Loading element for a draining device in a paper machine

Abstract: The invention concerns a rib for a draining device in a paper machine, which rib is used to support and/or to load a wire or wires in a paper machine and/or to doctor water from the face of a wire or wires, said rib being loaded by means of the pressure of a medium. Between the rib (41) and its frame part (43), a pressure space has been formed, which is defined by a flexible belt (46) and into which the loading pressure is passed, and the flexible belt (46) defines the pressure space so that the area of effect of the loading force is independent from the movement of the rib (41).

Description: The invention concerns a loading element according to the preamble of claim 1. 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, 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, 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, either 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 as a straight run in the plane of the fourdrinier wire through the MB unit, or the MB unit is placed in a gap former, in which the dewatering starts immediately through both of the wires. 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 to take 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. With respect to the prior art, reference is also made to the papers DE 40 09 627 and DE 42 42 658, in whose solutions for loading of a rib, in connection with the rib, a hose construction has been arranged, into which the loading pressure is passed, in which case the loading of the rib is not independent from the displacement of the rib, because the area of effect changes along with the loading degree. Thus, in the prior-art loading elements, it has been a problem that the loading force has not been sufficiently independent from the length of the movement of the rib in the direction of loading. Moreover, problems may have been caused by contamination of the loading elements as paper machine waters have access between the parts of the rib construction, which has resulted in problems in keeping the loading at the desired level. Moreover, these loading elements have been difficult to manufacture because of their high precision of manufacture. In the prior-art solutions, problems have also been caused by the fact that the rib construction has been quite rigid in the cross direction of the machine. Document DE 40 19 884 describes a loading element for a draining device in a paper machine comprising a rib, a frame part and a flexible belt. To doctor water from the face of a wire or wires of the paper machine, said wire or wires is/are supported or-loaded by said rib by means of a loading pressure of a medium passing into a pressure space. The arrangement of the rib, the frame part and the flexible belt is made such that the area of effect of the loading force is independent of the movement of the rib. The object underlying the invention is to achieve a loading element for a draining device in a paper machine comprising a rib for supporting and/or loading a wire or wires, wherein the area of effect of the loading force shall be independent of the movement of the rib and a reliable performance of the element shall be ensured. The object is achieved by the features of claim 1. By the described features a loading is achieved having a pressure space which is formed by a flexible belt, a rib and a frame part such that a reliable function of the loading element is ensured and the area of effect of the loading force is independent of the movement of the rib. According to the invention, the loading force can be made sufficiently independent from the length of the movement of the rib and, moreover, in the construction in accordance with the invention, the glide faces of the rib construction are placed in a closed space, so that the paper machine waters cannot contaminate them. The clean glide faces permit supporting of the element substantially free of play, and, at the same time, the problems arising from contaminations for the movements of the glide faces can be minimized. In an arrangement in accordance with the invention, the flexible belt protects the parts of the rib construction and controls the loading pressure so that loading forces as illustrated in Figs. 5A and 5B are obtained. As a function of the displacement of the rib, the loading force remains invariable, and as a function of the loading pressure, the loading force is linear. In the arrangement in accordance with the invention, especially the substantially U-shaped loops of the belt make the loading force linear in relation to the pressure, because the substantially U-shaped loops have the effect that the area of effect of the loading pressure is invariable. The rib construction in accordance with the invention is not flexible in the machine direction but is flexible in the cross direction of the machine, in which case the rib is shaped in compliance with the wire and, thus, loads the wire uniformly with the desired loading force in the cross direction of the machine. In a preferred exemplifying embodiment of the invention, in which a leaf-spring element is used for supporting the rib, a rib support free of play is obtained. In a second exemplifying embodiment of the invention, for supporting the rib construction in the cross direction of the machine, either a continuous support construction or a support construction consisting of pin-like support constructions placed at a distance from one another is used. In the invention, the belt is preferably attached to the rib and to the frame constructions by means of a shaped-profile/groove fastening, in which shaped profile a space that can be pressurized has been formed for the fastening, by means of which space the belt can be fastened as fully sealed. According to an advantageous additional feature of the invention, in connection with the rib construction, substantially in the vicinity of the edges of the rib, actuators are