US 2991218 A
Description (OCR text may contain errors)
y 4, 1951 A. J. CIRRITO ET AL 2,991,218
PAPER MAKING Filed Jan. 51, 1958 3 She ets-Sheet 1 July 4, 1961 A. J. CIRRITO ETAL 2,991,218
PAPER MAKING Filed Jan. 51, 1958 3 Sheets-Sheet 2 July 4, 1961 A. .r.v ClRRl-TO ET AL ,9
- PAPER MAKING Filed Jan. 31, 1,958 3 Sheets-Sheet 3 United States Patent O Anthony J. Cirrito, Grafton, and Nicholas M. Reitzel,
Worcester, Mass., assignors to Rice Barton Corporation, Worcester, M-ass., a corporation of Massachusetts Filed Jan. 31, 1958, Ser. No. 712,483 Claims. (Cl. 162-217) This invention relates to paper making and is more particularly concerned with novel methods and apparatus for improved web formation on a forming wire trained about a moving underlying structure which is provided with capacity therein for storing the drained water. The invention includes the improved control of drainage of liquid through the forming wire, utilizing the liquid so drained in combination with the novel underlying structure accordingly to control the remnant drainage and finally to control the discharge from the underlying structure of all the liquid so drained. 7
When forming a paper web on a suction breast roll adjacent to a Fourdrinier slice, it has been the practice to locate the slice close to the apex of the roll so that the centerline of the slice jet is approximately parallel to the Fourdrinier wire at the apex of the roll. It has been considered necessary for this type of installation to depend exclusively on vacuum to prevent the residual drainage from prematurely discharging radially immediately adjacent to the apex and accordingly disrupting the formation of lightweight sheets on the wire by reason of this premature throw-out or splash. I
Heretofore it has also been considered impractical in high speed paper making, that is, at 1500 f.p.m. and higher, to dischargea slice jet onto the ascending surface of a cylinder at a point significantly below the apex, in a relatively open zone where the flow on the wire is exposed to the atmosphere.
In low speed operations where gravitational force predominates, it is also desirable in the initial drainage zone immediately after slice discharge to retard the drainage, allowing sufficient time for the fibres to lay down in the plane of the web rather than transversely through the web, which would otherwise take place if the drainage is sudden.
With the foregoing in mind an object of this invention is to provide a shell structure of particular design to permit successful operation in a machine wherein a jet can be discharged substantially below the apex on the ascending side of the cylinder to form a web such that when the Fourdrinier wire separates from the roll at the apex (or any other point below the apex where separation of wire and roll is desired), the residual water remains in the shell, either for radial outward discharge at a time or distance from the apex where it is free from the Fourdrinier wire and accordingly cannot disrupt the paper web formed thereon, or for discharge into a vacuum receiver within the shell. I
A further object of the invention is to provide a novel roll or equivalent structure in which the drainage rate and discharge of the drained liquid can be accurately controlled, permitting use of the roll itself wound with a suitable wire as a cylindrical former for the web without the need of the true Fourdrinier wire to lead off the web.
A still further object of the invention is to provide a novel roll structure of the type described for use either as a cylindrical former or as a suction breast roll of a Fourdrinier type paper machine wherein the forming fibre mat traveling with the roll shell between the slice opening and the discharge of the web may be selectively subjected to negative or positive or neutral air pressure not only for controlling the drainage rate, but also for pulsing the web as it is formed, thereby relaxing compactness of fibres permitting rapid drainage of paper stocks in a Patented July 4,
2 short drainage area which ordinarily would require inordinate lengths of Fourdrinier wire to complete the drainage. 7
A still further object of the invention, particularly at low speed where gravity predominates and it is generally necessary to retard initial drainage, is to provide a novel combination of roll structure, vacuum boxes, slice and an auxiliary water supply such that the rate of drainage of water from a web of stock through a wire entrained about the roll may be accurately controlled by the application of positive or neutral or negative air pressure to a layer of water deposited in the periphery of the roll in advance of the slice opening. p i
Yet another object of the invention is to provide a roll structure and vacuum box arrangement having a storage zone of limited volume on its periphery to permit similar control of the rate of drainage of dilute stocks distributed thereon without the need for the auxiliary Water supply.
To achieve these and other objects which will become apparent from the following discussion, it is necessary to incorporate a honeycomb shell structure of significant depth and having holes of special critical dimensions as hereinafter explained. The object of the honeycomb and the depth together with the limited dimensions is to provide an optimum surface which, through the phenomena of drag, would cooperate with gravity and suction to prevent premature outward discharge due to centrifugal force, accordingly stabilizing the jet and flow on the roll on its travel around the apex. At slow speeds this same structure would cooperate with positive fluid pressure to oppose gravity to retard initial drainage accordingly improving the formation of the fibre mat.
In the case of forming sheets where drainage is completed to, the point where the residual flow inside of the shell has separated completely from the formed sheet, to the point where air is pulled through the wet web by suction, the finite distance in the shell for the air-water boundary may be as much as /2" in a carefully designed structure. For the flow of travel back out this finite distance, it must be decelerated to zero by centrifugal force and accelerated outwardly against gravitational components and surface drag. This entire operation will take a finite time of sufiicient magnitude to retard throw-out for safe and trouble-free operation. The cycle from the deceleration of the flow to zero, etc., of course takes place immediately after the last suction box.
