Set of ribs in a dewatering device in a paper machine

Abstract: The invention concerns a set of ribs in a dewatering device in a paper machine, which set of ribs is used to support and/or to load the wire (10) or wires in the paper machine and/or to doctor water off the inner face of the loop of the wire (10) or wires, said set of ribs (33) comprising at least two transverse ribs (45), which are placed one after the other at a distance from one another in the machine direction (F), whose height positions are adjustable, and which are interconnected in pairs by means of intermediate parts (47). The ribs (45) are interconnected in pairs by means of mechanisms (60) of four articulated joints, which mechanisms are placed at a distance from one another in the transverse direction of the wire (10) / wires, the positions of the ribs (45) in the horizontal direction remaining invariable irrespective of the height positions of the ribs (45) in relation to one another. The mechanism (60) of four articulated joints comprises intermediate parts (47) placed at a distance from one another in the vertical direction. The intermediate parts (47) in the mechanism of four articulated joints are attached to the frame parts (48) of the successive ribs (45) by means of articulated joints (61) so that one end of the intermediate part (47) is attached to the frame (48) of one rib (45) by means of an articulated joint, and the other end of the part (47) is attached to the frame (48) of the other rib (45), respectively.

Description: The invention concerns a set of ribs in a dewatering device in a paper machine, which set of ribs is used to support and/or to load the wire or wires in the paper machine and/or to doctor water off the inner face of the loop of the wire or wires, said set of ribs comprising at least two transverse ribs, which are placed one after the other at a distance from one another in the machine direction, whose height positions are adjustable, and which are interconnected in pairs by means of intermediate parts. In the web formers in paper machines, a number of different forming members are used. The primary function of these members is to produce compression pressure and pressure pulsation in the fibrous layer that is being formed, by means of which pressure and pulsation dewatering of the web that is being formed is promoted and, at the same time, for example, the formation of the web is improved. Said forming members include various forming shoes, which are usually provided with a curved ribbed deck and over which the forming wires placed one above the other and the web placed between said wires are curved. In the area of these forming shoes, water is removed through the wire placed at the side of the outside curve by the effect of its tensioning pressure, and this draining is promoted further by a field of centrifugal force. Draining of water also takes place through the wire placed at the side of the inside curve, which draining is, as a rule, intensified by means of negative pressure present in the chamber of the forming shoe. The ribbed deck of the forming shoe produces pressure pulsation, which both promotes the dewatering and improves the formation of the web. Further, from the prior art, so-called MB units are known (see EP-A-0 520 970), through which two opposite wires run, as a rule, as a straight run. In the prior-art MB units, inside the loop of one of the wires, there is a pressure loading equipment, and inside the loop of the other, opposite wire, a draining equipment provided with a set of guide and draining ribs is arranged. In the way known from the prior art, said MB unit is, as a rule, placed in the fourdrinier wire portion so that the MB unit is preceded by a single-wire portion of considerable length, in which portion a substantial amount of dewatering takes place before the web runs through the MB unit. In the prior-art MB formers, the lower unit consists of a support board, which consists of loaded ribs. These ribs are loaded each of them separately by means of a loading hose of its own. As regards the prior art, reference is made to the applicant's FI Patent No. 90,673, in which a twin-wire web former of a paper machine is described, which former comprises a carrying wire and a covering wire, which together form a twin-wire forming zone, in which a forming unit is fitted, which comprises a forming board and a drainage box placed one opposite to the other, which drainage box comprises a number of ribs, water being drained out of the web through the spaces between said ribs to a significant extent by the effect of negative pressure into the drainage box, in which forming board, placed facing the drainage box, there is a number of transverse loading ribs placed at a considerable distance from one another in the machine direction, and in the area of which forming unit the dewatering can be arranged as taking place both through the covering wire and through the carrying wire, also towards the forming board through the open spaces placed between its loading ribs. In the solution described in said publication, it has been considered novel that successive loading ribs are interconnected in pairs by intermediate parts, and that said intermediate parts, together with the loading ribs attached to them, form ribbed shoes, which can be loaded by means of loading hoses to produce a dewatering pressure in the web placed between the wires, while the ribs on said drainage box operate, in a way in itself known, as back-up members for the loading forces. In the way known from the prior, the ribs have been interconnected permanently, in which case, when the first rib and the upper rib placed between the ribs remove water, the stock web becomes thinner, in which case the latter rib must rise to a level higher than the first rib. It follows from this that the latter rib must be loaded to a greater extent than the first rib, whereby