US2882966A - Method and apparatus for forming an aqueous suspension of pulp fibres into a sheet - Google Patents

Description

.April' 21, 195.9

v Filed March 29, 1956 I S M. ZJJBERLYN 2,882,966 METHOD ANDAPPARATUS FOR FORMING AN AQUEOUS SUSPENSION 0F PULP FIBRES INTO A SHEET Y 2 Sheets-Sheet l /NVENTbR M. I Bzkly/v April 21, 1959 v MFJ. B ERLYN 2,882,

" 4 METHOD AND APPARATUS-FOR FORMING AN AQUEOUS SUSPENSION 1 OF PULP FIBRES INTO A SHEET Filed March 29, 1956 2 Sheets-Sheet'2 Q V/IVIIIENT'OR MIBERLyN METHOD AND APPARATUS FOR FORMING AN iQsli lEigi i s SUSPENSION OF PULP FERES INTO Martin J. Berlyn, Montreal, Quebec, Canada, assignor to Dominion Engineering Works Limited, Montreal, Quebec, Canada Application March 29, 1956, Serial No. 574,741

Claims. (Cl. 162-212) This invention relates to a high-speed sheet-forming method and apparatus for forming an aqueous suspension of pulp fibres into a sheet on a travelling foraminous sheet-forming element such as the forming wire of a Fourdrinier machine.

In the conventional Fourdrinier paper machine an aqueous suspension of fibre is flowed through a slice onto a moving endless wire screen, commonly referred to as the forming wire.

Some 98% of the original water is removed by the time the web leaves the wire.

Various devices such as flat suction boxes, table rolls and suction rolls are employed in conjunction with the Wire in order to speed up the drainage. Some of these devices impart frictional drag on the wire. This friction not only calls for considerable power to drive the wire but results in short wire life; about six days in the case of a modern high-speed newsprint paper machine. The wear of the wire is also accelerated by the presence in the stock of abrasive particles from the grindstones used in preparation of groundwood stock. These abrasive particles become embedded in the tops of suction boxes and attrition of the wire as it scrapes over these gritty surfaces, with normal loading augmented by suction, is inevitable.

To a certain extent the drainage of water through the wire is a function of time; this means that, for speeds substantially higher than those used at present, the wire would, using contemporary basic design, have to be longer than for present speeds, and even now wire lengths in the neighborhood of 130 feet are not uncommon.

In present-day newsprint paper machines, with their long taut Fourdrinier wires, a wire-change takes about two hours; more or less, varying with the detail design of the machine. This means down-time of around 100 hours per year, and may represent the loss of 1200 tons production of paper per year per machine.

One of the objects of this invention is to achieve higher speed of operation of a paper machine but with a shorter wire than those currently employed.

Another object is to obtain an increase in wire life.

Another object is to reduce the time taken to change a wire.

Other objects are to provide a smaller paper machine, consuming less power, costing less to build, less to operate, and less to maintain.

Proceeding now to a more detailed description of the invention reference will be had to the accompanying drawings, in which:

Fig. l is a schematic side elevational view of a Fourdrinier type sheet forming machine designed in accordance with my invention.

Fig. 2 is an elevational view of the breast roll and wire guide roll assembly schematically shown in Fig. 1.

Fig. 3 is an elevational view of the couch roll and slack adjusting roll schematically shown in Fig. 1.

As shown in these drawings, an endless, slack, Fourdrinier wire 5 (Fig. 1) is trained around a series of 282B66 Patented Apr. 21, 1959 horizontal rolls including a breast roll 6, a couch roll 7, and wire return rolls 8 and 9.

The breast roll 6 is power driven and serves to impart high-speed travelling movement to the wire 5 in the direction indicated by the arrow A in Figure 1. In the present instance, the driving means for the breast roll 6 is represented by a motor driven shaft indicated at 10 in Fig. 2. The couch roll 7 and wire return rolls 8 and 9 are mounted for free rotation and are rotated solely by contact with the travelling wire 5.

In the embodiment selected for illustration, the couch roll 7 is located at a higher elevation than the breast roll 6 and the upper run of the slack wire travelling from the breast roll 6 to the couch roll 7 is in a free catenary C between these rolls and is free of contact with friction surfaces such, for example, as the suction boxes employed in conventional Fourdrinier machines.

