US2893486A - Fourdrinier paper making machine - Google Patents

Description

July 7, 195.9 R. A. MARTI FOURDRINIER PAPER MAKING MACHINE s sheets-sheet 1 Filed Feb. 27, 1956 ILLW July 7, V1959 R. A. MARTI FOURDRINIER PAPER MAKING MACHINE 3 Sheets-Sheet 2 Filed Feb. 27, 1956 TIE.. E

LiquidRemova/ High Vacuum Slots Suction Box $14 ze 5g 19/ ,4

Low Vacuum Suction Box Structure Law Vacuum Suction Box Structure TI E.

Hlgh Vacuum Suction Box Liquid Removal Slots) INVENToR. y Russ/:N A. MARTI a Trae/VE v5.

July 7, 1959 v R. A. MART| 2,893,486

FOURDRINIER PAPER MAKING MACHINE T15, 5 HTIEZ 5 5155. 7

v INVENTOR.

@uses/v MARTI myu,

` A TTORNE V5.

United States Patent O "ice f 289348 I i i Patented July'7, 1959 disruption of the partially matted bers and frequently impairs the strength and quality of nished paper. 2893 486 Prior efforts to improve liquid drainage through the FOURDRINIER PAPER MAKING MACHINE Rueben A. Marti, Vancouver, Wash., assigner to Crown Zellerbach Corporation, San Francisco, Calif., a corporation of Nevada Application February 27, 1956, Serial No. 567,899

11 Claims. (Cl. 162-352) This invention relates generally to paper making from liquid pulp stock, and more particularly to an improved method and apparatus for effecting positive controlled liquid drainage Ifrom such stock during the making of paper on a Fourdrinier type paper making machine.

In che known processes for forming paper from paper pulp stock on Fourdrinier paper making machines, such stock is introduced onto a foraminous drainage support, such as the conventional Fourdrinier wire or screen, then is drained to remove liquid as it travels on such wire from the point of introduction thereof to the point at which they drained paper web is nally compacted by the application of high vacuum and then removed from the wire. AIn such processes it is essential that the stock be drained adequately prior to nal compaction by high vacuum so as to enable the `use of a relatively dilute stock.

A dilute stock is desirable because stock of relatively low consistency provides a better and more uniform formation of paper bers with consequent increase in strength and quality of such paper. Heretofore liquid drainage `from stock in early stages of formation on the Fourdrinier Wire during the irst part of its movement has been inadequate and this inadequacy of drainage has precluded the use of relatively low consistency stocks. Thus, in such prior processes the strength and quality of the paper sheet is impaired or at least the maximum paper strength and quality is not attained from a given stock. y

Inadequate drainage of liquid from the stock in the early stages of formation of the paper sheet causes the iibers of the stock to lump together into a non-uniform paper formation. Also, paper stock of relatively low free- 1 ness (i.e., a relatively large amount of loose ber strands) scan only be properly interlaced to give a strong paper L sheet formation if there is effective liquid drainage from such stock during early stages in formation of the paper. ',T-hfus, the inadequate drainage of prior methods llimits the use of low freeness stock. A further problem due Ato inadequate or slow drainage is that it slows down the entire operation because the Fourdrinier wire must be fmoved at a rate commensurate with drainage in order to zprovide a suicient period for proper `formation of the papen In heretofore employed commercial Fourdrinier fm-achines of the type described, the Fourdrinier l"wire is imoved across a series of rotatable table rolls which main- :tain it substantially level to permit formation of a paper 'web during passage of such wire across the rolls from fthe wet end of theV machine, where the stock is initially deposited, to the dry end of the machine where the paper -web is removed. Table rolls accomplish the purpose o-f maintaining the wire substantially level and provide low friction rolling surfaces over which it may pass. However, s-uch rolls possess certain disadvantages in that they cause liquid throwback due to the fact that some of the liquid drained onto the top of the roll is retained on its .surface and carried around to impinge against the lower side of the wire again. This throwback of liquid causes wires of Fourdrinier paper lmaking machines included the devising of structures to increase hydrostatic head on the wire along its entire length to enhance liquid drainage therethrough. Other prior suggestions to effect liquid drainage have proposed high vacuum suction boxes spaced along the length of the wire enclosing the underside of the wire as well as the table rolls and deckle straps. However, such proposals have not met with success as they are costly of construction7 difficult to control closely, and create considerable added wear on the wire through drag, thus contributing to increased operating expenses.

Moreover, many of the prior proposals impaired rather than improved paper quality. For instance, the use of high vacuum under the wire in conjunction with table rolls over whiehrthe wire was moved, often resulted in disruption of the fibers in the paper as it was formed due to the fact that relatively large amounts of liquid removed by the hilgh vacuum were thrown back by the table rolls to impinge against the bottom of the paper as it (on the wire) passed over the rolls. Y

In other words, even though the high vacuum rapidly removed liquid from the stock, the action of the table rolls returned at least part of it to the underside of the paper formation thus requiring re-removal and contributing to the aforementioned disruption of the paper form-ation. An additional mechanical difficulty brought about by the -use of high vacuum in such prior proposals was the fact that high drag was imposed on the wire 4as it moved across the high vacuum suction box edges. This resulted in added wear andV caused Ifrequent shut downs for replacement of the wire.

In order to avoid the above mentioned diculties, practically all commercial machines currently in use are so arranged as to provide only free gravity drainage of liquid through the Awire until the paper mat is substan tially formed and then to nally compact such paper formation into a self-supporting Iweb by applying relatively high sruction only at the dry end of the wire. Since drainage at the wet end of the wire during the important early stages of paper formation has been solely by gravity or free drainage, maximum eiciency of Fourdrinier machines and maximum potentials of paper stock as to paper quality have not been realized. l The present invention provides an improved method and apparatus for effecting positive uninterrupted liquid drainage from liquid pulp paper stock over a relatively large area of a foraminous drainage support or wire on which such stock is deposited Afor paper formation and in which such liquid drainage commences substantially as the stock is deposited on the wire and continues until a Ahigh quality paper formation is produced. The invention, thus provides for the rapid formation of a uniformly Vstrong paper and at the same time permits efficient use of liquid pulp stock of relatively low consistency and high or low freeness; a low freeness stock being one which has a relatively large amount of loose fiber strands enabling ready interlacing of the fibers, but requiring ade- Vquate drainage to permit such interlacing.

