Loading box adjustable in zones for the former of a paper or board machine

Abstract: The invention concerns a loading box adjustable in zones for the former of a paper or board machine. The former comprises a twin-wire section consisting of wires (13) placed one above the other and running in the same transfer direction (R), in which twin-wire section, at one side of the wires (13), a drain box has been mounted to remove water out of the fibrous pulp (P) running between the wires (13). At the opposite side of the wires, a loading box has been mounted, which is provided with a number of loading ribs (22), which are placed in the transverse direction in relation to the transfer direction (R) and which extend across the web width, said loading ribs being loaded towards the bottom of the drain box so as to produce the desired compression in the fibrous pulp (P) running between the wires (13). The loading box is provided with loading means (30), which are arranged to produce a locally raising or lowering force applied to the loading ribs (22) in the direction transverse to the transfer direction (R), said force being applied simultaneously to at least two successive loading ribs (22), so as to profile the compression force applied by said loading ribs (22) to the fibrous pulp (P) in said transverse direction.

Description: The invention concerns a loading box adjustable in zones for the former of a paper or board machine, which former comprises a twin-wire section consisting of wires placed one above the other and running in the same transfer direction, in which twin-wire section, at one side of the wires, a drain box has been mounted to remove water out of the fibrous pulp running between the wires, and in which, at the opposite side of the wires, a loading box has been mounted, which is provided with a number of loading ribs, which are placed in the transverse direction in relation to the transfer direction and which extend across the web width, said loading ribs being loaded towards the bottom of the drain box so as to produce the desired compression in the fibrous pulp running between the wires. Normally, the former of a paper machine comprises a twin-wire section, in which the upper wire and the lower wire run as substantially parallel one above the other and in which the fibrous pulp is introduced between the wires for draining. On the top of the upper wire, there is a drain box, in which a vacuum is present to absorb water out of the fibrous pulp. The lower wire is normally supported by means of a loading box, which is provided with loading ribs transverse to the running direction of the wires and which is stationary in relation to the drain box. In such a former, it is desirable that the magnitude of the gap between the wires can be changed and that the shape of the gap in relation to the transfer direction of the wires can also be changed. For this purpose, in the prior art, a number of different modes have been described for guiding and supporting the wires. For example, in the DE Patent 3,406,217 , a wire guide path is described in which the lower wire is supported by means of a number of ribs placed side by side and extending across the width of the wire, the lower wire resting against said ribs, and said ribs being pressed adjustably against the lower wire. In this solution, said ribs are placed tightly adjacent to one another, which results in the drawback that the ribs act upon one another by the intermediate of friction, for which reason it is difficult to provide a precise control. From the DE Patent 3,153,305 , a wire guide path is known in which a number of ribs are employed, which are arranged at a distance from one another and which rest and are supported against the lower wire. The pressing of these ribs against the lower wire is adjusted individually by means of spring members. From the FI Patent No. 90,572 , a solution is known in which the loading ribs are loaded against the lower wire by means of loading hoses parallel to the longitudinal direction of said ribs, i.e. transverse to the running direction of the wires, the desired compression of the rib against the lower wire being produced by regulating the pressure in said hoses. By means of the solution in accordance with said FI patent, each rib can be loaded with a force of the desired magnitude against the lower wire, for example, so that the loading of the ribs increases in the running direction of the wires. It has been a substantial drawback of the prior-art solutions described above that it has not been possible to make the moisture content of the web in the cross direction uniform, but the moisture curve or moisture profile in the cross direction has become such that the moisture content in the web has been considerably higher in the lateral areas of the web than in the middle areas. This comes primarily from the fact that the rib has been loaded against the lower wire substantially with a uniform load, in which case the rib that "floats" on a loading hose subjected to a uniform pressure behaves so that, owing to the points of discontinuity, at the ends of the rib, a torque is formed which attempts to bend the rib. Thus, by means of uniform loading of the rib, a uniform compression of the rib against the lower wire has not been achieved across the entire web width. In the prior art, attempts have been made to solve this adjustability or profiling in the cross direction, among other things, so that, for example, in a construction in accordance with the FI Patent 90,572 , the loading hose placed below each rib has been divided into separate chambers in the longitudinal direction of the rib, the pressure in each of said chambers being separately adjustable. Of course, by means of such a solution, adjustability in zones of the loading of the ribs is achieved, but the realization of this solution is highly complicated and quite difficult to control. The object of the present invention is to provide an improvement over the prior-art solutions described above and to eliminate the drawbacks involved in said solutions. In view of achieving this, the invention is mainly characterized in that the loading box is provided with loading means, which are arranged to produce a