CA2034829C - Papermaking machine press section - Google Patents
Papermaking machine press sectionInfo
- Publication number
- CA2034829C CA2034829C CA 2034829 CA2034829A CA2034829C CA 2034829 C CA2034829 C CA 2034829C CA 2034829 CA2034829 CA 2034829 CA 2034829 A CA2034829 A CA 2034829A CA 2034829 C CA2034829 C CA 2034829C
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- Prior art keywords
- press
- felt
- web
- nip
- roll
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- 229920003051 synthetic elastomer Polymers 0.000 description 1
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- Paper (AREA)
Abstract
A press section for a papermaking machine has four press nips and five press felts. In a preferred embodiment, each of the press nips is formed between press rolls having plain, water impervious surfaces. In each press nip, the paper web is supported between an upper and lower press felt to permit dewatering through both its surfaces. The web remains supported by at least one felt from the point where it is picked up from the forming wire to the point where it is transferred onto a dryer roll.
Description
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
This invention relates to papermaking. More specifically, this invention relates to the press section in a papermaking machine where the moist, newly formed paper web is pressed between cooperating press roll couples to mechanically extract water from the traveling web and into co-running felts. Still more specifically, this invention relates to a press section having four nips, each of which is double felted, and which utilizes a total of five felts.
DESCRIPTION OF THE PRIOR ART
In the papermaking industry, many types of press sections in a papermaking machine are known and used. Typically, the press section operates by passing the moist paper web between tWG nipped press rolls together with one or two looped felts to receive the water extracted under the pressure of the nip line of contact between the cooperating press rolls which are loaded together. The rolls have surfaces which can take various forms, such as plain, grooved and perforated with holes. Usually, but not always, the holes are drilled through 203~29 the roll shell to permit the application of sub-atmospheric (vacuum) pressure to the web through a felt by a source of vacuum pressure within the roll. Also, the rolls can have covers comprising natural or artificial rubber compounds having various degrees of hardness. The rolls also can be made of solid granite to provide a surface to which the web has a greater affinity than rubber. Each of the roll surface configurations has an advantage and, under some operating conditions, each configuration has some disadvantages.
Suction press rolls have the advantage of being able to receive water into their perforations and utilize vacuum pressure within the roll to hold the water in the roll cover perforations for a period of time sufficient to enable the roll cover to rotate past the nip at which time the vacuum pressure is released and the water is permitted to be flung outward into a save-all for disposal. However, such press rolls cannot retain substantial amounts of water in their perforated covers beyond certain roll rotational speeds and the perforated roll covers cannot withstand extremely high nip pressures. Finally, the perforations in the roll cover can also operate to limit the nip pressure since pressures beyond certain amounts can cause shadow marking in the paper web through the press felt.
~ Press rolls having a plurality of equally sp'aced, circumferentially extending annular grooves can generally operate to remove equal or greater amounts of water from the web through an intermediate felt at the same or greater speeds than suction press rolls, but grooved rolls also are susceptible to marking the web under certain operating conditions and dewatering the web unevenly between the lands and grooves.
Grooved rolls, perforated suction rolls, so-called blind drilled rolls (i.e. rolls having holes drilled into, but not through, their covers) and plain surfaced rolls have been used in various combinations as attested by the great number of patents relating to press sections in papermaking machines.
Some of these combinations of types of press rolls have utilized a single press felt and some have utilized double press felts with the paper web passing through the press nip between the felts. All of the prior press configurations have provided, with varying degrees of success, increased papermaking speed with equal or better quality of the particular grade of paper produced. Some press configurations have advantages in the rate of initial dewatering in the first or second press nip; some have an advantage in the total amount of dewatering provided at the end of the press section;
some provide superior runnability and speed.
The problem which occurs with each press roll configuration is that eventually a machine speed is reached at which the paper web cannot be further dewatered, at least not efficiently, or the quality of either or both of its surfaces cannot be maintained. Sometimes, the paper web can neither be dewatered nor have its quality maintained above a certain speed in a given press configuration. Sometimes, factors affecting the runnability of the press section, such as felt conditioning and broke removal, become more important than they otherwise would be.
other problems which occur at different speeds in different press configurations relate to rewetting of the web as it passes from a press nip, and web flutter which occurs when the web travels unsupported between successive nips.
Generally, rewetting occurs when the combination of roll cover configuration, felt and nip pressure are such that water emerges from the felt back onto the paper web surface immediately after the press nip due to the release of pressure which otherwise keeps the water in the felt or interstices in the roll cover. Web flutter occurs due to the instability of the paper web as it is buffeted by wind currents and machine vibration as a function of the distance of its open-draw span between supporting felts or roll surfaces.
SUMMARY OF THE INVENTION
The aforementioned problems relating to the operation of press sections in papermaking machines have been greatly diminished by this invention. Four, straight-through type press nips are provided, each of which is double felted to permit dewatering on either side of the paper web. In addition, the web is always carried on the surface of a felt from~one nip to the next nip between each of the four nips.
Each successive press nip alternately has a lower or upper felt which passes through the nip fresh from the felt - 20~829 conditioning apparatus which is in the loop of each felt after the most downstream nip through which it passes. Further, each of the successively arrayed felts in the downstream direction pass through only two press nips alternately on either side of the paper web traveling through the press section. The first felt nips the web over the forming wire and then passes through the first press nip. All this ensures more even dewatering, felt wear and control of the web between nips. Each nip is double felted; each nip utilizes two different press rolls; each nip is of the straight-through type; and each nip utilizes one freshly conditioned felt, which felt alternates from the upper to the lower side of the paper web as the web passes through successive nips. In a preferred embodiment, all of the press rolls comprise plain surfaced rolls.
Accordingly, it is an object of this invention to provide a press section having four press nips which utilize five separate felts.
Another object of this invention is to provide a press section having four press nips, each of which is double felted and wherein each felt passes through only two nips.
` Another object of this invention is to provide a press sect~on wherein each nip utilizes two separate rolls.
Still another object of this invention is to provide a press section having no open draws.
A feature of this invention is the use of four press couples, each of which utilizes plain surfaced press rolls.
An advantage of this invention is its runnability and ease of broke removal.
These, and other objects, features and advantages of this invention will be readily apparent to those skilled in the art upon reading the description of the preferred embodiments in conjunction with the attached drawings.
IN THE DRAWINGS
Figure 1 is a side-elevational view of the press section showing a preferred embodiment of the press roll configuration.
Figure 2 is a side-elevational view of the press section showing another configuration of the press rolls.
Figure 3 is a side-elevational view of another press section roll configuration.
-Figure 4 is a side-elevational view of still another press section roll configuration.
Figure 5 is a cross-sectional view of a press felt having a construction which can advantageously be used in this invention.
203~829 Figure 6 is a side-elevational view of a felt passing over a felt roll equipped with a cleaning doctor.
