US3823062A - Twin-wire papermaking employing stabilized stock flow and water filled seal(drainage)boxes - Google Patents

Abstract

IN THE INLET SECTION OF A PAPERMAKING MACHINE, STOCK IS ACCELERTED AND PASSED THROUGH A RELATIVELY LONG AND STRAIGHT PASSAGEWAY, THEREBY STABILIZING SUBSTANTIALLY THE ENTIRE FLOW OF THE SUSPENSION TO MOVE UNIFORMLY IN THE SAME DIRECTION AT THE SAME SPEED. THE STABILIZED SUSPEN: SION FLOWS BETWEEN A PAIR OF FORMING CARRIERS, PREFERABLY WITHIN THE INLET SECTION. WATER IS DRAINED FROM THE SUSPENSION BY FORCING IT THROUGH THE FORMING CARRIERS INTO

SEAL BOXES SUPPORTING THE CARRIERS, THEREBY FORMING A WEB, LATER DRIED TO FORM PAPER. THE SEAL BOXES ARE DISPOSED SUCCESSIVELY, AND THE FLOW THERETHROUGH MAY BE SEPARATELY CONTROLLED TO CONTROL WEB FORMATION. THE SEAL BOXES ARE KEPT FLOODED TO ASSURE THAT BOTH SIDES OF EACH OF THE CARRIERS ARE COVERED WITH WATER.

Description

July 9, 1974 5,1 WARD ETAL 3,823,062

TWIN-WIRE PAPERMAKING EMPLOYING STABILIZED STOCK FLOW AND WATER FILLED SEAL (DRAINAGE) BOXES Filed Feb. 28, 1972 5 Sheets-Sheet l July 9, 1974 1', WARD ETAL 3,823,062

TWIN-WIRE PAPERMAKING EMPLOYING STABILIZED STOCK FLOW AND WATER FILLED SEAL (DRAINAGE) BOXES Filed Feb. 28, 1972 3 Sheets-Sheet 11 FIG, 4

July 9, 1974 GT WARD ETAL 3,823,062 TWIN-WIRE PAPERMAKING EMPLOYING STABILIZED STOCK FLOW AND WATER FILLED SEAL (DRAINAGE) BOXES Filed Feb. 28, 1972 3 Sheets-Sheet 5 3,823,062 Patented July 9, 1974 TWIN-WIRE PAPERMAKING EMPLOYING STA- BILIZED STOCK FLOW AND WATER FILLED SEAL (DRAINAGE) BOXES George T. Ward, Greenwich, and John A. Means, Norwalk, Conn., and Charles A. Lee and Warren R. Furbeck, Knoxville, Tenn., assignors to International Paper Company, New York, N.Y.

Filed Feb. 28, 1972, Ser. No. 230,007 Int. Cl. D21f 1/00, 11/04 US. Cl. 162123 21 Claims ABSTRACT OF THE DISCLOSURE In the inlet section of a papermaking machine, stock is accelerated and passed through a relatively long and straight passageway, thereby stabilizing substantially the entire flow of the suspension to move uniformly in the same direction at the same speed. The stabilized suspension flows between a pair of forming carriers, preferably within the inlet section. Water is drained from the suspension by forcing it through the forming carriers into seal boxes supporting the carriers, thereby forming a web, later dried to form paper. The seal boxes are disposed successively, and the flow therethrough may be separately controlled to control web formation. The seal boxes are kept flooded to assure that both sides of each of the carriers are covered with water.

This invention relates generally to methods and apparatus for making paper and the like. More specifically, the invention relates to methods of forming a web of suitable fibers and to apparatus for carrying out the methods. The invention is particularly directed to the control of the suspension of fibers as it passes from the inlet section to the forming section of a machine and until the web is fully formed.

In papermaking an aqueous suspension of papermaking fibers, known as stock, is supplied to an inlet section including a chamber, known as a head box. From the head box the stock flows through an orifice, commonly known as a slice, into a forming section, pouring onto a moving endless foraminous forming carrier, commonly known as a wire. Water is drained from the suspension through the forming carrier, forming a web of the papermaking fibers on the carrier, the web being subsequently dried to form paper.

Certain non-uniformity of the finished paper, particularly in high speed operations, may be occasioned by aberrations in the free surface of the stock as it is moved along on the carrier into the forming section where the paper web is formed. Such aberrations are carried on through the machine and appear in the finished paper. It has therefore proved desirable to control the free surface of the stock on the carrier. It is known to utilize a so-called twin-wire machine wherein the stock is directed from the head box as a free jet into a space between a pair of endless forming carriers. The tubulence in the exposed surfaces of the jet between the head box and the forming carriers nevertheless permits certain non-uniformity in the surface of the stock as it is deposited between the forming carriers, again producing aberrations in the paper.