the element becomes inclined and the tips of the ribs are separated from the wire as a result of the change in angle. Then, the rib does not remove water, so that the loading pressure must be increased in order to bring the tip of the rib into contact with the wire. Owing to this use of an unnecessarily high loading pressure, the paper base may also be destroyed. Moreover, it is quite difficult to operate the latter rib with a low load. The object of the present invention is to suggest a solution by whose means these problems known from the prior art can be solved. In view of achieving the objectives stated above and those that will come out later, the invention is mainly characterized in that the ribs are interconnected in pairs by means of mechanisms of four articulated joints, which mechanisms are placed at a distance from one another in the transverse direction of the wire / wires, the positions of the ribs in the horizontal direction remaining invariable irrespective of the height positions of the ribs in relation to one another. In a loading element in accordance with the invention, the draining ribs are interconnected by means of articulated support arms placed, for example, in two vertical rows, in which case the foil angle of the draining ribs is invariable. Thus, the ribs can also be loaded one by one. According to a preferred exemplifying embodiment of the invention, when a mechanism of four articulated joints is used for fixing the ribs in pairs, the angles between the ribs do not change, in which case the faces of the ribs are in the desired position and the foil angle remains as desired on each rib. In this way, an efficient and controlled dewatering/loading ratio is obtained. As a further advantage of the invention, it is achieved that, when ribs provided with a trailing angle are used, the trailing angle of each rib remains correct, because the mechanism of four articulated joints prevents turning of the second rib into an inclined position. The arrangement in accordance with the invention is, in particular, suitable for such draining taking place in the wire section in which it is desirable to adjust the loading of the ribs. When the web becomes thinner as water is drained, by means of an arrangement in accordance with the present invention, an increased capacity of adjustment of the loading rib is obtained, in which case it is possible to run, for example, with every other rib, because each rib can be loaded separately. By means of the number of ribs in operation during running, the quality of paper is affected, and the suitable number of ribs is chosen depending on the paper stock, running speed, and on the thickness of the slice of the headbox. In the following, the invention will be described in more detail with reference to the figures in the accompanying drawing. Figure 1 is a schematic illustration of an exemplifying embodiment of the environment of application of the invention. Figures 2A and 2B are schematic illustrations of the loading element in accordance with the invention. Fig. 1 is a schematic illustration of an environment of application of the present invention, consisting of a former, which comprises a lower-wire loop 10 and an upper-wire loop 20. In connection with the lower-wire loop 10, after the headbox (not shown), there is the single-wire initial portion 10a of the web-forming zone, and owing to the draining elements 11a placed in said single-wire portion, the pulp web W 0 obtains a certain dry solids content and, at least in its lower face, a certain couching degree before it enters into the twin-wire zone, which is formed between the wires 10 and 20. The twin-wire zone starts at the breast roll 21 of the upper-wire loop 20. After the breast roll 21, in the twin-wire zone, inside the lower-wire loop 10, there is a forming shoe 12, which is followed by the loading unit 32 of the MB unit 30 in the twin-wire zone, in which loading unit there are loading ribs, which are interconnected in pairs one after the other and which extend across the entire width of the wires 10,20. The upper wire 20 is arranged to run over the turning rolls 16,17,18 and the breast roll 21, and the lower wire 10 runs as substantially parallel to the upper wire 20 below the upper wire 20. The wires 10 and 20 form a wedge-shaped inlet gap K, in which the web W 0 placed on the lower wire 10 is pressed continuously between the wires 10 and 20 as they make progress. After the wedge-shaped inlet gap K, in the transfer direction F, there is the MB unit 30, which comprises a drainage box 51. The bottom of the drainage box 51 consists of ribs 52, water being sucked out of the web W 0 through the gaps between said ribs into the drainage box 51 by means of vacuum. During its run, the upper wire 20 rests against said ribs 52. The MB unit also includes loading units 32 which permit drainage taking place downwards, sets of loading ribs 33 being placed on the upper faces of said loading units 32. Placed facing the sets of loading ribs 33, inside the upper-wire loop 20, there are said ribs 52, which constitute back-up parts for the pressure loading and which are placed facing the gaps of the sets of loading ribs 33. Moreover, in Fig. 1, a number of other parts and support constructions included in the former are seen, which are in themselves known and which will not be described in more detail in this connection. According to Figs. 2A and 2B, the frame parts 48 of the loading ribs 45 are interconnected in pairs by intermediate parts 47. Through the gaps between the intermediate parts 47, the water can drain from the web W 0 in the direction of the arrows F 1 . The pairs of ribs 45 are connected, for example, by means of groove-projection joints with the frame parts 48 of the rib elements. The frame parts 48 are of U-section, and into their interior, pairs of loading hoses 40a,40b and pairs of relief hoses 41a,41b penetrate. Between