US2884061A

US2884061A - Flow control apparatus

Info

Publication number: US2884061A
Application number: US621468A
Authority: US
Inventors: Lee Charles Allan
Original assignee: Kimberly Clark Corp
Current assignee: Kimberly Clark Corp
Priority date: 1956-11-09
Filing date: 1956-11-09
Publication date: 1959-04-28
Anticipated expiration: 1976-04-28

Description

April- 28, 1959 c. A. LEE

FLOW CONTROL APPARATUS 4 Sheets-Sheet 1 Filed Nov. 9, 1956 28, 1959 C, A LEE FLow CONTROL APPARATUS Filed Nov. 9, 195e I jai/@72275211 Aprilzs, 1959 GALL-:E

FLOW CONTROL APPARATUS 4 sheets-sheet WZQJL @e April 28, 1959 c. A. LEE

FLOW CONTROL APPARATUS 4 Sheets-Sheet v1l Filed Nov. 9, 1956' United States Patent 2,884,061 izaterxted Apr. 28, 1959 tice? FLUW CONTROL APPARATUS Charles Allan Lee, Neenah, Wis., assignor to Kimberly- 'Clark Corporation, Neenah, Wis., a corporation of Delaware Application November 9, 1956, Serial No. 621,468

6 Claims. (Cl. 162-317) The present invention relates to the manufacture of felted web and sheet products from uid suspensions of iibrous materials, and has particular relation to the manufacture of paper on papermaking machines of the inlet or pressure forming type.

In the operation of inlet or pressure forming type papermaking machines, an aqueous suspension of liber and such other papermaking materials as may be used, which suspension is commonly designated as stock, is supplied to a web-forming region through which the Fourdrinier wire is moved. The stock reaches the wire as a relatively high energy, flowing stream which is usually under substantial hydraulic pressure.

In certain improved forms of such apparatus, examples of which are illustrated in my prior U.S. Patent No. 2,756,648, the stock passes through a iiow control chamber located in the vicinity of the web-forming region and wherein a portion of the stock present in the flow control chamber is caused to recirculate. In general, such improved pressure forming type machines provide excellent control of the pressure and velocity relationship existing within the web-forming region.

The present invention is concerned with the further improving of such apparatus. As will hereinafter appear, the present invention includes the discovery that the provision of certain types of ow control mechanism, positioned to act on the stream of stock which circulates within the liow control chamber during the operation of the described pressure forming mechanisms, will effect improvement of the iiow characteristics of the owing stream of stock reaching the web-forming region. More specifically this is accomplished by the provision of one or more resistance elements within the flow control chamber. To accomplish the objectives of the present invention, such resistance elements must satisfy certain conditions with respect to form, dimensions and location.

Further objects and advantages of the present invention will be made more apparent in the following description and accompanying drawings of certain preferred embodiments of the invention as applied particularly to pressure forming or inlet type Fourdrinier papermaking machines.

In the drawings:

Figure l is a schematic view partially in vertical section and partially in side elevation of the wet end of a Fourdrinier pressure inlet type paperrnaking machine embodying certain of the features of the invention, and certain accessory equipment.

Figure 2 is an enlarged vertical, cross sectional view of the machine illustrated in Figure l, this View showing certain of the details and features of the iiow control mechanism in accordance with the invention which is embodied in that machine;

Figure 3 is a sectional View taken along line 3--3 of Figure 2;

Figure 4 is a sectional view taken around the line 4-4 of Figure 2;

Figure 5 is an enlarged vertical, cross sectional view similar to Figure 2 illustrating a modified form of ow control mechanism in accordance with the invention; and

Figure 6 is a sectional View taken along the line 6 6 of Figure 5.

The schematic view, Figure 1, illustrates the general structure and arrangement of a pressure-forming or inlet type Fourdrinier papermaking machine of the general character to which the .present invention has particular application. As there shown, the Fourdrinier wire 11 is supported upon a breast roll 13 anda couch roll 15 and is adapted to pass over a plurality of spaced table rolls 17 and suction boxes 19. The wire 11 is tensioned by additional guide or tensioning means, as illustrated at 21.

A tray 23, which ris adapted to collect the white water, i.e. the liquid drains through the wire during the webforming operation, is disposed within the upper and lower reaches of the wire 11, as illustrate-d, and this tray is arranged to discharge into a mixing tank 25, which is normally maintained about three-fourths filled. Fresh water for make-up purposes may be added to the mixing tank 25 through the pipe 27, and additional stock, as is necessary to maintain the proper consistency or iiber concentration in the uid suspension or stock being delivered to the Web-forming region, is added through a second inlet pipe 29.

The bottom of the mixing tank 25 is inclined, as shown, and a main flow line 31 is connected to the tank at the lower end thereof. The main flow line 31 includes a branch extension 33 having a valve 34 therein for use in draining the mixing tank, and the main flow line 31 also connects with the iniiow side of a stock or fan pump 35, which is the principal means relied upon to deliver stock to the web-forming region of the machine.

The outlet of the fan pump 35 is connected to the inlet structure of the machine by suitable piping, indicated generally at 37. Included in this piping is an automatically operable pressure regulating valve 39, a transition section 41, which converts the circular cross sectional stream delivered by the fan pump 35 and pipings 37 to a stream of rectangular outline, and a flow spreader 43. The ilow spreader 43 accomplishes the function of converting the uniformly dimensioned stream delivered by the transition section 41 into a relatively shallow stream of rectangular cross section which desirably has a transverse width substantially equal to the cross-machine width of the web-forming region of the machine.

The outlet end of the ow spreader 43 is connected to the web-forming region of the machine by an angle connection 44 and a conduit 45, which is provided in the lower or static-nary portion 49 of the ow control unit 47. The iiow passageways within the angle connection 44 and the conduit 45 are each rectangular in cross-section and may have of the same dimensions as the outlet end of the flow spreader 43. The piping 37 also includes a by-pass line 51 which connectsA the outlet side of the fan pump 35, upstream of the pressure regulating valve 39, with the mixing tank 25, as shown. The by-pass line includes a shutol valve 53. Suitable showers or sprays, indicated generally at 55, are provided for effecting continuous cleaning of the rolls and wire in accordance with usual papermaking practices.

The particular breast roll 13 constituting a part of the illustrated apparatus is of the open-surfaced type. The roll 13 comprises a cylindrical inner shell 57 which may be of bronze or other corrosion resistant material, and which is supported for rotation by means of a pair of shaft sections 59, each of which is mechanically connected to one end of the shell by a suitable header unit.