Another feature is to allow suflicient depth to the airresidual liquid boundary such that the volume between this boundary and the web is sufficient to receive enough air through the web to bring the web of slow stocks to conventional couch dryness, which is approximately 20% dry, while at the same time retaining all the liquid drained so that it may later be discharged outwardly or into an internal receiver or receivers of sufiicient size to handle all the flow. In the case of internal discharge, couch dryness may be achieved with freer sheets because the necessary air flow may pass through the holes in the conventional manner into the large suction receiver which also receives the large flow of white Water.
Another advantage of the honeycomb shell structure is that it insures the retention of the flow in the shell by suction against centrifugal force. It is common knowledge in the case of a gas or vapor boundary with a liquid, for example, in a glass tube, that the gas or 'vapor will not support the liquid against the force of gravity if the exposed area is large. When the area is critical in magnitude the tendency is for the liquid to flow down the wall and displace the gas so that finally the liquid would be at the bot tom of the tube and the gas or vapor on top, but the flow is slow and takes an appreciable time. Centrifuga'l'force would be expected to act in a manner similar to gravity in .control thereof is lost during the operation.
as used to describe the cross-sectional area of the holes of the, honeycomb shell structure is to be given a practical interpretation as denoting the maximum cross-sectional area thereof in which the liquid therein may be effectively held for the necessary time and distance .of travel for successful operation in accordance with the invention. Thus, under certain conditions of gravity or centrifugal force or both the critical cross-sectional area may be considered to be sufiiciently small, even though there is a tendency of liquid flow along the wall of the cavity, provided such flow does not result in a disruption of the liquid body so that For some conditions, the dimension must fall in the stable range,
,as where centrifugal force is high. As used'herein, therefore, the term cn'ticaPshall be deemed to refer to the maximum cross-sectional area which will produce effective stability for successful operation under the given conditions in which the machine is operating.
In view of the, great significance of the are-a of the liquid-gas interface, a diameter of W to and lower may be taken for the drilled holes immediately adjacent to the covering wire on the shell. Where optimum and complete retention is required over a large arc, the smaller area, more stable, shosuld be used. For example, if the arc begins with slice discharge approximately tangent to the shell surface at a point-approximately 20 above the horizontal centerline in the ascending quadrant, owing to the high retention possible with the smaller size holes (approximately A diameter), the arc drainage length may be considered as long as 200 from this point of beginning, thereby ending in the -lower quadrant on the descending side below the centerline where gravity and centrifugal force would act together,- counterbalanced only by drag approximating diameter holes where the liquid has the characteristics of ordinary tap water at room temperatures, andthis holds true over a reasonable range of temand air pressure. However, many applications are ade- .quately handled with cavities having cross-sectional areas peratures. Smaller diameters may be required if temperature is raised substantially or if the liquid includes wetting agents or the like.
Still further objects, features and advantages of the invention will become apparent from the following detailed description of presently preferred embodiments thereof, taken in conjunction with the accompanying drawings, in which like numerals refer to like parts in the several views, and in which:
FIG. 1 is a view in vertical cross-section of a portion of a web-forming machine having a drilled honeycomb shell and other features of the invention, the representation of some of the elements being exaggerated as to scale for the sake of clarity of description;
FIG. 2 is a plan view of a fragment of the surface of the perforated shell shown in FIG. 1; FIG. 3 is a fragmentary view similar to FIG. 1, showing a different mode of operation of the embodiment of FIG. 1;
FIG. 4 is a view similar to FIG. 1 of another form of machine employing the invention;
FIG. 5 is a view of the discharge portion of a machine in accordance with FIG. 4, illustrating a difiEerent mode of operation;
FIG. 6 is a fragmentary view in cross-section of an alternative form of perforated shell useful in practicing the invention;
FIG. ,7 is a view on an enlarged scale of the form of 4 the counterbored holes which may be employed in the perforated roll of FIGS. 1 through 6;
FIGS. 8 and 8a are diagrammatic representations showing the theory of operation by which the drainage of liquid in the shell periphery is controlled by differential of air pressure;
FIG. 9 is a view on a reduced scale similar to FIGS. 1 and 4, showing the invention as applied in the minimum degree to a Fourdrinier type machine;
FIG. 10 is a view similar to FIG. 1, illustrating the invention utilizing a modified shell structure and employing an auxiliary water supply beneath the stream discharged from the slice;
FIG. 11 is a cross-sectional view taken on line 11--11 of FIG. 10;
FIG. 12 is a view similar to FIG. 10, showing a still further modification of. the shell structure as shown in FIG. 10;
FIG. 13 is a cross-sectional view taken on line 13--13 of FIG. 12;
FIG. 14 is a substitute crosssection to FIG. 13 showing shallow large diameter counterbored cavities; and
FIG. 15 is a somewhat diagrammatic representation of a flexible belt type suction former employing the same principles and drainage cavities shown on FIGS. 1 through 9. I
The invention will first be described, and its principles explained in connection with the illustration of FIGS. 1*3.
