Drainage foil for a paper machine

Abstract: A counterblade assembly (10) for a wet section (1) of a paper machine, having a fixed structure (13) fixed to a frame (5) of the machine; and a counterblade (9) connected to the fixed structure (13) by a number of articulated-parallelogram connecting assemblies (22) enabling the counterblade (9) to be moved substantially vertically by an actuator (25) to exert pressure on the machine wires (2, 3).

Description: The present invention relates to a counterblade assembly for a paper machine. As is known, paper machines comprise a unit, or wet section, for separating water from the pulp, and where the pulp is fed and compressed between two permeable wires overlapping along a portion of their respective paths. At the overlapping portion, one of the wires (in particular, the top wire) slides in contact with a vacuum box; and the other wire is pressed against the first by a number of counterblades extending crosswise to the traveling direction of the wires. In known solutions, the counterblades are normally mounted to slide inside vertical runners, and, in one known solution, are pushed towards the wires by a flexible tubular pneumatic actuator located beneath each counterblade and "inflated" with compressed air. A major drawback of the above counterblade setup lies in the aqueous solution removed from the pulp compressed between the wires seeping between the counterblades and respective runners and forming deposits which, following stoppage of the machine, may result in the counterblades jamming, or in uneven lift of the counterblades across the width of the wires. This may therefore result in inconsistent quality of the paper. WO 98 38380 A discloses a counterblade assembly for a wet section of a paper machine having the features of the preamble of claim 1 and including, in particular, a plurality of articulated joints connecting the counterblade to a frame of the machine. The articulated joint elements are hinged about axes that are parallel to the travelling direction of the paper draining wires, i.e. parallel to the friction force that is generated between counterblade and the contacting wire. It is an object of the present invention to provide a counterblade assembly for the wet section of a paper machine, designed to eliminate the aforementioned drawbacks typically associated with known counterblade assemblies. According to the present invention, there is provided a counterblade assembly for a wet section of a paper machine as claimed in claim 1. A preferred embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a schematic side view of the wet section of a paper machine featuring a number of counterblade assemblies in accordance with the present invention; Figure 2 shows a partly sectioned side view of a counterblade assembly in accordance with the present invention; Figure 3 shows a front view of the Figure 2 assembly; Figure 4 shows a plan view of a detail of the Figure 2 assembly. Number 1 in Figure 1 indicates as a whole a unit, or wet section, for removing water from pulp on a paper machine. Unit 1 comprises two wires 2, 3 traveling along respective endless paths and overlapping along a substantially horizontal common portion P of the two paths P1, P2. Of the bottom wire 2, only a top work branch 2a carrying the pulp (not shown) is illustrated; the pulp is deposited on to branch 2a upstream from unit 1 in known manner not shown; and wire 2 is powered by known means not shown. The top wire 3 is supported, powered and kept taut by a number of cylinders 4 fitted to a fixed frame 5. Along portion P, where wires 2 and 3 overlap and compress the pulp, top wire 3 runs in contact with a vacuum box 6 connected to a suction system not shown. Vacuum box 6 is defined at the bottom by a number of bottom transverse elements 7 supporting wire 3 and conveniently defined by parallel ceramic inserts spaced apart and defining as a whole a guide surface 8 for guiding wire 3. Wires 2 and 3 are kept contacting each other and guide surface 8 by a number of counterblades 9, each of which forms part of a respective counterblade assembly 10 shown in detail in Figures 2 to 4. Since counterblade assemblies 10 are identical, only one, referred to as "assembly 10" for the sake of simplicity, is described below, the same obviously also applying to all the others. Assembly 10 comprises a fixed supporting structure 13 defined by a bar 14, fitted removably to frame 5 of unit 1 and extending across the full width of wires 2, 3, and by a number of posts 15 fixed to the top of, projecting from, and equally spaced along, bar 14. Purely by way of example, for wires 2, 3 of 3 m in width, six equally spaced posts 15 may be used. Counterblade 9 is defined by a main body 17 extending across wires 2, 3 and conveniently made of plastic material, and has a ceramic insert 18 extending along a top edge of body 17 and which slides against wire 2. A vertical face 20 of main body 17 facing fixed structure 13 is fitted with a number of equally spaced vertical bars 21, each facing and connected to a respective post 15 of fixed structure 13 by pairs of articulated rod elements 16. Each post 15 defines, with respective bar 21 and elements 16, an articulated-parallelogram connecting assembly 22 interposed between bar 14 and counterblade 9. By virtue of articulated-parallelogram connecting assemblies 22, counterblade 9 is movable in a substantially vertical direction with no need for runners. More specifically, each connecting assembly 22 comprises two pairs of elements 16 located on opposite sides of post 15 and bar 21, and each defined by two parallel elements 16 extending in a substantially horizontal direction. Each element has one end 16a hinged to post 15, and one end 16b hinged to bar 21 about respective horizontal axes A, B that are perpendicular to the traveling path P of wires 2, 3. Body 17 of counterblade 9 has a bottom longitudinal recess 24 partly housing a pneumatic actuator 25 defined by a flexible tubular element. Actuator 25 rests on a base plate 26 forming part of frame 5 of unit 1, and is connectable to and pressurised by a compressed-air source (not shown) to lift counterblade 9 into contact with wire 2 with a pressure depending on the pressure in the actuator itself. Counterblade 9 is movable between a top and a bottom limit position shown by the dash lines in Figure 2 and defined respectively by bars 21 contacting respective top stop plates 28 fixed to posts 15, and by bars 21 contacting bar 14. In the work position shown by the continuous line in Figure 2, elements 16 are substantially horizontal; and, within the adjustment range of counterblade 9 as a function of the pressure of actuator 25, the movement of counterblade 9 is substantially similar to a straight vertical translatory movement. The advantages of counterblade assembly 10 according to the present invention will be clear from the foregoing description. In particular, using articulated-parallelogram connecting assemblies 22, counterblade 9 can be connected to fixed structure 13 with no need for conventional runners. This therefore eliminates any problems posed by scale forming in the runners, and, in particular, any jamming of the counterblade or flaws in the paper caused by uneven lift of counterblade 9. Moreover, each counterblade assembly 10 can be removed by simply disconnecting bar 14 from frame 5.

