CA1277531C - Dewatering apparatus - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A hydrofoil blade and support for use in a paper making ma-chine, and a method using a hydrofoil blade for dewatering and forming a paper web on a paper machine forming medium wherein a single phase fluid is formed in a gap between the hydrofoil blade and forming me-dium, and the gap is extended a sufficient distance in the machine direction to prevent expansion and corresponding cavitation of the single phase fluid in the gap.

Description

1;~775;~
B~KO~L~ ~ ~L n~l 1. Field of the :~entiC~n mis inventi~n rel~tes to a ~rofoil s~rt or b~z for use in a paper ~ ma~hine of ~e type ~erein hydrofoil blades are positioned beneath a fo~g IT~di~n an~ exter~ded in the cross mac~ dire~ti~n r~
lative to the forming medium for draining water through the fo~ning me dium from a paper web being for~ed on the f~ m~dium and ~or fo¢ming the paper web. mi~ .Lnvention also relates to a hydrofoil blade and to a methDd using hydrofoil blades for dewatering and forming a paper web.

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2. Description Of th~ Prior ~rt In the typical Pburdrinier p~p~Dh~Cing machine, an aqueous sus-pension of fib~rs, called the "stock" is flowed from a headbox onbo a traveling ~ourdrinier wire or medium, generally a w~ven belt of wire and/
or synthetic material, to form a continuous sheet of paper or paper-like material. In this co~nectian, the expression "paper or paper-like mate-rial" is used in a ~road or generic sense and is intended to include 6udh items as paper, kraft, ~oand, pulp ~heets and nonrwoven sheet-like struc-tures. As ~he sbock travels along on ~he E~nnn~rInier wqre, formation of a paper web oocurs, a6 much of the waber oontent of the stock is removed ~y drainIng. Water rem~val is enhanced ~y the use of such well-known de-vi oe s as hydrofoil hlA~es~ table rolls and/or &uction devices. This in-vention relates to hyarofoil blades.
The hyarofoil blades used in paFermaking perform tw~ functions.
~he first function is to create a vacuum pulse over the dcwnward inclined face of the hydrofoil blade. This pulse remcves a porti~n of the white water from the lcwer side of the stock or three-dimensional fiber sus-pension which lays upon the forming medium and causes some of the fibers . .

~2775;~1 to ~e laid down an~ ormed into a web. Ihe amount of such water rem~val and web formation over a g.iven h~nDfoil blade is small, and therefore a oonsiderable ~umb~r of blades is required to form all of the fibers In a stock ~ sion into a two dimensional web. For example, the use of ten to fift~ hydrofoil blades is not urxxlnnon. In other w~rds, the sheet forming process is a step-ky-step filtration process as the forming ne-dium travels over the hyarofoil ~lades, with some of the fi~ers in the lower portion of the suspension over the partially-formed web being added to the web at each successive foil blade. The average net change in fiber ooncentration or consistency of this process ranges frcm the headbox oonsistency, w~i~h is usually abou~ 0.4~ to about 1~, up to about 2.5~.
The second function d a hydrooil blade is to maintain the fibers which are st;ll in suspension throughout the fc~ming-prccess in an as-well-as dispersed condition as possible; i.e., in a deflocculated condition. Thi5 function is extremely import~nt as fibers in the 0.5-2.5%
consistency range have a ~trong tendency to flocculate into clumps on their own in a matter of m~lliseconds once the fi~er dispersive forces have de~ayed. This flocculatiDn causes the final paper to ~ehi~hly non-uniform or flo ~ ted in appearance.
. The fiber dispersive function of hyarofoil blades is caused prim2r;ly by the decay of the dewatering vacuum pulse which imparts a momentary uçwzrd force or pulse into the sbock. This pul æ creates random small scale flows, i.e., turbulence, in the stock akave the partially-formed web. The greater the angle of the downwand inclined Fart of thc hydrofoil blade, the greater this aeflocculating pulse or turbulence. The speed of travel of the suspension over the blade is .

