US3127308A - Dual wire dewatering apparatus - Google Patents

Description

United States Patent On ice I 3,127,308 Patented Mar. 31, 1964 3,127,308 DUAL WIRE DEWATERING APPARATUS Edgar J. Justus and Jerome P. Brezinslti, both of Beloit, Wis., assignors to Beioit Iron Works, Beioit, Wis., a corporation of Wisconsin Filed Aug. 18, 1961, Ser. No. 132,495 1 Claim. (Cl. 162-349) The present invention relates broadly to the dewatering of web materials, and is more particularly directed to a Fourdrinier type paper making machine featuring the provision therein of an endless foraminous band within the loop of the forming wire and traveling in supporting relation therewith to control the drainage characteristics of the forming wire and minimize formation differences caused by the moving system.

As is well known, the conventional Fourdrinier type paper making machine comprises a looped traveling forming wire presenting a forming reach extending from a breast roll, at which the stock is flowed onto the wire, to a suction couch roll located approximately at the station at which the formed web is removed from the wire. Various dewatering devices are mounted beneath this reach of the forming wire, and one common dewatering device is known as a suction box and presents a flat perforate top to the bottom side of the wire. The interior of the suction box is exhausted to assist in drawing water from the web through the wire and through the perforations in the fiat top of the suction box.

A pressure difference thereby exists between the top and bottom surfaces of the forming web, and ideally this difference should be uniform entirely across the web as it moves on the forming wire along the suction box top. However, from any one of a number of causes, as for example, partial or complete blockage of one or more of the drain perforations in the suction box cover, a non-uniformity of pressure difference may exist in actual practice. This results in relatively faster white water drainage at a particular location in the forming web, carrying with it some of the fines and creating shadow marking in the paper product. Shadow marking cannot of course be tolerated in high quality papers exemplified by bond, book and like grades, while in thicker webs some uneven drainage can be tolerated since fiber redistribution can be effected in the press part.

A somewhat related problem exists with respect to table rolls on modern high speed paper making machines. Table rolls, of course, support the forming reach of the Fourdrinier wire, subject unformed pulp or slurry on the forming run to a series of vertical impulses which assist in distribution of fibers in the slurry, and have a pumping action which extracts water from the traveling web. This pumping or suction action, which is of the greatest magnitude at the roll-wire nip and increases with the rotative speed of the roll, again creates a pressure difference between the top and bottom surfaces of the forming web. Floc or agglomerated bundles of fibrous material not dispersed by the table rolls may be one cause of a nonuniformity in this pressure differential, and again, uneven drainage at a particular location in the sheet may occur.

The instant invention resides in a novel, simple and particularly effective arrangement for minimizing the non-uniformity of the pressure differential. In accordance with the present teachings, a drainage control medium in the form of an endless foraminous band is provided between the web dewatering member (one or more table rolls or one or more suction boxes) in supporting relation with the forming reach of the forming wire and within the loop of the forming wire. The looped drainage control band may or may not be more coarse than the forming wire, although for reasons of economy a band of a lower mesh size is preferred. Then too, in those applications wherein the drainage control band travels along the suction box top, a more coarse foraminous member has the advantage of a longer wear life.

The drain band of thisinvention may be woven with the conventional forming wire, or may be suitably attached thereto, thus being of approximately the same circumferential length as the forming wire and following the same path of travel. In such an application, the drainage control medium herein provided would desirably be of a relatively coarser mesh and would be within the loop of the conventional forming wire, so that the more durable drain band is the element of the combination which wraps the rolls and other wire supporting portions of the Fourdrinier papermaking machine. As stated, the drainage control medium of this invention minimizes the non-uniformity of the pressure difference existing between the top and bottom surfaces of the forming web. Relatively fast drainage through particular portions of the web is thereby prevented by interposing between the web dewatering member or suction inducing means and the forming wire a foraminous barrier which imparts to the moving supporting system a significantly greater resistance to drainage. In this manner, by preventing excessively fast drainage, shadow marking or other types of unwanted markings are avoided, and a superior product is thereby obtained.

