FI86753C - Press section for a paper or cardboard machine - Google Patents

Abstract

The invention concerns a press section of a paper or board machine, comprising a number of rolls (1,11,22,32,44,70) which form press nips (N1,N2,N3,N4) that dewater the web (in) with each other, the web being arranged to run through said nips. Of the rolls at least one roll (1;70) is a smooth-faced so-called centre roll, which forms a press nip (N2,N3;N4) with at least one other press roll (11,32;44), over which a press felt (10,30;40), which has been formed as an endless loop, is passed to absorb water out of the web (in) into said press felt (10,30;40). The centre roll (1;70) in accordance with the invention is a variable-crown roll, which comprises a metallic roll mantle (2;71) arranged revolving on a stationary roll axle (3;72). The roll includes at least one set of crown-variation means (4,5;73), which are arranged to load the roll mantle (2;71) in the direction of the nip plane (K2,K3;K4) of the centre roll (1;70) and the roll (11,32;44) that forms a press nip (N2,N3;N4) with said centre roll so as to regulate the profile of linear load in said nip (N2,N3;N4).

Description

86753 5

Press section for paper or board machine Pressparti för en pappers- eller kartonmaskin

The invention relates to a press part of a paper or board machine, which comprises a plurality of rolls which form press nips for removing water from the web, through which the web is arranged to pass, and at least one of which rolls has a smooth surface. a central roll forming press nips with two other press rolls over which press felts formed in an endless loop are passed to absorb water from the web into said press felts.

In a paper machine, a web of fibrous pulp is formed in a paper machine forming section, after which the formed web is supported and supported by paper machine felts to a paper machine press section, where the web and supporting felts are passed through nips formed by press rolls to absorb water from web to felts. From the press section 20, the web is further fed to the drying section of the paper machine. The conventional solution in the press section comprises a large and massive central roll and wire or felt loops grouped around it, the rollers inside which, either together or together with the central roll, form press nips through which water is removed from the web by the pressure. In the drying section, water is removed from the web by evaporation, which is very energy intensive and therefore expensive and uneconomical. As a result, the aim is to remove water from the web as much as possible before the drying section already in the press section by mechanical means. It is already known that water leaves the web much more easily when the temperature is raised, because the viscosity of the water and the compressive modulus of elasticity of the web are thus reduced at the same time as the surface tension. As a result, efforts have been made to raise the temperature of the track already in the press section. Based on previous experience, it can be shown that, for example, raising the temperature of 6-10 ° C in the press section causes an increase in the dry matter content of the web of the order of 1% or more. By increasing the dry matter content in the press section, considerable cost savings are achieved. For example, in paper machines, it can be considered a rule of thumb that if the moisture of the web 2 86753 is reduced by 1% in the press section, the steam consumption in the drying section is reduced by about 5%.

One disadvantage which has long been recognized in the press parts commonly used today consists in the central roll of the press part, the material of which is generally a suitable stone, for example granite. As is known, the fins are quite sensitive to large and sudden changes in temperature, the effects of which can be quite fatal. As a result, efforts have been made to develop suitable substitutes for granite rolls. As a substitute for a stone roll, e.g.

metal rolls coated with, for example, a polyurethane-stone-dust mixture in order to make the surface properties of the roll match. The advantages of the metal roll over the designs are e.g. the fact that they have a significantly better resistance to temperature fluctuations than 15 designs. In addition, as a result, they can be run considerably hotter than exports. In addition, the metal roller can withstand higher driving speeds than the rollers.

One conventional structure in the press section of a paper machine using 20 center rolls and press rolls grouped around it forms three press nips. The first press nip in such a structure is formed between the groove roll and the press suction roll. The second press nip is in turn formed between the press suction roll and the center roll and the third press nip is formed between the center roll and the second groove roll. Since the line pressures in the nips of the press part 25 have to be made as even as possible, in such a solution, generally said groove rollers are designed to be deflectably adjustable, preferably zone-adjustable. Thanks to the deflection adjustment of the groove rollers, a uniform line pressure is thus provided in the first and third nips of the press part. In order to also provide as uniform a line pressure as possible to the second press-nip nip, the casings of the press suction roll and the center roll forming the second press nip are generally bombarded. However, bombardment never results in a uniform line pressure on the nip and, moreover, the disadvantage of bombardment is that the bombardment is always "fixed". If the bombing has to be changed, the roller must always be ground. This, in turn, is a rather expensive and laborious operation. Since bombardment alone does not completely control the line pressure profile, the problem with currently used metal center rolls has been uneven heating. This has caused distortions in the line pressure profile. Because the groove rollers are equipped with deflection control devices, the groove rollers have been very expensive.

