US3215592A

US3215592A - Paper press arrangement with automatic control of press felt moisture content

Info

Publication number: US3215592A
Application number: US275764A
Authority: US
Inventors: Edgar J Justus; Edward D Beachler; Charles W E Walker
Original assignee: Beloit Corp
Current assignee: Beloit Corp
Priority date: 1963-04-25
Filing date: 1963-04-25
Publication date: 1965-11-02
Anticipated expiration: 1982-11-02

Description

.JUSTUS ETAL 3,215,592

NT WITH AUTOMATIC CONTROL OF EL MOISTURE CONTENT Nov. 2, 1965 PAPER PRESS ARRA PRESS Filed April 25, 1963 5 Sheets-Sheet 1 .[nVEntUT'5 V ATZTORNEYS Nov. 2, 1965 E. J. JUSTUS ETAL 9 PAPER PRESS ARRANGEMENT WITH AUTOMATIC CONTROL OF PRESS FELT MOISTURE CONTENT Filed April 25, 1963 5 Sheets-Sheet 2 Nov. 2, 1965 E. J. JUSTUS ETAL 3,215,592

PAPER PRESS ARRANGEMENT WITH AUTOMATIC CONTROL OF PRESSFELT MOISTURE CONTENT Filed April 25, 1965 5 Sheets-Sheet 3 A TORNE YS Nov. 2, 1965 E. J. JUSTUS ETAL PAPER PRESS ARRANGEMENT WITH AUTOMATIC CONTROL OF PRESS FELT MOISTURE CONTENT 5 Sheets-Sheet 4 Filed April 25, 1963 6.5% 10070 FELT 504 5 D/PY E/VTEAV/VG PEA-55 1965 E. J. JUSTUS ETAL 3,215,592

PAPER PRESS ARRANGEMENT WITH AUTOMATIC CONTROL OF PRESS FELT MOISTURE CONTENT Filed April 25, 1963 5 Sheets-Sheet 5 A ORNEYS United States Patent PAPER PRESS ARRANGEMENT WITH AUTO- MATIC CONTROL OF PRESS FELT MOIS- TURE CONTENT Edgar J. Justus, Edward D. Beachler, and Charles W. E. Walker, Beloit, Wis., assignors to Beloit Corporation, Beloit, Wis., a corporation of. Wisconsin Filed Apr. 25, 1963, Ser. No. 275,764 6 Claims. (Cl. 162-252) This is a continuation-in-part of our application Serial No. 13,902, filed March 9, 1960, which was copending with the instant application and is now abandoned.

The present invention relates broadly to the art of paper making, and is more particularly concerned with new and improved method and apparatus for mechanically removing water from a paper web, having among the features thereof separation of the functions of web water removal and felt water removal together with precise control of the loading at the web press nip, so that the web bulk is preserved while attaining a superior degree of water removal and a markedly improved web surface finish.

It is conventional practice in paper making machines to provide a press section immediately following the forming or Fourdrinier part of the machine, and such press sections generally comprise a number of pressing units having pairs of rolls in nip-defining relation to effect successive degrees of water removal from the paper web prior to its delivery into the following drying part. As is of course also recognized, the mechanical removal of water is substantially more economical than the use of heat energy.

It has also become common to employ suction press rolls in such press units to assist in the removal of water from the nip. In addition to the inherent advantages of the suction, the suction shell perforations provide additional space into which the water entering the nip in the web and in the felt may be displaced by the mechanical pressure in the nip. However, the non-uniformity of contact pressure and of water removal rate, occasioned by the perforations in the suction roll, frequently produce a pattern in the web which is termed in the art shadow markings. Additionally, the mechanical pres- :sure applied to the nip is limited by the total water volume and the fiber solids contained both in the web and in the felt. Thus, if more water is presented to the nip than can be accommodated by the inter-fiber spaces and/ or in the suction roll perforations, a backward flow condition occurs within the nip entry. When this occurs in or on the web, it is termed crushing in the :art, and constitutes a disruption in the desired fiber arrangement or formation.

In addition, production schedules for many paper machines require relatively frequent changes in the type and grade of product. Certain grades of paper demand that the pressing and other treatment not reduce the thickness or caliper of the web, and this in turn requires that the nip loads in a press part be relatively light; however, necessarily this reduces the effectiveness of the water removal, and consequently later amounts of water must be removed by the relatively more expensive thermal drying means. On the other hand, certain other paper products required from the same paper machine permit or even demand more severe pressing, and in order to achieve some measure of versatility with the same paper machine, one practice followed by the art to accomplish the noted changes is the removal of the press rolls for regrinding to a different amount of crowning. Obviously, this practice is both expensive and time consuming.

3,215,592 Patented Nov. 2, 1965 ice It is accordingly an important aim of the present invention to provide a novel method and apparatus for pressing paper and related fibrous materials, characterized by markedly improved water removal effectiveness .and the avoidance of machine structure changes in order to accommodate different types and grades of paper products.

Another object of this invention lies in the provision of a divided press assembly wherein the functions of Web water removal and felt water removal are separated and the loading in the web press nip controllably adjusted to a precise degree in accordance with the character of the web being processed, resulting in the important advantages of preservation of web bulk, greater water removal effectiveness and markedly improved web surface finish.

A further object of the instant invention is to provide a divided press assembly which comprises a looped press felt, a web pressing couple including a pair of press rolls receiving said felt and a paper web to remove water from the web by transfer to the felt, means for loading one of said press rolls in accordance with the character of the Web being pressed to attain a high degree of water removal without substantial reductions in the web bulk, and a felt pressing couple including a pair of press H rolls receiving said felt free of the web to remove a sufficient quantity of the transferred water from the felt' so that said felt is returned to the web pressing couple in a condition suitable for a high degree of water removal at said couple.

A still further object of this invention lies in the provision of a method of removing water from a traveling paper web contacted by a looped press felt, and which features the steps of advancing the web to a first press nip into pressing contact with the felt to transfer water from said web to said felt, controlling the pressure at said nip in accordance with the character of the web to attain a high degree of water removal without substantial reductions in the caliper of the web, and directing the water laden felt to a second press nip free of the web to remove a sufficient quantity of the transferred water so that said felt is returned to said first press in a condition less than saturated when said felt is compressed in said first press nip.

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.

