of the machihe, on the geometry of the drler ~ection, and on the permeability of the drying wire.
The regulation of the moisture profile ln the pockets is accomplished in the prior art by arran~ing hlow pipes in the pockets which ~re divided into blocks in the transverse direction, the blocks being ceparately opena~le and closeable so as to regulate the quantity of air directed into the pocket. In this conection, reference is made to Finnish Patent 68,2~8 assigned to applicants' assignee.
It is known that in a twin-wire draw cylinder drier, a moist boundary layer i~ produced on the drying wire as it runs on a cylinder a~ water vapor is evaporated from t~e web and diffuses through the wire. When the wire separate~ from the cylinder, this moist boundary layer passes through the wire into the pocket due to ::-: ~ ;
_ 1 33653~
the negative pressure present in the nip. It has not been possible to eliminate the boundary layer by means of prior art pocket ventilation devices. It is an object of the present invention to provide a solution for this problem.
An arrangement by which web fluttering within the open draws of the web can be substantially reduced to thereby lower the risks of web breakage, web wrinkling and extension of the w~b, is an object of the arrangement disclosed in US
patent 4,694,587. Another object of this US patent is to provide an arrangement for ventilating the pockets and for controlling the transverse moisture profile of the web. It is therein suggested that as the web and the drying wire separate from the drying cylinder, the web is subjected to a suction effect through the drying wire by providing an area of negative pressure at that portion of the drying wire run.
The web therefore adheres to the drying wire, thereby substantially reducing the length of the open draw of the web. Suction effect is produced by directing gas or air jets in the direction opposite to the direction of travel of the adjoining drying wire run and of the adjoining wire guide roll. The air jets act to eject air out of the spaces behind them to produce the areas of negative pressure.
On the other hand, in the apparatus disclosed in the above-mentioned US patent, it was considered novel that the device comprises a blow box which extends over substantially the entire width of the drying wire, that the blow box is ~3 ' r -provided with at least two nozzle slots which are placed and constructed so that separate gas or air jets are directed by them in a direction opposite to the direction of movement of the drying wire situated opposite to the first nozzle slot and in a direction opposite to the direction of movement of the free surface of the wire guide roll situated in opposed relationship to the second nozzle slot.
Since in the arrangement of the US patent, the web does not run in a straight path onto the next drying cylinder, but, rather, follows along with the drying wire up to the guide roll substantially to its horizontal center plane, the free unsupported draw of the web can be considerably shortened and thereby stabilized. Moreover, such an unstable web run in the outlet nip can be eliminated in which case an uncontrolled negative pressure at both sides of the web will exist. A negative pressure at both sides of the web has resulted in fluttering in prior art arrangements. The quantity of air pumped into the pocket can be adjusted by the apparatus disclosed in US patent 4,694,587 by regulating the negative pressure produced by means of the gas jets. In its simplest form, negative pressure is regulated by adjusting the pressure in the blow box. Negative pressure can be regulated independently of the permeability of the drying wire.
The arrangement disclosed in US patent 4,694,587 also effects both the quantity of air removed from the pocket as 3 3 6 5 3 ~
well as the transverse distribution of the air quantity, the latter effecting the moisture profile of the web. This takes place so that the gas jet or jets are directed on the run of the drying wire on which the wire returns from the guide roll to the drying cylinder onto the web, in a direction opposite to the direction in which the wire runs, preferably by means of the same blow box which acts to produce the areas of negative pressure. These gas jets produce a positive pressure which reduces the air flow pumped out of the pocket through the wire. The regulation of the moisture profile of the web is performed by means of this arrangement at the outlet side of the drying wire so that when a blow block is open, it results in a moistening effect on the web since air is not pumped out of the pocket. When the blow block is closed, a drying effect is produced on the run of the web that faces the block since air can be pumped from this portion of the pocket. Under the circumstances, the control of the moisture profile of the web takes place exactly in the opposite way as compared with prior art pocket ventilation methods.
Another advantage of the arrangement disclosed in US
patent 4,694,587 is that the arrangement permits the use of very open drying wires, i.e., of wires of high permeability, so that it is possible to use open drying wires having a permeability such as within the range of 10,000 to 15,000 m3/m2 x h, whereas the permeability of wires commonly used in prior art twin-wire drier sections is generally within the range of between about 1,500 to 2,000 m3/m2 x h. Since the drying wires are substantially more open than those used in conventional prior art arrangements, the evaporation that takes place on the cylinders through the wires increases again resulting in a reduction in the average moisture level in the pockets. The ventilation that takes place through the outlet nips between the cylinder and the drying wire is also increased due to the more open wires.
SUMMARY OF THE lNv~ lON
Accordingly, it is an object of the present invention to provide new and improved apparatus and methods in twin-wire draw cylinder driers of paper machines.
Another object of the present invention is a further development of the arrangement described in US patent 4,694,587 which retains the advantages provided by the disclosed arrangement so that the air-conditioning of the web can be intensified and the running quality of the paper machine improved in the area of the twin-wire draw. Since attempts are always being made to increase the running speeds of paper machines, higher requirements are satisfied in accordance with the invention.
- 7a -A further object of the present invention is to provide new and improved methods and apparatus in twin-wire cylinder driers wherein the negative pressure produced at the inlet side of the wire run from the cylinder to the guide roll can be signific~n~ly increased rel~ti~e prior art arrangement~, whereby the draw of the web is improved significantly.
An ~rrangement in accordance with the invention, may, if desired, ~e applied to a pocket ventilation arrangement provided at the outlet side of the wire run between the guide roll and the drying cylinder. The pocket ventilation arrangements can advant~geously ~e provided in blocks in the transverse direction of the paper machine so as to contro~ the ~oi~ture profile and prev~nt excessive drying of the lateral areas of the web.
Briefly, in accordance with the present invention, these and other objects are obtained by providing a method wherein an oblong passage is provided in the negative pressure zone prc~uced by the gas jet and by directing the gas ~et through the o~long passage. The oblong passa~e is defined by the outer Qurface of the iire which is situated on the drying cylinder and by the surf~ce of the wall of a ~low box. By means of the oblong passage, the boundary-layer flow following along with the drying wire i3 substantially rever~ed so as to become a flow in a direction opposite to the run of the wire. An adequate level of nega~ive pressure is also isolated in the spaces situated at the rea~ side of the passage.
In accordan~e with the apparatus of the inventioh, after the nozzle, which preferably comprisçs ~ Coand~ nozzle, in the direction of the gas jet, a wall of the blow box is arranged so that together with the outer surface of the wire situated on the surface of ~he drying cylinder facing that wall, an oblong passage is defined, the length of which is several times larger than its width.
The width of the passage is the distance between the outer surfa~e of the wire and the surface of the ~low box wall.
According to the invention, a relatively long counterflow blow pa~sage is employed on the run~ of the lower and upper wires between the drying cylinder and the wire guide roll outside of the wire loop. The length of the counterflow blow passage ic cho~en so that the boundary-layer flow following the wire on its outer surface oan be substantially co~pletely reversed by means of the counterflow in the passage so as to flow in the opposit~ direc~ion thereby effectively preventing any pumping action by the wire towards the nip formed between the wire and the ~ire guide roll.
In accordance with the invention, the length of the counterflow blow passage is generally within a range of between about loo to 500 mm, and preferably within a range of between about 250 to 350 mm.