Owing to the great difference in dimensions between the size of the drilled holes in the order of and the arcuate span of each suction box which may vary from 2 to 6" and higher, this relationship is drawn out of scale to point up other important relationships in the invention. For convenience conventional sealing strips between the suction box walls and roll shell are also not shown.
i A roll comprising a cylindrical metallic shell 20 in this embodiment is used as a cylindrical former for a web of paper. The shell is mounted for-rotation in the usual manner and, in accordance with the invention, may be used for very high speed paper formation if desired, say 1500 f.p.m. or higher. A slice 22 discharges a high velocity jet of dilute paper stock 24 onto the surface of a wire 26, trained about the periphery of the shell 20.
The wire 26 may be a Fourdrinier wire led 01f in the usual manner (as illustrated in FIG. 9), or it may be a forming wire wrapped tightly about the roll 20. Frequently a course mesh backing wire 59 is interposed between the roll 20 as shown on FIG. 10 and drainage wire .26 and wrapped tightly about roll 20. The shell is drilled and counterbored so that the outboard portions 28 of the holes are of greater diameter than the inboard portions 30. The dimensions of the portions 28 and 30 both as to cross-sectional area and depth, are calculated in accordance with the theoretical discussion hereinafter contained as is the total open area to be used in a particular installation.
Within the shell 20 and opening against the inner surface thereof is a series of suction boxes 32 having walls '33. The'individual boxes are connected by pipes 34 led out through a trunnion or an open end of the shell to independently controllable sources of fluid pressure (not shown), such that the pressure difierential between the interior and exterior surfaces of the shell which passes over successive boxes may 'be accurately controlled to positive, neutral or negative pressures. The partitions 33 have sealing strips 35 (not shown in detail) which bear against the inner surface of the shell in the conventional manner. It will be understood that the dimensions and proportions of the various parts shown in the drawings arenot intended to be to scale but have been chosen for convenience in explaining the principle and mode of operation of the invention. Those skilled in this art, utilizing the teachings of the theoretical discussion to follow, will have no difiiculty in selecting the dimensions including the relative dimensions, of the components for accomplishing the desired results for any particular installation. Thus the boxes 32'have been shown more or less schematically. They should have substantially greatervolu-me than the counterbored holes 28-30 with "which they communicate at any given instant. The boxes 32 and corresponding pipes 34 at the discharge zone 29should, if all the water is to be drained inwardly, be substantially larger than the other boxes; but this is not necessary if the water is to be thrown outwardly, as shown in FIG. 1. Enlarged receiver boxes of this type are shown in FIG. 5 and are designated by the numeral 32a.
The paper stock 24 fiows onto the surface of the wire 26 and the liquid drains therethrough into the portions 28 of the holes, causing a web of fibres to form on the outer surface of the wire. In the form of the invention shown in FIG. 1 this web 36 is couched oif by a felt 38 entrained about a roll .40, which optionally may have internal suction box 42, in a manner known in the art. The novel construction and mode of operation of the invention permits greatly improved control of the web formation as well as of the drained water. It is evident that the rate of drainage of the water from the paper stock depends upon a wide variety of fac- :tors, which have been the subject of extensive research in the paper industry. Generally speaking, it has been thought, and empirical formulae developed which show, that the rate of drainage is a function of numerous variables, including the drainage area, the drainage force, the viscosity, the specific drainage resistance, the consistency or mass ratio of dry fibre and water, the concentration of additives and fibre fines, and density. W. L. Ingmanson and Roy P. Whitney published a paper in TAPPI (publication of the Technical Association of the Pulp and Paper Industry, Easton, Pa), vol. 37, No. 11, pp. 523-34, for November 1954, entitled, The Filtration Resistance of Pulp Slurries. This article rel-ates to laboratory drainage evaluation of paper webs. According to an empirical formula developed from their work and published in the paper, one can determine the drainage time to form a web of known specific resistance "for a range of pressure diiferences exerted across the filtration area. Contrary to previous concepts, itwas found from this work that past certain limits with slow stocks, an increase in drainage force only served to increase the drainage time for constant final dryness.
Even from a rough correlation of this work with table roll drainage on a conventional Fourdrinier, it is readily seen that intermittent drainage as effected by the table rolls is much faster than continuous drainage in the laboratory. This also in spite of the fact that paper machine stock contains fines which tend to retard drainage.
It has been proposed to increase the rate of drainage on slow stocks by the use of a pressure differential such as suction beneath the wire and in the breast roll, to pull the water through. As pointed out by the work of Ingmanson and Whitney, it has been found that this expedient does not necessarily solve the problem, since webs may be damaged if excessive suction is employed, and further, if suction is applied in areas close to the slice opening to pull a sudden surge of water from the stock through the .wire, a tightly packed web forms immediately on the Wire, actingefiectively as a dam to retard further drainage of water from the remaining superposed layer of dilute stock. As will be shown, the invention to a large extent overcomes this problem to provide greatly accelerated drainage.
