FI75889C - SLUTET PRESSPARTI I PAPPERSMASKIN, SPECIELLT FOER TUNNA PAPPERSSORTER. - Google Patents

Description

75889 1 Closed press section of a paper machine, especially for thin grades of paper Slutet pressparti i pappersmaskin, speciellt för tunna papperssorter 5

The invention relates to a substantially closed press section 10 of a paper machine for removing water from a paper web, the press section comprising a compact press roll assembly comprising several press nips in connection with different rolls, between which the web passes supported by 15 between the roll and the hollow press rolls, around the press rolls of which a press felt receiving and displacing water passing through the nip formed by it is arranged, and the diameters of the central rolls being substantially larger than the diameter of all or most of said hollow or similar press rolls.

In paper machines, press sections are commonly used with a plurality of press nips formed by pairs of rollers through which a web and dewatering fabric, such as a press felt or a pair of felt, pass. For previously known press designs, reference is made, by way of example, to Applicant's FI Patent Applications 781426, 821995 and Applicant's U.S. Patent 4,209,361 and Beloit Corporation's Canadian Patent 10,685,255 and U.S. Patent 4,057,056.

Em. U.S. Pat. No. 4,209,361 discloses a press part of the applicant's "Sym-Press II" 30 (trademark) press, such a press has in practice become a standard solution for various paper machine manufacturers. This known press achieves several practically important advantages, the most important of which is that the paper web can be passed through the entire press section with a solid surface supported and closed export first between nips 1 and 2 with 35 pick-up felts over the press roll sector and then the press center roll. , which is usually rigid, supported against a smooth surface through the 3rd nip.

2 75889 1 It is an object of the present invention to further develop the applicant's "Sym-Press II" press section in order to provide a new and better press section, in particular for thin paper grades, meaning 2 grades with a basis weight of less than about 60 g / m 2.

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The invention has been based on the rich user experience that the applicant has gained with the "Sym-Press II" press section.

The general principles and theory of compression are not described in this context, 10 as they are known to those skilled in the art. However, of the special problems encountered in the compression of thin paper grades, we state the following as a background of the invention. A significant problem for thin species is the re-wetting of the ralna, which happens in the "Sym-Press II" press section, especially between the 1st and 2nd nip, where the same felt already acting as a pick-up felt is in each of the 15 press felts. A stone-vigilant conversation, on the other hand, does not rewet the web. When pressing thin grades of paper, there is a pressure constraint on the nipple of the press section in the lime. In the case of thin paper grades, double-sided dewatering is not necessary when the dry matter content of the ralna in the press section is increased, for example, from 16% to 45%, because the amount of water to be removed corresponds only to a water layer of about 0.18 mm. The double-felting of the first nip together with the soft coating of the suction roll causes a low peak pressure in the first nip, which reduces their efficiency.

The object of the present invention is to provide a new press section in which the above-mentioned special problems of pressing thin grades of paper have their advantageous solution.

It is a further object of the present invention to provide a press section in which no nip pressure loaded press rolls 30 are required at all. It is known that press squeegee rollers are quite expensive components in structure, they consume suction energy and their sheath fatigue resistance is limited. The suction roll is also poor in compression because it causes uneven dewatering due to its hole pattern. For this reason, there have been repeated requests and some suggestions for providing a press-free press section.

Presses such as the "Sym-Press II" press have the property that only one side of the web is pressed against a smooth stone surface or similar artificial surface, so that the web becomes somewhat asymmetrical, which does not have a significant adverse effect on most paper grades.

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The object of the present invention is to provide such a press part in which the nip pressure distributions, i.e. the shape of the pressure curve and the maximum compression pressure, are optimized, especially in view of thin paper grades. For example, newsprint, which is a very typical product application of the nozzle part of the invention, would be most preferably pressed at a higher maximum pressure in the first nipples than can be practically realized in the first double-felt nip of a "Sym-Press" press or the like. After all, the latter double felt is intended to provide efficient double-sided and symmetrical dewatering, which, as stated above, is not at all necessary with thin paper grades.

