FI122398B - Method in connection with a paper machine and a paper machine - Google Patents

Description

METHOD FOR THE PAPER MACHINE AND PAPER MACHINE

The invention relates to a method in connection with a papermaking machine, wherein the web is formed on a former surface of a wire, 5 - the web is displaced by tensile and vacuum release from the wire surface to a press section fabric or other support surface, supported by at least one fabric supported by at least one unidirectional by removing the press section support surface 10 to the drying section, the web is passed through the drying section to bring the web to final moisture, whereby the web is transported from the former to the drying section by a plurality of successively arranged endless support surfaces, therewith being subjected to several tensile separations from each of the previous support surfaces.

State of the art

The design of a paper machine pursues a number of goals in terms of good runnability and quality, which are measured in numerous quantities. One of the most important properties of paper is the symmetry between its surfaces, which comprises e.g. surface smoothness and absorption properties. In practice, compromises have always been made and a small amount of asymmetry is usually accepted. Current paper machine designs are not capable of producing fully symmetrical paper efficiently. Often the paper is rough on one side if the other 25 features are balanced and the runnability remains good.

Often good quality is obtained at the expense of runnability, one such good quality machine is described below with reference to Figures 1 and 2: i o ^ 30 Typical construction: x - Kitformer (generally web forming part) with loadable moldings

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- Press section 3 nip press with separate 4th press (SymPress B & 4th) with good σ> ^ water removal LT) go - Single wire drying o cm 35 - Single or double nip soft calender

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challenges:

The press section has two open exports (the web is not supported against a fabric or roll). Detaching from a smooth roller (center roller & 4 press counter roll) requires traction difference which increases as speed increases. On the other hand, a large tensile difference reduces the paper quality and destroys the stretching potential of the web. The increase in tensile difference decreases, for example, porosity, absorption property and pile strength. At high speed, the difference in tensile draws closer to the resistance of the paper and this leads to an increasing number of breakages. In practice, running speeds over 1800 m / min for woody grades are starting to be challenging with open export presses.

io - Although the 4th press removes water downward, thus smoothing up the dewatering level of the press member more symmetrically. However, the amount of water to be removed has proved to be insufficient, for example, to correct the absorption side. This concept has not been able to provide optimal paper structure. Nevertheless, this technology currently provides the best paper quality on the market, with at least 15 sided paper.

- The biggest limitations of this press are maximum running speed, moisture profile control, rewetting (same felt in nip 1 and nip 2), vibration problems, head turn and efficiency. The main limitations of the efficiency are the challenges of a separate four-squeezer and the heavy strain on the paper from open exports.

20 - The upstream runnability of the drying section is challenging. Due to the low dry matter, the tensile strength of the paper is still very low. In practice, low paper "strength" levels lead to a variety of problems. At the beginning of the drying section, the paper web tends to stick to the drying cylinders, which can lead to runnability problems and / or dirt accumulation at the beginning of the drying section. Efforts are being made to control runnability with the 25 most powerful runners in the pocket space defined by cylinders and swivel roller.

At the beginning of the drying section, only the top tuned technique achieves a good result.

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On the other hand, a press section of a good runnability machine and the beginning of a drying section are illustrated in g 30 in Figure 4.

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Typical construction: δ - Kitformer with potentially loadable moldings or flat wire m o - Two-nip shoe press with closed port and second nip lower position water transfer transfer, with more press 35 dewatering of the press section, known in the art - overhead blow

Single Wire Drying Challenges and Features:

The first press of the press section removes water in both directions. The second press nip 5 only removes water above the paper. In practice, such dewatering combined with the prior art wire section produces one-sided paper. In addition, it has been found that the underside of the paper also contains an abundant amount of unbound material, which can cause a dust problem in printing houses. In other words, the surface texture of the paper is not optimized or good enough for demanding grades. The one-sided structure 10 of the paper must be compensated by vigorous calendering.

According to dewatering theory, such a solution should achieve symmetry with the downward drain former.