The aqueous suspension of pulp fibres to be formed into a sheet is fed onto the concavely curved upper side of the catenary portion of the wire at the breast roll 6 and the formed wet sheet is removed, preferably in a vertical or substantially vertical direction, from the catenary portion of the wire at the couch roll 7. In order to obtain the best results the pulp suspension should be fed onto the breast roll end of the catenary portion of the wire under pressure and in a downward direction tangential or approximately tangential to the breast roll. While various types of head boxes and slices may be used for feeding the pulp suspension onto the wire in the prescribed manner, the optimum conditions for high speed formation of the pulp suspension into a satisfactory sheet are realized when the head box and slice assembly used is of the type described and claimed in my co-pending application Serial No. 594,142, filed July 2, 1956. This particular type of head box and slice assembly is schematically shown in Fig. 1 as comprising a substantially cylindrical head box 11 from which the pulp suspension is discharged downwardly through a tangential slice outlet 12 onto the breast roll end of the catenary portion of the wire. An important characteristic of this type of head box is that the pressure is raised within the cylinder 11 by whirling the stock about the axis of the cylinder. As set forth in my aforesaid copending application this whirling of the stock about the axis of the cylinder is achieved by the provision of an impeller rotating within the cylinder and having approximately the same axial length as the inside length of the cylinder. The head box 11 may be and preferably is trunnion mounted to provide for easy adjustment of the position of the slice outlet 12 in relation to the wire and the breast roll to best suit different operating conditions.

The removal of the wet and relatively weak formed sheet S from the couch roll end of the catenary portion of the wire may be achieved through the agency of a water shower 13, an air slice 14, and centrifugal rejection of the sheet by the rapidly rotating couch roll 7.

The water shower 13 is located below the upper run of the wire ahead of the couch roll 7. The water delivered through this water shower wets the underside of the wire and softens the sheet fibres wrapped around individual strands of the woven wire and thus conditions the wet sheet for lifting off the upper surface of the wire without tearing.

The air slice 14 is arranged so that the blast of air de livered therethrough is directed into the convergent space 15 between the surface of the couch roll 7 and the adjacent upwardly travelling portion of the Wire. This blast of air exerts on the underside of the formed sheet a pressure sufiicient to just float the sheet on the surface of the mesh of the Wire. The high speed of rotation of the couch roll 7 gives rise to a centrifugal effect at its surface powerful enough to reject the formed sheet S from the wire 5 at a tangent to the surface of the couch roll where the wire wraps on to said surface.

It is desirable that the formed sheet S, which is wet and relatively weak, be directed in a vertical or substantially vertical direction from the forming wire 5 in order to impose the minimum stress on the structure of the sheet and give maximum immunity from wet end breaks. In the embodiment of the invention shown in Fig. 1, this is provided for by the arrangement of the couch roll and the catenary portion of the wire, the high speed of rotation of the couch roll and the assistance given by the water shower 13 and air slice 14.

The removal of the wet sheet S in a vertical or substantially vertical direction from the couch roll end of the forming wire 5 makes it feasible to pass the wet sheet directly through a suitably located press section without the aid of a pick-up roll or press felt and this, in turn, makes it possible to substantially increase the water extracting efiiciency and operating speed of the press section. In order to illustrate this I have shown schematically in Fig. l a press section 17 through which the wet sheet is passed vertically from the couch end of the forming wire 5 without the aid of the pick-up roll, pick-up felt and press felt currently used to pass the wet sheet from the forming wire to and through the first press section.

As here shown, the press section 17 includes two relatively slender or small diameter high- speed press rolls 18 and 19 affording a press nip through which the Wet sheet S is passed vertically from the couch roll end of the forming wire. Each of these small diameter press rolls is backed up by two backing up rolls 20 and 21 of larger diameter. It will thus be seen that each of the press rolls 18 and 19 has three bearing points which enable it to be run at very high operating speeds without whip or whirling. Torque can be applied to the press rolls 18 and 19 without vibration by employing a press roll drive including worm speed increasing gears directly driving said press rolls. The small diameter of the press rolls brings the roll centres close to each other and this imposes a low limit on the diameter of driving gears mounted on the roll shafts but, by employing the worm and wormwheel type of speed-increasing gear train, in which the small-diameter worms are mounted on the roll shafts, adequate power capacity of the roll drive may be provided despite the inherently short distance between roll centres.

The high speed of rotation of the press rolls 18 and 19 gives rise to centrifugal effects at the roll surfaces which ensure that the sheet S will leave the press nip cleanly without sticking to or wrapping itself around either of the press rolls.

A basic and important novel feature of the invention described herein is the movement of the upper suspensioncarrying run of the Fourdrinier wire through a suitably curved path of travel from the press roll to the couch roll with sufficient rapidity to effect, by centrifugal action, a very rapid removal of water from the suspension through the drainage openings of the wire. This rapid centrifuging of the water from the suspension reduces the drainage time sufficiently to enable a Fourdrinier wire of given length to be run at very much higher speeds than is now feasible. Put in another way, the reduction of drainage time afforded by this invention makes it possible to increase the operating speed while decreasing the length of the Fourdrinier wire and this is directly contrary to current practice. The running speed of the Fourdrinier Wire is sufficiently high to generate centrifugal forces considerably greater than gravity in order to insure the rapid removal of water. Inasmuch as there are no external supporting surfaces between the extremities of the concave path of the wire, it can be seen that the wire assumes a path which is the resultant of the forces generated by the stock and centrifugal force.