The width of the passa~e, i.e., the distahce be~ween the blow box wall that defines the pas~age and the wire situated on the surface of the drying cylinder is generally within a range of between about 20 to 100 mm and preferably within a range of between about 40 to 70 mm. The width of the couhterflow passage can be chosen wit~ a view towards facilitating the install~tion of the blow box since the width is sufficient to assure secure operation.
By means of the invention, an increased negative pressure is pxovided at the inlet side of the wire in the nip ~ormed between the wire and the guide roll~ In particular, the negative p~essure level can be as high as about -100 Pa.
In a preferred em~odiment of th~ lnvention, the negative pressure is provided in the inlet nip5 between the wires and their respective guide rolls by using only a single nozzle a~d a sealing arrangement in which case the amount of air o~ gas required to '7 _ provide the air or gas jets can be significantly re~uced.
Generally, a distance of at least about 50 mm is required between the blow box and the ~urface of thQ moving wire for reasons of secur1ty. This distance can be provided without any difflculty in accordance with the invention. Nevertheless, the invention will provide an increased level of negative pressure in the inlet nip between the wire and its guide ~oll.
DE$CRI~TION OF THE DRAWING5 A more compl~te appreciation of the present invention and many of the attendant advantages thereof will be readily understood by reference to the following detailed description when considered in connection with the accompanying drawings, it being understood that the invention is in no way limite~ to the particular embodiments shown in the drawings, and wherein:
Fig. 1 is a schematic side elevation view of a twln-wire ~ylinder drier in accordance with the invention, Fig. 2 is a sohematic plan view of ~ blow box used in the arrangement of Fig. 1 viewed in the direction of arrow B of ~ig. l;
Fig. 3 is an enlarged schematic side elevation view of a first embodiment of the invention wherein two blow nozzles and pocket ventilation are provided;
Fig. 4 is a view similar to ~ig. 3 illustrating another emobodiment of the invention wherein o~ly a single blow hozzle i~
employed and wherein a se~lin~ arrangement is p~ovided as well a~ a pocket ventilation nozzle arrangemeht, Fig. 5 is a view similar to ~igs. 3 and 4 illu~tra~ing an embodiment of the inven~on in which two ~low nozzles are provided without provisions for pooket ventilation; and Fig. 6 is a view similar to Figs. 3-5 of an embodiment of the :::: : -.. , ~ .
inventiOn wherein only a single blow nozzle is employed without provisions for pocket ventilation.
~ETAILED DESCRIPTION OF THE PREFERRE~ EMBODIMENTS
Referring now to the drawings wherein like reference characters designate identical or corresponding parts throughout the several views, and more particularly to Fig. l, a twin-wire draw multi-cylinder drier in accordance with the invention includes a line of lower drying cylinders 31, 32, .~. and a oorresponding line of upper drying cylinders 41, 42, ... . A lower wire 30 is guided by guide rolls 34, 35, ... situated between adjacent pairs of lower cylinders 31, 32, ... . Correspondingly, an upper wire 40 is guided by guide rolls 44, ... . The paper web W is situated under the drying wires 30, 40 in direct contact with the surfaces of both the lower and upper drying cylinders. The web W has open draws Wp as it travels between the lines of cylinders and it is these open draws whi~h, as a rule, have been susceptible to fluttering in conventiohal drier sections of this type. On the other hand, evaporation of water from the web W takes place to a remarkable extent on these open draws Wp. The frame construction of the drier section is conventional and is omitted from the drawings for purposes of clarity~
As seen in Figs. 1-6, a blow box in accordance with the invention is provided in each of one or more of the spaces between the lower and upper cylinders, the blow boxes extending in the transverse direction over the entire width of the web ~ ahd d~yihg wires 30 and 40. A blow box 10 includes substantially verti~al walls 14 and 16 and suhstantially horizontal walls 15 and 17, the wall 15 being situated in opposed relationship to the free sector of a respecti~e one of quide rolls 34, 35 and 44, spaced a small distance there~om to form a small gap V. The walls 14 and 15 are reinforced by means of tubular me~bers lla and 12a which extend over the entire width of the blow box 10. AS shown in ~igs. 3 and 5, Coanda nozzle ~lots 11 and 12 are provlded in conne~tion with the tubular members lla and 12a, the nozzle slots 11 and 12 being in part de~ined by the tubular ~embers lla and 12a in combination with sheet members or edge folds of the walls 14 and 15. ~he tran ver~e end~ of blow box 10 are closed by walls 21 (Fig. 2). ~r d~cts 22 are provided in one or both of the wall~ 21 through which pressurized blow air and pocXet ventilation air, if any, a~e introduced into the ~ox 10. The pre~sure p of the blow air is preferably in the range of ~etween about 1000 to 1500 Pa.
The Coanda nozzle 11 of each blow box 10 is situated prOximate to a re~pective drying wire 30, 40 in the region where that drying wire separates from a respective drying cylin~er 31, 41 and i5 constLucted to direct a gas jet Fl (whlch generally eomprises an air ~et) along the drying wire 30, 40 in a direction opposi~e to the direction of travel of the drying wire. The other no~le slot 12 is si~uated proximate to the respective one of guide rolls 34, 44 and is constructed to direct an air jet F2 along the guide roll 34, 44 in a direction opposite to the direction of movement of the roll :
surface.
In accordance with the invention, the ga~ jet or jets Fl directed through the first Coand~ no~zle 11 is blown in a direction opposite to the direction of movement of the ~rying wire 30, 40 through an oblong pas~ge R. The leng~h L of passage ~ is generally within the ran~e of between about 100 to 500 mm, and preferahly within the range of between ~bou~ 250 to 350 mm. The width ~ of the passage, comprising the distance between the ~urved vertical wall 14 of blow ~ox 10 and the drying wire 30, 40 in opposed relationship thereto is generally within the range of between about 20 to 100 mm, 1 33653~
and preferably within tl-e range of between about 40 to 70 ~m, such as about 50 mm, which is usally the di~tance from the drying wire required for s~fety. Generally, the ratio of ~he length L of passage R to the width M of passage R, l.e. L/M, i~ generally withln the range of between about 3 to 10, and preferably within the range of between about 5 to 7. Such dimensions insure, fir~tly, that air is efficiently ejected from the negative pressure spaces A- and N-, and secondly, that the boundary l~yer flow th~t follows the outer ~urface of the wires 30, 40 is sub~tantially completely eliminated and rever~ed to a direction p~rallel but opposite to the direction of movemen~ of the drying wire.
~ y means of alr jets F1 and F2, air is e~eCted from the sp~ce A- between the drying w~re 30 and the wall 14 of blow box 10 as well ac from the wedge space N- betw~en the drying w re 30, 40 and the guide roll 34, 44 .n the directions of arrows El and E2 so that a negative pressure is e~ficiently produced in the spaces. The neg~tive pressur~ produced by the air jets, which may reach a level on the order of about -lOO Pa causes the web W to efficiently adhere to the drying wire 30, 40 after the web has been detached from the surface 31, 41 of the drying cylinder since the drying wires 30, 40 are relatively air permeable. The web W remains in contact with the ~urface of wire 30, 40 until the end of nip N~, i.e. up to a line where the dryin~ wire 30, 40 ~ontacts the guide roll 34, 44. This point of contact is situated in a horizontal plane containing the center point of the guide roll 30, 40 or a plane proximate thereto.
The web detaches from the drylng wire 30, 40 a~ter this point ~nd continues tow~rd~ the next drying cylinder having ~ substantially shorter free run Wp.