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also a fact~ in determin~ the int~nsity of this pulse. T~us, at high machine ~peeds, the siæ of ~che ~ydr~foil ~lade angle which can be used is limited lest the vacuun be s~ e that t:he pulse crea~ will thr~
s~ of 'che s~c l~pward into ff2e air. miS p~n knc~ as "sto~c j~p" can readily damage the ~iformit~y of 1:he ~heet.
Qne a~pect of }~ydr~foil blade dewatf~ring overlook~ in the past is that when the vacuum pulse creabed by the inclined angle of the hy-drofoil blade decays ~ack to atmDsE*~ric pressure, the decay is fio~ewhat of an unstable phos~Ysnon. Ihi5 iS because the hydrofoil blade generally discharges.the water removed from the suspension directly int~ the at-mDsphere. In othRr words, the decay cf the vacuum pulse occurs virtual-ly inst~nt~ne~usly at the point where the gap betwe~n forming medium and.
hydrDfoil blade beoames tco large to ~upport a cantinuous column of water.
The location of this point is extremely sensitive to ~ll of the forces and resistances affecting the dewatering process as evidenced ky the highly variableamount of water rem3ved frcm the suspension across the .
width of foil blades. This ~ariability can be readily obserYed on any paper n~Xing machine. The waber ~ fro~ the suspensicn ~y any one hydro~oil blade is largely carried along th~ underside ~f the forming n~dium to the next blade whose l~ing edge skives the water off the unaerside of the formin~ ~edium. The amDunt of skived water varies very considerably fm m point to point ac~Dss the width of a machine at.mDst hydrDfoil blade pc~itions.
The vaxiability of dewatering in the cross nachine direction o~ the hydrof~il blades is further exacerbated ky the slight nonruni-foDmity of wear of the high density ultra-high n~lecular weight ~x~lye-thylene of w~ich mDst hydr~foil blades are na~e, as ~ell as by the ncn-uniform kuild-up of fibrous n~terial on the leading dge d many blades.

' ' ' 1~77531 These problems of polyethylene hydrofoil blades have led bo the develop-ment of a variety of ceramic blades which are much re ~ear resistant.
~hile ceramic ~lades h31d their ~hape nm ~h better than polyethylene blades, they are extremel~ fragil~ prone to damage, a~a relatively ex-pensive. Since such blades are difficult bD handle, once a Fburdrinier table has keen laid out, Ex4x~n~aker5 are loathe bD alter blades. Thus, the use of ceramic ~ ofoil blades is limited.
The cross machine direction variability of dewa ~ring of hy-drofoil blades is one, if not the pr ~ source of ~he non-unifoLmity of the "dry line"j i.e.j the line acrDss the ~ourdrini~r where air is first introdu~ed into t~e wet web over the vacuum foils or suction ~oxes.
~his variability ultimately leads to the ross-direction variation in tbe moisture oontent of the fini~hed paFer, one of the most critical pro~lems facing the ~ industry.
Another problem cIeated ~y this hlrbulence-generating pulse of hydrofoil blades i~ that it loosens up the ~tructure of the partial-ly fcrmed web and allows for th2 finer fibers as well as the filler par*icles to be washed out of the web. Thus, the strong~r the ~acuum pulse of a foil ~lade, the lower the fines and filler retention in the e?r part of the web. .This tcp-to-bottom siae variation of fines and fillers in a sheet is a major source of n~L~y paper applica~ion problems well-known bo those s~iLLLed in the art.
. ~ now to another asFect of hy~rofoil blade ap~plications and prablems, a new forming strategy has been ev~lved in which it is desirable to ninimize or even botally eliminate ~he turbulenoe on the Fb~rdrinier wqre generated ky the hydrofoil bladesO Ihis new approach lZ7753~