locally raising or lowering force applied to the loading ribs in the direction transverse to the transfer direction, said force being applied simultaneously to at least two successive loading ribs, so as to profile the compression force applied by said loading ribs to the fibrous pulp in said transverse direction. WO-A-9114826 discloses a loading adjustable in zones for the former of a paper machine which is provided with loading means to produce locally raising or lowering forces. By means of the present invention, compared with the prior art, a number of advantages are obtained, of which the following should be stated in this connection. In the solution in accordance with the invention, the regulation of the loading of the ribs in the cross direction has been accomplished by means of oblong power elements fitted in the running direction of the wires, which elements act in the contrary direction as compared with the conventional loading elements parallel to the longitudinal direction of the ribs, so that the profiling of the loading is carried out by means of the same loading elements at the same time in two or more ribs, in which case the controllability and the stability of the loading is substantially better than in the prior art. The streaks that occurred in the fibrous pulp in the prior art can be amended more readily, because the oblong loading elements are parallel to the streaks. In the lateral areas of the web, where the profiling is particularly important, the loading elements in accordance with the invention can be fitted more densely than in the rest of the web, in which case the controllability of the lateral areas is also better than in the prior art. It is a substantial advantage of the present invention that, by means of the solution of the invention, it is easy to correct major errors and profile faults, and, in addition to this, the invention can also be applied to correcting of small-scale profile faults. The further advantages and characteristic features of the invention will come out from the following detailed description of the present invention. In the following, the invention will be described in detail with reference to the figures in the accompanying drawing. Figure 1 is a schematic general side view of a former to which the loading box adjustable in zones in accordance with the invention can be applied. Figure 2 shows an enlarged detail of the area of the loading box in the former as shown in Fig. 1, in particular illustrating the mode in which the possibility of loading of the ribs has been achieved. Figure 3 is a fully schematic sectional view taken along the line III-III in Fig. 2. Figure 4 is a fully schematic illustration of the loading board as shown in Fig. 2, viewed from the direction of the wires. Thus, Fig. 1 is a fully schematic side view of a former, which is denoted generally with the reference numeral 1. The former 1 is a so-called twin-wire former, which comprises an upper-wire loop 2 and a lower-wire loop 13. The former 1 may be installed, for example, on a fourdrinier wire, in which case said lower-wire loop 13 is exactly the fourdrinier wire. In the conventional way, the upper-wire loop 2 is arranged to run over the turning rolls 3,4,5,6, which turning rolls are mounted adjustably on the frame 7 of the former 1. The first turning roll 3 is not in contact with the fibrous pulp P, but it has been raised apart from the web so that a wedge-shaped inlet portion is formed between the wire loops 2,13, in which inlet portion the fibrous pulp P placed on the lower-wire loop 13 is pressed continuously between the wires 2,13 in its transfer direction R. After the wedge-shaped inlet portion, in the transfer direction R, in the former 1, inside the upper-wire loop 2, a drain box 8 is fitted in the normal way, the bottom of said drain box consisting of upper ribs 13, water being sucked through the gaps between said ribs out of the fibrous pulp P through the upper wire 2 into the drain box 8 by means of vacuum. The drain box 8 contains drain chambers 9,10,11,12, in which a vacuum is present, by whose means water is sucked out of the fibrous pulp P into said chambers. In the different chambers 9,10,11,12, preferably vacuums of different magnitudes are employed, so that the efficiency of dewatering of the fibrous pulp P is progressively increasing in the direction of transfer R. Below the drain box 8, underneath the lower wire 13, a loading box 20 is fitted, the lower wire 13 being pressed from below by means of the loading ribs 22 provided on said loading box 20, so that a compression of desired magnitude is produced and applied to the fibrous pulp P present between the wires 2,13 so as to drain water out of said fibrous pulp P. The loading ribs 22 are provided with suitable power members, such as loading hoses parallel to the loading ribs 22, the desired compression effect being produced upon the fibrous pulp P by means of compressed air passed into said hoses. The loading ribs 22 are loaded by means of the loading hoses favourably so that the compression effect applied to the fibrous pulp P by means of these loading ribs 22 is progressively increasing in the transfer direction R. The loading ribs 22 are mounted on a loading board placed in the loading box 20, below which board bellows 21 or equivalent power units are mounted, by whose means the desired pressure level can be regulated and by whose means the inclination of the loading board and, thus, of the loading ribs 22 present in same is regulated to the desired level in relation to the direction of transfer R. The construction of the loading box 20 is illustrated in more detail in Figs. 2,3 and 4. As was already stated above, Fig. 2 shows a detail of the loading box 20 shown in Fig. 1, in particular illustrating the adjustability of the loading ribs 22. Fig. 3 is a schematic partial sectional view taken along the line III-III in Fig. 2, and Fig. 4 is a schematic illustration of the construction of the loading ribs viewed from the top, i.e. from the direction of the wires. The loading ribs 22 comprise the body 23 of the loading rib, to which a wear piece 24 has been attached by means of a dovetail joint or equivalent, which wear piece 24 rests against the bottom