US3079990A - Wet end drainage system for paper machines - Google Patents

Description

March 5, 1963 G. l. TAYLOR ETAL WET END DRAINAGE SYSTEM FOR PAPER MACHINES 4 Sheets-Sheet 1 PATENT AGENT w N U u A N m M m E D. R m 5 fl wm m m es T R m ,F U5 5F-t 5N N mY 0 D. Rf; 56 N.. 5.0? C u w w EE babcd E m m. m z bh Duma@ PJM@ m 0 o o mm w m 2 l 0s 16 5'4 .o 2 l0. lemma a a o. a a

Filed June 18, 1959 March 5, 1963 G. l. TAYLOR ETAL NET END DRAINAGE SYSTEM FOR PAPER MACHINES Filed June 18, 1959 l "ZNTOR EN@ March 5, 1963 G. l. TAYLOR ETAL WET END DRAINAGE sYsTEN FOR PAPER MACHINES 4 Sheets-Sheet 5 Filed June 18, 1959 ATTORNFV G. l. TAYLOR ETAL 3,079,990

WE11 END DRAINAGE SYSTEM FOR PAPER MACHINES 4 sheets-sheet 4 March 5, 1963 Filed June 18, 1959 MNE/@Q25 PATENT AGENT United States Patent O M' Y3,679,990 WEE't` END DRAINAGE SYSTEM FR PAPER `MACILllllliilS Geoffrey Ingram Taylor, Cambridge, Engiand, and Kenneth C. Logan and James Marilou, Quebec, Quebec, Canada, assignors vto Anglo Paper Products, Limited,

Quebec, Quebec, Canada Filed June 18, 19:39, Ser. No. 821,233 Claims. (Cl. 162-350) This invention relates to drainage systems for wet ends of paper machines.

This application is a continuation-in-partof applicants prior copending abandoned application Serial No. 746,195, tiled July 2, 1958.

The manner of obtaining drainageof iibre suspensions at the wet ends of paper machines has not changed materially for a great many years. This conventional manner is therefore in widespread and universal use Ydespite the disadvantages thereof.

in the standard paper machine the paper stocker yfibre suspension is fed .from the head box through a slice onto the wire supported on breast and couch rolls. lBetween the breast and couch rollsdrainage is effected .by leading the wire over:

`(l) A plurality of table rolls which usually Areduce Ythe water-nbre ratio to from approximately 40 to 1, to 51o l, and

(2) a series of stationary vacuum boxes.

Good papermaking may be defined as the runningof the paper machine at high eciency with the production of paper of desired quality.

For themaximum strength of dry paper consistent-with the .grade of iibre used, the most uniform dispersion of fibres possible is required, both in the ,horizontal and in the vertical planes. This is also the criterion for obtaining the maximum wet web strength at any point on the paper machine for a given waterziibre ratio.

This desired distribution of fibres can be obtained initially by the production'of a stable and regular slice jet of even pressure entirely across the paper machine. With s uclra slice vjet, large adjustments of the iiexible-slicelip, which causes longitudinal ridges in the slice jet and subsequent crossing waves on the wire, can be avoided.

Even with this initial desired distribution of suspension, a relatively tremendous disturbanceof the same is introduced in its subsequent passageover the table rolls. (See Investigation of High Speed Paper Machine Drainage Phenomena, G. Burkhardand P. E. Wrist, Pulp and iaper Magazine of Canada, vol. 57, March 1956,pages 1GO-118; Flocculation, Formation and Headbox Design, part iIV, I. Mardon and N. Shoumatoff, Pulpand Paper Magazine of Canada, vol. 57, February 1956, pages 305- 319; and The Behaviour of Fibre Suspensions on the .Paper Machine Wire, J. Mardon, Proceedings of the Symposium on the Flow of Suspensions, National Research Council of Canada, November 1956.)

it is known that this disturbance is dependent to some `extent on roll size, wire-tension, and speed, and is largely due to the liexion of the wire around Athetable roll resulting in a combination of centrifugal force and downward acceleration. The higher the speedthegreater the vdisturbance, which, for a Ygiven machine, is absent below a certain speed. Qualitative connection has been established between the ease of running the machine and the `degree of disturbance of the stock on the Wire over the table rolls (see lThe Use of High Speed Cinematography -in Certain Aspects oiPapermaking, K. C. Logan, ,J.