It is also known to utilize a pressure forming machine wherein the forming carrier passes over a large opening at the outlet of the head box, and the stock is forced against the carrier under pressure. The water is drained from the stock in this pressure forming region to form a web on the carrier. Such systems have also included the use of a felt carrier passing into the head box and overlaying the formed web as it leaves the head box. Although in such apparatus there is no uncontrolled free surface of the stock on the forming carrier, the stock in the head box is turbulent. This condition produces great shear forces that may interfere with the orderly formation of the web, resulting in non-uniformity.

In accordance with the present invention, the stock is stabilized, and the web is formed while keeping the stock controlled at all times. There is no free surface of stock on the forming carriers, and substantially all parts of the stock move uniformly at the same speed in the same direction. Stabilized stock moving uniformly at the same speed in the same direction is placed between a pair of forming carriers and is captured thereby. It is then carried from the inlet section between the forming carriers prior to any substantial formation of the web. To this end the stock is accelerated in the inlet section, applying forces tending to straighten out the fibers, and the stock is then passed through a straight passageway over a relatively long distance. Thereby any great turbulence and speed differentials in the stock are damped and dissipated until the stock is stabilized and all moves in substantially the same direction at substantially the same speed without gross turbulence, except for such as inherenly occurs along the boundary layer of the flow, adjacent the walls of the containing conduit. The stabilized flow is then passed between a pair of forming carriers moving generally in the same direction as the stock. Preferably, the forming carriers move through the terminal portion of the inlet section, and the stock moves uniformly in the same direction as the forming carriers as the carriers leave the enclosed inlet section and move with the stock between them into the forming section prior to any substantial web formation. The web is then formed in the forming section by removing water through both forming carriers.

In the forming section each forming carrier is moved over a respective plurality of successive seal boxes. The seal boxes support the forming carriers to move in converging paths, and water is forced from the suspension through the forming carriers and into the seal boxes as the forming carriers converge, thereby forming webs on the respective forming carriers. The webs are joined to form a single web upon the convergence of the forming carriers. The webs are preferably formed without sudden pressure shocks. To this end, in accordance with one aspect of the present invention, the inlets to the successive seal boxes are kept water filled and the flow through respective seal boxes separately controlled. The controlled flow of water filled seal boxes permits a relatively gentle formation of the web. Further, the flow of water through the respective seal boxes may be controlled to maintain the direction and speed of the remaining suspension substantially constant, providing further control of web formation.

It is, therefore, an object of the present invention to provide an improved apparatus for forming a paper web wherein the stock is stabilized Within an inlet section and is controlled at all times from its exit from the inlet section to its formation into the web. Other objects and advantages of the invention will become apparent from the following detailed description, particularly when taken with reference to the drawings in which:

FIG. 1 is an illustration, partly diagrammatic and partly in section, showing a papermaking machine incorporating the present invention;

FIG. 2 is an enlarged sectional view of the inlet section of the apparatus shown in FIG. 1;

FIG. 3 is a further enlarged sectional view of the seal shown in FIGS. 1 and 2;

FIG. 4 is a plan view, partly diagrammatic, showing the apparatus of FIG. 1 with the flow paths of the sus pension of fibers and circulating water;

FIG. is an enlarged sectional view of the apparatus shown in FIG. 4 taken along line 5-5;

FIG. 6 is an enlarged sectional view of the apparatus shown in FIG. 5 taken along line 66;

FIG. 7 is an enlarged sectional view of a modified form of the terminal part of the inlet section shown in FIG. 2;

FIG. 8 is an enlarged sectional view of a modified form of the inlet and forming sections of the present invention for making two layered paper;

FIG. 9 is an enlarged sectional view of another modified form of the inlet and forming sections of the present invention for making multilayered paper; and

FIG. 10 is an enlarged sectional view of a further modification of the inlet and forming sections of the present invention for making multilayered paper, particularly filled paper.

In FIG. 1 there is illustrated a papermaking machine including an inlet section 10 fashioned in accordance with the present invention. The inlet section 10 has an inlet 12 for admitting a suspension of papermaking fibers and an outlet 14 for discharging the suspension. The suspension flows into the inlet 12 from a distribution system 15 which may be a conventional distribution system supplying a water suspension of papermaking fibers substantially evenly distributed over the width of the papermaking machine.

