US 3198693 A
Abstract available in
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Description (OCR text may contain errors)
Aug. 3, 1965 E. .1. JUSTUS SGAVENGING MEANS FOR GROOVED PRESS ROLLS Filed Aug; 21, 1964 8 Sheets-Sheet 1 INVENTOR. 544.? wary? BY 5 E M ATTORNEYS Aug. 3,1965 E. J. JUSTUS 3,193,693
SCAVENGING MEANS FOR GROOVED PRESS ROLLS Filed Aug. 21, 1964 a Sheets-Sheet 2 IN VEN TOR. 5 0 24? C/ a; Tae
BY ATTORNEYS Aug. 3, 1965 E. J. JUSTUS 3,193,593
SCAVENGING MEANS FOR GROOVED PRESS ROLLS Filed Aug. 21, 1964 8 Sheets-Sheet 5 INVENTOR. 524142 (J M05706 BY ATTORNEYS 3, 1965 E. J. JUSTUS 3,198,693
SCAVENGING MEANS FOR GROOVED PRESS ROLLS Filed Aug. 21, 1964 s Sheets-Sheet 4 INVENTOR. ZZ4 wen/6 ATTORNEYS Aug. 3, 1965 E. J. JUSTUS SCAVENGING MEANS FOR GROOVED PRESS ROLLS Filed Aug. 21, 1964 8 Sheets-Sheet 5 INVENTOR. Z2442 c/ /z/evz/e Aug. 3, 1965 E. J. JUSTUS SCAVENGING MEANS FOR GROOVED PRESS ROLLS Filed Aug. 21, 1964 8 Sheets-Sheet 6 x 1 VENTOR.
/ Jen/6* 0 ATTORNEYS Aug. 3, 1965 E. J. JUSTUS SCAVENGING MEANS FOR GROOVED PRESS ROLLS Filed Aug. 21, 1964 8 Sheets-Sheet 7 INVENTOR. [-2442 J 1/6706 2%,; AM? ATTORNEYS BY @7WJ Aug. 3, 1965 E. J. JUSTUS SCAVENGING MEANS FOR GROOVED PRESS ROLLS Filed Aug. 21, 1964 8 Sheets-Sheet 8 BY M ATTORNEYS United States Patent 3,198,693 SQAVENGHWG MEANS EUR GROOVE!) PRESS RQLLS Edgar J. Justus, Beioit, Wis, assignor to Beloit Corporation, Beioit, Wis, a corporation of Wisconsin Filed Aug. 21, 1964, Ser. No. 391,160 Claims. ((11. 162-272) This case is directed to scavenging means and devices for use with grooved rolls to clean the narrow grooves, continuously or intermittently, while the grooved press roll is in operation; and this case is a continuation-in-part of my applications Serial Nos. 214,589, filed August 3, 1962; Serial No. 258,391, filed February 14, 1963; 302,- 423, filed August 15, 1963; 305,713, filed August 30, 1963; 302,371, filed August 15, 1963; 302,270, filed August 15,1963; 302,422, filed August 15, 1963; 302,421, filed August 15, 1963; 305,992, filed September 3, 1963; and 378,217, filed June 26, 1964.
The present invention relates to an improvement in devices for removing liquid from a liquid-containing web material, and more particularly, to improved paper machine presses.
Although the instant invention may have a number of uses in different fields, it is used to particular advantage in the art of paper making and will be described primarily in connection therewith. In a web press, as used in a paper machine, a web nip is formed between opposed press rolls, and a traveling paper Web in engagement with a felt is passed through the nip. In prior art structures, the press rolls used have been plain, or the roll covered by the felt at the nip may be provided with a perforate shell having a suction gland opposite the nip for aiding in the removal of moisture from the web through the felt, as in the case of the conventional suction press. In other instances, as indicated in Walker US. Patent No. 3,023,805, the felt covered press roll may be provided with an imperforate shell having a blind drilled rubber cover thereon for at least temporarily receiving water expressed from the web and through the felt at the Web nip. In still other web presses, the felt covered press roll may be provided with other types of blind recesses or fine porous structure, or structures in the form of a woven wire or fabric wrap on the roll cover or surface portion of rolls provided with imperforate shells, and in such instances the felt ordinarily functions as a drying felt for the web and carries away a substantial amount if not all of the water that is to be removed from the Web at the web nip. This then requires a separate procedure and/ or apparatus for dewatering the felt before returning the same to the web press nip. In my copending application Serial No. 214,589, filed August 3, 1962, and Serial No. 258,391, filed February 14, 1963, certain improvements in devices for dewatering the felt at a separate, felt only press nip are described in detail. in addition, certain press roll structures were described in said application for dewatering the felt at the felt only press nip in a divided press and also for assisting in dewatering the felt at the web press (i.e. assisting in removal of water from the felt that has been pressed from the web through the felt at the web press nip).
Heretofore, press arrangements have been used for attempting to remove water from the felt at the web nip. Each of these arrangements has required an alteration of structure as compared with a plain press nip, by either incorporating additional materials in the nip or modifying the plain press roll which supports the felt in the nip, for example, by replacing this roll with a suction roll. The suction roll is capable of excellent performance in certain uses, but it must be appreciated that the manu- 3,198,093 Patented Aug. 3, 1965 facture of the perforated suction roll shells, plus the auxiliary equipment essential to the maintenance of the desired subatmospheric pressures in the suction roll gland, is relatively expensive. Moreover, the use of the suction roll gland within the perforate suction roll shell does not make it possible to use conventional or improved antideflection roll means mounted within the interior of the shell for maintenance of the most uniform nip pressures. The relatively large size of the suction roll perforations (plus the pressure differential created by the suction gland at the suction roll periphery) facilitates Water removal from the felt, but in situations involving the use of lightweight felts and/ or the production of comparatively sensitive paper webs or high quality papers Webs, there is a tendency for the webs to develop what is known as shadow marking as a result of such suction roll per forations, even though they are covered by a felt at the suction press nip.
In the more recently developed so-called divided press, efforts have been made to dispense with the use of the suction press roll at the Web press nip, by replacing the same with a plain press roll or with rolls of this general type having imperforate press roll shells but covered with a myriad of blind drilled holes, small blind recesses, pores, etc. These rolls with such recesses thereon are employed primarily to avoid overloading the web press nip with Water and to permit a portion of the weer load to be received in the recesses at the nip, although the water load in the recesses is generally returned substantialiy to the felt at the off-running side of the web nip. Various other press roll means, including suction press rolls, are then employed at a separate felt only press to dewater the felt to the extent necessary to prepare it for reentrance into the Web press nip in such divided press structure. The instant invention is directed to improvements not only in the web press structure but also in the felt only press structure, which are brought about primarily by the use of certain grooved press rolls in these press structures. A significant advantage of such press rolls, having generally peripherally or circumferentially aligned grooves, is that the roll surfaces at the press hips are vented via the grooves to ambient atmosphere so as to facilitate the dewatering function of the press roll at the press nip. It Will be appreciated that in such a grooved press roll, the grooves are applied to an imperforate shell which is capable of mounting with antieilection means and Without expensive auxiliary suction roll equipment. Still other significant advantages are obtained by the use of specific grooved roll structures and auxiliary equipment which will be described in greater detail herein.
The instant invention thus has as its primary object the provision of an improved press assembly for the ,removal of liquid from a liquid-containing web material (which might be a moist felt alone or a felt and Web combination).
Another object of the instant invention is to provide an improved divided press structure wherein the press rolls at the web press and/or the felt only press have improved structure and function.
Yet another object ofthe instant invention is to provide an improved press structure wherein the advantages or" anti-deflection roll mountings may be used, inexpensive roll structures are used, and simplified structures are provided for Water removal from a moist web or felt material and/ or from the surface of the press roll itself.
A further object of the instant invention is to provide an improved grooved press roll structure, that is inexpensive to manufacture, particularly useful and reliable in its water removal function, and readily maintained in functional operation. An additional object of the invention includes the provision of improved devices for cooperation with such grooved roll to clean and maintain the same, dewater the same during operation, and take advantage of the improved dewatering function of the same.
ther and further objects, features and advantages of the present invention will become apparent to those skilled in the art from the following detailed disclosure thereof and the drawings attached hereto and made a part hereof.
On the drawings:
FIGURE 1 is an essentially diagrammatic side elevat-ional View of a press mechanism embodying the instant invention;
FIGURE 1A is a fragmentary detail view taken substantially along the line AA of FIGURE 1;
FIGURE 2 is a fragmentary detail sectional view showing a portion of a suction press nip of the prior art;
FIGURE 3 is a View comparable to FIGURE 2 showing a portion of a press nip embodying blind drilled holes in one roll, as used in the prior art;
FIGURE 4 is a view comparable to FIGURES 2 and 3, but showing a portion of a press nip embodying the instant invention;
FIGURE 4A is a fragmentary detail sectional elevational view taken substantially along the line A-A of FIGURE 4;
FIGURE 43 is a sectional fragmentary enlargement taken substantially at the encircled portion designated IVB in FIGURE 4A;
FIGURE 5A is a fragmentary sectional elevational View comparable to that of FIGURE 4A but taken substantially along the line VAVA of FIGURES 1 and 6 showing another embodiment of the instant invention;
FIGURE 58 is a fragmentary enlargement taken from FIGURE 5A at substantially the encircled portion marked VB;
FIGURES 6, 8, 11, 12, 13 and 13A are essentially diagrammatic elevational views of press assemblies embodying the instant invention;
FIGURES 7 and 7A are enlarged fragmentary detail views taken substantially from the encircled portions of FIGURE 6 marked VII and VIIA, respectively;
FIGURE 73 is a slight enlargement of the view of FIGURE 7A showing a cleaning device of the invention and FIGURE 7C is a view of FIGURE 73 taken along the line VIIC-VIIC;
FIGURE 9 is a fragmentary secetional elevational view taken substantially along the line IXIX of FIG- URE 1;
FIGURE 9A represents an improved embodiment in a view comparable to FIGURE 9;
FIGURE 10 is a fragmentary sectional elevational view taken substantially along the line XX of FIG- URE 8;
FIGURE 12A is an enlarged fragmentary detail view taken from the encircled portion marked XIII of FIG- URE 12;
FIGURE 14 is a top plan view of another grooved press roll design concept, the use of which involves certain principles of the invention; and
FIGURES 15A, 15B and 15C are essentially fragmentary detail views taken, respectively, along the lines XVAXVA, XVB-XVB and XVC-XVC of FIG- URE 14.
