GB2174120A - Twin wire guiding apparatus - Google Patents

Abstract

Twin wires 13, 14 of a twin wire papermaking machine are guided by guiding apparatus comprising a drainage tank 19 above the upper wire 13 and a flexible plate 21 supported on inflatable bellows 22 below the wire 14. Pressure on the web 18 passing between tank 19 and plate 21 may be varied such that it increases in the direction of travel. A travelling endless wire (91, Figure 9) may be arranged between wire 14 and plate 21. The top of the plate may be provided with slots (52, Figure 5) or bars (62, Figure 6) in a direction transverse to the direction of travel of the wires. A double plate arrangement (71, 72, Figure 7) with openings in the uppermost plate leading to chambers therebetween to which suction can be applied may also be used. The flexible plate may be displaced by pistons (82, Figure 8) or floats (114, Figure 10). <IMAGE>

Description

SPECIFICATION Apparatus for guiding the screens of a paper or cardboard machine The invention relates to apparatus for guiding the screens, particularly of a double screen part, of a paper or cardboard machine of the type comprising at least one supporting table, such as a drainage tank or the like, over which the screens run, and a screen track opposite the supporting table on the other side of the screen, which can be moved in the direction perpendicular to the screen plane.

In US-PS 3,595,744 apparatus is described in which the lower screen runs over a supporting table of several drainage tanks disposed in the direction of travel of the screen one behind the other and extending over the width of the screen. The opposite upper screen is guided over a web which is also formed of several drainage tanks. These are flexibly coupled to one another and suspended on a supporting beam with the facility of adjusting their height.

This support beam is also connected to a fixed support and its height may be adjusted by joints. The screen track, which with the supporting table limits a gap having a wedge-shaped cross section in the direction of travel, may vary its contour by raising or lowering the individual drainage tanks. The lift of the screen track as a whole in the direction perpendiculay to the screen plane is limited with respect to too great deflection as a function of the desired track thickness issuing from the gap by stops between the supporting beam and the fixed support. On the other hand the screen track is able to yield in the direction towards the lower screen. In the event of increased material feed into the wedge-shaped gap or if the material is wet-beaten, conditions may arise in which the paper web coming out of the gap is not sufficiently drained.Because of the limitation of the lift of the track, the material suspension then flows back inside the gap, which results in faults and crushing in the laminated structure.

The object of the invention is to create simply designed apparatus which is consequently cheap to manufacture, of the type referred to above, the shape of which automatically adjusts to varying amounts of material suspension of different drainage capacity between the screens and exerts a freely selectable drainage pressure on the material suspension.

The object is solved by the features characterised in patent claim 1.

The solution is advantageous inasmuch as tracks can be manufactured from one plate with little expense, can be assembled or exchanged quickly and because of their elasticity do not form any unstable transitions in the event of variable deflection. The elasticity of the plate allows a yielding of the track in accordance with the respective gap width required between the two screens. Thereby the chosen drainage pressure is retained in a region which does not destroy the web being formed and enables economic drainage. Moreover in accord ante with requirements this pressure can be selected at varying heights during the progress of the track, i.e. it can be increased progressively in the direction of travel of the screen. Furthermore it is also possible to adjust the drainage pressure at right angles to the direction of travel of the screen.

Expediently the plate consists of a material with high resistance to wear and corrosion, for example plastic, such as polyurethane, or metal, such as stainless steel, bronze or the like (Claim 2).

The resilience of the plate in the direction of travel of the screen can be influenced by ridges disposed on the screen side on the plate and running mutually spaced at right angles to the direction of travel of the screen (Claim 3). These ridges can be formed by slits in the plate (Claim 4). Also the plate can be equipped with ridges fixed thereto (Claim 5). In the last case, with regard to the wear by the screen moving over them, the ridges can consist of a particularly suitable material, such as ceramics, for example.

The track may also serve to drain the material suspension supplied between the screens of the double screen part if the track consists of two plates moving parallel to one another, of which the plate on the screen side is slit or perforated and is connected to the plate turned away from the screen by spacers running at right angles to the direction of travel of the screen (Claim 6). The spacers consequently limit chambers extending between the two plates at right angles to the direction of travel of the screen, to which underpressure of a suitable height can be applied.