Mardon, A. Easson, R. vletersons and G. Samson, Eroceedings ofthe ATechnical Section of The British Paperc lBoard Makers Associataion, Y1956, vol. :37, part ,3, pages 'iiw@ Fatented Mar. 5, 1963 ICC 2 341-352). However, even at comparatively lowspeeds, the forces mentioned create a multiplicity of spouts in the liquid suspension with the result that the drops from the tops of the spouts .produce cavities and explosions, when they land.

-Thus, to retain the good qualities resulting from the perfect slice jet, it is clearly and highly desirable to re- Jmove or greatly reduce the disturbance caused by the table rolls.

`It is an object of this invention to provide a simple and effective apparatus for producing drainage at the wet end or a paper machine whereby uniform dispersion of fibres in the vliquid suspension is vsubstantially maintained by avoidance of disturbances therein during the drainage period.

It will be apparent that if one were to substitute for the Vusual table rolls a .conventional suction box with a dat top surface defined by the usual well spaced cross bars, :the wire will loopbetween the bars to a degree which will result in unstable and objectionable operation.

The invention contemplates the provision of drainage Yapparatus including a suction box arranged to receive a substantial portion of the length of the wire, said suction box dening a substantially arcuate Vpath of Vtravel for such portion of the wire, said path of Vtravel having a predetermined radius of curvature whereby it is possible Yto balance the degree of suction applied to the wire through the box and the tension of the wire without increasing the tension .to damaging values and thereby achieve stable operation of the drainage apparatus without substantial disturbance of the liquid suspension under treatment.

The invention will be described `with reference to the accompanying drawings, in which lFlGURESV l to 4 inclusive, are side elevations, in diagrammatic form, of various Vembodiments of the invention,

FIGURE 5 is a cross-sectional view of thesuction box Vshown in FIGURE 4,

FIGURE 6 is a side elevation of still another modification of the'invention,

FIGURE 6a illustrates a variation of the modification shown in FIGURBG,

FIGURE 7 is a graphical illustration of the form of arcs -taken by the wire under varying conditions,

FIGURE 8 is a graph illustrating drainage results achieved by the invention,

FLGURE 9 is a partialside elevation of Y,still another iform of the invention,

FIGURES l0 and Y1l are `side elevations illustratingdiagrarnmatically, application of apparatus in accordance with the invention to existing types of paper making machines.

'Referring to FIGURE l, the paper machiney shown comprisesa slice 1 adapted to deliver paper stock or waterbre `suspension onto a forming wire 2 carried by a breast roll 3, and a couch roll 4. Conventional suction boxes `Ef adjacent-the couch roll are shown.

A Wirefsupporting roll ois located adjacent the breast froll to provide -a -wire portion 7 `extending from the kbreast roll to the -rol1 6. .In accordance withfthe invention, this portion 7 of the forming wire is subjected to 4suction to remove the major portion of the Waterin the suspension carried thereby and thus eliminate the need for use of table rolls.

A suction `box is mounted beneath the wire portion 7, such box being located below the normal horizontalrplane fin which the top surfaces ofbreast roll 3 and supporting `-roll 6 lie. With appropriate adjustment of the Wire tension,

ysuction boxv, will curve downwardly to follow a generally `arcuate-patti. The initialwire supporting board 9 1ead- 'or be disposed in slight clearance therewith.

ing to the suction box from the breast roll, and the wireengaging cross bars lil of the suction box, define such arcuate path. Tension of the wire may be adjusted by means of a tension roll 11 engaging the lower travelling portion of the wire.