As illustrated in FIGS. 1 and 2 the stock may flow horizontally in the inlet section some distance above where the paper web is to be formed. The inlet section 10 Widens in a transition section 16 where the flow is turned by the curved wall sections 18 and 20 to flow downwardly through a narrow, elongated passageway 22. Vanes 24, disposed within the transition section 16, serve to separate the flow of stock suspension into smaller streams and direct the separated flow around the bend into the straight narrow passageway 22. By breaking the stream up into smaller parts and directing the individual parts, gross turbulence in the fiow is prevented. The relatively long passageway 22 is formed by relatively straight wall sections 26 and 28 which form a passageway 22 of substantially constant cross section and direct the stock suspension to move in a given direction, illustrated as vertically downward, and over a relatively long distance sufficient to permit any eddies to be substantially damped out.

Thus, in operation, the flow of the suspension of papermaking fibers enters the inlet 12 substantially uniformly distributed across the papermaking machine and is directed by the transition section 16 into the narrowed passageway 22. The passageway 22 has a substantially smaller cross section than the transition section 16, inherently producing a substantial increase in velocity. The acceleration occasioned by this change in cross section applies forces tending to straighten the fibers in the suspension. Acceleration changing the velocity by a factor of the order of 2:1 has been found satisfactory. The accelerated suspension then flows through the relatively long passageway 22. As the passageway 22 has a substantially constant cross section, the flow therethrough is at a constant velocity. The suspension becomes stabilized as the flow moves in the same direction at constant speed for a relatively long interval, whereby the suspension, as it approaches the outlet 14, is moving substantially uniformly in direction and speed. That is, all of the fibers and the suspending water move downwardly at substantially the same speed. There will, of course, be a boundary layer at the wall sections 26and 28, as will be discussed further below.

A pair of forming carriers or wires 30 and 32 are directed into the inlet section 10 upstream from the outlet 14. The forming carriers 30 and 32 enter the inlet section 10 through seals 34 and 36, respectively, which may comprise plastic sealing members 38 and 40, respectively. The forming carriers 30 and 32 enter the inlet section 10 over terminal wall sections 42 and 44, respectively. As shown best in FIG. 3, these terminal wall sections 42 and 44 are each preferably coated with a plastic coating 43 to alleviate wear of the forming carriers 30 and 32. The seal 34 admits the forming carrier 30 between the sealing member 38 and the plastic coating 43 on the terminal wall section 42. The seal 36 admits the forming carrier 32 between the sealing member 40 and the plastic coating 43 on the terminal wall section 44. The forming carriers 30 and 32 are bent over the wall sections 42 and 44 as they enter the inlet section 10 as this assures a smooth transition as the forming carriers enter the passageway 22. Inside the inlet section 10 the terminal wall sections 42 and 44 comprise the terminal sections of the walls forming the narrow passageway 22. These terminal wall sections 42 and 44 are substantially impervious to water, as are the straight wall sections 26 and 28, in order that the entire stabilized flow of suspension may move uniformly at the same speed between the forming carriers 30 and 32 and in the direction of movement of the forming carriers, as shown.

The suspension is captured between the carriers 30 and 32 and moves therewith out of the inlet section 10 into a forming section 46 prior to any substantial formation of a paper web. The forming section includes a plurality of seal boxes 48 and 50 disposed adjacent the sides of the forming carriers 30 and 32 opposite the suspension of papermaking fibers. The inlet of each seal box 48, 50 includes a respective foraminous carrier support 52, 54 which supports the respective carrier 30, 32 without impairing substantially the fiow into the seal boxes 48 and 50. The carrier supports 52 and 54 cause the respective forming carriers to converge as they move downwardly through the forming section 46. As the suspension moves downwardly through the forming section 46 between the carriers 30 and 32, the suspending liquid is forced through the forming carriers 30 and 32 and thence through respective carrier supports 52,54 of the respective seal boxes 48,50 and thence through the seal boxes themselves.

The carrier supports 52 and 54 may take a number of forms. They may, as shown, comprise simple narrow bars across the forming carriers 30 and 32; however they may take complicated shapes to provide strength and relatively small disruption of drainage through the forming carriers 30 and 32. Machine direction members of the carrier supports 52 and 54 are spaced from the respective carriers 30 and 32 so as not to mark the resulting paper. The supports 52 and 54 support the respective forming carriers 30 and 32 for movement along converging paths.