Figure 7 is a side-elevational view of a felt passing over a felt roll and having a hot air jet impinging upon the felt.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As shown in Figure 1, a papermaking machine forming wire F0 traveling in the direction of arrow A1 travels over a wire turning roll 20. A first press felt F1 is brought into co-running engagement with a paper web W over a span of the forming wire by a pick-up roll 9 over which it travels.
Downstream of pick-up roll 9 is a first press comprising press rolls 1,2. A lower press felt F2 is disposed to travel, together with web W and felt F1, through a nip N1 between nipped press rolls 1,2. Both felts Fl,F2 form an endless loop and have felt cleaning equipment 21,22 within their respective loops downstream of the last press nip through which they pass.
~ Downstream of nip N1 is a second press nip N2 formed between press rolls 3,4. An upper felt F3 is trained to pass thro~gh nip N2 together with web W which is carried on the upper (outer) surface of lower felt F2, which also passes through nip N2.
- Downstream of nip N2 is a third press nip N3 between press rolls 5,6. Downstream of nip N2, web W adheres to the lower (outer) surface of F3 and passes through nip N3 together with a lower felt F4.
Downstream of nip N3 is a fourth nip N4 between press rolls 7,8. Downstream of nip N3, web W has transferred to the upper (outer) surface of lower felt F4 and travels with the web through nip N4 together with upper felt F5. The web W
remains on felt F5 and is brought into engagement with a first dryer roll 15 to which the web transfers. The dryer felt FD
is brought into co-running engagement with the web over a downstream section of the surface of dryer roll 15, and the web transfers to felt FD for subsequent travel through the dryer section as exemplified by dryer roll 16.
In the drawings, corresponding elements in different figures are distinguished by different hundred series for purposes of discussion.
In the preferred embodiment shown in Figure 1, each of the press rolls 1,2,3,4,5,6,7 and 8 has a plain surface. That is, the surface of each roll takes the form of a smooth, continuous cylinder which comprises a relatively hard, water impervious rubber cover. The web is transferred to the desi~ed felt F2 after nip N1; F3 after nip N2; F4 after nip N3; and F5 after nip N4 by either or a combination of both of two techniques. First, and most preferred, is to use felts having progressively smoother web-contacting surface batts comprising finer fibers in the paper web contacting surfaces of successive felts Fl-FS. Thus, felt F2 would have a finer paper web side batt than felt Fl, and the web would tend to adhere to felt F2 after nip Nl. After nip N2, the web would tend to adhere to finer batt surfaced felt F3, and so on with respect to felts F4,F5.
The second technique is by positioning the felt guide roll 10 immediately following the particular nip to direct the other felt in any given nip to slightly wrap the press roll it is contacting for a greater distance, or angle of wrap, than the distance the felt to which it is desired the web should adhere wraps the press roll it is contacting. Thus, immediately after nip Nl, felt Fl is directed upwardly from the substantially horizontal plane in which felt F2 and web W
travel. Similarly, downstream of nip N2, felt F2 is directed downwardly at an angle to the plane of travel of felt F3 and web W which is substantially normal to a line between the axes of revolution of rolls 3,4. The configurations regarding nips N3 and N4 correspond to the description with regard to nips Nl and N2, respectively. In the straight-through nip configuration of nips Nl-N4 of this invention, neither of the felts in each of the double-felted nips wraps a press roll for any significant distance, although one of the felts in each nip wraps a press roll for a small distance to effect the web transfer onto the other felt.
All of the looped felts Fl,F2,F3,F4 and F5 travel over corresponding felt guide rolls 10 and have their surfaces conditioned by felt conditioning apparatus 21-25 which is somewhat schematically shown and which essentially dewaters the felts preparatory to passing through their respective initial nips. A cleaning/lubricating shower 26 is disposed over the outside of each felt upstream of the felt conditioning apparatus. The cleaning and lubricating showers can be separate apparatus.
Pressurized fluid jet means 12,13 and 14, which in a preferred embodiment comprise a cross-machine extending pipe having a plurality of nozzles spaced along its length and which are supplied by a source (not shown) of pressurized fluid, such as steam, are disposed on the web side of each of felts F2,F3 and F4, respectively, to direct pressurized air against the web in the span between nips Nl,N2; N2,N3 and N3,N4 to assist the web to remain in co-running association with its felt in the event that the web, or portions of the web, momentarily became disengaged from its felt.
Corresponding suction boxes 12',13',14' are disposed beneath the felts beneath each of the jet means 12,13,14 to assist this process.
In a preferred embodlment as shown in Figure 1, each of the~press rolls 1-8 comprises a so-called plain press roll.
That is, the surface of each press roll comprises a smooth, cont~nuous cylindrical surface. Preferably, the outer periphery of each press roll is made of a hard rubber cover.
- In alternate embodiments, shown in Figures 2, 3 and 4, the press rolls do not all comprise plain press rolls in the sense that their outer surfaces comprise a plain, smooth cylindrical surface. Thus, in Figure 2, each of the press rolls 101-108 comprises a grooved roll. Such grooved rolls preferably are rolls having rubber covers with a plurality of circumferential grooves, equally spaced axially along the surface of the roll. The rolls are thus water impervious, like the plain surfaced press roll shown in Figure 1, but the grooves accommodate water expressed from the web as it passes through the nip and into the felts on either side thereof.
This allows either more water to be expressed from the felt and web over the land areas of the grooved roll, or water to be expressed at a higher unit nip pressure, or both. The unit nip pressure is higher at a given loading force applied between nipped rolls due to the smaller area of contact along the nip line produced by the grooves.
In the embodiment shown in Figure 3, upper press roll 201 comprises a grooved press roll while lower press roll 202 comprises a suction press roll. Suction press rolls have a roll shell, preferably rubber covered, wherein a vast number of holes are drilled through the cover and roll shell in a uniform pattern to permit water expressed from the felt as it passes through the nip to be received into the cylindrical holes and held therein by a sub-atmospheric pressure (vacuum) applied to a longitudinally extending segment of the inner surface of the perforated roll shell by a suction gland indicated schematically at 219. The suction gland in the suction roll also operates to positively transfer the paper web onto the felt F2 over the suction roll 202. In this embodiment, the other press rolls 203-208 are plain covered, or grooved, press rolls.
In the embodiment shown in Figure 4, alternate lower and upper press rolls 302,303,306 and 307 are suction press rolls while press rolls 301,304,305 and 308 are plain covered, or grooved, press rolls. Each of the suction press rolls includes a suction gland 319,329,339 and 349 to provide the sub-atmospheric pressure within the respective rolls 302,303,306 and 307.
Under certain operating conditions, suction rolls 302, 303,306 and 307 could be replaced by so-called blind drilled rolls. Such blind drilled rolls have rubber covers which look like ordinary suction rolls except that the holes drilled into the covers do not extend through the roll shell so that no sub-atmospheric air pressure can be applied to the felt beneath the web in the nip from any source of vacuum pressure within the roll.
