US3622450A

US3622450A - Papermaking flow box

Info

Publication number: US3622450A
Application number: US830421A
Authority: US
Inventors: Brian William Attwood; Harold George Curry
Original assignee: St Annes Board Mill Co Ltd
Current assignee: St Annes Board Mill Co Ltd
Priority date: 1968-07-04
Filing date: 1969-06-04
Publication date: 1971-11-23
Anticipated expiration: 1988-11-23
Also published as: DE1930795C3; FR2012275A6; PL83181B3; GB1228385A; DE1930795B2; DE1930795A1; SE361691B

Abstract

A flow box for a papermaking machine including an explosion chamber having a stock inlet and stock outlet positioned on opposite sides of the explosion chamber, each of overall cross section less than the transverse cross section of the explosion chamber at the inlet and outlet. A baffle plate, having oppositely extending free ends, disposed transversely of the direction of flow of stock from inlet to outlet, divides the explosion chamber into two subchambers which are defined by two restricted passages formed between the free ends of the baffle plate and the walls of the explosion chamber. The explosion chamber creates turbulence and mixing of stock flowing therethrough without streaming thereof.

Description

United States Patent [72] Inventors Brian William Attwood [56] References Cited "Wham, Bristol; UNITED STATES PATENTS :E'f'f if??? g i' 'g 2,589,639 3/1952 Staege l62/338 2 I A l N 552 1 2,894,581 7/1959 Goumeniouk 162/343 x l ll Pd- 2 4 1969 3,328,236 6/1967 Burgess, Jr. et al. 162/347 X ga 5 ml 3,0l6,089 1/1962 Webster 162/339 [73] Assignee St. Annes Board Mill Com Limited ,565,758 2/l97l Higgins et al. 162/336 Bristol, England Primary Examiner-S. Leon Bashore 32 p i i J l 4, 1968 Assistant ExaminerAlfred A. Andrea, Jr. [33] Great Britain Attorney- Larson, Taylor and Hinds [3 l 31,974/68 ABSTRACT: A flow box for a papennaking machine includ- 54] PAPERMAKING FLOW BOX ing an explosion chamber having a stock inlet and stock outlet 12 Claims, 7 Drawing Fi positioned on opposite sides of the explosion chamber, each of S I 162 339 overall cross section less than the transverse cross section of [52] U. .C 162/ 343, the explosion chamber at the inlet and Outlet. A bame plate, Inn/l 06 having oppositely extending free ends, disposed transversely [5l] lnnfl}. 162 3/38 of the direction of flow of Stock from inlet to outlet divides [50] FM 0 3 the explosion chamber into two subchambers which are 34 3 21 3 defined by two restricted passages formed between the free ends of the baffle plate and the walls of the explosion chamber. The explosion chamber creates turbulence and mixing of stock flowing therethrough without streaming thereof.

, 56 34 fvc V,- 5

PATENTED 23 1971 3, 622.450

SHEET 3 [IF 3 PAPERMAKING FLOW BOX This invention relates to flow boxes for machines for dewatering watery pulp to form a sheet e.g. in the manufacture of board or paper and is an improvement in or modification of the invention disclosed and claimed in our copending British application No. 3,8983/66.

According to British application No. 38983/66 there is provided a flow box comprising an enclosed explosion chamber having a stock inlet and a stock outlet each of overall cross section less than the transverse cross section of the explosion chamber at the inlet and the outlet respectively, and an imperforate baffle plate disposed transversely to the flow paths of stock inlet and outlet, and dividing the chamber into two successive flow portions with a restricted passage therebetween.

The term explosion chamber" is known in the art to mean a chamber in which a high-speed stream of stock is very quickly changed in speed and direction of fiow by rapid expansion and/or impingement on an obstruction or baffle plate whereby the stream disintegrates or explodes thereby causing mixing and deflocculation of the stock by turbulence generation.