In runnability, this press design achieves speeds of more than 2000 m / min for woody species without the need for tensile separation of the press section destroying the structure and quality of the paper. This concept is limited by the runnability of the drying end.

The biggest limitation of this press relates to paper quality. With the wire parts currently available on the market, the press produces a fairly one-sided paper with other structural weaknesses (e.g., surface strength and printability).

The upstream runnability of the drying section is challenging. The paper has a very low tensile retention capacity due to its 20 dry solids. In practice, low paper "strength" levels lead to a variety of problems. At the beginning of the drying section, the paper web tends to stick to the drying cylinders, which can lead to runnability problems and / or dirt accumulation at the beginning of the drying section. The goal is to control the runnability with the more efficient runners. At the beginning of the drying section, only the top 25 tuned technology achieves a good result.

δ ^ Until now it has been concluded that after the former part the web is homogeneous over the thickness, i.e. the structure of Y is substantially uniform, i.e. unilateral. This conclusion is supported by the fact that the press section has been able to remove the water quite symmetrically on both sides of the Er 30 web.

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Summary of the Invention The object of the invention is to provide an improved papermaking method 35 and a corresponding paper machine. The method according to the invention is characterized in that the asymmetry of the dewatering of said single-drying press nip (N) is directed to the same side of the web so that the single-acting nip (N) removes downwardly and is a direct blow to the web just before the 1st drying cylinder. The paper machine according to the invention is characterized by 5 features as stated in claim 7. Surprisingly, it has been found that suitably fitted asymmetric strip tensile separations of the endless support surfaces and press dewatering provide a more homogeneous paper structure. Roughly, the asymmetry of the web (tensile) releases is calculated by calculating the difference between the up and down releases, but more precisely, ίο examines the total effect of the releases on each side, as the effect of the releases will vary due to different factors. This asymmetry of removals is surprisingly offset by asymmetric dewatering in the same direction. It is conceivable that each tensile separation from the support surface will degrade the quality of the surface detached from the support surface of the web, but that dewatering in the same direction will cause the same effect on another surface, whereby the effects will cancel each other out. Generally, each side will have an amount corresponding to the number of removals, more specifically the amount of dewatering corresponding to their total effect. The operation of the invention may not be definitively explained herein, but in any case, the solutions presented achieve a surprisingly good result.

According to the invention, there are more detachments downwards than upwards and correspondingly the one-sided drying nip removes water downwards. Preferably, the press section has a duplex dewatering nip before the unilateral dewatering nip.

DETAILED DESCRIPTION OF THE INVENTION 25

The invention will now be described, by way of example and with reference to the accompanying drawings, in which: Figures 1 and 2 show a prior art high-quality paper machine Y Figure 3 illustrates a prior art solution with a press section of a paper machine for good runnability

Er 30 Figure 4 shows a prior art paper machine with good runnability

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Figures 5 and 6 show an optimal paper machine δ tn o according to the invention. In Figures 1-6, the same reference numerals are used for the functionally similar parts. The main parts of the papermaking machine are formed 10, press 13, dryer 17 and roller 20. The 35 wires of Former 10 are denoted by reference numeral 8, the fabrics of the first nip of press 13 are denoted by reference numerals P1 (upper fabric) and P2 (lower fabric) 17 first tissues with reference number 22.

The direction of dewatering of the press section 13 at each nip is indicated by thin arrows which give 5 an idea of the unilateral dewatering of each section. Thin arrows under pressure / mechanical strips on the support are marked with thick arrows. These are discussed in connection with each example.

In Figure 1, the former is of the kitformer type. High-vacuum dewatering is denoted by reference numeral 9. These may also have an effect on asymmetry. The formed web is transferred to a press section 13 where it is guided through it, mainly supported by tissues and roll, to a drying section 17. Thereafter, the nearly finished web is passed through a soft calender 18 to a reel 20.