the hoses 40a,41a;40b,41b, the projection parts of the support parts 55 are placed, which are again supported on the frame parts 57 of the loading unit 32. In order to load the loading ribs 45 against the inner face of the lower wire 10 and in order to produce the dewatering pressure and the rib impulses on the paper web W 0 , a liquid or gaseous medium, preferably air, is passed into the hoses 40a and 40b with positive pressures p a ,p b , by means of which pressures the loading forces of the sets of loading ribs 45 are produced. By means of the back pressure p ac ,p bc of a liquid or gaseous medium, which is passed into the other, opposite pair of hoses 41a,41b, relief pressures of said pressures p a and p b are produced, i.e. relief and opening forces of a direction opposite to the loading forces. The loading ribs 45, such as ceramic ribs, are attached to the frame parts 48 by means of fastening ribs 46 and by means of a joint 54 similar to a T-joint. The hoses 40a and 40b loaded by means of the pressures p a and p b of a liquid medium are attached to the frame part 48 by means of a joint 44. At the sides of the loading hoses 40a,40b opposite to the joint 44, there is a rigid projection part 53, which rests against the top side of the frame part 55. The loading hoses 40a and 40b are placed behind the walls 59, being protected from splashes. By means of regulation of the magnitudes and the mutual proportions of the loading pressures p a ,p b in the loading hoses 40a,40b, it is possible to regulate the loading forces of the pairs of loading ribs 45. By means of the relief pressures p ac ,p bc of the hoses 41a,41b, it is possible to produce relief forces or loading-rib 45 opening forces of a direction opposite to the loading forces of the pressures p a ,p b . According to Figs. 2A and 2B, the frame parts 48 of the ribs 45 are interconnected in pairs by two intermediate parts 47, which are linked by means of articulated joints 61 at each end. In this way, a mechanism 60 of four articulated joints is produced, which permits separate loading of each rib 45 and, moreover, ensures that the position of the ribs 45 in relation to the web W 0 remains as desired. The articulation mechanisms 60 are placed at a distance from one another in the cross direction of the machine. The cross-direction distance L 1 is about 200...500 mm. The longitudinal L 2 distance between the ribs 45 is about 30...300 mm. Above, the invention has been described with reference to just one preferred embodiment of same. In the following, the patent claims will be given, and many variations and modifications are possible within the scope of the inventive idea defined in said claims.

Claims: A set of ribs (33) in a dewatering device in a paper machine, which set of ribs is used to support and/or to load the wire (10) or wires in the paper machine and/or to doctor water off the inner face of the loop of the wire (10) or wires, said set of ribs (33) comprising at least two transverse ribs (45), which are placed one after the other at a distance from one another in the machine direction (F), whose height positions are adjustable, and which are interconnected in pairs by means of intermediate parts (47), characterized in that the ribs (45) are interconnected in pairs by means of mechanisms (60) of four articulated joints, which mechanisms are placed at a distance from one another in the transverse direction of the wire (10) / wires, the positions of the ribs (45) in the horizontal direction remaining invariable irrespective of the height positions of the ribs (45) in relation to one another. A set of ribs as claimed in claim 1, characterized in that the mechanism (60) of four articulated joints comprises intermediate parts (47), which are placed at a distance from one another in the vertical direction, and that the intermediate parts (47) of the mechanism of four articulated joints are attached, by means of articulated joints (61), to the frame parts (48) of successive ribs (45) so that one end of the intermediate part (47) is attached by means of an articulated joint to the frame (48) of one rib (45), and the other end to the frame (48) of the other rib (45), respectively. A set of ribs as claimed in claim 1 or 2, characterized in that the articulation points (61) provided in the frame parts (48) of successive ribs (45) for the intermediate part (47) are placed substantially in the same vertical plane. A set of ribs as claimed in any of the claims 1 to 3, characterized in that the set of ribs (33) is fitted to be used in a twin-wire web former of a paper machine, in which, placed facing the sets of loading ribs (33) that are placed inside the lower-wire loop (10), inside the upper-wire loop (20) there are the ribs (52) of the drainage box (51), which ribs constitute back-up parts for the pressure loading and are placed facing the gaps of the ribs (45) in the sets of loading ribs (33). A set of ribs as claimed in any of the preceding claims, characterized in that the mechanisms (60) of four articulated joints are placed, in the cross direction, at a distance of about 200...500 mm from one another. A set of ribs as claimed in any of the preceding claims, characterized in that the rib (45) comprises a frame part (48), that in connection with said frame part (48) there are pairs of loading hoses (40a,40b) loaded by means of pressures of a medium, and that in connection with the frame parts (48) relief hoses (41a,41b) have been fitted, by whose means relief pressures and/or opening pressures of the loading pressures can be produced. A set of ribs as claimed in any of the preceding claims, characterized in that the ribs (45) in a pair of ribs can be loaded together or separately.

Inventors: JAAKKOLA JYRKI, SALMINEN SAMPPA J, JAAKKOLA, JYRKI, SALMINEN, SAMPPA J.
Applicants: VALMET CORP, VALMET CORPORATION
Application year: 1995
Main classification: D21F1
IPC codes: D21F1, D21F9