Each of the header units includes a plate section 63, the periphery of which is welded or otherwise attached to one end of the shell in water-tight relationship, together with a plurality of radially-extending, symmetrically spaced bracing members 65, which are welded to the inner end portions of the two shaft units 59.

At spaced intervals along the shell 57, the roll is provided with a plurality of outwardly-projecting ring units 67. The rings 67 are integrally attached to the shell 57 and are provided with spaced notches 69 (Figure 2) which support a plurality of elongated bar or vane members 71. These vane members 71 are of generally curved cross section, as shown particularly in Figure 2, and extend longitudinally of the roll surface with the longitudinal axes thereof substantially parallel to the axis of rotation of the roll.

The spaced vane members 71 are used to receive and to hold temporarily the liquid which is forced through the wire and the adjacent underlying surface of the roll during the web-forming operation. Each of the vanes 71, as shown particularly in Figure 2, includes a base or root portion which is rectangular in cross section, and which is adapted to t within the vane-supporting notches 69 in the ring units 67. The slots 69 are so arranged that the root portion of each Vane is disposed at an angle of about 15 degrees to the radius which intersects the base of that portion. This angle is illustrated at a in Figure 2, in which figure the radius is indicated by the line 73.

The remaining outer portion 75 of each of the vanes is inclined forwardly, in the direction of the roll movement at an angle of about 120 degrees with reference to the associated root section. The outer end portion 75 of each of the vane sections is tapered to a sharp edge with the result that each vane is, in effect, of curved crosssectional outline. A radius drawn through the forward edge of the root section will substantially intersect the sharp edge of the outer portion 75, as shown in Figure 2.

The outer edge portion 75 of each of the vane units is also notched, as shown particularly at 77 in Figure 3, and during the manufacture of the roll, an edgewise disposed ribbon 79 of bronze or other corrosion resistant material is wound into these slots 77 so as to provide a helical coil of closely spaced turns which extend along the periphery of the roll 13. This is shown particularly in Figures 2 and 3, and it will be noted that the helical ribbon 79 projects a substantial distance above the outer edges of the vanes 71. This arrangement permits free circulation of liquid between the cells or cavities formed in the roll periphery by the spaced vanes 71, and it also minimizes vane shadows in the formed web.

In roll construction of the general type illustrated, the vanes 71 are preferably spaced within the range of from about 5% to 1%. inches along the roll periphery, and the turns of the edgewise-wound wire ribbon 79 which denes the outer surface of the breast roll should be spaced sufciently close together to prevent appreciable deformation of the forming wire during the operation of the machine. In a practical embodiment of the invention, where the breast roll has an over-all diameter of approximately 24 inches, the helical ribbon winding 79 was wound at a pitch of 5 turns to the inch, and constituted a strip of bronze ribbon having a thickness of 0.35 inch, and a maximum cross-sectional dimension of .250 inch. In this same construction, the edges of the vanes were about .15 inch below the outer peripheral edge of the ribbon. A coarse mesh woven wire covering, such as a l2-14 mesh screen (not shown), may be applied over the ribbon winding, if desired.

As shown particularly in Figure 3, the vane support rings 81 at the two ends of the roll are of a somewhat greater height than the intermediate ring support members 67, and are adapted to co-act with locking rings 83 which engage notches in the end sections of the vanes, so as to lock the vanes in position. The particular arrangement of the vane elements and the ribbon support 79 for the forming wire present a minimum of resistance to the ow of fluid through the wire into the breast roll. At the same time, the vanes are operable to retain the liquid which is received therein during the period in which the forming wire moves out of the web-forming region.

Referring to Figure 1, it will be seen that the flow control unit 47 includes the lower or stationary section 49 which is integrally attached to the main frame 35 of the machine, and an upper or adjustable section 87, which is supported on the stationary section 49. The lower section 49 includes suitable plate and structural elements which define a frame portion 89 having a flat upper surface 90, a pair of upwardly-extending sides 91, and the walls of the closed conduit 45 through which the stock is conducted to the other elements of the ow control means.

The upper section 87 of the flow control unit is likewise of fabricated construction, and includes oppositely arranged side walls 93 which are connected together by suitable transversely-extending structural members 95 to define a generally horizontally disposed box structure, which is supported upon the at upper surface of the frame portion 89 of the stationary section 49 so as to be movable toward and away from the vertical center line of the breast roll 13.

To facilitate the accomplishing of this movement, the side walls 91 of the stationary section are provided with guideways 97 adapted to receive and to co-act with suitable guide members 98 constituting an integral part of the side walls 93 of the adjustable section 87. The coacting guides 98 and guideways 97 serve the additional function of preventing the hydraulic pressure which is developed within the ow passageways of the flow control unit 47 from displacing the adjustable section relative to the lower stationary section 49. To further aid in accomplishing this, it is generally desirable that the guides and guideways shall be constructed to fairly close tolerences. It may also be found desirable to include seals, as for example, the O-ring type seal illustrated at 99, between the engaging surfaces of the upper and

lower sections

87 and 49 to minimize the possibility of iluid leakage in the operation of the apparatus. Locking screws, as illustrated at 100, may also be used to aid in holding the sections in proper adjustment.

Two or more horizontally-extending, adjusting screws 101 are aixed to the adjustable section 87 at spaced intervals therealong, and these screws engage internally threaded gear wheels 102, which are supported upon suitable brackets 103, attached to the frame portion 89 of the stationary section 49. The gear wheel units 102 are rotated simultaneously by worm gear sections keyed to a shaft 105, which is journalled on the brackets 103, and a hand wheel 107 is provided for rotating the shaft 105. By this means, it is possible to move the entire adjustable section 87 of the flow control unit 47 toward or away from the vertical center line of the breast roll and thereby vary the dimensions and relative location of the web-forming region on the wire. The plane of separation between the upper and lower sections of the ow control unit, which plane is coincident with the surface 90, normally extends substantially parallel to the surface of the horizontal position of the forming wire 11.

The ow conduit 45 through which the stock is conducted from the discharge end of the angle connection 44 leading from the discharge end of the flow spreader is rectangular in cross section and may have the same cross-sectional area, and dimensions as that end Eof the ow spreader. The lower surface of the flow conduit 45 in the region adjacent the web-forming region is defined by an apron plate 109 which extends transversely across the full width of the machine. The lower surface of the outer or lip portion 111 of the apron plate is cut away, as shown, and desirably this surface is irved so as to provide with the adjacent surface of the wire 11, which is supported on the breast roll 13, a passageway 113 which is of increasing cross-sectional area in the direction opposite to the direction of movement of the wire. The apron plate is supported upon an underlying support plate 115 integral with the frame portion by means of suitable screw fastenings, not shown.