The respective pluralities of seal boxes 48, 50 are disposed successively along the respective forming carriers 30 and 32 from the outlet 14 of inlet section 10 to the point of convergence of the carrier supports 52 and 54, which defines the outlet 56 of the forming section 46.

As the suspending liquid is removed from the suspension, the suspended fibers are deposited upon the respective forming carriers 30 and 32 forming a web on each forming carrier. The respective webs are joined into a single integral web by the convergence of the forming carriers 30 and 32. The convergence of the forming carriers between carrier supports 52 and 54 blocks the passage of suspension from the outlet 56 from forming section 46, permitting only the forming carriers 30 and 32 with the formed integral web therebetween to pass out of the forming section 46.

Each of the pluralities of seal boxes 48 and 50 is preferably mounted on a respective common mounting which is movably mounted so that the outlet 56 of the forming section 46 may be adjusted to accommodate different forming carriers 30 and 32 and different thicknesses of web.

After leaving the forming section 46, the web may be further dewatered by conventional means, such as suction boxes 58, and then dried by a conventional or other dryer, not shown.

The forming carrier 30 is supported over its path by rolls 60, 62, 64, 66, 68, 70 and 72 as well as by the terminal wall section 42 and the carrier support 52. The forming carrier 32 is supported over its path by rolls 72, 74, 76, 78 and 80 as well as by the terminal wall section 44 and the carrier support 54. At least one roll in each set is a motor driven driving roll, driven by a motor 81 for driving the respective forming carriers 30 and 32 at the same linear speed. Certain of the rolls may be adjustable or biased to maintain proper tension in the repective forming carriers 30 and 32.

The formed web is confined between the two forming carriers 30 and 32 up to a sheet transfer roll 82, where the forming carrier 32 moves away from the web, leaving the web supported by the forming carrier 30. At a sheet transfer suction roll 84, the web may be transferred to a dryer fabric 86.

The complete flow paths of the suspension and the circulating water are best shown in FIGS. 4, and 6. The stock suspension is made up in a conventional manner in a stock make-up chest 100. The water therefor is supplied through a conduit 102 from a wire pit 104 which is a reservoir for the water withdrawn from the forming web. The fibers and other additives are supplied from a supply chest 106 through a conduit 108. The stock suspension is pumped from the stock make-up chest 100 through a conduit -110 by a fan pump 112 and forced thereby through conduits 114 and 116 to the distribution system 15. Flow and pressure may be controlled by a valve 118 between the conduits 114 and 116 and by controlling the pump drive. Further control is provided by a by-pass conduit 120 having a by-pass control valve 122 therein. The by-pass conduit returns a controlled portion of the output from the fan-pump 112 from the conduit 114 to the wire pit 104.

As described above the distribution system 15 applies the stock suspension evenly across the inlet 12 to the inlet section 10. From the inlet section it flows under the pressure generated by the fan-pump 112 into the forming section 46 where the water is forced from the suspension through the forming carriers 30 and 32 and into the seal boxes 48 and 50. As best shown in FIGS. 4, 5 and 6, the seal boxes 48 and 50 are closed to the atmosphere. Each of the seal boxes 48 and 50 has a single respective closed discharge conduit 124 extending from the respective seal box to the Wire pit 104 into which it discharges below the normal water level. A respective flow meter 126 and control valve 128 are disposed in each discharge conduit 124. Pressure indicators may be placed at various points in the flow path, as desired. Water removed from the circulating system is replenished by adding fresh water to the wire pit 104 through a conduit 129 from a source not shown.

An important aspect of the invention is that the machine can be operated in a flooded state. That is, the seal boxes 48 and 50 are kept filled with water. This assures that the inlets to the respective seal boxes 48 and 50 are water filled. Inasmuch as the flow of the suspension is closed from the fan pump 112 to the formation section 46, no air is admitted to the system until after formation of the web and its exit from the forming section 46 at its outlet 56. As shown, the seal boxes 48 and 50 tilt upwardly away from their inlets so that any air that may get into the system, as at start-up or dissolved or beat into the stock entering the fan pump 112, will rise above the inlets to the seal boxes 48 and 50. The discharge conduits 124 may leave the respective seal boxes 48 and 50 at their highest points to assure water filled seal boxes.

The seal boxes 48 and 50 are closed chambers but for the open inlets covered by the carrier supports 52 and 54 and the discharge conduits 124. They are formed by impervious top walls 134, bottom Walls 136, back walls 138, end walls 140 (FIG. 5) and common walls 142 separating successive seal boxes from each other. At the open inlet the common walls 142 are secured to the carrier supports 52 and 54 in a manner whereby the members of the carrier supports keep the successive seal boxes substantially separate up to the respective forming carriers 30 and 32, thereby assuring separate flow control.

