FI93035C - Wet cellulose web transport system and method - Google Patents

Description

This invention relates to the transfer and support of wet cellulosic webs between two moving elements. More particularly, this invention relates to a system and method for removing a rapidly moving wet cellulosic web from a web-supporting moving element, such as a press roll or belt, and directing the web to a receiving moving belt. The invention is particularly suitable for use in the pressing section of the drying section of a paper machine.

In the manufacture of paper, a cellulosic fibrous slurry, referred to as a pulp slurry, is applied to one or more motion molds or substrates and most of the water drains away. This cellulosic web or sheet, which is initially weak and wet, is transferred to a press felt which carries it to a press nip formed by two press rolls. The mechanical compression between the two press rolls seals the web 20 and removes some of the wet web water. The web usually leaves the press nip attached to another press roll and must be peeled from the roll before it can be moved to the next part of the paper machine. Paper machines generally have one to four presses in the press section, followed by a drying section with heated drying rollers, evaporating. most of the water left in the compressed web. In the manufacture of some grades of paper, the dry web is moistened using an aqueous suspension of sizing agents. This takes place in an adhesive press after the first drying step 30 and the moist glued paper is then transferred again to a second drying section where it is dried a second time.

While in various parts of the paper machine, the wet cellulosic web is usually supported by a permeable belt, such as a web-forming fabric, press felts, and a drying fabric, or the web is supported in other ways, such as by a press roll. Mechanical: support is often not available during the transfer of the web between the individual moving elements of the machine. Thus, during web transfer, there is an increased risk of the web or sheet tearing, especially if it is wet and the machine is running at high speed. To reduce the risk of sheet tears, it is sometimes necessary to reduce the speed of the machine, even if this leads to reduced production. The risk of tearing the sheets is sometimes reduced by adding chemicals or by increasing the ratio of a stronger but more expensive component, such as chemical pulp or long fiber pulp, in the pulp slurry 10 or the original fiber blend.

The most critical areas of sheet transfer are from the web forming section to the press section, between successive presses of the press section, and between the last press of the press section and the first roll of the drying section. In all of these transfer areas, the web or sheet is still wet and thus relatively weak. Several methods have been used to move the sheet in these areas. In one method, the sheet is pulled unsupported from one element to the next by so-called open drawing. The wet 20 web in open drawing is unstable at high speeds and responds to even small changes in method, and sometimes tends to vibrate or flutter. Excessive sheet flutter can cause deformation and wrinkling of the web and reduce product quality or completely tear the sheet 25 and interrupt production. Thus, paper machines with open. the tension between the web former and the first press rolls, usually operates at a speed of less than 750 m / min.

All machines operating at high speed, that is, at speeds greater than 1000 m / min, have continuous web support from the web former at least to the first nip of the press section. On machines with a multi-roll press arrangement, the web is continuously supported up to the second or third press rip. However, in all current paper-35 machines, the sheet travels with an open draw as it is peeled from the roll of the last press.

»93035 3

The open tension transfer method provides a reduction in excessive sheet flutter and stabilization of the web, sometimes by increasing the web tension. The tension required to peel the web and stabilize it in the open tension transfer may in some cases be high enough to cause the web to rupture and even if it does not rupture, the high stress can permanently stretch the web and therefore make it more susceptible to rupture during subsequent operations on the paper machine. This reduced extensibility is maintained in the final product and can lead to increased paper sheet tearing during processing and printing operations.

Another method of transferring a web from a permeable carrier or belt, such as a web-forming fabric, to another permeable carrier, such as a press felt, is by means of a rotatable roll provided with a vacuum chamber. Most high speed paper machines use such a vacuum capture system to transfer the web from the web former to the first press roll. However, in a vacuum capture system, only the suction roll can effectively transfer the web from the permeable carrier to another permeable carrier. The press rolls are generally solid rolls, and thus a vacuum system, such as a suction roll, cannot automatically begin to peel the web from the press closed roll, or even from an impermeable belt. In the case of a press roll, the web is normally fixed. fits better on a smoother and less permeable surface.