employs formation showers which create stock ridges which periodically collapse and reform on their own down the wire. The collapse and regeneration of these ridges creates a cross machine direction shear which deflocculates fibers in much the same way as the cross machine direction shear generated by the shake of slower papermaking machines. The advantage of these ridges over shakes is that the ridges can be employed and are effective at any machine speed including relatively high ones, whereas the effective application of the shake is limited to machine speeds below 300-400 m/min. The stock ridges formed by formation showers are extremely fragile fluid structures which are easily destroyed by the turbulence generated by hydrofoil blades.
It is clear from all of the foregoing that there is a need for hydrofoil blades wherein the amount of water removed from the suspension across each blade width; that is, the dewatering in the cross machine direction, is controlled by stabilizing the vacuum decay zone of each blade. In addition, the ab~ence of a strong pressure pulse following dewatering is desirable in order to obtaln a higher and more uniform fines and filler retentlon.
Further, there is a need in some applications for a dewatering hydrofoll blade system which does not generate turbulence.
SUMMARY OF THE INVENTION.
This invention achieves these and other objects by providing a hydrofoil blade support for use in a paper making machine of the type whereln hydrofoil blades are posltioned beneath a forming medium and extended in the cross machine direction relatlve to said forming medium for draining water , 5 ' -~ Z 77S31 through said forming medium while a paper web is being formed on said forming medium and for forming said paper web, said hydrofoil blade support comprising a plurallty of spaced hydrofoil blades which each comprise a forming medium bearing surface lying in a first plane and having a leading edge, and a trailing edge lying in a second plane parallel to said first plane, a first trailing surface diverging downward relative to said forming medium bearing surface from a first crease line to a second crease line, a first boundary forming surface extending from said second crease line to a third crease line in a third plane which is located intermediate of and parallel to said first plane and said second plane, and at least one other pair of tralling and boundary forming surfaces extendlng in tandem between said third crease line and said trailing edge, each additional of said boundary formlng surfaces lying in a plane which is located intermediate of and parallel to said second and third planes, the last of said boundary forming surfaces lying in said second plane and extending to said tra~ling edge, consecutive of sald planes being spaced from each other in the range of about 0.05 millimeters to about 4 milllmeters.
The lnvention also provides a hydrofoil blade for use ln a paper maklng machine of the type wherein hydrofoll blades are posltioned beneath a forming medium and extended in the cross machine direction relative to said forming medium for draining water through said forming medium while a paper web is being formed on said forming medium and for forming said paper web, said hydrofoil blade comprising a forming medium bearing surface lying in a first plane and having a leading edge, and a trailing edge ~ 6 ~''.

1.277531 lying in a second plane parallel to said first plane, a first trailing surface diverging downward relative to said forming medium bearing surface from a first crease line to a second crease line, a first boundary forming surface extending from said second crease line to a third crea~e line in a third plane which is located intermediate of and parallel to said first plane and said second plane, and at least one other pair of trailing and boundary forming surfaces extending in tandem between said third crease line and said trailing edge, each additional of said boundary forming surfaces lying in a plane which is located intermediate of and parallel to said second and third planes, the last of said boundary forming surfaces lying in said second plane and extending to said trailing edge, consecutive of ~aid planes being spaced from each other in the range of about 0.05 millimeters to about 4 milli~eters.
The advantages and other features of the present invention will be more fully described with reference to the accompanying 6a B

~1277531 drawings, in which:
Figure 1 is a diagrammatic representation of one embodi-ment of the present invention;
Figure 2 is a partial view of a diagrammatic representa-tion of another embodiment of the present invention;
Figure 3 is a partial view of a diagrammatic representa-tion of yet another embodiment of the present invention;
Figure 4 is a diagrammatic representation of a further embodiment of the present invention; and Figure 5 is a diagrammatic representation of a further embodiment of the present invention;
Figure 6 is a fragmentary view of Figure 5 having dimensions which have been exaggerated for the purpose of emphasis.
The embodiment of this invention which is illustrated in Figure 1 is one which is particularly suited for achieving the objects of this invention. Figure 1 diagrammatically depicts a portion of the forming section of a paper making machine of the type wherein a forming medium 2 receives stock from a headbox at a first end (not shown) and transfers a substantially self-supporting paper web from the forming medium 2 at a second end (not shown), the forming medium travelling in the machine direction generally designated by arrow 4. Hydrofoil blades are provided beneath the forming medium 2. The hydrofoil blades extend in the cross machine direction relative to the forming medium, the cross machine direc-tion generally designated by arrow 6. The functions of hydrofoil blades are to drain water through the forming medium 2 while the \~- 7 -, . . . - , , ,~.. . , ~ ' .

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'7S31 paper web 8 is being formed on the forming medium and to form the paper web. In the present invention, a hydrofoil support or box 10 is provided which includes at least a first hydrofoil blade 12 comprising a first forming medium bearing surface 14 lying in a first plane and having a first leading edge 16, and a first trailing surface 18 diverging downward relative to the first form-ing medium bearing surface 14 from a first crease line 20 to a first trailing edge 22. The first trailing edge lies in a second plane parallel to the first - 7a -- ,~ - . - ~.