On the drawings:

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

FIGURE 1 is a more or less diagrammatic representation of an illustrative pickup and press section of a Fourdrinier paper machine, and embodying therein an exemplary form of divided press assembly constructed in accordance with principles of this invention;

FIGURE 2 is a detail sectional view of a press roll covering which may be used at one or more locations in the arrangements of FIGURE 1;

FIGURES 3 and 4 are diagrammatic representations of modifications which can be effected in the divided press assembly of this invention;

FIGURE 5 is a diagrammatic view of a pair of plain presses and a separated suction press constructed and arranged in accordance with the novel concepts of this invention;

FIGURE 6 is an elevational view, with parts in section, of an anti-deflection roll which may be utilized as a part of the web press of this invention;

FIGURE 7 is a partial diagrammatic view of a felt press arrangement representative of one modification which can be effected in the structure of FIGURE 5;

FIGURE 8 is a graph plotting thereon a typical curve indicative of optimum felt dryness for the maximum removal of Water;

FIGURES 9, 10 and 11 are essentially diagrammatic views showing preferred embodiments of the invention.

Theory and advantages of invention The instant invention involves water removal from a moist web according to principles that differ completely from those involved in the conventional suction press nip. In the suction press nip, the roll shell is perforate, being provided with a multiplicity of holes of substantial size (i.e. at least about inch in diameter and usually having flared peripheral mouths of greater size) which. are drilled entirely through the roll shell (having at least about 1 inch thickness) to communicate with the suction gland extending the full width of the roll shell interior opposite the nip. At the suction nip a press felt is interposed between the web and the perforate suction roll shell (primarily as a water-permeable protective layer for the web) and water expressed from the Web passes completely through the felt and into these holes in the perforate shell. Some water continues into the gland and some is usually retained in these holes at the offrunning side of the nip, where the subatmospheric pressure in the gland tends to counteract centrifugal forces urging water droplets back out of the holes and against the felt under ambient atmospheric pressure. The felt may thus remain in contact with the Web at such offrunning side of nip without substantial re-wetting of the web (via water thrown back on the felt from the suction roll holes). Also, savealls are conventionally positioned between the felt and the perforate roll shell at the immediate off-running side of the nip to catch droplets released from the suction roll holes, particularly after these holes pass beyond the limit (i.e. the ofi-running seal) of the interior suction gland so there is no longer a pressure differential holding the droplets in the holes. The off-running felt must be guided to avoid such a saveall and this often results in guiding the felt with or against the web at the off-running side of the nip. The perforate suction roll with its suction gland, and with or without the saveall, thus functions to carry away substan tially all of the water expressed from the web at the nip.

In contrast, in the instant invention, the press roll shell (e.g. the steel shell 18a of FIGURE 2) is imperforate in that it does not have perforations or holes extending through to the interior of the shell. A myriad of very fine blind (drilled) holes such as those indicated in US. Patent No. 3,023,805 issued to Walker and in FIGURES 2 and 6 hereof may be used, but these have very small diameters (e.g. to 4 inch or even less in the case of the blind pores or micropores on other rolls used herein) and as such these holes do not cause the extreme shadow marking that is characteristic of the performance of the perforate suction rolls with most webs. The differences in the principles of Water removal, as well as function of the felt, are, however, fundamental, in nature.

In the web press part of the instant divided press, the felt is used not as a permeable member through which water is passed to some other device (such. as the suction roll gland and/or suction roll shell holes) for removal from the system. The basic process concept involves pressing a wet web against a felt having 60 to 70% (bone) dryness to transfer water to the felt (and substantially saturate the same under the pressure conditions of 200 to 450 lbs. per inch of machine width), then separating the felt and web and substantially simultaneously relieving thepressure, next pressing the felt alone at substantially the same and preferably slightly more pressure while subjecting the felt to a pressure differential (in a suction press) to reduce the water content again to 60 to 70% dryness, and, finally, bringing the felt back into Conta with the moist web.

If the web press involves two solid rolls, then the Water is transferred from the web solely to the felt, which is separated from the web at the off-running side of the web press nip. If the felt covers a blind drilled roll having an imperforate shell, some of the water temporarily enters the blind drilled holes at the web press nip (if the Water load is substantial), but most if not all of such Water is picked back up by the felt immediately after the nip, so the felt must be separated from the web as quickly as possible to minimize re-wetting. This is particularly true with a porous or blind drilled roll because there is theoretically a greater time interval involved with water passing from these pores in the roll through the felt to the web than with water passing merely from the felt body to the Web. The .felt does ordinarily reabsorb the Water from the pores or blind holes rapidly, however, because there is no suction gland resisting such movement of water. Instead, there may be small amounts of entrapped air under pressure at the bottom of blind holes urging the water back out against the felt at the ofi-running side of the web press nip.

It will thus be seen that, in the instant web press, the felt covered roll has an imperforate shell with a solid periphery or with a peripheral portion or cover having a myriad of small water-retaining recesses (e.g. Mi inch or less; and preferably Ms inch or less in average diameter) on the roll surface whereby water expressed from the felt at the web press nip may be received by such surface, retained therein at the nip and released therefrom at the off-running side of such nip.

In this respect, there is a distinct difference in result as well as principle in the shadow marking phenomenon. With a suction roll the large holes afford large areas of unsupported felt adjacent supported areas (i.e. suction roll land areas) and the marking tendency is additionally increased because the suction gland maintains substantially subatmospheric pressure behind the unsupported felt areas over the holes. In contrast, in the divided press the felt is completely supported by a solid roll or the felt is substantially completely supported by a porous or blind drilled (rubber covered) roll not only because the felt bridges only very small areas without solid backing but also because the water driven into these small areas or holes is ordinarily urged back against the felt by entrapped compressed air in such holes. The pressure difference between the supporting land areas and the small pores or holes containing water backed by compressed air is thus comparatively insignificant with respect to uniform support for the felt against the web. The entire force balance at the Web nip is thus radically different. The benefits of passing substantial loads of water through the press nip without crushing the webare thus obtained without the conventionally related disadvantage of shadow marking.

Still another important advantage of the instant divided press (as contrasted to the suction web press) is that the imperforate press roll shells which define the web press nip may be and generally are anti-deflection rolls, which can be supported on their shafts substantially inwardly from the shell ends so as to define extremely uniform Web press nips, and nip pressures on the web in the cross-- machine direction. Conventional anti-deflection roll structures or supports are not possible with suction roll. shells, mounting the conventional suction glands.

