US3565758A - Flowbox - Google Patents

Abstract

A FLOWBOX FOR A PAPER BOARD OR SIMILAR FIBROUS-WEBMAKING MACHINE COMPRISES AN ENCLOSED EXPLOSION CHAMBER OF LONGITUDINAL POLYGONAL CROSS-SECTION, A STOCK INLET AND OUTLET DISPOSED IN OPPOSED WALLS OF THE CHAMBER, EACH OF OVERALL CROSS-SECTION LESS THAN THE TRANSVERSE CROSS-SECTION OF THE EXPLOSION CHAMBER AT THE INLET AND OUTLET RESPECTIVELY, AND A TRANSVERSE PLANAR BAFFLE DISPOSED IN THE PATH OF STOCK ENTERING THE CHAMBER FOR DEFINING THEREWITH TWO SUCCESSIVE PORTIONS IN THE EXPLOSION CHAMBER, EACH OF DIVERGENT/CONVERGENT CROSS SECTION WITH A RESTRICTED PASSAGE THEREBETWEEN. STOCK IMPINGING ON THE BAFFLE AND FLOWING THROUGH THE SUCCESSIVE DEVERGENT/CONVERGENT PORTIONS OF THE CHAMBER UNDERGOES A RAPID CHANGE IN THE DIRECTION AND VELOCITY OF FLOW, THE STOCK BEING CAUSED TO REVERSE ITS DIRECTION OF FLOW AND PASS UPWARDLY OVER THE BAFFLE, SO THAT TURBULENCE MIXING AND DEFLOCCULATION IS PROMOTED.

Description

United States Patent FLOWBOX James A. Higgins, Pucklechurch, near Bristol, and Brian W. Attwood, Hanham, near Bristol, England, assignors to St. Annes Board Mill Company Limited, Bristol,

England, a company of England Filed July 26, 1967, Ser. No. 656,263

Claims priority, application Great Britain, Sept. 1, 1966,

Int. Cl. D21f 1/02 US. Cl. 162336 5 Claims ABSTRACT OF THE DISCLOSURE A flowbox for a paper board or similar fibrous-webmaking machine comprises an enclosed explosion chamber of longitudinal polygonal cross-section, a stock inlet and outlet disposed in opposed walls of the chamber, each of overall cross-section less than the transverse cross-section of the explosion chamber at the inlet and outlet respectively, and a transverse planar baffle disposed in the path of stock entering the chamber for defining therewith two successive portions in the explosion chamber, each of divergent/convergent cross section with a restricted passage therebetween. Stock impinging on the baflle and flowing through the successive divergent/convergent portions of the chamber under-goes a rapid change in the direction and velocity of flow, the stock being caused to reverse its direction of flow and pass upwardly over the baflie, so that turbulence mixing and deflocculation is promoted.

This invention relates to flowboxes (or headboxes) for machines for dewatering watery pulp to form a sheet e.g. in the manufacture of board or paper. Relatively recent developments of such machines employ two wires between which the pulp or stock is formed into a web by dewatering. These machines may be used in the manufacture of board or paper. One such well knOWn machine is the Inverform (registered trademark) machine. Although not so restricted this invention will hereinafter be described with reference to its use on a twin wire machine of this kind.

Such machines, although usable with conventional stock-feed devices such as those used on conventional machines e.g. Fourdrinier machines, may not provide optimum results due to shortcomings in the pulp supplied to them. Because of the very rapid drainage available with modern machines, almost instantaneous initial web formation is possible, and thus a well mixed fibrous suspension providing a deflocculated stock is required if excellent web is to be formed therefrom.

Stock-feed devices have been proposed employing shear slices to provide such a stock. However, particularly with multiply formation these devices are excessively long and present great problems. A long shear-flow channel is necessary, but its length creates problems since space is restricted on machines and the cantilevered channel is diflicult to strengthen. It is an object of the present inven tion to provide a stock-feed device which overcomes these problems by simplifying the design, thus reducing size and cost.

In general it has been found that flowboxes (or headboxes as they are also referred to) are unnecessarily large, complex and costly. Particularly in employing a flowbox for high-consistency use (i.e. stock solid content of 1.0%2.0%) it is common to find boxes in which turbulence generation, mixing and defiocculation are repeated unnecessarily, the flow between these operations often resulting in the opposite affects being achieved with resultant refloccing and formation of clots.

According to the present invention there is provided a flowbox for a paper board or similar fibrous-web-making machine 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 outlet respectively, and a baflie disposed in the path of stock entering the chamber, and dividing the chamber into two portions with a restricted passage therebetween whereby stock impinging on the bafile and flowing through the consecutive divergent/convergent portions of the chamber undergoes a rapid change in direction and velocity of flow, the outlet to the explosion chamber constituting the exit slice from the flowbox.

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 flow by rapid expansion and/or impingement on an obstructing plate whereby the stream disintegrates or explodes thereby causing mixing and deflocculation of the stock by turbulence generation.