- ~ ~

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plane. 1~ first and seoand planes ~ sch~natically r~resent~ at 24 and 26, r~tively. A water directin~ surface 23 ~ da~-ward fr~n the first trailing edge 22.
A secc~d adjacent ~rofoil blade 30 is also p~vided. Bl~e 30 cc~r~rises a sec~d fo~ang mediun beari~3 surfaoe 32 h~vir~ a second leading edge 36, a ~L~ t surfa oe 34 e~te=di ~ da ~ f m n the leading edge at an acute angle Jirelative ~ ~he ~ forming nedium bear-ing surfaoe, ana a second trailing surfa oe 38 diverging dcwnward r~lA-~ive bo the -Qecond forming nedium bearing surface 32 ~rom a ~eoond crease line 40 to a seoond trailing edge 42. As can be seen in Figure 1, the water directing surface 28 overlaps and i8 spaced from the front ~urface 34. m e dis~anoe 44 be ~ n the first plane 24 and the ueoood plane 26 i5 in the range of about .05 n~ met~r~ t~ about 4 n~llime-ters. Preferably, the distance between surfaces 28 and 34 i8 also in the range of about .05 millimeters to abwt 4 millimebers, the spacing n planes 24 and 26 and surfaces 28 and 34 preferably being simi-lar. me interrelationship of the overlapping and spacea surfaces 28, 34 which form a channel 46 bctwe~n adjaoent hy*rofoil blades, and the specifically dinen~ioned distance 44 between planes 24, 26, form n#ans forming a gap ke ~ n the fcrmin~ medium 2 and .the adjacent hydrofoil b~ades 12, 30, when the bydrofoil blade ~ t 10 is mounted on the paper maXing machine, so that during the paper mah ng operati~ the w~ater removed from the paFer web by suction created by the hydrofoil blade oompletely fills the gap in the absence of a~r thereky prevent-ing expansion and corresponding cavitation of the water in the gap.

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In the embodiment of Figure l, hydxofoil blade support 10 in-cluaes a plurality of adjaoent and alternating pairs of first hydro-foil ~lades 12 and seoon~ hyarofoil blades 30. Each hydrofoil blade is depicted as including a front surface ext~sxlLng dowrward from each respective leading edge at~an acute angle relative t~ each respective f q nedium bearing surface. Each hyarofoil blade is also depic*ed as incluaing a water dL~l~iting surface extending downward from each resEective trailing edge~ ~ach forming mediu~ ~#~ng surface lies in the ~rst plane aepicted at 24, and each trailing edge lies in the ~econd plane aepicbed at 26. In the ~mboaiment of Figure 1, as ~e-tween adjacent blades~ eac~ ~f the water ;recting surfaces overlaps and is sEaced from an ad~aoent front surface, and respec*ive first and seoond planes æ e spaced in the ~ange of about .05 mill~mebers bD
about 4 millimeters, to form said gap f q n~ans between aajacent hyarofoil ~lades.
Preferably, hyarofoil blade support 10 includes a ~lade or ~ades having ~ trailing surface which diverges d~ rh~Jdly to a thira crease line 48, and includes a ~ forming surface 50 lying in the seoond plane, iaentified at 26, ana extending fr~m the third crease line to the ~railing edge of each blade which includes such struc* re.:In other wcrds, each respective ~ forming surfa oe 50is paral1el~to each forming ~ediu~ bearing surface. In this emtYd1rYslt, t~e dist~nce 44 is measured between the $orming mediu~ bearing sur-face and the b~unda~y for~ing surface 50 o~ ea~ hydro~oil blade. ~y providing a boundary forming s~rface 50, an ex~ended channel iS
. formed between the forming medium and the hydrofoil blade along which water flcws m the absence of air.

