US3867766A

US3867766A - Dryer fabric for a papermaking machine

Info

Publication number: US3867766A
Application number: US342806A
Authority: US
Inventors: Joseph Robert Wagner
Original assignee: Huyck Corp
Current assignee: Huyck Corp
Priority date: 1967-12-22
Filing date: 1973-03-19
Publication date: 1975-02-25
Anticipated expiration: 1992-02-25

Abstract

This invention is directed toward an endless, fluid permeable, belt-like material, the permeability of which varies at selected locations across its width as a means for selectively controlling the moisture profile of a continuous web of sheet or sheet-like material, such as paper or the like, as it is being made.

Description

United States Patent 1191 Wagner [45] Feb. 25, 1975 DRYER FABRIC FOR A PAPERMAKING [56] References Cited MACHINE UNITED STATES PATENTS [75] Inventor: Joseph Robert Wagner, Leeds, 1,616,222 2/1927 Harrigan 162/348 England 2,180,054 11/1939 Hindle et al..

2,207,609 6/1940 Buchanan..... 1 Assignee: Huyck p t St o 2,271,295 1/1942 Gates Conn. 2,903,021 9/1959 Holden et a1. 139/383 A [22] Filed: n73 Primary Examiner-Kenneth W. Sprague [2]] App]. No.: 342,806 Assistant Examiner-James C. Yeung Related U 8 Application Data Attorney, Agent, ,or FirmWi1liam G. Rhines; Robert F. Ha t [63] Continuation of Ser. No. 692,806, Dec. 22, 1967, rges abandmed- 57 ABSTRACT This invention is directed toward an endless, fluid per- [52] '7"? 34/95 34/ /22 9 meable, belt-like material, the permeability of which [51] Int Cl F26) 13/26 varies at selected locations across its width as 'a means [58] Field 116 123 for selectively controlling the moisture profile of a 34/243, 9; 161/51, 75, 63, 64, 86; l62/DIG. 1, 358, 359, 360; 139/383 A, 425.5

continuous web of sheet or sheet-like material, such as paper or the like, as it is being made.

18 Claims, 6 Drawing Figures MACHINE DIRECTION PAIENTEUFEBZ5I975 a 8 67. 766

MACHINE DIRECTION FIG. 6 JOSEPH ROBERT WAGNER INVENTOR.

MACHINE DlRE/(FION By ATTORNEY BACKGROUND OF THE INVENTION In the typical papermaking machine, such as thesocalled fourdrinier machine, an aqueous suspension of fibers, called the furnish, is deposited onto a travelling forming medium, generally an endless belt of woven wire and/or synthetic material, to form a continuous web of paperor paper-like material. In this connection, the phrase paper or paper-like material is used in a broad or genericsense and is intended to include such items as paper, pulp, board, asbestos sheet and otherv similar sheet-like structures. As the furnish travels on the forming medium through the forming section of the machine, much of itswater content is removed and a somewhat self-supporting continuous paper web formed, this water removal being facilitated by the use of such well-known devices as hydrofoils, table rolls and/or suction boxes.

After leaving the forming section, the paper web is transferred to the press section of the-machine where still more of its water content is removed by passing it through a series of pressure nips formed by cooperating press rolls; these press rolls also serving to compact the web. The paper web is then transferred to the dryer section of the machine where it is passed about and held in intimate'heat transfer relation with upper and lower arrays of heated, generally cylindrical rolls in order to remove still further amounts of water therefrom. Subsequently, the paper web may be passed between a series of calender rolls where the sheet is compacted and any loose fiber ends on the paper web are laid down and the surface of the web provided with a smooth finish.