Preferably the passage from the outlet of the explosion chamber to the slice is non-divergent. Thus the passage may be convergent. With this arrangement, highly turbulent, defiocculated and well mixed stock is immediately ejected through the flowbox slice onto the machine wire with the minimum possible delay and by a flow path ensuring that from the inlet to the exit of the slice i.e. from the chamber to the wire, no slowing down of the stock occurs which would promote reclotting.

Preferably the chamber is substantially rectangular in cross-section, the inlet and outlet being disposed in 0pposed walls thereof adjacent a third wall from which said baflle projects into the chamber.

Preferably the baffle is inclined to both said opposed walls to define therewith two successive flow chambers of divergent/ convergent cross section.

The inlet passage may be inclined at an acute angle to the said third wall, the baflle being inclined thereto at a similar angle to cause stock impinging on the baflle and third wall of the chamber to reverse its direction of flow and pass upwardly over the baffie.

Preferably the outlet passage is generally parallel to the said third wall of the chamber.

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 0.4:1 to 4.021, preferably from 1:1 to 3:1.

In a preferred flowbox 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. Preferably the tubes are non-parallel whereby cross flows are set up in the common explosion chamber to destroy any irregularities in distribution across the width of the flowbox.

The slice which obtains stock directly from the explosion chamber with minimum delay, may be defined by a pair of co-operating spaced planar surfaces. Preferably the surfaces are substantially parallel or converge to prevent any decrease in the velocity of the stock flowing from the explosion chamber through the slice.

If desired, the slice may be defined by a pair of spaced surfaces providing turbulence-generators within the slice. Such a slice may be useful where lower-consistency stock is used e.g. in paper or tissue manufacture. Thus stocks of 0.1%1.0% solid content may be most usefully used with such a headbox. The turbulence generators are preferably provided by chambers of enlarged cross-sectional area compared with the remainder of the slice.

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

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

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

FIG. 2 is a plan view of some of the components shown in FIG. 1, and

FIG. 3 is an elevation of an alternative form of one of the components of the apparatus shown in FIGS. 1 and 2.

Referring to the drawings, there is shown in FIG. 1 the second-ply stage of a twin-wire board-making machine. The main wire containing a dewatered web from the first-ply stage, passes over a table roll 11 and a further roll 12 of the second-ply stage. An upper wire 13 of the second-ply stage passes around a forming roll 15 to pass over roll 12 in overlying relationship with the main wire 10. The lengths of wires between rolls 11 and 12 define therebetween a convergent gap 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 flowbox 130. This flowbox comprises a cross-flow feed tank 131 of cross-section decreasing in the direction of flow. Stock pumped through this tank is fed into a header tank 132 through a plurality of ducts spaced across the machine, only one such duct, 133 being shown. An overflow chamber 152 is provided in header tank 132. Stock within header tank 132 flows downwardly through a plurality of relatively narrow-bore friction tubes 134 into a vortex or explosion chamber 135. The outlet from the explosion chamber is the inlet to the slice constituted by a shear flow channel 136 through which the stock flows to the convergent gap 20.

The shear-flow narrow-bore tubes 134 are arranged in two superposed sets of parallel tubes 134a and 13417. The tubes in each set are disposed in one plane, and are skew relative to those in the other set to provide a crisscross arrangement as seen in FIG. 2. By this disposition of tubes, cross-flow of stock is achieved in explosion chamber 135 which creates turbulence and destroys any irregularities in stock consistency across the width of the machine. Thus regulation of web weight is achieved across the machine width preventing high spots and maintaining a consistent board density.

The chamber 135 is substantially rectangular, the tubes 134 entering through one side wall thereof and the exit slice 136 being disposed in the opposed wall. The overall cross-sections of the inlet and outlet are less than the transverse cross-section of the chamber 135 at the inlet and outlet respectively, as seen from FIG. 1. Disposed between and parallel to these walls is a baffle 144. The baflle 144 projects into chamber 135 so that the highspeed stream of stock entering chamber 135 from tubes 134 impinges on the baffle thereby exploding and becoming disintegrated. In the resulting turbulence generated, adequate mixing and deflocculation of the stock occur.

Due to the restricted enclosed nature of the explosion chamber 135, the stock immediately leaves the chamber via the relatively narrow exit which is also the entrance to slice 136.

Slice 136 is defined between convergent plates 140, 141 which thus do not allow any decrease in velocity of the high-speed stock, but eject it, as a high-speed jet of suspended entangled co-moving deflocculated fibrous suspension into the convergent gap 20 of the board machine. The slice can be parallel-sided without allowing any decrease in stock velocity and thus maintaining the highspeed deflocculated jet required. Plates 140, 141 are made relatively adjustable for varying the size and disposition of slice 136. For a machine of any width how ever and for stock consistencies of say 1.0% to 2.0%

Cir

4 solid content, the slice could be 6" x /2". 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 baflle 144 and out through the exit from the explosion chamber 135, some stagnation can occur behind the baffle 144 i.e. on the face opposite that onto which incoming stock impinges. Such stagnation can allow reclotting and should be avoided. A preferred design which does avoid this is shown in FIG. 3. As illustrated the baffle 144 is disposed at an angle to both the front and rear walls of the chamber to define sub-chambers 135a and 13511 of convergent section, with a restricted connecting passage 142 therebetween. Thus stock entering chamber 135 will explode in sub-chamber 135a, and will then flow through 135k on a convergent/divergent flow path before being ejected through slice 136. This convergent/divergent flow will of course also assist in creating further turbulence and thus maintaining or even increasing mixing and deflocculation. Additionally of course, stagnation around baffle 144a is avoided.