It is accordingly an important aim of the present invention to provide a web dewatering apparatus featuring therein a looped traveling foraminous band within the loop of the forming wire in a Fourdrinier type papermaking machine and movable with the wire in supporting relation thereto through at least a portion of travel of the forming wire and effective to provide more uniform drainage entirely throughout the forming paper web, thereby resulting in a product having a uniform appearance throughout.

Another object of this invention lies in the provision of an improved Fourdrinier type papermaking machine, in which within the looped forming wire thereof an auxiliary endless wire is provided in running relation to web dewatering means and which not only effectively controls white water drainage, but also markedly reduces wear of the forming wire.

A further object of this invention is to provide a dewatering apparatus including a suction device and a foraminous member trained thereover and which features a looped carrier band supporting the foraminous member over the suction device and having a different drainage characteristic than the foraminous member for controlling the rapidity of drainage therethrough.

A still further object of the instant invention resides in a paper machine which includes a suction device receiving thereover a looped forming wire, and in which the improvement is an endless drainage control band within the loop of the forming wire and supporting the wire during travel over the suction device, the control band having a percent open area and drainage time different than the forming wire to reduce the rapidity of drainage therethrough.

An even further object of the present invention is to provide web dewatering apparatus of the foregoing character in which the endless drainage control band takes the form of a relatively coarse wire having an open area and drainage time greater than the forming wire for accomplishment of the foregoing objectives.

Yet a further object of this invention is to provide apparatus of the general arrangement described, and wherein the forming wire and drainage control band are attached one to the other and thereby follow essentially the same path of travel.

Other objects and advantages of the invention will become more apparent during the course of the following description, particularly when taken in connection with the accompanying drawings.

In the drawings, wherein like numerals designate like parts throughout the same:

FIGURE 1 is a more or less diagramrnatic elevational view of a paper machine constructed in accordance with the principles of this invention, and showing how the drainage control band can be associated with suction means in order to minimize the non-uniformity of pressure differential between opposite surfaces of the web being formed on the forming wire;

FIGURE 2 is a fragmentary plan view of a conventional forming wire and illustrative of a plain weave which can be employed;

FIGURE 3 is a fragmentary plan view of the drainage control band of this invention and showing a twill weave which can be employed therefor; and

FIGURE 4 is a fragmentary vertical sectional view through a forming wire and supporting drainage control band provided with the weaves of FIGURES 2 and 3.

The forming wire of the invention has a weave, mesh size and wire diameter dependent upon the grade of paper being made, after taking into consideration the characteristics of the stock and the operating conditions of the machine. Forming wires for coarse papers, such as wrappings or news, ordinarily use a 60-n1esh wire, and special groundwood book papers and regular book sheets often require 70- to 80-mesh wire. Some special papers, on the other hand, such as very fine tissues similar to cigarette papers, may require an even finer wire, as a 90- or 100-mesh. The forming wire may have either a plain, twill, monoplane, triple chain, or single or double twist cable weave, again depending upon the grade of paper being made.

Illustratively, for the purposes of the instant invention, it will be assumed that a groundwood book paper is being made on the machine, and accordingly, the forming wire may have a plain weave with a warp count of either 70, 75 or 80. A wire of this character has a standard mesh designation identified by the same last three numbers, and if the mesh size is 70, there is 70 warp wires per inch (with a tolerance of minus 2) and 50 shute wires per inch, tolerance :2). Generally, a number 70 mesh wire utilizes a warp wire having a diameter of between 0.0075 and 0.0080 inch before weaving, and a shute wire with a diameter of between 0.0075 and 0.0085 inch before weaving.

A portion of the forming wire 11 having a standard or plain weave is shown in plan in FIGURE 2. As appears therein, a plain weave is formed by interweaving the shute (crosswise or weft) wire 22 over and under alternate warp (lengthwise) wires 23. The plain weave provides good support to the paper fibers, however, a longer wearing wire is generally obtained when the twill weave is utilized. As is known, in the twill weave the warp wire passes under two shute wires and over one and thereby makes a longer knuckle that presents a larger bearing area to the suction boxes. This may be desired in certain forms of the present invention, and as well, it may be desired to employ a monoplane weave which is regarded as providing maximum support to the sheet and good wire life. In the monoplane weave a hollow shute wire is used which crimps more readily in the weaving process, thereby leaving the warp and shute in one plane and giving smoothness to the finished paper.