The width of the nozzle slots ll and 12 is generally in ~he range of between about 2 to 5 mm. The speed of the air jets F1 and -F2 through nozzle slots 11 and 1~ i3 generally in the range of between about 15 to 50 m/s.
The particular features of the variou~ embodiments illu~trated in Figs. 3-6 and the differences between these embodiments will now be described. Referring to the embodiments shown in Figs. 3 and 4, the blow box includes an arrangement for ventilating or conditioning the air in the pookets defined between the adjacent free runs Wp of web W, the free sector of drying cylinder 32 and the drying wire 40 guided by guide roll 44. Ventllation of thiæ pocket is provided by producing a positive presæure area S+ on the return run of the drying wire 40 traveling between the guide roll 44 and the drying cylinder 42. The positive pressure area S+ provided on the side of t~e return run of the dry~ng wire reæults in a flow Fin being pro~uced through the wire 40 into the pockets ~ to ventilate the same. Acoording to the embo~iment of Fig. 2, the flow~ F3 are arranged in the oentral region of the web W since the lateral regions of the web have a natural tendency to dry more extensively.
The positive pressure area S+ 1~ produced by means of a noæzle 13 provided in the outer wall of blow box lO connected to an alr duct 18. As seen in Figs. 2, 3 ~nd 4, air jet~ F3 are directed through the nozzle 13 in a di~eo~-ion opposite to the direction of movement of the ~ire 30, 40 so that an area S+ of positive pressure is produced in the gap space between the straight run of the wire 30, 40 and the wall 1~ of blow box 10, as well as in the outlet nip ~etween the wire and the guide roll. The poæitive pre~æure is further incre~sed by the air jets F2 directed through nozzle 12 as is shown in ~ig. 3.
In the embodiment of Fig. 4, the second nozzle 12 employed i~
the embodiment of Fig. 3 i~ elimlnated. In thi~ embodiment, a seal 20 attached to a tuhular member l~ iæ provided which drags against the outer surface of a respective guide roll 34, 35, 44 ~nd seals ~nd ~14-, .~ ,. . .~ , - ...
~ i - ~, separate~ the neyative pressure areas A-, N- from the positive pressure area S+. In the embodlment of Fig. 4, an ejectlon flow E2 tFig. ~) is not produce~ through the gap space V.
~ eferring to Flg 2 which illu~trates the blow box lO of ~lgs. 3 or 4 from the direction B of Fig. 1, blow box 10 comprises a hlow nozzle 13 divided lnto blocks 131 ... 13N for pocket ventilatl~n. Adjustable air flow~ F31 ... F3~ are directed from ths blow nozzle blooks 13l ... l~N into the slot space S+.
PressUrized air for the ai~ flcws is pa~sed into the noz~le blocks 13l ... 13N through the duct l~ which is itself divided into block5 26l ... 26N. The duct blocks 211 ... 2~N are provided with adjusting valves ~51 Z5N ~Y means of which th~ magnitude of the air jets F31 ... F3N directed through the nozzle blo~k~
13~ 3N can be adjusted. The inlet flow Fin1 is passed through a duct 22 into the ~l~cks 26~ 6N of duct 18.
Correspondingly, the air passed through nozzles 11 and 1~ ~Fig. 3) or through nozzle 11 alon~ (Fig. 4) is introduced thro~gh the opposite duct 23 as inlet flow Fin2 The inlet air flow Finl for pocket ventilation comprlses hot, dry air. On the other hand, it is possible to use moi~t air for the gas jets F1. ~he air passed through the second nozzle 12 in the case of the embodiment of Fig. 3 is preferably dry air ~ince it enter~ into the pocket T for air-conditioning purposes.
As seen in Fig. l, the wire 40 and ~ree run wp of the we~ w arrive ~t the inlet nip N+ of cylinder 42 separately.
Instead of drying wires ~hich are conventionally used in twin-wire draw cylinder driers, whose permeability is ~ener~lly within the range of between about 1500 ~o 2000 m3/m2 x h, it is advantageous to use for the drying wires 30, 40, wire~ which are substantially more per~eable. Preferably, the permeability of drying wires 30, 40 is within the range o~ between abo~t 5000 to 20,0~0 m3/m2 x h, and most preferably within the range of between about 10,000 to 15,~00 m3/m2 x h.
In the illu~trations of Figs. 3-6, the respective proportions of the various gap spaces are shown in a subst~ntially accurate manner.
The size of the nozzle slot~ 13 has been exaggerated to some extent for purposes of ~larity. An e~ample of ~he dimensions of a twin-wire drier section in accordance with the invention is as follows, it bein~ under~tood that the inv~ntion i5 not limite~ to components havin~ these particular dimensions. The diameter of the drylng cylinders 31, 32, 41, 42 is 1,830 m~, the distance between planes containing the central axes of the upper a~d lower lines of drying cylinders i~ 200 mm, the spacing between the cylinder~ in the upper line and the lower line in the horizontal direction is 2,600 mm, and the diameter of the guide rolls 34, 35, ~4 is 700 mm.
AS iS well known, the initial cylinder groups in a paper machine drier section usually comprise single-wire draw groups, while twin-wire draw groups are used ln the subsequent groups, for example, in the third to fourth groups. The method and apparatuY of the invention are applied in one or several groups of twin-wire drier sections, either in one or in several spaces between adjacent cylinders. Advantageously, the invention may be ~pplied for example in one or two of the fir~t gro~ps of twin-wire draw drier sections in the direction of web runs where the web is most susceptible to fluttering ~ecause of its moisture level and its strength and elasticity properties.
Obviously, n~merous modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to ~e understood that within the scope of the claims appended hereto, the invention may be pr~cticed otherwise than as specifically disclosed herein.
~; ., .
`_ ~ACKG~OUN~ OF THE INYENTION
This invention relates generally to methods and apparatus in paper ma~ing machines and, more particularly, to methods and apparatus in twin-wire cylinder drier sections of paper machines.
Conventional cylinder driQrs include a line of upper heated drying cylinders and a line of lower heated drying cylinders. such cylinder drier sections can generally be ~ivided into two groups, namely, single-wire draw cylinder driers and twin-wire draw cylinder driers, In single wire draw cylinder driers, the web is passed over the heated drying cylinders running from one line of cylinders to the other whlle supported by a drying wire so that on one line of cylinders, the web is situated between th~ drying wire and the cylinder &urface, while on the other line of cylinders, the web is situated outside of the drying wire with the latter being situated between the cylinder s~rface and the web. Single-wire draw cylinder driers are a~vantageous in tha~ the web is supported at all times by the drying wire and has no open draws o~ any substantial length, whereby the possibilities of web breaka~e and wrinkle formation are substantially reduced.
In twin-wire draw cylinder driers, separate upper and lower wires are used in connection with the upper and lower cylinders respectively. The wires are guided by the surfaçes of the respective drying ~ylinders and by guide rolls situated in spaces between adjacent drying cylinders. In thls manner, the web is pressed by the upper wire in direct drying contact against the surfaces of the upper cylinders, and, ~orrespondingly, is pressed by the lower wire directly against the surfaces of the lower drying cylinders. The we~
passes between the lines of upper and lower cylinders as an open draw.
The present invention is directed to improvemehtS in methods and apparatus in twin~wire draw cylinder drier sections.