The apparatus illustrated in FIGURE 2 is substantially the same as that shown in FIGURE 1 except that a suction box 12 is provided which is surfaceless, i.e., the wire is substantially free of engagement with a surface thereof. Thus, the box has side walls 13 between which the wire portion 7 will loop and end walls 14 of less height than the side walls over which the wire will travel.

The wire may engage the top edges of the end walls D;

It is, o course, important that the top edges of end walls 14 be substantially lower than the upper common tangential plane of rolls 3 and 6 to permit unrestricted formation of the arcuate path of travel of the wire. of the suction box are as close as possible to the edges of the wire. It will be apparent that there will be a slight air leak between the wire and the side and end walls 13 and 14 of the suction box, but such air leak is not of signicance in the operation of the device.

Referring to FIGURE 3, an arrangement is shown wherein the looped or arcuate portion 7 of the wire 2 occupies substantially the entire upper travelling portion of the wire between the breast roll 3 and couch roll 4. A suction box 15 has its end walls 16 and 17 in close proximity to respective rolls V3 and 4. A wire supporting board 1S leading from the breast roll may be provided. Suction slots 19 are provided in one or both side walls 20 of the head box and suction is thereby imparted to the box from a suitable connection (not shown). Drainage outlets 2l are provided in the bottom of the box. The lower travelling portion of the wire is supported on guide rolls 22. The wire is also directed over a drive roll 23 positioned somewhat forwardly of the couch roll. The paper web 24 is taken oi the downwardly inclined portion of the wire between the couch roll and the drive roll 23. A conventional suction box 25 may be provided under the wire just prior to the take-oli which may be effected by a blower 26. As shown, the web 24 is then led over the irst press felt 27.

Tension of the wire is adjusted by means of a vertically adjustable tension roll 28.

FIGURES 4 and 5 show a modification which is quite similar to that illustrated in FIGURE 3. The suction box 29 has a suction slot 36 ina side wall 31 connected to a source of vacuum by a conduit 32. The suction box has a drainage outlet 33 in its bottom wall. A wire guide K roll 34 and a tension adjustment roll 35 are provided.

FIGURE 6 illustrates a modication wherein the entire upper travelling portion of the wire has a main downwardly looped portion 36; to which is imparted two arcuate sections 37 and 33 as by means of a roll 39 in a. suction box di). Suction slots 41 are provided in the suction box below each arcuate section 37 and 38. The suction box has a drainage outlet 41a. The return portion of the wire is provided with guide rolls 42 and a tension adjustment roll 43.

FIGURE 6a illustrates a variation in the modification shown in FIGURE 6 wherein the box 4b is provided with a partition 46a extending to the lower portion of roll 39 and dividing the box into two sections. In this instance,

Yit is possible to vary independently the degree of vacuum Lin each part.

It will be understood that the dimensional and other operational characteristics of the ldevice will vary in accordance with the required operating circumstances.

By way of example, with a suction box providing a drainage area 3 feet long on a three foot radius of curvature (430 square inches per foot width) and in order to provide drainage equivalent to 15 table rolls, then a suc- The walls 13 tion of 0.89 p.s.i must be applied. In such a case, a wire tension of approximately 30 lbs. per lineal inch would be needed to maintain equilibrium.

If, however, the maximum average length of nip be taken as beingV three-quarters inch with corresponding lower maximum and average pressures, then a tive foot unit would be needed and the radius of curvature could be greater. This would imply greater wire tension.

It will be appreciated that the suction may be balanced by wire tension. In a suction box having wire supporting surfaces, differences can be taken by friction of the wire on such wire supporting surfaces.

The relationship of the tension of the wire to the frictional pressure drop across the wire and the Vradius of curvature of the wire may be defined by the equation T=PR (1) where T is the tension of the wire in pounds per foot, P is the frictional pressure drop in pounds per square foot and R is the radius of curvature in feet. It will be apparent that the frictional pressure drop across the wire consists both of the suction applied and that of the centrifugal force dependent upon the radius of curvature. However, it has been determined that the suction caused by the curvature is negligible and thus may be substantially disregarded.