It is an object of the present invention to provide a press section which retains the inherent property of "Sjnn-Press" presses that the paper press is supported throughout the press section on a solid surface without substantial free traction.

It is a further object of the invention to provide a press section which is feasible with respect to the press body in such a way that it has a lower tendency to vibrate, which is achieved mainly by making the body of the press section lower and stiffer and lower.

In order to achieve the above and later objects, the invention is mainly characterized in that the two smooth surface surfaces belonging to the press part are spaced very short apart and that the web runs substantially all the way from the first nip to the last nip surface of the nozzle surface.

35 4 75889 1 The invention will now be described in detail with reference to several different embodiments of the invention shown in the figures of the accompanying drawing, to which, however, the invention is not narrowly limited.

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Figure 1 is a schematic side view of an embodiment of the invention with two overlapping centers as the web travels from upper to lower center.

Figure 2 shows an embodiment of the invention in which there are two overlapping centers and the compressible web runs from the lower to the upper center.

Figure 3 shows a "horizontal version" of the invention with two central rolls in succession and the web being introduced for the first discussion.

Figure 4 shows a variation of the invention according to Figure 3, in which the web is introduced first for the latter discussion.

Fig. 5 shows an embodiment of the invention in which the web is introduced into the first nip via a transfer nip formed in connection with the pick-up roll.

Figure 6 shows in the nip compression pressure / width coordinate system the preferred compression pressure distributions of the different nips of the press according to the invention and from the maximum compression pressure.

First, the common structural features of the press members shown in Figures 1-5 will be described. The web W enters the press section of the wire-forming section wire 10a 10a, from which it is separated by a downward run between the rollers 11 and 12 at a pick-up point P 1, P 1 and transferred to a pick-up felt 20, where it is gripped by the suction zone of the pick-up roll 21. 21a under reduced pressure. The web W is transferred directly by the pick-up felt 20 (Figs. 1,4 and 6) to the first nip or the web W is transferred from the pick-up fabric 20 to the first 35 compression fabric 28 at the second pick-up point? 2 (Figs. 2,3,5) and with which the first press fabric 28 transfers the web W to the first nip No. 5 75889 1 The press section includes two large diameters Cal and a smooth surface of the threads 30A and 30B, in connection with which press lips are formed to substantially remove water from the web W of the press section. The rollers 30A and 30B are rolls with rolls or a surface 5 having a corresponding web transfer property, e.g. rolls with a Microrock (TM) coating.

The first dewatering nip of the press is formed between the press roll 25 with the hinge 26 and the first spool 30A. In the first nip, the pick-up fabric 20 or the first press fabric 28 10 act as a press fabric and a member for transferring water away from the web W. The guide and spreading rollers of the pick-up fabric 20 and the first compression fabric 28 are denoted by reference numeral 22 and the rehabilitation devices by reference numeral 23.

After the first nip, the web W moves, supported and tightly adhered to the smooth surface of the first center 30A, between the second roll N 1 formed between the press roll 45 provided with the hollow surface 46 and the first center 30A. A water-receiving press felt 40 is passed through the second nip, which is guided by the guide and spreading rollers 42 and refurbished by the devices 43. Since the web 30A is more adhesive to the web W than the press felt 40, the web follows the second nip - as well as the first nip - the thread 30A is tightly pressed against its smooth surface 31, after which the web W moves to the second large diameter thread 25 with the shortest possible free pull. 30B, which is substantially similar to the first discuss 30A.

In connection with the second center 30B, there is a third press nip N 1 formed between the press roll 55 provided with the hollow surface 56 and the second center 30 30B. A spray fabric 50 is passed through the third nip, which is guided by the guide and spreading rollers 52 and refurbished by the devices 53. After the third and possible fourth nip, the web W is guided with a very short free pull to the drying wire 60 of the drying section, which is brought under the guidance of the guide roll 61 as close as possible to the second discussion 35 30B. Thereafter, the web W, adhered to the surface of the drying wire 60 and possibly guided by the guide roll 62, is passed to the lead-in cylinder 63 of the drying section and further to the first drying group formed by the drying cylinders 64, where e.g.