As shown on the drawings:
Referring to FIGURE 1, it will be seen that this figure shows a press section wherein a paper web vV-l is processed after it is removed from a forming wire W-Z turning about a couch roll 7. The paper web W-l. passes through a very short open draw beneath a web guide roll 8 and then through a first press 2 2, a second press It? and a third press 14 in the sequence shown in FIGURE 1. It will be noted that the first press 29 is composed of an upper plain roll 21 and a lower grooved 4 roll in a press assembly which is shown (from the reverse side of the machine) in FIGURE 6 hereof in considerable detail and will be discussed in detail in connection therewith.
The second press 1 3 is composed of a vertical stack of rolls i2, 13 and 15, which rolls are generally superimposed or mounted one above the other in the manner indicated in FIGURE 1, but are preferably in the substantially vertical stack arrangement shown in FIGURE 1. In the second press It), the rolls l3 and 15 are grooved press rolls which will be described in detail hereinafter.
T to web W-I passes from the second press is beneath another web guide roll indicated generally at 14c and into the third press nip N44, which could, if desired, have the general structure of the first press 2-3, but which may also be defined merely by a pair of plain rolls It-a and 1% as shown in FIGURE 1, when the function of the third press 14 is primarily that of further smoothing or finishing the wet paper web rather than effecting substantial additional dewatering ther of. If the additional dewatering were desire-d, then the third press 14 could be "laced by a third press having the structure of the first w press 22' so that the advantages of dewatering the Web that, using a grooved roll in a press, could be obtained. Referring first specifically to the three roll divided press assembly Id of FIGURE 1, it will be seen that there is provided a felt II mounted on guide rolls 3.11:, 1.7.1), 11c, 11d and a tensioninr roll lie. The paper web W4 enters the nip N4 of the press id at what is called a web nip N-I with the felt II which is wrapped around the middle grooved roll 13 of the press assembly 1 3. At the off-running side of the nip Ni the felt 11 is guided generally tangentially from the nip N4. and away from the web W-ll which follows the lower plain roll 12 briefly and is then guided away from the plain roll 12.
The press roll 13 is within the loop of the felt 11 and the press rolls 12 and 15 are outside of the loop of the felt I1 and the two press rolls 13 and 15', define a felt only press nip N42. whereat the felt 1'1 is dewatered to the extent desired and necessary to prepare it for re-entry into the web nip N-I for further dewatering of the traveling web W-E.
Both the middle press roll 13 and the upper press roll 15 are formed of a generally imperforate shell or base structure (such as in the case of the prior art blind drilled rolls such as are shown in Walker US. Patent No. 3,623,805, and my aforesaid applications recited herein, the disclosures of which are incorporated herein by referonce.
The press rolls l3 and 15 are thus contrasted to the conventional perforate suction roll (which has perforatrons such as are indicated in FIGURE 2 hereof), and the rolls I3 and 15 have a cover containing a plurality of line water-retaining recesses between land areas which support the felt II at the hips Nl and N-Z respectively.
More specifically, referring to FIGURE 1A, the cover structure for the rolls 13 and 15, which is indicated in cross section at 15a in FIGURE 1A, comprises a plurality of peripherally (or generally circumferentially) aligned land areas 15b with relatively fine or narrow grooves 15c between the land areas for receiving the water from the felt 11 at the nip (eg. at the nip N-Z for the roll 15). It will be appreciated that the land areas 151) are of sufficient width and the grooves 15c are sufficiently narrow to permit the felt 11 to be readily supported at the nip N2 (or at the corresponding nip N4 by the roll 13), so that water may be expressed under superatmospheric pressure from the felt 11 into the grooves 15:, but the felt 11 itself will not be pressed into the grooves to any significant extent; and in the case of the nip N-I, the felt 11 will not be deformed or otherwise temporarily modified in passing through the nip N-l so as to cause substantial or significant shadow marking on the web W-l as a result of the land and groove pattern on the surface of the roll 13.
Referring first briefly to FIGURE 9, which shows a fragmentary cross sectional view (in the cross-machine direction) of the nip N-Z, which is the felt only nip, it will be seen that the felt indicated in full view at 11 for purposes of simplifying the drawing is pressed between the land areas 15b and the land areas 13b of the two grooved press rolls; and it will further be seen that the land areas are offset or out of alignment to some extent for better control of water removal. The sizes of the grooves 130 and 150 are, of course, exaggerated in the view of FIGURE 9, but it will be apparent that the grooves 130 and 15c provide ample space for water to be expressed from the felt 11 and because this is a felt only press nip N-Z any nominal deformity or change in configuration of the felt 11 at the nip N-2, so long as it does not unduly accelerate the wear of the felt 11, can be tolerated because there is no web in this felt only nip N-Z and there is no problem of marking of the web.
The pair of grooved rolls 13 and 15 may thus be used.
to maximum advantage in the felt only nip N-Z for the most effective control of water removal to the extent desired at the felt only nip N-Z.
Referring also briefly to the auxiliary equipment which will be described in considerably greater detail in connection with FIGURE 6, it will be seen that the grooved roll 13 is so mounted that the grooved surface thereof moves away from the web nip N-l toward a close running saveall indicated at 13c diagrammatically, the grooves then pass beneath a wiper sheet w and then past a doctor d which wipes the land areas dry at the immediate oncoming side of the felt only nip N-Z. At the off-running side of the felt only nip N-Z, the grooved surface of the roll 13 again passes beneath a close running saveall 13), under another pumping type of wiper w and then past still another doctor d to dry the land areas at the immediate oncoming side of the felt and web nip N-1.
Referring briefly to the auxiliary equipment of t..e grooved roll 15, it will be seen that the grooved surface of the roll 15 is moved away from the felt 11 generally tangentially aligned with the felt only nip N-Z past a close running saveall 15e, past a pumping wiper w at the uprunning side of the grooved roll 51 and then around to a doctor d carried in a saveall section 15 at the downrunning side of the grooved roll 15 immediately ahead of the felt only nip N2 to dry the land areas just before the land areas come into contact with the felt 11 at the felt only nip N2.
In this respect, it should be noted that herein the longitudinal direction Will always be the direction of travel of the web or felt or other article referred to in connection with this direction; whereas the transverse or cross-machine direction will be at right angles to the longitudinal direction generally in the plane of the felt or web referred to. With respect to each nip (e.g. N-1 or N-2) the oncoming side of the nip is the side of the nip which the traveling web and/or felt approach; whereas the off-running side of the nip is the longitudinal direction from the oncoming side of any given nip and it is at the side of the nip where the web or the felt travels longitudinally away from the nip. Likewise, the oncoming or off-running sides of any piece of auxiliary equipment, such as the doctor at for the roll 15 will be, respectively, the direction from which the rotating surface of the roll approaches and the direction toward which the rotating surface of the roll leaves such doctor d. Thus, for example, the pumping wiper w for the grooved roll 15 is positioned at the off-running side of the felt only nip N-Z, but actually at the oncoming side of the doctor d, which in turn is at the oncoming side of the nip N-2, In each of the drawings hereof, the arrowheads indicate the direction of travel of elements on which such arrowheads are placed.
6 Referring again briefly to FIGURE 9, it will be seen that the grooved roll 15 is indicated therein as being a metal roll (actually having a steel shell 15g with a stainless steel cover 15h) and the grooved roll 13 is indicated as being formed of a metal shell (not shown) with a rubber cover in which the appropriate grooves have been cut. It will be appreciated that it is definitely preferred to provide press hips with at least one of the press rolls having a resilient rubber or similar type of solid elastomer cover thereon to minimize the chances of damage to the machinery. In the practice of the in-. stant'invention, it will further be appreciated that the grooved roll 13 is shown here as being the roll with the resilient rubber surface, so the plain roll 12 then is a relatively non-resilient granite or Microrok roll. It will further be appreciated, however, that the roll 12 in another embodiment of the instant invention is a plain roll having a rubber cover and in such instance the roll 13 will be provided with a stainless steel coverand the roll 15 could optionally be provided with a rubber cover.
Referring now to FIGURE 4A and FIGURE 4, it will be seen that FIGURE 4A is a detail sectional view comparable to FIGURE 1A, except that it is taken generally along the line IVA-IVA of FIGURE 1 at the nip N-1, so as to show fragmentarily the roll 12, the roll 13, the web W-1 (all in section) and the felt 11 in full view for simplification of the drawing. It will be seen that the roll 13, like the roll 15 of FIGURE 1A is provided with substantially equally sized and formed grooves and land areas 13b (which form the generally cylindrical peripheral surfaces of ridges also designated by the reference numer- FIGURE 4 is another fragmentary detail sectional view taken substantially along the line IV-1V of FIGURE 4A and FIGURE 4 shows the upper roll 12, the lower roll 13 (with parts shown in section and parts broken away), the web W-l and the felt 11 (in full view, with an arrow indicating the longitudinal direction). The groove 130 is indicated in FIGURE 4 as part of the alternating generally circumferentially aligned ridges 13b and grooves 13c on the roll 13, but the detail of FIGURE 4 is taken of such a small overall portion of the press assembly that the curvatures of the rolls 12 and 13, as well as the bot-.
toms of the grooves 130 are not emphasized. Referring to FIGURE 4B, however, it will be seen that the grooves 130 each have a very small or narrow axial dimension 16 at the mouth or peripheral portion thereof aligned with the generally cylindrical exterior surfaces 131; ,or land areas of the ridges, which ridge land areas have an axial dimension 17 that is shown in FIGURE 4B to be substantially the same as the axial dimension 16 of the grooves 130 at the outer periphery or mouths thereof. It will also be seen that the grooves 13c are defined between generally radial walls 130-1 and 130-2 which extend in generally parallel relationship spaced apart at least the axial dimension 16 for a substantial radial distance of their depth 18 which is greater than the axial dimension of the mouths of the grooves 16 and the axial dimension 17 of the land areas (in fact, being substantially twice either the axial dimension 16 or 17).