Because it is difficult to separate the leading edge of the wet web from the press roll or the belt supporting the web, paper machines are generally initially run in only in a narrow strip of web, sometimes called a tail. Once this narrow band has been successfully rotated through the machine, it is gradually expanded until the entire width of the paper machine le-35 is in use. This narrow paper band is initially very weak because it is so narrow and the air currents in fast-running machines repeatedly cause the narrow band to break, thus prolonging the starting operation. All paper, 93035 4 produced during machine start-up, is unusable and must be recycled. If the start-up time of the machine could be shortened and the machine was started at the full width of the sheet or web, then production losses could be reduced and higher efficiency achieved.

Interfering materials, which generally represent fractions of cellulosic fibers, often adhere to the rolls of various paper machines, such as press rolls, dryers or calender rolls, and are generally removed by so-called "scraper blades" with sharp edges placed tightly in the machine roll surfaces. in the vicinity and they peel the fibers stuck to the web and roll. The web removed in this way is generally densely wrinkled and corrugated and cannot be converted to plain paper. The scraper-wrinkled web can be used commercially to produce soft and thick tissue paper, which is used primarily for hygiene products. For high thickness and softness, it is desirable for the tissue paper to have regular and dense creasing brushes. Good crimping requires a sharp scraper blade and an optimal contact angle between the blade and the web that hits it. Canadian Patent 1,044,459 and Japanese Patent 43160 disclose methods for crimping using a hollow scraper blade from which a flat jet of compressed air is blown from an adjacent position of the blade. The primary object of each of these patents is to reduce roll wear by reducing or eliminating blade contact with the roll. These hollow scraper blades were designed for the production of crumpled paper rather than for initiating the transfer of the wet cellulosic web 30 in the press section or immediately before the drying section. Because wrinkling occurs when the web is removed from a flat surface, such as a press roll, with a blade, scraping has not been used as a transfer means for wet cellulosic webs when producing paper that requires a flat surface.

It is an object of the present invention to provide a system and method for removing a wet cellulosic web from a belt supporting a press roll or web and continuously supporting this web during its transfer to the next moving element.

It is a further object of the present invention to provide a transfer system that allows the safe transfer of a tail or full-sheet sheet during start-up of a paper machine. It is a still further object to provide a transfer system for transferring a wet fibrous web at a web speed greater than 1000 m / min. A still further object is to transfer webs that are weaker than those transferred in existing paper machines, without the need to increase the strength of the wet web and reduce the number of breaks that occur in conventional paper machines.

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A system according to the invention for transferring a fast moving wet cellulosic web from the surface of a web-supporting moving element to a web-receiving moving belt so that the web is continuously supported during transfer, the system comprising: a web-supporting moving element; a suction roll forming with said web-supporting element a nip through which the web is passed; a web-receiving permeable belt guided to pass through the nip 25 and down to the surface of the suction roll; and means for detaching the web from the surface of the web-supporting element and guiding it towards the suction roll and said permeable belt, the means comprising a scraper blade which contacts the surface of the web-supporting element immediately after the nip and causes the web 30 to detach from said surface, said means further comprising connected air ducts for producing an air jet adjacent the scraper blade between the web and said surface in a direction substantially opposite to the direction of web movement, said air jet providing means for supporting and guiding the web towards the suction roll and the permeable belt.

93035 6 The present invention can be used to transfer a tail or full-width band between a press roll or web-supporting belt and a subsequent movable element, and comprises a scraper blade for initially removing the web from the Telal-5 or carrier, an air jet blowing air in the opposite direction to the web. , between the web and the roll or support and a vacuum or suction roll which may have a permeable belt for holding the web as it is moved from the press roll or support.

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In one embodiment of the invention, the scraper blade and the air jet comprise a unit assembly having a source of compressed air connected to a tapered air chamber culminating in two lips having a gap between the lips that forms an air jet. One of the two lips forming the scraper blade is placed in contact with the surface of the roll or web-supporting belt.

In another embodiment, the compressed air source and the air chamber 20 form a unit assembly movable between the first and second positions, the assembly in the first position contacting the surface of the roll or web-supporting belt so that the air jet from it is directed toward the nip, the press roll and suction -25 roll forming, with the assembly in the second position set so that it is not in contact with the surface.