Control of draining is effected by the control valves 128. These are particularly effective when the discharge conduit 124 is filled with water at least up to the control valves 128. The flow meters 126 permit observation of the flow to permit adjustment of the control valves 128 to provide the desired flow rates. Generally it is preferable that the flow of stock suspension through the formation section 46 proceed at a constant rate. Otherwise turbulence is created which may disrupt the web formation. To this end the flow through successive seal boxes 48 and 50 is controlled by the respective valves 128 to just make up for the loss in cross section occasioned by the convergence of the forming carriers 30 and 32, assuring straight-through flow of the remaining suspension.

Although the paths of convergence of the forming carriers 30 and 32 in the forming section 46 may take various shapes, in a preferred form of the invention they are symmetrical to drain water equally from both sides of the suspension. As shown, it is a preferred form of the invention that the paths be straight through the forming section 46 so that the web may be formed uniformly along the paths. It is, however, also within the scope of this invention to provide paths shaped to remove water at different rates, as for example, to form the initial more delicate part of the web more slowly and gently than the rest.

The drainage of the present invention, particularly the controlled liquid to liquid drainage of water from the suspension, is less violent than the drainage from conventional Fourdrinier machines using table rolls, foils and suction boxes in the forming region. By withdrawing the water from the suspension without sudden pressure shocks as occasioned by the shaking and pulsing of conventional machines, the formation is better controlled and fines are better retained in the web, rather than lw-ashing through into the wire pit. In accordance with one aspect of the present invention, the forming web is preserved from such pressure shocks until its consistency is at least about 12 percent. This produces a cheaper product without loss of quality. 'It also reduces the build-up of fines in the white water and makes waste disposal less of a problem.

-As mentioned above, the convergence of the forming carriers 30 and 32 blocks the passage of suspension from the outlet 56 from the forming section 46. This assures that the water is drained from the suspension before the formed web exits from the forming section. After convergence, the forming carriers 30 and 32 with the formed web therebetween leave the forming section 46. Following the points where the forming carriers 30 and 32 leave their respective carrier supports 52 and 54, the inlets to the seal boxes 48 and 50 are closed by closure members 130 and 132 to keep .water from flowing back out of the seal boxes behind the forming carriers 30 and 32.

An important advantage to the liquid to liquid drainage system of the present invention is the reduction of entrained air and resulting froth which is difiicult to handle. It also inhibits oxidation of some of the additives that may be placed in the suspension. This is further aided by the discharge of the seal boxes 48 and 50 beneath the water level in the wire pit 104.

Various modifications may be made in the structure without departing from the scope of the invention. For example, the wall sections 26 and 28 have been described as substantially impervious, except of course as necessary to admit the forming carriers 30 and 32, and those are admitted through seals 34 and 36, respectively. On the other hand, it is within the present invention to withdraw some of the flowing suspension prior to its exit from the inlet section 10. In particular, it is sometimes desirable to withdraw at least part of the boundary layer of suspension adjacent the wall sections 26 and 28, particularly under the conditions of plug or frozen flow, as may be established by means well known in the art.

As is well known, under conditions of plug flow, the suspension moves substantially as a unitary plug, except at the boundaries of the flow adjacent the confining walls.

These boundary layers are inherently fiber-free, and it is at times desirable to withdraw this fiber-free water to maintain control of the flowing suspension. This phe nomenon is described in an article entitled Rheological Models and Laminar Shear Flow of Fiber Suspensions, Bugliarello and Daily, The T APPI Journal of the T echnical Association of The Pulp and Paper Industry, December 1961, Vol. 44, No. 12, pages 881-895. The article discusses the presence of the fiber-free water and the effect of turbulence in the fiber-free water in breaking up the plug flow condition.

To alleviate problems created by the boundary layer flow, part or all of this layer may be removed by the modified structure illustrated in FIG. 7. As there illustrated, the walls 26 and 28 are made slightly pervious to the water just upstream of the forming carriers 30 and 32, and the boundary layers flow through openings 188 and 190 in wall sections 26 and 28, respectively, into collecting boxes 192 and 194, whence the water may be disposed of as the water collected in the seal boxes 48 and 50.

The stabilized central part of the suspension is then placed upon the forming carriers 30 and 32 and is carried therebetween out of the inlet section without any substantial web formation on the forming carriers 30 and 32. The amount of suspension withdrawn in the boundary layer is negligible relative to the volume of the central flow.