. As shown on the drawings:

Referring nowto FIGURE 1, there is shown a paper machine generally designated by the numeral 10 and comprising a forming wire F looped over a suction couch roll 11 and a turning roll 12, the couch roll having a suction area 110, and if desired, a saveall 13 in association therewith. The forming wire F supports a paper web W thereon over the couch roll 11 and along a downwardly inclined wire run Fa.

The paper web W is removed from the downwardly inclined wire run Fa by a looped pickup felt 14 which urged against the web W by a suction pickup roll having a suction area 15a. The pickup felt 14 is also trained around a plurality of guide rolls 16, a tension roll 17 and a press roll 18 of a transfer press assembly, generally designated at 19, and further comprising a suction press roll 20 having a suction area 20a. By action of the pickup felt 14 and suction pickup roll 15, the paper web W is carried along the underside of lower run 14a of the pickup felt to the transfer press assembly 19.

If desired, the top press roll 18 may be constructed in the manner of FIGURE 2, comprising a cylindrical metal shell 18:! to which is suitably secured an elastomeric covering 18b provided along its outer diameter with an array of blind drilled holes 18c of predetermined depth, diameter and spacing (more specifically described in Walker US. Patent No. 3,023,805, incorporated herein by reference). The blind holes 180 are effective to receive water from the relatively wet pickup felt 14 upon entry of the felt into nip N, to hold the water in the blind holes during passage of the felt through the nip, and to release the water to felt upon its exit from the nip, whereby there is eliminated crushing occasioned by the presence at the nip of excessive volumes of water in both the pickup felt and the paper Web. If this type press roll is employed, the rubber covering 18b is desirably of relatively low deformability, so that substantial volumes of air are not entrained in the blind holes to spew the water from said holes when the pickup felt advances beyond the nip N to the off-running side thereof. As will be later noted, generally the structure of FIGURE 2 may be utilized with an anti-deflection roll in the improved divided press assembly of this invention.

At the transfer nip N the paper web W is transferred to a press felt 21 within the loop of which is a plurality of guide rolls 22 and a tensioning roll 23, while outside of the loop are additional guide rolls 24.

Downstream of the transfer or first press 19 is a second press 25 to which the paper web W is directed and carried by the upper surface of the top run 21a of the press felt 21. The second press section 25 is comprised of a top suction roll 26, having a suction area 26a, and a lower press roll 27 (which may be rubber covered) within the loop of the press felt 2.1. The top suction roll 26 may have in association therewith a saveall 28, and wrapping the suction roll 26 is an upper looped press felt 29 trained around a plurality of guide rolls 30, and if desired, around a tensioning roll 31.

It is, of course, appreciated that wide variety of pickup and press sections are known to the art, and it will therefore be understood that the arrangement of FIGURE 1 with respect to the felts 14, 21 and 29 is intended to be merely illustrative of an exemplary environment for the divided press assembly of this invention, generally designated in FIGURE 1 by the numeral 35. This assembly is illustratively indicated in FIGURE 1 as downstream of the second press 25, although it will be readily apparent as the description proceeds that the divided press 35 could as well be at the second press section, or at other locations benefitted by the novel results obtained through use of this improved press assembly. Additionally, while in FIGURE 1 both top and bottom press felts are shown, this is not necessary in all applications, as will be more fully appreciated when reference is made to succeeding views of the drawings (e.g. FIGURE 11). As well, while in FIGURE 1 a suction pressing couple is indicated in a bottom position, a modification is to have the suction pressing couple in a top position, which also will be specifically described in connection with other views of the instant application drawings (e.g. FIGURES 4 and 10).

Extensive investigations have demonstrated that markedly more effective water removal at the web press nip is obtained when the press felt is presented to the nip in a particular condition of dryness or in a less than saturated condition, and as a corollary, when the felt upon entry to the Web press nip is controlled as to its moisture content, substantially greater nip pressures can be applied without markedly effecting the web bulk or encountering the crushing conditionto which earlier reference was made. Desirably, precise control of the pressure at the web press nip is obtained by utilization at said nip of at least one anti-deflection roll, so that the nip pressure can be adjusted in accordance with the character of the web being processed, and thereby the roll crown and nip pressure varia tion obtained without the necessity of press roll removal for regrinding purposes. The instant invention further features separation of the functions of web water removal and felt water removal, and to assure that the felt is presented to the web press nip at optimum dryness, water may be added thereto either manually or in response to a signal provided by a web moisture content measuring device located in sensing relation with the felt. This same measuring device may control the nip pressure at the felt pressing couple, and the instant description will note with an explanatory theory that the nip pressure at the felt press is preferably at least equal to or in excess of the nip loading at the web press to assure that the felt is delivered to the web press at an effective optimum dryness.

More specifically, it has been discovered that as the moisture in the felt is reduced, the web is more effectively dried, subject, however, to the limitation that if the felt is dried beyond its particular optimum range, its aflinity for water appears to be reduced and the effectiveness of the instant method is diminished. In the extreme, of course, damage to the felt may occur as a result of overdrying. Up to the particular indicated optimum dryness, the removal of free moisture from the felt provides additional void space for the water expressed from the web by the nip pressures. This avoids the damaging backflow or crushing earlier noted.

Referring to FIGURE 8, there is plot-ted felt percent bone dryness entering the web press against the paper percent .bone dryness leaving the same press. It is pertinent to note that as the moisture in the felt is reduced, the paper is more effectively dried up to a point at which the felt contains approximately fiber. Beyond this point the water removal effectiveness tends to again decline.

It should be noted in this connection that the men tioned 65% fiber dryness applies to a 100% wool felt, while with a felt containing 20% synthetic fibers and 80% wool fibers, optimum dryness is fiber. A 100% cotton felt, on the other hand, has an optimum dryness generally between and However, in the discussion to follow, reference is made to a wool felt for illustration, and as noted, most effective water removal is obtained at 65% fiber in the wool felt (or approximately 60% to 70% Indicated on the same graph is an encircled point more or less arbitrarily chosen as the point of the selected operating condition of felt dryness, and generally speaking substantial departures from this point result in either crushing or felt damage, as will be further discussed hereinafter.