The dryer section of a papermaking machine generally includes two (one upper and one lower) arrays of heated, generally cylindrical rolls arranged and spaced in staggered, parallel rows. In most instances, the dryer rolls have a solid, generally imperforate surface for contacting the paper web; however, in some instances, it has been found desirable to provide the rolls with a gas pervious surface through which heated air and/or steam may be blown in order to increase the drying action on the paper web, one example of such a roll being described and claimed in US. Pat. No. 3,246,401 Walser et al. The paper web is generally passed to and fro between the arrays of dryer rolls in a generally serpentined manner to ensure that both sides of the paper web contact the dryer rolls. As the paper web passes over the dryer rolls, it is held in intimate heat transfer relation therewith by a belt, commonly referred to as a dryer felt or dryer fabric, which has been made endless either by the endless techniques which are well known in the field of papermakers felts and other papermachine clothing, or by having been woven flat and the end later joined, as by use of clipper hooks and a pintle. In the past, dryer fabrics generally have been substantially impervious structures of either woven or needled construction; however, the dryer fabric of this invention must be fluid permeable in order to permit moist air, steam and/or water vapor to pass therethrough. While open weave fabrics have been found to have many desirable characteristics, non-woven structures such as needled felts, perforated plastic belts and the like have also been found suitable.

In the description which follows hereinafter, reference will be made to a dryer fabric. In the cognizant arts, a dryer fabric usually is taken to mean a beltlike structure which has been woven from synthetic yarns, made from materials such as nylon or Dacron, with a relatively open weave; a type of structure which recently has won acceptance by papermakers as giving superior performance to the woven, or needled, structures of cotton duck, asbestos, and the like which previously were used. However, it should be noted that this reference is not intended to limit this invention, but is considered to apply to all fluid permeable, belt-like structures having the desirable characteristics which will enable their use as dryer fabrics.

In general, the dryer rolls are heated by introducing steam into the internal portions thereof, by infra-red radiation, or by other suitable means. In doing so, it has been found that the surface or shell temperature of the rolls may vary from end to end by as much as 40F, thus creating a distinct possibility that some portions of the paper web will be subjected to a greater drying action than other portions of the paper web, in turn creating the possibility that a non-uniform moisture profile will be set up in the paper web.

Further, in the dryer section of the machine, the water vapor generated as a result of the vaporization of water from the paper web tends to collect in enclosed areas or pockets in themachine. Some of these pockets are located in the areas enclosed by the individual dryer fabrics as they travel their respective endless paths while other of these pockets are located in the areas between the arrays of dryer rolls; these latter pockets being formed by the areas circumscribed by a dryer roll, the paper web as it serpentines its way through the dryer section of the machine, and a dryer fabric. If water vapor is permitted to build-up and collect in these pockets, it may, and generally will, affect further vaporization of water from the paper web. Generally more water vapor will accumulate in the central or middle portions of the pockets than in the portions of the pockets lying nearer the lateral edges of the machine, this being due to the fact that the lateral edges lie closer to the surrounding atmosphere and are thus more readily ventilated. Since such vapor does tend to build up unevenly in the pockets, this further increases the possibility that a non-uniform moisture profile will be set up in the web.

Thus, rather than having a flat moisture profile curve, the paper web usually will have a higher moisture content near the center than at the edges; a situation which is undesirable from the standpoint of quality control.

Furthermore, there is, in some cases, a tendency'for the peak of the profile to be shifted, more or less permanently for a given paper making machine, from the exact center of the sheet nearer one edge than the other. In large part, this is caused by the practice of, and necessity for, forcing ventilating air into the several pocket-like enclosures formed by the machine components, the dryer belts and the paper web from one side of the machine.

It will be apparent from the discussion which follows, however, that the principles of the invention herein disclosed may be practiced to rectify moisture profile discontinuities in a wide range of situations, regardless of their genesis or exact nature.