In order that the position of the apron plate 109 may be adjusted horizontally, the structure includes a removable spacer bar 117, which is adapted to be interposed between the apron plate 109 and the plate member 119, which constitutes the main defining element for the lower surface of the flow delivery conduit 45. It will be apparent that by the use of spacer bars of varying width, it is possible to readily adjust the position of the apron plate 109 relative to the center line of the breast roll, and thereby vary the horizontal dimension of the webforming region.

The outer edge of the plate 115 upon which the apron plate 109 is supported is also cut away in order to facilitate free backward ow of stock through the passageway 113 during the web-forming operation. Also, to aid in conducting away this ow from the web-forming region, the main frame may be provided with openings as indicated at 121 in Figure l.

The flow control unit 47 is operable to direct a flowing stream of stock onto and through the wire as the wire is moved through the web-forming region at the discharge side of that unit. The ow control unit includes transversely extending structural elements 123, integrally attached to the side walls 93, which define the walls of a generally cylindrical, flow control chamber 125, and a generally cylindrical flow control member 127 disposed within the ow control chamber 125. The cross-sectional outline of the generally cylindrical flow control chamber and/ or flow control member is not necessarily circular, and various oval, elongated and other forms may be used depending on the design of the papermaking machine. The unit also includes an adjustable throttling means, indicated generally at 129, which is positioned at the inflow side of the main flow chamber 125, and an adjustable slice mechanism 131, which defines the downstream edge of the pressure forming zone on the wire.

The flow control member 127 comprises a smoothsurfaced, cylindrical shell 133 which may be of bronze or other corrosion resistant material having a pair of end plates 135 which are welded or otherwise attached to the ends of the shell 133 to provide watertight closures therefor. The shell 133 has a diameter which is somewhat greater than one-half the diameter of the flow control chamber 125, wherein it is located. The axis of the ow control member 127 extends substantially parallel to the axis of the flow control chamber 125, and it is intended that the ow control member 127 can be adjusted over a rather substantial range of positions during operation of the machine.

To accomplish this adjustment, the flow control member 127 is provided with a pair of cylindrical shaft sections 137, which extend from either end thereof, and which are disposed eccentrically withl relation to the axis of the iiow control member 127. The inner ends of each of the shaft sections 137 extend through and are welded to one of the end plates 135 and an inwardly spaced transverse supporting plate 139. The shaft sections 137 are supported upon the side walls 93 of the is attached to the member 141 for effecting rotation of that member. By this means, it is possible by relative rotation of the shaft section 137 and the support members 141, to adjust the position of the flow control member 127 within the flow control chamber 125. The apparatus includes means for locking the flow control member 127 in any selected position, and also indicating scales 149 for aiding in a ready determination by the operator of the position of the flow control member 127. The flow control member 127 is locked in any selected position by means of a pressure element 151, which bears against the indexing members and 147.

As previously indicated, it has been discovered that certain improvements in the flow characteristics of the stream of stock reaching the web forming region can be attained by providing certain flow control means within the re-entrant flow passageway provided for that portion of the stock which is caused to circulate within the flow control chamber during the operation of the apparatus. This flow control means may take any one of a variety of forms. In general, it will constitute resistance elements which may comprise spaced plates, spaced ns, rods, bars, discs, or the equivalent thereof, positioned in certain specified locations within the flow control chamber. The How control means should be of such design that fiber hang-up and plugging will be avoided, and it should not introduce any flow instabilities into the owing stream of stock which can carry over into the web forming region.

In the embodiments of the invention illustrated in the drawings, the resistance elements are of such design that they cause the circulating stream of stock within the flow control chamber to iiow through a series of spaced secondary passageway arranged in a generally side-by-side relationship, each of these passageways having'a width at right angles to the direction of flow which is equal to from about 20 to 80 percent of the average radial distance between the surface of the flow control member and the defining wall of the flow control chamber, i.e. the average height of the passageway provided for the recirculating stream of stock. In the structure illustrated in Figures l to 4 of the drawings, the flow control means, which is indicated generally at 152, comprises a series of n or vane members 154 arranged to provide a series of spaced, secondary passageways 153 in side-by-side relationship. The width of these passageways is indicated as A in Figure 4. y

To prevent fiber hang-up and plugging within the passageway wherein the resistance elements of the flow control means are located, the solid projected area of each of the resistance elements in a plane transverse to the direction of stock flow should have a width at least approximately equal to the average length of the longest 5 percent by number of all of the fibers in the stream of stock. Preferably the leading edge of each of the resistance elements is approximately planar and the corners where the leading edge connects with the sides of the resistance element should be just broken to prevent hang up of the fibers in the stream of stock. While in some structures the resistance elements may have a width which is several times that of the length of the longest 5 percent by number of all of the fibers in the stream of stock, it is preferable to use as thin an element as possible to produce a minimum wake downstream thereof.

Furthermore the total open area provided bythe spaced passageways between the resistance elements should be as large as possible in order to minimize energy loss within the owing stream of stock. In general, the resistance elements should not occupy more than 60 percent of the average cross-sectional area of the passageway provided for the stream of stock which recirculates within the ow control chamber. The preferred width of the resistance element, as specified above, generally will occupy more than 30 percent of the average cross-sectional area of the passageway. l

Also, the resistance elements should extend into that passageway a distance which is not less than two-thirds the average radial distance between the surface of the flow control member and the defining wall of the flow control chamber, i.e. the average height of the passageway provided for the recirculating stream of stock. In general, the closer the resistance elements approach the opposing surface defining the passageway provided for the recirculating stream of stock, the better the control.

To prevent wakes or other secondary instabilities from carrying over into the web forming region, the resistance elements of the ow control means are located in the flow control chamber at an angular position of from about 30 to 180 degrees relative to the downwardly directed, vertical radial plane of the flow control chamber measured in the upstream direction (i.e. counter to the direction of movement of the recirculating stream). This angle is illustrated in Figures 2 and 5 at C.