More specifically, the press section and its attachment to former 10 and dryer 17 are shown in Figure 2. Former 10, the web is formed on wire 8, from which it is transferred by transfer suction 12 to the upper felt P1 of the first press nip NO. The transfer suction roll 12 performs the first draw-off underpressure release. Supported by top felt P1 and bottom felt P2, the web is guided through nip NO and further uppermost felt P1 to center roll 25. Between this and nip NO top roll 24 20 there is a second nip N1 with low dewatering efficiency since the felt is already wet in first nip NO. The third nip between N2 central roll 25 and shoe roll 26 again efficiently removes water to felt S2. From the central roll 25, the web is removed by tensile mechanical separation and transferred through the clearance to the transfer roll 24 and further to the lower felt S2 of the fourth nip N of the press. The web is trapped on the top roll of the fourth nip N, from which it is removed by a transfer suction roll 15 to the first fabric 22 of the drying section.

The upper single wire passage in the dryer section evaporates more from the lower surface of the web and only slightly through the wire from the upper surface, the forming and clamping portions collectively remove more water / more water through the lower surface of the web.

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Preferably, this arrangement also has a single nip soft calender thermo roll in the lower position o after the drying section, whereby the underside of the web is further smoothed and the surface roughness of the web is 0X1. On the other hand, the absorption between the surfaces of the web is then one-sided, the adjustment of which makes the web one-sided with respect to roughness.

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With the press, three nipples remove water on the upper side of the web and two on the lower side of the web - though there are two blankets on both sides of the web. On the other hand, the forming part has correspondingly high pressure suction on the lower side of the web, whereby the whole of the two dewatering parts is dewatered more often / more through the lower web surface. 5 Nipple removals without speed difference do not have the same detrimental effects as other removals. For example, the center roll in its first nip releases the web without a difference in speed from the previous support surface of the web.

The combination of traction differential and vacuum release is the best in the art, as the last 10 downward releases slightly compensate for previous upward releases. As a whole, the dewatering and traction separations are moderately smooth in this application, providing the best quality at the moment.

In Fig. 3, the web formed by former 10 is transferred from wire 8 to the first felt P1 of the first press nip which guides it together with the lower felt P2 through the NO. With the suction roll 11, the web is transferred to the lower felt P2, from which it is spaced apart by the transfer suction roll 14 to the upper felt S1 of the second nip N. This guides the web together with the transfer belt S2 through the second nip N. The dough grips nipple N on a smooth transfer belt S2 from which it is disengaged to the first fabric of the dryer section by means of a transfer suction roll 15.

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A prior art solution in which one nip of a two-nip press member removes water upwardly to prevent theoretically accumulation of fines on the underside of the web. However, the arrangement renders the web coarser on its upper surface and more absorbent on its lower surface.

25 With respect to tensile differential vacuum relief, this is the weakest state of the art with almost ^ upward detachments only and is therefore not suitable for the most demanding types of o w, ό

In Figs. 4, the papermaking machine shows the press section 13 and the first sections of the drying section 17, namely Ee 30, the vertical blow dryer 17.1 and 17.2 of the pre-blow dryer and the beginning of the cylinder group. The first dryer cylinder is denoted by reference numeral 17S and the first dryer fabric is denoted by reference numeral 22.

oo o o ^ The various parts of the arrangement, namely the press section, the blow dryers and the cylinder dryers, are 35 known in their basic structure. of the aforementioned patents.

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The twin-nip press 13 has nipples NO and N. As is known, the paper web is taken to the press section 13 by a pick-up roll 12 and is conveyed through the nips by means of press felts P1, P2 S1 and a transfer belt S2. Following the press section 11 (or integrated in the rest thereof) is a horizontal, i.e. pre-blow dryer 17.1, which uses a drying wire R2 against which the blowing unit is placed.

Referring to Figure 1, a paper web is taken from a transfer belt S2 by a transfer suction roll 15 to a transfer fabric R1 which conveys it to a horizontal overflow dryer 17.1 on a drying fabric R2 by a transfer suction roll 19.