5 In this respect, the high costs have also been influenced by the fact that the arrangement of deflection devices inside the groove roll has been difficult to carry out because the groove rollers are relatively small in diameter. If a fourth separate press is additionally connected to such a press part, a deflectably adjustable groove roll is also used in this press.

The disadvantages of the prior art can thus be summarized as the high cost of the structure, the temperature problems associated with the structure, and the difficulty in obtaining uniform and, if necessary, adjustable line pressure profiles.

It is an object of the present invention to provide a press section which minimizes the disadvantages described above and provides a substantial improvement in dry matter content and speed increase. It is a further object to provide a replacement structure for the designs used in the presses. To achieve these objects, the solution according to the invention is mainly characterized in that the center roll is a deflection-compensated roll comprising a metal roll shell rotatably arranged on the stationary roll shaft and deflection control devices arranged to load the roll shell in the nip plane. .

The invention achieves several advantages over the prior art, some of which have already been overlooked above. It is also desired to highlight the advantages, e.g. following. When using the solution according to the invention, if necessary, two deflection-adjustable rollers can be replaced by one deflection-adjustable roll. This results in significant cost savings. Because deflection control devices are used specifically in conjunction with the central roll, these devices are much easier to construct inside the roll because of the larger space available. When using the invention 4 86753, the line pressure profile of the nip between the press roll and the central roll can also be controlled, if desired.

The solution according to the invention further avoids the problems associated with the uneven heating of the prior art metal center rolls. By using the solution according to the invention, the casing of the central roll can be made thinner than before and thus better conductive of heat. If desired, the roller can also be used to heat the track. It is also not necessary to grind any bombs on the roll according to the invention. An additional advantage to be achieved by the invention relates to the construction of the groove rollers currently in use. The groove rollers are currently made in such a way that they are provided with a suitable coating, e.g. polyurethane. As a result, they have limited heat resistance. However, the deflection-adjustable rollers, and in particular the zone-adjustable rollers, generate a considerable amount of heat. Since the groove rollers do not have to be adjustable in deflection when using the solution according to the invention, they can simply be provided with cooling if necessary. As a further advantage, it can be pointed out that the invention as such can be applied as a retrofit to already existing presses.

Other advantages and features of the invention will become apparent from the following detailed description of the invention.

In the following, the invention will be explained in detail with reference to the figures of the accompanying drawing.

25

Figure 1 is a schematic side view of a press section of a paper or board machine to which the solution according to the invention has been applied.

Figure 2 shows a similar view of an alternative embodiment to the solution of Figure 1.

Figure 3 shows in a similar view a further alternative embodiment to the solutions according to Figures 1 and 2.

35 5 86753

Figure 4 is a further alternative embodiment of the solution according to the invention.

According to Figures 1, 2 and 3 of the drawing, the web W is formed on the web 50, which is either a flat wire or a wire carrying a two-wire forming portion. In the downward run between the wire 50, the wire suction roll 51 and the wire pulling roller 52, the web W is transferred in a suction line P in the suction zone 14 of the pick-up roll 13 to the first press felt 10, which thus also acts as a pick-up felt. The first press felt 10 10 leads the web W on its lower surface to a first press nip Nx formed between two press rolls, namely a press roll 11 and a groove roll 22 or a similar roll with a hollow surface 23. The first press felt 10 forms an endless loop by means of guide and guide rollers (not shown) which also keep said first press-15 felt 10 suitably taut. The first nip Nx is provided with two press felts, namely said first press felt 10 and a second press felt 20, which also forms an endless loop by means of guide and guide rollers 21 which maintain said second press felt 20 at a suitable tension. The Nx nip level of the first 20 nips is denoted by Ka.

After the first nip Nx, the web W is sucked from the second press felt 20 onto the surface of the first press felt 10 by means of the suction zone 12 of the press suction roll 11 and into the second nip N2 of the press section 25 under the direction of the press suction roll 11. For this purpose, the so-called first press felt is used as a so-called the pick-up felt and the press roll are provided with a suction zone 12 of suitable length which ensures that the web W detaches from the second press felt 20 onto the surface of the first press felt 10. The second nip N2 is formed between the press suction roll 11 and the central roll 30 1 of the press section. Said first press felt 10 of the second nip N2 is guided away from the central roll 1. Due to the surface characteristics of the central roll 1 (smooth surface roll), the web W detaches from the first press felt 10 after the second nip N2 and adheres to the surface of said central roll, under the guidance of which the web W then moves to the third nip 35 N3 of the press part. The third nip N3 is formed between the central roll 1 and the groove 32 or the corresponding roll provided with the hollow surface 33. A third press felt 30 is formed over said groove roll 32, which is formed into an endless loop by means of guide and guide rollers 31.