A seventy mesh forming wire having a plane or standard weave as described above has an open area expressed in percent of about 27.9. Open area is of course calculated by multiplying by 100 the product of (1-warp count warp diameter) and (l-shute count shute diameter). This same type wire when woven as indicated has a drainage time in seconds of about 21.0, the drainage time being the actual time in seconds for a given volume of water to run through the wire as determined by laboratory tests,

Although the forming wire 11 when woven as described has a drainage time which cannot be regarded as excessively fast or slow, as compared with a drainge time of 20.0 seconds for a fifty plain weave and a drainage time of 24.0 seconds for a one hundred plain weave, one or more areas of the wire may drain faster than other areas as the wire travels over the suction box. As was earlier stated, the application of suction forces to the underside of the wire as the wire with the forming web thereon passes over the suction box creates a pressure differential between the upper and lower surfaces of the web. Ideally this pressure difference should be uniform entirely across the web, however, any one of a number of conditions creates a non-uniform pressure difference. Fioc or agglomerated bundles of fibrous material may not have been completely dispersed, one or more drain perforations in the suction box may not be drawing effectively, or other conditions may exist which are known to those skilled in the art. As a result, the web drains relatively faster in one or more areas thereon, the fines in the slurry are drawn into the suction box and shadow markings appear in the web. Such markings cannot of course be tolerated in bond, book, mimeograph, lightweight kraft, and other intermediate weight papers. In relatively thin sheets as exemplified by the tissues, the presence of shadow markings is not a serious objection, while thicker sheets can have the water therein redistributed in the press part.

The looped drainage control band located within the loop of the forming wire is desirably provided by a woven wire of a substantially lower mesh number than the forming wire, although it is possible that the mesh sizes of both looped members could be approximately the same in the event that the forming wire was woven of plastic, which up to the present can be woven only to a relatively coarse weave of the order of 36 x 32 0.010 monofilament. In this regard, it is important to note that since the forming Wire 11 is supported and protected by the drainage control band during travel over the suction device, the use of plastic forming wires is now rendered more feasible, and further, the type of weave and mesh size of the forming wire can be modified to effect production economies. As for example, the forming wire can have a plain weave, in contrast with the more durable and more expensive twill and monoplane weaves, and subject to the qualification that there be no deleterious effects upon sheet formation, the mesh size of the forming wire 11 may be reduced.

Generally speaking, however, the forming wire is of the same mesh construction normally employed for groundwood book and other intermediate Weight paper grades and has either a 70-, 75- or -mesh number, as was earlier noted. The coarse inner wire loop used in combination therewith has an open area and drainage time which is greater than the outer loop, and illustratively, the drainage control band has a mesh size between 8 and 40. Desirably, the mesh of the inner loop has an open area greater than 27% and a drainage time less than twenty seconds so as not to resist to an excessive degree the drainage resistance through the forming wire. An illustrative drainage control band may be provided by a 30 x 30 plain weave which has an open area of 35.4% and a drainage time of about 17.1 seconds, or a 40 x 40 plain weave can also be used and which has an open area of 27.1% and a drainage time of 18.4 seconds. A 40 x 32 plain weave is also satisfactory, and this particular weave has an open area of 30.9% and a drainage time of 19.2 seconds. As is known, a 40 x 32 plain or standard weave employs a warp wire having a diameter between 0.0105 and 0.0115 inch and a shute wire of a diameter between the same minimum and maximum.

A twill or monoplane weave can also be used for the drainage control band 26, and both of these weaves have the advantage of longer wire life. A twill weave is illustrated in FIGURE 3 as being used for the drainage G) control band 26, and it may be seen therefrom that in this weave the warp wire 31 passes under two shute Wires 32a and 32b and over another shute wire 320, which makes a longer knuckle that presents a larger bearing area to the suction box top. The twill weave has approximately the same drainage time as was indicated for the exemplary plain weaves, and primarily *for the reason of longer wire life is preferred in the instant applications.

