FI115307B - Press section in a cardboard machine fitted with prepress - Google Patents

Abstract

The press section comprises at least two separate press nips (N1, N2) through which a web (W) to be pressed is passed as a closed draw. The first press nip of the press section is a pre-press nip (N1) formed between a roll (11) placed inside a forming wire loop (12) and a roll (21) placed outside the forming wire loop (12), which pre-press nip is an extended nip. The second press nip of the press section is a press nip proper (N2) provided with two water-receiving press felts (34, 42), through which nip the web (W) runs between said press felts (34, 42). An upper press fabric in the pre-press nip (N1) is formed of a water-receiving press fabric (24) lying against the outer surface of the water-receiving press fabric (24), in which connection the web (W) runs in the pre-press nip (N1) between the lower forming wire (12) and the upper water-permeable press fabric (26). The invention also relates to a method for removing water from a web in a press section provided with a pre-press nip.

Description

115307

FIELD OF THE INVENTION The invention relates to a press machine part of a cardboard machine with a pre-press according to the preamble of claim 1.

The invention further relates to a method for removing water from a web in a press section of a board machine with a pre-press, according to the preamble of claim 8.

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By a separate press nip, in this application is meant a press nip in which the opposing press members form only one press nip. The separate press nip may be a roll nip or a long nip. In contrast to the separate press nip, there is a press with a center roll, where the center roll forms a press nip with at least two other rolls.

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The function of the press section is to remove water from the web and to form a symmetrical web, whereby the absorption and roughness properties of both sides of the web are symmetric. In addition, the press section should be simple and efficient enough to apply to a variety of board grades.

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Especially at high speeds, the web passage in the press section should be as »i · · as possible. '· Straight. The aqueous and weak web entering the press section does not withstand the dynamic forces caused by high speeds and changes in direction, but causes web breaks and other • · * ;;; ' malfunctions that cause downtime.

* ···: 25. Applicant's U.S. Patent No. 5,792,320 discloses a method for dewatering paper-based paper. or by squeezing a cardboard web. In Figure 2 of the publication, a pre-press nip is formed between the on-bottom underside roll inside the forming wire loop and the upper shoe roll outside the forming wire loop. On the upper side of the shoe roll t * »·» • ·. 30 passes a substantially water-resistant, smooth-surface transfer belt, * * »'in the pre-press nip. ·. * to move the web from the pre-press nip to the »» 1 »» press felt below the first actual press nip. The dewatering in the pre-press nip forming the long nip occurs only in one direction, i.e. through the forming wire to the shell of the roll surface.

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Applicant's U.S. Patent No. 5,522,959 discloses a press section specifically for printing paper grades. In Fig. 6 of the publication, a pre-press nip is formed between an undercut roll located below the forming wire link and an upper shoe roll outside the forming wire link 5. A press felt runs through the pre-press nip on the upper shoe roll. Water is discharged in the long-nip pre-press nip in two directions, i.e. through the forming wire to the underside of the on-surface roll and to the upper press felt. The transfer of the web to the actual press section takes place with a pick-up roll from the forming wire after the pre-press nip.

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Applicant's U.S. Patent No. 5,820,731 discloses a method and apparatus for removing water from a web in a paper or board machine. In Figure 3 of the publication, a first pre-press nip is formed between an on-surface first lower roll inside the forming wire loop and a first surface roll with a smooth surface outside the forming wire loop.

A second pre-press nip is formed between a second lower roller having a smooth surface inside the forming wire loop and a second upper roller having an outer surface on the outside of the forming wire loop. The web runs in both pre-press nips between the forming wire below and the upper wire circling the upper rollers. Dewatering takes place in the first pre-press nip mainly through the forming wire to the sheath of the first lower on-roll roll,, and in the second pre-press nip mainly through the upper wire to the sheath of the second over-roll roll. Both pre-press nipples are roll nipples. The transfer of the web to the actual press section takes place by a pick-up roll from the forming wire after the second pre-press * * "pin.

It is an object of the present invention to provide a press section of a carton machine with a pre-press, which is particularly suitable for the production of board grades having a high basis weight. By high basis weight is meant here more than 100 g / irf. preferably greater than 200 grams per liter.

The press part according to the invention is essentially characterized by it. as set forth in the characterizing part of claim 1.

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The method of dewatering the press member according to the invention is essentially characterized by what is stated in the characterizing part of claim 8.