The object of the invention mentioned at the beginning is also solved by the characterising features of Claim 7. This solution is also distinguished advantageously from the solution according to Claim 1 in that tracks of various length can simply be formed by corresponding grouping of the ridges and can be adapted to altered conditions. Moreover it is possible to exchange damaged ridges without difficulty.

In accordance with another refinement the adjacent ridges interlock so that they can in fact deflect perpendicular to the screen plane, however with the return movement in the direction towards the supporting table none of the ridges can protrude out of the plane of the ridge side turned towards the screen or damage the screen (Claim 8).

By connecting the ridges with floats a particularly simple construction of the device according to the invention is achieved and the uplift of the floats is exploited to adjust the pressure on the associated screen (Claim 9).

The division of the water tank into chambers separated one from the other has the purpose of varying the pressure of the associated ridges over the progress of the track by filling the individual chambers with water to different levels (Claim 10).

To adjust the pressure on the screens of the double screen part, it is completely adequate if the pressure-exerting members act on the edges of the track running in the direction of travel of the screen, which then has to be constructed resistant to bending at right angles to the direction of travel of the screen, for example by ribs disposed at the side turned away from the screen (Claim 11).

However the pressure-exerting members can also act on the entire track, each member only working on one segment of the track (Claim 12). Hereby the pressure on the material suspension between the screens of the double screen part can be adjusted particularly sensitively not only in the direction of travel of the screen, but also at right angles to the direction of travel if necessary.

Cushions, membranes, piston-cylinder units or the like, which can be acted upon by a pressure medium, are suitable as pressure-exerting members (Claim 13). Expediently this is implemented with a pressure cushion by chambers extending at right angles to the direction of travel of the screen (Claim 14).

If, in accordance with a further refinement of the track, the ridges are constructed hollow and have suction slits open against the screen, the material suspension enciosed between the two screens can also be drained to the side of the track (Claim 15).

In order to prevent wear on the track side of the screen, a flexible belt, a screen or the like, which rotates in the direction of travel of the screen, can be disposed between the screens of the double screen part and the track (Claim 16).

Exemplified embodiments of the invention are explained in more detail below by means of drawings. They show: Figure 1 a segment of a double screen part of a paper machine having a device to guide the screens, this device consisting of a drainage tank assigned to the upper screen and a plate on the side of the lower screen and resting on pressure cushions, which forms a screen track, as the first exemplified embodiment, Figure2 a cross section along line Il-Il in Figure 1 through the drainage tank and the screen track, Figure 3 a cross section according to Figure 2, but with a plurality of pressure cushions running at right angles to the direction of travel of the screen and bearing the plate of the screen track, as second exemplified embodiment, Figure 4a cross section according to Figure 2 with a plate as the track, which is only supported at the edge on pressure cushions and moreover is reinforced by rigs, as the third exemplified embodiment, Figure 5a segment of a plate as screen track having slits running at right angles to the direction of travel of the screen, as the fourth exemplified embodiment.

Figure 6 a segment of a plate as screen track having ridges thereon, which etend at right angles to the direction of travel of the screen, as fifth exemplified embodiment, Figure 7a cross section of a screen track segment of two plates, of which the upper is perforated and connected by spacers to the lower plate, as sixth exemplified embodiment, Figure 8a cross section of a screen track segment the plate of which is borne by pistons guided in cylinders, as seventh exemplified embodiment, Figure 9 a view of the double screen part according to Figure 1 having a screen to prevent wear, which rotates between the screens guiding the material suspension and the screen track, as eighth exemplified embodiment, Figure 10 a segment of a double screen part according to Figure 1 having a device to guide the screens, this consisting of a drainage tank assigned to the upper screen and a water tank with floats on the side of the lower screen, which bear ridges forming a screen track, as ninth exemplified embodiment, Figure 11 a cross section along line ll-ll in Figure 10 through the drainage tank and the water tankwith the screen track, Figure 12 a view of the double screen part according to Figure 1, wherein however the ridges of the screen track rest on pressure cushions borne by a support tank, as tenth exemplified embodiment, Figure 13 a cross section through a ridge constructed hollow having a suction slit open against the screen, as eleventh exemplified embodiment on a larger scale, and Figure 14 a cross section of a track segment having ridges of the track interlocking on the foot side, as twelfth exemplified embodiment, on a larger scale.