Referring now to FIGURE 6, it will be seen that (the run of the felt and web W-6, shown from the back side of the machine of FIGURE 1 does not conform exactly to the run of the web W-1, hence the different reference numeral, and) there is-shown a press assembly indicated generally by the reference numeral 20 in FIGURE 6 which is a significant improvement over the embodiments of the invention indicated hereinbefore at the nips N-l and N-Z of FIGURE 1. The press assembly 20 comprises an upper plain press roll 21 comparable in structure to the plain press roll 12, and a lower grooved press roll 22 comparable in some respects to the grooved press rolls 13 and 15 hereinbefore described. The press rolls 21 and 22 define a press nip N-3 which receives a moist webW-6 engaging the plain press roll 21 carried on a felt 23 trained '2' over guide rolls 24a and 2415, which felt 23 travels with the web W-6 in contact therewith at the oncoming side, at the pressure area, and at the off-running side of the nip N-3, as here shown. The grooved roll 22 is provided with saveall indicated generally at 25 and shown with three sections 25a, 25b and 250.
The grooved roll 22 is shown in fragmentary detail in FIGURES A and 5B (FIGURE 5A being taken substantially along the line VAVA of FIGURE 6), and it will be seen that the grooved roll 22 is provided with a solid elastomer (rubber) cover 22a on an imperforate ductile iron shell 22x. The cover 22a may and preferably in certain cases is formed of stainless steel which Will also permit the cutting of fine grooves 220 between land areas 22b, in the dimension and configuration shown in FIG- URES 5A and 53. Referring more specifically to Fit}- URE 5B, it will be seen that the cover 22a of the grooved roll 22 is indicated in a view without section lines for ease in detailing the description thereof. The grooves 220 are here shown having a substantially uniformaxial dimension 26 that is 0.025 inch between generally cylindrical (smooth) land areas 221; on ridges alternating with the grooves 220, with such land areas 22b having an axial dimension 27 that is 0.100 inch, or substantially four times the groove mouth axial dimension 26, thereby giving an open area on the surface of the grooved roll 22 of substantially The grooves 220 extend radially inward to a depth 28 of A; inch (or 0.125 inch) which is greater than both the groove axial dimension 26 and the land area axial dimension 27, and such groove 22c thus has a volume value expressed in the cross sectional view of FIGURE 53 as equal to, 5 times the square of the groove mouth width, or 5x if x is the groove mouth width herein numbered 26. Such groove 220 is defined between generally radially extending, parallel walls 22(2-1 and 220-2,
which are axially spaced the distance 26 of the axial groove mouth dimension or greater than that distance (by not more than about 100% because of the undesirability of undercutting the land areas 22b), so that water entering the peripheral mouths of the groove 220 will not be restricted in its flow radially inwardly into the groove 22c.
Referring again to FIGURE 6, it will be seen that the water expressed from the web W-6 through the felt 23 at he nip N-3 is received in the grooves 220 of the grooved roll 20(each of which grooves 22c is vented directly to ambient atmospheric pressure on both the oncoming and off-running sides of the nip N-3) and to a substantial extent such expressed water is carried away from the felt 23 at the off-running side of the nip N3. The first'saveall section 25a is mounted in substantially the closest practical running relation with the off-running felt 23 and the off-running side of the roll 22 so as to capture droplets of water thrown by centrifugal force from the grooves 220 at the immediate off-running side of the nip N-S. The grooves 220 resist the tendency for centrifugal force to throw such. droplets away from the roll 22, however, par
ticularly at slower operating speeds. At higher operating speeds of 500 feet per minute and above, however, the tendency of the narrow grooves 220 to resist the release of water from the roll 22 because of centrifugal force is at least partly overcome and the saveall portion 25a functions to minimize rewetting of the underside of the web W6 in this respect.
A substantial amount of water, however, remains entrapped in the narrow grooves 220 in the grooved roll 20 until this roll passes past a wiper 29, which is unique in its simplicity (and is indicated diagrammatically merely with reference letter W in other views), consisting merely of a generally fiat sheet of moderately resilient material such as metal sheet 29a secured to a transverse cross bar 2% and urged as a continuously transverse sheet against the land areas 221] on the periphery of the roll 22. The wiper sheet 29a thus does not enter into the groovesZZc but merely presents a surface that is axially continuous for the transverse peripheral dimension of the roll 22 along the generally transverse line of contact (i.e. actually a limited peripheral area of contact), L-l, whereat the wiper 29 extends axially continuously from the off-running side of such line of contact L-1 so as to separate or diverge slowly from the olf-running periphery of the grooved roll 22 so as to effect, by pumping action, a drawing of the water in the grooves 220 (which is actually swept out of the grooves 22c by air rushing in to fill the partial vacuum created by the pumping action of the wiper 29). The water in the grooves which has been held therein in resistance to the combination of centrifugal and gravitational forces at the down-running side of the grooved roll 22 is thus substantially swept out of the grooves 220 and to a substantial extent into the second, bottom saveall portion 25b.
Some of the water thus drawn from the grooves 22c remains on the land areas (as a meniscus), and the mist or droplet of water generally present in the immediate vicinity of high speed press rolls in paper machines will also tend to deposit on the land areas 22!) of the uprunning side of the grooved roll 22, and such water on the land areas 22b is then removed by a conventional doctor means, preferably merely in the form of a conventional doctor blade 30 (which is indicated diagrammatically merely by the reference letter (2! in other views), which at high speeds will actually throw water droplets away from the roll surface as indicated in FIGURE 6 and against the third saveall portion 25c feeding into the bot tom saveall portion 25b. The doctor blade 30 thus provides a doctor means in close proximity to the oncoming side of the nip N-3 to dry the land areas. Preferably the doctor means 30 coacts with the land areas 225 within what constitutes at least the last 120, and preferably the last of travel of the grooved roll 22 approaching the nip N3, so that the land areas 2219 will be dry at the immediate oncoming side of the nip N-3. if some droplets of water are driven by the doctor 3% from the land areas 2211 into the bottom of the grooves 220, it has been found that the particular function of the grooved roll 22 is not sig nificantly impaired, Whereas retention of moisture on the land areas 22b does make a significant difference in the operation of the grooved roll 22, for reasons which will be described in detail hereinafter.
Theory and advantages of invention Although this particular case is concerned primarily with scavenging means for removing water. from and/or otherwise keeping the grooves clean (and also keeping the land areas clean), the theory of the press system itself is important. As previously indicated, certain aspects of the embodiment of the invention shown in FIGURE 6 (which is the first press 249 of FIGURE 1) involve significant and distinct improvements over other aspects of the embodiment of the invention shown in the second press 10 of FIGURE 1; and although it is not desired to limit the invention to any particular theory, it is believed that certain theoretical considerations will explain the superiority of the embodiments of both FIGURES 1 and 6 over the prior art.
Grooved rolls in the art of pressing paper webs were considered and discarded several generations ago. For example, in 1915, US. Patent No. 1,123,388 issued to Schaaning and was directed to a grooved press roll allegedly intended to replace felt covered rolls and having grooves of such configuration that Schaaning alleged that they would retain water by capillary action. As early as 1905, Fletcher (US. Patent No. 800,845) proposed a grooved roll made of certain segmental portions. in the 1920s, Goodfellow (US. Patent No. 1,369,335) proposed a press roll with circumferential grooves as Well as generally axial grooves interrupting the circumferential continuity of land areas, which were covered with the felt; and Wagner issued U.S. Patent No. 1,483,562 relating to grooved rolls used with a pair of press felts for cooperation with certain suction mechanisms outside of the press rolls. Wagner US. Patent No. 1,321,958 shows grooved rollers in a couching mechanism. Wagner U.S. Patent No. 1,520,489 relates to a grooved jacketed roll. Wagner U.S. Patent No. 1,517,036 relates to a pair of press rollers intended to press a traveling paper web with their bare unprotected surfaces, with one of such rollers having grooves in the surface thereof. Wagner U.S. Patent No. 1,552,098 shows very shallow as well as narrow grooves intended to dewater pulp entering the same.
As late as 1958, however, Wagner issued U.S. Patent No. 2,858,747 which was directed to grooved press rolls functioning with a suction device mounted outside of the roll shell with sealing elements extending into the grooves; but with occasional exceptions such as this in the patent art, it will be found that substantially the entire paper making industry devoted its attention to the perforate shell type of suction roll for water removal at a press nip, once this structure was discovered and introduced in the industry. In fact, for the past thirty or forty years the drilled perforte shell type suction roll has been used predominantly and practically exclusively in the paper making industry for the removal of water in any significant quantities from moist paper webs in paper making machine press assemblies.
As indicated in FIGURE 2 hereof, in the suction press nip N4, the roll shell 31 is perforate, being provided with a multiplicity of holes 32, 32 of substantial size (i.e. at least about inch in diameter but sometimes smaller and usually having flared peripheral mouths 32a of greater size) which are drilled entirely through the roll shell 21 (having at least about 1 inch thickness) to communicate with the suction gland G extending the full width of the roll shell 31 interiorly opposite the nip N-4. At the suction press nip N-d, a press felt 33 is interposed between the web WZ and the perforate suction roll shell 31 (primarily as a water-permeable protective layer for the web WZ), and water expressed from the web WZ passes completely through the felt 33 and into these holes 32, 32 in the perforate shell 31. Some water continues into the gland G and some is usually retained in these holes 32, 32 at the off-running side of the nip N-l, where the subatmospheric pressure in the gland G tends to counteract centrifugal forces urging water droplets back out of the holes 32, 32 and against the felt 33 under ambient atmospheric pressure. The felt 33 may thus remain in contact with the web WZ atsuch off-running side of the nip N-4 without substantial rewetting of the web WZ (via water thrown back on the felt 33 from the suction roll holes 32, 32). Also, savealls (not shown) are conventionally positioned between the felt 33 and the perforate roll shell 31 at the immediate off-running side of the gland G to catch droplets released from the suction roll holes 32, 32, particularly after these holes pass beyond the limit (i.e., the off-running seal, not shown) of the interior suction gland G so there is no longer a pressure differential hold-, ing the droplets in the holes 32, 32. The off-running felt 31 must be guided to avoid such saveall and this often results in guiding the felt with or against the web at the off-running side of the nip N-4. The perforate suction roll with its suction gland, and with or without the saveall, thus functions to carry away substantially all of the water expressed from the web at the nip.