'Ihe fin or vane members 154 of the Figure 2 embodiment extend at an angle of approximately 90 degrees from the downwardly directed, vertical radial plane of the flow control chamber 125. These fins are conveniently made of bronze or other corrosion resistant material and may be welded or otherwise suitably attached to the surface of the ow control member 127. In pressure forming machines designed for the manufacture of tissue by the use of conventional type pulps, the fins may be between 3% to 5A; inch in width and should extend radially to a point approximately 1%; to 1A; inch from the wall of the ow control chamber. The upper edge of the fins should extend approximately tangentially from the flow control member and slope downward as illustrated at 156, this construction assuring that any extremely long fibers which might staple over the fins will be washed downwardly and flow free. The lower edge of the fms is also shown as being inclined. However, the shape of the lower edge of the ns is not critical and could be changed considerably without producing any harmful effect within the flowing stream of stock.

In a flow control chamber which was 8 inches in diameter and having a generally centrally positioned flow control member approximately inches in diameter, it was found that fins shaped and positioned as speciled above which were approximately 1/z inch in thickness, spaced axially 1/2 inch apart l inch between centers) and which extended to within t inch of the wall of the charnber were generally satisfactory for the usual types of papermaking stock used in the manufacture of tissue and like papers.

The inow throttling mechanism 129 embodied in the apparatus is illustrated particularly in Figures l and 2. As there shown, it includes a bar or vane member 155, which extends completely across the width of the machine, and which is arranged to effect even and uniform throttling of the flowing stream of stock which is being delivered to the flow control unit through the flow conduit 45. The throttling member 155 is supported for limited movement toward and away from the apron plate 169, which defines the adjacent lower surface of the delivery conduit 45, by means of a suitable guide means 157 integrally attached to the transversely extending frame structure 123 of the ow control unit.

Movement of the throttling member 155 and accurate positioning of that member relative to the apron plate 109 is accomplished by means of a plurality of spaced rods 159, each of which is connected at one end to the throttling member 155 and is provided with a threaded end portion 161 at its other end. The threaded end portions 161 engage suitable internally threaded gear wheels 163, which are supported on the frame of the upper section 87 of the flow control unit 47. These gear units 163 are rotated in unison by co-acting worm units 165 supported upon and keyed to a suitable actuating shaft 167. The arrangement permits the throttling member 155 to be moved so as to vary and adjust the height of the opening through which stock is admitted to the flow control chamber.

To prevent leakage along the sides of the throttling member 155, it is desirable to include sealing means, such as the resilient sealing tubes 169, located intermediate the throttling member and the sides of the guide support 157 therefor. The edges of the support members are desirably curved to conform generally to the outline of the stream lines existing in the flow pattern within the apparatus during operation.

lt is desirable that the breast roll 13 be supported in such manner that its position relative to the ow control unit 47 can be accurately adjusted-this in conjunction with the adjustable support for the apron plate 109 and the permissive fore and aft adjustment of the upper section 87 ef the flow control unit 47, making possible very close control and adjustment of the dimensions of the webfonning region and the ow passageways adjacent that region. Adjustment of the position of the breast roll 13, is most easily accomplished by the use of an automatically operable adjustable roll support of a hydraulic or other type. Such mechanisms are commercially available and will not be described in detail.

The slice or discharge lip structure 131 is supported on the downstream end of the frame of the upper section 87 of the flow control unit. Essentially the slice structure 131 includes a transverse, beam support member 171, which is generally channel-shaped in outline, and which serves as the main support for the other elements of the structure. The beam member 171 extends completely across the machine and is attached to the frame 123 of the ow control unit by suitable screw fastenings 173 which Permit limited vertical movement of the slice structure. A tube or O-ring type seal 175 prevents leakage between the engaging surfaces of the beam 171 .and the frame structure.

The slice structure 131 serves as the downstream closure for the ow control chamber 125, and in order to accomplish that function, it includes a transversely-extending exible plate section 177, which is supported on the channel-shaped beam member 171, as shown in Figure 2. It is intended that the lower end portion of the plate member 177 may be warped during operation of the machine in order to effect both general and local adjustment of the spacing ybetween the downstream edge or lip 179 of the slice plate and the wire.

To accomplish the adjustment, the lip portion of the slice plate 177 is engaged by a series of spaced-apart support rods 181 which extend through the beam 171 `and which are fastened to the plate 177 by suitable sockets and pins 183, as illustrated. The upper end of each of the slice adjusting rods 181 is connected to a threaded adjusting unit 185, which can be rotated to effect the desired adjustment. The rotatable adjustment units `are supported upon the upper web of the beam 171. The adjacent dening surface of the main flow `control chamber is desirably faired into the cooperating surface of the slice plate 177, as illustrated at 187, in order to minimize the likelihood of localized turbulence.

The slice plate 177 is curved in the general form of a right circular cylinder and provides with the adjacent surface of the wire 11, a flow passageway 189 of substantial length and constantly decreasing cross-sectional area in the direction of movement of the wire, and the formed web. This arrangement, in combination with the available adjustment of the downstream edge or lip of the slice plate 179, makes possible accurate control of the amount of stock which is discharged from the flow control unit on top of the formed web and is of important value in assuring satisfactory operation of the mechanism.

The two sides of the ow control chamber 125 are closed by the end walls 93 of the ow control unit and suitable Sealing units 191, which are adapted to ride on the wire during the machine operation. The sealing units anse-1,661

191, as shown in Figs. 2 and 3, comprise L-shaped sections 193 of rubber or other resilient material which is backed by a rigid metal angle 195, the entire structure 'being yadjustably held in position by a support 197, which is bolted to the side of the flow control unit by suitable bolts 199. The support includes spaced adjusting screws 201, which bear against the angle 195 to eect accurate adjustment of the seal.

In the operation of apparatus of the type illustrated in Figures l through 4, the stock which comprises a fluid suspension of fibrous material is supplied to the flow control chamber as a high energy llowing stream having substantial velocity and pressure energy components. For most eicient operation it is quite important that the axis of this stream shall extend substantially parallel to the plane of the wire in the web-forming region.

Within the flow control chamber, the entering stream which is generally rectangular in cross-sectional outline is brought into contact with the outer periphery of a second stream of stock which is ilowing in a generally vorticular path. This second stream ows counter-clockwise as viewed in Figure 2.

The vorticular ow is produced by recirculation of :aIn portion of the stock within the flow control chamber, and the velocity of the recirculating, vorticular stream is controlled and determined largely by the positioning of the cylindrical flow contro-l member, which is located Within the flow control chamber.