The invention further provides a simple and inexpensive apparatus for use with Fourdrinier type paper making machines for applying a light uninterrupted suction from below the drainage support to effect liquid drainage commencing at a point adjacent the initial deposit of stock on such support and continuing until a strong high quality paper formation is produced. The invention also provides simple inexpensive apparatus for effecting support or holding of the drainage support (i.e. the Fourdrinicr wire) against sagging during such early formation stages without the disadvantageous use of table rolls. At

the same time the invention enhances positive removal of liquid from the bottom of such wire and eliminates entirely liquid throwback and consequent disruption of fibers in the paper formation such as caused by conventional table rolls.

In summary, the invention comprises ways and means for providing a light uninterrupted vacuum acting from below a Fourdrinier wire to maintain positive controlled liquid drainage from liquid pulp stock as it moves on such wire. To this end, the invention provides an apparatus in which a simple suction box structure is positioned below the Fourdrinier wire in sealed relationship therewith. Such suction box structure is substantially coextensive with the width of the wire at least as to the portion where stock is deposited and formed into paper. The suction box structure is also co-extensive with the wire along a substantial portion of its length commencing at the point where positive liquid drainage is to commence, which may be adjacent the point of initial deposit of stock on such wire or spaced therefrom as later explained; and such suction box structure extends under the wire to a point where a strong uniform paper formation has been produced.

After the desired paper formation has been produced by the light uninterrupted vacuum of the present invention, the web may be treated in the usual manner by subjecting it to high vacuum to insure final compaction into a substantially self sustaining web. However, since the bers will have been properly oriented and interlaced by the controlled early drainage of the present invention, no damage will be done by such high vacuum.

The invention also provides means to support the wire without the use of table rolls as it passes over ythe suction box structure and to simultaneously aid in liquid removal from the underside of such wire without liquid throwback. To this end the usual table rolls are omitted and a series of relatively narrow, spaced apart slats is provided in the suction box structure extending substantially transversely thereof. The upper edge surfaces of such slats are substantially on a plane with the under side of the Wire to provide a sliding nonsagging support therefor; such edge surfaces are substantially at and have relatively sharp edges to thus provide in elfect a doctor blade for positive removal of liquid by shearing it from the under side ofthe wire.

In this connection it is to be noted that one ofthe primary functions of the slats is to provide a shearing action to aid in liquid removal and also to support the wire against sagging; and it is important, as hereinafter discussed in more detail, that such slats bey relatively narrow to minimize 'any forming board effect which would interrupt free'drainage, and also to minimize friction on the screen.

In order to insure that substantially the entire area of the paper being'formed over the suction box structure is subjected to thelight vacuum, it is also important that the width of the slats be relatively small compared to the distance between slats. Thus, the total area of slats in contact with the wire is negligible as compared to the total area of wire to which vacuum is applied at any given time. The ratio of distance between slats to the vwidth of such slats should not be substantially less than about 3 to l and desirably above about 8 to 1.

In accordance with the invention, the suction box structure with its water removing wire support slats, is desirably constructed as a simple large box unit which may be detachably mounted on aniexisting Fourdrinier machine or constructed as a detachable or permanent acces- Vsory on new machines. However, as explained in greater detail later, the suction box structure can be composed of several smaller but still relatively large units, each having a plurality of water removing slats therein. Since only a low vacuum OA" to l2l water) is'applied by the suction box structure in accordance with this invention, a suflicient seal is provided merely by the end and' side .4 edges of the suction box structure in contact with the under surface of the wire and no complicated or expensive sealing mechanisms are required. Also, the low vacuum creates minimum drag on the wire passing over the slats.

In accordance with an important feature of the invention, only light vacuum in the order of from about Mr inch and not substantially in excess of l2 inches of water is employed for facilitating liquid drainage, and a desired range is from '1A inch to 3 inches of water. Utilization of at least 1//4 inch of water vacuum is important to insure a controlled positive liquid drainage as opposed to the heretofore employed gravity drainage which is uncontrolled and haphazard.

As to the maximum vacuum to be employed, it is important that liquid drainage not occur too rapidly because the fibers might then form a unidirectional mat of low strength. In other words, the vacuum should be high enough to insure positive controlled drainage but low enough to permit random orientation and interlacing of the bers during drainage of the liquid. Thus, the maximum vacuum to be applied under normal circumstances in accordance with this invention is not substantially in excess of about 12 inches of water as opposed to 'a vacuum of 75 to 90 inches of water heretofore proposed for solving the same problems.

Although vacuums of the magnitude of l2 inches of water Amay be employed, a lower vacuum not exceeding about 3 inches of Water `is desirable for forming paper from liquid pulp stocks of relatively low consistency and freeness. Such a range permits the efficient employment of paper pulp stocks having a consistency as low as 0.3% stock by weight as compared to conventional Fourdrinier paper making machines currently in use which cannot efficiently utilize stocks of a consistency lower than about 0.5% stock by weight. As abovernoted,a further advantage of the present invention isthat the mild vacuum emplyed rendersit unnecessary to employ complicated sealing mechanisms such as seals above the deckle straps or bars.

It is also to be understood that a vacuum slightly above l2 inches of water may be employed under certain conditions provided the liquid pulp stock being used will drain at such increased vacuum at a rate adapted to permit interlacing of the fibers for formation of a strong uniform web. In this connection, however, it is to be noted that the vacuum applied should not be so great that increased wear of the wire occurs otherwise any savings elfeeted by the more-rapid drainage will be lost due to the expense of extra `shutdowns for maintenance and repair.