face of the lower wire 13. The body 23 of the loading rib is mounted on a hollow beam 25 parallel to the longitudinal direction of the loading rib, to which beam is it fixed in a suitable way, for example by means of a backed-off joint shown in Fig. 2. In the cavity space 26 in the hollow beam 25, a loading member parallel to the longitudinal direction of the loading rib is fitted, preferably a loading hose 28 as shown in Fig. 2, and below the loading hose 28, adjustment wedges 27 are fitted, which are supported on support beams 29 parallel to the machine direction. Thus, by means of the pressure fed into the loading hoses 28, the loading ribs 22 are loaded with the desired force against the lower wire 13. As comes out especially from Fig. 2, in the transfer direction, the successive loading ribs 22 are preferably interconnected in pairs by means of connecting members 37. Into the loading hoses 28 in each loading rib 22 or, in the arrangement as shown in Fig. 2, into the loading hoses 28 in each pair of ribs, the desired adjustable pressure is fed so as to produce the desired compression force applied to the fibrous pulp P placed between the wires. The pressure supply and regulation members are not shown in the figures in the drawing, but these pressure supply and regulation members can be accomplished by means of existing prior-art solutions. In the construction of ribs of the sort described above, it has been found to be desirable to be able to regulate the compression force applied by the loading ribs 22 to the fibrous pulp P in the direction transverse to the direction of transfer R, i.e. in the longitudinal direction of the loading ribs 22. This regulation of the loading in the cross direction, i.e. profiling of the loading in the cross direction of the machine, has been accomplished in the invention as follows. In the loading board, which belongs to the loading box 20 and a part of which is denoted with the reference 20' in Figs. 2 and 4, beams 33 placed in the longitudinal direction of the machine, i.e. in the transfer direction R, have been installed, which beams 33 have been attached to the loading board 20' rigidly by means of purposeful fastening means 35,36. There is a number of such longitudinal beams 33, and they have been arranged at a distance from one another in the cross direction of the machine. The longitudinal beams 33 are fitted preferably so that the distances between them in the cross direction of the machine are shorter in the lateral areas of the wires 13,2 than in the middle area of the wires. On support of the hollow beams 25 of the loading ribs 22, U-section support pieces 31 have been suspended, the flange parts 30 of said pieces 31 being supported against the bottom of the cavity space 26 in the hollow beams 25 of the loading ribs 22. In the way shown in particular in Fig. 3, the U-section support pieces 31 surround the support beams 33 placed in the machine direction so that said longitudinal support beams 33 remain inside the U-section support pieces 31. Onto the bottom of the "fork" of the U-section support pieces 31, longitudinal supports 32 have been installed which extend across the length of the loading box, and onto these longitudinal supports 32, between the longitudinal supports 32 and the support beams 33 placed in the machine direction, longitudinal loading hoses 34 have been fitted. The longitudinal loading hoses 34 may extend across the entire length of the loading box 20, but it is essential that said longitudinal loading hoses 34 should extend at least across two successive loading ribs 22. In such a case, between the longitudinal support 32 and the support beam 33 placed in the machine direction, a number of longitudinal loading hoses 34 have been arranged one after the other. If the longitudinal loading hoses 34 extend across two successive loading ribs 22, it is preferable that, in such a case, they extend over those loading ribs 22 that have been interconnected as a pair of ribs by means of connecting members 37. When the desired loading pressure is fed into the longitudinal loading hoses 34, a force is applied to the loading ribs 22 which pulls said ribs 22 apart from the wire plane. Thus, by means of this solution, an effect is produced that reduces the compression force applied by the loading ribs 22 to the fibrous pulp P in the areas of said longitudinal loading hoses 34. In this way, by means of the solution in accordance with the invention, it is possible to correct the streak formations and other profile faults in the fibrous pulp. The embodiment described above and illustrated in the figures in the drawing is just one example of the ways in which the adjustment in zones of the loading box 20 in the former 1 can be accomplished. First, it is obvious that, in stead of the longitudinal loading hoses 34, it is also possible to use power units of other types, for example mechanical power units. In such a case, it would be one possibility that invariable pressures are arranged to act upon the longitudinal loading hoses 34, in addition to which the longitudinal support would be taken care of by means of mechanically adjustable power units. Further, it is obvious that, inversely in relation to the exemplifying embodiment shown in the figures in the drawing, the longitudinal loading members can be arranged so that they produce a force that increases the force that is applied by the loading ribs 22, in which case the adjustment in zones in accordance with the invention can also be carried into effect. Further, it is possible to imagine a solution in which, at every other longitudinal support beam 33, a force is produced that increases the compression applied by the loading ribs 22, and, in a corresponding way, at every other longitudinal support beam 33, a force is produced that reduces the compression. Above, the invention has been described by way of example with reference to the figures in the accompanying drawing. The invention is, however, not confined to the exemplifying embodiments illustrated in the figures alone, but, as was already stated above, different embodiments of the invention may show variation within the scope of the inventive idea defined in the accompanying patent claims.