One suggestion for controlling the moisture profile of a paper web (and in particular to provide the web with a substantially'flat or uniform moisture profile) is to eliminate the vapor build-up in the dryer pockets by providing air jets or exhaust means which create a fresh air movement laterally through the dryer pockets or even at intermittent positions within each dryer pocket so as either to force or to remove the vapor therein to the surrounding atmosphere. However, as the trend in the papermaking industry today is toward machines of ever-increasingoperating width (on the order of 400 inches) it becornes increasingly more difficult and more expensive to provide such means to remove effectively the watervapor or other moist air from such machines. In fact, and due to the large width of thse machines, such means may increase rather than decrease the non-uniformity of the moisture profile of the paper web 'due to the great distances the air must travel. As such devices are mechanical in nature and generally require mechanical adaptation of existing machines, they may in many instances also be expensive, or even untenable.

Another proposed arrangement for exhausting this moist air is to provide means for directing fresh air through the dryer fabrics into the dryer pockets disposed on the opposite side thereof to force the moist air therein to the surrounding atmosphere. However, such arrangements generally require large pressures to force the fresh air into the pockets, such a pressure greatly increasing the risk of sheet flutter and/or sheet tear. Further, suitable sealing means must also be provided in such arrangements, thus adding to the cost and mechanical adaption required to produce the desired structure. Finally, such mechanisms are complex and required a substantial amount of special construction in order to adapt them to use in given papermaking machines.

Therefore, one object of this invention is to provide an improved means for controlling the moisture profile of a continuous sheet-like material formed on a papermaking machine.

Another object of this invention is to provide a simplified method for selectively controlling the moisture profile of a continuous paper web.

7 Another object of this invention is to provide means for establishing a uniform moisture profile across the width of a continuous sheet of paper or paper-like material.

A further object of this invention is to provide an improved endless belt construction which is used for guiding a continuous sheet-like structure through means for evaporating water therefrom, the endless belt being so constructed as to remove moisture from the sheet-like structure as it passes over the evaporating means.

SUMMARY OF THE INVENTION In apreferred embodiment of this invention, there is provided for use in a papermaking machine a fluid permeable belt (commonly referred to as a dryer felt or dryer fabric) for guiding a continuous sheet-like structure (such as a paper web) past means for evaporating liquid therefrom; such dryer fabric being so constructed that its permeability in a direction taken substantially across its width, i.e.,the direction transverse to the direction of travel of the belt, is-selectively varied. As such, it will provide a construction which may be used to control the moisture profile across the width of a -sheet-like web of paper or paper-like material BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified cabinet view of a portion of the dryer section of a papermaking machine in which this invention may be employed; I

FIG. 2 is a plan view of a portion of a fabric made in accordance with the principles of this invention;

FIG. 3 is a sectional view of one embodiment of this invention and is taken along the lines A-A of FIG. 2;

FIG. 4. is a sectional view of an alternate embodiment of this invention and is also taken along the lines A-A of FIG. 2;

FIG. 5 is a sectional view of still another embodiment of this invention and is also taken along the lines A-A of FIG. 2; and

FIG. 6 is a plan view of a portion of still another embodiment of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Turning now to FIG. 1 and a brief description of this invention, there is shown a simplified view of a portion of a dryer section of a papermaking machine. For purposes of discussion, it will be assumed that the continuous sheet-like structure is a web of paper or paper-like material and is travelling from left to right as viewed in the drawing. As shown, the dryer section includes a first (upper) and a second (lower) array of horizontally disposed, generally cylindrical, heated dryer rolls of either perforate or imperforate construction. The upper array includes the dryer rolls l0, l2 and 14 with the lower array including dryer rolls l6 and 18. A continuous web of paper 20 is received from the press section (not shown) of the machine and is passed in a serpentined manner seriatim about the dryer rolls. Specifically, the paper web 20 is first passed over and about upper dryer roll 10, then under dryer roll 16, and then over dryer roll 12 and so forth until ultimately it is passed about a portion of the surface of each of the dryer rolls in the machine. As such, water and other fluids within the paper web 20 will be evaporated therefrom due to its being held in contact with the dryer rolls.