It isimportant that the vacuum, once appliedybe continued substantially uninterruptedly until formation of thepaper mat is complete. This is so because interruptions in vacuum mayeifect disruption of the fibers with consequent reduction in quality of the nished paper. In this connection it is to be noted that several directly adjacent independently controllable lowvacuum suction box structures may be utilized in a ysingle machine. Such an arrangement may be set up so that the lvacuum successively increases in each structure to thereby increase the overall drainage rate. However, care should be taken that the vacuum applied during the early stages is carefully controlled within the above described limits to insure proper interlacing of the fibers and the formation of paper of uniform quality.

The use of a plurality of suction box structures will also provide greater flexibility of operation in that if an initial period 'of gravity drainage is desired for a particular stock, it may be provided simply by operating the first box at atmospheric pressure. Also, `in such an arrangement, the duration of vacuum applicationmay be regulated'without changingv the speed of the drainage screen by discontinuing vacuum in one or more adjacent suction boxf structures at either end of the maf chine. However, in all such arrangements it is important that the vacuum be applied in adjacent structures so that vacuu-m, once applied, vis continued uninterruptedly until the paper is suciently strong to withstand disruption upon cessation of vacuum.

Due to the low vacuum employed by the present invention which makes sealing a minor problem, the suction .box structure may be relatively large as compared with the usual high vacuum suction boxes at the dry end of the machine. In` this connection, it is important that the low vacuum suction box'structure extend for a substantial portion ofthe Fourdrinierwire in order to insure a high strength paper formation. Desirably, such suction box structure extends from adjacent the slice substantially to the usual high vacuum suction boxes at the dry end of the wire as that insures highest quality paper formation.,

However, marked improvement in paper quality is obtained whenthe low vacuum suction box structure is mounted under onlyfa portion of the wire between the slice and the high vacuum boxes; and if such an arrangement is employed the low vacuum suction box structure should not be substantially less than about onetfth the length of the upper reach of the wire. For example in a Fourdrinier machine with a wire having an upper reach 221/2 feet in length between the slice and the couch roll,.an elongatedlow vacuum suction box 4 feet long was mounted under the wire 8 feet from the slice where pulp was initially deposited on the wire. Such box was adjacent the rst conventional high vacuum box and applied a low vacuum of about 3 inches of water. Such an arrangement has provided marked improvement in paper quality.

' It will be noted that in accordance with the present invention, a suction box structure of a size to cover only a portion of the wire will still be considerably relatively larger than any of the high vacuum suction boxes which, because of high drag and diiculty of maintaining a proper seal, m-ust be kept` relatively small.

In accordance with the invention, positioning of the suction box under the wire can be varied` to accommo date varying conditions of operation and different types of stock. For instance, the suction box may be positioned immediately adjacent and under the point on which the stock is initially deposited on the wet end of the Fourdrinier wire so that positive controlled drainage commences immediately. However, when making high basis weight paper or when using a highly hydrated stock, a short gravity drainage space between the slice, where the stock is initially deposited on-the wire, and the leading edge of the low vacuum suction box structure may be provided in which a slight amount of gravity drainage will take place. If such a drainage space is employed care should be taken that it not be too long for the stock being used lest undesirable non-uniform paper formation occur before the wire passes into the positive control area over the suction box structure.

In some cases, such as when using abstock of high freeness value or when low basis weight paper is being made, it may be desirable to provide a forming board immediately ahead of the leading edge. of the suction box so that stock deposited on the wire above the forming board will not drain immediately but will be maintained in a more or less quiescent state for a short period as it passes over the forming board. Such quiescent state gives the fibers an opportunity to settle and interlace in a desirable manner before any suction is applied or any drainage occurs.

' A forming board as referred to herein is simply a solid or imperforate flat member, such as a board, positioned under the Fourdrinier wire. T11-us, liquid drainage from the stock is inhibited while the wire passes over the board and the fibers are maintained in suspension to permit orientation in a desired manner prior toinitiation of drainage.

Although the arrangement of the invention enables the handling of stockof relatively low freeness and consistency with marked improvement in the strength and quality of paper formed, it is to beunderstood that the invention may also be used to improve strength and quality of paper made from stock of any consistency and freeness as employed with commercial Fourdrinier machines..

It is also understood that various changes can be made by one skilled in the art in the arrangement, form and construction of the apparatus disclosed herein and in the several steps of the method also disclosed herein without departing from the spirit or scope of the present invention.

In the drawings:

Fig. l is a fragmentary schematic side elevational view of a conventional Fourdrinier paper making machine, portions being shown in section to illustrate an embodiment of the improved liquid drainage system of the present invention as an attachment to the machine.

Fig. 2 is a schematic longitudinal vertical sectional view, partly in elevation, illustrating a modicaton of the invention in which the suction box structure comprises three independent adjacent boxes.

Fig..3 is a schematic longitudinal vertical sectional view, partly in elevation, showing a modilication of the invention in which a suction box structure is mounted underonly a portion of the wire.

v Fig. 4 is a sectional View taken in a plane of line 4-4 of Fig. l.

Fig. 5 is a cross `sectional view of a typical slat for use in the invention.

Fig. 6 is a cross sectional view of another type of slat useful in the invention.

Fig. 7 is a cross sectional view of still another Slat construction for use in the invention.

The present -invention has particular application as an kattachment to existing paper making machines of the well known Fourdrinier type which includes generally a stock head box at the wet end, :the usual high vacuum suction boxes at the dry end, and the paper forming wire positioned between the two ends and -in normally continuous motion from the wet end to the dry end. It is to be understood, however, that the principle of the invention can be incorporated in the initial manufacture of such Fourdrinier type machines as a detachable or permanent accessory rather than being employed solely as an attachment to existing machines.