One of the advantages of the control afforded by the present invention is the ability to produce a relatively square sheet. In convention-a1 papermaking machines, the fibers are preferentially directed in the machine direction, giving the resulting paper decidedly greater strength in the machine direction. With the present invention it is possible to make the machine and cross direction strengths relatively equal by making the speed of the forming fabrics 30 and 32 substantially the same as that of the suspension. On the other hand, the present invention permits control of the relative machine and cross direction strengths by controlling the speeds of the forming carriers relative to the speed of the suspension.

The present invention is particularly adaptable for making multilayered paper. Modifications of the inventron for making multilayered paper are shown in FIGS. 8, 9 and 10.

In FIG. 8 is illustrated a modification for making two layered paper. -A second stream of stock is supplied to the inlet section 10 through a second inlet 196, and the two streams are kept separated by a separating wall 198 which may extend substantially into the forming section 46 to assure that webs are separately substantially formed from the respective streams on the respective forming carriers 30 and 32. The separating wall 198 extends parallel to the wall sections 26 and 28 and thus, with the wall sections 26 and 28 forms two parts of the passageway 22, each of which stabilizes a respective stock stream. Following the end of the separating wall 196, the webs may be joined and processed as above. The two streams may be of different fibers, or of differently colored fibers, to make paper having different qualities on the two sides. It is also contemplated to use different kinds of fibers, such as those made from wood pulp and those made of synthetic material.

In FIG. 9 is illustrated a modification for making three layered paper where the outer layers are made from the same stock. In this case the second stock stream is supplied to the inlet section -10 through a second inlet 200. The second stream is introduced between two parts of the first stream and is separated therefrom by separating walls 202 and 204, extending parallel to the wall sections 26 and 28 and stabilizing the respective suspensions. In this form of the invention, the second suspension may, as in the preferred embodiment illustrated in FIG. 9, be effectively introduced into the forming section 46 only after substantial dewatering of the lfirst suspension has been effected through the respective forming carriers 30 and 32, whereby substantial webs are formed thereon from the fibers in the first suspension before any water is removed from the second suspension.

In FIG. 10 is illustrated a further modified form of the invention particularly useful in making a filled sheet. In many papers it is desirable to fill the sheet with additives, such as clay, which gives the paper greater opacity. Such filter material often is in the form of relatively fine particles, many of which are washed out of the web in conventional Fourdrinier papermaking machines. In the form of the invention illustrated in FIG. 10, the suspension of filler particles is introduced into the forming section 46 only after webs of papermaking fibers have been at least partly formed on the respective forming carriers 30 and 32, whereby the webs retain more of the filler particles than in the case where the filler is introduced in the stock of papermaking fibers. Like the form of the invention shown in FIG. 9, the second suspension is supplied to an inlet 206 and thence between walls 208 and 210 into the forming section 46 between the forming carriers 30 and 32 some distance downstream from the initial web formation.

The present invention has application to the formation of webs of various materials. Therefore, it should be noted that the term paper as used herein is not limited to webs made from any particular fibers. In addition to the relatively short wood fibers commonly used in making paper, the present invention may utilize relatively long synthetic fibers in the formation of the web or the various layers thereof. Where long fibers are used, they may be introduced under pressure after the fan pump 112 to avoid the difficulties attendant in pumping long fibers.

What is claimed is:

1. In a method of making paper or the like, the forming of a web of fibers by the steps comprising passing a dilute aqueous suspension of fibers into an inlet section having an outlet, passing a pair of endless foraminous forming carriers each moving at the speed of the other continuously into said inlet section, stabilizing the flow of suspended fibers by passing the suspension through an extended passageway of substantially constant cross section disposed within the inlet section to cause substantially the entire flow to move substantially uniformly in speed and direction toward said outlet, disposing the stabilized suspended fibers moving substantially uniformly in speed and direction between said carriers, passing said forming carriers with the stabilized moving suspended fibers therebetween out of said outlet prior to any substantial drainage from the suspension, and thereafter forming a web of fibers between said forming carriers in a forming section by moving said forming carriers over converging paths and forcing water under pressure from said suspension substantially without suction through each of said forming carriers into a respective plurality of successive seal boxes disposed adjacent that forming carrier on the side thereof opposite the flowing suspension, at the same time maintaining the water level in the respective seal boxes above the points of entry of water from the respective forming carrier, and [while] separately controlling the rate of flow of water through respective seal boxes, the convergence of the forming carriers substantially blocking the flow of said suspension out of the forming section between the forming carriers.