Means areprovidedfor guiding the paper web 20 through the dryer section of the machine. Specifically, a first or upper fluid permeable belt 22 which has been made endless either by being woven as such or by being joined (hereinafter referred to as a dryer fabric) is arranged to press and maintain the paper web 20 in intimate heat transfer relationship with the upper array of dryer rolls,'by pressing the paper web against the surface of the heated dryer rolls to remove water and/or other fluids therefrom. As previously mentioned, the dryer fabric 22 is generally a woven structure which in this instance, must be a fluid permeable construction in order to permit readily the flow of air and/or water vapor therethrough. However, as previously mentioned, non-woven structures such as perforated plastic belts and the like have also been found suitable as it is not the intention of this invention to be limited to such examples as they are set forth by way of example only.

Fabric guide rolls 24 are provided on the machine and together with the dryer rolls define the path of travel of the dryer fabric 22 as well as maintain the fab ric 22 on the machine. While this invention is not directed to the particular construction of the fabric guide rolls 24, it should be noted that they do extend the width of the dryer fabric and are so arranged that sufficient tension is maintained on the fabric to ensure that v the paper web is held in intimate heat transfer relation with the upper array of dryer rolls.

A second or lowerfluid permeable endless belt 26 is associated with the lower array of dryer rolls for guiding the coutinuous paper web 20 through the machine.

good heat transfer relationship with the lower array of dryer rolls.

As the paper web 20 travels through the dryer sec- 25 tion, water is removed therefrom due to the web being maintained in intimate heat transfer relationship with the dryer rolls, in this instance by being held in physical contact therewith. The result is that water vapor, moist air and/or steam from the paper web tends to collect in the tent-like pockets between the dryer rolls. Since, by virtue of the ventilation problems previously discussed, a greater concentration of moist air and/or steam will tend to collect nearer the central or middle portions of the machine than at those portions nearer the lateral edges thereof and because all points of the dryer roll shell may not be at the same temperature, a nonuniform moisture profile and the paper web usually is experienced.

In accordance with the principles of the present invention, and referring now to FIGS. 2-6, there is shown means for selectively controlling the rate of water re.- moval (i.e., evaporation of moisture) from the paper web and which may be used to provide a uniform moisture profile ina paper web if such is desired. Specifically, there is shown in FIGS. 2-6 improved dryer fabrics which may be used to selectively control the rate of vaporization of water from the continuous web of paper 20. While it is understood that such dryer fabrics may be used as either an upper 22, lower 26 or both dryer fabrics in a machine, for purposes of explanation the fabric will be discussed as being disposed in the upper position and as such, will be associated with the upper array of dryer rolls.

Accordingly, the dryer fabric 32 shown in FIG. 2 is a woven construction having yarns 27 extending substantially in the machine direction (the direction in which the web travels) and yarns 29 extending substantially in the cross-machine direction (the direction across the width of the fabric or transverse to the path of travel of the fabric).

Referring now to FIG. 2 and the specific construction of the dryer fabric shown therein which has a selectively contolled permeability, it can be seen that the portions nearer the lateral edges of the fabric 32 have open areas which are smaller than those near the center, by virtue of which the edge regions are of a relatively low permeability in comparision to the center region while at the center or middle portion of the fabric the fabric is of a relatively higher permeability. While not wanting tobe limited to the specific arrangement of yarns as set forth above, it will be apparent that a selectively controlled moisture profile can be obtained in the continuous paper web 20 through use of a fabric made in accordance with this invention because those sections of the dryer fabric having relatively low permability provide only a small amount of open area through water vapor liberated from the web in process may escape. Thus, smaller amounts of water will be evaporated from the paper web in the edge areas than in the center region. However, in those areas of the fabric where a relatively high degree of permeability exists (such as in the middle), larger amounts of open area are present and thus, relatively larger amounts of water may be evaporated in those areas at the web, thereby permitting control of the moisture profile of the web. Specifically, since greater amounts of vapor accumulate in the center of the machine and therefore inhibit the vaporization rate from the web, those portions of the paper web adjacent the lateral edges of the machine are made to have a lower vaporization rate through reduction of the permeability of the dryer fabric in those areas of the machine.