In order to enhance the performance of this press section and~maximize its operation, a felt 31 having a relatively finer textured surface 32 on the side which contacts the paper web,~and a relatively coarser, more open mesh on the surface 33 away from the web, is preferred. Such a felt is shown in cross section in Figure 5. Since this press section utilizes four, straight-through types of press nip configurations _-(i.e., the web passes straight through the nip without significantly wrapping a roll) in conjunction with a freshly conditioned felt in each nip, the individual nips provide superior water removal from the web. In a straight-through nip configuration, the web passes through the press nip and then remains on a felt over a roll surface for either a very small segment of circumferential travel on a roll surface, or is directed away from both rolls in a plane which is substantially perpendicular to an imaginary plane containing the axes of revolution of the rolls in the press roll couple.
Such a straight-through press couple configuration provides less opportunity for rewetting of the web by water emerging from the felt as the felt is depressurized upon its passage through the nip. Further, the four consecutive nips, each of which utilizes two different press rolls with each successive nip utilizing two felts with a fresh felt alternately in the lower and upper positions in successive nips, permits a relatively closed felt to be utilized. This both allows improved dewatering while promoting superior fines retention and surface uniformity on both sides of the paper due to the symmetry of the application of the felts to the upper and lower surfaces of the web in conjunction with the fine textured surface of the felts. Finally, four, separately felted press nips result in enhanced dryness of the web leaving the press section as machine speed increases.
The felt fibers in the first and second nip felts are preferably coarser than the fibers in the third and fourth nip felts. Thus, first and second nip felts might be comprised of about 15 denier range fibers, and third and fourth nip felts might be comprised of about 3 denier range fibers on their web contacting surfaces. Their other sides (the side opposite to the sheet side of the felt) would have coarser fibers for easier dewatering.
Figure 6 illustrates how a driven felt guide roll 10' can be positioned within a looped felt, preferably felt F4 and/or F5, and operated to dewater the felt. Roll 10' is driven at a speed from about 110 percent to about 150 percent of the felt speed to induce water through the felt and out of the relatively open mesh on its inner surface. A doctor 27 engages the surface of the roll to skim water carried thereon from the felt off for collection and eventual discharge. Such a driven felt guide roll is shown within felt F5 in Figure 1, but can be used in conjunction with the apparatus in Figures 2-4.
Figure 7 illustrates a dewatering and felt conditioning apparatus comprising a nozzle 30 which projects a jet of hot air against the outer surface of the felt which contacts the paper web W when the web passes through the nip. The hot air jet is very narrow, such as about 0.02 inches, and extends the full width of the web to impinge upon the web as it passes over a felt guide roll 10". The web is thus conditioned and dewa~ered to be fresh before it passes through the first, upstream nip in its looped path of travel.
~ 2~8~-q _ The purpose of the dewatering apparatus shown in Figures 6 and 7 is to keep felts F4 and F5 running as dry as possible.
Either device can be used in conjunction with either felt F4,F5. They are considered illustrative only and not limiting as to the type of dewatering apparatus which can be used.
In operation, with particular reference to Figure 1 and general reference to Figures 2-4, web W is urged from forming wire FO by the sub-atmospheric air pressure in suction gland 17 of pick-up roll 9 which presses felt F1 against the web over the forming wire. The web is carried on the underside of felt F1 and comes into co-running engagement with lower felt F2 at, or immediately before, nip N1 between rolls 1,2 through which it passes. As previously stated, the preferred manner of transferring the web from the felt which does not travel through the next downstream nip to the felt which does pass through the next downstream nip is to use felts having successively finer batts on their sides which face the paper web alternating in the lower and upper positions in successive nips. Thus, felt F5 is finer than felt F4 which is finer than felt F3 which is finer than felt F2 which is finer than felt F1.
.~
- The other web transfer technique is to use either felts of~choice, or successively finer batt felts as described above, in conjunction with positioning the felt coming off the web relative to the felt to which the web will adhere. In this technique, felt guide roll 10 immediately downstream of nip N1 within looped felt F1 guides felt F1 at a small angle 203~829 upwardly from the plane of travel of felt F2 between press rolls 2 and 4. This produces less area of felt F1 against the web relative to the area of felt F2 against the web in the immediate vicinity downstream of nip N1 with the effect that web W is maintained on felt F2 as it travels toward nip N2 between press rolls 3,4. To further ensure that the web is urged to remain on felt F2, a steam pressurized nozzle 12 is disposed outside the web over felt F2 in the span between felts F1 and F3 to maintain a stream of pressurized steam against the web.
As the web is carried on felt F2 toward nip N2, looped felt F3 is guided by its felt guide rolls 10 into co-running engagement with the outer surface of the web over felt F2 immediately before, or at, nip N2 between rolls 3,4.
Immediately downstream of nip N2, looped lower felt F2 is guided by a felt guide roll 10 downwardly away from the plane of travel of felt F3 between rolls 3 and 5. This produces a relatively larger area of contact between the web and felt F3 compared to the area of contact between the web and felt F2 in the immediate vicinity of the out-going side of nip N2 with the corresponding effect that the web rem~; n~ on felt F3. A
pressurized air nozzle 13 is disposed outside the web over felt F3 between felts F2,F4 and directs pressurized air agalnst the web to urge it to remain in contact with felt F3 between nips N2,N3.
Downstream of nip N2, the web is traveling on felt F3, and looped lower felt F4 is brought into co-running engagement with the web either at, or immediately before, nip N3 between press rolls 5,6. Downstream of N3, felt guide roll 10 within looped felt F3 guides felt F3 upwardly and away from the plane of looped lower felt F4 between lower press rolls 6,8. The paper web W is transferred to the lower felt F4 in the same manner as described in conjunction with the web transfer from felt Fl onto felt F2. The web is thus transported on felt F4 into nip N4 between press rolls 7,8.
As the web on felt F4 approaches nip N4, looped upper felt F5 is directed by a felt guide roll 10 to come into co-running engagement with the web either at, or immediately before, nip N4. The web thus passes through nip N4 in double-felted engagement with felts F4,F5 in a manner similar to its double-felted passage through nips Nl,N2,N3.
Downstream of nip N4, a felt guide roll 10, within looped lower felt F4, directs felt F4 away from the plane of upper felt F5 in the portion of its travel between nip N4 and the top surface of dryer roll 15 over which felt F5 is guided by a downstream felt guide roll 10 within looped felt F5. The web W is transferred onto the outer surface of felt F5 in the same manner it is transferred onto the outer surface of felt F3 as described in conjunction with its emergence from nip N2.