In spite of the excellence of the performance of perforate suction rolls for a number of uses in paper making, it must be conceded that these rolls and their auxiliary equipment are expensive to manufacture. The suction gland therein, also, substantially precludes the use of conventional anti-deflection roll structures for greater versatility and uniformity in nip pressure control. In addition, the substantial size of the perforation mouths 32, coupled with the pressure differential created by the suction gland against the unsupported portions of the felt 33 opposite such perforations 32, has a tendency to cause shadow marking of the web in certain instances.
Only in recent times, after many years of commercial use of perforate suction rolls, there has been developed what is referred to by applicant and his co-workers as the divided press type of structure which does not require the use of the perforate suction roll at the web press. In the divided press, the felt alone is cleaned, dewatered and conditioned at a separate press nip, and then fed with the moist web into what is called a web nip which is defined between rolls having imperforate shells (as contrasted to the perforate suction roll shells). As indicated in FIGURE 3, ordinarily the amount of water load at such a web nip N-5 is such that at least one of the press rolls 32, 35a is provided with recesses 36 on the surface thereof to temporarily take the load of water entering the web nip N-S to prevent crushing of the web W3 carried by the felt 37. As indicated in FIGURE 3, a preferred form of such recess 36 is provided by a rubber cover on a press roll 35 that contains a myriad of comparatively fine blind drilled holes (i.e. of approximately to A1 inch or even less diameter, as in the case of Walker U.S. PatentNo. 3,023,805); and such fine holes 36, 36 will in the case of most conventional webs W3 and felts 37 substantially avoid or eliminate the shadow marking characteristic of the performance of certain perforate suction rolls, but sometimes plugging of these fine hole-s presents problems. In the divided press, the water removal principle is substantially different. The water is not carried away from the nip N-4 by the suction roll shell 31 and, instead, the water pressed from the web W3 into the felt 37 is carried away from the web W3 substantially entirely by the felt 37 at the off-running side of the nip N-S. Excess water at the nip N-5 which is driven into the blind hole perforations 36, 36 to relieve the load at the nip N5, ordinarily entraps a certain amount of air in the bottom of these blind perforations 36, 36 and this, coupled with the ability of the felt to absorb water when it expands at the off-running side of the nip N-5, results in a substantial removal of water from the system via the felt 37 which, as previously mentioned, is then passed through a felt only press where it is dewatered to the extent desired at a separate press nip. The principle of the water removal at the web press nip N-S of the divided press also involves what amounts to a comparatively good force balance at the nip itself, whereat the Web W3 is squeezed so that it is dewatered but it is squeezed against a felt 37 that is maintained on a substantial amount of land area 36A inbetween the mouths of the myriad of perforations 36, 36 and the perforations 36, 36 are filled with water under aconsiderable amount of pressure (particularly when air is entrapped in the bottom of the blind holes 36, 36) so that the bridging or unsupported felt areas at the nip N-S corresponding to perforation openings of as much as A; or A of an inch in diameter (or even less than 4; inch) are actually very well supported from beneath and there is little significant evidence of lack of support for such felt areas in the resulting pressed web W3 ordinarily (i.e. little, if any, evidence in the form of shadow marking). In addition, the imperforate shells 35, 35a effectively defining the web press nip N-S of such construction that they lend themselves readily to support by various anti-defiection means, so that the web press N-S is afforded substantial advantages in versatility of nip pressure conirol and maintenance of generally uniform axial nip oads. 2
The grooved r-oll structure employed in the instant invention, however, as exemplified in the embodiments of FIGURES 4, 4A and 4B, as Well as the improvements thereon represented in FIGURES 5A, 5B and 8 is based upon still another different and distinct fundamental principle of water removal at press nips. For one thing, the
instant invention provides a unique improvement in the divided press assembly (FIGURE 1) whereby a grooved roll is used in the place of the roll 35 described in connection with FIGURE 3 (or as will be explained hereinafter at the felt only nip) so as to obtain either a number of distinct advantages over the divided web press structure just described (at some sacrifice in other advantages), or to obtain all of the advantages of the divided press just described, plus a num er of additional advantages.
Gne of the essential concepts of the instant invention involves that of using a grooved roll with land areas 13!] and 22b (of the FIGURE 4 and FIGURE series) that are substantially circumferentially continuous so that the land areas present continuous generally cylindrical, smooth exterior or peripheral outer operating surfaces for engaging the web material or felt 11, 23 and supporting the same. Circumferentialiy discontinuous land areas are substantially impossible to clean during rotation of the roll. Also essential in consideration of this first concept is the use of such land areas having a very narrow axial dimension 17, 27 between the alternating grooves 13c, 22c which are also of small axial dimension In, 26 but which are vented (peripherally) to ambient atmosphere so that water pressed at the press nips, N1, N2 and N-3 will have no resistance in this respect to flow through the web material or felt axially as well as radially and into such vented groove months (which are wide enough to readily receive the water under pressure). The grooves are provided in a size of sufficient magnitude to receive the water load at the press nip, while being vented to ambient atmosphere and thus in a manner so as not to resist flow into the grooves, by virtue primarily of the groove depth (as comprised to increased groove axial dimensions 16, 26 to accommodate increases in water load). The groove depth 18, 28 in most paper machine uses must thus be substantially greater than the groove opening 16, 26 at the roll periphery, so that the very essential venting function is accommodated. In practical embodiments of the instant invention, the ratio of groove depth 18, 23 to groove axial dimensions 16, 26 at the roll periphery is preferably at least about 2:1 and may be as much as about :1 or more depending upon practical, additional consideration such as roll strength, ease of cutting the groove, etc. In addition, it has been found important to make sure that the groove is able to readily receive the water load in that it is provided with side walls 13c1, 30-2 -or 220-1, 22c-2 which are (generally radially aligned) at least as far apart axially as the groove mouth 16, 26 for at least an initial groove depth substantially equal to the axial dimensions of 16, 26 of the groove mouth (or a minimum of about 0.05 inch, and preferably A; inch) and preferably for substantially the entire groove radial dimension 18, 28. It will be seen that a minimum groove cross sectional area may be computed as 2x on the basis of the example of 0.025 inch groove width x and 0.050 inch groove depth, although a greater area is preferred in the neighborhood of 52: for a depth of 0.125 inch. This concept would permit interior groove axial dimensions greater than the mouth axial dimensions 16, 25, if the forming of the same is practical and does not subtract from the strength and other con mercial considerations such as cleaning of the roll but this concept would preclude shallow tapered grooves which would be intended to resist the entrance of water therein (and/or the venting thereof) but a taper between the walls of relatively deep grooves, such that the Walls would be functionally parallel (for the operating purposes described) would not be precluded.
In addition to the ability of the grooves 130 and 220 to vent to ambient atmosphere at the press nip and thus readily accommodate the receipt of water (by the roll thus contacted, touched or, in the language of the art Wrapped by the felt), an even more important consideration has now been found to be a part of this concept, and this is the consideration which involves the use of a minimum axial dimension 1.7, 27 to the smooth genererally cylindrical land area on the ridges between the grooves. As indicated in FEGURE 5B, the maximum axial disamassa l2 tance which water must travel through the felt 23 (in compressed form) is from approximately the midpoint M of the land area 221) to the edge of the groove 22c adjacent thereto. Such midpoint M lies in a generally radial plane bisecting the individual ridge and land area 221) and the axial distance to the groove is approximately /2 of the land area 2?.
Liquid per se in any medium, such as water in the web type of medium provided by the felt 23, resists flow under any circumstances, and in the compressed felt 23,
which has a dimension within the range of about to /s inch (0.0625 to 0.125 inch) the resistance to water flow is sufiiciently great to cause considerable care to be taken in defining this dimension 27 /2 so as to maintain maximum dewatering CfiiClfil'iCj/ at the nip. (Lightweight felts are often to 5 inch thickness; in such instances the axial land dimension 17, 2'7 may be 3:1 to 10:1 in relation to felt thickness.) In this respect, the axial land dimension 17, 27 should be about 25% to 200% (is. up to about 200% of A; inch or 0.25 inch) of the radial felt thickness 23a in compression for the best performance in Water flow axially laterally through the compressed felt and into the grooves 22c on either side of each land area 2215. The range of axial land dimension 17, 27 to felt thickness 23a in compression may thus be 1:5 to 3:1 but preferably is within 1:2 to 1:1.
Still another important consideration in the practice of the instant invention with respect to the axial groove dimension 16, 26 at the mouth thereof is that of shadow marking in the case of webs passing through the nip. It will be appreciated that shadow marking per se is not of any consequence in connection with a felt only press, nor is it a significant factor in the case of certain types of lower quality webs or in the case of certain paper machines wherein extra heavy felts are used. In such instances, it might be possible to use grooves having substantial axial dimensions 16, 26 up to as much a about A; inch, above which the felt would tend to enter the grooves to too great an extent, causing unnecessary additional Wear of the felt, possible plugging of the water flow and/or venting effect, etc. A careful study of this matter has revealed, however, that axial groove dimensions 16, 26 which are significantly greater than about 0.035 inch tend to cause undesirable marking on certain webs and/or the undesirable temporary entrance of the felts of most weights into the grooves under the nip load, so as to increase the wear of the felts; and a maximum groove dimension of 0.035 has been found to be a very significant cutoff point for most pressing operations. The minimum practical axial groove dimension 1.6, 26 which accommodates receipt of water and the essential venting function, is in the neighborhood of about 0.005 inch. As previously indicated excellent results are obtained using a groove axial dimension of substantially 0.025 inch, although more recent Work indicates a distinct preference for 0.020 inch.