The specific features of the variations of the invention shown in Figures 1-6 are described below.

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According to Figure 1, the web W is guided upwards diagonally by the pick-up fabric 20 after the pick-up point P to the first nip Nj, where the press fabric is a pick-up felt 20. The first nlpp is located at the top of the circumference of the first central roll 30A and the second nlpp is about 90 ° at the end of the sector 10 from the first nip N 1, after which the web U follows the first central roll 30A for a further 90 ° sector so that the side sector of the web W at the first center 30A α & 180 °. On the free sectors of the rollers 30A and 30B, cleaning scrapers 32 are provided to keep the surfaces 31 of the rollers 30A and 30B clean. Figure 1 shows a vertical version of the conversations, with a second conversation 30B below the first conversation 30A, in connection with which a third nip and a possible fourth nip in connection with the roll 51 are formed. The web W bypasses the second thread 30B in sector b so that sector b is 180 ° ... 270 °.

According to Fig. 2, the web W detached from the forming wire 10 by the pick-up felt 20 at the pick-up point 10 is transferred at the second pick-up point P1 to the first press fabric 28 passing over the slir roll 29 provided with the suction zone 29a. In this case, a first nip is formed on the lower circumference of the lowest first panel 30A between a nozzle roll 25 with a hollow 25 or an elastic coating 26 'or a large diameter nozzle roll 25'. If an elastic coating 26 'and / or a large diameter roll 25' is used, the nip length L (Fig. 7) can be substantially increased relative to the sharp roll nip. The above applies to all solutions according to Figures 1 ... 6. In Fig. 30 2, a second nip Nj is formed about 90 ° to the end of the sector from the first nip and a third nip to the upper circumference of the second panel 30B, after which the web is removed from the smooth surface 31 of the panel 30B and transferred to the drying wire 60.

According to Fig. 2, when a large diameter roll 25 'and / or a soft coating, e.g. a polyurethane coating having a hardness of 7 75889 1 in the range 5..25 P & J, is used in the first nipple instead of a hollow surface roll such as a grooved roll or a blind drilled roll, even a large spray pulse and line load without the risk of curling the web W. This also applies to all the solutions according to Figures 1-6.

Figure 3 shows a "horizontal version" of the invention in which the discussions 30A and 30B are in a substantially horizontal plane H-H. The web W is transferred by the pick-up fabric 20 to the pick-up point where it is transferred to the first press felt 29 in the suction sector 29b of the spinning roll 29. The web W is then passed down the first fabric 28 to the first nip N 1.

The first nipple is formed on the upper half of the first conversation 30A at a sector distance of about 45 ° from the above-mentioned horizontal plane H-H. The second nip is at or near the bottom of the perimeter of the first conversation 30A and the third nip is at or near the top of the perimeter of the second conversation 30B. The web W is detached as free tension at a substantially horizontal plane 15H-H from the second web 30B.

As shown in Fig. 4, the web W is transferred from the pick-up point P on the lower surface of the horizontal run of the pick-up felt 20 to the first center 30A, which is now the second center of the press as viewed from the forming section. For the first quarter of the first chat 30A, both nips Nj and and the third nip N1 are formed for the web-side dosing side of the second chat 30B. In addition, in connection with the second discussion 30B, there is a fourth press nip N 1 formed by a press roll 57 provided with a hollow surface 58 in its connection. A press felt 59 is guided through the fourth nip and guided by the guide rollers 25 and the spreading rollers 52. After the fourth nip, the web W is drawn from the smooth surface 31 of the roll 30B and guided by the guide roll 62 to the drying wire 60 of the drying section.

According to Fig. 5, the web is transferred in a transfer nip Nq on the pick-up roll 21 Nq to a first pressing fabric 28 passing over the roll 29, which transfers the web W to the first nip Np. In the silrton nip Nq no dewatering takes place, at least not substantially. In other respects, the structure is as shown in Figure 2.

