FI111561B - A web transfer method from a press section of a papermaking machine to a subsequent drying section - Google Patents

Description

111561

A web transfer method from a press section of a papermaking machine to a subsequent drying section

Ett förfarande för överföring av banan frän et pressparti account, efterföljande torkparti 5 (dividing the expired pat. No. 961518 / 04.04.1996)

The invention relates to a web transfer method according to the preamble of claim 1, from a press section of a papermaking machine to a drying section.

Increasing the speed of paper machines brings with it new problems, most often related to machine runnability. Today, speeds of up to about 1500m / min are used. At these speeds the so-called. closed press members comprising a compact press roll combination fitted around a si-15 flanged surface roller generally perform satisfactorily. Examples of these press sections include the applicant's Sym-Press II ™ and Sym-Press O ™ press sections.

As paper machine speeds increase, paper machine runnability problems 20 become more pronounced because the aqueous and weak web does not withstand excessive and sudden compressive pressure impulses or high-speed dynamic forces, but causes web breaks and other malfunctions that cause downtime and significant economics.

25 Recently, the speed of paper machines has begun to be so much planned; high speeds than about 40 m / s = 2400 m / min. The implementation of such high speeds, especially on wide machines, exposes more difficult problems to be solved, the most important of which are machine runnability and sufficient drainage capacity at high line speeds.

With respect to the patents related to and related to the present invention, reference is made to 30 2 111561, which discloses FI patches 81854,82500, 84194, 85044 and 93563, FI applications 842115 (filed May 25, 1984), 950451 (filed February 2, 1995), and No. 5,959,193 (filed Apr. 24, 1995), U.S. Patents 4,483,745.4,561,939,44,448,942.4,915,790.4,943,351, 4,988,410, 5,087,325, 5,169,501, and 5,368,697, EP. publications 0 159 280 B1, 0 344 088 A2 and 0 496 965 B1, DE publications 3 604 522 A1, 3 742 848 A1, 4 227 000 A1 and 4 402 629 A1, 10 WO publications 88/08051 and 95 / 16821 and CA Publication 2034829.

Many prior art arrangements include transferring a web from one web to another or further, or ensuring that the web follows exactly the intended compression fabric of the forwarding country, by a transfer suction roller or other suction device. However, the drawback of using these suction devices is that they cause the web to rehydrate due to its suction effect. This re-wetting is particularly detrimental especially after the last nip of the press section, where the web is already relatively drier absorbent and thus particularly susceptible to re-wetting. The aforementioned risk of rewetting has set considerable limits on the use of transfer suction devices and the application of sufficiently high negative pressures for the transfer of the web.

The press section of the papermaking machine also utilizes various essentially water-impermeable and impermeable transfer belts for transferring the web, the operation of which is mainly based on their surface properties, since the suction effect promoting or securing its transfer cannot be passed through the belts.

It is a general object of the present invention to further develop the aforementioned prior art in such a way that the above-mentioned disadvantages are essentially avoided and the foregoing and later objects of the invention are achieved.

3, 111561

The main object of the present invention is to provide a new method for transferring the web from the last press nip of the press section to the drying section.

It is a specific object of the invention to provide a web transfer method which preferably provides a final nip in a double felt long nip wherein the dewatering is performed substantially symmetrically through both surfaces of the web so as to obtain symmetric surface and density distribution properties of the web.

10

The web transfer method according to the invention is essentially characterized by what is said in the characterizing part of claim 1.

In the method of the invention, sufficiently low vacuum levels and small angles of change of direction are applied during the continuous running of the paper machine at the suction zones of the transfer suction devices 15 so as to allow the use of speed differences for tensioning the web. This also reduces the reduction in dry solids content, i.e. rehydration, caused by the transfer suction devices.

The web transfer according to the invention is preferably carried out in such a way that at least continuous when running, the web has a particularly straight line passage and closed passage through the entire press section with a maximum angle of change of less than about 15 °.

In the following, the invention will be described in detail with reference to some preferred embodiments of the invention schematically illustrated in the figures of the accompanying drawings, in which the invention is by no means limited to detail.

Figure 1 illustrates an application environment for the method of the invention using two consecutive long nip zones.