\
~ The web is thus guided onto, and transferred onto, dryer roll 15 by felt F5 which is directed into contact with dryer roll 15 by downstream felt guide roll 10 which can move vertically up and down as shown by directional arrow 28. As 203~829 the felt travels over the surface of dryer roll 15, dryer felt FD traveling in the direction of arrow A2 is brought into co-running engagement with the web, and the web is transferred onto the outer surface of looped felt FD with the assistance of suction roll 34 and is thus directed through the remainder of the dryer section as exemplified by roll 16.
All of the looped felts are equipped with cleaning showers 26 and felt conditioning apparatus 21-25 to condition and dewater the felts to a desired degree of dryness. In addition, as shown in Figures 1 and 6, upper felt F5 is equipped with a doctor 27 engaging the surface of felt guide roll 10' to further dewater that felt. Similarly, as shown in Figures 1 and 7, lower felt F4 is equipped with a hot air type of doctor 30 which directs a pressurized stream of hot air onto the outer side of the felt to further dry and condition the felt before it comes into contact with the web in nip N3.
This four nip, five felt, straight-through press arrangement is thus seen to exhibit several features and operational advantages. In each of the press nips, in addition to being double felted, both felts come into engagement with the press rolls and come out of engagement with the press rolls in a substantially symmetrical manner and do`not travel over the surface of any press roll for a significant distance. The web is removed from contact with a felt essentially immediately after a nip which results in higher sheet dryness.
- 203~829 - Immediately after nips N2,N4, looped lower felts F2 and F4 provide an opportunity to direct broke downwardly into broke pits beneath the papermaking machine. Paper is thus prevented from traveling any great distance through the papermaking machine, and especially through more than two press nips, thus mitigating potential damage to the felts and roll covers due to wads of paper web passing through a nip.
Each of the press nips has one felt which has been freshly conditioned for entering a nip. Further, in each press nip, the freshly conditioned felt alternates between being the lower felt and the upper felt in successive nips.
Thus, in nip Nl, lower felt F2 has been freshly conditioned;
in nip N2, upper felt F3 has been freshly conditioned; in nip N3, lower felt F4 has been freshly conditioned; in nip N4, upper felt F5 has been freshly conditioned. This provides additional symmetry to the dewatering process as the web passes through successive nips which promotes less two-sidedness in the paper produced.
Finally, and perhaps most importantly, this invention, particularly the plane surfaced press roll configuration shown in Figure 1, promotes uniformity of the dewatering process due to the cross-machine uniformity of the surfaces of the press rolls which load the press nips in the press dewatering process. From a papermaking standpoint, this means that water flows essentially evenly from both surfaces of the paper web to provide more uniform paper formation. In this regard, as shown in Figures 2-4, in this apparatus, such grooved roll and suction roll press configurations are also symmetrical to provide both the advantages of the application of grooved and suction rolls while still incorporating the symmetry, cross-machine uniformity of nip surfaces and runnability of this invention.
Naturally, variations and modifications of the apparatus can be made without departing from the spirit and scope of the invention disclosed. Accordingly, such modifications and conditions as might become clear to those skilled in the art are intended to fall within the scope of the invention as defined by the claims.
FIELD OF THE INVENTION
This invention relates to papermaking. More specifically, this invention relates to the press section in a papermaking machine where the moist, newly formed paper web is pressed between cooperating press roll couples to mechanically extract water from the traveling web and into co-running felts. Still more specifically, this invention relates to a press section having four nips, each of which is double felted, and which utilizes a total of five felts.
DESCRIPTION OF THE PRIOR ART
In the papermaking industry, many types of press sections in a papermaking machine are known and used. Typically, the press section operates by passing the moist paper web between tWG nipped press rolls together with one or two looped felts to receive the water extracted under the pressure of the nip line of contact between the cooperating press rolls which are loaded together. The rolls have surfaces which can take various forms, such as plain, grooved and perforated with holes. Usually, but not always, the holes are drilled through 203~29 the roll shell to permit the application of sub-atmospheric (vacuum) pressure to the web through a felt by a source of vacuum pressure within the roll. Also, the rolls can have covers comprising natural or artificial rubber compounds having various degrees of hardness. The rolls also can be made of solid granite to provide a surface to which the web has a greater affinity than rubber. Each of the roll surface configurations has an advantage and, under some operating conditions, each configuration has some disadvantages.
Suction press rolls have the advantage of being able to receive water into their perforations and utilize vacuum pressure within the roll to hold the water in the roll cover perforations for a period of time sufficient to enable the roll cover to rotate past the nip at which time the vacuum pressure is released and the water is permitted to be flung outward into a save-all for disposal. However, such press rolls cannot retain substantial amounts of water in their perforated covers beyond certain roll rotational speeds and the perforated roll covers cannot withstand extremely high nip pressures. Finally, the perforations in the roll cover can also operate to limit the nip pressure since pressures beyond certain amounts can cause shadow marking in the paper web through the press felt.
~ Press rolls having a plurality of equally sp'aced, circumferentially extending annular grooves can generally operate to remove equal or greater amounts of water from the web through an intermediate felt at the same or greater speeds than suction press rolls, but grooved rolls also are susceptible to marking the web under certain operating conditions and dewatering the web unevenly between the lands and grooves.
Grooved rolls, perforated suction rolls, so-called blind drilled rolls (i.e. rolls having holes drilled into, but not through, their covers) and plain surfaced rolls have been used in various combinations as attested by the great number of patents relating to press sections in papermaking machines.
Some of these combinations of types of press rolls have utilized a single press felt and some have utilized double press felts with the paper web passing through the press nip between the felts. All of the prior press configurations have provided, with varying degrees of success, increased papermaking speed with equal or better quality of the particular grade of paper produced. Some press configurations have advantages in the rate of initial dewatering in the first or second press nip; some have an advantage in the total amount of dewatering provided at the end of the press section;
some provide superior runnability and speed.
The problem which occurs with each press roll configuration is that eventually a machine speed is reached at which the paper web cannot be further dewatered, at least not efficiently, or the quality of either or both of its surfaces cannot be maintained. Sometimes, the paper web can neither be dewatered nor have its quality maintained above a certain speed in a given press configuration. Sometimes, factors affecting the runnability of the press section, such as felt conditioning and broke removal, become more important than they otherwise would be.
other problems which occur at different speeds in different press configurations relate to rewetting of the web as it passes from a press nip, and web flutter which occurs when the web travels unsupported between successive nips.
Generally, rewetting occurs when the combination of roll cover configuration, felt and nip pressure are such that water emerges from the felt back onto the paper web surface immediately after the press nip due to the release of pressure which otherwise keeps the water in the felt or interstices in the roll cover. Web flutter occurs due to the instability of the paper web as it is buffeted by wind currents and machine vibration as a function of the distance of its open-draw span between supporting felts or roll surfaces.
SUMMARY OF THE INVENTION
The aforementioned problems relating to the operation of press sections in papermaking machines have been greatly diminished by this invention. Four, straight-through type press nips are provided, each of which is double felted to permit dewatering on either side of the paper web. In addition, the web is always carried on the surface of a felt from~one nip to the next nip between each of the four nips.