In twin-wire draw cylinder drier ~ections, the web usually h~s a substantially long open draw as it passes from one line of cylinders to the other. These open draws have been susceptible to fluttering often re6ulting in breakage and formation of wrinkles in the web.
These draw~acks have been particularly acute in the initial part of the drier section where the web is still relatively moist and, therefore, of low strength and i~s elastic propertles are such as to render the web susceptible to fluttering.
Attempts have been made in ~he past to eli~inate these drawbacks by reducing the length of the open draws of the web in the initlal part of the drying section by moving the cylinder~ of the upper and lower liJles clo~er to each other, i.e., by situating the imaginary planes con~ining the axes of the upper and lower lines of the cylinders at a shorter distance from each other. ~owever, this ~end~
to reduce the drying efficiency of the arrangement.
It has also been suggested to convert the third and fourth groups of drying cylinders in the drier section to single-wire draw arrange~ent~. However, this is considered to be an extreme 601ution since lt results in reduced efficiency of evaporation ~nd increased difficulty in air-conditioning.
Attempts have also been made to reduce fluttering of the paper web in twin-wire draw cylinder drier~ by di~placing the felt or wire guide rolls in a manner such that the unsupported run o~ the web is reduced in leng~h. U.S. pateht 3,753,2~8 dlscloses such an arrangement. Moreover, a Swedish paper machine in which the guide r~lls are positioned in accordance wLth U.S. patent 3,753,298 is described in the paper "Engineering Consideratien for Lightweight Paper Drying in High Speed Machines", Paper Technology In Industry, July/AugUst 1978. This machine ~as reached a running speed of 853 _ 1 ~36535 m/min. However, fluttering of the we~ ha~ continued to be a diffic~lty.
The fluttering of a paper web has also been considered ~n the paper "Paperin valmistus" (Manufacture of paper) (Suomen Paperi-insinoorien Yhdistyksen oppi - ~a kasikirja III osa 1 -Textbook and Manual of the Association of Paper Engineers in Finland, Vol. III, Part 1) on pages 699 to 700. This article suggests that fluttering of the edge of a web ls generally not caused by air flows which had been frequently assumed. Under such circumstances, the fluttering of a web could not be prevented to ~ significant extent by guiding the air flows in the drying section, which has, however, often been attempted.
Web fluttering is today considered to result essentially from excessively strong airflows in the pockets defined inside the cylinder drier by the free surface6 of the drying cyl inders and the wire~ or felts guided by the guide rolls, and ~rom differences in pressure prevailing both in the pockets and in the nips for~ed by the web and the wire and by the cylinder surfaces. The strohg airflows and the differences in pressure that are produced are results of boundary-layer flow~ which are induced by the wires, by the web, and by the cylinder surfaces, as they mov~.
~ he pockets defined by adjacent open draws of the we~, the free surfaces of the corresponding drying cylinders, and the wires or felts guided by the guide rolls, are open at their ends but are otherwise closed. The venti~ation or air-conditioning of such pocketg has been considered an important factor with respect to the ef~iciency and uniformity of ~he drying accomplished in ~he ~ulti-cylinder drier sectiOh.
In recent years, the running speed of paper machines has ~een ~onstantly in~reased and is now approachlng 1500 m/min. As the running ~eeds of paper machines increase, the fluttering of the open draws of the web becomes a more serious problem hampering the running ~uality of the paper machine. Transferring the web from the pres~
section to the drier section and the ~upport of the web within the area of a single-wire draw drier section can be controlled by means of arrangements suggested in earlier patents and patent applications of applicants' assignee. ~owever, in the case of the twin-wire draw cylinder dr~ing groups and, p~rticularly, in the case of the third and fourth dryin~ groups, difficultles often occur at h~gh running speeds. The prior art arrangements are not directed to arrangements which affect the quantities of air pumped into the pocke~s of the drier section so that the web should be suctioned into contact with the drying wire as it separates from a drying cylinder to enter into a pocket.
In prior art twin-wire draw cyllnder driers, the quantity of air pumped into the pocket depends mainly on the speed of the machihe, on the geometry of the drler ~ection, and on the permeability of the drying wire.
The regulation of the moisture profile ln the pockets is accomplished in the prior art by arran~ing hlow pipes in the pockets which ~re divided into blocks in the transverse direction, the blocks being ceparately opena~le and closeable so as to regulate the quantity of air directed into the pocket. In this conection, reference is made to Finnish Patent 68,2~8 assigned to applicants' assignee.
It is known that in a twin-wire draw cylinder drier, a moist boundary layer i~ produced on the drying wire as it runs on a cylinder a~ water vapor is evaporated from t~e web and diffuses through the wire. When the wire separate~ from the cylinder, this moist boundary layer passes through the wire into the pocket due to ::-: ~ ;
_ 1 33653~
the negative pressure present in the nip. It has not been possible to eliminate the boundary layer by means of prior art pocket ventilation devices. It is an object of the present invention to provide a solution for this problem.
An arrangement by which web fluttering within the open draws of the web can be substantially reduced to thereby lower the risks of web breakage, web wrinkling and extension of the w~b, is an object of the arrangement disclosed in US
patent 4,694,587. Another object of this US patent is to provide an arrangement for ventilating the pockets and for controlling the transverse moisture profile of the web. It is therein suggested that as the web and the drying wire separate from the drying cylinder, the web is subjected to a suction effect through the drying wire by providing an area of negative pressure at that portion of the drying wire run.
The web therefore adheres to the drying wire, thereby substantially reducing the length of the open draw of the web. Suction effect is produced by directing gas or air jets in the direction opposite to the direction of travel of the adjoining drying wire run and of the adjoining wire guide roll. The air jets act to eject air out of the spaces behind them to produce the areas of negative pressure.
On the other hand, in the apparatus disclosed in the above-mentioned US patent, it was considered novel that the device comprises a blow box which extends over substantially the entire width of the drying wire, that the blow box is ~3 ' r -provided with at least two nozzle slots which are placed and constructed so that separate gas or air jets are directed by them in a direction opposite to the direction of movement of the drying wire situated opposite to the first nozzle slot and in a direction opposite to the direction of movement of the free surface of the wire guide roll situated in opposed relationship to the second nozzle slot.
Since in the arrangement of the US patent, the web does not run in a straight path onto the next drying cylinder, but, rather, follows along with the drying wire up to the guide roll substantially to its horizontal center plane, the free unsupported draw of the web can be considerably shortened and thereby stabilized. Moreover, such an unstable web run in the outlet nip can be eliminated in which case an uncontrolled negative pressure at both sides of the web will exist. A negative pressure at both sides of the web has resulted in fluttering in prior art arrangements. The quantity of air pumped into the pocket can be adjusted by the apparatus disclosed in US patent 4,694,587 by regulating the negative pressure produced by means of the gas jets. In its simplest form, negative pressure is regulated by adjusting the pressure in the blow box. Negative pressure can be regulated independently of the permeability of the drying wire.
The arrangement disclosed in US patent 4,694,587 also effects both the quantity of air removed from the pocket as 3 3 6 5 3 ~
well as the transverse distribution of the air quantity, the latter effecting the moisture profile of the web. This takes place so that the gas jet or jets are directed on the run of the drying wire on which the wire returns from the guide roll to the drying cylinder onto the web, in a direction opposite to the direction in which the wire runs, preferably by means of the same blow box which acts to produce the areas of negative pressure. These gas jets produce a positive pressure which reduces the air flow pumped out of the pocket through the wire. The regulation of the moisture profile of the web is performed by means of this arrangement at the outlet side of the drying wire so that when a blow block is open, it results in a moistening effect on the web since air is not pumped out of the pocket. When the blow block is closed, a drying effect is produced on the run of the web that faces the block since air can be pumped from this portion of the pocket. Under the circumstances, the control of the moisture profile of the web takes place exactly in the opposite way as compared with prior art pocket ventilation methods.