fitted, by whose means the loading can be increased or reduced locally. Of course, such actuators can also be added to other desired points in the cross direction of the rib construction. In the following, the invention will be described in more detail with reference to the figures in the accompanying drawing, the invention being, however, not supposed to be strictly confined to the details of said illustrations. Figure 1 is a vertical sectional view in the machine direction of an exemplifying embodiment of the environment of application of the invention, Figure 2 is a schematic vertical sectional view of an exemplifying embodiment of the loading element in accordance with the invention, Figures 3A and 3B are schematic illustrations of a second exemplifying embodiment of the invention, Figure 4 is a schematic illustration of an embodiment of the arrangement of the rib in accordance with the invention in a portion of the draining device, Figure 5A is a schematic illustration of the loading force as a function of the pressure when a rib in accordance with the invention is employed, and Figure 5B is a schematic illustration of the loading force as a function of the displacement of the rib when a rib in accordance with the invention is employed. Fig. 1 is a schematic illustration of an environment of application of the invention, which environment consists 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, in which initial portion, owing to the draining elements 11a placed in said portion, the stock web W 0 receives a certain dry solids content, and at least its lower face receives a certain couching degree, before the web 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, inside the lower-wire loop 10, the twin-wire zone includes a pre-loading board 12, after which there follows the loading unit 32 of the MB unit 30 in the twin-wire zone, in which loading unit 32 there are loading ribs, which are preferably interconnected in pairs and one after the other and which ribs extend across the entire width of the wires 10,20. The upper wire 20 has been arranged to run over the turning/reversing rolls 16, 17,18 and over the breast roll 21, and the lower wire 10 runs as substantially parallel to the upper wire 20 underneath 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 the wires make progress. After the wedge-shaped inlet gap K, in the transfer direction F, there is a MB unit 30, which comprises an upper dewatering box 51. The bottom of the dewatering box 51 consists of ribs 52, water being sucked out of the web W 0 through the gaps between said ribs into the dewatering box 51 by means of a vacuum and air. On its run, the upper wire 20 rests against said ribs 52. The MB unit 30 also includes loading units 32 which permit dewatering that takes place downwards, and on the top face of said loading units 32 there are sets of loading ribs 33, which consist of loading ribs. Further, Fig. 1 shows a number of other parts and support structures included in the former, which parts and structures are known in themselves and will not be described in further detail in this connection. The loading rib 41 as shown in Fig. 2 comprises cross-direction frame parts 43, on which the loading rib 41 is supported by the intermediate of a glide rail 44. The loading rib 41, in which there is a longitudinal groove 54, is fitted to move vertically while supported by the loading rail 44. The plane top side of the loading ribs 41 drags against the face of the wire 10;20 and loads said wire while water operates as the lubricating fluid. By means of the loading ribs 41, water to be drained out of the web W 0 is doctored from the lower face of the wire. The loading rib 41 is supported in its site of operation typically by means of a continuous glide rail 44, which is made of the same part with the frame part 43. Preferably to the lower edge of the loading rib 41, a flexible belt 46 has been attached, which has been attached preferably to the top portion of the frame part 43 so that U-shaped loops 48 are formed towards the bottom. To the sides of the rib 41, outside the belt 46, shield plates 55 have been fixed, which restrict the movement of the belt 46 in the lateral direction. The belts 46 are attached to a groove made into the rib 41 and into the frame part 43, respectively, preferably by means of a shaped-profile joint, whose interior space 56 has been shaped so that it can be pressurized when necessary, in which case a simple, sealed joint is provided. By means of the fastening member 58, the rib 41 is fixed to the rest of the frame constructions of the machine. In the construction shown in Fig. 2, the loading force is produced by passing the loading pressure by the intermediate of a medium, such as air, through the duct 57 into the space defined by the flexible belt 46, the rib 41, and by the frame part 43. The loading pressure is relieved by reducing the pressure, and the force of gravity of the earth returns the rib 41 down. The belt 46, whose thickness is, for example, 0.1...3 mm, preferably 1...2 mm, and which is made of rubber or an equivalent resilient material, is attached from its top edge to the rib 41 and from its lower edge to the frame part 43 by the intermediate of fastening parts 56, so that U-shaped loops 48 are formed downwards, which loops 48 permit movements of the rib 41 in the direction up and down. The lateral supports 55 restrict widening of the belt 46 in the lateral direction, so that the area of effect of the pressure is not changed when the rib 41 is shifted in the loading direction. The principal features of the exemplifying embodiment of the invention illustrated in Figs. 3A and 3B are similar to those of the exemplifying embodiment of the invention shown in Fig. 2, and corresponding parts have been denoted with the same reference numerals. The reduction of the loading pressure and the returning of the rib 41 have been accomplished by means of a leaf spring 53, which