Each successive press nip alternately has a lower or upper felt which passes through the nip fresh from the felt - 20~829 conditioning apparatus which is in the loop of each felt after the most downstream nip through which it passes. Further, each of the successively arrayed felts in the downstream direction pass through only two press nips alternately on either side of the paper web traveling through the press section. The first felt nips the web over the forming wire and then passes through the first press nip. All this ensures more even dewatering, felt wear and control of the web between nips. Each nip is double felted; each nip utilizes two different press rolls; each nip is of the straight-through type; and each nip utilizes one freshly conditioned felt, which felt alternates from the upper to the lower side of the paper web as the web passes through successive nips. In a preferred embodiment, all of the press rolls comprise plain surfaced rolls.
Accordingly, it is an object of this invention to provide a press section having four press nips which utilize five separate felts.
Another object of this invention is to provide a press section having four press nips, each of which is double felted and wherein each felt passes through only two nips.
` Another object of this invention is to provide a press sect~on wherein each nip utilizes two separate rolls.
Still another object of this invention is to provide a press section having no open draws.
A feature of this invention is the use of four press couples, each of which utilizes plain surfaced press rolls.
An advantage of this invention is its runnability and ease of broke removal.
These, and other objects, features and advantages of this invention will be readily apparent to those skilled in the art upon reading the description of the preferred embodiments in conjunction with the attached drawings.
IN THE DRAWINGS
Figure 1 is a side-elevational view of the press section showing a preferred embodiment of the press roll configuration.
Figure 2 is a side-elevational view of the press section showing another configuration of the press rolls.
Figure 3 is a side-elevational view of another press section roll configuration.
-Figure 4 is a side-elevational view of still another press section roll configuration.
Figure 5 is a cross-sectional view of a press felt having a construction which can advantageously be used in this invention.
203~829 Figure 6 is a side-elevational view of a felt passing over a felt roll equipped with a cleaning doctor.
Figure 7 is a side-elevational view of a felt passing over a felt roll and having a hot air jet impinging upon the felt.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As shown in Figure 1, a papermaking machine forming wire F0 traveling in the direction of arrow A1 travels over a wire turning roll 20. A first press felt F1 is brought into co-running engagement with a paper web W over a span of the forming wire by a pick-up roll 9 over which it travels.
Downstream of pick-up roll 9 is a first press comprising press rolls 1,2. A lower press felt F2 is disposed to travel, together with web W and felt F1, through a nip N1 between nipped press rolls 1,2. Both felts Fl,F2 form an endless loop and have felt cleaning equipment 21,22 within their respective loops downstream of the last press nip through which they pass.
~ Downstream of nip N1 is a second press nip N2 formed between press rolls 3,4. An upper felt F3 is trained to pass thro~gh nip N2 together with web W which is carried on the upper (outer) surface of lower felt F2, which also passes through nip N2.
- Downstream of nip N2 is a third press nip N3 between press rolls 5,6. Downstream of nip N2, web W adheres to the lower (outer) surface of F3 and passes through nip N3 together with a lower felt F4.
Downstream of nip N3 is a fourth nip N4 between press rolls 7,8. Downstream of nip N3, web W has transferred to the upper (outer) surface of lower felt F4 and travels with the web through nip N4 together with upper felt F5. The web W
remains on felt F5 and is brought into engagement with a first dryer roll 15 to which the web transfers. The dryer felt FD
is brought into co-running engagement with the web over a downstream section of the surface of dryer roll 15, and the web transfers to felt FD for subsequent travel through the dryer section as exemplified by dryer roll 16.
In the drawings, corresponding elements in different figures are distinguished by different hundred series for purposes of discussion.
In the preferred embodiment shown in Figure 1, each of the press rolls 1,2,3,4,5,6,7 and 8 has a plain surface. That is, the surface of each roll takes the form of a smooth, continuous cylinder which comprises a relatively hard, water impervious rubber cover. The web is transferred to the desi~ed felt F2 after nip N1; F3 after nip N2; F4 after nip N3; and F5 after nip N4 by either or a combination of both of two techniques. First, and most preferred, is to use felts having progressively smoother web-contacting surface batts comprising finer fibers in the paper web contacting surfaces of successive felts Fl-FS. Thus, felt F2 would have a finer paper web side batt than felt Fl, and the web would tend to adhere to felt F2 after nip Nl. After nip N2, the web would tend to adhere to finer batt surfaced felt F3, and so on with respect to felts F4,F5.
The second technique is by positioning the felt guide roll 10 immediately following the particular nip to direct the other felt in any given nip to slightly wrap the press roll it is contacting for a greater distance, or angle of wrap, than the distance the felt to which it is desired the web should adhere wraps the press roll it is contacting. Thus, immediately after nip Nl, felt Fl is directed upwardly from the substantially horizontal plane in which felt F2 and web W
travel. Similarly, downstream of nip N2, felt F2 is directed downwardly at an angle to the plane of travel of felt F3 and web W which is substantially normal to a line between the axes of revolution of rolls 3,4. The configurations regarding nips N3 and N4 correspond to the description with regard to nips Nl and N2, respectively. In the straight-through nip configuration of nips Nl-N4 of this invention, neither of the felts in each of the double-felted nips wraps a press roll for any significant distance, although one of the felts in each nip wraps a press roll for a small distance to effect the web transfer onto the other felt.
All of the looped felts Fl,F2,F3,F4 and F5 travel over corresponding felt guide rolls 10 and have their surfaces conditioned by felt conditioning apparatus 21-25 which is somewhat schematically shown and which essentially dewaters the felts preparatory to passing through their respective initial nips. A cleaning/lubricating shower 26 is disposed over the outside of each felt upstream of the felt conditioning apparatus. The cleaning and lubricating showers can be separate apparatus.
Pressurized fluid jet means 12,13 and 14, which in a preferred embodiment comprise a cross-machine extending pipe having a plurality of nozzles spaced along its length and which are supplied by a source (not shown) of pressurized fluid, such as steam, are disposed on the web side of each of felts F2,F3 and F4, respectively, to direct pressurized air against the web in the span between nips Nl,N2; N2,N3 and N3,N4 to assist the web to remain in co-running association with its felt in the event that the web, or portions of the web, momentarily became disengaged from its felt.
Corresponding suction boxes 12',13',14' are disposed beneath the felts beneath each of the jet means 12,13,14 to assist this process.
In a preferred embodlment as shown in Figure 1, each of the~press rolls 1-8 comprises a so-called plain press roll.
That is, the surface of each press roll comprises a smooth, cont~nuous cylindrical surface. Preferably, the outer periphery of each press roll is made of a hard rubber cover.