In the control and adjustment of the operating conditions of papermaking machines of the general type illustrated in Figures l through 4, the most important available controls .are the pressure at which the stock is delivered to the inlet side of the flow control unit 47, the throttling elect which is acco-mplished by the transverse throttling member 155, the relative speed of the Vorticular recirculating ow which exists within the main ilow control chamber 125, the position of the slice 177, and the dimensions of the web-forming region on the wire 11.

Adjustment of the throttling member 155 determines the pressure and velocity at which the stream of stock is introduced into the flow control chamber 125 of the flow control unit. By control of the velocity at which the stream is introduced into the flow control cham-ber, it becomes possible to control, over a rather wide range, the machine direction to cross machine direction strength ratio of the formed web. To a certain extent, this adjustment also affects the rate of recirculation in the vorticular stream which exists within the liow control chamber, since the throttling of the stock inflow produces a region of the low pressure transversely across the machine in the region of the flow control chamber which is forward of the throttling member 155, which low pressure induces, and to a considerable extent regulates, the recirculation flow.

Major control of the recirculating, vorticular ow is accomplished, however, by control of the position of the ow control member which is located within the main flow control chamber.

The physical dimensions of the web-forming region, specically its length in the direction of wire movement, can be adjusted !by longitudinal movement of the upper section 87 of the flow contro-l unit 47, and to some extent by adjustment of the apron plate 109.

The axis of the stream entering the ilow control unit is preferably parallel to the surface of the wire in the 4web-forming region. The minimum possible ratio of machine direction to cross machine direction strength will be realized when the velocity of the stream is approximately equal to the wire velocity, and increased machine direction to cross-direction strength ratios will Ibe produced when the velocity of the stream is greater or less than the wire velocity. The pressure of the stream may vary within quite wide limits, depending on the type of pressure pattern required, the speed of formation, and

10 also upon whether or not any formation at atmospheric pressure will occur later downstream of the slice.

In accomplishing the most satisfactory web formation and overall stability of operation under certain operating conditions and especially during very high speed operation, it is desirable that a portion of the flowing stream of stock delivered to the web-forming region shall flow backwardly along the moving wire, through the passageway 113 existing between the under surface of the apron plate lip 111 and the wire 11. When the stream velocities existing within the ow control unit are high, i.e. 1500-2000 feet per minute or above, certain instability conditions which are inherent in pressure forming type machines tend to appear, and these instabilities can be avoided by the creation of a stable, backwardly flowing stream of stock which passes out of the ow control chamber in the region where the wire enters that chamber. As disclosed in my prior Patent No. 2,756,651, this backwardly flowing stream eliminates substantial pressure fluctuations in the flowing stream of stock reaching the web-forming region during operation.

When operating under conditions which involve relatively low wire speeds and low stream velocities, this tendency to instability is substantially reduced and under such conditions, it may not be necessary to provide the backwardly owing stream of stock. The provision of the backwardly flowing stream of stock at the upstream end of the web-forming region has, however, an important further advantage over and above instability control in that it removes from the web-forming region the lower boundary layer of the stream which is owing into the flow control chamber. Removal of that layer accomplishes the very desirable result of assuring that only the central or core portion of the stream reaches the upstream edge of the web-forming region. This materially facilitates the adjustment of the tlow velocity in the wire forming region.

When the backwardly owing stream exists, the amount of stock which is discharged in that manner may constitute a substantial portion of the total stock delivered to the ow control chamber. For example, amounts of stock up to 40 or even 50 percent of the total ow have been discharged in this manner in certain arrangements. However, in most flow control units for high speed operation, wherein the stock is delivered to the web-forming region as a high energy flowing stream having a velocity approximately equal to the wire velocity, it will rarely be found necessary to institute back flow in excess of about l0 percent of the total flow into the How control unit. In most instances, Where boundary layer removal only is the primary consideration, back ow in the amount of 2 to 5 percent will usually be adequate.

The amount of stock which is circulated within the flow control chamber, in order to produce the vorticulal stream which intermixes with the upper layer of the stream, will vary, depending upon the position of the ow control member, the relative dimensions of the ow control member and the tlow control chamber, and the particular ratio of machine direction to cross machine direction strength which is desired in the nished sheet product. In the manufacture of tissue weight sheets at speeds within the range of 500 to 3000 feet per minute, by the use of machines of the type illustrated in Figures 1 through 4 and by the use of stock having a consistency within the range of .05 to .25 percent, satisfactory operation has been attained where the amount of recirculating ow was within the range of from 20 to 30 percent of the total ow into the ow control unit. In the manufacture of heavier weight papers, for example, book grades having basis weights within the range of l5 to 30 pounds or heavier, for 480 sheets, 24 x 36 inches, recirculation in amount equal 2O to 40 percent of the total flow into the webforming unit have been used with good results.

The amount of stock which flows out of the flow control chamber on top of the formed web is controlled by lill' the positioning of the slice lip or other means defining the downstream edge of the pressure forming region. Under all conditions of operation, it is advisable to so position the slice lip that there will be a suicient amount of stock on the wire as it passes beneath the slice lip to effect lubrication of the web and prevent its derangement. Generally, the discharge with the formed web of an amount of stock equal to from about to 8 percent of the total amount delivered to the flow control unit to effect formation of the web will accomplish satisfactory lubrication of the formed web. In instances where a portion of the web is to be formed downstream of the pressure forming region, i.e. in instances Where a portion of the web is forming at atmospheric pressure, the adjustment of the slice lip will be such that substantially greater amounts of stock will flow out of the ow control chamber on top of the wire.

When the amount of stock which is discharged from the flow control chamber beneath the slice exceeds that which is necessary to effect lubrication of the formed web, it is important that this stock shall be spouted out of the ow control chamber at a Velocity which is approximately equal to the wire velocity. When the amount is merely that required for lubrication purposes, somewhat less careful adjustment of this velocity is required.

The exact velocity of How of the layer of stock which is discharged with the web is very difficult to determine, due to the fact that considerable shear is present at the slice lip and in the decreasing area or other passageway through which the web and the stock layer reach the slice lip. As a result, the portion of the layer of stock immediately adjacent the slice surface has approximately zero velocity, whereas the portion or lamina directly overlying and contacting the web is necessarily at wire velocity. Hence, when referring to the velocity at which the layer of stock is discharged with the web, what is meant is the average velocity existing in that layer, and it is that average Velocity which should be approximately equal to wire velocity.

The slice mechanism accomplished the important function of conducting the formed web out of the web-forming region Without disturbing or deranging the web fibers. This involves the accomplishment of a transition action during which the pressure existing in the formed web must be reduced from the pressure existing in the webforming region within the flow control mechanism to atmospheric pressure.