The encircled point on the plot in FIGURE 8 may be noted to :be beyond the optimum 65% felt dryness. Investigations have established that when the felt is delivered to the web press nip at optimum bone dryness, there is still contained in the web more water than can be accommodated at the nip, with the result that there is not sufficient void space left to take on more water. The crushing condition earlier noted may then arise unless the press roll adjacent the felt contains pores or small holes as in FIGURE 2 to accommodate the water. Such holes in the press roll may cause some rather slight press marking of the sheet (which is actually very nominal in most paper webs compared to the substantial marking of the web caused by the holes drilled through the perforate shell of a suction roll as previously stated) so that the alternative is to operate with no holes and the felt drier than optimum. The felt should not, however, be drier than is necessary for this purpose, since loss of water removal from the Web result-s, as indicated in FIGURE 8, and there is a danger of damaging the felt which can occur if the felt is too dry. The encircled point in FIGURE 8 indicates a desirable compromise, and will be the point of effective optimum dryness. When a blind drilled or porous press roll is used in the web press, the point of optimum felt dryness will also be the effective optimum dryness.

Markedly improved water removal effectiveness, a superior web surface finish, and preservation of the web bulk are obtained by the instant divided press assembly 35, featuring means to precisely load the web press nip to particular values in accordance with the character of the web being processed, and further featuring separated web pressing couples and felt pressing couples whereby the felt moisture content is accurately controlled and the earlier noted difficulties associated with a suction press roll at the web press nip eliminated. Referring now again to FIGURE 1, one form of divided press assembly 35 may comprise a first or plain press 36 providing a web pressing couple, and comprised of an upper press roll 37 defining a nip N-2 with a lower press roll 38, each having rotary imperforate shells. An exemplary structure for at least the upper press roll 37 will be shortly described (i.e. FIGURE 6). Received at the nip N-Z in wrapping relation with the upper press roll 37 is a looped press felt 39 trained about guide rolls 40. Obviously, as will be noted in connection with succeeding views of the drawings (e.g. FIGURES 3 and 11), an upper press felt 39 is not always used in the instant invention, and also, suction press couple 44 could be in an upper position above the couple 36 and acting upon the felt 39 (as in FIGURE In this modification the lower felt 41 would of course not necessarily be used (e.g. FIGURE 12). In FIGURE 1 (and FIGURES 4 and 10) two felts are used so that the web obtains better protection at the press nip N-2, and one obtains the advantages of having either or both press rolls 37 and 38 with water-retaining pores therein to minimize crushing of the web. The felt 35 here shown has nominal function in water removal from the web W, but it protects the web W against marking by the blind drilled holes on the surface of the roll 37 (see FIGURE 6, infra) while still permitting these holes to function to relieve crushing of the web at the nip N-Z.

The lower press roll 38 of the web pressing couple 36 is wrapped by a lower press felt 41 trained about guide rolls 42, and if desired, tensioning rolls (not shown) can be employed in the manner known in the art. The lower press felt 41 in the embodiment of FIGURE 1 receives water transferred from the web W at the nip N-2, and whether the top felt 39 is or is not employed, the lower press felt 41 upon passage through the nip N-2 with the-web water transferred thereto is directed to a felt pressing or suction press couple 44 to remove a quantity of the transferred water therein, whereby the press felt 41 is returned to the nip N-Z in a less than saturated condition or in a condition for maximum water removal effectiveness at said nip.

The felt pressing or suction press couple 44 is comprised of an upper plain press roll 45 in nip-defining relation with a lower suction press roll 46 having a suction area 46a therein (outside the loop of the felt 41). The rolls of the felt pressing couple 44 define a nip N-3. In order to evenly distribute the water within the press felt 41, to assit in washing the paper web fibers from the felt, and to assist in water removal at the nip N-3, shower means 47 may be employed at the oncoming side of said nip within the loop of the felt 41. The shower means may operate continuously or intermittently, and may be manually under control of valve means 48 to discharge a predetermined water volume into the felt 41, so that the felt 41 is delivered or presented to the nip N2 in a condition of effective optimum dryness. As will be noted hereinafter, the shower 47 may be under control of moisture detection means.

It will be appreciated that fibers, clay, and the like loose solids tend to collect on the operating or peripheral outside of the felt 41 which actually engages the web W at the nip N-Z. The suction roll 46 engages the operating or outside of the felt loop to pick such'solids off the felt surface, rather than trying to draw them through the body of the felt which would greatly decrease the operating life of the felt. Water is applied at the shower 47 from within the loop of the felt 41 so that (the solids are not washed into the felt and) the flow of water in the felt 41 will tend to be outwardly past the operating sur face and toward the suction area 46a of the suction roll 46 outside the left loop.

In accordance with this invention, one or preferably both of the rolls of the web pressing couple 36 is provided as an anti-deflection roll in order to readily and accurately control the pressure at nip N-2 in accordance with the particular type or grade of paper product be ing pressed. An exemplary form of anti-deflection roll is illustrated in FIGURE 6 and the numeral 37 has been appended thereto. As shown, the roll 37 comprises a generally cylindrical inner shell 49 having a shaft or axle 50 extending axially therethrough. The shaft 50 is provided with an axial internal bore 50a extending substantially along the entire length thereof, and which communicates with a suitable fluid such as air under pressure through a conduit 50b. The terminal end of the bore 50a communicates with a pair of radially extending fluid flow passages 50c and 50d, although of course more than a pair of passages may be provided. As appears in FIGURE 6, the shaft 50 is provided with a plurality of pairs of radially extending peripheral shoulders 50a spaced axially on either side of the passages 50c and 50d.

Between each of the sets of shoulders 50e and bearing against the shaft 50 and shell 49 is a resiilently inflatable tire 51 of generally toroidal shape and having therewithin an annular space 52 which is inflated with the fluid under pressure. The inner annular space 52 of each tire 50 communicates through the radial flow passages 50c and 50d with a source of pressurized fluid, admitted to the axial bore 50a through the inlet 50b.

Carried by the outer diameter of the cylindrical shell 49 and suitably secured thereto is an elastomeric cover ing 53. The rubber covering 53 on the cylindrical shell 49 may be noted from FIGURE 6 to be provided with a plurality of blind drilled holes 53a, provided for the purpose of receiving, retaining and releasing moisture transferred to the upper press felt 39 from the web W passing through the nip N-Z. Essentially, in this respect the holes 53a in the rubber covering 53 and the holes in the rubber covering 18b perform the same function. As will be later noted, generally similar results may be obtained by utilization of a cylindrical press roll shell to which is molded or otherwise secured a ceramic shell having a controlled degree of porosity.