It will also be apparent that the tension will be alected by the velocity of the belt and the layer of stock on top. Because the belt and the stock have mass, a definite force will be required to maintain their motion in a circular path. The magnitude of this pressure is readily shown l in which U :the velocity of the belt. ,o1-:density per unit length of the belt and stock.

T =PR+P1U2+PIU2 (3) It can be seen that if the device is run with constant tension the radius of curvature will be specilied by Equation 3 and the length of the belt will be automatically adjusted by moving the weight. If, on the other hand, the length of belt is xed, the radius of curvature and shape of the belt will be determined by the length available. It cat!V be seen that if a very llat curve is speciied, the radius of curvature will be large and hence very high tensions Will be induced by average pressures. With these ideas, control schemes for starting the device can be readily devised. It has been determined that the wire will maintain a stable curve in operation. The following table gives results of tests with varying speeds of wire travel:

Tension Radius of Diff. Tension Wire speed, f.p.m. applied. Curvature, Pressure. Computed.

lb./u1. ft. in. water T=pR,

lb./in.

l0. 6 16. 0 1. 7 1l. 9 10. 6 16. l 1. 45 10. 3 17. 3 17. 9 2. l) 15. 6 2l. 0 23. 5 2. l 21. 5

It will be apparent that successful drainage in a con- 'struction in accordance with the invention is dependent upon obtaining drainage to the desired dryness with the;

permissible -suction in the time allowed by the :dimensions of the equipment. FIGURE 8 illustrates thedrainage results of tests employing a device of the present invention and using newsprint stock at normal headbox consistency to produce wet newsprint with a basic weight of 30 lbs. per 3000 square feet. These tests indicate that the -device is entirely adequate fordraining a sheet todryline condition.

Whereas the preferred form of the invention resides 1n ,the provision of a suction box such as, for instance, shown in FIGURE 3, which is -large enough that separation of air and water occurs in the box, the water being pumped out or removed by barometric leg and the air being removed by'vacuum pump, -itis possible `to produce a form of the invention wherein the box is kept almost full and air and water removed by one pump to a separator. 'Such a form ofthe invention is shown in FIG- URE 9, wherein a shallow box 60 is employed having an inclined bottom wall 61. YBottom wall 61 has a slit 62 ,leading to `a dow spreader box 63, to which suction is applied, preferably from both ends thereof,'by pipes 64.

FIGURES 10 and ll illustrate application of the Yinvention to existing types of paper machines. In each figure, there is indicated, in conventional form, the wire 80, breast roll 81, couch S2, table rolls 83, suction boxes S4 adjacent the couch, and guide rolls 85. In FIGURE l0, a suction box 86 for imparting an arcuate loop S7 to the wire is interposed directly following the breast roll. Thus, the loop extends substantially from the breast roll to a supporting roll S8 adjacent the other end of the box. FIGURE l1 shows the box 86 interposed between the last table roll 83 and the rst suction box 84, the loop S7 being supported on rolls 89. It will be understood that the number of table rolls 83 and suction boxes 84 will be adjusted as required by each particular installation.

In each of the modifications of the invention as illustrated, the ends of the curved or arcuate portion of the wire have been shown as disposed in a substantially horizontal plane. It will be understood that, in order to meet certain operational circumstances, it may be necessary to change the orientation of the arcuate portion as a whole with respect to the slice and/or other parts of the paper machine. Thus, the curve forming suction box and supporting roll or rolls may be positioned to tilt the wire curve as a whole whereby its ends lie in a plane which is angular to the horizontal.

it will be understood that the longitudinal extent of the arcuate path of travel of the wire is a substantial portion of the length of the wire. By substance portion as employed in this specification and claims is meant a length of at least several feet.