In order to facilitate and simplify further discussion of this invention, it is to be noted that when a fabric is woven endless, the loom weft or filling yarns will lie in the direction of travel of the fabric (commonly referred to as the machine direction) whereas the loop warp yarns will lie in the direction transverse to the direction of travel of the fabric (commonly referred to as the cross-machine direction). However, it may be desired to weave the fabric flat and subsequently render it endless by interconnecting or joining the opposed ends (as by weaving or utilizing suitable mechanical means such as a pintle-clipper hook arrangement). In those instances, the loom warp yarns generally will lie in the machine direction whereas the loom weft or filling yarns generally will lie in the cross-machine direction.

Turning now to FIG. 3, there is shown that a dryer fabric which is one embodiment of the present invention, having a selectively controlled permeability across its width as a result of weaving the yams in such a manner that selected of those yarns, (e.g., those in the edge regions) which ultimately lie in the machine direction become more closely spaced with respect to one another in selected portions of the fabric than in other (e.g., center region) portions thereof. In this instance, those machine direction yarns 27A which lie nearer the lateral edge of the fabric 32 are made to be more closely spaced than are those machinedirection yarns 273 which lie nearer the middle portions of the fabric. Thus, the permeability of the dryer fabric will be less nearer the lateral edges thereof than in the middle portion. When the fabric is woven endless, such a yarn density variation may be accomplished by selectively varying the pick count as the fabric is woven so that there are more picks per unit length near the fabric edges than near its center. However, when the fabric is flat woven, such a result may be achieved by selectively varying the end count during weaving by increasing the density of warps in selected areas of the loom.

Turning now to FIG. 4, there is shown another embodiment of the fabric of this invention wherein a fabric also is made to have a selectively controlled permeability across its width. In this arrangement, the selectively controlled permeability is obtained by selectively varying the. diameter of the machine direction yarns. That is, those machine direction yarns 27C which lie in the area in which it is desired to reduce the vaporization rate of water from the web will be made to have a diameter greater than those machine-direction in order to provide a less. permeable area. Preferably, the center to center spacing of the individual machine direction yarns will be held constant; however, it may be selectively varied if such is desired. As with the embodiment of this invention shown in FIG. 3, the embodiment shown in FIG. 4, having a reduced open area or permeability of the fabric in those portions which lie nearer the lateral edges thereof, tends to compensate for the reduced vaporization rate nearer the center of the machine due to the greater moisture accumulation therein, thus permitting production of a paper web having a more uniform moisture profile.

Turning now to FIG. 5, thereis shown still another embodiment of this invention. In this instance, the machine direction yarns 27E which lie nearer the lateral edges of the fabric are made of a higher bulk construction than are those machine direction yarns 27F which lie near the central portions of the fabric. When such a fabric is run on a machine the higher bulk machine direction yarns 27E which lie nearer the lateral edges of the fabric will tend to flatten and close-off the effective open area between adjacent yarns, thus reducing the permeability of the fabric in these areas. Since thereby the higher bulk yarns prevent moist air from passing through .the yarns themselves, whereas the lower bulk density yarns more readily permit fluids to pass therethrough, a controlled moisture profile may be obtained across the paper web by selectively varying the bulk density of these yarns. Of course, bulk density in this context is to be distinguished from diameter per se in that the former contemplates deformability as well as size.

One such fabric may be made having selectively varied permeability by constructing the machine direction yarns 27F, which lie nearer the central portions of the fabric of a high twist. As such, they will be more able to resist flattening than will those machine direction yarns 27E which are located nearer the lateral edges of the fabric. As such, the center portions of the fabric will retain greater amounts of open space between adjacent yarns than will the portions of the fabric nearer the lateral edges.