A method according to the invention for transferring a rapidly moving wet cellulosic web from the surface of a web-supporting movable element 30 to a web-receiving movable, permeable belt passing through a nip formed by said web-supporting element and a suction roll and along the suction roll surface, the web being continuously supported during transfer through and 35 along the surface of the web supporting element; the moving web is removed from said surface with a scraper blade which is brought into contact with the surface immediately after the nip; and the detached web is guided towards the suction roll and said permeable belt so as to come into contact with the belt, characterized in that air ducts use air ducts fixedly connected to the scraper blade, producing an air jet adjacent the scraper blade between the web and said surface. , which is substantially opposite to the direction of movement of the web, said air jet providing means for supporting and guiding the web towards the suction roll and the permeable belt.

Fig. 1 is a schematic side elevational view of a solid roll forming a nip with a suction roll and a conventional scraper according to the prior art;

Figure 2 is a partial side elevational view of a combined scraper-15 and air jet in accordance with one embodiment of the present invention;

Figures 3 and 4 are partial side views showing different air chamber shapes for a combined scraper blade and 20 air jets;

Figures 5, 6 and 7 are detailed side views showing different edges of the scraper blades; Fig. 8 is a partial side elevational view showing a combined scraper blade and air jet positioned adjacent a solid roll forming a nip with a suction roll;

Fig. 9 is a schematic side elevational view of a paper machine showing a transfer system of the present invention for transferring a web from a final nip of a press section; and

Fig. 10 is a schematic side elevational view of still another embodiment of a transfer system according to the present invention, wherein the transfer takes place between an impermeable web-supporting belt and a permeable drying fabric.

93035 8

Reference is now made to the drawings, in which Figure 1 illustrates a solid roll 10, the last roll of a paper machine press section, with a web 12 of cellulosic fibers moving on a roll 10 from a nip 14 formed with a previous press roll 16. A suction roll 18 forms a nip 19 with a solid roll 10 in the form of a fabric belt moves around the suction roll 18 and through the nip 19. The second support belt 22, which is also permeable, moves around an additional roll 24 positioned below the suction roll 18 to provide a gap for the web 12 between the first support belt 20 and the second support belt 22. The purpose of the suction roll 18 is to provide a suction to detach the web 12 from the surface of the solid roll 10 and guide it between the support belts. However, since the solid roll 10 does not allow air to pass through, the suction roll 18 has little effect on detaching the web 12 from the solid roll 10. As can be seen in Figure 1, the web 12 passes down to a conventional scraper blade 26 which separates the web 12 and wrinkles or crimps the web. from roller 10. Figure 1 illustrates a prior art system 20 that is not considered satisfactory.

The combination of scraper blade and air jet 30 is shown in Figure 2, comprising a compressed air space 32 in the form of a tube with a slot or series of holes 34. Air passes into an air chamber 36 formed by two tapered walls 38 which taper into a first lip 40 and a second lip 42. Figure 2 shows the first lip 40, which represents the scraper blade, in contact with the press roll 10 so that the web 12 is shown to be detachable adjacent the scraper blade lip 40. The second lip 42 30 is shown to extend not quite as long as the first lip 40 and the gap or gap 44 between the two lips 40 and 42. provides a longitudinal jet of air to blow out a medicated jet of air. Because the word "shower" is used throughout the specification, this terminology includes a longitudinal flow of il-35 that exits out of a gap or gap 44.

Figure 3 shows one embodiment of an air chamber 36 in which the tapered walls 38 engage a first lip 40 and a second lip 42 which curve inwardly between the ends 44 of the lips 40 and 42. Figure 4 shows another embodiment in which the two lips 40 and 42 are parallel to each other, thus the gap 44 represents a parallel gap and gives a flat jet of air therefrom.

Figures 5, 6 and 7 show different tips of the scraper blade 40. The contact angle alpha, seen in Figure 5, is similar to that used in conventional blades, where the edge of the blade scratches the surface of the roll 10. One or both of the lips in the assembly can be replaced if the lip or lips are damaged or worn.

The optimal palate width depends on production parameters such as machine speed, product quality, web adhesion, etc. The palate width between the two lips may be 0.1-3.0 mm, and is preferably in the approximate range of 0.3-0.8 xranm.

Figure 8 shows the suction roll 18 positioned above the scraper blade and il-20 jet assembly. In the first stage of the start-up operation, the assembly 30 is in position A and the leading edge of the tail or full-width strip 12 is removed from the roll 10 when it strikes the scraper lip 40. The air jet then forces the web 10 toward the suction roll 18 and draws a vacuum on the roll. The web 12 is thus transferred to the felt 20. When the movable web 12 is transferred to the felt 20, the assembly 30 is no longer required and is switched to position B and the air supply is cut off. If a web break occurs, the web is re-rotated initially by the assembly 30 at position A. During the duration of the broken web-30, the assembly is left at position A.