Referring to Fig. l, liquid pulp stock flows from a conventional stock head box 10 at the wet or infeed end of the machine onto a foraminous drainage support 11, namely, the Fourdrinier wire; the rate of stock ilow from the head box is controlled in conventional fashion by the usual adjustable gate, not shown -in the drawing, but normally positioned at the outlet 12 of the head box. The wire 11 comprises the usual endless wire mesh `vconveyor which Iis mounted for continuousmovement at a uniform rate by conventional drive means (not shown) over a breast roll 13 at .the wet or infeed end of the machine and a couch roll 14 at the dry end or discharge of rthe machine at which point the paper web 16 is removed from the machine land handled in the customary manner by the usual pressing, drying andY calender rolls (not shown) Although not shown in the drawing, -a so-called wire: pit, which is simply an open liquid collecting sumpis positioned below the entire conveyor assembly ex tending from the wet end to the dry end of the wire.. In conventional practice, liquid from such a sump is continuously mixed with fresh measured amounts ofi pulp and recirculated to the head box 10 in a manner'4 well known.

As can be seen from Figs. 1 and 2, a so-called save-- all or drainage tray 17 is xedly supportedon theframe' machine bypmeans including upright frame members 18 and transversely extending frame members 19. The save-all tank is thus supported below the upper reach of the wire 11 in spacedrelation thereto and extends from the Wet end adjacent the head box along the upper reach of the wire 11 in spaced relation thereto to its dry or discharge end.

Conventional deckle straps are provided and are mounted in the usual manner adjacent opposite side edges of the wire 11`to provide longitudinally extendingv guide members to conne paper pulp stock deposited therebetween on the wire. Such deckle straps 20 pass over Wheels-21 adjacent the wet end of the machine and over wheels 22 adjacent the dry end of the machine, both straps being driven in a conventional manner (not shown) in correlation with the speed of movement` of the wire. Thus, Vthe straps are in contact with the top surface` ofthe upper reach of the wire 11 from a point adjacent the headV box 10 -at the wet end of the Wire to a point `adjacent the dry end of the wire. Wheels 211V are mounted on a usual shaft 23 suitably journalled -in-bracket members 23', while wheels 22 Iat the dry end of thel machine are mounted on a suit-` able shaft 25 journalled in bracket members 25'; all of which is conventional.

Inplace of the moving deckle straps illustrated, conventional fixed deckle boards may be employed. How-V ever, the use of rubber orV other resilient deckle straps is desirable as that enhances the seal between the suction box structure 26 and the underside of the Wire at the sidesthereof. Inthis connection, it will be noted that sealing at the ends 27 of the suction box structure 26 is provided solely by the top edges 28 thereof in contact with the underside of the wire. This is an adequate seal at the ends becausethe paper stock is continuous and so extends past both ends 27 of the suction box structure 26.

Adjacent the dry end of wire 11 a plurality of conventional high vacuum suction boxes 29 is provided over which the upper reach of -the wire travels in the final stages of formation of the paper web. As is hereinafterV more fully explained, such suction boxes apply a relatively high vacuumvto finally compact the stock so that it becomes a substantially completely formed self-sustaining paper sheet by the time it is removed from the dry end of the Wire. As is usual, the high vacuum suction boxes 29 may be spaced apart either as single boxes as shown or as `groups of small boxes. As shown in Fig. 3, conventional freely journalled wire supporting table rolls 30 may be provided to support the screen 11 as it passes over the portion of the machine adjacent the high vacuum suction boxes 29.

As is well known `in the `type of machine under discussion, the wire 11 is usually vibrated laterally as it passes from the wet to the dry end of the paper `forming section. For this purpose, the wire and light vacuum suction box structure are vibrated by means of conventional table or shaker rails 31 which are vibrated in a known manner.

The elements of the apparatus thus far described are conventional in commercial yFourdrinier type paper making machines. For purposes of clarity, their specic details of construction are not illustrated or described in detail.

As hereinbefore noted, in the conventional commercial operation of Fourdrinier machines,rliquid drainage between Ythe wet end of the Wire up to the high vacuum suction boxes 29 has been by free or gravity drainage. Prior efforts to apply desirable positive suction to the stock on the wire to obtain the advantageous results of the present invention have not been satisfactory because ofthe several reasons heretofore mentioned, such as the cost of construction and maintenance of high vacuum means, added wearon the wire, and other parts and reduced .Y paper quality.

The preferred apparatus of the present invention for eifecting positive controlled drainage under the wire ahead' ofthe high vacuum suction boxes 29 comprises a separate suctionl box structure 26 positioned under the wire 11 and coextensive of'its length between the wet end of the machine and the, point at which the deckle straps areV removed from contact with the wire adjacent the dry endV of the machine. Suction box 26 is provided'with ends 27 andside members 32 which are coextensive with each other as to height and over the edges of which the wire 11 passes, therebyrforming a seal and defining the area in which light vacuum is applied by such suction box stnucture 26. In this connection, it will be noted that the side members 32 of such suction box structure are positioned under. and are parallel to the deckle straps 20 to cooperate with such straps to enhance sealing at the sides of the suction box.

.It will be noted that suction box 26 is positioned between the wire 11 .and the save-all tank 17 so that liquid draining into such suctionlbox can be gravity discharged into the subjacent save-all tank 17. Such liquid discharge is accomplished by means of a downcomer 33 which leads from the bottom ofsuction box 26 into save-all tank 17. In order to maintain vacuum in the suction box, the downcomer 33' terminates inthe save-all tank 17 at a point adjacent the bottom of such tankV and below the normal liquid level therein, to thus maintain a seal and prevent atmospheriopressure in the save-all tank from entering suction box 26 to .upset conditions therein.