According to the present invention there is provided a flow box for a paper, board or similar fibrous webmaking machine comprising an enclosed explosion chamber having a stock inlet and an opposed stock outlet each of overall cross section less than the transverse cross section of the explosion chamber at the inlet and outlet respectively, an imperforate bafile plate disposed transversely of the inlet and outlet and dividing the chamber into two successive flow portions with two restricted passages therebetween around the transversely opposed edges of the plate.

Thus the present invention provides a development of the basic flow box of our prior case in that two flowpaths are provided around opposed edges of the baffie. The stock flowing around these paths must meet to pass through the common exit from the flow box. Since the stock fiows around the opposed edges of the plate or baffie, the two stock streams collide at the exit, thus causing further turbulence and mixing and ensuring that no streamting" of the stock occurs. By streaming" is meant occurrence of high spots or areas of excess stock compared with the remainder of the stock jet across the width of the flow box. Such areas result in productionof a sheet having an uneven surface. By causing the stock flows to collide immediately prior to the slice, any such streaming of the stock will be destroyed by the turbulence and intermixing of the streams. A more even and better sheet results from this stock.

Preferably the baffle plate comprises two planar portions one of which is disposed obliquely with respect to the other, the plate being arranged in the flow box with said planar portions inclined to the flow path of stock through said inlet.

There are preferably two inlets to the chamber, each being directed at one of the planar portions of the baffle. The chamber may be divided by an imperforate well extending from between said inlets to said baffle.

In a preferred embodiment the flow box is rectangular in cross section, said inlet or inlets and outlet being disposed in one opposed pair of walls, and the baffle defining the restricted flow passages with the other pair of opposed walls thereof.

With the present invention, the highly turbulent, deflocculated and well-mixed stock is ejected immediately from the flow box onto the machine wire with the minimum possible delay, by a flow path ensuring that, from the chamber to the wire, no slowing down of the stock occurs which would promote reclotting. To effect this, the outlet to the flow box itself can constitute the slice. Alternatively a very short nondivergent passage may be provided.

It has been found that for high-consistency stock (i.e. from 1.0-2.0 solid content) the ratio of outlet area to inlet area should be from 0.421 to 4.0:1 preferably from 1:1 to 3: 1.

The flow box may however be used with lower consistency stock e.g., in paper of tissue manufacture. Thus stocks of 0.1-1.0 percent solid content may be usefully used with such a headbox.

In a preferred flow box according to the present invention, the inlet to the explosion chamber is provided by a plurality of ports communicating with a plurality of tubes through which stock is fed to the chamber from a headbox.

On a multiply machine the flow box is preferably used on at least the second and any subsequent plies, but may also be used on the first ply.

The invention is illustrated, merely by way of example, in the accompanying drawings in which:

FIG. 1, is a diagrammatic side elevation of part of a boardmaking machine including a flow box according to the present invention.

FIG. 2 is a front elevation of the flow box shown in FIG. 1,

and

FIGS. 3 to 7 are side elevations of alternative forms of flow box according to the present invention.

Referring to the drawings, and particularly FIGS. 1 and thereof, there is shown the second ply stage of an lnverform (Registered Trade Mark) boardmaking machine. The main wire 10 containing a dewatered web from the first ply stage, passes over a table roll 11 of the second ply stage. An upper wire 13 of the second ply stage passes around a forming roll 14 and converges on wire 10 to define therebetween a convergent gap 20 within which stock is initially dewatered to form the second ply of the web.

To feed the stock into gap 20 there is provided a flow box 30 comprising a header tank 31 and an explosion chamber 32. Stock is pumped into header tank 31 through a tapered crossflow pipe 33 of decreasing cross section in its direction of fiow. Stock pumped through this pipe is fed into header tank 31 through a plurality of ducts spaced across the machine, only one such duct, 34 being shown in FIG. 1. The tank 31 includes a baffie plate 35 disposed in the flowpath of incoming stock from pipes 34. The stock impinging on plate 35 will be disintegrated, causing mixing and turbulence. The stock flows around the opposed upper and lower edges of the plate 35 through the

narrow passages

36, 37 and through two parallel sets of

shear flow tubes

38, 39 in the lower end of the chamber. It will be noted thatpipes 34 are narrow compared with the cross section of tank 31, and thus turbulence is effected as stock enters the tank merely by the divergence of the flow.