Another advantage of the arrangement disclosed in US
patent 4,694,587 is that the arrangement permits the use of very open drying wires, i.e., of wires of high permeability, so that it is possible to use open drying wires having a permeability such as within the range of 10,000 to 15,000 m3/m2 x h, whereas the permeability of wires commonly used in prior art twin-wire drier sections is generally within the range of between about 1,500 to 2,000 m3/m2 x h. Since the drying wires are substantially more open than those used in conventional prior art arrangements, the evaporation that takes place on the cylinders through the wires increases again resulting in a reduction in the average moisture level in the pockets. The ventilation that takes place through the outlet nips between the cylinder and the drying wire is also increased due to the more open wires.
SUMMARY OF THE lNv~ lON
Accordingly, it is an object of the present invention to provide new and improved apparatus and methods in twin-wire draw cylinder driers of paper machines.
Another object of the present invention is a further development of the arrangement described in US patent 4,694,587 which retains the advantages provided by the disclosed arrangement so that the air-conditioning of the web can be intensified and the running quality of the paper machine improved in the area of the twin-wire draw. Since attempts are always being made to increase the running speeds of paper machines, higher requirements are satisfied in accordance with the invention.
- 7a -A further object of the present invention is to provide new and improved methods and apparatus in twin-wire cylinder driers wherein the negative pressure produced at the inlet side of the wire run from the cylinder to the guide roll can be signific~n~ly increased rel~ti~e prior art arrangement~, whereby the draw of the web is improved significantly.
An ~rrangement in accordance with the invention, may, if desired, ~e applied to a pocket ventilation arrangement provided at the outlet side of the wire run between the guide roll and the drying cylinder. The pocket ventilation arrangements can advant~geously ~e provided in blocks in the transverse direction of the paper machine so as to contro~ the ~oi~ture profile and prev~nt excessive drying of the lateral areas of the web.
Briefly, in accordance with the present invention, these and other objects are obtained by providing a method wherein an oblong passage is provided in the negative pressure zone prc~uced by the gas jet and by directing the gas ~et through the o~long passage. The oblong passa~e is defined by the outer Qurface of the iire which is situated on the drying cylinder and by the surf~ce of the wall of a ~low box. By means of the oblong passage, the boundary-layer flow following along with the drying wire i3 substantially rever~ed so as to become a flow in a direction opposite to the run of the wire. An adequate level of nega~ive pressure is also isolated in the spaces situated at the rea~ side of the passage.
In accordan~e with the apparatus of the inventioh, after the nozzle, which preferably comprisçs ~ Coand~ nozzle, in the direction of the gas jet, a wall of the blow box is arranged so that together with the outer surface of the wire situated on the surface of ~he drying cylinder facing that wall, an oblong passage is defined, the length of which is several times larger than its width.
The width of the passage is the distance between the outer surfa~e of the wire and the surface of the ~low box wall.
According to the invention, a relatively long counterflow blow pa~sage is employed on the run~ of the lower and upper wires between the drying cylinder and the wire guide roll outside of the wire loop. The length of the counterflow blow passage ic cho~en so that the boundary-layer flow following the wire on its outer surface oan be substantially co~pletely reversed by means of the counterflow in the passage so as to flow in the opposit~ direc~ion thereby effectively preventing any pumping action by the wire towards the nip formed between the wire and the ~ire guide roll.
In accordance with the invention, the length of the counterflow blow passage is generally within a range of between about loo to 500 mm, and preferably within a range of between about 250 to 350 mm.
The width of the passa~e, i.e., the distahce be~ween the blow box wall that defines the pas~age and the wire situated on the surface of the drying cylinder is generally within a range of between about 20 to 100 mm and preferably within a range of between about 40 to 70 mm. The width of the couhterflow passage can be chosen wit~ a view towards facilitating the install~tion of the blow box since the width is sufficient to assure secure operation.
By means of the invention, an increased negative pressure is pxovided at the inlet side of the wire in the nip ~ormed between the wire and the guide roll~ In particular, the negative p~essure level can be as high as about -100 Pa.
In a preferred em~odiment of th~ lnvention, the negative pressure is provided in the inlet nip5 between the wires and their respective guide rolls by using only a single nozzle a~d a sealing arrangement in which case the amount of air o~ gas required to '7 _ provide the air or gas jets can be significantly re~uced.
Generally, a distance of at least about 50 mm is required between the blow box and the ~urface of thQ moving wire for reasons of secur1ty. This distance can be provided without any difflculty in accordance with the invention. Nevertheless, the invention will provide an increased level of negative pressure in the inlet nip between the wire and its guide ~oll.
DE$CRI~TION OF THE DRAWING5 A more compl~te appreciation of the present invention and many of the attendant advantages thereof will be readily understood by reference to the following detailed description when considered in connection with the accompanying drawings, it being understood that the invention is in no way limite~ to the particular embodiments shown in the drawings, and wherein:
Fig. 1 is a schematic side elevation view of a twln-wire ~ylinder drier in accordance with the invention, Fig. 2 is a sohematic plan view of ~ blow box used in the arrangement of Fig. 1 viewed in the direction of arrow B of ~ig. l;
Fig. 3 is an enlarged schematic side elevation view of a first embodiment of the invention wherein two blow nozzles and pocket ventilation are provided;
Fig. 4 is a view similar to ~ig. 3 illustrating another emobodiment of the invention wherein o~ly a single blow hozzle i~
employed and wherein a se~lin~ arrangement is p~ovided as well a~ a pocket ventilation nozzle arrangemeht, Fig. 5 is a view similar to ~igs. 3 and 4 illu~tra~ing an embodiment of the inven~on in which two ~low nozzles are provided without provisions for pooket ventilation; and Fig. 6 is a view similar to Figs. 3-5 of an embodiment of the :::: : -.. , ~ .
inventiOn wherein only a single blow nozzle is employed without provisions for pocket ventilation.
~ETAILED DESCRIPTION OF THE PREFERRE~ EMBODIMENTS
Referring now to the drawings wherein like reference characters designate identical or corresponding parts throughout the several views, and more particularly to Fig. l, a twin-wire draw multi-cylinder drier in accordance with the invention includes a line of lower drying cylinders 31, 32, .~. and a oorresponding line of upper drying cylinders 41, 42, ... . A lower wire 30 is guided by guide rolls 34, 35, ... situated between adjacent pairs of lower cylinders 31, 32, ... . Correspondingly, an upper wire 40 is guided by guide rolls 44, ... . The paper web W is situated under the drying wires 30, 40 in direct contact with the surfaces of both the lower and upper drying cylinders. The web W has open draws Wp as it travels between the lines of cylinders and it is these open draws whi~h, as a rule, have been susceptible to fluttering in conventiohal drier sections of this type. On the other hand, evaporation of water from the web W takes place to a remarkable extent on these open draws Wp. The frame construction of the drier section is conventional and is omitted from the drawings for purposes of clarity~
As seen in Figs. 1-6, a blow box in accordance with the invention is provided in each of one or more of the spaces between the lower and upper cylinders, the blow boxes extending in the transverse direction over the entire width of the web ~ ahd d~yihg wires 30 and 40. A blow box 10 includes substantially verti~al walls 14 and 16 and suhstantially horizontal walls 15 and 17, the wall 15 being situated in opposed relationship to the free sector of a respecti~e one of quide rolls 34, 35 and 44, spaced a small distance there~om to form a small gap V. The walls 14 and 15 are reinforced by means of tubular me~bers lla and 12a which extend over the entire width of the blow box 10. AS shown in ~igs. 3 and 5, Coanda nozzle ~lots 11 and 12 are provlded in conne~tion with the tubular members lla and 12a, the nozzle slots 11 and 12 being in part de~ined by the tubular ~embers lla and 12a in combination with sheet members or edge folds of the walls 14 and 15. ~he tran ver~e end~ of blow box 10 are closed by walls 21 (Fig. 2). ~r d~cts 22 are provided in one or both of the wall~ 21 through which pressurized blow air and pocXet ventilation air, if any, a~e introduced into the ~ox 10. The pre~sure p of the blow air is preferably in the range of ~etween about 1000 to 1500 Pa.