2. The method of claim 1 wherein the forming web is preserved from sudden pressure shocks until its consistency is at least about 12 percent.

3. The method of claim 1 wherein the stabilized flow of suspended fibers is directed symmetrically between the forming carriers, and the rate of Withdrawal of water through the respective seal boxes as the forming carriers converge is controlled to maintain the direction and speed of the remaining suspension substantially constant.

4. The method of claim 1 wherein at least a part of the boundary layer of flow is removed from the suspension before the suspension reaches the forming carriers.

5. The method according to claim 1 wherein a plurality of suspensions are passed between said forming carriers at the same rate and are processed together to form a layered web.

6. In a method of making paper or the like, the forming of a web of fibers by the steps comprising passing a dilute aqueous suspension of fibers moving substantially uniformly in direction and speed between a pair of endless foraminous forming carriers moving continuously into and through a forming section over paths converging within the forming section, and forming a web of fibers between said converging forming carrier in the forming section by forcing water under pressure from said suspension substantially without suction through each of said forming carriers into a respective plurality of successive seal boxes disposed adjacent that forming carrier on the side thereof opposite the flowing suspension, at the same time maintaining the water level in the respective seal boxes above the points of entry of water from the respective forming carrier, the convergence of the forming carriers substantially blocking the flow of said suspension out of the forming section between the forming carriers.

7. The method of claim 6 wherein each forming carrier is water covered on both sides until the consistency of the web reaches at least about 12 percent.

8. The method of claim 6 wherein the flow of suspended fibers is directed symmetrically between the forming carriers and the rate of withdrawal of Water through the respective seal boxes as the forming carriers converge is separately controlled.

9. In a method of making paper or the like, the forming of a web of fibers by the steps comprising passing a dilute aqueous suspension of fibers moving substantially uniformly in direction and speed between a pair of endless foraminous forming carriers moving continuously into and through a forming section over paths converging within the forming section, and forming a web of fibers between said converging forming carriers in the forming section by forcing water under pressure from said suspension substantially without suction through each of said forming carriers into a respective plurality of successive seal boxes disposed adjacent that forming carrier on the side thereof opposite the flowing suspension at the same time maintaining the respective seal boxes substantially filled with water to a level above the points of entry of water from the respective forming carrier, and separately controlling the rate of flow of water through respective seal boxes, the convergence of the forming carriers substantially blocking the flow of said suspension out of the forming section between the forming carriers.

10. The method of claim 9 wherein the flow channels of the seal boxes are maintained substantially filled with water at least up to respective valves for separately controlling the rate of flow therethrough.

11. The method of claim 9 wherein the water forced into the respective seal boxes is discharged therefrom into a wire pit below the water level in the wire pit to minimize aeration, fibers are suspended in water from the wire pit, and the resulting suspension is forced into said inlet section.

12. The method of claim 9 wherein at least a part of the boundary layer of flow is removed from the suspen sion before the suspension reaches the forming carriers.

13. The method according to claim 9 wherein a plurality of suspensions are passed between said forming carriers at the same rate and are processed together to form a layered web.

14. The method of claim 13 wherein at least one suspension is kept separate from another until after substantial drainage of water from at least one of the suspensions.

15. The method according to claim 13 wherein at least one suspension is introduced between said forming carriers only after there has been substantial web formation on said forming carriers.

16. In a web forming machine the combination comprising (A) an inlet section having (1) substantially impervious walls with inlet means for admitting an aqueous suspension of fibers and terminal wall sections forming an outlet for discharging the suspension to a succeeding forming section,

(a) said walls forming an extended exit passageway of substantially uniform cross section leading to said outlet for stabilizing the flow of said suspension to cause substantially the entire flow to move substantially uniformly in speed and direction toward said outlet (B) a pair of endless foraminous forming carriers;

(C) means for supporting said forming carriers for movement over respective paths into said inlet section and out of said outlet and into and through the forming section,

(1) said forming carriers being supported by said terminal wall sections within said inlet section, and

(2) said paths being generally in the direction of flow as they leave said inlet section with the stabilized suspension moving substantially uniformly in speed and direction disposed between facing surfaces of the respective forming carriers;

(D) means for moving said forming carriers over said paths at substantially the same rate; and

(E) the forming section including 1) a first plurality of successive seal boxes disposed adjacent one of said forming carriers on the side opposite the suspension and a second plurality of successive seal boxes disposed adjacent the other of said forming carriers on the side opposite the suspension,

(a) each of said seal boxes of said first and second pluralities having (i) an open inlet end for admitting water,