The great increase in the running speed of aFourdrinier wire which is made possible by the drastically reduced drainage time afforded by this invention can also be taken advantage of to narrow the width of a Fourdrinier machine without such loss of output capacity as this would entail in the case of conventional machines. At feet per second a 66-inch width newsprint machine could produce approximately 250 tons of newsprint per 24 hours and it is obvious that, if such a machine could be made appreciably shorter in overall length than present newsprint machines, attractive economies in cost of machines and buildings would be realized. The provision of such a narrow width, high-speed, high-output machine is feasible if the Fourdrinier section is designed in accordance with the principles of this invention to effect rapid centrifuging of the water from the wirecarried pulp suspension during travel thereof from the breast roll to the couch roll.

In the case of the proposed high-speed narrow-width Fourdrinier machine such, for example, as a 66-inch width machine, the permissible reduction in the lengths of the breast roll 6, couch roll 7 and wire return rolls 8 and 9 makes it feasible to provide an open-side Fourdrinier section by cantilevering the said rolls in the manner illustrated in Figs. 2 and 3. As here shown, each of the rolls is supported, on the cantilever principle, from a frame structure 23 at one side of the Fourdrinier section so that the end of each roll remote from the frame structure is free. The open-side Fourdrinier design, the elimination of the conventional table rolls and suction boxes, and the slack condition and narrow width of the Fourdrinier wire enable wire changes to be efiected with much greater ease and rapidity than has heretofore been possible.

In addition to facilitating wire changes the elimination of the conventional table rolls and suction boxes, as contemplated by the present invention, increases the useful life of the wire by reducing the frictional drag and wear thereon and also reduces the power required to drive the wire.

Another advantage of the invention is that, in the embodiment shown in the drawing, the design of the Fourdrinier section is simplified and made more economical by the cantilever mounting of the wire rolls and by the fact that only four wire rolls are employed for moving and guiding the wire through its prescribed path of travel.

The wire return rolls 8 and 9 are mounted for approprrate adjustment to enable roll 8 to be used as a trimming roll or wire guide for keeping the wire in its prescribed path of travel and to enable the roll 9 to be used as a slack adjusting roll for regulating the length of wire in the catenary C. To this end the roll 8 is mounted so that it may be slightly canted out of parallel with the breast roll 6 in a vertical plane to keep the wire in lts proper path of travel and the roll 9 is mounted so that its distance from roll 8 may be varied to give slack adjustment control for regulating the length of wire in the catenary C. So far as the present invention is concerned the adjustable mounting of the rolls 8 and 9 may be accomplished in any suitable manner and various suitable methods of mounting and adjusting the rolls will, be obvious to those skilled in the art. It is preferred, however, that the rolls 8 .and 9 be mounted and adjusted in accordance with the invention disclosed in my co-pending application Serial No. 595,223 filed July 2, 1956. Accordingly, I have shown in Fig. 2 and generally indicated by reference numeral 24 component parts of the roll mounting and adjusting means more fully described in said application Serial No. 595,223, for tilting the Wire guiding return roll 8 in a vertical direction. Similarly, I have indicated in Fig. 3 a slide 25 which carries the slack adjusting return roll 9 and is movable horizontally between parallel guide rails 26 on the frame structure 23 to effect lateral adjustment of said roll 9. The slide 25 is secured in adjusted position by means of clamping bolts 28 which pass through elongated holes (not shown) in the wall of frame structure 23.

The specific arrangement of the component parts of the Fourdrinier section shown in Fig. 1 is intended to be illustrative rather than limiting since, in practice, various modifications of the illustrated arrangement may be resorted to. For example, the extent to which the couch roll is elevated in relation to the breast roll is variable to give any desired variation of the catenary curvature of the path through which the upper run of the wire travels from the breast roll to the couch roll. The breast roll and couch roll may also be arranged with their axes in a common horizontal plane or with the breast roll positioned at a higher elevation than the couch roll. The removal of the wet sheet in a vertical direction from the couch roll end of the wire is an important but not an indispensible feature. Also, it would be feasible to direct the formed sheet S in a downward vertical or substantially vertical path from the couch roll end of the wire 5 to and through a high-speed press section 17 positioned below the couch roll. These and other modifications are within the scope and spirit of the invention as defined by the appended claims.