Claims: A loading box adjustable in zones for the former of a paper or board machine, which former (1) comprises a twin-wire section consisting of wires (2,13) placed one above the other and running in the same transfer direction (R), in which twin-wire section, at one side of the wires (2,13), a drain box (8) has been mounted to remove water out of the fibrous pulp (P) running between the wires (2,13), and in which, at the opposite side of the wires, a loading box (20) has been mounted, which is provided with a number of loading ribs (22), which are placed in the transverse direction in relation to the transfer direction (R) and which extend across the web width, said loading ribs being loaded towards the bottom of the drain box (8) so as to produce the desired compression in the fibrous pulp (P) running between the wires (2,13), characterized in that the loading box (20) is provided with loading means (30,34), which are arranged to produce a locally raising or lowering force applied to the loading ribs (22) in the direction transverse to the transfer direction (R), said force being applied simultaneously to at least two successive loading ribs (22), so as to profile the compression force applied by said loading ribs (22) to the fibrous pulp (P) in said transverse direction. A loading box as claimed in claim 1, characterized in that the loading means (30,34) comprise longitudinal support beams (33), which are fitted underneath the loading ribs (22) at distances from one another in the cross direction, the loading ribs (22) being supported on said support beams (33) by means of a power unit (34). A loading box as claimed in claim 1 or 2, characterized in that the power unit (34) is a loading hose (34) or equivalent which can be pressurized, which is parallel to the support beam (33), and which acts upon at least two loading ribs (22) at the same time. A loading box as claimed in claim 2 or 3, characterized in that the loading hose (34) or the equivalent power unit is mounted below the longitudinal support beam (33) and coupled with the loading ribs (22) by means of a support piece (31) so as to apply a lowering force to said loading ribs (22). A loading box as claimed in claim 2 or 3, characterized in that the loading hose (34) or the equivalent power unit is mounted above the longitudinal support beam (33) and supported on the loading ribs (22) by means of a support piece so as to apply a raising force to said loading ribs (22). A loading box as claimed in any of the preceding claims, characterized in that the longitudinal support beams (33) included in the loading means are attached to the constructions of the loading box (20) rigidly. A loading box as claimed in any of the preceding claims 1 to 5, characterized in that the longitudinal support beams (33) included in the loading means are mounted on the constructions of the loading box (20) adjustably, so that the magnitude of the force applied to the loading ribs (22) can be regulated by adjusting the position of the support beam (33). A loading box as claimed in claim 7, characterized in that the adjusting of the positions of the longitudinal support beams (33) is carried out mechanically. A loading box as claimed in claim 7 or 8, characterized in that an invariable pressure is connected to act upon the loading hoses (34) that are employed as power units. A loading box as claimed in any of the preceding claims, characterized in that the distance of the longitudinal support beams (33) and of their related power units (34) from one another is, in the direction transverse to the direction of transfer (R) of the fibrous pulp (P), substantially smaller in the lateral areas of the wires (2,13) than in the middle area of the wires.

Inventors: POIKOLAINEN ANTTI, POIKOLAINEN, ANTTI
Applicants: VALMET CORP, VALMET CORPORATION
Application year: 1995
Main classification: D21F1
IPC codes: D21F9, D21F1