AT506986A2 - METHOD RELATED TO A PAPER MACHINE AND A PAPER MACHINE - Google Patents

Description

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Method in connection with a paper machine and a

paper machine

The invention relates to a method in connection with a paper machine, wherein in the method, a web is formed in the former on the wire surface, the web is removed with train difference and negative pressure from the wire surface and transported to a fabric or other support surface on a press section, the web is guided at least by a fabric at least through a single-side drying press nip, the web is transported with a train difference and with a negative peel from a support surface on the press section to a dryer section, the web is passed through the dryer section, so that the Web receives its final moisture, wherein the web is transported by the former by means of a plurality of successively arranged endless support surfaces from the forming section to the dryer section, wherein the web between the support surfaces before several detachments with Zugunterschieden of each underlying support surface is subject to each subsequent support surface.

State of the art

When planning a paper machine several goals are aimed at a good running behavior and a good quality, which are measured with numerous sizes. One of the most important properties of paper is the symmetry between its surfaces, which includes, among other things, smoothness and absorption properties of the surface. In practice, one has always been forced to compromise, and usually a small asymmetry is tolerated at any size. In current paper machine designs, it is not possible to effectively produce perfectly symmetrical paper. If other properties are stabilized and good running behavior is maintained, the paper on one side is often rougher.

Good quality is often achieved at the expense of runnability, such a good quality producing machine is described below referring to FIGS. 1 and 2:

Typical construction:

Spaltformer (generally a Bahnbildpartie) with load-bearing strips

Press section, a press with 3 nips and a separate 4th press (SymPress B & 4th), with which drainage is good single-wire drainage

Soft calender with one or two nips reel

Out of order:

The press section has two open draws (the web is not supported on the fabric or on a roll). The detachment from a smooth roll (center roll and counter roll of the 4th press) requires a draw difference which increases with an increase in speed. In turn, a large draw difference degrades paper quality and destroys the stretching potential of the web. An increase in the train difference deteriorates, for example, porosity, absorption property m < -3 · · · · · · · · ··············································································································································································· At high speed, the paper's tolerance limit approaches that of the difference in tension, and this leads to increasing tears. In practice, operating speeds in excess of 1,800 m / min in open-draw presses are a challenge for wood-containing grades.

The 4th press also dewaters down and thus balances the drainage balance of the press section more symmetrically upwards. However, the amount of water to be removed has proved to be insufficient, for example, to correct one-sidedness in the absorption. With this concept an optimal structure of the paper could be achieved. Nevertheless, with this technology in the market, the best paper quality in terms of minimum paper two-sidedness is currently being achieved.

The biggest limitations of this press are maximum operating speed, moisture profile control, re-wetting (same felt in 1st and 2nd nip), vibration problems, web insertion and efficiency. The main constraints on efficiency are the challenges posed by a separate fourth press and the heavy load on the paper caused by open draws.

The running behavior at the beginning of the dryer section is also challenging. The resilience of paper is still very low because of the low desiccant content. In practice, a low " strength level " from paper to many problems. The paper web tends at the beginning of the dryer section. to adhere to the dewatering cylinders, which can lead to runnability problems and / or dirt accumulation at the beginning of the dryer section. The aim is to get the running ability under control even more effectively with stabilizing boxes in a pocket space bounded by the cylinders and a deflecting roller. At the beginning of the dryer section you will achieve a good end result only with extremely sophisticated technology.

On the other hand, the press section and the beginning of the dryer section of a machine with good runnability is shown in FIG.

Typical construction:

Gap former possibly with resilient strips or a wire

Shoe press with double press nip and with closed draw and in the lower position of the second press nip a water-impermeable conveyor belt (transferbeit), wherein the dewatering at the press section mainly takes place above, a known theory according to impingement drying on the transfer wire single-wire draw dewatering

Challenges and Features: - The first press of the press section dewatered in both directions. In the second press nip, the drainage takes place only on the top of the paper. In practice, such dewatering associated with a prior art wire section produces single-sided paper. It has also been observed that there is an unusually high amount of unbound material on the underside of the paper which can cause dust problems in printers. In other words, the surface texture of paper is not formed optimally or sufficiently well for demanding qualities. The one-sided structure of paper has to be compensated with intensive calendering.