A standpipe 40 communicating with the upper wall of the tank 31 maintains a head of stock sufficient for efficient running of the flow box and ensures that tank 31 can be maintained full, thus avoiding crusting and aeration of the stock.

Stock leaving header tank 31 flows to the vortex or explosion chamber 32 via the shear fiow

narrow bore tubes

38, 39. The tubes in each set are disposed in one plane and are parallel to one another. However the tubes in one set could be inclined relative to those in the other set to provide a skew arrangement. By this disposition of tubes, crossfiow of stock is achieved which creates turbulence and destroys any irregularities in stock consistency across the width of the machine (i.e. destroys streaming of the stock). Thus regulation of web weight is achieved across the machine width preventing high spots and maintaining a consistent board density.

The chamber 32 is substantially rectangular, the

tubes

38, 39 entering through the upper wall thereof and an exit 50 being disposed in the opposed wall. Disposed between these opposed walls is an imperforate baffle 51. The baffle com prises two

planar plates

52, 53 inclined to one another and extending across the full width of the explosion chamber 32 (as seen in FIG. 2). As well as being inclined to one another,

plates

52, 53 are disposed obliquely relative to the incoming stock flow through

tubes

38, 39.

An imperforate wall 54 extends from the upper wall of the explosion chamber (between the pipes 38, 39) to the meeting line between

plates

52, 53, thus dividing and separating the incoming stock flows.

Due to the inclination of

plates

52, 53 each half of the explosion chamber 32, as viewed in FIG. I, is divided into two successive flow areas with a restricted passage therebetween, the passage being defined between the free edges of the

plates

52, 53 and the walls of the chamber 32. The flow areas also define divergent/convergent/divergent/convergent flowpaths for the stock from

inlets

38, 39 to the outlet 50.

Stock entering chamber 32 will expand rapidly due to the rapid change in section from

tubes

38, 39 to chamber 32. This expansion will create turbulence. The stock from

tubes

38, 39 will also impinge upon

plates

52, 53 respectively thus causing further turbulence and disintegrating the flow. The turbulent stock when speeds up as it flows around the edges of the plates into the lower half of chamber 32, where a rapid expansion causes further turbulence.

In flowing to exit 50 from around

baffle plates

52,53, the two stock flows collide head-on" at exit 50, thus creating yet more turbulence and destroying any streaming of the stock which may be created by the

tubes

38, 39.

Due to the restricted enclosed nature of the explosion chamber 32, the stock immediately leaves the chamber via the relatively narrow exit 50 flowing into a short passage 55. Passage 55 is defined between convergent plates which thus do not allow any decrease in velocity of the high-speed stock, but eject it, as a high-speed jet of homogeneous, suspended entangled comoving deflocculated fibrous suspension into the convergent gap 20 of the board machine through slice 56. The passage 55 can be parallel sided without allowing any decrease in stock velocity and thus maintaining the high-speed deflocculated jet required. The plates defining passage 55 are made relatively adjustable, e.g., by screws 57 on the upper plate for varying the size of slice 56. For a machine of any width however and for stock consistencies of say 1.0 2.0 solid content, the slice could be one-half inch high, the passage 55 being 6 inch long. Thus it will be appreciated that a very narrow and short exit is provided from the explosion chamber to ensure that work done in the chamber to provide turbulent stock is not lost in directing the stock onto the machine.