As can be seen from Figures 1-5, an essential feature of the invention is that the web W is moved along a substantially S-shaped (or mirror-shaped) path in support of the smooth surfaces of the discussions 30A and 30B so that the first discussion 30A has its surface The surface of the roll W opposite the 31 rougher spray fabric 20,28,40 is changed by the latter discussion 30B to be pressed against the smooth surface 31 of this roll. Thus, both surfaces of the web W become symmetrically treated 5 and the structure of the web is made substantially symmetrical with respect to the filling and fine-grained distribution, also taking into account the dewatering directions.

According to Fig. 2, one of the discussions, namely the roll 30B, is provided with its own mechanical drive 71 and the driving force is transmitted to the lower 10 rack with the guide 30A by a mechanical transmission 70, which is shown only schematically in Fig. 2. In this way, it is ensured that the ratio of the circumferential speeds of the rollers 30A and 30B is very precisely desired, so that there is optimal traction and stretching in the free space, which prevents e.g. the wrinkling of the web W, and the tension as well as the release angle are made to remain very precisely constant at all times.

From the point of view of minimizing vibrations of the body part (shown) of the drilling part, the most preferred embodiments of the invention are the "horizontal versions" shown in Figures 3 and 4, since all the nipples are formed in connection with rolls 20 which can be placed quite down in the body part. In this case, the proportion of the body carrying large masses and loads is made very low and the body thus rigid and its vibration sensitivity further reduced. Thus, even the lowest specific oscillation frequencies of the body are made reasonably quite high.

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The following table shows the preferred sizing and operating parameters of the press part according to the invention.

TABLE

30 1. Nipple 2. Nipple 3. and 4. Nipple Νχ N2 N3 and N4

Line load kN / m 60 ... 150 80 ... 160 100 ... 170 35 Peak MPa 3 ... 7 4 ... 10 6 ... 12

Nip length mm 30 ... 120 20 ... 40 20 ... 90

The diameters D of the press rolls 0 mm 800 ... 1600 600 ... 1200 600 .., 1600 9 75889 1 The diameters DA 30A and 30B are generally in the range 1400 ... 2000 mm, preferably in the range 1500-1750 mm, for example approx. 1600 mm. In the invention, the diameters D of the discussions 30A and 30B are substantially larger than the diameters D of the press rolls 25,45,55,57 which form 5 nips N 1 -N 2 in connection with the discussions. Most preferably, the ratio of the diameters D of the conversations to the diameters of the on-surface purge cavities is in the range D / Dj ^ 1.2 .., 3, preferably in the range D / Dj ^ - 1.6 ... 1.9.

As can be seen from the table above, the line load 10 of the nips and the peak pressure PmnyM are gradually increased as the web W passes from the previous nip to the next nip. With regard to the length of the nips, which is indicated by L in Fig. 6, the first nip can advantageously also be made in the so-called into a long nip (L 40..120 mm), either with a soft roll coating or using an elastic press mat (not shown) passed through the first nip according to the principles set out in the applicant's FI patent applications Nos. 843895 and 850087.

The rollers 30A and 30B are placed as close to each other as possible, taking into account the construction and operating aspects of the machine. In Fig. 20, the distance between the above rollers 30A and 30B is denoted by h. This distance h is usually in the range h - 20..80 mm, preferably between h 40..50 mm.

The diagram of Fig. 6, in which the horizontal axis is the nip width L (mm) and the vertical axis compression pressure (MPa), shows the preferred nip pressure distributions of the different nips N 1 -N 2 of the press according to the invention. Figure 6 shows the nip pressure of the first nip with a broken line and it is noted that the length of the nip is about 50 mm and the maximum compression pressure is about 5 MPa. The nip pressure of the second nip is shown by a dotted line and it can be seen from Figure 6 that the maximum nip pressure has been slightly increased from the previous 30, i.e. it is about 7 MPa. The nip pressure distribution of the third nip is shown in whole wool, and it is observed that the length of the nip is about 35 mm and the maximum compression pressure P ^ fly ^ about 8 MPa. The compression pressure prevailing in the fourth nip is shown by a dotted line and the length of the nip is about 38 mm and the maximum compression pressure Pmax ^ n · 10 MPa. The pressure distributions are substantially 35 symmetrical with respect to the center plane of the nip.