In the construction illustrated in Figures l through 4 this transition is accomplished by the decreasing area in the flow passageway 189 provided between the wire 11 and the exible plate section 177 of the slice mechanism. It will be understood that other slice or discharge lip constructions may be used and may have particular advantages in certain instances.

For the purposes of this application, the web-forming region may be defined as that region wherein the concentration and deposition of those fibers which ultimately constitute the formed web is actually taking place. Alternatively, the web-forming region may be defined as that region, wherein there is substantial flow through the web-forming member of the white water or other uid carrier for the fiber.

Under ordinary operating conditions of the apparatus illustrated in Figures l through 4, where the amount of stock discharged beneath the slice lip is merely suicient to lubricate the web, almost all of the fiber deposition and flow of white water through the wire will occur in the region included between radial lines drawn from the center of the breast roll 13 to the downstream tip of the apron plate 109 and to the slice lip 179, which region might also be described as the region of pressure forming. There may be some deposition of fibers from the backwardly flowing stream of stock which is discharged through the passageway 113, although this is usually of rather small magnitude. Also, in instances where a subl2 stantial amount of stock is discharged from the flow control chamber beneath the slice lip 179, and onto the upper surface of the partially formed Web, there will be substantial ber deposition downstream of the slice lip.

When paper making apparatus of the type illustrated in Figures l through 4 is to be placed into operation, the fore and aft positioning of the upper section 87 of the ow control unit 47, which determines the location and dimensions of the web-forming region, the pressure at which stock is delivered to the flow control unit, the positioning of the throttling member the apron lip 111 and the slice structure 177, and the location of the flow control member will usually be based upon the approximate calculated position of those elements. Generally, the first adjustment to be made will be of the throttling member 155 to assure the attainment of the desired stream velocity and recirculation within the flow control chamber. By the use of pressure or velocity taps in the side walls 93 of the upper section 87 of the flow control unit or in other of the defining surfaces of the flow control chamber, it becomes possible to ascertain immediately following the admission of stock to the flow control unit whether or not the projected operating conditions are being attained. Other means of measuring the flow are possible and have proven practical. For example, electrical flow measuring mechanisms which employ a heated search unit are available; these units may be placed in contact with flowing streams of iiuid and calibrated to read flow directly.

The next adjustment to be accomplished will probably be location of the flow control member. This adjustment may conveniently be based upon the examination of the sheet being manufactured. Adjustment of the slice may also be made to assure that the formed web is passing out of the flow control chamber without derangement. Some fore and aft adjustment of the oW control unit and even adjustment of relative position of the breast roll may also be found desirable, particularly at the start-up. Inspection of the formed web will be relied upon to a considerable degree for determining the optimum position of the various control units.

Apparatus formed in the manner `described above is capable of forming sheets over a wide range of basis weights, with any desired relationship between the machine direction and cross machine direction strength ratio in the formed sheets and with a high degree of physical uniformity in the formed paper product. The physical uniformity of the paper product in the cross machine direction is at least partially obtained through the provision of the resistance elements located within the recirculating passageway of the flow control chamber.

In certain instances where a greater fiexibility of pressure and velocity control within the web forming area is required, the ow control member may constitute a driven roll. An embodiment of the invention utilizing such a flow control member is illustrated in Figures 5 and 6. Except for the iiow control member with its support and rotating means and the form of the resistance elements utilized within the re-entrant passageway of the forming chamber, the structure shown in these figures is similar to the arrangement illustrated in Figures l through 4.

Referring directly to Figure 5, it will be seen that the flow control member 205 comprises a solid right circular cylindrical roll which extends the full length of the chamber 125 and is supported for free rotation therein by suitable bearings, not shown. The peripheral diameter of the flow control member or roll 205 generally is slightly larger than one-half the diameter of the flow control chamber 125 and the roll 205 is connected to a suitable drive means in order that it may be driven at a predetermined speed during the operation of the apparatus.

The roll drive means, which may include a motor (not shown), sprockets 211, and a drive chain 213, should be capable of driving the roll 205 at a relatively high speed. For example, in a structure using a flow control roll approximately 6 inches in diameter, within a flow control chamber 9 inches in diameter, the drive means should be capable of driving this roll at a speed Within the range of from about 400 to 600 revolutions per minute during normal operating conditions of the machine. l

vIn this structure, ilow control means 215 positioned within the re-entrant passageway 150 are provided for improving the flow characteristics of the stock reaching the web-forming region. Since this structure employs adriven roll, it is necessary to attach the resistance elements forming the ow control means to the wall of the chamber instead of the roll surface. In the illustrated structure the resistance elements comprise two transversely extending rows of axially-spaced, generally rectangular, bar or plate elements 217 formed of bronze or other corrosion resistant material which extend somewhat more than two-thirds of the distance from the wall of the chamber to a point adjacent the periphery of the rotating roll.

The bar elements 217 are arranged in two rows and provide a plurality of spaced, secondary passageways 218, disposed in side-by-side relationship within the passageway 150 and through which the recirculating fluid must flow prior to intermixing with the main stream entering the flow control chamber. The bar elements 217 in the upper row are staggered relative to the bar elements in the lower row to provide a wider spacing between the bar elements in each row than would be possible if only one row of such bar elements were used. The construction has the advantage of providing somewhat less resistance to the flow of the stock than would be the case if all the bar elements were in a single row. The individual bar elements in the two rows may be suitably attached by means such as welding to a removable section 219 of the structural element 123 which forms the wall of the ow control chamber 125.

As previously set forth the resistance elements, which in this case constitute the bar elements 217', are located upstream of the web-forming region and are angularly spaced at an angle between 30 and 180 degrees and preferably between 80 and 110 degrees from the downwardly directed vertical radial plane of the flow control chamber 205. Each of the secondary passageways 218 has a width at right angles to the direction of flow which is equal to from about 20 to 80 percent the average height of the re-entrant passageway 150 through which the recirculating stream is caused to flow. The width of these passageways is indicated as B in Figure 6.

As previously set forth, the width of the leading edge of each of the bar elements 217 should be as small as possible, but to avoid fiber hang-up the width should be at least approximately equal to the average length of the longest percent by number of all of the bers in the stock suspension. When using stock suspensions of the type normally employed in the manufacture of tissue, in an inlet having a 9 inch diameter chamber and a 6 inch diameter driven roll, this will result in the use of bar elements which are from 3A; to 5/8 inch in width.