: ~ ' , 1277531 ~
It will be noted that the overlapping of the wate:r directing surface and the adjacent fr~nt surface define~,e channel 4~ ~ebet~.
lb this en~, yreferal~ly ~undary fo~ni.ng surfaoe 50 is termi~ted just ahead of the leadi~ ~e of the ne~ct bydrofoil ~lade and is follaw~3d ~y the d~rd inclined wat~ ecti ~ surface ~ ic~h ex ~ ds at an angle of 30 to 45 relative to the boundary forming surface ~0. One or mDre of adjaoent frant surfaces ana water directing surfaces can be parallel as depictea in Figure 1. It is also within the teachings herein that one or nore of such surfaces ~e slightly ccnvergent to-wards the forming medium bearing surface as deFiCted in Figure 2 or slightly oonvexgent sway fxom the f~ medium bearing surface as depicted in Figure 3. After E~x~vi ~ a short parallel or a~m~st par~l-lel channel between the two hydrDfoil blades, the trailing face of the blade abruç*ly changes its angle to 90 relative tD the bDundary formang sur~a oe 50, and the white water is flung into the atmosphere.
At this point, the change in pressure is much smaller than that at the point w~ere oonventional hydrofoil blades discharge their white water intD the abmDsphene. Thus, the w~ite water is r ~ from thé under-side R the fonming medium as a oontinuous and uniformly thick oolumn of water withcut an akrupt change in pressure at the face of the formr Inthe eD!xxiinent of Figure 1, the height of the gap between the forming nEdiu~ ana the b ~ forming surface 50 of the hydro-foil blade oontnDls the amount of its dewatering. m erefore, the size of this gap csrdon~LLih1e is desira~le so ~hat the amount of dewatering at every point on the fcrming n~dium can be oontrolled and regulated. Ihe present invention includes features directed bo sùch a variable drainage rate hydrDfoil blade. ~ar example, in the e~bcdiment of Figure 4, w~icih depicts a hydrofoil blade having a configuration .
- . , ~ , . '- ~. ' . , .-,' ~

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similar tD that of Figure 1, reference characters corresponding to tho e of Figure 1 are used for similar structure. In Figure 4, the trailing surfa oe 18 is pivotally connected to the forming nedium kear-in~ surface 14, and to the boundary formung surface 50 at the third crease line 48. Far exa~ple, Figure 4 depicts trailing surfaoe 18 as a flexible nember extending from surface 14 to surface 50. It will be apparent tD those skilled in the art that other types of pivotal oon-nections can be E~x~vided. Mbans are provided ooupled bo the boundary fornung surfa oe 50 for varying ~he distance between surface 50 and the first plane, in which lies the forming n~dium ~earing surface 14, so that such distance can be oDntrDlled as desired. For example, by way of example only, Figure 4 schematically depicts a pistcn 52 and cylinder 54 for hydraulically or pneumatically raising and lowering boundary form~ng surface 50. In cperation, the raising of pisbon 52 decreases the degree ky which surface ~0 diverges from surface 14 and decreases the vertical distance between the first plane identified at 24 and the ~econd plane identified at 26 bo decrease the size of the gap. Iowering of piston 52 increases the degree ky which surfa oe 50 diverges from surface 14 and increases the vertical distance between the planes identified at 24 and 26 to increase the size of the gap.
Illustrative of one eo~xJI~ment, the forming medium bearing surface 14 is about c~e cent~meter in length, the trailing surfa oe 18 is about 3 to 15 centimeters in length, and the k~und2ry forming sur-face 50 is abcut 1 to 15 cent~meters in le~gth. The diverging angle of the trailing surface 18 is 0 to 5 as described in Wrist, United States Patent No. 2,948,465.

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, s of the p~sent ~venti~, a m~tlrxl is praviaed us~
~ydrofoil blades for dewa~ring and fo~ning a p~er w~b an a paper ma~

'{i.OI~ r -~ried t~y~ ~y SU~C~ crea~ fo~
and including the critical st~s of (1) ~ning a single phase flu~d in a gap ~et~een a~ljacent ~drofoi~ blades and the :E~oin~ m~i~n, and (2) 0ctending the gap a~uffi~i~nt distance in the ma~ne ll;~ection to E~rev~t ~ion and oarre~pandi~ cavitaticxn of ff~e single Ehase fluid in the gap. In this mann ~ , instead of en ~ ing ff~e white wa~er removed ~y the vacuun created by-the inclined surfaoe of the hydr~foil b~a~e ~rectly intD the atmDsphere, such water is carried along the un~ersiae of ~he f ~ medium in an air free gap between the under-side of the f ~ nedium and adjacent ~ foil blades. As the ~acuum decays-in this gap,-the ~ec~y is gradual rather than-- ~ , and there-fore is not unstable. It-is gr ~ because the ExurtiaIly-fo ~ web an~ stock over the fo ~ n~dium represent a oonsiderable resistance ~;.
- -bo the pressure differential ~etween this gap and the atm~sphere akcve the sbock.
It should be noted that in the es}~XL~nent of Figure 1 it i5 ..
the creaticn of the fixed horizontAl gap fol ~ the vacuNmrinducing dbwnward sloping face 18 of t ~ ~ foil blade whL~ih literally forces ;the ~lade t~ dewater the same amount of wa-ter from the cuspension fnom bD point across the entire length of the blade.~ 9y E~rvuaing a gap which is sufficiently narrow and cann~t cavitate back ~ram its exit : .point bo the abrosphere, the gap will be ~ully filled with ~luid pulled -in from a~ove thrDugh the fc~mLng nedium.