The press section of the invention has at least two separate press nipples. The first press nip, which is the first press nip, is formed between an inner roll inside the forming wire loop and an outer roll outside the forming wire loop. The pre-press nip is a long nip formed between the shoe roll and the counter roll. The long nip achieves a higher dry matter content than the roll nip due to the longer 10 nip and higher line load.

Two separate press fabrics are used as the press fabric above the pre-press nip. A water-permeable press felts against the outer roll and a water-permeable wire against the outer surface of this water-receiving press felts. The web 15 runs in a pre-press nip between two wires.

By using a separate wire loop outside the upper press felt loop in the pre-press nip, contamination of the upper press felt can be significantly reduced. This is especially important when producing high basis weight board grades »· (: 20 at high speed. Depending on the running speed, basis weight. And mass quality, the board web generally has a dry content of less than 20% when it arrives at the pre-press nip. increases by about 10-15%.

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The press section according to the invention is also not sensitive to variations in pulp quality and to the abrasive effects of pulp. Due to the overhead wire, the pulp does not come into direct contact with the overhead press felt in the pre-press> _ ·: · nip.

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.... j The wire loop outside the top press felt also reduces the re-wetting of the web after the pre-press nip. Water bound to the upper press felt in the pre-press nip, ** ·· 30 cannot pass through the upper wire back into the web by the pre press • * ·

»» I

,,,,: after pin.

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The press section of the invention can drive a paperboard web having a basis weight ranging from about 100 to about 500 g / m 2. A cardboard web having a basis weight of about 400 g / m2 having a dry matter content of about 20% before the pre-press nip can be run at a speed of about 600 m / min, whereby the production capacity of the press becomes about 4 kg / sm.

In the process of the invention, water is removed from the web in a press section of a board machine equipped with a pre-press. The web to be extruded is guided in closed export through at least two separate press nipples. The first press nip of the press section is a long press nip formed between the inner roll of the forming wire loop and the outer roll of the forming wire loop. The second press nip of the press section is an actual press nip having two water receiving press felts through which the web passes between said press felts. The web runs in a pre-press nip between the lower forming wire and the upper water-permeable wire, which in turn is positioned against the outer surface of the water-receiving press felt against the outer roll.

The invention will now be described in detail with reference to the accompanying figures. . Embodiments of the Invention, the details of which are not, however, limited to the invention. '. 20 is by no means narrowly restricted.

Fig. 1 schematically shows one pre-press nip and one actual • ·. · *. a press section of a carton machine according to the invention with a press nip.

Fig. 2 is a diagrammatic representation of a modification of the press section shown in Fig. 1 in accordance with the invention.

Fig. 3 schematically shows another modification according to the invention in Fig. 1. ..: of the press section shown.

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Fig. 4 schematically shows a third modification of the press part according to the invention according to Fig. 1.

Figure 1 shows a press section of a carton machine according to the invention with two separate press nipples N1 and N2. The first press nip is the pre-press nip N1 and the second press nip is the actual press nip N2.

The pre-press nipple N1 consists of an upper first shoe roll 22 and a lower underside first counter roll 11 having a hollow surface 11a. The first counter roll 11 is located inside the forming wire loop 12 and the shoe roll 22 is located outside the forming wire loop 12. The shoe roller 21 is rotated inwardly as a loop by an upper first press felt 24 and an outer loop by an overhead wire 26. The inner presser upper loop 24 has press felt 24 retreading means 25.

15! The actual press nip N2 consists of a lower second shoe roll 31 and a second upper shoe 41 provided with an upper surface 41a, the second shoe roll being located inside the second press felt loop 34 and the second shoe roll 41 located inside the upper third press felt loop 42. The lower second press loop, V 20, has a felt loop 34 with press felt 34 retreading means 35 and an upper third * ·. ·· Similarly, press bar loop 42 has press bar reconditioning devices 43.

t • · · »* · '*' issä Press nipples Nl. N2 used shoe rolls. i.e., the structure of the hose reels 21. 31 is ;; · * known per se, comprising a flexible hose sheath 22. 32. within which is a press shoe 23 loaded with a hydraulic '· * ·' 25 pressurized medium to provide the necessary clamping pressure on the nipples N1. N2 to the web passing through W. The hose diaper is in such a ra-11! the structure preferably has a surface 22a. 32a. from soil it can also have a smooth surface.

Railia W is introduced by the forming wire 12 over the suction boxes 13 30 at the end of the forming part to the pre-press nip N1. Railia W passes between the forming wire 12 and the forming wire 26 in the pre-press nip X1 forming the long nip. Further, between the upper shoe 26 and 6 115307 the first shoe roll 21 of the first shoe roll 21 passes an upper first press felt 24. Dewatering takes place in the pre-press nip N1 in two directions, i.e. through the lower forming wire 12 to the lower a belt diaper 22 on the upper first shoe roll 21 21.