The foregoing venting concept which is essential to the practice of the instant invention is based upon certain fundamental theories which involve the design of grooves having the best ability to receive Water and vent the nip pressure, plus the design of land areas having superior ability to efiect axial or transverse flow of Water through the compressed felt and into the grooves with a minimum amount of interference and a minimum amount of pressure gradient across the land areas. in the case of a web nip such pressure gradient is a function of the fluid pressure existing at the interface between the felt and the web, and it is important in pressing to vent or relieve such fluid pressure in the felt to as low a level as possible, which is best done by opening up the back side of the felt so that Water need travel only substantially the thickness of the felt in compression to ambient atmosphere in the grooves.
Another aspect of the instant invention which has been found to be very important is that of minimizing such flow of water through the compressed felt and into such grooves, by preparation of the land areas at the oncoming side of the nip. in this respect, attention is directed to FIGURE 7A, which shows in a transversely directed view the outer peripheral land areas 22b alternating be tween the grooves 22c but with droplets D of water (in the form of a meniscus) adhering to the land areas 22b. It will be appreciated that in the operation of paper machinery involving press sections, a substantial amount of Water is being handled and this water includes droplets in mist in the air as well as the water actually remaining in droplet form on the roll surface, so that the roll surface ordinarily tends to be continuously wet. It must be appreciated, however, that any such droplet D carried on the land areas 22b into the nip N3 (or N-l, N2) is first immediately pressed into the body of the felt and then must travel the aforesaid axial dimension through the compressed felt and into the vented grooves on either side of the land area 2212. This is a phenomenon which is avoided in accordance with the practice of the instant invention by a very simple expedient. In FIGURE 1, the doctor means d (in the form of the doctor 30 of FlGURE 6) wipe such droplets off the land areas to dry the same at the oncoming side of the nips N-l, N-2 (within at least approximately about 120 at the oncoming side of the nip on the grooved press rolls, and preferably within substantially the last quarter or 90 of rotation of the groove approaching the nip). Although an air doctor could be used (FIGURE 12), the press assembly 26 of FIGURE 6 demonstrates the use of a more simple, sturdy, inexpensive and advantageous doc tor means for accomplishing the result desired with greater ease, and without the necessity of atomizing or blowing droplets into the ambient atmosphere for redeposit on other operating members. This is done essentially by the use of the doctor blade 30 which is a conventional doctor blade in all other respects and has this advantage. It is mounted, however, at the immediate oncoming side of the nip N3 so as to make sure that the land areas 22b are dry approaching the nip 1 -3. In this respect, it will be seen that the doctor 35 which presents what constitutes an axially continuous surface urged against .(or in very close running relation to) the roll periphery is a greatly simplified structure in that it is not complicated by devices for reaching into the grooves 22c.
An important aspect of the invention resides in the fact that devices for reaching into the grooves 22c at this particular location are not essential, since the grooves 220 are designed with sufficient depth 28 to accommodate the return of at least a small amount of water into the nip N-3 in the grooves without interfering with the overall operation of the press 20. The important point to consider here is that of avoiding an unnecessary additional flow of water axially through the compressed felt by the introduction of water at the land areas 22b at the nip N-3.
Still another very important point to consider is that in the press roll 22 which is the preferred embodiment of the instant invention, the generally circumferential, alternating grooves 22c and ridges 2219 are in the form of continuous spirals, as contrasted to exactly circumferentially aligned and axially spaced grooves and ridges throughout the entire roll periphery. This latter roll structure can be used in the practice of the instant invention with a number of desirable results, and the spiral grooving is distinctly superior from the point of view of manufacture and use as will be demonstrated hereinafter. Machine tools are available for cutting the desired grooves (in the form of spiral threads) on the surface of such rolls with considerably greater ease and accuracy than can be done in the practical shop operation involving the cutting of grooves that are exactly circumferential. Moreover, the doctor 36 presents an axially continuous surface which is uniquely capable of cooperating with the spiral grooving for dewatering the land areas lid only, whereas any device reaching into the grooves of spiral grooving could not be retained as a fixed simple functioning device such as the instant doctor 30.
Referring now to FIGURE 7, it will be seen that the wiping device 29 also provides a unique arrangement for dewatering grooved rolls generally, and particularly for dewatering the spiral groove rolls of the type just described. The Wiping device 29 does not enter into the grooves 220, but carries out its function of pumping Water from the grooves 22c by virtue of its unique, simple structure and it carries out this function at the oncoming side of the doctor 30, so that it will not take water from the grooves 220 and put it on the land areas 22b such that the water will be conveyed into the nip N-3 on such land areas. In essence, the wiper 29 has an axially continuous surface portion 2% extending from close proximity to (actually being urged against) the roll surface 22 at the peripheral surface portions or land areas 22b thereof, which surface portion 29a extends gradually away from such roll surface or land areas 22b (from the region of contact L-i) so as to define with the offrunning roll periphery a gradually diverging pair of surfaces for pumping liquid out of the grooves 22c as it moves past the wiper means 29. As indicated in FIG- URE 7, the combination of centrifugal force, gravitational force and the reduced atmospheric pressure that is created at the underside 29c of the sheet 29a for the wiper 29 results in the drawing of the water (indicated at 29d diagrammatically) out of the grooves 220 and off in the general direction of the underside 290 of the sheet 2%. This is done, of course, to an appreciable extent by the sweeping or inrushing of air A7, as indicated diagrammatically, along the peripheral surfaces of the grooves 220 to compensate for the partial vacuum that is being created by this pumping effect. It will be appreciated that the wiper structure thus shown is unique in its simplicity, ease of assembly, installation, operation, repair, etc., and in addition it is unique in its function with respect to generally spiral grooves 220 in that it will dewater the same without reaching into such grooves and thus having the inherent axial travel motion imparted to the wiper device 29 that would result from continuously riding in spiral grooves. It has been found that the fundamental and simple wiper 29 and doctor 3!) structures cooperate in a unique manner in connection with the press assembly 29 for obtaining the best operating results. The doctor 30 per so has the unique function of improving the efficiency of the press at the nip N4), and the Wiper 29 per se has the unique function of drawing water out of the grooves 220 by a very simple structure and phenomenon. Both of these devices 29 and 3t}, individually and in combination, are uniquely superior for operation with the preferred spirally grooved press roll in improving the basic operation thereof.
In addition to the, previously mentioned advantages of spiral grooving on the roll 22, which include the more inexpensive and foolproof cutting of such rolls on a lathe, there is a unique cooperation between the spiral land areas 22b and the doctor 3% and/or wiper 29 which is not injurious to the felt 23. At the nip N 3 the spiral grooves 220 and ridges 22b come into momentary contact with the felt 23 under compression (moving'tr-uly circumferentially) and for such momentary contact the grooves 220 and ridges 22b are substantially (and practically) circum-ferentially aligned in their travel and the axial extent of the travel is so extremely minute that no felt damage is caused thereby. Just the opposite function between the ridges 22b and the doctor 36 and/or Wiper 29 is obtained, however, because these latter devices remain in fixed position engaging the ridges 22b so that their spiral (axial motion) component has the net effect of continuously cleaning, wiping and/or scraping the engaged surfaces of the doctor 30 and/or wiper 29.
In many respects, the foregoing structures of the at a grooved rolls 13 and 22. are particularly useful even though the groove months 16, may be rather sub stantial in size (eg. up to 0.1 inch or more at the felt only nip N-Ia), even to the extent of causing some marl:- ing at one of the web nips N2 or T l-3. in the preferred embodiment of the instant invention, however, marking is avoided by the use of very narrow groove openings 16, 26, of an axial dimension that is not greater than about 0.035 inch (and preferably about inch). This axial dimension, as a maximum, has been found to be distinctly superior for use in the practice of the instant invention. It has been found that axial dimensions signiticantly greater than this do not give significantly better performance in any of the ordinary uses of the instant roll, whereas such bigger axial dimensions do have a tendency to cause web marking in most instances. in the manufacture and sale of grooved press rolls for the uses contemplated in the practice of the instant invention, it has thus been found particularly desirable to maintain groove axial dimensions of 0.035 or less. Among other things, this has the advantage of avoiding any special instructions in connection with mill use by the grooved rolls, since such grooved rolls can be used at felt only presses, as Well as web presses involving dif erent felt weights and diiferent qualities and types of webs. in fact, most recent work has indicated that a prefe' ed maximum is about 0.020 inch with 0.1 or 0.105 inch lands (the preferred ranges being 0.020 to 0.025 inch grooves with 0.08 to 0.1 or 0.105 lands).
Within the limitations hereinbefore set forth, it will be understood that certain relationships between the grooves and ridges in the felt covered press roll,(e.g. 15 of FIGURE 1) of a web press in a divided press may not be so critical because the felt lit is adapted to carry away most of the water expressed from the web W-l and re-wetting of the web is avoided in FIGURE 1 by guide means separating the web and felt at the immediate oil-running side of the nip Nl. The ratio of axial groove dimension 16 to axial land dimension 17 is at least about 1:1 and preferably at least within the range of 1:2 to 1:3 (i.e. inch to about to inch) for satisfactory removal of water from the web, which actually involves open area ranges of 50% to about 33 /37: and 33 /a% to 2025% or less, which latter range is the preferred open area and is actually used on roll 22.
