Suction roller and combination press for a fiber web machine

Abstract

The invention relates to a suction roller for a fiber web machine. The suction roller (17) has a perforated roller shell (24) in which a vacuum box (25) is located, which, together with the roller shell (24), defines one or more vacuum chambers (26, 27). The vacuum box (25) is equipped with a liquid collection device (36) for collecting water, and the liquid collection device (36) is connected to a liquid extraction device (37). The invention also relates to a combination press of a fiber web machine.

Description

[0001] The invention relates to a suction roll for a fiber web machine, wherein the suction roll has a perforated roll shell in which there is a vacuum box which, together with the roll shell, defines one or more vacuum chambers.

[0002] The suction roll has a perforated roll shell containing a vacuum box that forms a vacuum system for the suction roll. A common vacuum box contains two vacuum chambers. The vacuum box has side walls equipped with axial seals and end seals that extend to the inner surface of the roll shell. The end seal is also called an edge seal. This defines each vacuum chamber. A negative pressure, or vacuum, is created in the vacuum chambers, forming vacuum zones on the surface of the roll shell. The vacuum removes water through the roll shell.

[0003] The suction roll is usually located in the press section of a fiber web machine. There is also usually at least one counter roll, which together with the suction roll forms a nip. Furthermore, a fabric supporting the fiber web runs across the nip. Pressing removes water from the fiber web. A large portion of the water is removed through the saturated felt into the suction roll, while some of the water is used for felt conditioning.

[0004] In practice, however, the capacity of the vacuum box may be insufficient. As a result, the water is collected unevenly, resulting in an irregular moisture profile of the fiber web. On the other hand, the suction roll may even be overfilled. In other words, there is excess water that flows back to the holes in the roll shell via the vacuum chamber and may splash out of the suction roll. The water then rotates around the suction roll. This re-moistens the fabric or even damages the fiber web itself. Web breaks may also occur. Furthermore, due to the limited dewatering capacity, it is difficult to improve the productivity of the fiber web machine. In the worst case, the production speed of the fiber web machine must be reduced.

[0005] It is an object of the present invention to provide a novel suction roll for a fiber web machine with improved dewatering performance and better adjustability. The characteristic features of the suction roll according to this invention are set forth in the appended claim 1. A further aim of the invention is to create a novel combination press for a fiber web machine having improved dewatering properties. The combination press is equipped with the suction roll according to the invention. This avoids any problems with remoistening and increases the production speed of the fiber web machine. The characteristic features of the combination press according to the invention are set forth in the appended claim 14. Furthermore, the suction rolls currently in use can be easily upgraded to a suction roll according to the invention. The suction roll consists of simple components and requires little energy.In practice, energy can be saved if dewatering is ensured by other unique and surprising structures. At the same time, the number of web breaks will decrease, and the fiber web will have a higher dry content after the combi press than before.

[0006] The invention will be described in detail below with reference to the accompanying drawings which illustrate some embodiments of the invention. Fig. 1 shows a known press section of a fiber web machine, Fig. 2 shows a cross section of the suction roll according to the invention, Fig. 3a shows a basic side view of the suction roll according to the invention, Fig. 3b shows a modification of the suction roll from Fig. 3a.

[0007] Fig. Figure 1 shows a known press section of a fiber web machine. Some parts of the preceding wire section are also shown. Here, the fiber web W enters the press section on top of a forming fabric 10 belonging to the wire section. Before a so-called combination press 11, the fiber web W, together with the forming fabric 10, passes through a press nip 12 formed by a suction roll 13 and a lump breaker 14. This press nip increases the strength of the fiber web and reduces the amount of fiber lumps in the fiber web. The fiber web W then enters the combination press 11. The combination press 11 has two nips 15 and 16 formed by a suction roll 17 and two lower press rolls 18 and 19. In addition to the forming fabric 10, two press felts 20 and 21 run through the combination press 11. The press felts support the fiber web during two successive pressing processes.In the first nip 15, the fiber web W is located between the forming fabric 10 and the first press felt 20. The second nip 16 is double-felted. In other words, the fiber web is located between two press felts 20 and 21. After the combination press 11, the fiber web W runs over an open draw 22 to a shoe press 23 and then to a dryer section (not shown).