In the embodiment of Figures 1, 2 and 3, the press part further comprises a fourth separate press 5, the fourth nip NA of the press being formed between a second central roll 70 corresponding to the central roll 1 and a groove roll 44 or a corresponding roll with a hollow surface 45. After the third nip N3, the web W detaches from the third press felt 30 on the surface of the central roll 1, from which it is detached by means of the transfer suction roll 63. An open export is thus formed between said transfer suction roll 63 of the central roll 1 and 10.

From the transfer suction roll 63, the web W is transferred to the fourth press felt 40 in the suction zone 42 of the suction roll 41 acting as a pick-up roll. There is also an open export between the transfer suction roll 63 and the suction roll 41. The fourth press felt 40 is also a so-called pick-up felt. The fourth press felt 40 is formed into 15 endless loops by guide and guide rollers 43. Said fourth press felt 40 transfers the web W to the fourth press nip NA, after which, due to the surface properties of the second center roll 70, the web W detaches from the fourth press felt 40 onto the surface of the second center roll 70. The nip level of the fourth nip N4 is marked with the reference mark K4. From the second center roll 70, the web W is transferred to the drying wire 60 by the transfer rollers 61 and 62 as the drying wire 60 transfers the web W to the drying section (not shown).

Figure 1 shows a first preferred embodiment of a press part according to the invention. According to Figure 1, the central roll 1 of the press section is a deflection-compensated roll comprising a metallic roll shell 2 rotatably arranged on a fixed roll shaft 3. In the embodiment of Fig. 1, inside the central roll 1, in the nip plane K2 of the second nip N2 and in the nip plane K3 of the third nip N3, or adjusting devices 4 and 5 are arranged to load the roll shell 2 in said nip planes K2 and K3 to obtain the desired line pressure profile. In the embodiment of Figure 1, said deflection control devices comprise load shoes supported on the roll shaft 3, which act on the inner surface of the roll shell 2. Thus, in the embodiment of Figure 1, the central means 1 is a zone-adjusted roll 35 in which deflection compensation is provided in two directions forming an angle α with each other. In the embodiment of Figure 1, the line pressure profile . Since the central roll 1 according to Fig. 1 has two deflection compensation directions, the above-mentioned load-5 shoe structures must be used as the deflection control devices 4 and 5. If the center roll 1 were provided with deflection compensation in only one direction, either to the nip plane K2 of the second nip N2 or to the nip plane K3 of the third nip N3, any deflection control devices implemented in the prior art could be used as deflection control devices in this direction. This is not shown in Fig. 1, but if necessary, the deflection control devices could also be arranged in the groove roll 22, whereby the line pressure profile could also be controlled in the first part N1 of the press part.

As already mentioned in the previous description, the press part according to Fig. 1 also includes a fourth press nip N 1 formed by a separate press. Thus, in the embodiment of Figure 1, the second center roll 70 is arranged as a deflection-adjustable roll such that the second center roll 70 comprises a hollow, metal roll shell 71 rotatably disposed on the fixed roll shaft 72. Inside the roll shell 71, deflection control devices 73 are arranged, by means of which the fourth nip N4 is loaded in the direction of the nip plane K4 in order to obtain the desired line pressure profile. Fig. 1 shows that a load shoe structure similar to that described above in connection with the central roll 1 is used as the deflection control devices 73 in the second central roll 70. However, since only one direction of control has to be controlled in the four-to-25 tendon press, any structure implemented with the prior art can be used as the deflection control devices 73. Thus, in the detection method according to Figure 1, the line pressure profiles can be controlled in all the press nipples of the press section, if necessary.

30

The second embodiment of the invention shown in Fig. 2 differs from that shown in Fig. 1 in that the deflection control devices 4 are arranged in the central roll 1 only in the nip plane K2 of the second nip N2. As a result, any structure implemented with the prior art can be used as the deflection control devices 4 35 in the embodiment of Fig. 2. It is further shown in Fig. 2 that in this embodiment, the first nip N! in the direction of the nip plane K3, a line pressure profile so that the groove roll 22 is formed as a deflectably adjustable roll. The groove roll 22 thus comprises a tubular roll shell 24 rotatably arranged on a fixed roll shaft 25. Inside the roll shell 24 the necessary deflection control devices 26 are arranged to adjust the line pressure profile of the first nip Nx. Since only one control direction is involved here, any control devices that can be implemented, e.g. with current technology, can be used as deflection control devices.