We claim:

l. In a paper machine having an endless forming wire, rolls supporting said wire, said wire having upper and lower paths of travelling movement, and a slice for delivering liquid suspension onto said wire during said upper path of movement, apparatus for effecting drainage of said suspension comprising, in combination with a pair of said rolls defining therebetween a section of said upper path extending from one to the other of said pair of rolls, a suction box located beneath said section of travel of said Wire and having a single uninterrupted suction area extending throughout the major longitudinal extent of said section of travel, said wire having an arcuate portion in its upper path of movement depending between said pair of rolls into said suction area, said arcuate portion of said wire being of uninterrupted contour and having an under surface free from bearing contact throughout said suction area and an unconstrained upper surface reely exposed to atmospheric pressure, means for applying suction to said box to cause formation of said arcuate portion of said wire, and means for applying tension to said wire to adjust the radius of curvature of said arcuate portion.

2. Drainage apparatus as dened in claim 1, said suc 6. tion-box having an open ztop, side #walls extending vabove said `upper path of travel, 'and 'end walls each having -a'n upperedge disposed belowsa'id'npper-path of travel, `said Itension applying means :comprising -a `.tension Vroll :en- '-gaging -said wire tin its 'lower path of travel.

3. Drainage apparatus .as defined in claim 2, said'pair Aof -rolls comprising' abreast vvroll :and -a couch roll.

4. kDrainage apparatus .as defined inclaim l,-said-suc .tion box having side lwalls-extending above -lsaid upper path Yof travel, said `arcuate portion of said -wire `substanftially `throughout its extent extending transversely from one `of `said side walls =tothe lotherio'f said -side 1walls, -said 4arcuate portion being .freely Isuspended between Isaid side `walls.

5. Drainage apparatus -as deinedin claim -Lsaid radius of curvature of said varcuate -portion'being solely responsive totensionand pressure approximately in accordance withtheequation T=PR `where'I i's-the tension, P is the `frictiona'l pressure drop across -the=wire lin-said box',and -R is said .radius of curvature, wherebya-stable configuration of said arcuate portion -is obtained at :substantially all speeds of traveltofsaidwire.

6. Drainage apparatus as defined in claim l, said suction box having an open top, upstanding side walls extending above said upper path of travel, and end walls each having an upper edge disposed below said upper path of travel, said arcuate portion of said wire being substantially freely suspended between said side walls of said suction box.

7. In a paper machine having an endless forming wire, rolls supporting said wire, said wire having upper and lower paths of travelling movement, and a slice for delivering liquid suspension onto said wire during said upper path of movement, apparatus for effecting drainage of said suspension comprising, in combination with a pair of said rolls defining therebetween a section of said upper path extending from one to the other of said pair of rolls, a suction box located beneath said section of travel of said wire and having a single uninterrupted suction area extending throughout the major longitudinal extent of said section of travel, said suction box having a wire-engaging roll therein, said Wire having a pair of arcuate portions in its upper path of travel each disposed between said last-mentioned roll and one of said pair of rolls and depending into said suction area, means for applying suction to said box to cause formation of said arcuate portions of said wire, and a tension roll engaging said wire in its lower path of travel to adjust the radius of curvature of each said arcuate portion.

8. In a paper machine having an endless forming wire, rolls supporting said wire, said wire having upper and lower paths of travelling movement, and a slice for delivering liquid suspension onto said wire during said upper path of movement, apparatus for eiecting drainage of said suspension comprising in combination with a pair of said rolls defining therebetween a section of said upper path extending from one to the other of said pair of rolls, a suction box located beneath said section of travel of said wire and having a single uninterrupted suction area extending throughout the major longitudinal extent of `said section of travel, said Wire having an arcuate portion in its upper path of movement depending between said pair of rolls into said suction area, said arcuate portion of said wire being of uninterrupted contour and having an under surface free from bearing contact throughout said suction area and an unconstrained upper surface freely exposed to atmospheric pressure, and means for applying suction to said box to cause formation of said arcuate portion of said wire.