The Coanda nozzle 11 of each blow box 10 is situated prOximate to a re~pective drying wire 30, 40 in the region where that drying wire separates from a respective drying cylin~er 31, 41 and i5 constLucted to direct a gas jet Fl (whlch generally eomprises an air ~et) along the drying wire 30, 40 in a direction opposi~e to the direction of travel of the drying wire. The other no~le slot 12 is si~uated proximate to the respective one of guide rolls 34, 44 and is constructed to direct an air jet F2 along the guide roll 34, 44 in a direction opposite to the direction of movement of the roll :
surface.
In accordance with the invention, the ga~ jet or jets Fl directed through the first Coand~ no~zle 11 is blown in a direction opposite to the direction of movement of the ~rying wire 30, 40 through an oblong pas~ge R. The leng~h L of passage ~ is generally within the ran~e of between about 100 to 500 mm, and preferahly within the range of between ~bou~ 250 to 350 mm. The width ~ of the passage, comprising the distance between the ~urved vertical wall 14 of blow ~ox 10 and the drying wire 30, 40 in opposed relationship thereto is generally within the range of between about 20 to 100 mm, 1 33653~
and preferably within tl-e range of between about 40 to 70 ~m, such as about 50 mm, which is usally the di~tance from the drying wire required for s~fety. Generally, the ratio of ~he length L of passage R to the width M of passage R, l.e. L/M, i~ generally withln the range of between about 3 to 10, and preferably within the range of between about 5 to 7. Such dimensions insure, fir~tly, that air is efficiently ejected from the negative pressure spaces A- and N-, and secondly, that the boundary l~yer flow th~t follows the outer ~urface of the wires 30, 40 is sub~tantially completely eliminated and rever~ed to a direction p~rallel but opposite to the direction of movemen~ of the drying wire.
~ y means of alr jets F1 and F2, air is e~eCted from the sp~ce A- between the drying w~re 30 and the wall 14 of blow box 10 as well ac from the wedge space N- betw~en the drying w re 30, 40 and the guide roll 34, 44 .n the directions of arrows El and E2 so that a negative pressure is e~ficiently produced in the spaces. The neg~tive pressur~ produced by the air jets, which may reach a level on the order of about -lOO Pa causes the web W to efficiently adhere to the drying wire 30, 40 after the web has been detached from the surface 31, 41 of the drying cylinder since the drying wires 30, 40 are relatively air permeable. The web W remains in contact with the ~urface of wire 30, 40 until the end of nip N~, i.e. up to a line where the dryin~ wire 30, 40 ~ontacts the guide roll 34, 44. This point of contact is situated in a horizontal plane containing the center point of the guide roll 30, 40 or a plane proximate thereto.
The web detaches from the drylng wire 30, 40 a~ter this point ~nd continues tow~rd~ the next drying cylinder having ~ substantially shorter free run Wp.
The width of the nozzle slots ll and 12 is generally in ~he range of between about 2 to 5 mm. The speed of the air jets F1 and -F2 through nozzle slots 11 and 1~ i3 generally in the range of between about 15 to 50 m/s.
The particular features of the variou~ embodiments illu~trated in Figs. 3-6 and the differences between these embodiments will now be described. Referring to the embodiments shown in Figs. 3 and 4, the blow box includes an arrangement for ventilating or conditioning the air in the pookets defined between the adjacent free runs Wp of web W, the free sector of drying cylinder 32 and the drying wire 40 guided by guide roll 44. Ventllation of thiæ pocket is provided by producing a positive presæure area S+ on the return run of the drying wire 40 traveling between the guide roll 44 and the drying cylinder 42. The positive pressure area S+ provided on the side of t~e return run of the dry~ng wire reæults in a flow Fin being pro~uced through the wire 40 into the pockets ~ to ventilate the same. Acoording to the embo~iment of Fig. 2, the flow~ F3 are arranged in the oentral region of the web W since the lateral regions of the web have a natural tendency to dry more extensively.
The positive pressure area S+ 1~ produced by means of a noæzle 13 provided in the outer wall of blow box lO connected to an alr duct 18. As seen in Figs. 2, 3 ~nd 4, air jet~ F3 are directed through the nozzle 13 in a di~eo~-ion opposite to the direction of movement of the ~ire 30, 40 so that an area S+ of positive pressure is produced in the gap space between the straight run of the wire 30, 40 and the wall 1~ of blow box 10, as well as in the outlet nip ~etween the wire and the guide roll. The poæitive pre~æure is further incre~sed by the air jets F2 directed through nozzle 12 as is shown in ~ig. 3.
In the embodiment of Fig. 4, the second nozzle 12 employed i~
the embodiment of Fig. 3 i~ elimlnated. In thi~ embodiment, a seal 20 attached to a tuhular member l~ iæ provided which drags against the outer surface of a respective guide roll 34, 35, 44 ~nd seals ~nd ~14-, .~ ,. . .~ , - ...
~ i - ~, separate~ the neyative pressure areas A-, N- from the positive pressure area S+. In the embodlment of Fig. 4, an ejectlon flow E2 tFig. ~) is not produce~ through the gap space V.
~ eferring to Flg 2 which illu~trates the blow box lO of ~lgs. 3 or 4 from the direction B of Fig. 1, blow box 10 comprises a hlow nozzle 13 divided lnto blocks 131 ... 13N for pocket ventilatl~n. Adjustable air flow~ F31 ... F3~ are directed from ths blow nozzle blooks 13l ... l~N into the slot space S+.
PressUrized air for the ai~ flcws is pa~sed into the noz~le blocks 13l ... 13N through the duct l~ which is itself divided into block5 26l ... 26N. The duct blocks 211 ... 2~N are provided with adjusting valves ~51 Z5N ~Y means of which th~ magnitude of the air jets F31 ... F3N directed through the nozzle blo~k~
13~ 3N can be adjusted. The inlet flow Fin1 is passed through a duct 22 into the ~l~cks 26~ 6N of duct 18.
Correspondingly, the air passed through nozzles 11 and 1~ ~Fig. 3) or through nozzle 11 alon~ (Fig. 4) is introduced thro~gh the opposite duct 23 as inlet flow Fin2 The inlet air flow Finl for pocket ventilation comprlses hot, dry air. On the other hand, it is possible to use moi~t air for the gas jets F1. ~he air passed through the second nozzle 12 in the case of the embodiment of Fig. 3 is preferably dry air ~ince it enter~ into the pocket T for air-conditioning purposes.