Referring again to FIGURE 6, it is believed noW apparent that when pressurized fluid is admitted to the annular passages 52 of the inflatable tubes 51, the shell 49 is so supported at intermediate points that the deflection due to nip loading is reduced to an amount which is negligible in practice. Anti-deflection rolls are well known to the art, and illustrative constructions are disclosed in Patent Nos. 2,648,122; 2,651,103 and 2,651,241, and in co-pending U.S. applications Serial No. 102,571, filed April 12, 1961 and Serial No. 154,801, filed November 24, 1961, in the name of E. J. Justus, all of which are included herein by reference. By the structure of FIGURE 6, and in contrast with the noted prior art expedient, the nip pressure at N-2 may be readily varied in accordance with the character of the web being processed, and there is no longer required the expensive and time consuming tasks of removing and recrowning the press rolls.

A comon feature of all of such anti-deflection rolls is that the rolls are provided with imperforate shell structures (with or without blind drilled rubber covers, porous covers, etc.) which are supported substantially or appreciably axially inwardly from the shell ends by support means within the shell carried on shaft means for rotation of the shell. As used herein, the term anti-deflection roll means a roll having such structure described in any of the aforesaid patents and/or applications. This type of structure is not possible with the conventional suction roll shell (having an axially co-extensive interior suction gland). In fact, the perforate suction roll shell is comparatively more delicate than the convention imperforate shell structure; and particularly in the case of high pressure nips using suction rolls, it has been found preferable to load the suction roll from beneath, either with a supporting anti-deflection roll (as in the case of the roll 102 of FIGURE 7 which is explained in detail hereinafter) or with an operating nip-defining roll as shown in FIGURES 10, 11 and 12. Loading of the suction roll in this manner is usually preferred for matching or exceeding the nip loads at the web press nip.

The nip N2 is loaded to a predetermined degree by the anti-deflection roll 37, and as is indicated on the upper press roll 45 of the felt pressing couple in FIGURE 1, the roll 45 mounts suitable load applying means. In this manner there is obtained independent control of loading suitable to the separated requirements of maximum water removal from the web being treated and optimum water removal from the felt alone. Both the web and the felt may be regarded as elastic materials, and as such are reduced in total thickness to an appreciable degree during passage through the nip of a pressing couple. Generally speaking, the reduction in thickness of the felt is a much greater fraction of its unpressed thickness than is the reduction of thickness of the web. The water carried into the nip either by the web or by the felt is of course incompressible. The elastic expansion of both the felt and the web on leaving the nip tend to create suction forces, in addition to capillary attraction, which cause both to accept any available water. If the felt is too dry, air will remain in its interstices even under compression and with its expansion suction will be reduced. Under these circumstances, the web will draw water from the felt on leaving the nip. Any such rewetting of the web is, of course, minimized by separation of the felts 39 and 41 from the web W at the immediate off-running side (i.e. right hand side in FIGURE 1) of the nip N-2, which is done by the off-running guide rolls 40 and 42.

In the operation of the web press part 36 of this invention, it is preferable that the nip pressures used be limited to permit the felt and web to pass through the extreme pressure zone of the nip so that the combination is in a less than completely filled or saturated condition, or in a saturated condition when auxiliary means are employed to remove excess water provided the risk of nominal shadow marking can be tolerated. This is thought to promote the most effective water transfer from the web to the felt. It also insures that the damage resulting from crushing will be avoided. It will then be apparent that the felt only press couple will preferably be operated at nip pressures at least as great, and usually greater, than the nip pressures of the web press. In the nip containing only the felt, it is necessary to employ nip pressures sufficiently high to drive an excess of water from the felt in order to remove it. To accomplish this, the felt passing through the nip N-3 must be so compressed that it is saturated with less water than is actually brought to the nip, whereby an excess is driven (along with any solids or dirt on the outside of the felt 41) into the perforations of the suction roll 46. This is possible because the back-washing effect is much less damaging to the woven fabric structure of the felt, than it would be to the nonwoven fiber network of the web. The nip pressures used will be limited, as previously mentioned, by the upper limits of the particular optimum dryness range, as well as by the need to avoid physical damage to the felt.

It has earlier been noted that in substitution for the anti-deflection roll 37 (or for a similar roll at 38 if used), there may be employed a porous ceramic press roll to receive, retain and release moisture from the web at the press nip N2. This is illustrated in FIGURE 3, wherein press rolls and 56 forming a web pressing couple 57 are more or less diagrammatically indicated as being provided with a ceramic shell. Suitable known porcelains and like materials having controlled degrees of porosity can be utilized, and the ceramic shell may be molded or otherwise formed on the inner imperforate cylindrical shell 49 shown in FIGURE 6. The upper roll 55 engages the web and its porosity is thus very fine (i.e. comparable to the conventional granite bare press roll) and it functions essentially as a plain-surface roll; whereas greater porosity is permitted in the lower roll 56, covered by the felt 141, so that it may function to minimize overloading of the nip N402 with water in the manner hereinbefore described. In other respects the divided press assembly indicated at 58 in FIGURE 3 is essentially identical to the lower press assembly 44 in FIGURE 1, and according ly, like numerals have been applied thereto in the 100 series.

It has further been noted hereinabove that the instant invention is not restricted to an arrangement inwhich the web pressing couple is in the top position and the suction press couple is in the lower position with respect to the traveling paper web. This is clearly illustrated in FIGURE 4, and the divided press assembly therein is designated generally by the numeral 59. As shown, a web pressing couple 5t comprised of an upper plain press roll 61 defining a nip N-4 with a lower press 62 is in a lower position. The lower plain press roll 62 may be Wrapped, if desired, by a lower press felt 63 trained around guide rolls 64 in generally the manner of the upper press felt 39 of FIGURE 1, although it is of course understood that a lower press felt 63 is not at all times required (e.g. as in FIGURE 12).