' :~ ' ' An in~ t~t a~pect of the present invention is to identif~y the nagnit~e of dis~ance 44 to assure ~at the gap betwe~ the under-side of the f~ m~i~ ar~ a~ljacent }~ydrofoil blades is filled with - water in the a~ce of air; that is, tc~ cause a single ~ihase fluid ~e car.ried al~g t~e una~rside of the fc~ming nediun in ffle gap.
sidering ~at t~ r~l ~r~foil blade is designed b~ have a ~ail~
s~rface diverging at an angle of 0 to 5 as desc~ibed ill lInited States Patent l~o. 2,948,465, the critical din~ion ~n definig the.distance 44 is the le~ of the trailing s~fa oe 1~. In or~er tc~ ass~re t~hat ~e gaE~ i5 pletely filled with a sin~le Ehase fluid, .i.e., is filled wit~ watèr in the absence of air, ~he height 44 for ~he ~ilades bei~
used can be as~tained ~y calcl~lating the aifference betbæen the sto~k thickness at the slioe~penir~ and at t~e end of .the fc~nning zone, using the e~atian:

T = W
C x R x J

wherein T is the sto~k thickness, W is the basis we~ght ~ the fini~
Bheet, C i8 the stock consisten~y ex~ressed as a fractian, R is ff~e a~erall machine retention downstream f m n the point under ~ sideratia~, and J is the jet-to-forming ~edium fipeed ratio.
Ihe use of this equat~n w~ll ncw be demonstrated, by way of example onay, in~c~cx-ation with a paper making machine F~cducins news-pri~t-type paper. The a~ove equation is first used to determine the stock thickness Tl at the slice cpening. Assuming that the ~asis weight Wl is 50 g.s.m., the consistency Ci is 0.5%, the retention Rl is 60~ and the jet-to-forming medium speed ratio Jl is 0.95, then the thickness of the sbock at the slice oQening is:

. 0050 Tl ~ Wl- = ---------------- = 1.75 om Cl x Rl x Jl .005 x .6 x .95 .

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.~, ' 1277s3~. ( The stoc3c thic}mess T2 at 'che e~ of ff~e web f~ zane can be c:alallated in a Li.tæ ma7n~ suming that t~e basis weig~t W2 is s'cill 50 g.s.m., the o~nsist~y C2 ~as in~eased tc) 2.5Y6, ffle overAl~
retentic~n R2 of the balaru~e of t~e paper ~ mac~hine i~ 90%, and the jet-to f~nni~ n~iun ~d ratio J2 has increased tt~ 1.0, then the thiclmess of the sto~c at t:he ~ of ~e w~b fonning zane is:

W . 0050 T = 2 = _ . = . 22 an 2 C2 x R2 x J2 ~025 x .9 x 1 me ff~i~s of ~ater Q r~v~3d fran ffle fo~min~ sectic%l is equal to the differ~ce be~ the sto~c thic~mess at the slice .in~ and ff~e stock thi~lmess at ff~e end of the w~b :Eonning zane, ar Q ' Tl - T2 = 1-54 As ~ that in the past ~ enty co ~ ainal 1 an~.2 hg~
drofoil blades have been reguired to cktain this resu}t, then the gap 44 should b2: -1.54 ~
_ _ - = .08 cm Further, assuming that it is desired to use t~enty five 1 blades tc cc~3n~ate for wear of surface 14 and to acco~plish similar - ~ - -dewater m gj then in .order to assure the existence of a .08 cm g~q~ 44, i -. .. the length L of the ~rai~liny surfaoe i8 L - .08 tan 1 C A.6 om . .