9. Drainage apparatus as defined in claim 8, said suction box having upstanding side walls extending above said upper path of travel, said arcuate portion of said wire within said box being substantially unsupported for substantially free movement between said opstanding walls of said box.

7,.. Y l0. Inapaper machine having an endless forming wire, rolls supporting said wire, said wire having upper and lower paths of travelling movement, and slice for delivering liquid suspension onto said wire during said upper path of movement, apparatus for effecting drainage of said suspension comprising, in combination with a pair of said rolls defining therebetween a section of said upper path extending from one to the other of said pair of rolls, a suction box located beneath said section of travel of said wire and having a single uninterrupted suction area extending throughout the major longitudinal extent of said section of travel, said Wire having an arcuate portion in its upper path of movement depending between said pair of rolls into said suction area, the space above said arcuate portion of said wire below a straight ,line joining the ends of said arcuate portion being uninterrupted whereby the upper surface of said arcuate portions is unconstrained and freely exposed to atmospheric pressure, -said arcuate portion of said wire having an under surface free from bearing contact throughout said suction area, means for applying suction to said box to cause formation of said arcuate portion, and means for 8. applying tension to said wire to adjust the radius of curvature of said arcuate portion.

References Cited in the tile of this patent UNITED STATES PATENTS 1,629,607 Witham May 24, 1927 1,876,399 Catala et al Sept. 6,1932

1,940,594 Johnson et al. Dec. 19, 1933 2,473,269 Adams Tune 14, 1949 2,694,345 Hornbostel Nov. 16, 1954 V 2,858,746 Goodwillie Nov. 4, 1958 2,859,668 Berlyn Nov. 11, 1958 FOREIGN PATENTS 501,257 Germany Iuly 5, 1930 OTHER REFERENCES Pulp and Paper Manufacture, 1953, vol. 3, pages A91-92. f

Claims (1)

1. IN A PAPER MACHINE HAVING AN ENDLESS FORMING WIRE, ROLLS SUPPORTING SAID WIRE, SAID WIRE HAVING UPPER AND LOWER PATHS OF TRAVELLING MOVEMENT, AND A SLICE FOR DELIVERING LIQUID SUSPENSION ONTO SAID WIRE DURING SAID UPPER PATH OF MOVEMENT, APPARATUS FOR EFFECTING DRAINAGE OF SAID SUSPENSION COMPRISING, IN COMBINATION WITH A PAIR OF SAID ROLLS DEFINING THEREBETWEEN A SECTION OF SAID UPPER PATH EXTENDING FROM ONE TO THE OTHER OF SAID PAIR OF ROLLS, A SUCTION BOX LOCATED BENEATH SAID SECTION OF TRAVEL OF SAID WIRE AND HAVING A SINGLE UNINTERRUPTED SUCTION AREA EXTENDING THROUGHOUT THE MAJOR LONGITUDINAL EXTENT OF SAID SECTION OF TRAVEL, SAID WIRE HAVING AN ARCUATE PORTION IN ITS UPPER PATH OF MOVEMENT DEPENDING BETWEEN SAID PAIR OF ROLLS INTO SAID SUCTION AREA, SAID ARCUATE PORTION OF SAID WIRE BEING OF UNINTERRUPTED CONTOUR AND HAVING AN UNDER SURFACE FREE FROM BEARING CONTACT THROUGHOUT SAID SUCTION AREA AND AN UNCONSTRAINED UPPER SURFACE FREELY EXPOSED TO ATMOSPHERIC PRESSURE, MEANS FOR APPLYING SUCTION TO SAID BOX TO CAUSE FORMATION OF SAID ARCUATE PORTION OF SAID WIRE, AND MEANS FOR APPLYING TENSION TO SAID WIRE TO ADJUST THE RADIUS OF CURVATURE OF SAID ARCUATE PORTION.

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