The upper plain press roll 61 of the web pressing couple may or may not be an anti-deflection roll, although as indicated in FIGURE 4, suitable means are provided to load the roll 61, so that the nip loading at the felt pressing couple 65 is generally greater than the nip loading at the web pressing couple 60 in order that the upper press felt is delivered to the web press nip N-4 at the earlier noted effective optimum dryness. The upper press felt 70 is trained around guide rolls 66, and a tensioning roll 67 may be employed if desired. The upper press felt 70 has a predetermined quantity of the water transferred at the web press nip N-4 removed at a suction press nip N-S defined by an upper plain press roll 68 and a lower suction press roll 69 having a suction area 69a. The upper plain press roll 68 is adjustable to control the loading at N-5, and to assure that the felt 70 is presented to the web press nip N4 at effective optimum dryness and for the other reasons noted in connection with the shower 47, a shower 71 controllable by valve means 72, may be used in the arrangement of FIGURE 4. As in the case of other showers or liquid applying means shown herein, the shower 71 is mounted within the loop of the felt 70 at the oncoming side of the felt only press nip N-5 in FIGURE 4. The variable nip pressures at N-4 to accommodate paper webs of different characters, and the actions of the separate web pressing couple and felt pressing couple are essentially the same as earlier described, and accordingly, additional description of FIG- URE 4 is not believed to be necessary.

In FIGURE 5 a divided press assembly generally designated at 75 comprises a pressing couple 76 provided by an upper plain bare press roll 7 8 defining a nip N-6 with a lower plain roll 80. The upper plain press roll 78 is loaded as indicated, and the press rolls forming the web pressing couple 76 have imperforate shells and may be (and in this instance are) of the anti-deflection type and the bottom roll 80 may have such drilled rubber coverings or porous ceramic shells as were earlier described.

Received at the nip N-6 with the web W is a looped press felt 82 trained around guide rolls 83 and a tensioning roll 84 and separated from the web W at, both sides of the nip N-6 (Le. at the immediate oncoming and off-running sides of the nip, as shown in all the drawings hereof).

In the arrangement of FIGURE 5, water in the web W is effectively transferred to the press felt 82 at the nip N6, and the press felt is then directed to a felt or suction press couple 87 comprised of an upper plain press roll 88, which may be of the anti-deflection type, and a lower suction press roll 89 having a suction area 89a and defining a nip N8 with the upper plain press roll 88. As is indicated in FIGURE 5, the top press roll 88 is suitably loaded so that the nip pressure at N-8 is in excess of the pressures at the nip N-6 whereby the press felt 82 is delivered to the nip N6 at the effective optimum dryness.

"It was noted in connection with FIGURES 1, 3 and 4 that in order that the felt be presented to the web press nip at its effective optimum dryness, particular circumstances may render it desirable that water be applied to the felt by means of a shower located within the felt loop at the oncoming side of the felt press nip or somewhat upstream therefrom (so as to apply water to the felt on the side opposite to the side of the felt which engages the suction roll at the felt only nip N-3 in FIGURES 1 and 3, N-S in FIGURE 4 and N-S in FIGURE The amount of water removed from the felt at the suction press nip is of course relatively constant under fixed machine conditions, and will remain generally stable under the same conditions of felt composition, felt speed, felt nip pressure and amount of negative pressure applied to the suction area. Accordingly, to raise or lower the felt moisture content to a level desired at the web press nip, the water applied to the felt by the shower is either increased or decreased, and in the arrangements of FIG- URES 1, 3 and 4, this is accomplished by the valve means described.

However, there may occur a change in certain of the machine conditions and if the felt becomes more dry, it will then, as was noted, accept less water from the web thereby tending to become even more dry so that there appears to be a degree of instability in the felt at any point in its dryness curve between optimum and 100% bone dry condition, which includes the effective optimum dryness condition described earlier, and if for some reason the felt becomes more dry, the felt press will remove slightly less water from the felt, but not always sufficiently less to overcome the instability. If this effect continues, the felt will become overdried and damage may result thereto. On the other hand, if the felt tends to become more wet and hence more receptive to water in the web nip, and if the conditions at the felt press remain unchanged, the felt will become progressively more wet until crushing occurs.

In accordance with the novel concepts of this invention, means are also provided to control the moisture content of the felt coming from the felt press so as to overcome this instability. As appears in FIGURE 5, a water shower 90 to which water is supplied at 91 is under control of a modulating valve 92 which is in turn controlled by a measuring device 93, which may take the form of a beta meter. The output from the measuring device 93 is fed to a control instrument 94, which converts the signal from the beta meter 93 into an output signal which modulates the quantity of water delivered to the shower 90.

It may be observed from FIGURE 5 that the measuring device 93 is located at the off-running side of the nip N8, while the water shower 90 is in advance of or at the oncoming side of the nip. Application of water to the felt ahead of the nip has the important advantage of distributing the water evenly throughout the felt and to a particular percentage per unit area of the felt. Additionally, the water shower 90 effectively assists in washing from the felt paper web fibers unavoidably removed from the web during pressing, and as well, by adding water to the felt it has been found that a greater volume of water can be removed at the suction press nip N8. As for example, if x gallons of water are added to the felt by the shower 90, under particular conditions there can be removed from the felt the x gallons, plus a percentage thereof. The measuring device 93 of course measures the felt moisture content at its actual value and adjust it as near as possible to effective optimum dryness, or at a condition of dryness required for maximum water removal effectiveness at the web press nip N-6. Thus, the signal from the measuring device 93 modulates the valve 92 to add that volume of water which, when combined with the felt moisture level prior to passage under the shower 90, will produce effective optimum dryness, adjusting also for variations in negative pressure at the suction area 89a, and other operating conditions.

It would, of course, be possible to locate both the measuring device 93 and the water shower downstream of the suction press nip N-8, or at the off-running side thereof. The measuring device would then signal for the addition of sufficient water to provide effective optimum dryness in the felt 82, however, there would not be obtained in this arrangement the noted advantages of flushing paper web fibers from the felt and the desired even water distribution prior to passage through the suction press nip.

Unit loading in the nip of a press is a function of the flexure curve, and uniform loading is achieved only with a particular amount of crown. It is obviously impractical to change the crown of the suction press roll of the felt pressing couple, or to change the crown of the mating roll in the felt press. To overcome this problem, and to effectively modulate the quantity of water removed at the first press nip, means are herein provided to vary the nip loading so that the felt is presented to a web pressing couple at its effective optimum dryness.