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Since the basi~ ~ght of the finished sheet ~W), stock can-si¢t~ (C), averaLl mac~ine re~tian ~) ar~ jet-t~forming ~
~peed ratio ~J) are ~lentifi~le in a h~wn ma~ far ar~ pa~ mac-hine al: ~he slice ~ arx~ at ~e ~nd of the w~b foq:mis~ zane, ~e a ~ ve equatio~s can ~e used to identi~y the din ~ iion of gap 44 and the length ~ of the trailing surface for any paper ~aXing application.
Dewater ~ using hy~r~foil blades of the present invention ~iffers from that of oonventional blades in that the dewa ~ is car-riea out entirely in a confined and controllable gap, and hence dewa-tering will ~e highly uniforn along the cross n~chine airection of each klade. .EtJt~eDmore, the pressure EniLse causing a loss of fines an~
filler particles will be substantially eli~inated, and the so-called "twDrsidedness" of paper as well as the intensity of the ~ell-kna~n ~wire mark" will be substantially decreased. Finally, the ~epetitive ridges formed by formation shDwers ~ill not be subject to dbsd~ tLve pulses, an~ will carry them much further d ~ the forming nxdiu~ ~h~n is presYntly the case..
Another emboaiment of ~ e present invention i8 depic~ed in Fiyure 5 whish depict8 a hydko~oil ~lade support 60 ccmpri8ing a plu-rality of s ~ kyd~Dfoil blades 62 which oomprise B formhng nediu~
~earin3 surface 64 lying in a first plane iaent~ied schematically at 66 and having a leading edge 68, and a trailing edge 70 lyqng in a second plane, identified schematically at 72, parallel to the ~ ~
plane. A f;rst tra;ling ~urfa oe 74 diverges dcwnward relative bD ~he ..
form~ng ~edium bearing surSboe 64 ~ron a first crease line 76 tD a sec-cnd crease line 7~. A firstlbc~Ylary forming surface 80 e#~ends from .
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~27'7S3~

the second crease line 78 to a thixd crease line 82, and at least one other pair or trail~ng and ~oundary forming surfaces extend in tandem between the third crease line 82 and the trailing edge 70. For example, blade 62 includes a plurality of pairs 84, 86, 88 of trailing surfaces 74 and boundary forming surfaces 80 which extend in tandem, one pair following the next in the ~achlne di-rection. As depicted in Figure 6, each of the boundary forming surfaces lie in planes, schematically depicted at 80~ in Figure 6, parallel to the forming medium bearing surface 64, consecutive of planes 66, 80~, 72 being spaced from each other in the range of about .05 millimeters to about 4 millimeters. Although not neces-sary in this embodiment, if it is desired to prolong the length of the gap between adjacent hydrofoil blades a water directing surface 90 is provided as in the other embodiments herein extending down-ward from the trailing edge 70. When using the blades 62, the height of the gap 92 ~eingcOnsecuti~e of planes 66, 80~, 72 corres-ponds to dimension 44 of Figure 1, and is measured in the same manner. It should be noted that the equations set forth herein are equally applicable to the embodiment of Figures 5 and 6. In particular, although the equations demonstrate how to identify the magnitude of gap 44, they are equally applicable in identifying the magnitude of each gap 92, the critical dimension in defining the height of each gap 92 being the length L of each respective trailing surface 74. In other words "L" can be equated to the length of trailing surface 18 in using the equations to identify '- ', - ., -: - ,- . -:

. '- ~ ~ . -. .

127753~

the magnitude of gap 44 in Figure 1 or to the length of each trailing surface 74 in Figures 5 and 6 in using the equations to separately identify the magnitude of each gap 92~ Without being limited to any theory of operatlon, it is believed that the water removed at each trailing surface 74 in the embodiment of Figures 5 and 6 travels along each respective gap 92. At the end of each respective gap 92 such moving water continues to travel but under the water being removed by the next trailing surface 74. In other words, the water removed at each trailing surface 74 travels through the gap 92 associated with such trailing surface and is then carried under the water removed by each succeeding trailing surface 74, all of such water being removed at the end of the hydrofoil blade.
The embodiments which have been described herein are but some of several which utillize this invention and are set forth here by way of illustration but not of limitation. It is apparent that many other embodiments which will be readily apparent to those skilled in the art may be made without departing materially from the spirit and scope of this invention.