Theforegoing methodv of discharging liquid from the low vacuum suction box through the downcomer 33 into thelower save-all tank 17,' or optionally into the customary wire pit`(not shown), provides an important additional advantage in that the downwardly flowing liquid acts as a Siphon p umpand so maintains .a slight vacuum at all times in the low vacuum suction box 26. Under normal conditions, the foregoing drainage system alone may provide vacuum `up to 3 inches of water and this may be suicient to maintain the desired vacuum on the underside ofthe wire..11 for effecting positive liquid' drainage therethrough. In an installation where the suction box 26extends under a substantial portion of the wire 11,V i.e. from adjacent the slice to the rst high vacuum suction box 29, the save-all tank 17 may be entirely omittedfrorn the assembly, and downcomer 33 extended around the lower reach of wire 11 `into the wire pit, the lowermost end of.downcomer 33 being submerged in the wire pit water.

However, due to variations in operating conditions and in the ilowability of the liquid pulp stock, there may be occasions when vacuum higher than 3 of water is desired.' To accomplishy this,.the downcomer 33 may be extended downwardly to Aa water seal pit (not shown) located below the usual wire pit water level, or, a supplemental vacuum pump `34, driven by a suitable motor 3S in conventionatmanner maybe provided. The vacuum pump 34 is connected to suction box 26 by means of a standard valved conduit 36 which has a flexible section 37 to absorb vibration. A bleed valve 38 is provided in a conduit 39 leading from suction box 26 for use in relieving excessive vacuum in the suction box should that be desired for any reason or should it be required to maintain a desirably low uniform vacuum therein.

The vacuum existing in suction box 26 is read by means of a conventional manometer -41 mounted on the side ofsuchbox and in communication with the interior thereof. If desired, manometer 41, bleed valve 38, and vacuum pump34 may be incorporated into an automatic control systemV (not shown) in a conventional manner so that a uniform vacuum, controlled to lie within a. close range, may be automatically maintained in such suction box.

To insurel a sufficient liquid level in the save-all tank. 17 to maintain a seal at the dischargeeud of downcomer 33, an overflow discharge pipe 42 is provided which leads from an outlet point 43 in the save-all tank 17 abovethe bottom thereof at an elevation above the discharge end of downcomer 33. Thus, outlet 43 from the save-all tank acts as an overflow weir and maintains a liquid level in the tank above the discharge end of the downcomer 33 from which liquid ows from suction box 26 into save-all tank 17.

As hereinbefore pointed out, the usual prior Fourdrinier machine is equipped with a series of table rolls over which the wire 11 passes as it progresses from the Wet to the dry end of the machine and, as previously noted, such table rolls result in the throwback of liquid against the underside of the wire, thereby disrupting formation of libers on the Wire and impair the quality and strength of the paper. The present invention overcomes this prior disadvantage by eliminating the table rolls and providing instead a series of relatively narrow slats 44 located substantially transversely of the suction box structure 26 and having their tops on a plane with the nlpper surface edges of ends 27 and sides 32 of the suction box. Such slats have sharp leading edges 45 and are desirably perpendicular to the line of travel of the wire, but may be in any other transverse position, such as oblique to the line of travel, as long as they are not longitudinal to the line of travel.

In the embodiment illustrated, suction box 26 is maintained level and at proper elevation for sealing relationship with the screen 11 by means of a bracket 47 and leveling screw 48 by which it is connected to the table or shaker rail 31 which, as above noted, vibrates the wire and suction box structure. Although not described in detail, it is to be understood that the construction and mounting of the various elements of the Fourdrinier machine under discussion may be in accordance with general current practice in common use on such machines, and that driving of the various moving parts of such machines may be accomplished in conventional fashion.

In the particular modification of the Fourdrinier machine illustrated in the drawings, the suction box 26 is not positioned directly adjacent outlet or slice 12 of head box 10, but is spaced a short distance toward the dry end of the machine. A forming board 49 is positioned under the head box and extends to the edge of the suction box 26, thereby providing an area in which drainage through the wire 11 is inhibited, thus providing a shortperiod of quiescence during which iibers of the stock have an opportunity to orient themselves prior to application of low vacuum by the suction box.

As hereinbefore noted, the invention may be utilized as an attachment on aFourdrinier machine and to that end may be employed as shown in the drawings. If desired, the forming board 49 may be eliminated and the suction box positioned directly beneath the head box. Another alternative is to remove the forming board, leave the suction box in position as shown in the drawing, and permit free drainage through the wire forl a short period prior lto the application of vacuum.

`In the embodiment illustrated in Fig. l, a single suction box 26 is employed in which a uniform vacuum is maintained for substantially the entire length of the wire between theslice and high vacuum suction boxes. However, if a plurality `of suction boxes 26 is desired in whichgradually increasing low vacuums are applied, then such boxes would be arranged as adjacent boxes with substantially no spaces therebetween. Such an arrangement is schematically illustrated in Fig. 2 which shows three low vacuum suction box structures v26 mounted adjacent each other under a single Fourdrinier wire 11.

vEach of suchV structures is similar to the one shown in'Fignl and drains into a save-all tank 17 which maintains a seal. To provide for independently varying vacuum inthe suction boxes, .eachmay be connected to its own separate vacuum pump, not shown, but which is similar to that shown in Fig. 1, by conduit 36; and is provided with its own bleed valve 38 and manometer 41. Mounting and operation of the suction box structures of Fig. 2 may be the same as described for Fig. l. In the modification shown in Fig. 2, it is important that there be no substantial space between suction boxes because of the fact that the low vacuum once applied Vshould be continued uninterruptedly until a mat is formed in order to prevent undesirable disruption of fiber formation by interruptions in vacuum during drainage through the wire.

Fig. 3 illustrates schematically a modification simi-lar to the structure shown in Fig. 1, except that the elongated suction box structure 26 extends for only a portion, about one third, of the length of the upper reach of the wire. In the structure shown in Fig. 3, conventional rotatable table rolls 30 are employed between the low vacuum suction box structure 26 and the usual high vacuum suction boxes to support the wire after it passes beyond the low vacuum suction box structure, but since the paper has been formed and drainage is substantially complete, no undesirable liquid throwback will occur. However, as in the structures of Figs. l and 2, slats 44 are mounted within the suction box structure 26 to support the wire while effecting positive liquid removal; and no table rolls are employed within such suction box structure itself.