In order to adjust the line pressure profile also in the third nip N3 of the press section, in the embodiment of Fig. 2 the groove roll 32 of said third nip N3 is formed as a deflection-adjustable roll corresponding to the first nip N3 groove roll 22 described above. on the roll shaft 35. Furthermore, deflection control devices 36 are arranged inside the roll shell 34, which act on the nip plane K3 of the third nip N3 to adjust the line pressure profile. Since in this case too only adjustment in one direction is required, the deflection adjustment devices 36 can be implemented as desired. As load deflection devices 20 36, for example, the load shoes shown in Fig. 2 can be used, but instead, for example, a pressure fluid chamber or a series of chambers arranged between the roller shaft 35 and the roll shell 34 can also be used. Also in the fourth separate nip N4 of the press section, in the embodiment of Fig. 2: the adjustment of the line pressure profile is handled in a different way from Fig. 1. Namely, in the embodiment of Fig. 2, the groove roll 44 of the fourth nip NA is arranged as a deflection-adjustable roll such that the roll 44 comprises a tubular roll shell 46 rotatably arranged on the roll shell shaft 47. Inside the roll shell 46 a third nip N3 in connection with the deflection control devices 26 and 36 of the groove rollers 22 and 32. Thus, in this embodiment, in the fourth nip N4, a completely conventional metal roll or even a design can be used as the center roll 70.

The third embodiment of the invention shown in Figure 3 is in a way a combination of the embodiments shown in Figures 1 and 2. In the solution of Fig. 39 86753, the adjustments of the line pressure profiles in the first, second and third nips N1 (N2, N3) of the press section are implemented in the same way as in the solution of Fig. 2 and in the fourth nip N4 in the same way as in Fig. 1. For the embodiment of Fig. 3 fiche.

The embodiment according to Fig. 4 differs from the embodiments shown above as follows. For the first nip N3 of the press section, the solution is similar to the previous embodiments. Instead, in Fig. 4, the second nip N2 of the press section is not formed between the press roll 11 and the center roll 1, but in this embodiment a groove roll 15 or a corresponding hollow surface roll 16 is formed for running the first press felt 10 after the press roll 11. . The first press felt 10 is formed as an endless loop as in previous embodiments by means of guide and guide rollers 17. The structure and operation of the central roll 1 in the embodiment of Fig. 4 is identical to that shown in Fig. 1. The groove roll 32 of the third nip N3 and the associated structures are also identical to that shown in Fig. 1 in this embodiment. The solution of Figure 4 does not show a fourth separate press at all, but in this solution the web W can be transferred directly to the drying wire (not shown) by means of the transfer roller 63. However, it is quite clear that a fourth separate press similar to that explained in connection with the previous embodiments can also be connected to this embodiment. Correspondingly, it is quite clear that the embodiments of Figures 1, 2 and 3 can also be implemented without a fourth separate press.

The invention has been described above by way of example with reference to the embodiments shown in the figures of the accompanying drawing 30. However, it is not intended to limit the invention to the examples given, but many modifications are possible within the scope of the inventive idea defined in the appended claims.

35

Claims (3)

A press section in a paper or cardboard machine comprising several rollers (1,11,15,22,32,44,70) forming between each other a press nip (N1, N2, N3, N *) which removes water from the web (W), through which the nip web is arranged to run, and of which rolls at least one roller (1; 70) is a so-called. center roller with a smooth surface forming press nip (N2, N3; N <) with two other press rolls (11,15,32; 44) over which press blankets (10.30; 40) are formed which are formed into endless loops to suction water from the web (W) 10 into said press blankets (10.30; 40), characterized in that the center roller (1; 70) is a bending compensated roller which comprises a metal roller sheath (2; 71) arranged rotatably on top of the roller shaft <3; 72) and bending control means (4,5; 73) which are arranged to fully roll the roller sheath (2; 71) in the directions of the nip plane (K2, K3; K ^) of the middle roller (1; 70) and rollers (11 , 15.32; 44) which form press nip (N2, N3; Na) therewith to regulate the line pressure profile in the bed nip (N2, N3; N <). Press section according to claim 1, characterized in that the nip plane (K2, K3) forms between each other an angle (a) which deviates from 180 °. Press section according to claim 1 or 2, characterized in that the bending control devices (4,5) comprise known pressure shoe structures known per se which act on the inner surface of the roller sheath (2) and are supported against the roller shaft.