/ Wholly apart from considerations of increasing the rate of drainage in paper making, for some applications it would appear that advantages can result if the drainage is controllable to a predetermined rate, as, for example, by reducing the flow so that the deposited fibres forming the web will tendv to lie primarily in the plane 6 of the'web rather than be pulled by'the drainage 'e'fiect to upset positions extending transverse of the web.
In general practice, it has been found in making lightweight tissue from very free stock which may adequately be formed at high speeds in areas as short as 5" that, except for safe handling of the web once formed, the rigorous drainage controls heretofore described are not necessary. This is pointed up by the fact that good tissue may be formed at high speed with one or two or no suction boxes. Since a major aspect of this invention involves a multiplicity of boxes, this mode of the invention may be extended to tissue as means of gradually easing the delicate sheet off thewire which tends in a short drainage arrangement to imbed itself detn'mentally into the wire. Practical applications however are more extensive in heavier. papers, and include a variety of grades too numerous for separate analysis. Instead, a rough analogy will be given to clarify the dimensional scope of the invention. As it is intended in general to' retard initial drainage until good formation of the fibre mat is assured and following this zone with alternate suction and neutral (or slightly positive pressure) stations as isnece'ssary for optimum drainage rate (pulsing as defined below), the number'of boxes in the initial and subsequent drainage zones may approximate the aggregate number of table rolls and suction boxes necessary on a conventional Fourdrinier for the same grade. For flexibility the size of boxes used in this invention may be narrow in the order of 2" and all the same size. Wider boxes being provided in a simple manner where necessary in practice by removing intermediate sealing strips from between the box walls and the roll shell.
As used herein pulsing, in its simplest form, describes the action upon the forming web which occurs when it passes over a series of boxes, the first and remaining odd numbered ones of which are-operated with negative. pressure to apply drainage force, while the evennumbered boxes are operated at neutral or positive pressure with respect to the pressure above the web thereby periodical- 1y to relaxthe fibre compaction. The term also describes more complex systems involving the operation of successive gro p of boxes at different pressures rather than individual boxes. The zone in which pulsing is employed, of course, may extend through-all or only a part. of the drainage zone.
The present invention it will be seen provides a-unitary solution to a variety of problems in paper making, including those just mentioned. Before returning to the specific embodiments of FIGS. 1 and 2, reference will now be had to the diagrammatic representations of FIGS. 8 and 8a, illustrating the theory of operation of one aspect of the invention. It'is known, as mentioned in the preamble of this specification, that under given conditions of surface tension, viscosity, etc., a column of liquid (for convenience here called a slug) may be supported by a column of gas, substantially intact, in a tube having a certain maximum diameter. The principle is illustrated in FIGS. 8 and 8a, where there is diagrammatically shown a slug 44 of liquid held in a vertical tube 46 against the force of gravity'by air pressure constituting the difierence between pressures P-1 and P4. FIG. 8a is indicative of water at room temperature in an diameter glass tube and is acceptably stable for the slug will rise if P-l is increased. FIG. 8 is a slug under similar conditions in a 7 diameter tube and is completely stable. As the cross-sectional area of the tube 46 is increased over there will be an increasing tendency of the liquid to start running down the interior walls, as indicated at 48, since the integrity of the slug is no longer maintainable. If viscosity and/or surface tension decrease due to temperature rise or some other reason, instability of the slug for a given diameter of tube increases, and the diameter of the tube 46 must be reduced in order to hold the slug. Referring to FIGS. 7 and .8, we may compare the glass tube to thejhole 28 in shell 20.
the holes are closely spaced on. the shell, we speak of the open area on the surface in percent of the total surface. In the preferred embodimentthe holes are of constant cross section for'a significant depth to establish volume. This depth is spoken of as related to the projected open area. The importance of low projected open areas is that the depth of all the fluid drained into the shell is proportionately and substantially greater than the jet depth at the slice relatedto 100% open area where the jet velocity is equal to wire speed. This operates to insure greater stability for slugs in the cavities.
Employing the above principles, demonstrated with a glass tube, if the holet28 in the shell 20 is no more than the critical cross-sectional area, a slug 44 of water may be maintained therein by the application of a differential air pressure. But here additional factors are introduced. Centrifugal foroe, dependent upon the diameter of the shell 20 and its speed of rotation, and the varying angular position of the hole 28 as the shell revolves significantly modify the result. Thus the action of centrifugal force may more than counterbalance the force of gravity and tend to fling the slug 44 outwardly, in which event a negative pressure must be applied at 30 to retain the liquid in the cavity 28. When the cavity 28 assumes a position at a substantial angular distance from the apex of the roll 20, as, for example, in FIG. 1 in the location near the suction roll 40, the force of gravity is acting in a different direction on the slug and tends more readily to break down its integrity, causing it to spread out on one of the side walls of the cavity 28. Other variables which may aifect the operation include temperature and chemical composition of the liquid, frictional drag on the cavity walls, etc. It will thus be seen that if it is desired to hold a slug of liquid in any of the openings 28, no exact rule can be established by which the dimensions can be quickly determined. However, in practice, we have found that in a machine of the type shown in FIGS. 1 and 2, in a shell having a 46" diameter, control of this character may be achieved by employing openings 28 having a diameter of in the large cavity and A in the small cavity. The portions 30, of course, may be of this diameter, or smaller, but control is improved and shell strength maintained if the portions 30 are of less diameter than the portions 28.