One form of felt nip pressure modulating means is illustrated in FIGURE 7 as applied to a felt pressing couple comprised of a pair of plain press rolls 101 and 102 between which is a suction press roll 103 having a suction area 103a acting against the looped press felt 82. The plain press rolls 101 and 102 may be antideflection rolls of the structure indicated at 37 in FIG- URE 6, and the moisture content in the felt 82 is controlled to the desired level by a measuring device 93a positioned downstream of the off-running side of the felt press nip, the measuring device 93a sending a signal to the control instrument 94a which operates to modulate the nip loading by means of a loading cylinder or diaphragm 104. Of course, an arrangement of three press rolls as shown in FIGURE 7 is not at all times required, and it is within the contemplation of this invention that the felt pressing couple 87 of FIGURE 5 be provided by a pair of plain press rolls of the antideflection type without drilled rubber coverings thereon, and that the measuring device 93 and control instrument 94 modulate the nip pressure by connection to the upper plain press roll in generally the manner of the roll 101 in FIGURE 7. Thus, if plain press rolls are utilized as suggested, the nip loading is modulated to press from the felt any water therein in excess of the effective optimum dryness, and in the arrangement of FIGURE 7, excess water is driven by the upper plain press roll 101 into the perforations of the suction area 103a. Generally speaking, the structure of FIGURE 7 would be utilized in a higher speed paper machine requiring a suction roll for maximum effective water removal, whereas the positioning of a pair of plain press rolls in nip-defining relation would be utilized in a relatively low speed paper machine.

As indicated hereinbefore (and also in connection with the immediately previous discussion of FIGURE 7) it has been found preferable to load the suction roll in the felt only press nip from beneath either with a supporting anti-deflection roll such as the roll 101 of FIGURE 7, or with an anti-deflection roll of substantially identical structure which actually defines the felt only nip with the underside of the perforate suction roll, as is indicated in FIGURES 10, 11 and 9 hereof. In such an arrangement it is not necessary to support the suction roll from above with an additional press roll and nip pressures at the felt only press can be obtained against the underside of the perforate suction roll shell which are as great as or preferably greater than the nip pressures obtained at the web press.

In the embodiments of FIGURES 10, 11 and 9 similar elements are designated by the same reference numerals in the 200, 300 and 400 series, respectively.

In FIGURE 10, the web W-200 passes through a web nip N200, separating immediately after the nip N-200 from press felts 201 and 202, and then traveling over a guide roll 203 and on to the surface of a conventional dryer drum 204. The press felt 202 is trained about guide rolls 205, 205 and functions in substantially the manner described in connection with the felt 39 of FIGURE 1.

The felt 201 is mounted on a plurality of felt guide rolls indicated generally at 206, 206, etc., and a conventional felt tensioning roll 207, which guide rolls 206 take the felt 201 away from the web W-200 at the immediate off-running side of the nip N200 and then guide the looped felt 201 into a suction press nip N201 defined by a press roll 208 within the loop of the felt 201 and having an imperforate shell mounted on anti-deflection means of the type hereinbefore described, and specifically of a preferred type described in the aforesaid application Serial No. 102,571. The press roll 208 has a plain rubber cover and it cooperates with a conventional rubber covered suction roll 209 having the conventional suction roll perforate shell and mounted outside the loop of the felt 201. Controlled pneumatic means indicated diagrammatically by the double headed arrow at 210 are provided for loading the press roll 208 against the suction I011 209 at the felt only nip N-201 to obtain the pressure hereinbefore described for dewatering the felt 201. A conventional shower 211 is provided within the loop of the felt 201 with a control valve 212 for controlling the amount of water applied by the shower 211 to the felt 201.

The web nip N-200 is defined by a pair of press rolls 213, 214 each having imperforate shells and each being equipped with anti-deflection means of the structure described in detail in the patents mentioned hereinbefore (but preferably of the structure described in the aforesaid application Serial No. 102,571). Controlled pneumatic means indicated diagrammatically by the two headed arrow at 215 cooperate with the anti-deflection means to load the press rolls 213 and 214 against each other to define the desired uniform pressure across the nip N400. The press roll 213 within the loop of the press felt 201 is provided with a blind drilled solid elastomer cover 213a, such as the cover already described for the roll shown in FIGURE 6, and having blind drilled holes therein ranging from /2 to 1 inch in depth and having an average diameter of about 4; inch. The other web press roll 214 is provided with a micro-porous surface portion (designated in the trade by the name Microrok).

It will be seen that the shower 211 applies water to the wet felt 201 at the oncoming side of the felt only suction press nip N-201, and water is removed from the felt 201 at this felt only press nip N201 to the extent desired to clean, dewater and condition the felt 201 for reentry into the web nip N-200. In the case of the all wool felt 201 here shown, the resulting dryness at the off-running side of the nip N-201 is held close to 65% (i.e. bone dryness), and within the range of 60% to 70%. The moisture at the off-running side of the felt only nip N-201 is sensed by a beta gauge type of moisture sensing device 216 which sends a signal through the signal line 216a to a signal panel 217. The signal panel 217 is provided with a pneumatic signal control line 210a for the pneumatic pressure loading means 210, another pneumatic signal control means 215a for the pneumatic leading means 215 and still another pneumatic signal control line 212a for control of actuation of the water control valve 212 on the shower 211. Control signals may be sent separately or simultaneously by manual controls at the control panel 217 for each of the control signal lines 210a, 212a and/or 215a; or the control panel 217 may be of a conventional type of control panel which will convert the moisture signal from the moisture signal line 216a to a control signal for one or more signals which the machine operator may select at the control panel 217 for automatically controlling the loading means 210, the loading means 215 and/ or the shower control means 212, all in response to the moisture content in the web 201 at the off-running side of the nip N201.

In FIGURE 11, elements which carry out substantially the same function as those already described in FIGURE 10 are designated by the same reference numeral in the 300 series. It will be noted that the web W-300 here passes from one dryer 304a over a guide roll 303a and through the web nip N300 on over the guide roll 303 and onto another dryer drum 304. The upper roll 314 of the roll couple 313314 is provided with the microporous surface (having a sufficiently fine porosity on such surface 314a to function substantially as a plain surfaced roll); whereas the lower roll 313 is provided with the blind drilled elastomer cover 313a.

It will be appreciated that in each of the embodiments of FIGURES 10, 11 and 9, the web press is the last press (or the only press) to which the web is subjected before being placed on a dryer drum, and the felt in each case is subjected to a press nip load only at the web press and at the felt only press. The pressures employed at the presses, for example N-400 and N-401, and at the presses N-200 and N-201, is in the range from about 300 pounds per inch to about 450 pounds per inch, which pressures are ideal for the second or third presses in paper machines using the instant divided press structures. In the embodiment of FIGURE 11, the nip pressures may be as high at 1000 pounds per inch of nip, since this divided press structure is employed between dryer sections. The high nip pressures described are used with great advantage using the instant divided press arrangement with anti-deflection rolls in the manner just described.