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The paper web passes over the drying fabric 17 under the blowing unit 20.1, thereby exerting a strong heating effect. In the short blowing zone drying happens quite a bit, but the web is heated up and the top surface layer dries out a bit. However, this is important for runnability. At the same time, the moisture gradient of the web in the thickness direction is strongly increased towards the lower surface.

After the horizontal blow blower dryer 17.2, the paper web is transferred from the dryer wire R2 after the vacuum roller 30 to the dryer wire 22 of the first dryer cylinder group. The same dryer wire 22 is also used by the vertical blow dryer 17.2. In a manner known per se, the paper web is transferred to a drying wire 22 by means of a top roll 31 acting as a low pressure roller (suction roll or VAC roll) in a vertical blow dryer 21.

In the blow dryers (17.1, 17.2), the temperature of the blowing gas is preferably in the range 200 ° C to 700 ° C, most preferably in the range 250 ° C to 400 ° C. Also, the humidity of the blowing air 25 (by circulating the blowing air) can influence the temperature of the web.

δ ^ The horizontal blowing dryer has a blowing length of up to 50%, most preferably i Y 15 to 35% of the total blowing length. With a larger pre-blowing length, drying can be achieved even in addition to preheating.

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Fig. 4 shows the directions of the tensile differential vacuum depressions on the transfer rolls 12, 11, 14, 15 cg, and 19. The tensile differential vacuum pressures of the web from the support surface are more upward than downward. It is conceivable that each tensile differential vacuum release detracts from the surface of the web. The magnitude of the adverse effect depends on the degree of humidity of the web, the smoothness of the surface 35 and other factors. The asymmetry of dewatering in different directions here ultimately leads to the asymmetry of the structure. Further detachments in the drying section, such as roller 31 and after 8, no longer significantly affect the structure of the paper.

Figure 4 further illustrates a prior art solution having an overflow application on a transfer wire. However, here the draw-off vacuum depressions are no more top surface 5 releases.

With respect to tension differential vacuum reliefs, this application still uses too many upward releases when the dewatering asymmetry is down.

ίο The runnability of the drying section is maintained by the use of overflow technology. A preferred solution is the blower concept known as the Applicant's trade name "OptiDry Twin", which provides a large amount of blast drying (drying) prior to the first drying cylinder. This avoids the problems of adhesion, runnability and contamination of the cylinder drying section. The dry solids content after blasting is about 5-10% units higher than the puris-15 tin solids.

The inflatable solution is known from WO97 / 130131 and WO2005 / 068713.

Figure 4 shows how the blowing is combined with a conventional high runner press. It will be seen, inter alia, that a separate transfer fabric R1 is needed here to transfer the paper web from the underside transfer belt S2 to the first blow dryer 17.1. The one-sidedness caused by the press section 13 is unchanged in this solution.

Figures 5 and 6 show a paper machine according to the invention, which achieves both good runnability and good quality, comprising perfect symmetry of the paper structure. The Formed 10 and the first nip NO of the press 13 are substantially similar. The web is taken by transfer suction roll 12 to the first upper felt P1 and guided together with the lower felt P2 to the first? through the NO nip. Thereafter, the web is taken directly to the lower felt S2 of the next nip from the first upper felt P1 by a transfer suction roll 14. The web is guided between the second lower felt S2 and its opposite Er 30 transfer belt S1 through the second nip N to transfer the web to the transfer belt S1. From here

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the web is again transferred directly to the fabric R2 of the vertical blow dryer 17.1, which takes it to the horizontal blow dryer 17.2. This is constructed to use the fabric 22 of the first cylinder group. Here, the rollers 30 and 31 have the same function as the solution of Fig. 4.

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Again, the drying section 17 comprises the blowing units 17.1 and 17.2 as well as a plurality of cylinder drying groups. Thereafter, the web is guided, after the soft calender 18, to the rewinder 20.