After the pre-press nip N1, the wires 12, 26 and the press felt 24 follow some distance from the trailing edge of the shoe 23, after which the lower forming wire 12 is separated from the outer 10 by the nip plane T of the pre-press nip W follows the upper wire after 26 pre-press nips N1. The gripping and retention of web W after the pre-press nip 24 on the lower surface of the upper wire 26 is enhanced by the suction box 27 inside the upper first press felt nipple 24. a roller 36 on the upper surface of a second press felt 34 rotating below, the upper surface of which is supported by the web W being introduced into the actual press nip N2.

The figure also shows the drop jets 28. whereby the web W can be removed from the overhead wire · · · · 26 and driven into a pulper below the press section.

In the actual long-nip forming press nip N2, web W passes between a lower press felt 34 and a third press felt 42 above. The water ♦ · 25 is thus discharged in the actual press nip N2 to the underside of the second press felt ... 34 and to the underside of the second shoe roll 31 belt strap 32 and above. * · · I to the third press felt 42 and to the surface 41a of the upper second counter roll 41.

, After the actual press nip N2, the third press felt 42 above is separated • ♦ * »»

. 30 below the second press felt 34. In this actual press nip, N2 of web W

the angle between the travel direction after the press nip N2 and the nip plane is blunt, whereby the 7115307 web W follows the second press felt 34 below, in a straight run. From the lower second press felt 34, the web W is moved at a second transfer point S2 in the suction zone 51a of the second transfer suction roll 51 to the lower surface of the upper drying fabric 52 rotating said transfer suction roll 51, further supported on the web W.

Figure 2 shows a modification of the embodiment shown in Figure 1. The top wire 26 and the top first press felt 24 are removed from the bottom forming wire 12 immediately after the pre-press nip N1. The angle α between the direction S of the passage 10 of the web W pre-press nip N1 and the nip plane T is obtuse here, whereby the web W follows the forming wire 12 below the pre-press nip N1. From the underside run of the forming wire 12, the web W is detached at the pick-up point P in the suction zone 44a of the pick-up suction roll 44 and gripped on the outer surface of the third press felt 42 rotating above the pick-up suction roll 44. When the direction of web W is reversed with the pick-up suction roll 44, the web W 15 is first moved, in a straight run, first only on the lower surface support of the upper third press felt 42 and then between the lower second press felt 34 and the upper third press felt 42 The embodiment shown in Fig. 2 is inclined to correspond to the embodiment shown in Fig. 1.

Fig. 3 shows another variation of the embodiment shown in Fig. 1, the embodiment differs from the embodiment of Fig. 2 with respect to the structure of the pre-press nip N1 and the actual press nip N2. The pre-press nip N1 is formed by a first shoe roll 21 and an upper counter roll 11 having a smooth pin jacket. The first shoe roll 21 is now located inside the forming wire loop 12 and the first shoe roll 11 is located outside the forming wire loop 12. The first counter roll 11 is rotated inwardly by the upper first lip and, as the outer loop, the upper side, they are a wire 26. The actual press nip N2 consists of a lower shoe roll 31 with a smooth surface belt 32 and a second counter surface 41 with a smooth surface 30. in part, this embodiment corresponds to the embodiment shown in Figure 2.

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Figure 4 shows a third modification of the embodiment shown in Figure 1. This embodiment differs from the embodiment of Figure 3 with respect to the pre-press nip. The pre-press nip N1 consists of an underside of an on-surface la 11a first counter roll 11 and an upper 5 of a first shoe roll 21 provided with a smooth-faced belt diaper 22. Here the nip plane of the pre-press nip N1 forms an angle of

The passage of the web through the press section is particularly straightforward in the embodiment shown in Figure 1, so that the web is not subjected to high dynamic forces due to the change of direction of travel. The web thus remains well adhered to a support surface such as a wire or press felt.

The press members shown in the figures have only two press nips, i.e., a pre-press nip N1 and an actual press nip 192. However, the press member according to the invention may contain, in addition to these two press nips N1, N2, one or more press nips after the second press nip N2. For example, if the basis weight of the web W to be formed is high, a third press nip may be used to increase the fiber content of the web W before the web W is transferred to the drying section.