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Ui _ ······· »* · -s- · .. ·· .. ·· .. ·

According to a theory related to drainage, one should achieve symmetry with such a solution along with a down-going former. - In terms of runnability, this press design achieves speeds of more than 2,000 m / min for wood-based grades, without the need for differences in draws on the press section to destroy the structure and quality of paper. The ability to run at the beginning of the dryer section proves to be a limitation of this concept.

The biggest limitation of this press concerns paper quality. The press is producing fairly single-sided paper with the sections of wire currently on the market, which also has other structural weaknesses (for example, in surface strength and printability).

The runnability at the beginning of the dryer section is also challenging. The resilience of paper is still very low because of the low desiccant content.

In practice, a low " strength level " from paper to many problems. The paper web tends to adhere to the dewatering cylinders at the beginning of the dryer section, which can lead to runnability problems and / or dirt accumulation at the beginning of the dryer section. The aim is to get the running ability with even more effective stabilization boxes under control. At the beginning of the dryer section you will achieve a good end result only with extremely sophisticated technology.

So far, it has been concluded that the web is homogeneous in thickness after molding, and the structure is substantially uniform or not one-sided. The conclusion was supported by the fact that a drainage in the "······························································· ...

Drying section could be made fairly symmetrical on both sides of the web.

Summary of the invention

The object of the invention is to obtain a paper-making process which is better than in the past and a corresponding paper machine. It is characteristic of a method according to the invention that the one-sided drainage on said press nip and the asymmetry of the total effect of said detachments are directed to the same side of the web. Surprisingly, it has been observed that in the same direction asymmetrically adjusted, train-wise separation of the web from the endless support surfaces and drainage in the press give the paper a better homogeneous structure than before. The asymmetry of the (differential in tension) detachment of the web is roughly obtained by calculating the difference of the upward and downward peelings, but more precisely the matter can be determined by examining the total effect of peeling on both sides, since the action of the peelings varies due to various factors, which are explained below. This asymmetry of detachment is surprisingly compensated by an asymmetrical drainage in the same direction. It is conceivable that any detachment with different tension from the support surface will degrade the quality of the surface detached from the support surface of the web, but a corresponding dewatering in the same direction causes a similar phenomenon on the other surface, the effects being mutually exclusive. to lift. In general, on both sides, there are corresponding quantities of detachments, more precisely, a quantity of drainage, which amounts to -7- " Corresponds to its overall effect. In any case, the solution presented achieves an astonishingly good result.

In an advantageous embodiment, the separations are made in the majority down and not up and drained accordingly drying a press nip on one side down. The press section advantageously has a double-sided dewatering press nip in front of the single-sided dewatering press nip.

Detailed description of the invention

The invention is described below with examples and reference is made to the attached figures:

Figures 1 and 2 illustrate a prior art paper machine which produces good quality.

Fig. 3 illustrates a prior art solution for achieving good runnability in the press section of a paper machine.

Fig. 4 illustrates a prior art paper machine having good runnability.

Figs. 5 and 6 illustrate an optimum paper machine according to the invention.

In FIGS. 1 to 6, the same reference numerals have been used for functionally similar games. In these, the main parts of the paper machine include a former 10, a press 13, a dryer section 17 and a reel-up 20. The screen for the former 10 is identified by reference numeral 8, which corresponds to * < -8th- • · · • · # * · • · · • · ·· · • ··· · ··· • · · * " • · · · · ··· • · • · ··

Fabrics in the first nip of the press 13 are identified by reference PI (top fabric) and P2 (bottom fabric) and the first fabric on the dryer section 17 by reference 22.

The direction of drainage at the press section 13 is marked in each nip with thin arrows; through these you get an idea about the two-sidedness of the drainage at each batch. The differences in tension and under pressure / mechanical detachment from the support surface are marked with thick arrows. These are described in conjunction with each example.

In Fig. 1, the former of the type is a gap former. The high / low pressure drains are identified by the reference numeral 9. These may also have an effect on the asymmetry. The formed web is transported to the press section 13, in which it is guided mainly by the felt sheets and by the roller through the press section to the drying section 17. Thereafter, the almost finished web is guided over a soft calender 18 to the reel 20.