4, 111561

Figure 1A shows a modification of the application environment of the invention of Figure 1.

Figure 2 otherwise illustrates such an embodiment of the invention, mainly according to Figure 1, except that only one long nip zone is used.

Figure 3 illustrates an alternative embodiment of the transfer method of the invention using suction boxes.

10

Figure 4 illustrates an embodiment of the transfer method of Figure 3 wherein the first transfer suction device is a transfer suction roll instead of a transfer suction box.

Figure 5 shows a preferred arrangement of the suction zones of the transfer suction roller within the dryer wire loop according to the invention.

First, the common structural features of the press section geometries of the embodiments of the invention according to Figures 1-2 will be described. 1-2, the press section 20 of the paper or board machine having a closed entry of web W comprises a first water-receiving upper fabric 20 to which web W is transferred from suction zone 21a of pick-up roll 21 from pick-up point P after its suction roll 11.1a1. This is followed by the wire drawing roll 12, from which the return run of the wire 10 begins. As shown in Figs. 1-2, the press has one or two consecutive nipples NP1 and 25 NP2 which effectively drain the web W, between which the web W has a completely closed outlet so that it is supported by the fabric at all times. In Figures 1-2, all the water-removing press nipples NP1 and NP2 are so-called. long nipples having a compression zone substantially longer than a sharp roll nip. In Figures 1-2, all press nipples NP1 and NP2 are further provided with two water-receiving press fabrics 20, 30, 40, 50 so that the water is discharged substantially symmetrically through both surfaces of web W.

5, 111561

In Figures 1-2, the first upper fabric 20 is guided by the guide, clamping, and guide rolls 22,22S. The first long nip NP1 includes a water-receiving lower fabric 30 which is guided by the guide, tension, and guide rolls 32,32S. The first-5 long-nip NP1 as well as the second-long nip NP2 are implemented e.g. with the applicant's Sym Belt Press. The compressed structure is essentially such that the long nip NP1 consists of a hose reel 35; 55 and a counter roll 25, 45 provided with a flexible jacket 20 '. Inside the hose jacket 20 'is a hydrostatically and / or dynamically lubricated sliding shoe 210, with associated hydraulic loading devices pressing the shoe 210 against a counter roll 25; 45. The counter roll 25; 45 is an on-surface 25 '; 45' press roll, e.g., the applicant's deflection-controlled Sym-Z Roll ™.

According to Figure 1, the press member includes a second upper fabric 40 guided by guide, tension and guide rolls 42. In Figure 1, the second long nip NP2 is two to 15 woven, comprising a lower fabric 50 guided by tension, guide and guide rolls 52. The long nip NP2 is formed between the sheath 201 of the lower hose reel 55 and its possible on-surface, the press fabrics 40.50, and the upper press roll with the on-surface 45 '.

In the application environment of Figure 2, one web is used in the press section. W dewatering long nipples NP1.

The application environments of Figures 1 and 2 have in common the transfer of the web W in that the web W is transferred as a closed export from the second upper fabric 40 (Fig. 1) or the first upper fabric 20 (Fig. 2). to the smooth surface 82 'of the drying cylinder 82a or a similar lead-in cylinder or roll utilizing a lightly loaded transfer nipple NS. This nip NS is formed by a press roll fitted with an on-surface 29 '; 49' in the loop of the upper fabric 20; 40 together with the first drying cylinder 82a or the like.

30 Due to the compression pressure applied to the transfer nip NS, the web W engages the smooth surface 82 'of the cylinder 82a and follows as the upper fabric 20; 40 is separated by a guide roll 22S; 42 6 111561

From the dough W. Adhered to the smooth surface 82 'of the cylinder 82a, the web W is moved under the drying fabric 80 which touches the cylinder 82a. The web W is adhered to the drying fabric 80 by means of a blowing suction device 85 or the like, whereupon the web W passes over the suction cylinder 86 provided with a vacuum groove surface 86 'on the outer side of the drying fabric 80, for example the applicant's VAC ™ suction cylinder 82. The first drying cylinder 82a and the subsequent drying cylinders 82 are provided with surface-cleaning patterns 83.