As seen in Fig. l, the wire 40 and ~ree run wp of the we~ w arrive ~t the inlet nip N+ of cylinder 42 separately.
Instead of drying wires ~hich are conventionally used in twin-wire draw cylinder driers, whose permeability is ~ener~lly within the range of between about 1500 ~o 2000 m3/m2 x h, it is advantageous to use for the drying wires 30, 40, wire~ which are substantially more per~eable. Preferably, the permeability of drying wires 30, 40 is within the range o~ between abo~t 5000 to 20,0~0 m3/m2 x h, and most preferably within the range of between about 10,000 to 15,~00 m3/m2 x h.
In the illu~trations of Figs. 3-6, the respective proportions of the various gap spaces are shown in a subst~ntially accurate manner.
The size of the nozzle slot~ 13 has been exaggerated to some extent for purposes of ~larity. An e~ample of ~he dimensions of a twin-wire drier section in accordance with the invention is as follows, it bein~ under~tood that the inv~ntion i5 not limite~ to components havin~ these particular dimensions. The diameter of the drylng cylinders 31, 32, 41, 42 is 1,830 m~, the distance between planes containing the central axes of the upper a~d lower lines of drying cylinders i~ 200 mm, the spacing between the cylinder~ in the upper line and the lower line in the horizontal direction is 2,600 mm, and the diameter of the guide rolls 34, 35, ~4 is 700 mm.
AS iS well known, the initial cylinder groups in a paper machine drier section usually comprise single-wire draw groups, while twin-wire draw groups are used ln the subsequent groups, for example, in the third to fourth groups. The method and apparatuY of the invention are applied in one or several groups of twin-wire drier sections, either in one or in several spaces between adjacent cylinders. Advantageously, the invention may be ~pplied for example in one or two of the fir~t gro~ps of twin-wire draw drier sections in the direction of web runs where the web is most susceptible to fluttering ~ecause of its moisture level and its strength and elasticity properties.
Obviously, n~merous modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to ~e understood that within the scope of the claims appended hereto, the invention may be pr~cticed otherwise than as specifically disclosed herein.
~; ., .
Claims (18)
1. In a twin-wire cylinder drier section of a paper machine including a line of upper drying cylinders, a line of lower drying cylinders, upper guide rolls, each situated between a pair of adjacent upper cylinders, lower guide rolls, each situated between a pair of adjacent lower cylinders, an upper drying wire running over upper surfaces of said upper cylinders guided by said upper guide rolls, and a lower drying wire running over lower surfaces of said lower cylinders guided by said lower guide rolls, spaces being defined between respective pairs of adjacent drying cylinders in said upper and lower lines by respective runs of said upper and lower drying wires between said pairs of adjacent drying cylinders, and by free sectors of respective ones of said upper and lower guide rolls situated between respective pairs of adjacent drying cylinders, and wherein a paper web runs through said drier section contacting said upper and lower surfaces of said upper and lower cylinders between said cylinder surfaces and said upper and lower wires respectively, and has open draws between the lines of cylinders, a blow box situated in one of said spaces, comprising:
first nozzle means including at least one nozzle slot for directing a gas jet in a direction opposite to the direction of movement of one of said drying wire runs; and a first wall situated after said nozzle means in the direction of said gas jet in opposed relationship to a run of said drying wire situated over the surface of said drying cylinder traveling towards said guide roll, said wall together with the outer surface of said drying wire defining an oblong passage having a length and a width defined by the distance between the outer surface of the drying wire and the outer surface of said wall, and wherein the length of said oblong passage is several times greater than its width and said oblong passage is substantially of uniform width.
first nozzle means including at least one nozzle slot for directing a gas jet in a direction opposite to the direction of movement of one of said drying wire runs; and a first wall situated after said nozzle means in the direction of said gas jet in opposed relationship to a run of said drying wire situated over the surface of said drying cylinder traveling towards said guide roll, said wall together with the outer surface of said drying wire defining an oblong passage having a length and a width defined by the distance between the outer surface of the drying wire and the outer surface of said wall, and wherein the length of said oblong passage is several times greater than its width and said oblong passage is substantially of uniform width.
2. The combination of claim 1 wherein said first nozzle means comprises a Coanda nozzle.
3. The combination of claim 1 wherein the length of said oblong passage is in the range of between about 100 to 500 mm and the width of said oblong passage is in the range of between about 20 to 100 mm.
4. The combination of claim 1 wherein the length of said oblong passage is in the range of between about 250 to 350 mm and the width of said oblong passage is in the range of between about 40 to 70 mm.
5. The combination of claim 1 wherein the ratio of the length of said oblong passage to its width is in the range of between about 3 to 10.
6. The combination of claim 1 wherein the ratio of the length of said oblong passage to its width is in the range of between about 5 to 7.
7. The combination of claim 1 wherein said blow box further includes, a second wall situated in opposed relationship to said free sector of said guide roll defining said space forming a small gap therewith, and second nozzle means provided at said second wall for directing a gas jet in a direction opposite to the direction of movement of said free sector of said guide roll.
8. The combination of claim 7 wherein said second nozzle means comprises a Coanda nozzle.
9. The combination of claim 1 wherein said blow box further includes sealing means situated proximate to said free sector of said guide roll defining said space for sealing a first negative pressure space defined by an incoming run of said drying wire traveling towards said guide roll from a second positive pressure space defined by an outgoing run of said drying wire traveling away from said guide roll.
10. The combination of claim 1 wherein said blow box further includes, an additional wall situated in opposed relationship to and at a small distance from a run of said drying wire, and additional nozzle means provided at an outer part of said additional wall for directing a gas jet into a space between said additional wall and drying wire run to produce a positive pressure in said space.
11. The combination of claim 10 wherein said additional wall is substantially planar.
12. The combination of claim 10 wherein said nozzle means comprise a Coanda nozzle.
13. The combination of claim 10 further including duct means coupled to said additional nozzle means for supplying said additional nozzle means with drying pocket-ventilation air, and said duct means being adjustable in blocks for controlling the transverse moisture profile of the web.
14. A method in a twin-wire cylinder drier section of a paper machine including a line of upper drying cylinders, a line of lower drying cylinders, upper guide rolls, each situated between a pair of adjacent upper cylinders, lower guide rolls, each situated between a pair of adjacent lower cylinders, an upper drying wire running over upper surfaces of said upper cylinders guided by said upper guide rolls, and a lower drying wire running over lower surfaces of said lower cylinders guided by said lower guide rolls, spaces being defined between respective pairs of adjacent drying cylinders in said upper and lower lines, respective runs of said upper and lower drying wires between said pairs of adjacent drying cylinders, and by free sectors of respective ones of said upper and lower guide rolls situated between respective pairs of adjacent drying cylinders, and wherein a paper web runs through said dryer section contacting said upper and lower surfaces of said upper and lower cylinders between said surfaces and said upper and lower wires respectively, and has open draws between lines of cylinders, and wherein upon a web and a drying wire departing from a drying cylinder, the web is subjected to a suction effect through the drying wire within a negative pressure zone provided at a portion of the web run in which it contacts the drying wire to reduce the length of the open draw of the web, a suction effect being produced by directing a first gas jet in a direction opposite to the running direction of said drying wire in the region of said negative pressure zone, said first gas jet ejecting air from spaces behind it to produce said negative pressure zone, said method including an improvement comprising the steps of:
said gas jet directing step including directing the first gas jet through a passage which is oblong in the direction of the first gas jet, said passage being defined by an outer surface of a run of said drying wire situated over the surface of said drying cylinder and traveling towards said guide roll and by a wall of a blow box situated in said space such that the boundary layer flow following said drying wire run is substantially reversed to a direction opposite to the run of said drying wire whereby a negative pressure is created in areas at a rear side of said passage.
said gas jet directing step including directing the first gas jet through a passage which is oblong in the direction of the first gas jet, said passage being defined by an outer surface of a run of said drying wire situated over the surface of said drying cylinder and traveling towards said guide roll and by a wall of a blow box situated in said space such that the boundary layer flow following said drying wire run is substantially reversed to a direction opposite to the run of said drying wire whereby a negative pressure is created in areas at a rear side of said passage.