Employing the foregoing principle of operation, it will now be seen that if the pressure differential between the exterior of the shell and selected ones or more of the boxes 32 is accurately controlled a wide variety of effects may be achieved. By applying positive pressure to the first three to five boxes beneath the slice, initial drainage through the wire may be moderated, thereby preventing the quick formation of a dam-like web which wouldthen serve to impede further drainage. The water can then be pulled into the cavities 28 by the use of negative'pressure in the next succeeding group of suction boxes, and held therein even if water level drops below the internal surface of the wire, as in the area close to the take-off roll 40. Thereafter, by applying a positive pressure-to the remaining boxes 32, it is possible to prevent the water from draining into the boxes, and after passage beyond the last box, the water may be thrown exteriorly of; the shell bycent rifugal force, the openings 30 in the of area are determined having in mind this volume requirement. Presupposing jet speed equal to shell speed and taking a jet depth at the slice opening of one-half inch, the aggregate volume of the cavities should be significantly more than the equivalent liquid volume repre- "sentedby 'a one-half inch depth and a 100% openarea.
In cases where it is desired to bring the web to couch dryness (approximately 20% dry) it is necessary to increase the aforementioned volume by an additional space needed for pulling the necessary air through the sheet. The shell proper according to the invention may have a projected open area as low as 60% for which a residual depth up to one inch depending on slowness of stock is expected to be adequate to achieve this degree of dryness. However, this depth may be somewhat greater in instances where a cylindrical former is substituted for the Fourdrinier concept since the liquid must be stored for an appreciable time and a layer of air must be present above it at 29 in order to assure safe couching by a suction type of roll or a plain couch. For a specific example on tissue grades and lightweight production papers, cavities 28 may have a diameter of and a depth of one inch while the holes 30 may be hi in diameter and of a depth of three quarters of an inch.
In FIG. 3 the etfect just described is shown as even further exaggerated, where positive pressure is applied to the first eight of the boxes 32, thus permitting only extremely slow drainage through the wire. a
A further advantage, in accordance with the invention, is obtainable, as illustrated in FIGS. 1-3, in that the suction boxes 32, in all or any part of the drainage area, may be used to apply different pressures in sequence, thus pulsing the web as it forms, and very substantially modifying the drainage rate, in a manner analogous to the use of multiple table rolls on aFourdrinier wire as mentioned above. In accordance with our invention this pulsing effect is of a nature susceptible to a high degree of control, and a very large number of pulses may be applied in a very short drainage area since the boxes are numerous and close to each other.
Turning to the remaining figures, in FIG. 4 a cylindricalformer is shown comprising a shell 20 of the same construction as shown in FIG. 1, in which the slice 22 is located approximately below the apex of the roll. Operation over an arc ofeven 200 is obtainable by the use of the novel drainage control feature of the present invention. The pressure dilferential between the first few suction boxes and the exterior is such as to hold the liquid on the wire 26 and produce drainage even if the liquid is beingdischarged at a very steep upward angle from the slice. Rate of drainage can be controlled so that with free stocks slow drainage occurs over the area, whereas very slow stocks may be run with sufiiciently rapid drainage by pulsing action to permit very high speed operation.
In the showing of FIG. 4 the drained water is permitted to discharge outwardly against the shield 50. If desired, however, as shown in FIG. 5, the suction on the last boxes 32 may be increased sufliciently to draw all liquid into the boxes for discharge so that none or a negligible amount is thrown off by centrifugal force and the boxes and associated. piping will be built of suflicient size and capacity to handle all the water.
Even though by the use of the novel method and apparatus of the invention, it is possible substantially to increase drainage rates, if desired, thus greatly shortening the required drainage area for many paper stocks, significantly long drainage areas may nevertheless still be required for heavier grades of paper running at high speeds. To provide such increased drainage areas using a suction roll of the type shown in FIG. 4 can be achieved by increasing the roll diameter far beyond conventional diameters currently employed. According to the invention it is contemplated that diameters of the order of seven to twenty feet, or more, for the shell 20 can be used.
Such extraordinarily large shells, of course, present a manufacturing problem and could be expensive and diificult to build if manufactured in a conventional way. In FIG. 6 we have shown one form of composite roll useful to solve this problem. The structural strength, according to this concept, is provided by an internal metal shell 20a having drilled therein the relatively small diameter holes 30. This inner shell may have a thickness of, say, three quarters of an inch. Carried on the outer surface of the shell 20a is a relatively inexpensive, lightweight, auxiliary shell 20b, of non-metallic material, easy to work, which may be selected from suitable plastics now readily obtainable or from available rubber-like materials. The outer shell is provided with the larger cavities 28 which register with the holes 30 to produce in composite fashion a shell having the same functional characteristics as-that shown in the previous embodiments, but less expensive .and much lighter in weight.