Here attention should be paid to the web in the direction of the tensile differentials with the transfer suction rolls 12, 14 5 and 15 and to the drainage direction at the other nip N.

Contrary to the known theory, more water is removed through the bottom surface of the web, and preferably over-blow drying is applied immediately after the press, which first blows the upper surface of the web by heating it and removing some water through that surface. Next, the lower surface of the web is blown immediately thereafter, preferably over a longer portion, whereby the lower surface of the web is evaporated efficiently, whereby the web is ready for cylinder drying by means of an overhead single-wire feeder.

Dewatering in the last nip through the bottom surface of the web is 12-16%, which is a significant proportion.

In the forming section, the drained web has a dry solids content (Kap) of> 9% and the high pressure pressures through the lower surface of the web additionally have a Kap portion of about 20-50% and further dewatering through the lower surface gives a symmetrical web. In this case, drying also advantageously removes more through the bottom surface of the web (completely overhead single-wire threading or combined blow-drying, which also removes more through the bottom surface of the web).

The effect-sealing effect theory of the dewatering web does not alone explain the two-sidedness of the press and the surprising result presented above. In addition, the effect of the tensile differential vacuum release on the web surfaces is taken into account in the present invention, resulting in a web having a absorption δ and a symmetrical roughness. The surface of the web Y is most affected by the release from the adhesive surface, since then some of the fines of the web surface adhere to the adhesive as the web proceeds by suction / tension with the next supporting surface. Here, the effect of speed difference or suction transfer mainly in the nipples Er 30 does not affect the surface characteristics of the web.

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^ but mainly based on the choice of a more adhesive surface.

δ tn o Wet web transfers prior to drying are considered to be significant. The surfaces of the wet section also have different adhesive properties, whereby the smoothest belt and center roll surfaces grip the web 35 most firmly, while the wire and felt have a lower adhesion effect. Vacuum removal (transfer suction roller or transfer suction box) exerts more than 10 free space transfers on the surface. Instead, the displacements in the nip do not stress the surface of the web since they do not have any tensile difference.

In the drawings, the tensile differential release under vacuum is illustrated by a thick arrow in connection with the displacements, whereby the arrow indicates the direction of transfer and then the opposite web surface experiences the mechanical stress caused by the release.

In the solution according to the invention, more downward dewatering affects the quality of the lower surface and correspondingly more downwardly dewatering affects the quality of the upper surface of the web 10, which results in very uniform surfaces of quality.

Aligning the Press and the Wire Part By inverting the drainage direction of the other press (Fig. 6), said isomeric transfer fabric is saved and a more economical solution is reached. The transfer belt in the overhead position is also known per se. By combining the overhead conveyor belt and the overflow shown, it is already a very interesting and inexpensive entity. On the other hand, in theory disadvantageous in the press section (one-sided) dewatering will only turn upside down, which would result in a weak paper side to form the upper surface of the paper. So that the compound-20 is not suitably incorporated into this assembly, the asymmetry of the releases is still suitable so that the symmetry of the paper is improved. This is a solution according to the invention wherein the asymmetry of the dewatering after the press section is corrected by a drying section which no longer affects the paper structure whose symmetry is achieved at the beginning or even before the drying section.

By combining the unilateralities of the removals and the press section, a paper with little structural unilaterality is achieved. Thus, an absorption profile can be obtained, which δ is better than either of the prior art machines. Preliminary trial runs have found i

It is possible that level 1 can be achieved on the absorber side. Improved paper structure symmetry is also reflected in reduced calendering requirements. Normal top quality newspaper quality ek 30 is achieved with just one soft calender. To achieve an even higher level of quality

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two soft calendars can also be used.

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00 o o 0X1 One solution according to the invention: 35

Structure: 11

The kitsformer (with potentially loadable moldings), and most of the high vacuum water drains (typically 20 to 80 kPa) are on the underside of the paper.