The press section and its connection to the former 10 and to the dryer section 17 are shown in greater detail in FIG. The web is formed in the former 10 on the wire 8, from which it is transported by a transfer suction roll 12 further to the top felt P1 in the first press nip NO. The transfer suction roll 12 performs the first detachment with draw difference \ oppress. The web is guided by the top felt P1 and a bottom felt P2 supported by the press nip NO, and further to a center roll 25 on the top felt P1. Between this and the top roller 4 € • • • • ·· · • • • • ··· > ··· ··· Since the felt was already moistened in the first press nip NO. A third press nip N2 between the center roll 25 and a shoe roll 26 again effectively dewaxes the felt S2. The web is peeled off from the central roll 25 with a differential mechanical peel and conveyed over a free distance to a transfer roll 24 and further to the lower-side felt S2 at a fourth press nip N of the press. The web remains on the upper roll of the fourth press nip N, from where it is detached with a transfer suction roll 15 on a first fabric 22 at the dryer section.

In an upper-side single-wire draw at the dryer section, the underside of the web is predominantly dewatered and only slightly through the sieve on the surface; in the mold and the press section together more / more water is removed through the bottom of the web. According to one theory, this leads to an accumulation of fines and thus to an asymmetrical quality in connection with the surface in question.

Also of advantage in the subject arrangement is a soft calender thermo roll having a nip in a down position after the dryer section, whereby the lower surface of the web becomes smoother and the surface grip on the surfaces of the web is congruent. On the one hand, the absorption between the surfaces of the web remains unilaterally, the adjustment of the absorption, the web is one-sided in terms of their surface grip.

The surface of the web is dewatered in three press nips of the press, and the underside of the web is dewatered in two press nips - all -10- ······ • · · · · · · · · ···. ·······························································.

There are two felts on both sides of the web. On the other hand, in the forming section, there are corresponding high-pressure suckers on the underside of the web, whereby as a whole these two drainage sections drain more often / more over the underside of the web. Cancelations in the press nip without a speed difference do not interfere in the same way as other detachments. Among other things, the central roller triggers the web in its first press nip with no difference in speed from the previous support surface.

A combination of pull difference and reduced release is best known in the art because the last downward release slightly compensates for peel earlier directed upward. Overall, in this application, which is currently producing the best quality, drainage and train separation are almost the same.

In Fig. 3, the web formed in the former 10 is transported from the wire 8 to the top felt PI at the first press nip NO; the upper-side felt passes the web together with the lower-side felt P2 through the press nip NO. The web is transported by a suction roll 11 to the lower-side felt P2, to which the web adheres and is peeled off after a clearance with the transfer suction roll 14 on the upper-side felt S1 in the second nip N. This top-side felt passes the web together with the conveyor belt S2 through the second press nip N. The web adheres in the press nip N on the smooth conveyor belt S2, from which the web is removed with the transfer suction roll 15 on the first fabric of the dryer section. Λ • 9 • · · • 9 9 · · · · · · · 9% 9 999 -11- • · · ··· ·····

A prior art solution in which the second nip of the two nip press section dehydrates upward to prevent accumulation of fines on the underside of the fibrous web. However, the arrangement causes a grip from its upper side and more absorbent from its underside path.

With regard to a detachment that takes place with difference in pull and negative pressure, this is the weakest state of the art with almost exclusively upwardly directed detachments and is therefore not suitable for the most demanding types.

In Fig. 4, a press section 13 and the first sections of a dryer section 17 are shown from a paper machine, namely the vertical impingement dryer 17.1 and 17.2 of an upstream impingement dryer and the beginning of a cylinder group. A first drying cylinder is identified by the reference numeral 17S and a drying fabric of the first group by the reference numeral 22.

The various parts of the device, namely press section, impingement dryer and cylinder dryer, are known from their basic construction, inter alia, from the aforementioned patent publications.

The equipped with two press nips press 13 has the press nips NO and N. The paper web passes in a known manner with a pick-up roller 12 in the press section 13 and is transported with the press felts PI, P2 S1 and the conveyor belt S2 through the press nips. After the press section 11 (or integrated in its end part), the horizontal or upstream impingement dryer 17.1, which drives a drum R2, follows that the impingement unit is directed.

Referring to Fig. 1, the paper web is guided with the transfer suction roller 15 from the conveyor belt S2 on the transport screen RI, from where the paper web with the transfer suction roller 19 is transported to the drying wire R2 of the horizontal impingement dryer 17.1.