Extensive research has revealed, however, that distinctly superior performance is obtained using a substantially smaller open area of not more than about 25% (eg. not more than inch grooves with j inch lands). This is a significant difference between the rolls 13 and 2.2. This is notwithstanding the fact that an essential aspect of the invention involves ease of reception in the grooves of substantial quantities of water. The reason for the preferred open area upper limit of about 25% (and preferably 20% with the 0.025 inch grooves and 0.100 lands of FEGURE 5B) is that it has been found that this comparatively low open area does not signii cantly impede water removal from the web (via the felt) at the nip pressures used while it does carry out perhaps the second most important function that provides great versatility for the grooved roll of the invention. This function is that of minimizing re-wetting of the felt at the off-running side of the nip N-3. Although this function greatly assists the dewatering operation in the web (divided) press nip and reduces or minimizes the water load carried away by the felt from the web in the divided press, it is actually capable of effecting substantially all water removal (via the grooved roll at a web press nip) so as to replace a conventional suction roll web press, as indicated in FIGURE 6 (at the first nip N3 as well as the third press nip N-M in the particular embodiment of FIGURE 1).
Referring now to FIGURES 7B and 7C, it will be seen that an additional aspect of the instant invention involves a means for cleaning a spirally grooved roll such as the rol 22 while it is operating. This device 300 is reliable and quite simple in structure, comprising a baci- 1g memher 301 which. may be made of wood and which has rigidly mounted or embedded on the underside 301a thereof a plurality of spaced, thin, relatively short substantially parallel guide means in the form of metal strips 593a through 3M8. Each of the strips 302a through 302e is adapted to ride in adjacent grooves 22c between the lands 2% on the periphery of the roll 22. The outer guides 35, 302b, 302d and 302s are comparatively shallow in their (radial) dimension so that they do not reach the bottoms of the grooves 220 but merely ride therein for guiding the element 300. The central element 3020, however, is preferably the element which does the cleaning and this element has a greater thickness or radial dimension so that it will ride along the bottom of one of the grooves 22c, as indicated in FIGURE 73 and clean the same as it rides in this groove. The backing member 301 is also provided with a leading edge 301!) which generally defines an acute angle with the backs of the guide elements 303.- etc. (or the general plane in which they all lie), so that the leading edge of the doctor blade 30 will fit against this leading edge 3011) and permit relative axial movement between the doctor blade 30 and the backing member 301. In this fashion, the generally spiral grooves 220 will effect an axial movement of the chaser 3th), as the roll 22 operates continuously urging the chaser against the doctor 30. The grooves 22c, will of course, be positioned in the roll 22 so as to extend beyond the axial dimensions of the doctor 30 or to the complete edge of the shell for the roll 22, so that the chaser 300 can be started at one edge of the roll 22 and then taken off the doctor 30 at the opposite end of the roll 22. when the chaser 300 has traversed the full width of the roll 22 (in the transverse direction). it will be appreciated that the angle of the overall spiral of the grooves 220 is only a very few degrees, so that substantially straight guides Sofia, etc. will ride easily in the grooves 220, although they will be moved axially in the manner hereinbefore described, while the cleaning guide 302C ei ects the removal of undesirable material from the groove in which it rides along its leading edge indicated at 302c-1.
It will thus be seen that the chaser 300 is the device for cleaning continuously rotating generally cylindrical press roll shells having a peripheral surface portion presenting alternating generally circumferentially aligned grooves 22c and ridges 225, with the grooves 220 defining a continuous spiral on the periphery of the roll 22. The device 300 is adapted to slidably engage the edge of ti c doctor 30 for relative axial movement carrying a plurality of spaced peripherally aligned parallel guide means 3021:, b, etc. slidably receivable in the grooves on the roll periphery, with the guide means 302s engaging the bottoms of the grooves 22c.
It will thus be seen that the instant chaser 300 affords a unique, sturdy and foolproof device for easily cleaning the grooved (spirally grooved) rolls of the invention during operation, which can be used with any doctor blade, e.g. the doctor blade 30, or can be used with a separate guide element presenting an edge comparable to the doctor blade edge, preferably at the oncoming side of the doctor and preferably for a number or" operations on the down-running side of one of the grooved rolls, so that the chaser will be urged against such device not only by the frictional or dragging effect of the grooved roll, but also by gravity and there will be less chance for the chaser to travel off the end of a doctor, when the operator is not watching, and perhaps drop into operating parts of the machinery. The skilled operator will be able to provide safeguards against such a situation, and the essential structural requirement in the cooperation between the roll and the cross piece is that the spiral groovings on the roll must extend transversely beyond the fixed cross piece or doctor, or the spiral grooves must extend to the end of the roll shell, so that the chaser device can be started and taken E without movement of the doctor or other cross piece to be used for guiding the same in axial movement.
Referring to the grooves 22c shown in FIGURE 70 to be substantially vertical in parallel alignment in the small portion of the roll surface shown in this view, it will be appreciated that the spiral angle or the angle of these grooves 22c to the centroidal axis of the roll shell should be comparatively small angle, alpha, which might be expressed for a 20 inch diameter (i.e. inch radius) press roll as tangent alpha equals approximately 0.125 divided by 10, or 0.0125. The range for tangent alpha should be within about 0.003 to about 0.03, preferably It will be appreciated that spiral angles up to 20 or 30 may be used, particularly if it is desired to have the spiral grooves intersect from time to time, as explained hereinafter with reference to FIGURE 14 and the FIGURE series.
In general, the simple generally circumferential grooves (with a slight helix) have already been described as being preferred for use in the practice of the invention and grooves of this type are distinctly superior for a number of reasons. Nevertheless, there may be instances when it might be desirable to use other grooved structures and such other grooved structures are indicated in FIGURE 14, in top plan view of a fragmentary, small portion of a roll surface, with the views 15A, 15B and 15C indicating fragmentary sections taken in these structures.
For example, in the view of FIGURE 14, it will be seen that the roll surface indicated generally by the reference numeral 200 is provided with a first plurality of helical grooves 201a, 201b, 2010, etc., which are shown as having a helix angle substantially greater than that previously described in connection with the preferred generally circumferentially aligned grooves and ridges. Likewise, the structure of the roll 200 is provided with a second set of generally helical grooves indicated in part at 202a, 202i: and 2020 which have a comparable helix angle to the grooves of the 201 series, but are reversed in direction so as to intersect the grooves of the 201 series thereby obtaining generally diamond-shaped land areas indicated at 203a and 203b. It will be appreciated that the maximum axial dimension of such land areas is represented in FIGURE 15C as extending from a groove intersection R to a groove intersection S shown in plan view in FIGURE 14. The groove width of x compared to the land axial dimension y shown in FIGURE 150 is still within the scope of the instant invention, being on the average about a ratio of xzy to 1:6 or 1:7, and the groove width x that is adapted for use in a web press in the practice of the instant invention will still be within the groove Width range hereinbefore specified (i.e. about 0.005 to about 0.035 inch). The land width y in FIGURE 15C is, of course, closer to the upper limit of about 0.25 inch hereinbefore specified for the land width, in order to minimize cross-machine flow in the plane of the web, here indicated diagrammatically at W9 and thus minimize cross-machine crushing flow. The grooves of the intersections R and S are thus sufficiently close together to avoid the necessary venting to ambient atmosphere at the underside of the felt F44 for the purposes already described herein.
In FIGURE 15B, it will be seen that the generally parallel (although slowly helical) grooves 201]) and 201c have a more narrow land width yB therebetween in the section shown in FIGURE 15B, so that crushing flow in the web is avoided in the direction of the section line XVB-XVB for the reasons hereinbefore described. In the section of FIGURES 15A, it will further be seen that a still more narrow land area yA even in the cross-machine direction of the section line XVAXVA is afforded between the grooves 202a and 20117, as there shown. It will thus be seen that the overall average land width y is within the parameters already set forth, and the grooves of the 201 and 202 series may thus function in the manher hereinbefore set forth, i.e. the overall open area does not exceed 33%% and/or the overall average land to groove ratio is 2:1 or more in the cross-machine direction. The previously described pumping wiper may also be used to remove water from the grooves of this type also, but a rotary brush such as the brush 133x in FIG- URE 10 of my application Serial No. 378,217, filed June 26, 1964, would also be preferred for use in conjunction with the pumping type wiper in order to maintain the grooves in a relatively clean condition for best operation. Also, it will be noted that the roll itself is provided with a rubber cover 200A on a ductile iron shell 200x; and in forming the surface structure indicated in FIG URE 14, it is normally necessary to run the rubber covered roll 200 through a first cutting operation to cut, for example, the helical grooves of the 201 series in one direction and then process the roll 200 a second time to cut the helical grooves of the 202 series in the opposite direction.
The grooves of the 201 and 202 series of FIGURE 14 are actually vented peripherally before and after any nip and on the underside of the felt indicated diagrammatically at F-14 at such nip and they are sufilciently narrow to carry out many of the other functions hereinbefore described. Having such a large helix angle, however, these grooves 201 and 202 are not vented to ambient atmosphere through the shortest distance, as would be the case in the previously described generallycircumferential grooves.
Also, assuming that the dimensions yB between the generally parallel helical grooves 201b and 2010 is approximately 0.1 inch and the grooves are 0.020 inch, it will be appreciated that this would (in the absence of the other set of helical grooves 202) form a basis for an open area of 16%; but the inclusion of the other set of grooves 202 increases the open area to at least about 20%, using grooves 202 of the same size as the grooves 201. Actually, the open area in patterns such as that of FIGURE 14 may be as much as about 33%, particularly if the machine is to be operated relatively slowly and the grooves are themselves cut with substantial volume so that they may function as water troughs. In such instances, land areas of approximately /a of the total area may effect the desired pressing and the initial open area for grooves receiving water flowing away from the nip may be useful. Likewise, the land areas of maximum dimension, such as the land area y of FIGURE 15C may be as much as 0.3 inch in its maximum dimension. It will be appreciated that this maximum happens to be in only one particular direction (i.e. exactly the cross-machine direction) whereas the land sizes here are so small compared to the overall nip size that in a relatively slowly operating machine, the escape routes for the water to the grooves 201 or 202 may well be much shorter, as indicated in FIGURES 15A and 15B, and satisfactory venting of the upper side of the felt W-14 is readily accomplished to afford the function of water troughs for the groove system here described.