Another construction of the dryer fabric having higher bulk yarns nearer the lateral edges thereof than in the central portions is one in which the machine direction yarns nearer the center portions of the fabric are of a continuous filament construction with the machine direction yarns nearer the lateral edges of the fabric being of a spun yarn construction. As with the previous arrangement, such a fabric construction has a higher degree of fluid permeability in the middle portions thereof than in those portions which lie nearer the lateral edges because the spun yarns in the edge regions will have a greater tendency to flatten than will those in the central regions.

Turning now to FIG. 6, there is shown still another embodiment of this invention in which the permeability of a fabric 32 may be selectively varied along portions across its width. As is well known in the papermakers art, fabrics such as dryer fabrics may be treated prior to being installed on the machine in order to provide them with good wear resistant qualities, to eliminate any tendencies to shrink or lengthen when subjected to the elevated temperatures and moisture conditions in the dryer section to stabilize them against sleaziness; one such treatment being described and claimed in U.S. Pat. No. 3,032,441 Beaumont et al. When such fabrics are not so treated, they may wrinkle and become sleazy, the result being to produce paper of unsatisfactory quality. In accordance with such treatments, the fabric is generally'treated with a suitable chemical, such as resin, the resin being cured and the fabric then being heat set at an elevated temperature.

According to the principles of this invention, selected portions of the fabric may be made to receive greater amounts of the treatment resins in order to vary selectively the permeability of the fabric across its width.

This effect may be achieved along with, independent of, or in addition to the aforesaid treatment for other purposes. In accordance with the aim of constructing a fabric which will provide a uniform moisture profile in a paper web, the portions 33 of the fabric 32 which lie nearer the lateral edges will have applied to them greater amounts of the treating chemical than those portions 35 which lie nearer the center portions of the fabric 32. As such, the treatment material will effectively close-off the open areas of the fabric, this apparently being due to the greater amounts of chemical encasing and/or becoming impregnated within the fabric yarns, thereby reducing its permeability in this area.

While not implying any limitation thereto, one method for selectively applying coating to the fabric is to spray greater amounts of an appropriate chemical onto those areas 33 of the fabric 32 which are to be of reduced permeability. In other instances, it may be possible to add the chemical to the fabric selectively while the fabric is on the machine, this, of course, permitting existing fabrics to be modified without being removed from the machine. Curing can then be done by infrared heaters or heated rollers. Still another method for treating the fabric, and this is generally done as the fabric is being made, is to run the fabric through a container in which the chemical is deposited. The container may be so designed that the desired portions of the fabric spend a longer period of time in the chemical, as by extending the length of the resin tanks in these regions.

While not wanting to be limited to specific fibers which may be utilized in the construction of such a dryer fabric, it is noted that multi-filament, monofilament, and/or yarns spun from staple fibers have all been found suitable for such a construction. Yarns may be made from synthetic materials such as nylon, Orlon, Dacron, Saran; natural fibers such as cotton, wool and staple fibers; and blends of both synthetic and/or natural materials.

It is obvious, of course, that various combinations of the above-mentioned arrangements can be used to vary selectively the permeability of a fabric across its width. This is because each machine, due to the type of paper or material being formed thereon and also due to the number and efficiency of the machine dryer rolls, may require individually tailored fabrics. However, from the preceding discussion, it can be seen that if a dryer fabric is constructed in accordance with the principles of this-invention, it provides a means for producing a continuous web selectively controlling the moisture profile of a paper or paper-like material. Further, such may be accomplished without changes or modifications or additions to the existing machine structure.

While I have shown and described only preferred embodiments of this invention, it will be obvious to those skilled in the art that additional changes and modifications may be made thereto without departing from this invention in its broader aspects. Therefore, it is the intention of the appended claims to cover all such changes and modifications'as fall within the true spirit and scope of this invention.