It will be appreciated that, in flowing over the

baffle plates

52, 53 and out through the exit from the explosion chamber 32 some stagnation can occur in the comers of the chamber and behind the baffle, i.e., on the face opposite that onto which incoming stock impinges. The

plates

52, 53 must be so inclined to one another and to the chamber walls that such stagnation (which can allow reclotting) is avoided.

To avoid stagnation in the corners of the

rectangular chambers

31 and 32, these may be rounded using corner inserts or by suitably reshaping the corners of the chamber while preferably retaining the generally rectangular cross section.

The relative dimensions of the flow box illustrated will be maintained across the machine for any width of machine. Generally, for consistencies of -l.02.0 percent solid content of stock, the passage 58 will be 6 inches long, 1 inch deep at inlet and one-half inch at its outlet (the slice 56) corresponding dimensions for the explosion chamber 32 could be 4 inches high by 6 inches long with, say, seven

tubes

38, 39 per 20 inch width of machine, each tube being of 1 inch internal diameter. Thus inletzoutlet ratio of chamber 135 is of the order of 2: 1. Experiments show that this ratio should be in the range of 0.4:l to 4:1 for good results.

With these dimensions it will at once be appreciated that a very compact flow box has been devised. Thus the box can be accommodated in a length of some 2 feet with the design of FIGS. 1 and 2. Such dimensions must be compared with the 6 feet or more encountered in present flow boxes designed to achieve the same high-speed well-deflocculated stock employing shear slice methods. The advantages of the present flow box design are obvious.

Referring briefly to FIGS. 3 to 7, variations on the basic idea illustrated in FIGS. 1 and 2 are shown in these figures.

FIGS. 3 to all employ the same header tank,

tubes

38, 39 and explosion chamber 32 as described above with reference to FIGS. 1 and 2. However, in FIG. 3 the baffle plate, while employing a similar portion 54, has a single planar plate 60 disposed at 90to partition 54 and

inlet tubes

38, 39. As with the FIG. 1 embodiment stock flows around the plate 50 and two streams of stock meet at exit 50. With this arrangement, a single splash plate 61 is disposed obliquely with respect to the outlet flow path to deflect stock onto machine wire 10. A plate 63 adjustable laterally of exit 50 by screws 64 controls the size of the slice which is provided by exit 50.

In FIGS. 4 and 5 the

baffle plates

52, 53 are provided as in FIG. 1. However difi'erent exit passages are provided. In FIG. 4 the exit passage comprises a linear section 65 followed by an obliquely disposed plate 66 directing stock onto wire I0. An adjustable plate 67 adjusted by a screw 68 defines with plate 66 an adjustable slice 70.

In FIG. 5, the exit is provided by a splash plate 71 similar to that disclosed in FIG. 3. Again a plate 72 adjusted by a screw 73 provides an adjustable slice coincident with exit 50.

Referring to FIGS. 6 and 7, the explosion chamber 32 and supply of stock thereto through

tubes

38, 39 is similar to that for FIG. 1. However these FIGS. demonstrate how the explosion chamber can be tilted relative to machine wire 10, the exit passage from the explosion chamber being modified accordingly. In FIG. 6 the exit passage is cranked and nonadjustable. However the final lip of the slice 81 could be made adjustable. In FIG. 7 the outlet passage 82 is linear, and horizontal ending in a convergent section 83 providing slice 84.

Many variations of the apparatus described above may be effected without departing from the scope of the present invention. Thus the header tank 31 may be pressurized, open to atmosphere or under vacuum. The size, shape and orientation of the explosion chamber 32 may be varied to suit the stock and machine requirements. The machine on which the flow box is employed can be of many designs. Thus, for example, the two-wire Inverform arrangement shown in GB. Pat. No. 859083 may be used, this being a common arrangement in present day Inverform machines.

Again, regarding header tank 31, a second inlet (indicated in broken lines in FIG. 1) could be employed. The

pipes

38, 39 could be skew to one another (as shown in FIGS. 6 and 7) and also the tubes in any one set could be skew to one another in that set.