The inner shell 20a of metal also provides that longwearing surface needed in sliding engagement with the sealing strips of the partitions forming the internal suction boxes. The outer shell need only be of a material having adequate compression strength and toughness to be machined and also must be compatible with the materials included in the paper stock to be run. To wear between the backing wire 59 and the non-metallic .shell 20b, the shell may be helically grooved in the conventional manner to receive a winding wire 52 which may raise the backing wire only slightly, not impairing the drainage control function of the invention. The depth of the outer shell is optional, and this depth will, at least in part, be governed by the necessary depth of metal, such as bronze, of the inner shell, as well as considerations of the liquid storage volume desired. In the interest of economy it will ordinarily be desirable in a com posite shell to provide an aggregate storage volume in the cavities 28 to store all the liquid in the shell until the sheet is couched off or carried off by the Fourdrinier wire. This will permit the use of small volume suction boxes in the drainage area as they will handle air and little or no water. The stored water will ultimately be discharged outwardly, or, if desired, inwardly through sufliciently large suction boxes located after the sheet discharge area of the type shown in FIG. 5, for example.
In FIG. 9 the invention is shown in connection with a known type of Fourdrinier machine in which web-formation takes place in a relatively short drainage area, as in making tissues from free stocks. Here although the slice 22 is shown positioned close to the apex of the breast roll 20 as compared with FIG. 4, for example, but still substantially below the same as contrasted with conventional practice at high speeds. The roll 20 is provided with counterbored openings 28, 30, as before. Trained about the roll is Fourdrinier wire 26:: which leads oif the sheet after formation has occurred. Within the shell 20 are mounted a pair of suction boxes $20 and 32d which function in essentially thesame manner as the boxes 32b of FIG. 5. The partitions defining these boxes are provided with sealing strips 35 hearing against the inner surface of the shell 20. Pressure within the boxes 32c,
32d can be individually controlled by appropriate mechanism (not shown). By establishing a substantial pressure differential substantially all or any portion of the water drained through the wire can be discharged through the boxes acting as receivers, or the water can be stored in the shell and discharged outwardly beneath the upper run of the wire 26a as indicated in FIG. 9. In this form of theinvention it is contemplated that there will be suffi cient retention of the water in the shell so that danger of disruption of the sheet in the drainage area extending beyond the roll apex is avoided. By rotation the boxes may 'be positioned so that the forward box area may be completely separated from the wire and operated to receive practically all of the water stored in the shell. While this leaves only one box for controlling the drainage, several boxes may be used in place of it where a longer drainagezone is required.
The arrangement of FIG. 9 is also applicable to the drainage of relatively heavy or slow sheets, in which it may not be desirable, for example, in existing machines where space is limited, to remove substantially all of the water in the drainage zone provided. The water extracted' overthe suction rollis retained by the roll and carried away from the wire. The remaining undrained stock is carried with the partially formed web by means of the wire onto a conventional Fourdrinier drainage zone containing a multiplicity of rolls 21 or other drainage devices in conventional use, wherein the remaining water is drained.
' This type of operation, by providing exact control of initial drainage conditions, will alleviate many of the undesirable conditions caused by uncontrolled dranage on a conventional Fourdrinier encountered at the slice discharge, such as waves and splashing of stock on the wire and loss of fine components of the paper stock through the wire, and the development of unequal sheet characteristics on top and bottom of the sheet.
The controlled drainage of the present invention is also applicable in certain cases to machines employing a shell having an open cellular structure on its periphery, as distinguished from the special drilled openings of the previous embodiments. This is possible, we have found, if in the drainage area there is maintained a continuous liquid layer between the undersurface of the web. being formed on the wire and the surface of the shell at the bottom of the open cellular structure thereof.
Such an application may be made at speeds and roll diameters which develop low centrifugal forces at the periphery of the roll so that gravity forces predominate at all times in influencing the drainage and drained water in cooperation with air pressure dilferences across the fibre mat. I
This feature of the invention is illustrated in FIGS. '10-13, wherein a modified form of shell 20:: is shown having openings 30a therein of less than the aforementioned critical diameter, and being provided on its surface with a deck constituting an open cellular structure, which may be to open as compared with the 60% to 80% of the previous embodiments. The outer peripheral portion of the cylinder is provided with a plurality of cells 52, the walls of which are formed by a series of radially disposed baffles or partitions 54. These partitions may be set into the shell 20a of the roll, extending outwardly therefrom and run longitudinally thereof dividing the periphery into the cells 52 which extend from one end to the other. The shell 20a is pierced with holes 3011, of less than the critical diameter, which establish communication between the inner ends of the cells 52 and the shell interior. As seen in FIG. 11, the holes 30a are arranged in close series extending longitudinally of the respective cells. The outer end of each of the apertures may be countersunk, as illustrated. Gripping the outer edges of the partitions 54 is a wire 58 which is wound around the shell from one end of the roll to the other; or a plurality of wires may be used each embracing the periphery of the roll. As shown in FIG. 11, the outer edges of the wires 58 are flush with the outer edges of the partition 54 and these wires, with the partitions, form a backing for a wire 59 of coarse mesh which surrounds the cylinder and forms a suitable support for the forming wire 26a.