. What I claim as new and novel and describe to secure by Letters Patent of the United States is:

1.'A papermaking machine including,

a. An array of heated, generally cylindrical rolls for drying a continuous web of material passing at least a portion of the surface thereof; and,

b. An endless, fluid permeable backing fabric associated with said array of dryer rolls and arranged to maintain the web in intimate contact with at least a portion of the surface of each of said dryer rolls, thepermeability to fluids of said fabric varying selectively at selected points across its width dimension, said areas of said fabric having a high permeability lying adjacent those areas of the paper web having a high moisture content and said areas of said fabrichaving a low permeability lying adjacent those areas of the paper web having a low moisture content.

2. An endless fluid permeable woven belt, having yarns extending in the direction of travel of said belt and yarns extending in the direction of the width of said belt, for guiding a continuous sheet-like structure past means for evaporating liquids from said structure while pressing said structure against said means, said belt being characterized by having a permeability to fluids which is selectively varied in a direction taken substantially across the width of said belt at least in part by varying the amount of treatment material applied to the finished fabric.

3. An endless permeable belt as described in claim 2 wherein the permeability of said belt in the areas nearer the lateral edges thereof is substantially lower than the permeability of said belt in the areas nearer the central portions thereof.

4. A woven fluid permeable papermakers dryer fabric for use in the dryer section of a papermaking machine comprising yarns extending substantially in the machine direction and yarns extending substantially in the cross-machine direction, the number of said machine direction yarns per unit of width of said fabric being greater in those areas of said belt nearer the lateral edges thereof than in those areas nearer the central portions thereof so that the permeability of said fabric across its width is greater in those areas nearer the middle portions of said fabric than in those areas nearer the lateral edges thereof.

5. A woven fluid permeable papermakers dryer fabric for use in the dryer section of a papermaking machine comprising yarns extending substantially in the machine direction and yarns extending substantially in the cross-machine direction, the diameter of said machine direction yarns being larger in those areas of said fabric nearer the lateral edges thereof than in those areas nearer the central portions thereof so that the permeability of said fabric across its width is greater in those areas nearer the middle portions of said fabric than in those areas nearer the lateral edges thereof.

6. A woven fluid permeable papermakers dryer fabricfor use in the dryer section of a papermaking machine comprising yarns extending substantially in the machine direction and yarns extending substantially in the cross-machine direction, the spaces between yarns in those portions of said fabric which lie nearer the lateral edges thereof containing a greater amount of added treating chemical than the spaces between yarns in those portions of said fabric which lie nearer the center thereof so that the permeability of said fabric across its width is greater in those areas nearer the middle portions of said fabric than in those areas nearer the lateral edges thereof.

7. In an apparatus for drying a continuous sheet of material, in combination, drying means an endless fluid permeable belt movable in conjunction with said sheet and arranged to press said sheet against the drying means in said apparatus wherein as to the portion of said belt lying between the selvedges thereof the permeability of said belt in the areas nearer the lateral edges of said portion differs substantially from the permeability of said belt in the areas nearer its central por tion.

8. In an apparatus for drying a continuous sheet of material, in combination, drying means an endless fluid permeable belt movable in conjunction with said sheet and arranged to press said sheet against the drying means in said apparatus wherein as to the portion of said belt lying between the selvedges thereof the permeability of said belt in the areas nearer the lateral edges of said portion is substantially lower than the permeability of said belt in the areas nearer the central portions thereof.

9. An endless fluid permeable belt as described in claim 8 wherein said belt is a woven structure having yarns extending in the direction of travel of said belt and yarns extending in the direction of the width of said belt.

10. An endless fluid permeable belt as described in claim 9 wherein the permeability of said woven fabric structure across its width dimension is selectively varied at least in part by varying the number of yarns per unit of width which extend in the direction of travel of said belt.

11. The endless fluid permeable belt described in claim 9 in which the permeability of said woven fabric structure across its width dimension is selectively varied at least in part by varying the bulk of at least some of the yarns in said areas which extend in the direction of travel of said belt.