- In alternate embodiments, shown in Figures 2, 3 and 4, the press rolls do not all comprise plain press rolls in the sense that their outer surfaces comprise a plain, smooth cylindrical surface. Thus, in Figure 2, each of the press rolls 101-108 comprises a grooved roll. Such grooved rolls preferably are rolls having rubber covers with a plurality of circumferential grooves, equally spaced axially along the surface of the roll. The rolls are thus water impervious, like the plain surfaced press roll shown in Figure 1, but the grooves accommodate water expressed from the web as it passes through the nip and into the felts on either side thereof.
This allows either more water to be expressed from the felt and web over the land areas of the grooved roll, or water to be expressed at a higher unit nip pressure, or both. The unit nip pressure is higher at a given loading force applied between nipped rolls due to the smaller area of contact along the nip line produced by the grooves.
In the embodiment shown in Figure 3, upper press roll 201 comprises a grooved press roll while lower press roll 202 comprises a suction press roll. Suction press rolls have a roll shell, preferably rubber covered, wherein a vast number of holes are drilled through the cover and roll shell in a uniform pattern to permit water expressed from the felt as it passes through the nip to be received into the cylindrical holes and held therein by a sub-atmospheric pressure (vacuum) applied to a longitudinally extending segment of the inner surface of the perforated roll shell by a suction gland indicated schematically at 219. The suction gland in the suction roll also operates to positively transfer the paper web onto the felt F2 over the suction roll 202. In this embodiment, the other press rolls 203-208 are plain covered, or grooved, press rolls.
In the embodiment shown in Figure 4, alternate lower and upper press rolls 302,303,306 and 307 are suction press rolls while press rolls 301,304,305 and 308 are plain covered, or grooved, press rolls. Each of the suction press rolls includes a suction gland 319,329,339 and 349 to provide the sub-atmospheric pressure within the respective rolls 302,303,306 and 307.
Under certain operating conditions, suction rolls 302, 303,306 and 307 could be replaced by so-called blind drilled rolls. Such blind drilled rolls have rubber covers which look like ordinary suction rolls except that the holes drilled into the covers do not extend through the roll shell so that no sub-atmospheric air pressure can be applied to the felt beneath the web in the nip from any source of vacuum pressure within the roll.
In order to enhance the performance of this press section and~maximize its operation, a felt 31 having a relatively finer textured surface 32 on the side which contacts the paper web,~and a relatively coarser, more open mesh on the surface 33 away from the web, is preferred. Such a felt is shown in cross section in Figure 5. Since this press section utilizes four, straight-through types of press nip configurations _-(i.e., the web passes straight through the nip without significantly wrapping a roll) in conjunction with a freshly conditioned felt in each nip, the individual nips provide superior water removal from the web. In a straight-through nip configuration, the web passes through the press nip and then remains on a felt over a roll surface for either a very small segment of circumferential travel on a roll surface, or is directed away from both rolls in a plane which is substantially perpendicular to an imaginary plane containing the axes of revolution of the rolls in the press roll couple.
Such a straight-through press couple configuration provides less opportunity for rewetting of the web by water emerging from the felt as the felt is depressurized upon its passage through the nip. Further, the four consecutive nips, each of which utilizes two different press rolls with each successive nip utilizing two felts with a fresh felt alternately in the lower and upper positions in successive nips, permits a relatively closed felt to be utilized. This both allows improved dewatering while promoting superior fines retention and surface uniformity on both sides of the paper due to the symmetry of the application of the felts to the upper and lower surfaces of the web in conjunction with the fine textured surface of the felts. Finally, four, separately felted press nips result in enhanced dryness of the web leaving the press section as machine speed increases.
The felt fibers in the first and second nip felts are preferably coarser than the fibers in the third and fourth nip felts. Thus, first and second nip felts might be comprised of about 15 denier range fibers, and third and fourth nip felts might be comprised of about 3 denier range fibers on their web contacting surfaces. Their other sides (the side opposite to the sheet side of the felt) would have coarser fibers for easier dewatering.
Figure 6 illustrates how a driven felt guide roll 10' can be positioned within a looped felt, preferably felt F4 and/or F5, and operated to dewater the felt. Roll 10' is driven at a speed from about 110 percent to about 150 percent of the felt speed to induce water through the felt and out of the relatively open mesh on its inner surface. A doctor 27 engages the surface of the roll to skim water carried thereon from the felt off for collection and eventual discharge. Such a driven felt guide roll is shown within felt F5 in Figure 1, but can be used in conjunction with the apparatus in Figures 2-4.
Figure 7 illustrates a dewatering and felt conditioning apparatus comprising a nozzle 30 which projects a jet of hot air against the outer surface of the felt which contacts the paper web W when the web passes through the nip. The hot air jet is very narrow, such as about 0.02 inches, and extends the full width of the web to impinge upon the web as it passes over a felt guide roll 10". The web is thus conditioned and dewa~ered to be fresh before it passes through the first, upstream nip in its looped path of travel.
~ 2~8~-q _ The purpose of the dewatering apparatus shown in Figures 6 and 7 is to keep felts F4 and F5 running as dry as possible.
Either device can be used in conjunction with either felt F4,F5. They are considered illustrative only and not limiting as to the type of dewatering apparatus which can be used.
In operation, with particular reference to Figure 1 and general reference to Figures 2-4, web W is urged from forming wire FO by the sub-atmospheric air pressure in suction gland 17 of pick-up roll 9 which presses felt F1 against the web over the forming wire. The web is carried on the underside of felt F1 and comes into co-running engagement with lower felt F2 at, or immediately before, nip N1 between rolls 1,2 through which it passes. As previously stated, the preferred manner of transferring the web from the felt which does not travel through the next downstream nip to the felt which does pass through the next downstream nip is to use felts having successively finer batts on their sides which face the paper web alternating in the lower and upper positions in successive nips. Thus, felt F5 is finer than felt F4 which is finer than felt F3 which is finer than felt F2 which is finer than felt F1.
.~
- The other web transfer technique is to use either felts of~choice, or successively finer batt felts as described above, in conjunction with positioning the felt coming off the web relative to the felt to which the web will adhere. In this technique, felt guide roll 10 immediately downstream of nip N1 within looped felt F1 guides felt F1 at a small angle 203~829 upwardly from the plane of travel of felt F2 between press rolls 2 and 4. This produces less area of felt F1 against the web relative to the area of felt F2 against the web in the immediate vicinity downstream of nip N1 with the effect that web W is maintained on felt F2 as it travels toward nip N2 between press rolls 3,4. To further ensure that the web is urged to remain on felt F2, a steam pressurized nozzle 12 is disposed outside the web over felt F2 in the span between felts F1 and F3 to maintain a stream of pressurized steam against the web.
As the web is carried on felt F2 toward nip N2, looped felt F3 is guided by its felt guide rolls 10 into co-running engagement with the outer surface of the web over felt F2 immediately before, or at, nip N2 between rolls 3,4.