[0008] Fig. Figure 2 shows the combination press 11 enlarged. Here, the perforated roll shell 24 of the suction roll 17 is shown in cross-section, revealing the interior of the suction roll 17. The suction roll is part of a fiber web machine. In practice, there are several suction rolls in the fiber web machine. However, as already mentioned, water causes problems, especially in the combination press. As shown, the suction roll 17 has a perforated roll shell 24. Grooves or other shapes may also be present on the outer surface of the roll shell to increase the void volume for water. Inside the roll shell is a vacuum box 25, which, together with the roll shell 24, defines one or more vacuum chambers 26 and 27. Fig. 2, only the axial seals are shown. The vacuum box 25 has several walls, and the axial seals and the end seals are supported by the walls that define the vacuum chambers against the roll shell. At one end of the suction roll 17, there is a channel 28 with a partition wall 29. In this way, different vacuum or negative pressure levels can be created. In other words, the vacuum level in the first vacuum chamber 26 differs from the vacuum level in the second vacuum chamber 27. Together with the air flow, the water leaves the suction roll 17 through the channel 28. The corresponding vacuum lines 30 and 31 are in the Fig. 3a and Fig. 3b shows the principle. The vacuum lines are connected to the vacuum source like one or more blowers (not shown).

[0009] The first vacuum chamber 26 begins before the first nip 15 and ends after the second nip 16. The first vacuum chamber 26 forms a so-called suction zone on the surface of the suction roll. The vacuum between the nips 15 and 16 keeps the fiber web W in contact with the first press felt 20 and simultaneously sucks water into the suction roll 17. The first vacuum chamber 26 is defined by the first axial seal 32 and the second axial seal 33. Similarly, the second vacuum chamber 27 is defined by the third axial seal 34 and the fourth axial seal 35. The second vacuum chamber 26 forms a so-called cleaning zone on the surface of the suction roll. The vacuum in the second vacuum chamber 27 empties the holes in the roll shell 24 so that the suction roll can absorb water again in the first nip.If the drainage capacity of the suction roll is insufficient, the water level in the vacuum chamber rises, which hinders the cleaning of the roll shell.

[0010] According to the invention, the vacuum box 25 is equipped with a liquid collecting device 36 for collecting water. In practice, the liquid consists mainly of water, but some air, fines, and fibers may also be present. The liquid collecting device is therefore more of a water collecting device. In addition, the water is free water in the suction roll that has already been sucked in by the vacuum chambers. In other words, the free water can be discharged from the suction roll. In addition, the liquid collecting device 36 is connected to a liquid extraction device 37. In practice, the water is collected with the liquid collecting device and then removed with the liquid extraction device 37. These two components are simple and small, and therefore easy to attach to the suction roll and the combination press.

[0011] As in Fig. As shown in Figure 2, the liquid collection device 36 is connected to the last of the vacuum chambers 26 and 27 in the direction of rotation 38 of the roll shell 24. In practice, the last vacuum chamber, which forms the cleaning zone, should be sufficiently empty to avoid rewetting and other problems. With the liquid collection device according to the invention, the excess free water is efficiently removed. This ensures the proper functioning of the suction roll.

[0012] The liquid collection device can be freely located within the suction roll. However, it is more advantageous for the liquid collection device 36 to be located below the respective vacuum chamber 26 or 27 in a wall 39 of the vacuum box 25, which is arranged to collect water in the direction of gravity. In practice, the liquid collection device is located in the lowest part of the vacuum chamber. This way, the water naturally flows into the liquid collection device through gravity. At the same time, the liquid extraction device 37 primarily removes water, thereby increasing efficiency and keeping the size of the components small. Furthermore, the liquid collection device 36 is located far away from the roll shell 24 and its suction openings. Thus, the rotation of the roll shell would not disturb the water collection.

[0013] Surprisingly, even a small liquid collector is sufficient to remove excess free water. In practice, the liquid collector only covers part of the length of the vacuum box in the axial direction. Generally, the length L of the liquid collector is 10-20% of the length of the vacuum box. In practice, the length L of the liquid collector is then 600-1200 mm. In principle, a standard-sized liquid collector fits into any suction roll. However, the larger the suction roll, the longer or larger the liquid collector. As long as water reaches the liquid collector, it is removed by the liquid extraction device. As the amount of water increases, the liquid collector is emptied more frequently.