The paper web runs on the drying wire 17 under the impingement unit 20.1, wherein on the web a strong thermal effect is applied. In the short impingement zone, the drying effect is quite low, but the web heats up and the top layer on top dries slightly. This is important in terms of runnability. At the same time, the moisture gradient of the web in the thickness direction increases strongly towards the lower surface.

After the horizontal impingement dryer 17.2, the paper web is transported by the drying wire R2 after a vacuum roller 30 to the drying wire 22 of the first drying cylinder group. The same drying wire 22 is also driven by the vertical impingement dryer 17.2. The paper web is transported in a manner known per se by means of an upper roller 31 of the vertical impingement dryer 21 serving as a vacuum roll (suction roll or VAC roll) to the drying wire 22.

The temperature of blowing gas in the impingement dryers (17.1, 17.2) is advantageously in a range of 200 ° C to 700 ° C, most advantageously in the range 250 ° C to 400 ° C. Also by means of the humidity of impingement air (by circulatory fluid) - ····························································································. The air temperature of the web can be affected by the blowing air.

The Einwirklänge the horizontal impingement dryer is a maximum of 50%, most preferably 15 to 35% of the total length of the impingement drying line. With a larger Einwirklänge a drying is achieved in addition to the preheating.

In Fig. 4, the directions of the peel and offset peelings are marked with the transfer rollers 12, 11, 14, 15 and 19, respectively. The separation of the web from the support surface, which takes place with difference in draws and underpressure, are directed in the majority upwards and not downwards. It is conceivable that any delamination occurring with tension difference and depression will degrade the surface of the web. The magnitude of the harmful effect depends on the moisture level of the web, the smoothness of the surface and other factors. An asymmetry of the drainage in different directions leads here finally to an asymmetry of the structure. Further detachments in the dryer section as well as on the roller 31 and thereafter no longer have a significant effect on the paper structure.

Fig. 4 illustrates another prior art solution which has impingement drying on the transport screen. Here, however, the separations that take place with the difference in train and the negative are not in the majority of detachments of the surface.

With regard to the peel-off and the release, the use of this application is still too high -14- ········ # + ············································································ »* ·% ····················································································································································································

The runnability of the dryer section is accomplished by means of impingement technology. An advantageous solution is one under the trade name " OptiDry Twin " Applicant's known impingement concept, with which a high impingement drying (drying) is achieved before the first drying cylinder. In this way, sticking, runnability and contamination problems are avoided. The desiccant content after the impingement drying is about 5 to 10% higher than the desiccant of the press section.

An impingement solution is known from the publications: WO97 / 130131 and WO02005 / 068713.

From Fig. 4 it can be seen how the impingement drying is associated with a conventional press for good runnability. Among other things, it can be seen that here a separate transport fabric RI is needed, with which the paper web is transported from the lower-side conveyor belt S2 to the first impingement dryer 17.1. The two-sidedness caused by the press section 13 still exists in this solution.

In Figs. 5 and 6, a paper machine according to the invention is shown, with both a good runnability and a good quality is achieved, which has a perfect symmetry of the paper structure. The former 10 and the first press nip NO on the press 13 are substantially similar. The web passes with the transfer suction roll 12 on the first top side felt PI and, together with the bottom felt P2, passes through the first nip NO β · β · β · β · · · · »9 φ • · · · · · · · · · · · · · · · · · ·. Thereafter, the web is fed with the transfer suction roll 14 from the first top felt PI directly to the bottom felt S2 of the next nip. The web is guided through the second press nip N, which lies between the second underside felt S2 and the conveyor belt S1 lying opposite thereto, the web being transferred to the conveyor belt S1 in the press nip. From here, the web is again transferred directly to the fabric R2 of the vertical impingement dryer 17.1, which leads the web to the horizontal impingement dryer 17.2. This is designed to drive the fabric 22 on the first cylinder group. Here, the rollers 3 0 and 31 have the same task as in the solution of Fig. 4th

Again, the drying section 17 comprises the impingement units 17.1 and 17.2 and a plurality of cylinder drying groups. After this, the web is fed to a soft calender 18 and then to a reel 20.