The suction roll 18 is shown as having three zones. The first zone 50, located closest to the nip 35 19, has a maximum vacuum level to assist in making first contact between the web 12 and the felt-covered suction roll 18. The second zone 52 downstream of the first zone 50 is a larger zone and operates as a holding zone 93035 10 at a lower vacuum level. For example, the first zone may have a vacuum level in the range of 10-80 kPa and the second zone 52 may have a vacuum level of 0-50 kPa. The second zone 52 is sufficient to hold and support the web 12 by the felt 20. The third zone 54 provides a low positive air pressure to ensure that the web 12 easily disengages from the felt 20 as the felt 20 disengages from the suction roll 18.

The air pressure in the compressed air 32 depends on production variables such as scraper spacing, width, machine speed, product quality, and web attachment to the roll, but is preferably about 400-600 kPa. The most suitable air pressure for an air blade with a gap width of 0.5 mm was found to be between 34 kPa and 100 kPa.

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Figure 9 illustrates a transfer system of the present invention used to transfer a web from a closed roll 10 of a final press, which is the center roll of a three-roll tilted press. Figure 10 illustrates two transfer systems, one of which transfers from a permeable or impermeable web support belt 60 to a drying felt 70. The device could be used to transfer thin materials of different flexibility and is particularly suitable for transferring weak and stretchy sheets such as wet paper or paperboard. crumpled toilet paper or non-woven products.

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Example 1

The pilot paper machine was used to make paper in two 30 different ways. The paper was first made using direct transfer from the press section using the transfer roller arrangement using the air scraper of the present invention, and second, the paper was transferred from the solid roll using conventional direct drawing operation. The elongation properties of the papers so made were compared 35 ago.

The pilot machine comprised a roll former with suction capture,. a three-roll tilted press and sampler as shown in Figure 9. The transfer system was installed between the second press nip and the sampler as shown in Figure 9. The paper machine produced a 0.33 m wide web with an initial weight of about 50 g per square meter at a speed of 800 5 m / min using newsprint pulp. The load of the first and second nips was 60 and 120 kN / m, respectively, and the solids content of the paper after the second press was about 42%.

The wet paper used for the laboratory tests was wound at a minimum draw (less than 1%) for transfer roll tests using an air scraper and at several 2-4% draws for open draw tests. The results of the experiments are shown in the following table.

15 TABLE

Paper Elongation (Open Draw vs. Air Scraper - Transfer Roller Arrangement) STRETCH% _Wet Paper ** _ Dry Paper * 20 Tensile_Elongation_Elongation%% 2.1 3.1 1.4 2.1 3.6 3.6 1.4 2.2 3.0 1.2 25 2.4 3 .9 1.2 3.2 3.7 1.2 4.0 2.7 1.2 <1.0+ 4.4 1.5 30 Sample size 1.5 x 10 cm Sample size 2.5 x 10 cm Tension rate 100 mm / min + Using transfer roller arrangement using air scraper 35 (Sampler) - (Second press)

Tensile = ......-............................ speed x 100% (Second press) 93035 12 Wet elongation measurements were made on samples , cut from a spool (2.5 x 10 cm) sealed in a bag and treated in such a way that moisture losses were minimal. Other samples were dried between suction plates in a light-5 image dryer and cut into strips (1.5 x 10 cm). Both wet and dry samples were tensioned at 100 mm / min in a laboratory tensile tester. Measurements on both wet and dry paper illustrate that the paper produced by the transfer system of this invention had more elongation than that produced using the open drawing system. These results mean that the paper is less likely to tear in subsequent open stretches in the paper machine and in processing or printing methods.

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Example 2 Using the arrangement shown in Figure 9, a web weighing 45 g / square meter was transferred to a sampler at a speed of 1000 m / min at a rate of 20 times for ten attempts. After the transfer of the sheet was started with the transfer system of the present invention, it was maintained even if the air supply to the air nozzle was interrupted. Without the use of this transfer system, even experienced machine users could not perform web transfer at full machine speed.