In FIGURE 6, it will be noted that the felt 23 is aligned substantially at (or preferably slightly above) a nip tangent plane TT at both the oncoming 23a and offrunning 23b sides by means of the upper surfaces of the guide rolls 24a, 2411 which are positioned on the side of the tangent plane TT opposite the roll 22 so that the felt 23 will have minimum contact with the roll 22 (only at the nip N23), will not tend to have portions entrapped in the grooves 220, wil not tend to close'olf ambient atmosphere at the oncoming or off-running sides of the nip N-3, will undergo minimum wear from contact with the land edges (e.g. at 22b1 of FIGURE 5B which are preferably rather sharply cut to obtain the other advantages described herein), will undergo minimum wear from the limited axial movement of the spiral lands 22b at the nip N-3, will permit the proper positioning of the saveall 25, and will withdraw or receive a minimum amount of water from the grooves 220 at the off-running side 2311 of the nip N-3. The grooves 22c, of course, resist release of water by centrifugal force (particularly more at the uprunning or top of the roll 22 than at the downrunning side when gravity adds to the centrifugal force) but whatever is released (at D-3) is substantially thrown against the upper part of the saveall 25a at the immediate off-running side of the nip N-Ei between the roll 22 and the felt 2317.
Although the travel of the felt 23b at the off-running side is important for many uses, the open area is still very important because some re-wetting of the felt 23b at the off-running side of the nip N-3 is almost instantaneous as the felt expands when the nip pressure is released and the felt is then very absorptive. At this instant the water path is reversed back out of the grooves 22c toward the most remote portion of the absorptive felt 23, which would be along the center line or plane M (FIG- URE B) above each land 2212. It has now been found that in the preferred structure of the roll 22 this reversal of water travel is minimized by the use of a ratio of groove width 26 to land width 27, of a practical minimum of 1:2, and preferably 1:3 to a practical maximum of about 1:20 below which de-watering of the web and/ or felt is unduly hampered at the press nip N-3 (and permits a maximum practical open area of 33%%, but preferably an open area from about 25% to about for practical purposes).
Particularly using the combination of the foregoing (groove-to-land) ratio of 1:2 or 1:3 to 1:20, lands of substantially 0.05 to 0.15 or 0.25 inch width, and grooves of 0.01 to 0.035 inch width, one obtains an unusually versatile press roll for use throughout a press assembly (e.g. at any and preferably all of the grooved roll positions in dicated in the drawings hereof). Excellent results have been obtained using substantially the exact dimensions disclosed for the roll 22 (i.e. 0.025 but preferably about 0.02 inch grooves with about 0.1 inch lands). Groove depths 28 at least sufficient to carry the water load are used, and preferably the foregoing combination includes (substantially radial) groove depths of at least about 2 to 10 times the groove width, at least about equal to the land Width, and at least about 0.1 inch, with maximum groove depth being defined primarily by practical considerations, although square or rounded groove bottoms not substantially deeper than about inch are generally superior to other structures for the combination of strength, cleaning and manufacturing purposes.
Within the foregoing parameters, open areas of 33 /3 (but preferably 25%), 20% and (successiveiy) may I be used in the first, second, and third web presses of a machine, taking 05 less water at each press (e.g. 0.020
inch grooves with 0.030 inch lands typical for and 0.020 inch grooves with 0.105 inch lands typical for about 16% divided press (e.g. at the positions of the rolls 13 and 1.5 of FIGURE 1 with a resulting nip cross section of FIG- URE 9A with corresponding parts indicated by the same reference numerals in the 100 series), one obtains advantages in moisture content control and minimized felt wear, among others. the felt condition entering the web press nip with guide means 11a, 11b, 11c, 11d maintaining the felt at least substantially tangential with the nips N-l, N2, and with additional guide means 24b, 14c separating the'web W11 from the felt 11 at the immediate oncoming and off-- running sides of the Web press nip N-1 for better control of the water transfer from the web W-l to the felt 11 and vice versa.
Referring briefly now to FIGURE 8, it will be seen that FIGURE 8 shows a somewhat different embodiment of the invention, showing an overall press assembly in a View which corresponds generally to the view of FIGURE 1. Parts shown in FIGURE 8 which are substantially identical to parts shown in FIGURE 1 are designated by Using the press roll 22 of the invention in a One obtains superior control of the same reference numeral. Parts which do not correspond exactly to those of FIGURE 1, however (which parts are primarily in the second press designated by the reference numeral 210) are designated by reference numerals in the 200 series whenever there is a general correspondence between the parts of this second press 210 and the parts of the second press 10 of FIGURE 1. Thus the felt and guide rolls are indicated in the 211 series. Also, the stacked press rolls are designated as a Microrok plain bottom roll 212, an intermediate plain press roll 213 deiining the web press nip N201 which receives the web W-3 and the felt 211; and the top grooved roll 215 is indicated in FIGURE 8 as having a grooved roll surface, but this grooved roll surface is that of the previously described roll 22 (particularly with respect to the land and groove relationship). As indicated in FIGURE 10, the felt only nip N402 is thus defined between a plain rubber covered and felt wrapped intermediate or middle roll 213 and a stainless steel clad grooved upper roll 215, having the land and groove relationship previously indicated in FIGURES 5A and 5B hereof. The advantage of this particular press assembly 210 includes the fact that the only grooved roll used 215' is a metal clad roll and the groove arrangement will thus have long wear characteristics. Another advantage is that the metal roll 213 is rubber covered so as to accommodate pressure variations from both the top and bottom. In this respect, the upper grooved roll 215 is mounted with suitable pneumatic pressure positioning and adjusting means of the type known in the art and indicated generally by the double headed arrow P-l. The lower Microrok roll 212 is also mounted by pneumatic positioning and pressure applying means of P-2 of the type now well known in the art. The middle roll 213 may thus be mounted in fixed position and the top and bottom rolls 215 and 212 may be movable for the purposes ordinarily desired in maintenance and operation.
In the arrangement of the press 210, it will be seen that the web W-8 passes through the second press nip N-201 between two plain surfaced rolls 212, 213, so that there is absolutely no opportunity for any marking whatsoever of the web W-t, but because of the divided press arrangement for the press 210, the water expressed from the Web W-8 is transferred at the first press nip N2G1 immediately to the off-running felt 211 which is guided away from the web W-8 and guided into the felt only nip N-202 where it is dewatered by virtue of the grooved roll 215 which is equipped with auxiliary wiper and doctor and saveall elements substantially identical to those employed with the roll 15 of the press 10 in FIGURE 1.
In addition, since it will be appreciated that a certain amount of water will have a tendency to travel on the surface of the plain intermediate roll 213, the roll 213 is provided with an off-running saveall 213e (with doctor a' at the oncoming side of the felt only nip N202), and an oncoming doctor d for the web nip N-201 mounted with a conventional saveall 213 It will also be noted that in the first press 20 and in the third press 14 of FIGURE 8 pneumatic positioning and pressure applying means indicated diagrammatically at P-3 and P-4 are provided for the top rolls in each of these presses (and the bottom rolls 14b and 22 in these two presses may thus be mounted in a comparatively more fixed position).
Another important feature of the invention involves the use of anti-deflection mounting means, which may be used in the practice of, the instant invention to advantage in the mounting of either movable or fixed rolls, although there are certain advantages in mounting the fixed rolls on anti-deflection arrangements or means. Hence, fixed rolls indicated at 13, 213, 14b and 22 may be advantageously mounted on anti-deflection means such as are shown in US. Patent Nos. 2,684,122; 2,651,103; and 2,651,241. In addition, in my co-pending applications Serial No. 102,571, filed April 12, 1961, and Serial No.
'21 154,801, filed November 24, 1961 (now, respectively, U.S. Patent Nos. 3,097,590 and 3,097,591), and also in my US. Patent No. 3,119,324, preferred embodiment of anti-deflection roll mounting means for such rolls are disclosed, and the anti-deflection roll mounting means involving mounting on rubber sandwiches on a through shaft as shown in my application Serial No. 102,571 are employed for mounting the rolls 13, 213, 14.5 and 22 in the embodiments illustrated herein. The deflection control oil-cover shoe system of my US. Patent No. 3,119,324 may instead be used in the rolls 13, 2.13, 14b and 22, and such structure is used in subsequently described grooved rolls 422, 452, 442, 622 and 723, which deflection control subject matter is incorporated herein by reference.
In addition, such grooved press rolls with imperforate shells and mounted on anti-deflection means hereinbefore described, may be employed in automatic, semi-automatic or operator controlled press assemblies for varying the pressures of the various press nips and such controls may include conventional moisture content sensing devices such as the known moisture measuring (beta gauge) devices.
Referring to the grooves 220 which are indicated, for example, in FIGURES A and 513 as having a generally helical or spiral configuration (which cannot actually be shown in the views of FIGURES 5A and 5B), it will be appreciated that the spiral angle or the angle of these grooves 22 with the centroidal axis of the roll shell should be a comparatively small angle, alpha, which might be expressed for a 20 inch diameter (i.e. inch radius) press roll as tangent alpha equals approximately 0.125 divided by 10, or 0.0125. The range for tangent alpha should be within about 0.003 to about 0.03, preferably. This is also the approximate range for a plurality of (continously parallel) helical grooves which may be conven- .iently cut in the roll surface simultaneously (such that the cross section would still look like that of the FIG- URE 5 series); but as previously mentioned greater helical angles can be used (not only for the just mentioned purpose but also) when it is desired to have the grooves intersect from time to time as in the FIGURE series.
It will be noted that in certain views herein (e.g. FIG- URE 6) the grooves in a grooved roll are indicated diagrammatically by dashed lines whereas in other views (e.g. FIGURE 1) grooved rolls are indicated merely by a G centered or within the diagrammatic showing of the roll itself.