Here, attention must be paid to the direction of the different train detachment of the web with the transfer suction rolls 12, 14 and 15 and the direction of drainage in the second press nip N.

Here, the drainage is done contrary to a known theory more about the underside of the web and the use of an impingement drying advantageously directly after the press, where the surface of the web is first blown, this so warming and slightly vornehmend a drainage over the area in question. Next, immediately thereafter, the underside of the web is blasted, advantageously on a longer section, effectively evaporating the moisture at the bottom of the web and allowing the web to pass with the top of the web. • · • · ·

• to be brought to the cylinder drying on the side of the single-wire draw.

The drainage in the last press nip over the bottom of the web is 12 to 16%, which represents a significant proportion.

In the forming section, the desiccant content of the filtered web is > 9% and the high pressure suction is across the bottom of the web; moreover, the desiccant content of the press section is about 20 to 50%, and dewatering further over the bottom results in a symmetrical path of absorption and surface hand. Drying also advantageously dewaters over the underside of the web (a full top single-wire draw or a combined impingement-drying which also drains more of the bottom of the web).

A theory that the dewatering direction strengthens the surface of the web does not alone explain the two-sidedness of the press and the surprising result presented above. In addition, this invention takes into account the effect of traction differential and depression on the areas of the web, thereby providing a path symmetrical of their absorption and surface hand. Detachment from an adhesive surface is most likely to affect the surface of the web, because some of the fines from the surface of the web will adhere to the next supporting surface as the adhesive web continues to rise due to suction / draw difference. The effect of a transport mainly in the press nip without speed differences or suction does not affect the surface properties of the web, but is primarily due to the choice of a more adhesive surface.

Of importance are transfers of a wet web before drying. The surfaces in a wet end also have different adhesive properties, with the smoother belt and central roller surfaces holding the web more firmly against their surfaces while the adhesion to a wire or felt is weaker. An underpressure (transfer suction roll or transfer suction box) loads a surface more heavily than a transfer over a free stretch. On the other hand, the surface is not affected by the web guides in press nips, since there are no differences in the train.

In the figures, a detachment with draw difference and an underpressure is marked in connection with transports with thick arrows, here an arrow represents the transport direction and the opposite surface of the web is subject to a mechanical load caused by the detachment.

In a solution according to the invention, a more downwardly directed drainage affects the quality of the underside and correspondingly more downwardly directed detachments act on the quality of the web surface, whereby one obtains from their quality very uniform surfaces.

Combination of press and wire section

By reversing the dewatering direction of a second press (FIG. 6), said transport fabric is spared and a more advantageous solution is thus obtained. One in one

side position conveyor is in and of itself a well-known technique. By combining a top-side conveyor belt and the impingement drying shown, one already obtains a very interesting and advantageous whole. On the one hand, the (in principle) unfavorable (one-sided) dewatering of the press section only reverses, which would lead to the formation of a weak paper side on the paper top. In order that this would not be the case, with this totality the asymmetry of the detachments is suitably connected in such a way that one obtains a good symmetry of the paper. This is a solution according to the invention in which the asymmetry of dewatering after the press section in the dry part is corrected and no longer affects the structure of the paper whose symmetry is reached at the beginning of the dryer section or even before.

By combining the two-sidedness of the peelings and the press section, one obtains a paper in which there is virtually no structural one-sidedness. Thus, an absorption profile can be achieved, which is better than from the two machines according to the prior art.

In preliminary trial runs, it was found that the level of absorption can be reached at level 1. A better symmetry of the paper structure is also evident from a lower calendering requirement. Normal quality specifications for the highest quality newsprint are only achieved with a single soft calender. To achieve an even higher quality level, two soft calenders can also be used.

A solution according to the invention: -19- * 'f -19- *' f • ··· • · · • ··· ··· • · · · · · · · · ·

Construction:

Gap former (possibly with load-bearing bars), most of the high / low pressure drainage (typically 20 to 80 kPa) is from the bottom of the paper. The press section has two longitudinal nips. In the first press nip are two felts and in the second press nip a felt and a water-impermeable conveyor belt, from which the web is transported directly onto the first fabric for impingement drying without a separate transfer fabric. - After the impingement drying follows a single-wire draw drying

Soft calender with one or two press nips (thermo rolls in such an order that paper two-sidedness is finished to a peak level) - reel-up