As shown in Figs. 5, 6 and 7, the upper surfaces 52 of the narrow slats 44 used for liquid removal and wire support are flat and have sharp leading edges 45. Consequently, they act as doctor blades to skim or shear liquid from the underside of the wire 11 as it moves across the slats. This is impor-tant because it aids in liquid drainage by positively removing liquid from the underside of the screen and at the same time eliminates liquid throwback.

As best shown in Fig. 4, the slats are supported within suction box 26 by a longitudinally extending center support 53 positioned in the lower portion of the suctionv box. Obviously, other means of supporting the slats may be provided if desired.

Figs. 5, 6 and 7 illustrate various forms of slats that may be employed in the present invention. Fig. 5 shows, in section, a slat 44 comprising a simple vertical memberV having a iiat upper surface 52 and sharp leading edge 45 to elect shearing of liquid from the underside of a wire 11 passing thereacross.

Fig. 6 illustrates a modified slat construction in which the Slat 44 is vertical as in Fig. 5, has a flat upper surface 52 and sharp leading edge 45. The upper end of the slat has a recess 54 at its trailing edge 56 which facilitates drainage as the wire passes trailing edge 56.

Fig. 7 illustrates a slat 44 adapted to be mounted obliquely from top to bottom. Such slat 44 has a flat upper wire engaging surface 52, and a sharp leading edge 45. formed by upper surface 52 and front side 57 which join to include an acute angle, presents a relatively sharper edge for shearing liquid. To insure against liquid pile up adjacent the trailing edge 56 of the slat, the angle between the trailing side 58 of the slat and wire 11 should not be less than about 30, and desirably not less than about 45. To insure positive liquid removal by shearing, the front or leading side 57 and upper surface 52 should have an included angle at leading edge 45 not substantially greater than 90.

Y Fourdrinier machines are available in a variety of sizes and for a variety of particular purposes and so may be relatively short, such as the one illustrated, or may be extremely long and employ several high vacuum suction boxes 27 adjacent the dry end of the machine. The machine shown in Fig. l is broken adjacent the dry end to indicate that such an extension may be employed, in conventional manner. lObviously the section.

lt will be noted that the leading edge 45,

1.1 of themachine adjacent the wet end thereof may be` similarly extended.

The slats used for water removal and support members should not be so wide at their wire engaging upper surfaces 52 as to interfere with the application of vacuum. The slats may vary in width from about 1/8 to 2", but preferably are in the range from 1A to l to thereby provide sufficient support for the wire and at the same time not interfere with the application of vacuum or contribute a forming board effect of quiescent settling. In this connection, it should be noted that a slight vacuum may be created by a surface tension effect from the action offthe at surfaces of the slats as the wire passes thereacross.V This is desirable and will not interfere with operation of the apparatus.

As to spacing between slats, it should be sufficient to maintain the wire substantially level as it passes across the vacuum structure. Such spacing will be determined by the tension and weight of the wire 11 as well as the weight of the stock being deposited thereon, and also by the vacuum applied by the suction box 26. In general, a space between slats of from 3 to 12 is to be preferred, although distances up to 48 may be employed'when making extremely light weight paper.

The slats are most advantageously constructed of wood because of its inexpensiveness of construction. Also, because wood is much softer than the wire, which is usually a Phosphor bronze material, wear of the more expensive Wire is minimized. Y

It is to be understood that the dimensions of a Fourdrinier machine can and will vary Widely in accordance with the use to which it is put; and that the dimensions of the low vacuum suction box structure of the present invention can be varied to accommodate conditions of the machine with which it is associated.

Example l As a typical example, a low vacuum suction box strncture of the invention has been incorporated into a Fourdrinier machine having a length of 2l feet on the upper reach of the wire and a width of wire substantially 6% feet between deckle straps. In such installation, a single suction box 6% feet wide and 4 feet long was employed. Transverse slats in such suction box of the general type illustrated in Fig. 5, were 1A inch wide at the top and spaced apart a distance of 3 inches. The leading edge of the box was spaced from the slice a distance of 2% feet and a forming board was mounted in such space under .the wire. A series of conventional table rolls was mounted under the wire between the trailing edge of the low vacuum suction box and the usual high vacuum boxes.

The above apparatus was employed to form Mulch paper having a basis weight of 21.3 lbs. 1000 square feet. Feed stock used was one having a consistency of 0.5% and a freeness of 317 (Canadian Standard). The wire was operated at a linear speed of 261 feet per minute and a vacuum of 3 inches of water was applied through the low vacuum suction box. The completed paper was found to have an increased Mullen bursting strength of 85 as compared to Mulch paper made from the same stock on the same machine without the low vacuum suction box structure which only had a Mullen bursting strength of 73. Thus, even when used to apply light vacuum for only a portion of the wire, paper strength is materially enhanced.

Example Il.

In another installation on a Fourdrinier machine having a 7 foot width and a length of 22.5 feet on the upper reach of the wire, an elongated suction box structure v3 feet 11 inches long and 7 feet wide was employed. Transverse slats in the box of the type illustrated in Fig. were 3%: inch wide at the top and spaced apart 2% inches. The leading edge of the box was spaced 8 feet from the sliceto permit some gravity drainage prior to applica- 12 tion of low vacuum. Conventional table rolls were used to support the wire outside of the vacuum box structure.