An embodiment of the invention is illustrated in FIG- URE 1. As appears therein, a forming wire generally designated by the numeral 60 is comprised of an inner wire loop 61 of relatively coarse construction which travels together with an outer wire loop 62 of relatively finer mesh. The wire loops 61 and 6?. may be woven together, or in some other manner suitably connected one to the other, or the two forming wires 61 and 62 need not be attached and can be run either independently or in unison. To minimize friction therebetween, however, it is preferred that the two wire loops 6-1 and 62 be connected.

The combined forming wire 60 of FIGURE 1 woven together is further illustrated in FIGURE 4, and in this view the relatively coarse inner wire loop 61 is woven in a twill weave wherein a warp wire 61a passes under two shute wires 61b and 61c and over a single shute wire 61d. As was stated earlier, the drainage control band 61 can be provided in different weaves, although the twill configuration does have a relatively longer life by reason of a longer knuckle, indicated at 61c which presents a larger bearing area to the suction boxes. Also shown in FIGURE 4 is the outer wire loop 62, which may be a conventional forming wire woven in a plain weave as illustrated. Such a weave has a warp wire 62a running over one shute wire 6% and under the next shute wire 62c. Again, a plain weave is not at all times required, and other weaves known to those skilled in the art may be utilized.

Referring now again to FIGURE 1, the combined formin wire 60 has an upper forming run supported upon table rolls 413 and web dewatering apparatus generally designated by the numeral 70. Such apparatus is shown as taking the form described and claimed in Edgar I. Justus application Serial No. 708,878, filed January 14, 1958, U.S. Patent No. 2,981,328. As is disclosed in the mentioned Justus application, the suction box 71 has a generally fiat top with drain penforations therein and land areas intermediate the perforations, and an endless fiexible perforate belt 72 covering the suction box top and trained about a pair of rolls '73 and 74, one or both of which may be driven by motive means (not shown). The endless elastomeric belt 72 has drain perforations therein which register with drain perforations in the suction box top, and the suction box cover also has fluid supply passages therein which flow a fluid along the land areas of the cover to lubricate the under side of the belt during thereover, thereby reducing the power required to move the belt along the suction box top.

The web dewatering apparatus of FIGURE 1 may at all times not apply uniform suction pressures entirely across the forming web W, for example, by reason of uneven belt travel, fiber agglomerations in the web or from other causes. This creates a nonuniformity in the pressure differential between the top and bottom surfaces of the web, causing formation difierences. However, by provision of the drainage control band 61 within the loop of the forming wire 62, a significantly greater resistance to drainage is provided, with the result that uneven drainage rates throughout the web are controlled and a sheet of good appearance obtained.

Various forms of the invention have been shown and described herein, and it is believed apparent therefrom that other modifications may be efifected without departing from the novel concepts of this invention.

We claim as our invention:

A paper web dewatering apparatus comprising an endless looped Fourdrinier wire having an inner loop portion of relatively coarse construction and an outer loop portion of relatively finer mesh, said loop portions woven together, means for supporting the Fourdrinier wire with an upper run on which a paper web is supported, a suction box beneath the wire, and an endless elastomeric belt looped over the suction box and extending between the suction box top and said Fourdrinier wire with said belt having drain perforations so that a significantly greater resistance to drainage of the web on the Fourdrinier wire is provided so that a sheet of good appearance is obtained from the web.

References Cited in the file of this patent UNITED STATES PATENTS 635,266 Marshall Oct. 17, 1899 762,431 McGrath June 14, 1904 777,362 Youngs Dec. 13, 1904 1,071,021 Bauer Aug. 26, 1913 1,514,011 Pope Nov. 4, 1924 1,787,047 Loetscher Dec. 30, 1930 1,827,177 Thomson Oct. 13, 1931 1,880,686 Berry Oct. 4, 1932 2,039,308 Evans May 5, 1936 2,981,328 Justus Apr. 25, 196 1 OTHER REFERENCES Kitano: Double Wire Fourdrinier May Improve Wire Life and Formation, Paper Trade Journal, Dec. 19, 1960, pages 41-43,

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