A slice 22a discharges onto the surface of the Fourd-rinier wire 26a. The interior of the shell 20a is provided with boxes 32a, pressure in which may be selectively controlled as inthe previous embodiments. A sp ut 60 is arranged just below the slice 22a and discharges a flat stream of water beneath the stream of dilute paper stock emerging from the slice opening. In this embodiment the depth of the peripheral cellular structure of the roll is greater than the depth of the sheet of dilute stock spouted thereon from the slice opening. Therefore, if no other provision were made, the water would quickly drain through the wire 26a and leave an air space beneath the wire 26a, as in known types of paper machines. However, in accordance with the invention, we have found that if this cellular structure be kept completely full of liquid in the drainage area, drainage control can be achieved in much the same manner as in the previous 1 1.. embodiment. Therefore, if prior to the slice opening a sheet of water is discharged into the cellular periphery, substantially filling the same, and then the dilute stock is spouted onto the wire, a solid layer of liquid will extend from the inner surface of the wire to the openings 30a. The openings 3011 are less than the critical dimensions previously mentioned, and by applying positive or negative pressure to the boxes 32a, the rate of drainage can be controlled and the sheet of liquid held in the open cellular periphery of the shell can be retained so as either to be drawn into receivers through the shell structure after the wire leaves the shell, or to be discharged outwardly by release of the pressure difierential as shown in FIG. 10. It is also possible to fill the shell as described by flowing water from the first box or boxes 32 into the holes in the shell from the interior of the shell. In FIGS. l2 and 13 a structure similar to that of FIGS. and 11 is shown, but in this case the depth of the open cells 52 has been reduced so that the auxiliary water supply furnished at 60 in FIG. 10 is no longer necessary, since the volume of liquid in the paper stock is of suflicient thickness completely to quickly fill the cells, thus permitting the controlled operation in accordance with the invention.
In FIG. 14 there is shown an alternative construction for the shallow open cell structure employed in FIGS. 12 and 13. The shell is pierced with holes 30b countersunk in a shallow fashion at 28b, the construction being very analogous to that shown in the previous embodiments, except that the cross-sectional area of the counterbored portions 28b is not necessarily limited to the theoretical critical dimension wherein a slug of liquid could be substantially held therein by air pressure alone. When the volume of drained liquid fills the counterbores 28b and the layer of liquid engages the undersurface of the wire 26a, drainage control can be achieved as in the embodiments of FIGS 10-13 even though under the particular conditions of operation the theoretical critical diameter is exceeded by the openings 28b. Under these conditions, the slug of liquid is bounded by the wire 2611, the holes 28b, and the controllable liquid in the holes 30b. The slug of liquid in the region between wire 26a and hole 30bis restrained by the large surrounding area operative on a small volume of liquid and may thus be controlled against centrifugal force with almost the same facility as described for the cellular structures of FIGS. 1, 2, 3, etc., under the conditions of speed and roll diameter, storage volume previously described.
FIG. 15 illustrates an alternative embodiment for use in practicing the invention. This embodiment employs a flexible belt 70 in place of the metallic shell shown in the previous embodiments. The belt is of appreciable thickness and is provided with a similar series of counterbored cavities 28 and30 having the critical dimensions, mentioned in connection with FIG. 1, for example. The jet of dilute stock is laid down on a straight line path on which dewatering occurs to form a web. The path shown in FIG. 15 is horizontal, although web-formation and drainage will function equally well along upward or downward sloping paths within reasonable limits readily ascertainable for particular applications. Preferably the aggregate volume of the combined cavities in the belt 70 will be suflicient to store all the liquid drained from the web, although this is not a necessary function for controlling the rate of drainage according to the invention. Even though some water passes into the boxes 32, our novel drainage control can be employed by applying positive, neutral or negative pressure to the boxes 32 to retard drainage or achieve pulsing. Incremental drainage may also be achieved by applying different pressures to successive boxes. The advantage of storing all the liquid in the belt is that it may more conveniently be discharged either into a large suction receiver 32c, or,-held stored in the belt for radial outward discharge into the collector 50. The flexible belt 70 may be composed entirely of 'a suitable rubber-like composition or it may be lined with a flexible metal belt to increase its 'wear resistance .over the suction boxes in the conventional manner. The backing wire 59 is shown snugly and completely wrapping the flexible belt while the forming wire 26a is extended beyond the backing wire. Alternatively both the backing and forming wires could be wrapped to travel in close, snug relation to the belt, the sheet being couched off along a line located either in advance of or followingthe receiver 32c. A still further alternative is to arrange both wires 59 and 26a to depart from the belt, returning in a lower reach remote from the belt and rejoining the latter at the roll 72, the thus separated wires following the same or divergent paths as desired.
While there has been illustrated presently preferred embodiments of the invention, it will nevertheless be understood that the invention is not intended to be limited to the specific embodiments shown, and that the same is susceptible of various modifications and changes by those skilled in the art. Therefore, it is our intention that the invention be limited only to the proper scope to be afforded the appended claims.