To avoid stagnation in the corners of the rectangular chamber 135, these may be rounded using corner inserts or by suitably reshaping the chamber.

The relative dimensions of the flowbox illustrated will be maintained across the machine for any width of machine. Generally, for consistencies of 1.0%-2.0% solid content of stock, the slice will be 6 inches long, /2" deep at inlet and /2" or A1 at its outlet. Corresponding dimensions for the explosion chamber could be 4 high by 3" long with, say, seven tubes 134 per 20" width of machine, each tube being of 1" internal diameter.. Thus inlet: outlet ratio of chamber 135 is of the order of 2:1. Experiments show that this ratio should be in the range of 0.4:1 to 4:1 for good results.

With these dimensions it will at once be appreciated that a very compact fiowbox has been devised, Thus the box can be accommodated in a length of some 2 feet. Such dimensions must be compared with the 6 feet or more encountered in present flowboxes designed to achieve the same high-speed well deflocculated stock employing shear-slice methods. The advantages of the present flowbox design are obvious. The most useful application of these flowboxes is on multi-ply paper and board machines e.g. Inverform machines. Due to the compact nature of the flowboxes, a 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 in situ. 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 flowboxes of these designs that better stock is produced. With such boxes, standard Inverform machines may well run at lower .speeds and may also produce board of higher basic weight. Also machines may be run at higher speeds to increase output, in all cases without reducing the quality of board produced.

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

Many variations of the apparatus described above may be effected without departing from the scope of the present invention. Thus the header tank 132 may be pressurised, open to atmosphere or under vacuum. The size, shape and orientation of the explosion chamber 135 may be varied to suit the stock and machine requirements.

Although the plates 140, 141 are preferably planar to define a smooth shear flow channel 136, shear-turbulence generators may be provided to assist in creating shear turbulence within the stock. Thus the shear-turbulence generators may comprise a series of enlarged chambers spaced along channel 136.

The machine on which the flowbox is employed can be of many designs. Thus for example, instead of the twin-wire machine shown in the drawings, the two-wire Inverform arrangement shown in Great Britain Pat. No. 859,083 may be used, this being a common arrangement in present-day Inverform machines.

We claim:

1. A flowbox in combination with a paper, board or similar fibrous-web making 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) a stock inlet to the explosion chamber and a stock outlet from the explosion chamber disposed in opposed vertical walls thereof, said inlet and outlet being of overall cross-section less than the transverse cross-section of the explosion chamber at the inlet and outlet respectively, the inlet being directed downwards at an acute angle to the floor of the chamber, and the outlet being generally parallel to the floor of the chamber,

(c) a transverse planar bafile projecting into the chamber from the floor of the chamber, said baflle being inclined towards and disposed in the path of stock entering the chamber to define first and second successive portions of the explosion chamber and extending to a position in proximity to the upper wall of the chamber to define a restricted passage between said portions, the shape of each said portion being such that stock on entering that portion diverges and on leaving that portion converges, the stock thereby undergoing a rapid change in direction and velocity of flow in the first portion, reversing its direction of flow and passing upwardly over the bafile, to promote turbulence mixing and deflocculation.

2. A flowbox as claimed in claim 1 wherein the outlet passage constitutes a non-divevrgent passage leading to an exit slice from the flowbox for ejecting stock onto a machine wire.

3. A flowbox as claimed in claim 1 wherein the ratio of total outlet area to total inlet area to the explosion chamber is from 0.4:1 to :1.

4. A fiowbox as claimed in claim 3 wherein the ratio is from 1:1 to 3: 1.

5. A flowbox as claimed in claim 1 wherein the inlet through which stock is fed to the explosion chamber is provided by a plurality of ports communicating with a plurality of tubes arranged in two superposed non-parallel skew sets, the tubes in each set being mutually parallel, wherein cross flows are set up in the common explosion chamber to destroy any irregularities in distribution across the width of the flowbox.

References Cited UNITED STATES PATENTS 2,894,581 7/1959 Goumeniouk 162-339 2,920,699 1/ 1960 Fasoli l62343 3,309,264 3/1967 Parker ct a1. 162-336 739,596 9/1903 Friesland 465 1,774,554 9/1930 Honigmann et a1. 55465X REUBEN FRIEDMAN, Primary Examiner T. A. GRANGER, Assistant Examiner

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