[0014] In the illustrated embodiments, the liquid collection device 36 is a tray 40 located at one end of the vacuum box 25. The tray 40 is easiest to implement at the end, but the tray 40 would also work elsewhere, for example, in the center of the vacuum box. In practice, the excess water would naturally collect at the ends of the vacuum box. The free water would therefore end up in the tray at the end of the vacuum box.

[0015] The shape and size of the tub can vary. Preferably, the tub 40 has a sloped bottom 41. This calms the water collected in the liquid collection device. Here, too, gravity helps collect water. Here, the bottom 41 is sloped toward the end of the liquid collection device 36. At this point, there is a suction line 42 connected to a lower part 43 of the bottom 41 of the liquid collection device 36. The suction line 42 begins with a suction opening 51. In this way, the liquid collection device with the liquid extraction device 37 is completely emptied. The suction line 42 can run through the liquid collection device 36, as in Fig. 3a, or from above, as in Fig. 3b. Additionally, the liquid extraction device 37 includes a water separator 44 located outside the suction roll 17 and connected to the liquid collection device 36 via a separate suction line 42. Since the suction line 42 is located at the lower part 43 of the base 41, the suction line 42 is below the water surface when free water is present in the suction roll. This completely empties the tank. Devices other than the water separator 44 can also be used to remove water from the air.

[0016] As already mentioned, the suction roll 17 is connected to a vacuum source 45, from which vacuum is supplied to the vacuum chambers of the vacuum box. The liquid extraction device 37 according to the invention also uses the same vacuum source 45. In practice, the water separator 44 is connected to the vacuum source 45 via a vacuum line 46. In this way, only a few simple components are required to ensure efficient dewatering and efficient removal of free water.

[0017] In the illustrated embodiment, the vacuum line 46 has a control valve 47. This makes it possible to adjust the liquid extraction device 37. However, the vacuum level required for water removal is slightly higher than the vacuum in the roller, and the vacuum line can be small. This would allow the liquid extraction device 37 to function even without the control valve. In practice, the water separator is always in operation. When the water level in the lower part 43 drops and air also flows to the water separator 44, the vacuum in the water separator 44 automatically drops to almost the same level or to the same level as the vacuum in the vacuum box. This means that the removal balances itself, and any water that enters the liquid collection device is removed. It is a kind of self-controlled system.If the vacuum in the water separator 44 were lower than in the suction roll 17, the flow direction would be toward the suction roll. The water separator 44 is therefore connected to a higher vacuum than the vacuum box. The liquid extraction device 37 automatically resumes operation and adjusts to the amount of free water. In other words, if the liquid collection device is empty and some air flows through the suction line, the air interrupts the outflow for a short time. The outflow and the vacuum difference are automatically restored when enough water needs to be removed from the liquid collection device. The vacuum line 46 is so small that the vacuum at the water separator 44 increases due to the vacuum source 45 when water needs to be removed. If air comes along with the water, or only air comes, the vacuum at the vacuum source 45 is automatically equal to or only slightly higher than the pressure in the vacuum box.When water is present in the liquid collection device 36, the vacuum automatically increases because less air is coming out of the vacuum box, and water removal begins. In practice, the vacuum source can be turned down due to the efficient water removal with the liquid collection device, thereby saving energy or allowing a higher vacuum level at the vacuum box, as the lower water flow simultaneously results in fewer losses at the air outlet. With the suction roll according to the invention, the majority of the water is removed with the liquid extraction device, and the remainder is removed via the vacuum outlet of the suction roll.

[0018] The Fig. 3a and Fig. 3b show two embodiments. In Fig. 3a, the water separator 44 is arranged so that it slopes down to a seal water tank 48. Thus, no additional energy is required. In Fig. 3b, the water separator 44 is arranged so that it slopes down to a suction or extraction pump 49. The extracted water is pumped further by the extraction pump 49. The edge seals 50 are also arranged in the Fig. 3a and Fig. 3b.