As stated and as can be seen from the table above, in the press according to the invention 1075889 1, the line load combination is preferably selected so that the first nip has the lowest peak pressure and the subsequent nip gradually increases the maximum nip pressure Pmaxjj so that P <P <P <(P).

maxl max2 max3 max4; 5

When, according to the principles illustrated in the example of Figure 6, the nip pallets of different nips N 1 -N 2 are selected, i.e. the distribution of nip pressures substantially comprising nip length L and maximum compression pressure ^ max ^> provides an optimal compression result for thin paper sheets with a weight less than n 60 g / m. In Fig. 6, the areas under the different curves represent the total impulses of the dewatering compression of the web W, which are limited by engineering considerations and are thus always proportional to the line load.

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

20 25 30 35

Claims (7)

A substantially closed press section of a paper machine for removing water from a paper web (W), the press section comprising a compact press roll assembly having a plurality of press flaps (N 2 -N 2) formed between different rolls, between which the web (W) passes supported by the roll surface without substantially long free drawings in which the press-water lime substantially water-removing press nips (N 2 -N 2) are formed between two surface-surfaced centers (30A and 30B) and hollow-surface press rolls (25,45,55,57) 10, around the press rolls of which a nip formed by it is arranged. a press felt receiving and displacing water from the nip, and having diameters (D) of substantially larger than the diameter (D 2) of all or most of said hollow or similar press rolls, characterized in that the press part comprises two smooth plates ( 30A and 30B) are spaced a very short distance (h) apart, and that ra ina travels substantially all the way from the first nip (N 1) to the last nip (N 2; N 2) of the press section, gripping the surface of the smooth discussions. 20 1 Claims Press part according to Claim 1, characterized in that at least two dewatering press nips (N 1, N 2) are formed in connection with the first panel (30A) and one or two dewatering press nips (N 2, N 2) in connection with the latter (30B). 25 Press part according to claim 1 or 2, characterized in that the diameters of the discussions (30A, 30B) are in the range D = 1400 ... 2100 mm, most preferably in the range 1600 ... 1800 mm, and / or that said press rolls (25, 45 , 55,57) the diameters (D 1) are in the range 30 700 ... 1600 mm, most preferably in the range 950 ... 1100 mm and / or that the shortest distance (h) between the circumferences of the central rollers (30A, 30B) is in the range h 20 ... 150 mm, preferably in the range h * 40 ... 50 mm. Press part according to one of Claims 1 to 3, characterized in that the sides (a, b) of the web (W) in the discussions (30A.30B) are of the order a * · b * 180 ° or somewhat larger. 12 75889 Press section according to one of Claims 1 to 4, characterized in that the press nip pressure (PTtlflvN) is gradually increased from the previous nip to the next nip, preferably so that the peak compression pressure in the first nip (N 1) is in the range Pmax 1 to 3 MPa, 5 in the second nip. in the press nip (Nj) in the range m 4 .. 10 MPa and in the third and possible fourth nip in the range Pmax ^ 4 “6..12 MPa, and / or that the lengths of the nip (L) are in the following ranges starting from the first nip: Lj - 30 .. 120 mm, * 20..40 mm, ^ - 20..90 mm. Press part according to one of Claims 1 to 5, characterized in that the second pulley (30A, 30B) is provided with a drive (71) and that the driving force is transmitted to the second pulley (30B, 30A) by means of a transmission (70) between said rollers. the rollers (30A, 30B) are provided with a certain speed ratio that can be precisely set or adjusted. Press part according to one of Claims 1 to 6, characterized in that the press has a large-diameter roll and / or a roll with a soft coating and / or a flexible belt having a hardness of 20 as a component forming the first nip (N 2) with the center (30A, 30B). is in the range 5..35 P & J, and where a large line load of the order of 200 kN / m can be used without the risk of curling the web (W). 25 30 35 13 75889