The segment shown in Figures 1 and 2 of a double screen part 10 of a long screen paper machine (not shown) has an upper screen 13 running around two screen guide rollers 11 and 12 and also a lower screen 14. Both screens 13 and 14, the direction of travel of which is shown by arrows 15,18, form a wedge-shaped gap 17, which tapers in the direction oftravel. To drain the material suspension 18 inserted between the two screens 13 and 14, between the screen guide rollers 11 and 12 is disposed a drainage tank 19, against which the upper screen 13 is supported.

On the other hand the lower screen 14 runs over a track 20, which, as the first exemplified embodiment formed by a plate 21 approximately the size of the area of the drainage tank 19. The plate 21 rests on a plurality of pressure cushions 22 disposed one behind the other in the direction of travel of the screen 16 and extending at right angles to the direction of travel of the screen over the entire plate thickness, the said cushions being supported on a fixed bed 23. The pressure cushions 22 consist of respectively a rubber bellows, which can be acted on by a pressure medium, such as compressed air.

Thereby the pressure cushions exert a pressure on the plate 21 increasing from the screen feed side to the outlet side. The pressure can be adjusted individuallyforeach pressure cushion 22 and/or for groups of pressure cushions. Because the plate 21 is designed elastically flexible, as it consists of plastic, for example polyurethane, or of metal, such as bronze, ittransfersthis pressure to the screens 13 and also 14 and the material suspension 18 inserted between them. In contrast, the plate 21 can deflect in the direction perpendicular to the screen plane against the constant resistance of the pressure cushions 22. The drainage tank 19 and the screen track 20 form a device for guiding the screens 13 and l4ofthe double screen part 10, with which adjustable pressure on the material suspension 18 increasing in the direction of travel of the screen can be exerted.

In the following exemplified embodiments the same reference numbers are used insofar as they relate to similar components or other similar information.

The exemplified embodiment shown in Figure 3 of a screen track 30 differs from the preceding one only in that the pressure cushions 31 following one another in the direction of travel of the screen are also dissected at right angles to the direction of travel of the screen. Consequently it is also possible to adjust the pressure on the material suspension 18 at right angles to the direction of travel of the screen.

In the exemplified embodiment of a screen track 40 according to Figure 4, the plate 41 is only supported with its edges running in the direction of travel of the screen on pressure cushions 42, which sit on associated beds 43. In the intermediate area the plate 41 is provided with ribs 44 extending at right angles to the direction of travel of the screen.

The plate 41 is consequently flexible in the direction of travel of the screen, but on the other hand is resistant to bending at right angles to the direction of travel of the screen.

Figure 5 shows the segment of a relatively thickwalled plate 51 as the track 50, in which a plurality of ridges 53 are formed by slits 52 running at right angles to the direction of travel 16 of the screen. This increase the elastic flexibility of the plate 51 in the direction of travel 16 of the screen.

In the exemplified embodiment according to Figure 6 the plate 61 of a track 60 is constructed with thin walls. On the screen side it bears a plurality of ridges 62 disposed spaced one from the other and extending at right angles to the direction of travel 16 of the screen, which are fixed to the plate in a way not shown, e.g. by glueing.

In the exemplified embodiment according to Figure 7 to the thin-walled plate 71 of a track 70 a second plate 72 running parallel is assigned on the screen side. The connection between the two plates 71 and 72 is produced in the form of narrow bars by a plurality of spacers 73 disposed evenly spaced one from the other and running at right angles to the direction of travel 16 of the screen. The plate 72 assigned to the lower screen 14 is provided with openings 74 which are connected with chambers 75 formed between the plates 71 and 72 by the spacers 73. By using underpressure at the chambers 75 the material suspension 18 can therefore be drained through the lower screen 14 and the openings 74. By the use of elastically deformable components this type of construction is also sufficiently elastically flexible in the direction perpendicular to the screen plane.

In the exemplified embodiment of a track 80 shown in Figure 8, on the side of the plate 81 turned away from the screen acts a plurality of pistons 82, the cylinders 83 of which are combined to form one component which is supported against the bed 23.

The pistons 82 extending at right angles to the direction of travel 16 of the screen are acted upon with compressed air and exert an adjustable pressure on the elastically flexible plate 81.