1. In combination, a suction roll, a forming wire trained therearound,. said roll comprising a cylindrical shellrhaving a multiplicity of holes therethrough for receiving and storing white water drained through said wire, the cross-sectional area of each of said holes. being such that liquid stored therein can be held intact and controlled as to movement therein by pressure differential applied across the opposite ends thereof, means for discharging a stream of dilute paper stock onto said wire and roll, and a series of suction boxes engaging the inner surface of said shell and in communication with the inner ends of said holes, said boxes being adapted to be connected to different sources of controlled air pressure whereby the pressure differential between the pressure within each box and that above the wire may be selectively controlled as to whether it is positive, negative, or neutral.
2. The combination as defined in claim 1 wherein at least the final box of said series is sufliciently large to receive all the white water passed through said wire and stored in the holes of said shell. 3. The method of forming a paper web which comprises discharging a stream of dilute stock of given thickness onto the surface of a revolving roll having a shell of predetermined thickness pierced with holes to provide an aggregatedvolume sufiicient to accommodate at least all the water drained from said stock, the cross-sectional area of each of said holes being such that liquid stored therein can be held intact and controlled as to movement therein by pressure differential applied across the oppo site ends thereof, passing a desired portion of the water from said stream in a forming zone through a forming wire trained about said roll into said holes while controlling the rate of drainage in said zone by controlling the fluid pressure differential applied across said holes, pulsing the web as it forms by applying varying pressure diflierentials across said holes at closely spaced points within said forming zone to control the movement of the intact slugs of liquid into said holes, retaining said water in said holes at least to the end of said forming zone by suitably controlling said pressure differential, and effecting discharge-of said water beyond the end of said zone by changing said pressure differential.
4. The method of forming a paper web which comprises discharging a stream of dilute stock onto the surface of a revolving suction roll having a perforated shell, passing a desired portion of the water from said stream in a forming zone through a forming wire trained about said roll and through said roll while controlling the rate of drainage in said zone by controlling the fluid pressure differential applied across said shell, while pulsing the web as it forms by applying different fluid pressures,
13 to successive transverse areas of the interior of the shell at a multitude of closely spaced stations within the shell.
5. In the use of a web-forming apparatus comprising a forming wire supported by and traveling with a supporting sub-structure through a forming zone, said substructure having cavities therein which are open at opposite ends, which have an aggregate volume sufficient to store all liquid drained through said wire in the forming zone, andwhich are transversely dimensioned such that liquid so stored can be held intact and controlled as to movement therein solely by pressure ditferential applied across said opposite ends, the method which comprises discharging a stream of dilute stock onto said wire at the beginning of said zone so as to drain liquid therefrom into said cavities while depositing a web on the surface of said wire, pulling said liquid further into said cavities by applying pressure differential across said cavities so as to separate said liquid from said wire, so holding the liquid thus spaced from said wire while removing said web in a path divergent from that of said sub-structure, and thereafter discharging said liquid from said cavities.
6. The method as defined in claim wherein the speed of drainage through said wire in said forming zone is retarded by the application of a pressure differential across said cavities opposed to the flow of liquid through said wire.
7. The method as defined in claim 5 including the step of controlling the flow of liquid into said cavities at spaced stations in said forming zone by applying positive and neutral pressure differentials thereacross at different locations in said zone to control the deposition of the web on said wire.
8. In a machine for forming paper webs, a rotary shell, a traveling forming wire trained about said shell, means for supplying a stream of dilute paper stock of given depth to said wire and shell so that white Water therefrom will drain through the wire within a drainage zone comprising an area thereof overlying the shell, an
open cellular structure in the periphery of the shell extending over the entire circumference of the latter, said structure having an efiective depth of the order of said given depth and said machine having means in advance of said drainage zone for supplying an auxiliary quantity of water to said wire and shell to approximate the diiference between the volume of water drained from' said stream and the aggregate volume of said open cellular structure, said shell having holes communicating between said structure and the interior of said shell, the said holes being transversely dimensioned such that liquid therein can be held intact and controlled as to movement therein by pressure differential applied across the opposite ends thereof, and means for applying a controlled fluid pressure across said holes for controlling drainage and discharge of said water from said structure.
9. A machine as defined in claim 8 wherein said means for applying fluid pressure comprises a multiplicity of boxes in engagement with the inner surface of said shell and conduits therefrom adapted to be connected to independently controllable sources of fluid pressure.
10. A machine as defined in claim 8 wherein said open cellular periphery comprises a structure independent of said shell affixed to the surface thereof which includes a multiplicity of cells and said holes are in communication with said cells.
References Cited in the file of this patent UNITED STATES PATENTS 1,581,656 Monaghan Apr. 20, 1926 1,822,023 Giebeler Sept. 8, 1931 2,077,614 Campbell Apr. 20, 1937 2,418,600 Ostertag et al. Apr. 8, 1947 2,714,340 Brown Aug. 2, 1955 2,714,839 Mazer Aug. 9, 1955 FOREIGN PATENTS 629,633 Great Britain Sept. 23, 1949