The press section has two long nipples. The first nip has two felts and the second nip has a single felt and an overhead waterproof transfer belt from which the web is transferred 5 directly to the first blow cycle of the blowing without separate transfer tissue. After blasting, there is a single wire drying

Single or double nip soft calender (Thermal rolls in the order that paper is finished finishing to the top level)

Reelin 10 This unit achieves:

In terms of paper quality, virtually one-sided paper with good printing properties

Running potential that seems to reach over 2200 m / min at 15 δ

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Claims (8)

A method in connection with a paper machine, according to which the web is formed with a web former (10) on the surface of the web (20), 5. The web is moved by means of release (12) with tensile difference and suppressed from the web former (10) on the web ( 20) surface to the web (P1) of the press portion (13) or to another support surface, the web being supported by at least one (P1, P2, S1, S2) tissue through a press nip (N) which dries unilaterally, thereby providing an asymmetric dewatering; The web is moved by means of release (15) with tensile difference and suppression from the supporting surface of the press portion (15) to the cylinder drying portion (17), the web is passed through the cylinder drying portion (17) to set the web to its final moisture, the web being transported from the web former (10). ) to the drying portion (17) by means of multiple endless support surfaces (20, P1, P2, S1, S2, R1, R2, 22) arranged after each other, wherein several detachments are directed towards the web (12, 11, 14). , 15, 19) with tensile difference from the preceding supporting surface to the respective following supporting surface, characterized in that the dewatering of the one-sided drying press nip (N) and the asymmetry in the overall effect of the said detachments (12, 11, 14, 15, 19) with tension difference is directed to the same side of the web. that the unilateral nip (N) removes downwardly and the loosening (12, 11, 14, 15, 19) loosely lower than eaten, and that in the beginning of the cylinder dryer portion (17) there is a direct mating (17.1, 17.2) to the web just before the first drying cylinder (17S). Method according to claim 1, characterized in that the web in the press is pressed for a double-sided dewatering with the arranged nip (NO) before said unilaterally drying nip (N), o (M). ? Method according to claim 1, characterized in that the web is moved from the web former (10) with an upwardly directed release (12) with tensile difference and suppression to the upper web (P1) of the first press nip 30 and with a second downward release (14) to the web. the second CL2 weave (S2) of the second press nip and with a third downward release (15) from the second press nip's upper web S (S1) to the web (22) at the beginning of the drying portion (17). 00 o o Method according to Claim 1, characterized in that in the said sabotage there is first a sabotage (17.1) at the top and then a longer sabotage (17.2) underneath. 15 Method according to any one of claims 1 to 4, characterized in that simple web guide is used from above in the drying portion (17). Method according to any one of claims 1 to 5, characterized in that a maximum of two soft calendars (18) are used. A paper machine comprising a web former (10) for forming the web of the web (8), a pressing portion (13) with support surfaces (P1, P2, S1, S2) supporting the web for removing water from the web. formed by the web former (10), the paper web including at least one single-sided dewatering and thus asymmetrical dewatering press nip (N), a cylinder drying portion (17) with webs covering the web and including a double-sided paper-blowing unit (17) and 17 (17.1) cylinder drying groups, and wherein the web is arranged to be transported from the web former (10) to the drying portion (17) by means of several successively arranged endless support surfaces (8, P1, P2, S1, S2, R1, R2, 22) between which there are pickup rollers (12, 11, 14, 15, 19) for detaching the web from each preceding support surface to the following support surface, respectively, characterized in that the dewatering of said unilaterally dewatering press nip (N) and the asymmetry in the overall effect of the said tensioning solutions (12, 11, 14, 15, 19) are arranged on the same side of the web so that the tensioning solutions are lowered than up and the direction of the drainage in the unilaterally dewatering press nip (N) is lowered. 25 Paper machine according to claim 7, characterized in that the pressing portion (13) comprises a nip o (NO) arranged for double-sided dewatering prior to said unilateral dewatering nip (N), C C \ X X CL σ> S m oo oo C \ J