supports the loading rib 41 at the same time without play in the machine direction. The loading force is produced by passing the pressure of the medium along the duct 57 into the space defined by the belt 46, by the rib 41, and by the frame part 43. The belt 46 has been attached to the rib 41 and to the frame part 43 by means of a shaped profile 56. Expansion of the belt 46 in the lateral direction is restricted by means of the lateral support 55. If necessary, by changing the angle/shape of the lateral support 55, it is possible to look for a loading curve of the desired shape. As is shown in Fig. 3B, there are preferably several leaf springs 53 in the cross direction of the machine. If it is desirable to reduce the load in the lateral areas of the wire, it is possible to place actuators, for example springs 61, in the lateral areas of the rib 41 so as to reduce the load. Of course, such actuators can be fitted in any location in the cross direction of the rib 41 in which it is desirable to regulate the loading locally. As is shown in Fig. 4, the first loading ribs 41 in the sets of loading ribs 33 have been interconnected in pairs by means of intermediate parts 42. Through the gaps between the intermediate parts 42, water can drain from the web in the direction of the arrow P. As is shown in Fig. 4, in the draining device in the paper machine, above the wires 10,20 and above the web W 0 placed between the wires, there may be the ribs 52 of the upper draining device and, preferably alternatingly with said ribs, there are the ribs 41 in accordance with the invention. The ribs 41 may also be interconnected in pairs by means of intermediate parts 42. In Fig. 4, the ribs 41 as shown in Fig. 2 are shown as interconnected, but, of course, the ribs 41 in accordance with the exemplifying embodiment shown in Figs. 3A...3B can also be interconnected by means of intermediate parts. In the embodiment shown in Fig. 4, there is first a pair of ribs as shown in Fig. 2, and thereafter there are individual ribs as shown in Figs. 3A and 3B, which ribs are provided with leaf springs 53. As is shown in Fig. 4, the ribs 41 may be attached to the rest of the frame constructions of the machine by means of fastening members 58, or they may be fixed to the frame constructions of the machine permanently, for example, by welding 59. As is shown in Fig. 5A, when the arrangement of the invention is used, the loading force F is linear as a function of the loading pressure and, moreover, the loading force F of Fig. 5B remains invariable irrespective of the displacement S of the rib. The rib of the present invention has been accomplished so that it is rigid in respect of bending taking place around the X and Y axes and resilient in relation to bending taking place around the Z axis, which Z axis is parallel to the paper web, Fig. 4.

Claims: A loading element for a draining device in a paper machine comprising a rib (41), a frame part (43) and a flexible belt (46), which rib (41) is used to support and/or load a wire (10) or wires in a paper machine and/or to doctor water from the face of a wire (10) or wires, said rib (41) being loaded by means of the loading pressure of a medium passed into a pressure space so that the area of effect of the loading force is independent from the movement of the rib (41), characterized in that said pressure space is formed by said flexible belt (46), said rib (41) and said frame part (43). A loading element, characterized in that said flexible belt (46) has been arranged between said rib (41) and said frame part (43) so that the guide and glide faces of said rib (41) are placed inside said pressure space. A loading element as claimed in claim 1 or 2, characterized by intermediate parts (42) for interconnecting different ribs (41). A loading element as claimed in any of the claims 1 to 3, characterized in that said loading force is relieved by means of the gravity of the earth. A loading element as claimed in any of the claims 1 to 4, characterized in that the loading force is relieved by reducing the loading pressure. A loading element as claimed in any of the preceding claims, characterized in that said rib (41) is supported in the cross direction by means of a glide rail (44). A loading element as claimed in claim 1, characterized in that between said rib (41) and said frame part (43) an actuator (53) is fitted for relieving or compensating said loading pressure. A loading element as claimed in any of the preceding claims, characterized in that said flexible belt (46) is attached to said rib (41) and to said frame part (43) by means of a shaped profile. A loading element as claimed in any of the preceding claims, characterized by lateral supports (55) of said flexible belt (46) for regulating the shape of the loading curve. A loading element as claimed in claim 7, characterized in that said actuator (53) is a leaf spring. A loading element as claimed in any of the preceding claims, characterized in that said flexible belt (46) is made of a resilient material, for example rubber. A loading element as claimed in any of the preceding claims, characterized in that said rib (41) is provided with actuators (61) for the regulation of the loading of said rib (41) locally. A loading element as claimed in any of the preceding claims, characterized in that a set of loading ribs (33) is fitted to be used in a twin-wire web former in a paper machine inside the lower-wire loop (10), as backup parts of the pressure loading, wherein inside the upper-wire loop (20) there are ribs (52) of a dewatering box (51), which ribs (52) are placed facing the gaps between said ribs (45) in the set of loading ribs (33), for example in the middle of said gaps.

Inventors: HENTILAE ESA, JAAKKOLA JYRKI, SALMINEN SAMPPA J, HENTILAE, ESA, JAAKKOLA, JYRKI, SALMINEN, SAMPPA J., Hentilä, Esa
Applicants: METSO PAPER INC, METSO PAPER, INC.
Application year: 1996
Main classification: D21F1
IPC codes: D21F1