' (ii) support means for supporting the respective one of said forming carriers over said open end of the respective seal box, and

(iii) discharge means for discharging liquid from said seal box,

(b) said support means of the seal boxes of the respective first and second pluralities being disposed to support the respective ones of said forming carriers to receive therebetween the suspension discharged froni said outlet means and to converge gradually within the forming section in the direction of flow, (i) the convergence of said forming carriers substantially blocking the flow of said suspension out of the forming section between said forming carriers, and

(2) flow control means operatively associated with respective discharge means for separately controlling the rate of flow of water through respective seal boxes, said seal boxes operating without connection to suction means providing any significant negative pressure on the side of the respective one of said forming carriers opposite the suspension.

17. The combination of claim 16 wherein said substantially impervious walls are slightly pervious to water just upstream from said forming carriers to remove at least a part of the boundary layer of flow before the suspension reaches the forming carriers.

18. In a web forming machine having means for passing a suspension of fibers between a pair of endless foraminous forming carriers supported for movement over respective paths into and through a web forming section,

-1 l and means for moving said forming carriers over said paths at subtsantially the same rate, the improved forming section comprising (A) a first plurality of successive seal boxes disposed adjacent one of said forming carriers on the side thereof opposite the suspension and a second plurality of successive seal boxes disposed adjacent the other of said forming carriers on the side thereof opposite the suspension,

(1) each of said seal boxes of said first and second pluralities having (a) an open inlet end for admitting water, (b) support means for supporting the respective one of said forming carriers over said open inlet end of the respective seal box, and (c) discharge means for discharging water from said seal box without connection to suction means providing any significant negative pressure on the side of the respective one of said forming carriers opposite the suspension, (2) said support means of the seal boxes being disposed to support the respective ones of said forming carriers to receive the suspension therebetween and to converge gradually within the forming section in the direction of flow,

(a) the convergence of said forming carriers substantially blocking the flow of said suspension out of the forming section between said forming carriers, and (3) means for keeping the water level in each seal box above the inlet end thereof. 19. In a web forming machine having means for passing a suspension of fibers between a pair of endless foraminous forming carriers supported for movement over respective paths into and through a web forming section, and means for moving said forming carriers over said paths at substantially the same rate, the improved forming section comprising (A) a first plurality of successive seal boxes disposed adjacent one of said forming carriers on the side thereof opposite the suspension and a second plurality of successive seal boxes disposed adjacent the other of said forming carriers on the side thereof opposite the suspension,

(1) each of said seal boxes of said first and second pluralities having (a) an open inlet end for admitting water,

(b) support means for supporting the respective one of said forming carriers over said open inlet end of the respective seal box, and

(c) discharge means for discharging water from said seal box,

(2) said support means of the seal boxes being disposed to support the respective ones of said forming carriers to receive the suspension therebetween and to converge gradually within the forming section in the direction of flow,

(a) the convergence of said forming carriers substantially blocking the flow of said suspension out of the forming section between said forming carriers, and

(3) each of said discharge means including a conduit extending above the respective one of said inlet ends for keeping the water level in each seal box above the inlet end thereof, and

(B) flow control means operatively associted with respective discharge means for separately controlling the rate of flow of water through respective seal boxes.

20. The apparatus of claim 19 further including a wire pit for containing water, said discharge means discharging water from respective seal boxes into said wire pit below the normal liquid level therein, means for suspending fibers in water removed from the wire pit, and means for conducting the resulting suspension under pressure to said forming section.

21. The apparatus of claim 19 including means just upstream from said forming carriers to remove at least a part of the boundary layer of flow before the suspension reaches the forming carriers.

References Cited UNITED STATES PATENTS 3,645,842 2/1972 Ward l62-203 XR 3,440,136 4/1969 Nelson et al 162-203 XR 3,149,028 9/1964 Robinson 162303 2,028,952 1/1936 Reimer 162-348 XR 3,190,790 6/1965 Ploetz et al. 162--343 XR 1,927,378 9/1933 Street 162344 XR 3,351,522 11/1967 Lopas 162337 1,875,075 8/1932 Mason 162203 XR 3,743,571 7/1973 Ward 162-203 3,726,758 4/1973 Parker et al 162303 XR 3,092,538 6/1963 Parker 162-216 3,764,465 10/1973 Bartley et a1. 162-351 FOREIGN PATENTS 1,582,914 10/1969 France 162203 S. LEON BASHORE, Primary Examiner R. H. T USHIN, Assistant Examiner US. Cl. X.R.

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