•; In the press portions shown in the figures, the shoe roll 31 is always provided as a roll below the actual press strap N2, but the shoe roll 31 can also act as a roll above the actual press nip N2, wherein the roll below the press nip N2 is a counter roll.

The maximum line load t used in the pre-press nip N1 according to the invention depends on the structure of the counter roll 21 and the wires 12. 26. Line loads of at least about 600 kN / m are possible. In the actual press nipple N2, • line loads of at least 1500 kN / m can be used. The shoe rolls 21. 31M I t to the web surface 22a of the webbing 22, 32. The degree of 32a is in the range of 15-35%. preferably. 30 25% and counter rolls 11. 41 on the surface 11a. The degree of transparency of 41a is in the range of 40-70%.

'K' is preferably 60%.

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The fabric 26 or equivalent press fabric acting as the outer fabric of the pre-press nip N1 should be a well-water-permeable thin fabric, but still stiff enough to function. The press fabric 245 or equivalent press fabric acting as the inner top fabric of the pre-press nip N1, in turn, must be a well-water-absorbing fabric with sufficient water space and weighing more than 2000 g / m 2.

The following claims are made within the scope of the inventive idea defined by the various details of the invention which may vary and differ from those set forth above by way of example only.

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Claims (8)

115307 ίο A press section of a carton machine with a pre-press comprising at least two separate press nipples (N1, N2) through which the pressable web (W) is guided in closed configuration 5, wherein the first press nip of the press section is an inner roll (11) and a pre-press nip (N1) formed between the outer roll (21) which is a long nip and the second press nip of the press section is an actual press nip (N2) provided with two water receiving press felts (34, 42) through which the web (W) passes said press felts (34, 42). ), characterized in that the press fabric (24) facing the outer roll (21) and the water permeable wire (26) facing the outer surface of the water receiving press (24) are the press fabric over the pre-press nip (N1). passes through the pre-press nip (N1) the forming wire (12) below and the upper support between the water-permeable wire (26). 15 Press section according to Claim 1, characterized in that the roll outside the pre-press nip (N1) is a shoe roll (21) with a press shoe system (23) and a belt diaper (22) and the counter roll inside the pre-press nip (N1) is a roll (11a). dewatering in the pre-press nip (N1) occurs through the forming wire (12). # 20 through the caliper (11a) of the caliper (11) and through the wire (26) above to the press felt • 1. • (24). • · · • · · • »» 1 · t ]! 3. Press section according to Claim 2, characterized in that the belt roll shell (22a) of the outer roll of the pre-press nip (N1) has a hollow surface (22a), whereby the press is also drained. · · ·, 25 through a tin blanket (24) to a shoe roll (21) on a webbed (22a) belt diaper (22). * · • · · .... j Press section according to Claim 1, characterized in that the inner roller of the pre-press nip (N1) • 1 1 1 · is a shoe roll (21) with a press shoe system (23) and a webbing (22a) with an on-surface (22a) and external to the pre-press nip. the counter roll is a smooth • • a • a. ···. A 30-inch roll (11), whereby dewatering in the pre-press nip (N1) occurs through the forming wire (12) through the shoe roll (21) to the surface (22a) of the forming roll (21) ) through the belt diaper (22) and through the upper wire (26) to the press felt (24). Press section according to one of Claims 1 to 4, characterized in that the second press nip following the pre-press pin (N1) is a long nip (N2). Press section according to one of Claims 1 to 5, characterized in that the second press nip (N2) is formed between a shoe roll (21) with an on-surface (22a) belt diaper (22) and an on-surface (41a) counter roll (41). 10 Press section according to one of Claims 1 to 5, characterized in that the second press nip (N2) is formed between a shoe roll (21) with a smooth-faced belt diaper (22) and a smooth-faced counter roll (41). A method of dewatering a web (W) in a press section of a board machine with a pre-press, wherein the web to be pressed (W) is guided in closed export through at least two separate press nipples (N1, N2) 11) and a pre-press nip (N1) formed between the outer roll (21) of the forming wire loop (12), which is a long nip and the second press nip of the press section 20 is provided with two water receiving press felts • # 1 ·; (34, 42) provided with an actual press nip (N2) through which the web (W) passes between said press felts (34, 42), characterized in that the web (W) passes through a pre-press nip (N1). ) between the forming wire (12) below and the water permeable wire (26) above, which water permeable wire (26), in turn, rests against the outer roll (21). 25 against the outer surface of the incoming water receiving press felt (24). • • • »I • • • • • • •••••••••••••••••••••••••• i 115 i