Unlike the web transfer shown in Figs. 1 and 2, Figs. 3 and 4 show a web transfer arrangement in which the web W is applied to a drying wire 80 by a suction transfer roll 81 using the vacuum 50, 50B of its suction zone 81a. Following the suction transfer roll 81, the retention of the web W on the underside of the drying fabric 80 is ensured by blowing simulators 87 or the like, after which the web W is guided to the first drying cylinder 82 and thereafter as a single-wire delivery.

The following describes the different features of each of the different application environments of Figures 1-5.

20th In Fig. 1, after the first long nip NP1, a transfer suction roll 33 is imbedded inside the lower felt loop 30, the vacuum acting on the suction zone 33a ensures that the web W reliably follows the lower felt 30 and differs from the upper felt 20. 34,. after which the web W is transferred in the suction zone 41a of the transfer suction roll 41 to another upper fabric 40. Instead of the transfer suction roll 33, a corresponding stationary suction shoe may be used. The transfer of web W to the lower felt 30 is also ensured, if necessary, by a suitable felt angle. In Figure 1, the lower fabric 30 differs from the web W, guided by a guide roll 32 30, after which the retention of the web W on the lower surface of the second upper blanket 40 is ensured by the vacuum of the transfer suction boxes or blowing suction boxes 43.

• ♦ 7 111561 Thereafter, web W passes through another long nip zone NP2. After the long nip NP2, the web W is tracked to follow the second upper felt 40 and to depart from the second lower felt 50 by the vacuum pressure 47a of the transfer suction roll 47. The angles of the felts 40.50 on the transfer suction roller 47 are arranged to be suitable for the transfer. After the transfer suction roll 47, the retention of the web W on the lower surface of the second upper blanket 40 is ensured by the vacuum of the transfer suction box or blowing suction box 48. After the transfer suction box 48, the web W is applied to the transfer nipple NS using a relatively light line pressure, usually in the range of 0 ... 40 kN / m. Thereafter, the web W passes as described above.

10

Figure 1A shows a modification of the press portion of Figure 1 which differs from that shown in Figure 1 in that the web W is moved from the first elongated NP1 upper fabric 20 to the second elongated NP2 lower fabric 50 utilizing a transfer suction belt 23 from the first upper fabric loop 20 web by W

departs from the lower fabric 30 and follows the underside of the upper fabric 20 where it is detached and transferred to the lower fabric 50 of the second long-nip NP2 within the suction zone 53a of the inner suction roll 53 thereafter. The web W follows the lower pressure of the the transfer is above that shown in Figure 1. like.

•

Figure 2 differs from Figure 1 in that, in Figure 2, only one long nip zone NP1 is used, after which the web W is tracked 25 to follow the upper felt 20 under the effect of a negative pressure acting on the suction zone 27a of the transfer suction roll 27. Thereafter, the web W is retained on the underside of the upper blanket 20 by two successive suction boxes or blowing simulation 28, followed by the flow of web W followed by the lightly loaded transfer nipple NS described above in connection with the first drying cylinder 82a or the like. In Fig. 2, the last guide roll 32S of the lower felt 30 is disposed in an adjustable position, as is the last guide roll 22S of the upper felt 20.

8 111561 Arrows S illustrate this position adjustment. Said adjustment S is used to adjust the size of the curved sectors of the felts 20,30 by the transfer suction roll 27 and the drying cylinder 82a or the like.

Figures 1-2 show dewatering troughs 26,36,46,56 located on the outermost sides of the long nipples NP1 and NP2, which collect the water discharged from the web W on the roll surfaces 25 ', 45', 201 and pass them to the side of the paper machine.

The press sections shown in Figures 1-2 are either press sections with one single nip generally provided with a pit-10 nip NP1 (Figure 2) or so-called. tandem press members having two or more separate nipples NP1 and NP2 (Figure 1). If only one nipple NP1 is used, it is specifically a long nip in the invention. If, on the other hand, two or more consecutive press nips are used as a tandem, the last nip (nipple NP2 in Figure 1 and nipple NPn in Figures 3 and 4) is the long nip and the previous nip or nips 15 are / are long nip and / or roll nip. Above, there has been talk of dewatering nipples, not transfer nipples.