12. The belt described in claim 9 in which the width dimension permeability is selectively varied at least in part by varying the amount of treatment material applied to the finished fabric.

13. In apparatus for removing moisture from a web of paper in the dryer section of a papermaking machine, in combination, a plurality of rotatable dryer cans over which a web of paper to be dried is guided seriatim, and means for driving an endless fluid permeable woven dryer fabric through an endless path to hold said web in heat transfer relation with a substantial portion of the periphery of at least one of said dryer cans, said dryer fabric being characterized by comprising yarns extending substantially in the machine direction and yarns extending substantially in the cross-machine direction, each of said yarns being so spaced from each next adjacent of said yarns that as to the portion of said belt lying between the selvedges thereof the permeability of said fabric across its width is greater in those areas nearer the middle of said portion than in those areas nearer the lateral edges of said portion.

14. The dryer fabric as described in claim 13 wherein the number of said machine direction yarns per unit of width of said belt is greater in those areas of said belt nearer the lateral edges thereof than in those areas nearer the central portions thereof.

15. A dryer fabric as described in claim 13 wherein the diameter of said machine direction yarns is larger in those areas of said belt nearer the lateral edges thereof than in those areas nearer the central portions thereof.

16. The dryer fabric described in claim 13 wherein the bulk of said machine direction yarns of those yarns which lie nearer the lateral edges of said fabric is higher than those yarns which lie nearer the middle portions of said fabric.

17. The dryer fabric described in claim 13 wherein the spaces between yarns in those portions of said fabric which lie nearer the lateral edges thereof contain a greater amount of added treating chemical than are those portions of said fabric which lie nearer the center thereof.

18. Papermakers dryer fabric means for use in a machine for drying webs of material wherein said machine has at least one rotatable dryer roll about which a web to be dried is passed and wherein said dryer fabric is driven through an endless path to .hold said web in heat transfer relation with a substantial portion of the periphery of said dryer roll, said fabric being characterized by having the lateral edges of the portion thereof lying between the fabric selvedges having open areas which are smaller than the open areas near the center of said portion.

Claims

1. A papermaking machine including, a. An array of heated, generally cylindrical rolls for drying a continuous web of material passing at least a portion of the surface thereof; and, b. An endless, fluid permeable backing fabric associated with said array of dryer rolls and arranged to maintain the web in intimate contact with at least a portion of the surface of each of said dryer rolls, the permeability to fluids of said fabric varying selectively at selected points across its width dimension, said areas of said fabric having a high permeability lying adjacent those areas of the paper web having a high moisture content and said areas of said fabric having a low permeability lying adjacent those areas of the paper web having a low moisture content.

6. A woven fluid permeable papermakers dryer fabric for use in the dryer section of a papermaking machine comprising yarns extending substantially in the machine direction and yarns extending substantially in the cross-machine direction, the spaces between yarns in those portions of said fabric which lie nearer the lateral edges thereof containing a greater amount of added treating chemical than the spaces between yarns in those portions of said fabric which lie nearer the center thereof so that the permeability of said fabric across its width is greater in those areas nearer the middle portions of said fabric than in those areas nearer the lateral edges thereof.

7. In an apparatus for drying a continuous sheet of material, in combination, drying means an endless fluid permeable belt movable in conjunction with said sheet and arranged to press said sheet against the drying means in said apparatus wherein as to the portion of said belt lying between the selvedges thereof the permeability of said belt in the areas nearer the lateral edges of said portion differs substantially from the permeability of said belt in the areas nearer its central portion.

18. Papermakers dryer fabric means for use in a machine for drying webs of material wherein said machine has at least one rotatable dryer roll about which a web to be dried is passed and wherein said dryer fabric is driven through an endless path to hold said web in heat transfer relation with a substantial portion of the periphery of said dryer roll, said fabric being characterized by having the lateral edges of the portion thereof lying between the fabric selvedges having open areas which are smaller than the open areas near the center of said portion.