In such a structure, which is illustrated in Figs. 5 and 6, the bar elements 156 in each row are spaced apart approximately 11/2 inches, and the ends of the bar elements extend to within ls to 1A inch of the surface of the driven roll. Since the bar elements 156 in the two rows are staggered this provides openings or ow passageways therebetween approximately 1/2 inch in width through which the recirculating uid in the passageway is caused to flow. The leading edges of the bar elements 156 are preferably inclined downwardly in the direction of the driven roll so that any very long fibers which staple around the bar elements are washed downwardly and into the flowing stream of stock. As in the previously described embodiment, the leading edges of the bar ele- 14 ments should be generally planar and the corners formed between the leading edges and the sides of the bars should be smoothly broken so as to avoid burrs which could catch iibers as the stream of stock passes thereby.-

In general, the resistance elements should not occupy more than 6() percent of the average cross-sectional area of the passageway 150.

The most important aspect of the invention, and the aspect which is common to all of the described structural embodiments, is the provision of resistance type ow control elements arranged for location in the recirculating portion of the stock stream within a specified range of positions and having certain dimensional limits, as previously set forth. When used in the specified manner, these elements are effective to accomplish important improvement in the flow characteristics of the flowing stream of stock reaching the web-forming region. This is apparently accomplished by improved `control of the pressure and velocity relationship existing in the stream of stock which is circulated within the ow control chamber during the operation of the apparatus. Maximum effectiveness of the resistance elements as control elements results when there is minimum restriction of the passageway through which the recirculating flow occurs. If the width of the resistance elements is made equal to the average length of the longest 5 percent by number of all of the fibers in the stream of stock reaching the flow control chamber, the additionally desirable result of increased freedom from plugging and stapling is also accomplished.

It should be understood that other forms of structural members may be used to provide the desired flow control within a recirculating passageway.

Also the structures of the papermaking apparatus including the shape of the forming member may vary considerably from that disclosed. Whenever the apparatus includes a llow control chamber located adjacent the web-forming region and wherein a portion of the stock is caused to recirculate within a curved passageway of .substantial height, the flow control means of the present invention will be found desirable.

Various features of the invention believed to be new are set forth in the appended claims.

I claim:

l. In web-forming apparatus of the pressure-forming type, a continuous web-forming member, a breast roll :supporting said member for movement into and through the web-forming region of said apparatus, a source of supply of a uid suspension of fibrous material, and a :ow control unit having an inflow opening connected to said source of supply, and having an outflow opening through which a conned owing stream of said iluid is discharged onto said forming member under pressure forming conditions as that member is moved through said web-forming region, said web-forming region being located at, and being substantially coextensive with, the outflow opening of said flow control unit, said ow control unit including means dening the walls of a transversely extending generally cylindrical ow control chamber which is closed except for said inflow and said outflow openings, and through which the fluid delivered to said web-forming region is caused to flow, a transversely extending, generally cylindrical flow control member disposed in a generally central position within said chamber .so as to provide a re-entrant passageway within said chamber, means for causing a portion of the Huid within the ow control chamber to flow through said re-entrant `passageway to produce a circulating stream of fluid which intermixes with the stream of iiuid which flows into the flow control chamber, and flow control means disposed within said re-entrant passageway upstream of the Webforming region and angularly spaced between about 30 to degrees from the downwardly directed vertical radial plane of the flow control chamber, said ow control means providing a plurality of spaced, secondary passageways through which said uid must flow in passing through said re-entrant passageway, each of said spaced secondary passageways having a width at right angles to the normal direction of flow through said reentrant passageway which is equal to from about 20 to 8O percent of the average height of said re-entrant passageway, said ow control means being operable to improve the flow characteristics of the fluid reaching the webforming region during operation of the web-forming apparatus.

2. In web forming apparatus of the pressure-forming type, a continuous web-forming member, a breast roll supporting said member for movement into and through the web-forming region of said apparatus, a source of supply of a fiuid suspension of brous material, and a fiow control unit having an inflow opening connected to said source of supply, and having an outflow opening through which a confined fiowing stream of said fluid is discharged onto said forming member under pressure forming conditions as that member is moved through said web-forming region, said web-forming region being located at, and being substantially coextensive with, the outfiow opening of said fiow control unit, said ow control unit including means defining the walls of a transversely extending generally cylindrical flow control chamber which is closed except for said inflow and said outfiow openings, and through which the fluid delivered to said web-forming region is caused to flow, a transversely extending, generally cylindrical fiow control member disposed in a generally central position within said chamber so as to provide a re-entrant passageway within said chamber, means IEfor causing a portion of the fiuid within the ow control chamber to flow through said re-entrant passageway to produce a circulating stream of fiuid which intermixes with the stream of fiuid which flows into the flow control chamber, and flow control means disposed within said re-entrant passageway upstream of the webforming region and angularly spaced between about 30 to 180 degrees from the downwardly directed vertical radial plane of the fiow control chamber, said flow control means including a plurality of resistance elements which provide a plurality of spaced, secondary passageways through which said fiuid must flow in passing through said re-entrant passageway, each of said spaced secondary passageways having a width at right angles to the normal direction of flow through said re-entrant passageway which is equal to lfrom about 20 to 80 percent of the average height of said re-entrant passageway, and said resistance elements extending into said re-entrant passageway a distance at least equal to about two-thirds the average height of said re-entrant passageway, said flow control means ybeing operable to improve the fiow characteristics of the flowing stream of fiuid reaching the web-forming region during the operation of said apparatus.

3. In web forming apparatus of the pressure-forming type, a continuous web-forming member, a breast roll supporting said member for movement into and through the web-forming region of said apparatus, a source of supply of a fiuid suspension of fibrous material, and a flow control unit having an inflow opening connected to said source of supply, and having an outiiow opening through which a confined flowing stream of said fluid is discharged onto said forming member under pressure forming conditions as that member is moved through said web-forming region, said web-forming region being located at, and being substantially coextensive with, the outow opening of said flow control unit, said fiow control unit including means defining the walls of a transversely extending generally cylindrical flow control chamber which is closed except for said inflow and said outflow openings, and through which the fluid delivered to said web-forming region is caused to iiow, a transversely extending, generally cylindrical flow control member disposed in a generally central position within said chamber so as to provide a re-entrant passageway within said chamber, means for causing a portion of the uid within the fiow control chamber to flow through said re-entrant passageway to produce a circulating stream of fluid which intermixes with the stream of fiuid which flows into the flow control chamber, and flow control means disposed within said re-entrant passageway upstream of the webforming region and angularly spaced between about 30 and 180 degrees from the downwardly directed radial plane of the fiow control chamber, said flow control means including a plurality of resistance elements which provide a plurality of spaced, secondary passageways through which said fiuid must fiow in passing through said re-entrant passageway, the leading edge of each of said resistance elements being approximately planar and having a width at least approximately equal to the average length of the longest 5 percent of all of the libers inthe fluid suspension, each of said secondary passageways having a width at right angles to the normal direction of ow through said re-entrant passageway which is equal to from about 20 to 80 percent of the average height of said re-entrant passageway, said flow control means being operable to improve the ow characteristics of the fiowing stream of fluid reaching the web-forming region during the operation of the web-forming apparatus.