With this totality is achieved:

Paper quality in practice Paper with virtually no one-sidedness and good printing properties A runnability potential that makes us expect speeds over 2,200 m / min

claims:

Claims (11)

* «» Λ -20- • · • ··· • · ♦ · 4 • ♦ ♦ · 4 • · GIBLER & ΡΟΤΗ Patent Attorneys OEG Dorotheergasse 7 - A-1010 Vienna - patent@aon.at Tel: +43 (1) 512 10 98 - Fax: +43 (1) 513 47 76 Claims 1. A method in connection with a paper machine, wherein in the Method of forming a web in the former (10) on the screen surface (20), the web having a draw differential and negative release (12) from the surface of the web (20) in the former (10) to a web (PI) or is transported to another support surface in the press section (13), the web at least by a (PI, P2, Sl, S2) tissue is supported by at least one unilaterally drying and thus causing an asymmetric dewatering press nip (N), the web with a tension difference and with a negative peel (15) is transported from a support surface in the press section (13) to a dryer section (17), the web is passed through the dryer section (17), the web their final The web is transported by the former (10) by means of a plurality of successively arranged endless support surfaces (20, PI, P2, Sl, S2, RI, R2, 22) to the dryer section (17), wherein the web between the support surfaces more Detachments (12, 11, 14, 15, 19) subject to draw differences from each preceding support surface to each following support surface, characterized in that the drainage on the single-side drying nip (N) and the asymmetry of the entirety of the train-differentiated release (12 , 11, 14, 15, 19) is directed to the same side of the web. 2. The method according to claim 1, characterized in that the web in the press in an adapted to the two-sided drainage press nip (NO) before the unilaterally drying press nip (N). 3. The method according to claim 1 or 2, characterized in that the unilaterally acting press nip (N) dewaters down and taking place with train difference detachments (12, 11, 14, 15, 19) directed in the majority down and not upwards are. 4. The method according to claim 3, characterized in that the web from the former (10) with an upwardly occurring with train difference and negative pressure release (12) on an upper fabric (PI) on the first press nip and with a second downward detachment (14) transported on a lower fabric (S2) on the second press nip and with a third downward detachment (15) from an o-Beren fabric (Sl) at the second press nip on a fabric (22) at the beginning of the dryer section (17) becomes. 5. The method according to any one of claims 1 to 4, characterized in that at the beginning of the drying section (17) an impingement drying (17.1, 17.2) immediately before a first drying cylinder (17S) is present. 6. The method according to claim 5, characterized in that in the impingement drying first an upper-side impingement dryer (17.1) and then a lower-side impingement dryer (17.2), which is longer than the former, is present. 7. The method according to any one of claims 1 to 6, characterized in that in the dryer section (17) an upper-side single-wire draw is used. 8. The method according to any one of claims 1 to 7, characterized in that a maximum of two soft calenders (18) are used. 9. Paper machine with a former (10) for forming a web on a wire (8) and a press section (13) together with supporting support surfaces (PI, P2, Sl, S2) for dewatering the paper web formed in the former (10), the comprises at least one press-nip (N) which drains on one side and thus causes an asymmetric drainage, a drying section (17) together with the fabrics covering the web, which have a double-sided impingement -23 - * .. * * · • · · · · · · · · ··· ··· ··· drying unit (17.1, 17.2) and cylinder drying groups, and arranged so that the web is separated from the former (10) by means of several successively arranged endless support surfaces (8, PI, P2, Sl , S2, RI, R2, 22) is transferred to the dryer section (17), and between the support surfaces there are transfer rollers (12, 11, 14, 15, 19) for detaching the web from each preceding support surface to each following support surface that the Entw the unilaterally dewatering nip (N) and an asymmetry in the overall effect of the differential draw (12, 11, 14, 15, 19) on the same side of the web. 10. The method according to claim 9, characterized in that the press section (13) adapted to a two-sided drainage press nip (NO) in front of said one-sided dewatering press nip (N) heard. A paper machine according to claim 9 or 10, characterized in that peel-apart separations are directed downwardly and not upwardly in the plural and point the direction of drainage of the unilaterally dewatering press nip (N) downwardly. tentanwalt G I B P a t Dorothj Tel: +43 (1) 512 P Ο T H OEG: ent@aon.at 513 47 76