Claims: A counterblade assembly (10) for a wet section (1) of a paper machine, comprising a fixed structure (13) fixed to a frame (5) of the machine; a counterblade (9) connected to said fixed structure (13) and movable, with respect to it, by actuating means (25) to exert pressure on two wires (2, 3) travelling between said counterblade (9) and a guide surface (8) along a substantially horizontal traveling path (P); and connecting means (22) interposed between said counterblade (9) and said fixed structure (13), characterised in that said connecting means (22) are articulated-parallelogram type connecting means and include a plurality of articulated rod elements (16) hinged to said fixed structure (13) and to said counterblade (9) about respective horizontal axes (A, B) perpendicular to said travelling path (P). An assembly as claimed in Claim 1, characterized in that said articulated-parallelogram connecting means comprise a number of connecting assemblies (22) spaced along said counterblade (9); each of said connecting assemblies (22) comprising a first connecting element (15) integral with said fixed structure (13), a second connecting element (21) integral with said counterblade (9) and facing a respective said first connecting element (15), and at least one pair of parallel, articulated rod elements (16), each having a first end (16a) hinged to said first connecting element (15), and a second end (16b) hinged to said second connecting element (21). An assembly as claimed in Claim 2, characterized in that said fixed structure (13) comprises a bar (14) fixed removably to said frame (5) and crosswise to said wires (2, 3); and a number of posts (15) fixed to and projecting from said bar (14) and defining said first connecting elements. An assembly as claimed in Claim 3, characterized in that said second connecting elements are defined by a number of bars (21) fixed to said counterblade (9) and facing respective said posts (15). An assembly as claimed in Claim 4, characterized by comprising, for each said connecting assembly (22), two pairs of rod elements (16) located on opposite sides of said post (15) and said bar (21). An assembly as claimed in any one of the foregoing Claims, characterized in that said counterblade (9) comprises a body (17) of plastic material; and an insert (18) made of ceramic material and cooperating in sliding manner with said wires (2). An assembly as claimed in any one of the foregoing Claims, characterized in that said actuating means (25) are a flexible tubular element located beneath said counterblade (9) and connectable to a compressed-air source.

Inventors: TONELLO FABRIZIO, TONELLO, FABRIZIO
Applicants: PMT ITALIA S P A, PMT ITALIA S.P.A.
Application year: 2001
Main classification: D21F1
IPC codes: D21F1