Also, in connection with the discussion of the rolls 13 and 15 and their relative covers, as described in connection with FIGURE 9, it will be appreciated that the versatility of the invention is represented therein in that the grooved covers or surfaces for roll used in the practice of the instant invention are shown as being composed of either the resilient yieldable solid elastomer (i.e. rubber) cover for the roll 13 as well as the non-resilient, non-yieldable, durable, non-corrosive stainless steel cover for the roll 15. It will be appreciated that in the case of any of the rolls used in the practice of the instant invention, which are the so-called grooved rolls, the manufacture of such rolls involves expense substantially les than that ordinarily associated with the manufacture and installation of a suction roll, but it is still a manufacturing expense that is somewhat greater than the expense involved in the manufacture of a plain roll which is to be used as a press roll. In fact, the manufacturing expense of the instant grooved rolls is substantially less expensive than that of the blind drilled rolls, such a the structure indicated in FIGURE 3 hereof, even though the structures are comparable in this respect in that the coverfor the roll is, in each case, applied to a generally imperforate roll shell structure which is mounted on anti-deflection means and which may be mounted also with fluid actuated mounting means or other essential equipment for press roll operation. The cutting of grooves is simply less expensive and less complicated than the drilling of the blind drilled holes.
On the other hand, it will be appreciated that, in paper making press assemblies, it is ordinarily considered practical to define press nips with at least one of the rolls having a yieldable surface, so that damage to the two rolls is minimized during operation, in the event of some operating accident which might involve passage of foreign material or even .a sudden change in web or felt thickness through the nip. On the other hand, it will be appreciated that the stainless steel cladding on the surface of a normal imperforate roll shell is ordinarily more expensive than a conventional rubber cover; but the stainless steel cladding is much more durable and the somewhat greater expense which might be involved in machining the grooving therein is ordinarily more than compensated for in the practice of the instant invention by the much greater wearing life of the grooved stainless steel clad roll as compared to a grooved or rubber covered roll. Thus, the grooved roll 15 would be expected to be (and, in fact, is) much more durable in its wearing characteristics and much longer lasting in life in the operation of the press assembly than the corresponding rubber covered roll 13; but the rubber covered roll 13 afiords the distinct advantage of being the so-called yield-able or yielding roll that is between two rolls 12 and 15 which have comparatively nonyielding surfaces. This aifords the additional advantage of the use of the grooved roll 13 in conjunction with a granite or Microrok roll 12.
In FIGURE 9A, it will be seen that a view comparable to that of FIGURE 9 is shown (although slightly en larged for purposes of clarification), but the improvement contemplated in the practice of the instant invention is shown in FIGURE 9A, in that the improved structure of land to groove area is shown in FIGURE 9A. It must be appreciated that FIGURE 9A is representative of the structure which results if FIGURE 1 is modified by the replacement of the rolls 13 and 15 with grooved rolls 113 and 115, respectively, having the groove structure of the roll 22, already described. It Will be seen that the rolls 113 and are indicated as both having rubber covered surfaces, and this is still another concept of the invention, although it will be readily appreciated that in the embodiment of FIGURE 9 the upper roll 115 may well have a stainless steel cover in place of the rubber cover 11511 with the advantages already described. An essential aspect of the showing of the View in FIGURE 9A relates in the advantage of offsetting the grooves 115c and 1130, respectively, so that web damage at the felt only web nip N-102 is minimized and various other advantages are achieved in load balance and the like. Also, the effective distance of one-half of the land area (corresponding to the distance 27 /2 of FIGURE 5B) is now cut in onehalf in the arrangement of FIGURE 9A for the simple reason that the total axial dimension of land area between grooves (even though it will be between a pair of opposed grooves 115a and 1130) has been cut in half.
It must also be appreciated that whenever the grooves 113c and 1150 are truly circumferential (as contrasted to generally spiral), the alignment of the grooves 115cand113r: in a generally offset relationship is easily done and is, of course, preferred. On the other hand, if the grooves 115a and 113s are cutin the generally spiral configuration hereinbefore described as being preferred, then the continuous maintenance of an offset relationship between the grooves of the two rolls is somewhat more difiicult to accomplish in that the relationship between roll size, rotation speed, relative land to groove area relationship in each roll, and the like, must be carefully controlled so as to obtain the maintenance of a truly continuous offset relationship in the area of the press nip N-102. (3n the other hand, it will be appreciated that a substantially continuous offset relationship at the nip pressure area can readily be maintained in the arrangement shown in FIGURE 9A merely by the use of different relationships between the land and groove areas in the two rolls. Thus, the groove widths or openings in each of the two rolls may be maintained substantially equal (or they may also be different), but the open area of the two rolls may be different and in such situations the grooves of the two rolls will generally be continuously offset at the nip area. For example, in the embodiment of FIGURE 9A, the open area for the roll 113 is substantially 20%, whereas the open area for the roll 115 is substantially 25 This relative relationship between the open areas of the two rolls 115 and 113 is employed, notwithstanding the fact that the grooved rolls in each case separate from the nip at which dewatering is carried out along the top side of such nip. Thus, the roll 113 separates from the location of the web nip N-ll (which for purposes of FIG- URE 9A would be numbered N-ltll) along the top side of this nip, so the tendency for the roll to rewet the felt at the off-running side of the nip is somewhat greater than if the grooved roll were to be operating along the underside of the felt. It should be mentioned that the rewetting of the felt in a divided press and the subsequent possibility that the felt itself might throw water back down on the web W-1 is considered in the placing of the auxiliary saveall 11cc in FIGURE 1. Essentially, however, the limited open area of the roll 113 is such that this roll will retain a substantial amount of water collected at the web press nip and this water is then removed by the wiper w and doctor d in the saveall (indicated in FIGURE 1 at 13a). The felt will carry away an additional amount of water and this water is then removed at the felt only nip, which is indicated in FIG- URE 9A as N102, and wherein the open area of the upper roll 115 is approximately 5% greater than the open area of the lower roll 113 so that there is a tendency for at least to a substantial extent from the interior of the felt 111 peripherally outwardly to the grooves of the roll 115, to wash the outer peripheral face of the felt clean. A limited amount of dewatering in the opposite direction, is, of course, not harmful and has advantages in that a certain amount of conditioning of the inner peripheral surface of the felt loop is also desired.
Another aspect of the instant invention resides in the control of nip pressures not only at the first, second and third web press nips (i.e. N-3, N-1 and N-14, respectively of FIGURE 1) but also in control of the nip loads between a web press and the felt only press associated therewith in a divided press structure. Thus, it is preferred in the practice of the instant invention to employ an initial nip load at nip N-3 (of FIGURES 1 or 8) of about 200 pounds per lineal inch, and using an open area of about 25% on the roll 22, so that maximum dewatering takes place without the use of maximum nip loads on the initial relatively delicate web. Next, at the second web press nip N-l, a higher nip load of 300 pounds per inch is used. Likewise, an open area of only about 20% in the grooved roll 13 is preferably used, as indicated in the arrangement described in connection with FIGURE 9A. It has previously been pointed out that the arrangement of FIGURE 9 which was described initially in connection with the roll 13 was described for purposes of showing one aspect of a grooved roll divided press arrangement embodying the instant invention and it was described initially for purposes of comparison with the superior operation of rolls III having superior land to groove relationships such as the rolls 22, 113 and 115, etc. Nevertheless, the nip loads at the hips N4 and N-Z will require that the felt only nip load N-2 should be at least as great as the nip load N-l and preferably greater. The nip load used at N-Z is 325 pounds per inch. The nip load at N402 is also 325 pounds per lineal inch (using a nip load of 300 pounds per lineal inch for the corresponding web press nip N-ltil); whereas the nip load N-202 in the divided press of FIGURE 8 is about 350 pounds per inch, using a web press nip load of 300 pounds per inch at N-201, for the reason that all of the dewatering must take place via the grooved roll 215 and the entire felt dewatering and reconditioning takes place by virute of the presence of the grooves 2150 on the face of the roll 215, which is employed with an open area of 20%. In such instances, the third web press nip N-14 of FIGURE 8 may be operated as indicated, primarily as a smoothing and compacting nip between two plain rolls, or this third press nip N-14 may be operated using a structure that is identical to the press structure 20 hereinbefore described in detail, including an upper plain press roll 21 and a lower grooved press roll 22, with the sole exception that the lower press roll 22 would be operated with an open area of about 15% for the relatively minimum amount of mechanical dewatering required at this last nip N14 and for the use of maximum land area contact with the web protected by the felt, and the nip load at such last nip is thus preferably about 400 pounds per inch.
The advantages of the present invention in that a grooved roll may be substituted for a suction roll in a number of different positions, will be readily appreciated when one considers that the suction roll, because of the perforate suction roll shell and the necessary auxiliary equipment for suction rolls can be mounted for purposes of resisting deflection only by complicated and expensive mounting mechanism, if at all. Thus, in particular, in the case of the press couple 20, a perforate suction roll in the position of the grooved roll 22 would necessarily have limitations in its operation with respect to the application of a uniform (axially applied) nip load, even though the average nip load employed at the first web press nip N3 is comparatively low. It will further be appreciated that as the nip loads are increased, the advantages of the grooved roll become more and more apparent, for the reason that the suction roll has definite limitations in connection with the application of uniform nip loads axially at high average nip loads. Thus, if a grooved roll is used to replace the roll 14b at the underside of the third nip N-M, in the manner already described, the distinct advantage of the grooved roll over a suction roll will become readily apparent at the high nip loads used.
Referring now to the press assembly shown in FIG- URE 11, it will be seen that the second web press nip N-31 is formed of a three-roll divided press wherein the elements shown are substantially the same as those shown in second press 10 of the embodiment of FIGURE 1 and elements having the same structure and functionas those shown in FIGURE 1 are designed by the same reference numeral in the 300 series. Thus, the second press is designated 310. Also, the third press N-23 is formed of an upper plan roll 321 and a lower grooved roll 322 having an open area of about 16% (i.e. 0.020 inch grooves with 0.105 inch lands); and the elements of the third press N-23 which corresponds substantially in function and structure to those elements of the first press 20 of FIGURE 1 are designated by the same reference numerals in the 300 series in FIGURE 11. FIG- URE 11 thus shows a press assembly wherein the third press N23 is also formed by press rolls which include a grooved roll 322.
Referring now to the first web press nip N-33 in FIG-