15. The method of claim 14 including the step of selecting the speed of said first gas jet and the dimensions of said passage such that in the spaces defined by said wire after sa1d passage, the web adhering to the opposite side of said wire, said wire guide roll, and said blow box wall, a negative pressure is produced in the range of between about -75 to -150 Pa.
16. The method of claim 15 wherein said negative pressure is about -100 Pa.
17. The method of claim 14 comprising the further step of directing a second gas jet into a gap æpace between a free sector of said guide roll and A second wall of said blow box to eject air from a nip formed by said drying wire and said guide roll.
18. The method of claim 15 including the step of reducing an area of positive pressure in a region of a run of said drying wire traveling from said guide roll to a drying cylinder by directing an additional gas jet through a gap space defined between an additional wall of said blow box and said drying wire run.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI872691 | 1987-06-17 | ||
| FI872691A FI80103C (en) | 1987-06-17 | 1987-06-17 | Method and apparatus in the cylinder dryer of a paper machine, in which a double-weave pull is used |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1336535C true CA1336535C (en) | 1995-08-08 |
Family
ID=8524682
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 569636 Expired - Lifetime CA1336535C (en) | 1987-06-17 | 1988-06-16 | Apparatus and method in a paper machine twin-wire cylinder drier section |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JP2631226B2 (en) |
| CA (1) | CA1336535C (en) |
| DE (1) | DE3818600A1 (en) |
| FI (1) | FI80103C (en) |
| SE (1) | SE467626B (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5792318A (en) * | 1996-11-18 | 1998-08-11 | Mancini; Ralph | Method to stabilize sheet between press section and dryer section of a paper-making machine |
| US6260287B1 (en) | 1997-08-08 | 2001-07-17 | Peter Walker | Wet web stability method and apparatus |
| US7435315B2 (en) | 2002-12-19 | 2008-10-14 | Metso Paper, Inc. | Arrangement for stabilizing a web |
Families Citing this family (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FI82095C (en) * | 1987-09-29 | 1991-01-10 | Valmet Paper Machinery Inc | FOERFARANDE OCH ANORDNING I CYLINDERTORKEN AV EN PAPPERSMASKIN. |
| US4891891A (en) * | 1988-10-11 | 1990-01-09 | Beloit Corporation | Dryer section apparatus and method |
| DE3914761A1 (en) * | 1989-03-08 | 1990-11-15 | Voith Gmbh J M | GUIDE ROLLER FOR A POROUS BAND, FOR EXAMPLE FOR A DRY SCREEN OF A PAPER MACHINE |
| FI92420C (en) * | 1992-04-10 | 1994-11-10 | Valmet Paper Machinery Inc | Stabilizer for a paper web in a cylinder group contained in the drying portion of a paper machine |
| JPH06185142A (en) * | 1992-12-16 | 1994-07-05 | Sekisui Chem Co Ltd | Wall panel connecting structure |
| DE4404726C2 (en) * | 1993-03-11 | 1996-04-25 | Voith Gmbh J M | Pocket ventilation in a two-wire cylinder dryer |
| SE9400728L (en) * | 1993-03-11 | 1994-09-12 | Voith Gmbh J M | Cylinder dryer with two wires |
| FI96332C (en) * | 1993-04-05 | 1996-06-10 | Valmet Paper Machinery Inc | A method for ventilating the pocket spaces of a paper machine multi-cylinder dryer and a device for ventilating the pocket spaces of a paper machine multi-cylinder dryer |
| FI93875C (en) * | 1994-02-17 | 1995-06-12 | Valmet Paper Machinery Inc | Procedure for drying a paper web and drying part in a paper machine |
| US5661911A (en) * | 1994-02-17 | 1997-09-02 | Valmet Corporation | Dryer section of a paper machine |
| FI98387C (en) | 1995-02-01 | 1997-06-10 | Valmet Corp | Method for the production of surface-treated paper, in particular fine paper, and the dry end of a paper machine |
| US5840101A (en) * | 1995-05-27 | 1998-11-24 | Wet Tex Maschinenbau Gmbh | Method and apparatus for treatment of an endless web of material with vacuum |
| US6076280A (en) * | 1995-07-26 | 2000-06-20 | Voith Sulzer Papiermaschinen Gmbh | Method and device for drying a fiber web |
| DE19527289C2 (en) * | 1995-07-26 | 2000-09-14 | Voith Sulzer Papiertech Patent | Pocket ventilation method and an air guide box for performing the method in a two-wire dryer section of a papermaking machine |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3753298A (en) * | 1971-12-17 | 1973-08-21 | Beloit Corp | Web dryer |
| DE3236576C2 (en) * | 1982-10-02 | 1988-03-24 | J.M. Voith Gmbh, 7920 Heidenheim | Air guide box for the dryer section of a paper machine |
| FI73259C (en) * | 1985-09-13 | 1987-09-10 | Valmet Oy | Method and apparatus in the cylinder dryer of a paper machine |
-
1987
- 1987-06-17 FI FI872691A patent/FI80103C/en not_active IP Right Cessation
-
1988
- 1988-05-27 SE SE8801979A patent/SE467626B/en not_active IP Right Cessation
- 1988-06-01 DE DE19883818600 patent/DE3818600A1/en active Granted
- 1988-06-16 CA CA 569636 patent/CA1336535C/en not_active Expired - Lifetime
- 1988-06-16 JP JP63147071A patent/JP2631226B2/en not_active Expired - Lifetime
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5792318A (en) * | 1996-11-18 | 1998-08-11 | Mancini; Ralph | Method to stabilize sheet between press section and dryer section of a paper-making machine |
| US6260287B1 (en) | 1997-08-08 | 2001-07-17 | Peter Walker | Wet web stability method and apparatus |
| US7435315B2 (en) | 2002-12-19 | 2008-10-14 | Metso Paper, Inc. | Arrangement for stabilizing a web |
Also Published As
| Publication number | Publication date |
|---|---|
| DE3818600A1 (en) | 1988-12-29 |
| FI872691A (en) | 1988-12-18 |
| FI80103B (en) | 1989-12-29 |
| SE8801979L (en) | 1988-12-18 |
| DE3818600C2 (en) | 1991-09-19 |
| JP2631226B2 (en) | 1997-07-16 |
| JPS6414392A (en) | 1989-01-18 |
| SE467626B (en) | 1992-08-17 |
| FI872691A0 (en) | 1987-06-17 |
| SE8801979D0 (en) | 1988-05-27 |
| FI80103C (en) | 1990-04-10 |
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| MKEX | Expiry |