It is also a feature of the press members shown in Figs. 1-2 that the web passage from the pick-up point P to the first dryer cylinder 82a or 20 to the respective lead-in cylinder or dryer wire 80 is quite straightforward, preferably with a maximum web deflection angle em. less than about 15 °.

Figures 3 and 4 show transfer methods in which the last nip 25 NPn is a long nip. N represents the stiffness number of the nip, which is generally in the range N = 1 ... 3 or sometimes even N = 4, especially if one or more roll nipples are used instead of the long nip. As shown in Figure 3, the web W is arranged after the nip NPn to follow the lower felt 50 due to the reduced pressure prevailing on the curved lid 58a of the transfer suction box 58A. After the transfer suction box 58A, the retention of the web W 30 on the upper surface of the lower felt 50 is ensured by the transfer suction boxes 58C, the latter extending to the beginning of the suction zone 81a or 9111561 of the transfer suction roll 81 of the drying fabric 80. In Figures 3 and 4, the guide rolls 22S of the upper felt 20 are tracked in an adjustable position, as illustrated by the arrows S.

Figures 3 and 4 show three different positions 5 of the upper fabric 20 and its guide roll 22S, namely, a full line drawing, wherein the upper fabric 20 has a straight run of longitudinal nip. The dashed dashes show two extreme positions of the upper fabric 20 and its guide roll 22S, namely the upper position where the upper fabric 20 is completely removed from the suction zones 58a; 58b of the suction devices 58A; 58B. In the lower position shown by dotted lines, the upper fabric 20 forms the pivoting sector over the suction zone 58a; 58b and the latter lower position is used for threading the web W and possibly in other exceptional situations, while the intermediate and upper positions of the fabric 20 are used. The upper position of the fabric 20 is the least wettable and is used where runnability permits. The adjustment described above affects the angle of curvature at which the felt 20 curves over the suction zone 58b of the transfer suction box 58A or the transfer suction roller 58B at its respective position in Fig. 4.

Figure 5 shows a preferred arrangement for the suction zone 81a of the transfer wire 81 of the drying wire 80 to be applied in connection with the invention. A similar arrangement 20 may also be used in other transfer suction rollers applicable to the invention, i.e., transfer suction rolls 33,41,47 shown in Fig. 1, transfer suction roll 27 of Fig. 2 and transfer roll 58B of Fig. 4. As shown in Figure 5, the dimension of the suction zone 81a of the transfer suction roll 81 is denoted by a. Within this sector a is a sector b which corresponds to the angle at which the drying fabric 80 or the like fabric curves against the surface 25 of the roll 81 after the lower web 50 or the corresponding puncture site. Inside sector a, there is an open uncovered sector c of the drying fabric, which represents the area of the suction zone 81a that is open after the outlet of the drying fabric 80 or the like (sector a = b + c). Through the open sector c, the suction action of the suction zone 81a and the suction flow I can be applied to the bottom of the web 81 and the opening wedge after the drying fabric 80 or the like 30, lowering its pressure level thereby promoting the transfer of web W to the forward fabric 80. the fabric 80 is shown in Figure 1 as a lower felt 30 and a top felt 40, in Figure 2 the upper felt 20 and in Figure 4 the lower felt 50.

In the transfer method of Figure 5, the contact-5 angle of the press fabric 50 with respect to the transfer suction roll 81 can be adjusted such that the contact angle at the head flaps is greater and smaller during continuous travel. The adjustment may be effected, for example, by the actuating apparatus of the guide roll 52, schematically represented by the arrow S. The position of the lower fabric 50 and its guide roll 52 shown in FIG. 5 corresponds to the tapping position and the dashed positions to the continuous running position.

10

In the invention, the suction sectors 27a, 33a, 47a, 58b, 58a, 81a of the transfer suction rollers 27,33,47,58B, 81 or similar suction boxes 58A utilize a pressure differential selected to be such that a reliable export of web W is achieved, but so small, so that said suction does not substantially wet the web by 15 W. For this purpose, the vacuum level of said suction zones is generally set in the range of -2 ... -30 kPa, preferably in the range of -3 ... -20 kPa.