In FIGURE 9, it will be seen that the roll 408 is a plain rubber covered (408a) roll, the roll 413 is a blind drilled rubber covered (413a) roll and the roll 414 has a Microrok cover 414a. All of these

rolls

408, 413, 414 have imperforate shells supported internally by rubber sandwiches appreciably axially inwardly from the shell ends on through shafts rotatably mounted, as more fully shown in the aforesaid Serial No. 102,571 so as to be anti-deflection rolls providing uniform nip pressures in this case at the felt only nip N-401 slightly greater (e.g. approximately 425-450 pounds per linear inch) than at the web press nip N-400 (e.g. approximately 400-425 pounds per linear inch).

It will be understood that modifications and variations may be effected without departing from the spirit and scope of the novel concepts of the present invention.

We claim as our invention:

1. A divided press assembly, comprising a looped press felt, a web pressing couple including a pair of press rolls each having rotary imperforate shells receiving said felt and a paper web in a press nip to remove water from the web by transfer to the felt, one of said pair of press rolls being within the felt loop and having a myriad of small water-retaining recesses on its surface whereby water expressed from the web and into the felt at said nip may be received by said surface and retained thereon at the nip and then released therefrom to the felt at the offrunning side of the nip, a felt pressing couple including a press roll having a rotary imperforate shell and a suc- ,tion press roll removing a quantity of the transferred water fromv the felt, moisture detecting means sensing the moisture content of the felt prior to its return to the web press couple, and liquid means connected to the moisture detecting means and responsive to a signal obtained .the'refr'om to apply liquid to the felt so that the moisture level of said felt determined by said detecting means is lat effective optimum dryness for maximum effective re- ,moval of water from the web.

2. A divided press assembly, comprising a looped press ffel't,a Web pressing couple including a pair of press rolls each having rotary imperforate shells receiving said felt and apaper web in a press nip to remove water from the web by transfer to the felt, one of said pair of press rolls -being' within the felt loop and having a myriad of small water-retainingrecesses on its surface whereby water expressed from the 'web and into the felt at said nip may be received by said surface and retained thereon at the nip and, then released therefrom to the felt at the olf-running side of the nip said pair of press rolls being anti-deflection {rolls having means interiorly of the ends of the shells fthe reof for varying the nip loading in accordance with the character of the web being pressed, a felt pressing ;oup1 including a pair of press rolls, one having a rotary ,i'm'perforate shell and the other having a rotary perforate suctioiiroll-shell,,removing a quantity of the transferred wa'ter' fro'm the felt, moisture detecting means sensing the moisture content of the felt prior to its return to the Web ,pressing couple, and means connected to the moisture detecting means and responsive to a signal obtained thereifrfomjto vary the loading of the felt pressing couple so that Ithe moisture level of said felt as determined by said de- Zt e'ctingimeans is at effective optimum dryness for maxiimam effective removal of water from the web.

."3. A divided press assembly, comprising a looped press ,felt, a web pressing couple including a pair of plain press ,rolls'receiving said felt and a paper web to remove water "from the web by'transfer to the felt, a felt pressing couple including a plain press roll and a suction press roll removing a quantity of the transferred water from the felt, moisture detecting means sensing the moisture content of the felt prior to its return to the web press couple, and liquid applying means connected to the moisture detecting means ,andresponsive to a signal obtained therefrom to apply liquid to the felt so that the moisture level of said felt as determined by said detecting means is ateffective optimum dryness for maximum effectiveremoval-of water from the web.

4. A divided press assembly, comprisinga looped press felt, a web pressing couple including a top plain press roll and a bottom plain press roll in nip-defining relation receiving said felt and a paper web to remove water from said web by transfer to the felt, means for varying the nip loading in accordance with the character of the web being pressed, a felt pressing couple including a top plain press roll and a bottom suction press roll in nip-defining relation receiving said felt without the'webto remove a portion of the transferred water from the felt, moisture, de-

tecting means at the off-running side of thefeltpressnip upstream of the web press nip, and a watershower corinected to the detection means and located at 'the oncoming side of the felt press nip downstream of the web press nip and actuated in response to a'moisture content signal from the detecting means to add water to the felt as re.- quired so that said felt when presented to the web press nip is at effective optimum dryness. Q I

5. A press assembly as claimed in claim l wherein said one of said pair of press rolls has a solid elastomefcover presenting a myriad of blind drilled holes on its surface.

6. A press assembly as claimed in claim 2 whereinsaid one of said pair of press rolls has a solid elastome'r' co'ver presenting a myriad of blind drilled holes on its surface References Cited by the Examiner UNITED STATES PATENTS, p

Smith 372 OTHER REFERENCES Osborn et 211.: Beta Ray Measurements of Moisture'in Running Felts, TAPPI, vol. 39, No. 7, July 1956, pp. 480-485.

DONALL H. SYLVESTER, Primary Examiner.

Claims

3. A DIVIDED PRESS ASSEMBLY, COMPRISING A LOOPED PRESS FELT, A WEB PRESSING COUPLE INCLUDING A PAIR OF PLAIN PRESS ROLLS RECEIVING SAID FELT AND A PAPER WEB TO REMOVE WATER FROM THE WEB BY TRANSFER TO THE FELT, A FELT PRESSING COUPLE INCLUDING A PLAIN PRESS ROLL AND A SUCTION PRESS ROLL REMOVING A QUANTITY OF THE TRANSFERRED WATER FROM THE FELT, MOISTURE DETECTING MEANS SENSING THE MOISTURE CONTENT OF THE FELT PRIOR TO ITS RETURN TO THE WEB PRESS COUPLE, AND LIQUID APPLYING MEANS CONNECTED TO THE MOISTURE DETECTING MEANS AND RESPONSING TO A SIGNAL OBTAINED THEREFROM TO APPLY LIQUID TO THE FELT SO THAT THE MOISTURE LEVEL OF SAID FELT AS DETERMINED BY SAID DETECTING MEANS IS AT EFFECTIVE OPTIMUM DRYNESS FOR MAXIMUM EFFECTIVE REMOVAL OF WATER FROM THE WEB.