Immediately downstream of nip N2, looped lower felt F2 is guided by a felt guide roll 10 downwardly away from the plane of travel of felt F3 between rolls 3 and 5. This produces a relatively larger area of contact between the web and felt F3 compared to the area of contact between the web and felt F2 in the immediate vicinity of the out-going side of nip N2 with the corresponding effect that the web rem~; n~ on felt F3. A
pressurized air nozzle 13 is disposed outside the web over felt F3 between felts F2,F4 and directs pressurized air agalnst the web to urge it to remain in contact with felt F3 between nips N2,N3.
Downstream of nip N2, the web is traveling on felt F3, and looped lower felt F4 is brought into co-running engagement with the web either at, or immediately before, nip N3 between press rolls 5,6. Downstream of N3, felt guide roll 10 within looped felt F3 guides felt F3 upwardly and away from the plane of looped lower felt F4 between lower press rolls 6,8. The paper web W is transferred to the lower felt F4 in the same manner as described in conjunction with the web transfer from felt Fl onto felt F2. The web is thus transported on felt F4 into nip N4 between press rolls 7,8.
As the web on felt F4 approaches nip N4, looped upper felt F5 is directed by a felt guide roll 10 to come into co-running engagement with the web either at, or immediately before, nip N4. The web thus passes through nip N4 in double-felted engagement with felts F4,F5 in a manner similar to its double-felted passage through nips Nl,N2,N3.
Downstream of nip N4, a felt guide roll 10, within looped lower felt F4, directs felt F4 away from the plane of upper felt F5 in the portion of its travel between nip N4 and the top surface of dryer roll 15 over which felt F5 is guided by a downstream felt guide roll 10 within looped felt F5. The web W is transferred onto the outer surface of felt F5 in the same manner it is transferred onto the outer surface of felt F3 as described in conjunction with its emergence from nip N2.
\
~ The web is thus guided onto, and transferred onto, dryer roll 15 by felt F5 which is directed into contact with dryer roll 15 by downstream felt guide roll 10 which can move vertically up and down as shown by directional arrow 28. As 203~829 the felt travels over the surface of dryer roll 15, dryer felt FD traveling in the direction of arrow A2 is brought into co-running engagement with the web, and the web is transferred onto the outer surface of looped felt FD with the assistance of suction roll 34 and is thus directed through the remainder of the dryer section as exemplified by roll 16.
All of the looped felts are equipped with cleaning showers 26 and felt conditioning apparatus 21-25 to condition and dewater the felts to a desired degree of dryness. In addition, as shown in Figures 1 and 6, upper felt F5 is equipped with a doctor 27 engaging the surface of felt guide roll 10' to further dewater that felt. Similarly, as shown in Figures 1 and 7, lower felt F4 is equipped with a hot air type of doctor 30 which directs a pressurized stream of hot air onto the outer side of the felt to further dry and condition the felt before it comes into contact with the web in nip N3.
This four nip, five felt, straight-through press arrangement is thus seen to exhibit several features and operational advantages. In each of the press nips, in addition to being double felted, both felts come into engagement with the press rolls and come out of engagement with the press rolls in a substantially symmetrical manner and do`not travel over the surface of any press roll for a significant distance. The web is removed from contact with a felt essentially immediately after a nip which results in higher sheet dryness.
- 203~829 - Immediately after nips N2,N4, looped lower felts F2 and F4 provide an opportunity to direct broke downwardly into broke pits beneath the papermaking machine. Paper is thus prevented from traveling any great distance through the papermaking machine, and especially through more than two press nips, thus mitigating potential damage to the felts and roll covers due to wads of paper web passing through a nip.
Each of the press nips has one felt which has been freshly conditioned for entering a nip. Further, in each press nip, the freshly conditioned felt alternates between being the lower felt and the upper felt in successive nips.
Thus, in nip Nl, lower felt F2 has been freshly conditioned;
in nip N2, upper felt F3 has been freshly conditioned; in nip N3, lower felt F4 has been freshly conditioned; in nip N4, upper felt F5 has been freshly conditioned. This provides additional symmetry to the dewatering process as the web passes through successive nips which promotes less two-sidedness in the paper produced.
Finally, and perhaps most importantly, this invention, particularly the plane surfaced press roll configuration shown in Figure 1, promotes uniformity of the dewatering process due to the cross-machine uniformity of the surfaces of the press rolls which load the press nips in the press dewatering process. From a papermaking standpoint, this means that water flows essentially evenly from both surfaces of the paper web to provide more uniform paper formation. In this regard, as shown in Figures 2-4, in this apparatus, such grooved roll and suction roll press configurations are also symmetrical to provide both the advantages of the application of grooved and suction rolls while still incorporating the symmetry, cross-machine uniformity of nip surfaces and runnability of this invention.
Naturally, variations and modifications of the apparatus can be made without departing from the spirit and scope of the invention disclosed. Accordingly, such modifications and conditions as might become clear to those skilled in the art are intended to fall within the scope of the invention as defined by the claims.
Claims (13)
1. In a papermaking machine for making a paper web, including a forming section having a paper web forming wire, a pick-up roll for urging the paper web from the forming wire, and a dryer section having at least one dryer roll for receiving the paper web to be dried, a press section comprising:
first and second press rolls, each having a plain, water impervious surface, forming a first press couple nip;
third and fourth press rolls, each having a plain, water impervious surface, forming a second press couple nip;
fifth and sixth press rolls, each having a plain, water impervious surface, forming a third press couple nip;
seventh and eighth press rolls, each having a plain, water impervious surface, forming a fourth press couple nip;
a first looped press felt disposed about the pick-up roll and receiving the web transferred from the forming wire and passing with the web through the first press nip;
a second looped press felt disposed about the second and fourth press rolls and passing through the first nip with the web and first felt;
a third looped press felt disposed about the third and fifth press rolls and passing through the second nip with the web and second felt;
a fourth looped press felt disposed about the sixth and eighth press rolls and passing through the third nip with the web and third felt;
a fifth looped press felt disposed about the seventh press roll and passing through the fourth nip with the web and fourth felt.
a fifth looped press felt disposed about the seventh press roll and passing through the fourth nip with the web and fourth felt.
first and second press rolls, each having a plain, water impervious surface, forming a first press couple nip;
third and fourth press rolls, each having a plain, water impervious surface, forming a second press couple nip;
fifth and sixth press rolls, each having a plain, water impervious surface, forming a third press couple nip;
seventh and eighth press rolls, each having a plain, water impervious surface, forming a fourth press couple nip;
a first looped press felt disposed about the pick-up roll and receiving the web transferred from the forming wire and passing with the web through the first press nip;
a second looped press felt disposed about the second and fourth press rolls and passing through the first nip with the web and first felt;
a third looped press felt disposed about the third and fifth press rolls and passing through the second nip with the web and second felt;
a fourth looped press felt disposed about the sixth and eighth press rolls and passing through the third nip with the web and third felt;
a fifth looped press felt disposed about the seventh press roll and passing through the fourth nip with the web and fourth felt.
a fifth looped press felt disposed about the seventh press roll and passing through the fourth nip with the web and fourth felt.