Example 3 Using the transfer system described herein, a full machine width web was transferred from the pilot paper machine press to the sampler at a full machine speed of 1200 m / min. Without this transmission system, this could not be done.

The transfer system 35 described and claimed herein is capable of transferring weak wet webs, such as those made from 100% mechanical pulp. Prior to this, it has not been possible without losing speed or without having to add a certain percentage of chemical mass. Thus, the present invention allows paper to be made from weaker and cheaper starting materials.

When the transfer system described herein is applied to practice, the number of web tears is reduced and the speed of the paper machine can be increased above the highest speeds of conventional machines, on the order of about 1400 m / min.

Although Figure 9 shows only one transmission system, several transmission configurations 10 may be provided at different positions in the machine.

Several modifications may be made to the embodiments described herein without departing from the scope of the present invention, which is limited only by the appended claims.

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Claims (13)

A system for moving a moist cellulose web (12) in rapid motion from the surface of a moving element (10, 60) supporting the web to a moving band (20, 70) receiving the web, so that the web is continuous supported during movement, the system comprising: an element (10, 60) in motion carrying the web; a suction roller (18) which together with said element supporting the web forms a nip (19) through which the web is led to pass; a permeable belt (20, 70) receiving the web which is passed through the nip (19) and along the surface of the suction roll (18); and means (30) for detaching the web from the surface of the member supporting the web and guiding it against the suction roll and said permeable belt, the elements comprising a blade (40) touching the surface of the web (10, 60) supporting the web. immediately after the nip (19) and causes the web to detach from said surface, characterized in that said element further comprises air ducts (32, 34, 36, 44) firmly connected to the blade (40) to generate an air jet next to the blade. the web and said surface in a direction substantially opposite to the direction of movement of the web, said air jet forming a means for supporting the web and guiding it against the suction roll (18) and the permeable belt (20, 70). System according to claim 1, characterized in that the element in motion supporting the web (12) is a closed press roll (10), the nip (19) being formed between the closed press roll and the suction roll (18). System according to claim 1, characterized in that the system comprises a first element (10) in motion carrying the web (12), a permeable band (20) first receiving the web and a second element in motion (22, 60). carrying the web, on which the web is finally transmitted. 93035 18 System according to claim 1, characterized in that said element (30) comprises a compressed air duct (32) connected to a tapered air chamber (36) which leads to two lips (40, 42), one of which ( 40) forms a scraper blade and having between them a gap (44) which produces the air jet. System according to claim 4, characterized in that the lips (40, 42) are of equal length. 10 System according to claim 4, characterized in that the lip (40) forming the blade is longer than the second lip (42). 7. System according to claim 4, characterized in that the abutting walls of the lips (40, 42) are bent inwardly against the gap (44). System according to claim 4, characterized in that the walls of the lips (40, 42) are parallel to the gap (44). System according to claim 4, characterized in that the gap (44) which produces the air jet has a width within the range of about 0.1-3.0 mm. 25 System according to claim 9, characterized in that the air ducts (32, 33, 36, 44) are connected to a compressed air source which generates a pressure within the range of about 14-600 kPa. System according to claim 4, characterized in that the compressed air duct (12) and the air chamber (36) are of a piece (30) which can be moved between two stations, the piece of one station touching the surface of the element (10) movement carrying the web and at the second station, the piece is separated from said surface. A method for moving a damp cellulose web: (12) in rapid movement from the surface of an element (10, 60) supporting the web to a movable permeable belt (20, 70) receiving the web and passing through the nip (19), formed by said element supporting the web and the suction roll (18), and along the surface of the suction roller, the web being continuously supported during movement, the web being measured through the nip and along the surface of the web carrying member; the movable web is detached from said surface by a blade (40) which is contacted with the surface immediately after the nip; and the detached web is guided against the suction roll and said permeable strip so that it comes into contact with the strip, characterized in that, in releasing the web (12), air ducts (32, 34, 36, 44) which are firmly connected to the forming blade (40) are used. ) and generating an air jet adjacent to the blade between the web and said surface in a direction substantially opposite to the direction of movement of the web, said air jet le forming a means for supporting the web and guiding it against the suction roll (18) and the permeable belt. (20, 70). The method of claim 12, characterized in that the web (12) is moved from the movable permeable band (20) to the second element (22, 60) in motion receiving and carrying the web. «