The exemplified embodiment of a double screen part 90 according to Figure 9 differs from that according to Figure 1 only in that between the screen track 20 and the lower screen 14 a screen 91 also rotates. To guide this screen 91 a guide roller 92 and 93 respectively is arranged infront of and behind the track 20. By the suitable choice of material the screen 91 decreases the wear on the lower screen 14, but without reducing the effect of the plate 21 on the material suspension 18.

The segment of double screen part 100 shown in Figures 10 and 11 as a further exemplified embodiment corresponds above the lower screen 14 with the segment according to Figure 1. On the side opposite the drainage tank 19 there is a water tank 111 having several chambers 113 separated by partitions 112 and open at the top. In these chambers 113 are guided several floats 114which can be moved in the direction perpendicular to the screen plane. These act from below on an elastic supporting layer 115, which at the top tightly seals the water tank 111. On the supporting layer 115 sit ridges 116 extending over the screen width and lying close to one another. To each float 114 is assigned a ridge 116, which consists of a wear-resistant material, such as ceramics or plastic. The ridges 116 form a track 110, against which the lower screen 14 is supported.

The individual chambers 113 of the water tank 111 are filled to different heights with water. Hereby upward forces of varying magnitudes effective on the floats 114 are transferred to the individual ridges 116 which exert a corresponding pressure on the lower screen 14 and the material suspension 18. By filling the chambers 113 with water to different levels, this pressure can be varied in accordance with requirements. As is shown in Figure 10, in the direction of travel the water level in the chambers 113 and consequently the pressure increases by steps against the end of the gap 17. By inserting further partitions 112 into the water tank 111 the adjustment of the pressure can be even finer.The pressure of the ridges 116 can also be automatically adjusted by means of a control system, the water level in the chambers 113 of the water tank 111 being varied as a function of the quantity and drainage capacity of the material suspension 18 supplied.

Changes in position of the lower screen 14 in the direction perpendicular to the screen plane can be followed by the ridges 116 because of the elasticity of the supporting layer 115, without the pressure exerted by the ridges differing substantially. Thereby the supporting layer 115 consisting of a reinforced rubber blanket, for example, prevents the penetration of screen water and material particles into the water tank 111.

In the exemplified embodiment of a double screen part segment 120 shown in Figure 12, there are differences according to Figure 10, for example, only in that the ridges 116 are supported by interposing the elastic supporting layer 115 on several pressure cushions 121 running at right angles to the direction of travel 16 of the screen, which rest on a supporting tank resistant to bending 122. Instead of several pressure cushions 121, an individual cushion may also be used which has chambers extending at right angles to the direction of travel of the screen. By filling the pressure cushions 121 with air at different pressures the effect of the ridges 116 of the screen track 125 on the lower screen 14 and the material suspension 18 can be varied.

In the rectangular cross section of a ridge 130 shown in Figure 13 this ridge is provided with a hollow space 131 which has a suction slit 132 open at the screen side. By connecting the hollow space 131 of the individual ridges 130, from which the track 110 according to Figure 10 or 125 according to Figure 12 can be assembled, to an appliance producing underpressure, the screen track can also be used to drain the material suspension.

The ridges 53 and 62 according to the exemplified embodiments according to Figures 5 and 6 can also be constructed in the form of the ridge 130 and accordingly used to drain the material suspension.

In the segment of a track 140 shown in Figure 14, as can be used in the exemplified embodiments according to Figures 10 and 12,the ridges 141 sitting on an elastic supporting layer 115 are provided with a recess 143 along one longitudinal side 142. Along their other longitudinal side 144 the ridges 141 have a projection 145 which engages suitably in the recess 143 of the adjacent ridge. if the sides 146 of the ridges 141 turned toward the lower screen 14 run in one plane, the respective projection 145 lies at the recess 143 of the neighbouring ridge at the top (left half of Figure 14). The ridge 141 respectivelyfollowing in the direction of travel 16 of the web can therefore not project over the preceding ridge up out of the track 140. As the projection 145 of ridges 141 points against the direction of travel 16 of the web, the ridges however may deflect in steps perpendicular to the screen plane, without a longitudinal edge of the ridges projecting against the approaching lower screen 14 protruding from the track 140 (right half of Figure 14).