4. In the web forming apparatus of the pressure-forming type, a continuous web-forming member, a breast roll supporting said member for movement into and through the web-forming region of said apparatus, a source of supply of a fluid suspension of fibrous material, and a fiow control unit having an inflow opening connectedr to said source of supply, and having an outflow opening through which a confined flowing stream of said fluid is discharged onto said forming member under pressure forming conditions as that member is moved through said web-forming region, said web-forming region being 1ocated at, and being substantially coextensive with, the outfiow opening of said flow control unit, said flow control unit including means defining the Walls of a transversely extending generally cylindrical flow control chamber which is closed except for said infiow and said outflow openings, and through which the fluid delivered to said web-forming region is caused to flow, a transversely extending, generally cylindrical fiow control member disposed in a generally central position within said chamber so as to provide a re-entrant passageway within said chamber, means for causing a portion of the uid within the fiow control chamber to flow through said re-entrant passageway to produce a circulating stream of uid which intermixes with the stream of fiuid which flows into the flow control chamber, and fiow control means disposed within said re-entrant passageway upstream of the Webforming region and angularly spaced between about and degrees from the downwardly directed radial plane of the ow control chamber, said ow control means including a plurality of resistance elements which provide a plurality of secondary passageways arranged in a side-by-side relationship transversely of generally, the normal direction of fluid fiow through said re-entrant passageway and through which said uid must fiow in passing through said re-entrant passageway, the leading edge of each of said resistance elements being approximately planar, being inclined relative to the vertical plane of movement of said fiuid suspension within said reentrant passageway and having a width approximately equal to the average length of the longest 5 percent of all of the fibers in the fluid suspension, said flow control means being operable to improve the iiow characteristics of the flowing stream of liuid reaching the web forming region during the operation of said apparatus 5. In web forming apparatus of `the pressure-forming type, a continuous web-forming member, a breast roll supporting said member for movement into and through the web-forming region of said apparatus, a source of supply of a fluid suspension of fibrous material, and a. iiow control unit having an infiow opening connected to said source of supply, and having an outow opening through which a confined flowing stream of said fluid is discharged onto said Iforming member under pressure forming conditions as that member is moved through said web-forming region, said web-forming region being 1ocated, and being substantially coextensive with, the outflow opening of said flow control unit, said ow control unit including means defining the walls of a transversely extending generally cylindrical flow control chamber which is closed except for said inow and said outflow openings, and through which the fluid delivered to said web-forming region is caused to flow, a transversely eX- tending adjustable generally cylindrical flow control member disposed in a generally central position within said chamber so as to provide a re-entrant passageway within said chamber, means for causing a portion of the fluid Within the 110W control chamber to ow through said reentrant passageway to produce a recirculating stream of uid which intermixes with the stream o'f uid which Hows into the flow control chamber, and flow control means disposed within said re-entrant passageway located upstream of the web-forming region and angularly spaced between about 30 and 180 degrees from the downwardly directed radial plane of the ow control chamber, said ow control means including a plurality of axially spaced tins, each of which connects with and extends outwardly from the flow control member to a point adjacent the wall of the ow control chamber to thereby provide a plurality of spaced, secondary passageways through which said uid must ilow in passing through said re-entrant passageway, each of said secondary passageways having a width at right angles to the normal direction of flow through said re-entrant passageway which is equal to from about 2O to 80 percent of the average height of said re-entrant passageway and said fins projecting into said passageway a distance at least equal to about two-thirds the average height of said re-entrant passageway, said ow control means being operable to improve the ow characteristics of the owing stream of fluid reaching the web-forming region during the operation of the said apparatus.

6. In web forming apparatus of the pressure-forming type, a continuous web-forming member, a breast roll supporting said member for movement into and through the web-forming region of said apparatus, a source of supply of a uid suspension of fibrous material, and a ow control unit having an inllow opening connected to said source of supply, and having an outow opening through which a confined flowing stream of said uid is discharged onto said forming member under pressure forming conditions as that member is moved through said web-forming region, said web-forming region being 1ocated at, and being substantially coextensive with, the outflow opening of said flow control unit, said flow control unit including means defining the walls of a transversely extending generally cylindrical flow control chamber which is closed except for said inilow and said outow openings, and through which the fluid delivered to said web-forming region is caused to ilow, a transversely extending, adjustable, generally cylindrical ow control member disposed in a generally central position within said chamber so as to provide a re-entrant passageway within said chamber, means for causing a portion of the iluid within the flow control chamber to ow through said re-entrant passageway to produce a circulating stream of fluid which intermixes with the stream of fluid which flows into the flow control chamber, and ilow control means disposed within said re-entrant passageway, located upstream of the web-forming region and angularly spaced between about and 110 degrees from the downwardly directed radial plane of the flow control chamber, said ilow control means including a plurality of axially spaced ns, each of which connects with and extends radially from the flow control member to a point adjacent the wall of the flow control chamber to thereby provide a plurality of spaced, secondary passageways through which said fluid must flow in passing through said re-entrant passageway, the leading edge of each o'f said fins being approximately planar and having a width at least approximately equal to the average length of the longest bers in said fluid suspension, each of said secondary passageways having a width at right angles to the normal direction of flow through said re-entrant passageway which is equal to from about 20 to 80 percent of the average height of said re-entrant passageway, said ow control means being operable to improve the ow control characteristics of the flowing stream of uid reaching the web-forming region during the operation of said apparatus.

References Cited in the le of this patent UNITED STATES PATENTS 1,552,629 Mason Sept. 8, 1925 2,677,991 Goumeniouk May 11, 1954 2,756,648 Lee July 31, 1956