[0019] With the suction roll according to the invention, the combination press of a fiber web machine runs efficiently and without problems. Excess free water is removed safely and with low energy consumption. Furthermore, the required components are simple and robust and require little or no control. The vacuum level remains stable even if the excess water does not fill the cross-section of the vacuum channel. At the same time, the required vacuum level can be achieved with a smaller vacuum pump, which further reduces energy consumption. On the other hand, even higher vacuum levels can be achieved with the existing vacuum source. In addition, the length of the cleaning zone can be degreased, creating a higher vacuum level within the suction roll and a slightly lower air flow through the roll shell without covering the holes of the cleaning zone with press felt. The vacuum within the cleaning zone, i.e.the air flow through the roll shell is necessary to prevent water circulation on top of the suction roll.

[0020] The above-mentioned control valve is used to control the vacuum level in the water separator. In practice, the required air flow from the liquid collector is extremely low. Therefore, the vacuum line can be small. The vacuum in the water separator varies, and the vacuum level is not much higher than in the cleaning zone. During operation, the vacuum in the water separator rises and falls, but only by a few kPa. This means that the liquid collector is not constantly full. When the liquid collector is empty, more air flows in, and the vacuum in the water separator reduces degreasing, stopping the drain. Then the liquid collector refills, and the vacuum in the water separator increases because no more air flows in. This starts the drain and empties the liquid collector. This process is repeated.In practice, the vacuum level in the cleaning zone remains unchanged because the airflow through the water separator is so low. The control valve can be used to adjust how quickly dewatering restarts after the end of the dewatering process.

Claims

[1] Suction roll for a fiber web machine, wherein the suction roll (17) has a perforated roll shell (24) in which there is a vacuum box (25) which, together with the roll shell (24), defines one or more vacuum chambers (26, 27), characterized by that the vacuum box (25) is equipped with a liquid collecting device (36) for collecting water, and that the liquid collecting device (36) is connected to a liquid extraction device (37). [2] Suction roll according to claim 1, characterized by that the liquid collecting device (36) is connected to the vacuum chamber (26, 27), preferably to the last of the vacuum chambers (26, 27) in the direction of rotation (38) of the roller shell (24). [3] Suction roll according to claim 2, characterized bythat the liquid collecting device (36) is located below the respective vacuum chamber (26, 27) in a wall (39) of the vacuum box (25) and is arranged so that it collects water in the direction of gravity. [4] Suction roll according to claim 3, characterized by that the liquid collecting device (36) is located at the lowest part of the vacuum chamber (26, 27). [5] Suction roll according to one of claims 1 to 4 characterized by that the length (L) of the liquid collecting device (36) in the axial direction is 600 - 1200 mm. [6] Suction roll according to one of claims 1 to 5, characterized by that the liquid collecting device (36) is a tray (40) located at one end of the vacuum box (25). [7] Suction roll according to claim 6, characterized by that the tub (40) has an inclined bottom (41). [8] Suction roll according to one of claims 1 to 7, characterized bythat the liquid extraction device (37) has a water separator (44) which is arranged outside the suction roller (17) and is connected to the liquid collecting device (36) by a separate suction line (42). [9] Suction roll according to claim 8, characterized by that the suction line (42) is connected to a lower part (43) or a bottom of the liquid collecting device (36). [10] Suction roll according to claim 9, characterized by that the suction roller (17) is a device with a vacuum source (45) to which the water separator (44) is connected via a vacuum line (46). [11] Suction roll according to claim 10, characterized by that the vacuum line (46) has a control valve (47). [12] Suction roll according to one of claims 8 to 11, characterized by that the water separator (44) is arranged so that it slopes down towards a sealing water tank (48). [13] Suction roll according to one of claims 8 to 11, characterized bythat the water separator (44) is arranged so that it slopes down towards an extraction pump (49). [14] Combined press of a fiber web machine, the combined press comprising two lower press rolls (18, 19) arranged against a common suction roll (17) having a perforated roll shell (24) inside which there is a vacuum box (25) which, together with the roll shell (24), defines one or more vacuum chambers (26, 27), characterized by that the vacuum box (25) is equipped with a liquid collecting device (36) for collecting free water, and that the liquid collecting device (36) is connected to a liquid extraction device (37). [15] Combined press according to claim 14, characterized by that the suction roll (17) is a suction roll (17) according to one of claims 2 to 13.

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