The following describes the most important features and the most advantageous embodiments of the web transfer method according to the invention. In the preamble of the application, the disadvantages of being caused by the underpressure of the transfer suction device were explained. re-wetting of web W. The magnitude of this re-wetting depends

the vacuum level used and the common cone sectors of the drying felts over the vacuum surface and web W. To minimize re-wetting in the method of the invention, the W tip of the web is used in transfer suction rollers 33,47,27,58B or equivalent transfer suction boxes or blowing suction boxes 58A.

and possibly also other displacement suction boxes or blower suction boxes 34,43,48,28,58C, 85 higher vacuum levels than continuous running, whereby the vacuum level of said suction devices is dropped to a level that maintains good runnability. In addition, in the method of the invention, the curved sectors, i.e. the angles of change of direction, of the drying blankets passing over the transfer suction devices 30 are adjusted larger than in continuous running. In this case, in the continuous run 11111561, vacuum zone 81a or similar vacuum zones of other suction devices, as shown in Figure 5, extend beyond the curved sector of the webs 50.80. When a transfer suction roll is used as the transfer device, it is preferably provided with suction sector sealing strips and seal locking devices 11a, in order to avoid wetting of the web W. The low vacuum applied to the transfer suction device and the small curved sectors of the drying voids during continuous travel allow for the speed differences required to tighten the web W and reduce the reduction in the dry solids content of the web W after the nip.

10

For the purpose described above, the vacuum in the various suction zones 27a, 33a, 47a, 58a, 58b, 81a in the head tapping are generally set to -5 ...- 45 kPa, preferably in the range -7 ...- 30 kPa, whereas in continuous running the corresponding vacuum -2 ...- 30 kPa, preferably in the range -3 ...- 20 kPa.

15

The claims which follow, within the scope of which the inventive idea is defined, may differ significantly from the exemplary preferred embodiments and environments of the invention as set forth above by way of example only.

20 1 ♦ ·

Claims (5)

A web transfer process from a last press nip (ΝΡι, NP2, NPn) in a press section of a paper machine to a drying portion in the form of a closed draw, the web 5 (W) passing through the last press nip (ΝΡι, NP2, NPn) between a first (20, 30, 50) and a second (20, 40, 50) tissue and separated from the first tissue (20, 30, 50) after said last press nip (ΝΡι, NP2, NPn) by means of an excess ring suction roll (27, 47, 58B) or the corresponding transfer suction (58A), whereupon the web (W) is transferred supported by the second tissue (20, 40, 50) to the drying portion, characterized in that the tip (W) of the web (W) is used. a higher suppression level in the transfer suction roll (27, 47, 58B) or in the corresponding transfer suction (58A), and a larger crease angle of the first tissue (20, 30, 50) over the transfer suction roll (27, 47, 58B) or the corresponding transfer suction (58A) ) than in continuous operation. Path transfer method according to claim 1, characterized in that the suppressing zone (a) of the transfer suction roller (27, 47, 58B) or the corresponding transfer suction sleeve (58A) is placed at a direction change angle relative to the tissue (20, 40) which extends over this surface. that said suppression zone (a) extends longer 20. the running direction of the web (W) (sector c) than said directional change angle (b). 3. A web transfer method according to claim 1 or 2, using a transfer suction roller as a transfer device, characterized in that the transfer suction roll (27, 47, 58B) is provided with sealing strips in the suction sect without water lubrication or reading devices for the sealing contact or reducing sealing device. the sealing strips and the inner surface of the suction roll jacket. • Path transfer method according to any of claims 1-3, characterized in that during continuous operation the speed differences in the transmission device needed for tensioning the web (W) with relatively low suppression level and relatively small directional change angle are possible and the immersion is reduced. rewetting of the dry matter content after the last nip (NP1, NP2, NPn) of the web (W) provided by the transfer suction means. Path transfer method according to any of claims 1-4, characterized in that, during continuous operation, the suppression levels of the suction zones are stalled by the transfer devices within the range -2 ... -30 kPa, advantageously in the range -3 ... 20 kPa, and during the tip drawing, the suction zones of the suction zones of the transfer means are stalled in the range -5 ...- 45 kPa, advantageously in the range -7 ...- 30 kPa. 10 «1«