Claims (12)

1. A hydrofoil blade for use in a paper making machine of the type wherein hydrofoil blades are positioned beneath a forming medium and extended in the cross machine direction relative to said forming medium for draining water through said forming medium while a paper web is being formed on said forming medium and for forming said paper web, said hydrofoil blade comprising a forming medium bearing surface lying in a first plane and having a leading edge, and a trailing edge lying in a second plane parallel to said first plane, a first trailing surface diverging downward relative to said forming medium bearing surface from a first crease line to a second crease line, a first boundary forming surface extending from said second crease line to a third crease line in a third plane which is located intermediate of and parallel to said first plane and said second plane, and at least one other pair of trailing and boundary forming surfaces extending in tandem between said third crease line and said trailing edge, each additional of said boundary forming surfaces lying in a plane which is located intermediate of and parallel to said second and third planes, the last of said boundary forming surfaces lying in said second plane and extending to said trailing edge, consecutive of said planes being spaced from each other in the range of about 0.05 millimeters to about 4 millimeters.

2. The hydrofoil blade of claim 1 including a water directing surface extending downward from said trailing edge.

3. A hydrofoil blade support for use in a paper making machine of the type wherein hydrofoil blades are positioned beneath a forming medium and extended in the cross machine direction relative to said forming medium for draining water through said forming medium while a paper web is being formed on said forming medium and for forming said paper web, said hydrofoil blade support comprising a plurality of spaced hydrofoil blades which each comprise a forming medium bearing surface lying in a first plane and having a leading edge, and a trailing edge lying in a second plane parallel to said first plane, a first trailing surface diverging downward relative to said forming medium bearing surface from a first crease line to a second crease line, a first boundary forming surface extending from said second crease line to a third crease line in a third plane which is located intermediate of and parallel to said first plane and said second plane, and at least one other pair of trailing and boundary forming surfaces extending in tandem between said third crease line and said trailing edge, each additional of said boundary forming surfaces lying in a plane which is located intermediate of and parallel to said second and third planes, the last of said boundary forming surfaces lying in said second plane and extending to said trailing edge, consecutive of said planes being spaced from each other in the range of about 0.05 millimeters to about 4 millimeters.

4. The hydrofoil blade support of claim 3 wherein said hydrofoil blades include at least a first and second adjacent hydrofoil blade, said second hydrofoil blade being adjacent to and downstream of said first hydrofoil blade and having a front surface (a) which extends downward in a downstream direction from said leading edge of said second hydrofoil blade at an acute angle relative to said forming medium bearing surface of said second hydrofoil blade, and, (b) which is spaced from and superposed relative to a water directing surface of said first hydrofoil blade which extends downward in a downstream direction from said trailing edge of said first hydrofoil blade at an angle relative to said second plane of said first hydrofoil blade, to form means in the form of a gap between said adjacent hydrofoil blades, when said hydrofoil support is mounted on said paper making machine, for removing water from said paper web by suction created by said first hydrofoil blade during the paper making operation and completely filling said gap with said water in the absence of air thereby preventing expansion and corresponding cavitation of said water in said gap.

5. The hydrofoil blade of claim 4 including at least one other pair of said first and second hydrofoil blades, each of said first and second hydrofoil blades of said at least one other pair including one of said water directing surfaces and one of said front surfaces, and adjacent of said water directing surfaces and front surfaces forming said water removal and filling means.

6. The hydrofoil blade support of claim 3 wherein at least one of said trailing surfaces is pivotally connected to its adjacent forming medium bearing surface and to its adjacent boundary forming surface, and including means coupled to said adjacent boundary forming surface for varying the distance between said adjacent boundary forming surface and said first plane.

7. The hydrofoil blade support of claim 4 wherein said front surface and said water directing surface are parallel.

8. The hydrofoil blade support of claim 4 wherein said front surface and said water directing surface converge towards said forming medium bearing surface.

9. The hydrofoil blade support of claim 4 wherein said front surface and said water directing surface converge away from said forming medium bearing surface.

10. The hydrofoil blade support of claim 5 wherein said front surfaces and said water directing surfaces are parallel.

11. The hydrofoil blade support of claim 5 wherein said front surfaces and said water directing surfaces converge towards said forming medium bearing surfaces.

12. The hydrofoil blade support of claim S wherein said front surfaces and said water directing surfaces converge away from said forming medium bearing surfaces.