On the above machine, corrugating paperboard having a basis weight of 36 lbs./ 1000 square feet was formed from stock having a consistency of 0.45%. Wire speed was 205 feet per minute and a vacuum of 4 inches of Water was applied by the low vacuum suction box struc` ture. The resulting paperboard was of high quality. To form comparable paperboard from the same stock on the same machine without the low vacuum suction box, it was necessary to increase the stock consistency to 0.6%, which contributed to decreased paper quality. Thus, the apparatus of the present invention enables the use of lower consistency stock which, as hereinbefore noted, produces paper of more uniform quality and strength.

l claim:

1. In a Fourdrinier paper makingV machine having a breast roll, a couch roll spaced from said breast roll, an endless conveyor foraminous drainage support about said rolls, and means adjacent said breast roll for feeding pulp stock onto the upper reach of the support; apparatus for enhancing formation of paper on said support comprising an elongated non-rotatable suction box structure located between said rolls and having side and end walls the upper edges of which lie in substantially the same horizontal plane and engage the underside of said upper reach, said suction box structure occupying not substantially less than about one-fifth the length of said upper reach, means for applying a relatively light suction to said box to effect removal of liquid from said pulp on said support, and means cooperable with said suction means to enhance said liquid removal without effecting throwback of liquid on said support, said means including a plurality of relatively narrow spaced apart slats in said box, said slats extending transversely with respect to said support and upon which said upper reach rides, the upper edges of said slats being in contact with the underside of said upper reach and the spacing between said slats being such that the 4total area occupied by all of the upper edges of said slats is relatively small compared to the total area Linder said upper reach occupied by said box structure whereby substantially uninterrupted relatively light suction is maintained on said stock as it passes over said box structure.

2. In a Fourdrinier paper making machine having a breast roll, a couch roll spaced from said breast roll, an endless conveyor foraminous drainage support about said rolls, and means for feeding pulp stock onto the upper reach of the support; apparatus for enhancing formation of paper on said support comprising an elongated non-rotatable suction box structure located between said rolls and having side and end walls the upper edges of which lie in substantially the same horizontal plane and engage the underside of said upper reach, said suction box structure occupying not substantially less than about one-fifth the length of said upper reach, means for applying a relatively light suction to said box to effect removal of liquid from said pulp on said support, and means cooperable with said suction means Vto enhance said liquid removal without effecting throwback of liquid on said support, said means including a plurality of relatively narrow spaced apart slats in said box extending transversely with respect to said support and upon which said upper reach rides, the upperV edges ofV said slats being in cont-act with the underside of said upper reach and said slats having a substantially negligible total area in contact with said support with respect to the total area of application of said light vacuum whereby substantially uninterrupted relatively light suction is maintained on said stock as it passes over said box structure.

3. In a Fourdrinier paper making machine having a breast roll, a couch roll spaced from said breast roll, an endless conveyor foraminous drainage support about said rolls, and means for feeding pulp stock onto the upperreach of the support; apparatus for enhancing fop mation of paper on said support comprising an elongated non-rotatable suction box structure located between said rolls and having side and end walls the upper edges of which lie in substantially the same horizontal plane and engage the underside of said upper reach, said suction box structure occupying not substantially less than about Aone-fifth the length of said upper reach, means for applying Aa relatively light suction to said box toelfect removal of liquid from said pulp on said support, and means cooperable with said suction means to enhance said liquid removal without effecting throwback of liquid n said support, said means including a plurality of relatively narrow spaced apart slats in said box extending transversely with respect to said support and upon which compared to the total area under said upper reach occupied by said box structure whereby substantially un-A interrupted relatively light suction is maintained on said stock as'it passes over said box structure; y

4. In a Fourdrinier paper making machine having a breast roll, a couch' "roll spaced from said breast roll, an endless conveyor foraminous drainage support about said rolls and means for feeding pulp stock onto the upper reach of the support; Vapparatus for enhancing formation of paper on said support comprising an elongated non-rotatable suction box located between said rolls and having side and end-walls the upper edges of which lie insubstantiallyA the same horizontal plane and engage the underside of said upper reach, said suction box occupying not substantially less than about one-fifth the length of said upper reach, means for applying a relatively light suction to said box to effect removal of liquid from said pulp on said support, means cooperable with said suction means to enhance said liquid removal without effecting throwback of liquid on said support, said means including a plurality of relatively narrow spaced apart slats in said box extending transversely with respect to said support and upon which said upper reach rides, the upper edges of said slats being in contact with the underside of said upper reach, said slats having a substantially negligible total area relative to the total area of application of said light vacuum, to provide sub stantially uninterrupted relatively light suction on said stock as it passes over said box structure, and said box being supported by means providing for vibration of both said support and said box.

5. In a Fourdrinier paper making machine having a breast roll adjacent its wet end, a couch roll spaced from said breast roll adjacent the dry end of the machine, and an endless conveyor foraminous drainage support mounted for movement between its wet end and its dry end, longitudinally extending stock retaining guide members mounted on said machine adjacent the sides of said foraminous support and in contact with the upper surface of said support, means for depositing liquid pulp stock on said support between said guide members adjacent said wet end to effect liquid drainage from said stock to yield a paper formation, and means adjacent said dry end to finally compact said paper formation into a substantially self-supporting paper web; means mounted on said machine under said support between said wet and dry ends for uninterruptedly applying a relatively light vacuum to said stock on said support to eifect relatively rapid positive liquid drainage from said stock prior to compaction of said formation, said means comprising an elongated non-rotatable suction box structure open at the top and having its opposite end edges substantially transverse to said foraminous suppornthe sides of said strucl ture being mounted directly under and substantially parallel to said longitudinally extending guide members to form a seal adjacent the side of said foraminous support, said structure occupying not substantially less than about one-fth the length of the upper reach of said foraminous support, means for creating a controlled light vacuum in said structure under said foraminous support to effect liquid drainage through said support into said structure, and means in said structure for holding said foraminous support against sagging as it passes over said structure and for effecting positive removal of liquid from below said support, said means comprising a series of relatively narrow spaced apart slats mounted transversely of said structure and in engagement with the underside of said foraminous support, the spacing between said slats being such that the total area occupied by -all of the upper edges of said slats is relatively small compared to the total area under said support occupied by said structure whereby substantially uninterrupted relatively light suction is maintained on said stock as it passes over said structure.