With all the flow boxes described above, stock flow through

tubes

38, 39 will reach a high speed due to the narrowness of these tubes. The high-speed streams of stock will impinge on the baffle of explosion chamber 32 thus disintegrating and causing deflocculation and mixing due to the turbulence generated. The two stock streams will collide at exit 50 causing more turbulence. In view of the enclosed nature of the chamber, well-mixed, deflocculated stock immediately exits through the slice and machine gap 20. Due to the absence of any passage or the use of a nondivergent passage from the flowbox, the stock flows at a very high speed therethrough with no opportunity to reclot.

Indeed, because of the shear forces acting on the stock and due to the shear turbulence generated therein, the action of chamber 32 will be improved thereby to form the stock into a jet of substantially homogeneous suspended entangled comoving deflocculated stock fibers.

It will be noted that the jet so formed is directed into the convergent forming gap 20 with as little delay as possible. Since the stock may tend to reflocculate within a very short distancea matter of inches only-it is advisable to dewater the stock as quickly possible after it leaves the slice or shear channel. Thus the spacing between the slice and the gap 20 is kept at a minimum. The most useful application of these flow boxes is on multiply paper and board machines, e.g., Inverform machines. Due to their compact nature they take up very little space and considerable saving in overall machine length is achieved. Being simple and compact they are also cheaper to make and install, with less problem of support. However it should also be borne in mind that these advantages are achieved without decreasing the quality of the stock generated. Indeed it has been found with experimental flow boxes of these designs that better quality stock is produced. With such boxes, standard lnverform machines may well run at lower speeds and may also produce higher basis weight board. Also machines may be run at higher speeds to increase output, in all cases without reducing the quality of board produced.

Experiments with these flow boxes also indicate that stocks of higher solid content, e.g., up to 2 percent may be successfully used. Lower consistencies may also be employed, e.g., 0.1 percent for tissue or paper machines provided the size is increased to accommodate the additional throughput of water experienced with such stock.

We claim:

1. A flow box in combination with a paper, board or similar fibrous webmaking machine, comprising,

a. an enclosed explosion chamber of rectangular cross section when sectioned in a vertical plane parallel to the general direction of flow of stock.

b. means defining a stock inlet to the explosion chamber in one wall of said chamber and means defining a stock outlet from the explosion chamber in an opposed wall of said chamber, said inlet and outlet each being of an overall cross section less than the transverse cross section of the explosion chamber at the inlet and outlet respectively, and

a baffle plate, having oppositely extending free ends,

disposed transversely of the direction of flow of stock from inlet to outlet for dividing the chamber into two successive subchambers interconnected by first and second restricted passages defined by the spacing between said free ends of said baffle plate and two walls of the chamber.

2. A flow box in combination with a paper, board or similar fibrous webmaking machine, comprising,

a. an enclosed explosion chamber of rectangular cross section when sectioned in a vertical plane parallel to the general direction of flow of stock,

b. means defining first and second stock inlets to the explosion chamber and means defining a stock outlet from the explosion chamber, the inlets being disposed in one wall of said chamber and the outlet being disposed in a wall in said chamber opposed to the said one wall, said inlets and outlet each being of overall cross section less than the transverse cross section of the explosion chamber at the inlets and outlet respectively.

c. a baffle plate, having oppositely extending free ends, disposed transversely of the wall including the inlets and the wall including the outlet, for dividing the chamber into two successive sub chambers interconnected by first and second restricted passages defined by the spacing between said free 'ends of the baffle plate and two walls of the chamber.

3. A flow box as claimed in claim 2 wherein the bafile plate comprises two planar plates inclined to each other and individually opposed to a respective one of the two inlets.

4. A flow box as claimed in claim 1 wherein the stock outlet defining means comprises means defining a nondivergent passage leading to an exit slice from the flow box for ejecting stock onto a machine wire.