2. A press section as set forth in claim 1, wherein:
all of the press rolls have water impervious surfaces.
all of the press rolls have water impervious surfaces.
3. A press section as set forth in claim 1, wherein:
all of the press rolls have plain, water impervious surfaces.
all of the press rolls have plain, water impervious surfaces.
4. A press section as set forth in claim 1, wherein:
the first press roll is a grooved roll;
the third press roll is a suction roll, whereby the web is transferred onto the second felt after the first nip and carried thereon into the second nip.
the first press roll is a grooved roll;
the third press roll is a suction roll, whereby the web is transferred onto the second felt after the first nip and carried thereon into the second nip.
5. A press section as set forth in claim 1, wherein:
the second, third, sixth and seventh press rolls are suction rolls.
the second, third, sixth and seventh press rolls are suction rolls.
6. A press section as set forth in claim 1, wherein:
the fifth felt carries the web from the fourth press nip into the dryer section.
the fifth felt carries the web from the fourth press nip into the dryer section.
7. A press section as set forth in claim 1, wherein:
the web remains on the second felt after passing through the first nip;
the web remains on the third felt after passing through the second nip;
the web remains on the fourth felt after passing through the third nip;
the web remains on the fifth felt after passing through the fourth press nip.
the web remains on the second felt after passing through the first nip;
the web remains on the third felt after passing through the second nip;
the web remains on the fourth felt after passing through the third nip;
the web remains on the fifth felt after passing through the fourth press nip.
8. A press section as set forth in claim 7, further including:
pressurized fluid jet means disposed between the first and second press nips for directing pressurized fluid against the web on the second felt, the second and third press nips for directing pressurized fluid against the web on the third felt, and the third and fourth press nips for directing pressurized fluid against the web on the fourth felt to facilitate the conveyance of the web between the respective nips.
pressurized fluid jet means disposed between the first and second press nips for directing pressurized fluid against the web on the second felt, the second and third press nips for directing pressurized fluid against the web on the third felt, and the third and fourth press nips for directing pressurized fluid against the web on the fourth felt to facilitate the conveyance of the web between the respective nips.
9. A press section as set forth in claim 1, wherein:
one or more of the felts which pass through a press nip downstream of a given press nip have finer batts on their web facing sides than the other felt which passes with them through the given press nip.
one or more of the felts which pass through a press nip downstream of a given press nip have finer batts on their web facing sides than the other felt which passes with them through the given press nip.
10. A press section as set forth in claim 1, wherein:
each successive felt of the felts arrayed in the downstream direction have finer batts on their web facing sides.
each successive felt of the felts arrayed in the downstream direction have finer batts on their web facing sides.
11. In a papermaking machine for making a paper web, a forming section having a paper forming wire, a pick-up roll for urging the paper web from the forming wire, and a dryer section having at least one dryer roll for receiving the paper web to be dried, and a press section including a plurality of press rolls and press felts, the method of pressing and dewatering the paper web comprising the steps:
passing the paper web between first and second press felts through a first press nip comprising a first and second roll couple;
transferring the web onto the second felt;
passing the web between second and third press felts through a second press nip comprising a third and fourth roll couple;
transferring the web onto the third felt;
passing the web between third and fourth press felts through a third press nip comprising a fifth and sixth roll couple;
transferring the web onto the fourth felt;
passing the web between fourth and fifth press felts through a fourth press nip comprising a seventh and eighth press roll couple.
passing the paper web between first and second press felts through a first press nip comprising a first and second roll couple;
transferring the web onto the second felt;
passing the web between second and third press felts through a second press nip comprising a third and fourth roll couple;
transferring the web onto the third felt;
passing the web between third and fourth press felts through a third press nip comprising a fifth and sixth roll couple;
transferring the web onto the fourth felt;
passing the web between fourth and fifth press felts through a fourth press nip comprising a seventh and eighth press roll couple.
12. The method of pressing and dewatering a paper web as set forth in claim 11, further including the step of:
transferring the web onto the fifth felt.
transferring the web onto the fifth felt.
13. The method of pressing and dewatering a paper web as set forth in claim 11, wherein:
the transfer of the web after at least one of the press nips is effected by having the felt to which transfer is made comprised of a finer batt on its side facing the web.
the transfer of the web after at least one of the press nips is effected by having the felt to which transfer is made comprised of a finer batt on its side facing the web.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US48882990A | 1990-03-06 | 1990-03-06 | |
| US07/488,829 | 1990-03-06 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2034829C true CA2034829C (en) | 1994-12-27 |
Family
ID=23941291
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2034829 Expired - Fee Related CA2034829C (en) | 1990-03-06 | 1991-01-23 | Papermaking machine press section |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPH05222690A (en) |
| CA (1) | CA2034829C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5888354A (en) * | 1996-04-04 | 1999-03-30 | Valmet Corporation | Transfer of a web in a paper machine from a two-felt press nip to a dryer section |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE102009034383B4 (en) * | 2009-07-23 | 2014-02-13 | Siemens Aktiengesellschaft | Press felt and its use |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5111202A (en) * | 1974-07-19 | 1976-01-29 | Hitachi Construction Machinery | |
| JPS5115161A (en) * | 1974-07-29 | 1976-02-06 | Hitachi Ltd | GASUSHADANKI |
| US4441664A (en) * | 1982-07-26 | 1984-04-10 | Anderson Bros. Mfg. Co. | Apparatus for feeding web material from a supply roll |
| FI81854C (en) * | 1982-09-15 | 1990-12-10 | Valmet Oy | PRESS SPRING WITH PRESS SHEET I EN PAPER MACHINERY. |
| JPH01139890A (en) * | 1987-11-25 | 1989-06-01 | Mitsubishi Heavy Ind Ltd | Press apparatus of papermaking machine |
-
1991
- 1991-01-23 CA CA 2034829 patent/CA2034829C/en not_active Expired - Fee Related
- 1991-03-05 JP JP3823491A patent/JPH05222690A/en active Pending
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5888354A (en) * | 1996-04-04 | 1999-03-30 | Valmet Corporation | Transfer of a web in a paper machine from a two-felt press nip to a dryer section |
| US5951821A (en) * | 1996-04-04 | 1999-09-14 | Valmet Corporation | Arrangement and method for transferring a web in a paper machine from a two-felt press nip to a dryer section |
| US6103066A (en) * | 1996-04-04 | 2000-08-15 | Valmet Corporation | Methods for transferring a web in a paper machine from a two-felt press nip to a dryer section |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH05222690A (en) | 1993-08-31 |
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