6. In a Fourdrinier paper making machine having a breast roll Vadjacent its infeed end, a couch roll-spaced from said breast roll adjacent the discharge end of the machine, and an endless conveyor foraminous drainage support mounted for movement between its infeed end and its discharge end, longitudinally extending stock retaining guide members mounted on said machine in contact with the upper surface of said fo-raminous support adjacent the sides thereof, means for depositing liquid pulp stock on said support between said guide members adjacent said infeed end to effect liquid drainage .from

f said stock to yield a paper formation, and vacuum means adjacent said discharge end `to apply a high vacuum to nally compact said paper formation into a substantially self-supporting paper web; means interposed between said infeed and discharge for holding said foraminous support against sagging while effecting uninterrupted positive liquid drainage from said stock through said foraminous support prior to compaction of said formation, said means comprising an elongated non-rotatable box open at the top and mounted under said foraminous support so as to occupy not substantially less than about one-fifth the length of the upper reach of said foraminous support, means for maintaining a relatively light vacuum in said box, the top edges of said box being in sealing contact with the underside of said foraminous support, a plurality of slats mounted in said box adjacent the top thereof, said slats being mounted transversely of said foraminous support and having sharp edges in contact with the underside of said foraminous support to thereby effect liquid removal by shearing action While holding said foraminous support against sagging as it passes over said box and the spacing between said slats being such that the total area occupied by all of the upper edges of said slats is relatively small compared to the total area under said upper reach occupied by said box structure whereby substantially uninterrupted relatively light suction is maintained on said stock as it passes over said box structure.

7. Apparatus according to claim 6 in which the means for maintaining a vacuum in said box comprises in combination with said box a lower container adapted to maintain a liquid level therein, and a conduit extending from the bottom of said box into said lower container to effect a vacuum in said box during liquid drainage therefrom into said lower container, said conduit terminating in submergence in said lower container to provide a seal between said box and said lower container.

8. In a Fourdrinier paper making machine having a breast roll adjacent its infeed end, a couch roll spaced from said breast roll adjacent the discharge end of the machine, and an endless conveyor drainage wire mounted for movement between its infeed end and its discharge end, stock retaining guide members on said machine mounted in contact with the vupper surface of said wire adjacent its opposite sides, means for depositing liquid pulp stock on said wire between said guide members ad; jacent said infeed end to effect liquid drainage from said stock to yield a paper formation, and high lvacuum means adjacent said discharge end `to nally compact said paper formation into a substantially self-supporting paper web; means interposed between said infeed and discharge for uninterruptedly applying a relatively light vacuum to said stock between said guide members on said wire to effect relatively rapid positive liquid drainage from said stock prior to compaction of said formation by said high vacnum, said means comprising an elongated non-rotatable suction box structure mounted on said machine below said wire with its upper side and end edges in contact with the underside of said wire to provide a seal when stock is on said wire, said box structure occupying not substantially less than about one-fth the length of the upper reach of said wire slats in said box mounted transversely of said wire and in Contact with the underside thereof to hold said wire against sagging, said slats having relatively sharp edges to shear liquid from said Wire, the spacing between said slats being such that the total area occupied by all of the upper edges of said slats is relatively small compared to the total area under said wire occupied by said box, and means to maintain a `vacuum in said box in the range from 1A to 12 of water.

9. The combination with a Fourdrinier paper making machine having a breast roll adjacent its wet end, a couch roll'spaced from said breast roll adjacent its dry end, an endless conveyor drainage wire about said rolls, means adjacent said breast roll for depositing liquid pulp stock onto the upper reach of said wire, and relatively high vacuum suction box means adjacent said couch roll; of apparatus for enhancing formation of paper on the upper reach of said wire comprising an elongated non-rotatable suction box structure underneath said upper reach and located between said breast roll and said high vacuum suction box means with one end of said box structure adjacent said breast roll, said box structure havingopposite side walls extending-longitudinally with'respeet to the upper reach of said Wire and opposite end walls extending transversely with respect to said upper reach, the upper edges of said side and end walls lying in substantially the same horizontal plane and being in engagement with and supporting the underside side of said wire, said box structure occupying not substantially less than about one-fifth the vlength of said upper reach,` avacuumpump connected tosaid box structure for applying a relativelylight suction to said boxA structure to eiectsuction removal of water from stock carried by saidupper reach over said box structure, and non-rotatable means cooperable withV said box structure to enhance said liquid removal without effecting throwback of liquid on said wire comprising a plurality of relativelynarrow widely spaced apart slats fixed in said box structure and extending transversely with respect to said upperl reach, the upper edges of said slatsvlying in substantially said horizontal plane in sup# porting engagement with the'underside of said wire, the spacing between said slats being-such that the-total area occupied by all of the upper'edges-of said slats .is relatively small compared to the total area undersaid wire occupied by said box structure vWhereby'substantially uninterrupted'relatively light suction istmaintained on said stock as it passes over-said box structure.

10. The combination of claim-9 in which the ratio of the minimum distance between said slats to the width of said slats is Vat the least about 3 to l.

11; The combination'of claim 9 in which the ratio of the distance between said slats to the width of said' slats is greater thanfabout 8 tol.

References Cited in the le of this patentk UNITED STATES PATENTS 1,742,991 Heys Jan. 7, 1930 1,826,735 Cofrin Oct. 13, 1931 1,832,844- Cofrin Nov. 24, 1931 1,917,098 Cofrin July 4, 1933 1,928,286 Germanson Sept. 26, 1933 2,118,491 Chuse May 24, 1938 2,170,109 Berry Aug. 22, 1939 2,345,647 Witham Apr. 4, 1944 2,608,913 Bratton Sept. 2, 1952 2,666,371V Bechler Jan. 19, 1954 2,672,078 Hornbostel Mar. 16, 1954 2,714,839- Mazer Aug. 9, 1955 FOREIGN PATENTSI 577,195 Germany May,29, 1933 399,739 Great Britain Oct. 12, 1933`

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