I claim:

1. A method of forming an aqueous suspension of fibres into a sheet on an endless foraminous sheet-forming wire screen which comprises the steps of feeding the stock in a stream substantially tangentially to a concave section bound by the wire screen, moving the stock and screen simultaneously through a concave path at a speed sutficient to generate centrifugal forces greater than gravity, expelling the water from the stock through the screen by said centrifugal force, separating the sheet of fibres from the screen at the end of said concave path, and maintaining the screen free from contact with external support between the extremities of said concave path whereby the path assumed is the resultant of the forces generated by said stock and centrifugal force.

2. A method of forming an aqueous suspension of fibres into a sheet on an endless foraminous sheet-forming wire screen movable on a breast roll and couch roll having horizontal axes which comprises the steps of feeding the stock in a stream substantially tangentially to a concave section bound by the wire screen adjacent the breast roll end thereof, moving the stock and screen simultaneously through a concave path at a speed sufficient to generate centrifugal forces greater than gravity, expelling the water from the stock through the screen by said centrifugal force, separating the sheet of fibres from the screen at the couch roll end of said concave path so that the sheet of fibres is disposed in a substantially vertical plane, and maintaining the screen free from contact with external support between the extremities of said concave path whereby the path assumed is the resultant of the forces generated by said stock and centrifugal force.

3. Apparatus for forming an aqueous suspension of fibres into a sheet comprising an endless travelling Fourdrinier wire trained around a breast roll and a couch roll between which the run of the wire travels in a curved path of greater length than the distance between the breast and couch roll and assumes a concave shape adiacent the breast roll and is free of contact with any restrain imparting surfaces, means for feeding the suspension tangentially onto the concavely curved surface of the wire at the breast roll end thereof and at substantially the velocity of the wire, and means for moving said wire at a high rate of speed, said apparatus being characterized in that the curvature and speed of travel of the run of the wire effects, by centrifugal action of a force greater than gravity, rapid removal of water from a suspension fed on to and carried by the concavely curved surface of the wire.

4. Apparatus according to claim 3 and further including means for varying the length of the run of wire travelling from the breast roll to the couch roll.

5. Apparatus according to claim 3 in which the breast roll is a driven roll and constitutes the wire driving means for imparting travelling movement to the Fourdrinier wire.

6. Apparatus for forming an aqueous suspension of fibres into a sheet comprising an endless travelling Fourdrinier wire trained around a breast roll and a couch roll journalled on horizontal axes, the wire between the breast roll and couch roll being of greater length than the distance therebetween, the wire travelling in a curved path between the breast roll and couch roll and being free of contact with any restrain imparting surfaces, means for feeding the suspension tangentially onto the upper concavely curved surface of the wire at the breast roll end thereof, means for moving said wire at a high rate of speed, said apparatus being characterized in that the curvature and speed of travel of the upper run of the wire effects, by centrifugal action of a force greater than gravity, rapid removal of water from a suspension fed on to and carried by said upper run of the wire.

7. Apparatus according to claim 6 and further including means for varying the length of the upper run of wire travelling from the breast roll to the couch roll.

8. Apparatus for forming an aqueous suspension of fibres into a sheet comprising an endless travelling Fourdrinier wire trained around a breast roll and couch roll, the wire between the breast roll and couch roll being of greater length than the distance therebetween, the wire travelling in a curved path between the breast roll and couch roll and being free of contact with any restrain imparting surfaces, means for feeding the suspension tangentially onto the concavely curved surface of the wire at the breast roll end thereof and at substantially the velocity of the wire, means for moving said wire at a high rate of speed, means for facilitating the removal of the formed sheet from the wire at the couch roll end, said last-named means including a water shower through which water is delivered against the underside of the wire at a point in advance of the couch roll to soften the sheet fibres wrapped around the individual strands of the woven wire.

9. Apparatus according to claim 8 wherein said last named means further includes an air slice located between the water shower and the couch roll and through which air is directed against the underside of the formed sheet to float the sheet on the surface of the neck of the wire.

References Cited in the file of this patent UNITED STATES PATENTS 1,101,725 Buchanan June 30, 1914 1,410,856 Warburton Mar. 28, 1922 1,544,904 Herb July 7, 1925 1,599,376 Smith Sept. 7, 1926 1,905,911 Kellett Apr. 25, 1933 1,931,062 Darby Oct. 17, 1933 2,204,426 Millspaugh June 11, 1940 2,694,346 Goodwillie Nov. 16, 1954 2,698,972 Keeler Jan. 11, 1955 FOREIGN PATENTS 9,585 Great Britain of 1915 OTHER REFERENCES Witham: Modern Pulp and Paper Making, page 397, second edition, (1942) published by Reinhold Publishing Co., New York, N.Y.

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