5. A flow box as claimed in claim 1 wherein the stock outlet defining means comprises means defining a slit in a wall of the chamber, the slit further providing an exit slice from the flow box for ejecting stock into a machine wire, said flow box further comprising a plate disposed obliquely with respect to the flow path at the outlet for deflecting stock directly onto the machine wire.

6. A flow box as claimed in claim 1 wherein the stock outlet defining means leads to an exit slice from the flow box for ejecting stock onto a machine wire and is adjustable in cross section to vary the slice size.

7. A flow box as claimed in claim 2 further comprising an imperforate wall extending from between said inlet defining means to said bafile late.

8. A flow box as c aimed in claim 7 wherein the outlet defining means is aligned with the junction between said baffleplate and said imperforate wall.

9. A flow box as claimed in claim 1 wherein the defining means comprises a plurality of tubes spaced across the width of the chamber.

10. A flow box as claimed in claim 9 wherein the plurality of tubes comprises two sets of inlet tubes communicating with a header tank on opposed sides of a planar partition generally parallel to the flow path through said tubes, the inlet to said header tank being normal to said partition.

11. A flow box as claimed in claim 10 wherein the partition is spaced from the walls of the header tank at opposed edges thereof to provide flow passages around either edge of the partition between the opposed sides thereof.

12. A flow box as claimed in claim 11 wherein the inlet to the header tank is provided by a plurality of tubes from a tapered manifold.

Claims

2. A flow box in combination with a pAper, board or similar fibrous webmaking machine, comprising, a. an enclosed explosion chamber of rectangular cross section when sectioned in a vertical plane parallel to the general direction of flow of stock, b. means defining first and second stock inlets to the explosion chamber and means defining a stock outlet from the explosion chamber, the inlets being disposed in one wall of said chamber and the outlet being disposed in a wall in said chamber opposed to the said one wall, said inlets and outlet each being of overall cross section less than the transverse cross section of the explosion chamber at the inlets and outlet respectively. c. a baffle plate, having oppositely extending free ends, disposed transversely of the wall including the inlets and the wall including the outlet, for dividing the chamber into two successive subchambers interconnected by first and second restricted passages defined by the spacing between said free ends of the baffle plate and two walls of the chamber.
3. A flow box as claimed in claim 2 wherein the baffle plate comprises two planar plates inclined to each other and individually opposed to a respective one of the two inlets.
4. A flow box as claimed in claim 1 wherein the stock outlet defining means comprises means defining a nondivergent passage leading to an exit slice from the flow box for ejecting stock onto a machine wire.
5. A flow box as claimed in claim 1 wherein the stock outlet defining means comprises means defining a slit in a wall of the chamber, the slit further providing an exit slice from the flow box for ejecting stock into a machine wire, said flow box further comprising a plate disposed obliquely with respect to the flow path at the outlet for deflecting stock directly onto the machine wire.
6. A flow box as claimed in claim 1 wherein the stock outlet defining means leads to an exit slice from the flow box for ejecting stock onto a machine wire and is adjustable in cross section to vary the slice size.
7. A flow box as claimed in claim 2 further comprising an imperforate wall extending from between said inlet defining means to said baffle plate.
8. A flow box as claimed in claim 7 wherein the outlet defining means is aligned with the junction between said baffle plate and said imperforate wall.
9. A flow box as claimed in claim 1 wherein the inlet defining means comprises a plurality of tubes spaced across the width of the chamber.
10. A flow box as claimed in claim 9 wherein the plurality of tubes comprises two sets of inlet tubes communicating with a header tank on opposed sides of a planar partition generally parallel to the flow path through said tubes, the inlet to said header tank being normal to said partition.
11. A flow box as claimed in claim 10 wherein the partition is spaced from the walls of the header tank at opposed edges thereof to provide flow passages around either edge of the partition between the opposed sides thereof.
12. A flow box as claimed in claim 11 wherein the inlet to the header tank is provided by a plurality of tubes from a tapered manifold.