Claims (9)

1. Apparatus for guiding the screens of a double screen part of a paper or cardboard machine, of the type comprising at least one supporting table, such as a drainage tank or the like, over which the screens run, and also having a screen track opposite the supporting table on the other side of the screen, which can be moved in the direction perpendicular to the screen plane, characterised in that the track (20) consists of at least one elastically flexible plate (21), on whose side, turned away from the screen, of a deflection of a plate resistance-producing members (22l act, the pressure of the said members on the plate being adjustable individually and/or in groups.

2. Apparatus according to Claim 1, characterised in that the plate (21) is of plastics, e.g. polyurethane or metal (Figure 1).

3. Apparatus according to Claim 1, characterised in that on the screen side ridges (53; 62) running at rightangles to the direction of travel (16) of the screen are disposed on the plate (51; 61) mutually spaced (Figure 5 and 6).

4. Apparatus according to Claim 3, characterised in that the ridges (53) are formed by slits (52) in the plate (51) (Figure 5).

5. Apparatus according to Claim 3, characterised in that the ridges (62) are fixed on the plate (61) (Figure 6).

6. Apparatus according to Claim 1, characterised in that the track (70) consists of two plates (71,72) running parallel, of which the plate (72) on the screen side is slit or perforated and is connected by spacers (73) running at right angles to the direction of travel (16) of the screen with the plate (71) turned away from the screen (Figure 7).

7. Apparatus for guiding the screens of a double screen part of a paper or cardboard machine, of the type com- at least one supporting table, such as a drainage tank or the like, over which the screens run, and a screen track opposite the supporting table on the other side of the screen, which consists of elements connected to one another, which can be moved in the direction perpendicular to the screen plane, characterised in that the track (110) is formed by ridges (116) lying close to one another and extending over the screen width, on whose side, turned away from the screen, of a deflection ofthe ridges act resistance-producing members (114), whose pressure can be adjusted to the ridges individually and/or in groups (Figure 10).

8. Apparatus according to Claim 7, characterised in that each ridge (141) has a recess (143) along one longitudinal side (142), in which recess a projection (145) of the neighbouring ridge engages, the projection coming to rest in the recess on the screen side if the side (146) of the ridges turned towards the screen lie at least approximately in one plane (Figure 14).

9. Apparatus for guiding the wires of a twin-wire forming section of a paper or cardboard machine constructed, arranged and adapted for use substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

9. Apparatus according to Claim 7, characterised in that the ridges (116) sit at the top on pressureexerting members in the form of floats (114), which are guided in a water tank (111), a float being assigned to each ridge (Figure 10).

10. Apparatus according to Claim 9, characterised in that the water tank (111) has chambers (113) for the floats (114) separated from one another (Figure 10).

11. Apparatus according to Claim 1 or 7, characterised in that the pressure-exerting members (42) act on the edges of the track (40) running in the direction of travel of the screen, which is constructed resistant to bending at right angles to the direction of travel of the screen (Figure 4).

12. Apparatus according to Claim 1 or7, characterised in that the pressure-exerting members (31) act on the entire track (30), each member only working on one segment of the track (Figure 3).

13. Apparatus according to Claim 1,7, 11 or 12, characterised in that the pressure-exerting members are formed by cushions (22; 31; 42; 121) which can be acted upon by a pressure medium, membranes, piston-cylinder units (82, 83) or the like (Figure 1,3, 4,8 and 12).

14. Apparatus according to Claim 1, characterised in that pressure cushions (121) have chambers extending at right angles to the direction of travel of the screen (Figure 12).

15. Apparatus according to one of Claims 3 - 5,7 - 9, characterised in that the ridges (130) are constructed hollow and have suction slits (132) open against the screen (Figure 13).

16. Apparatus according to Claim 1 or 7, characterised in that between the screens (13, 14) of the double screen part and the track (20) a flexible belt, screen (91) or the like rotates in the direction of travel of the screen (Figure 9).

17. Apparatus for guiding the screens of a doublue screen part of a paper or cardboard machine constructed, arranged, and adapted for use substantially as herein before described with reference to the accompanying drawings.

Amendments to the claims have been filed, and have the following effect; (a) Claims 1-17 above have been deleted (b) New or textually amended claims have been filed as follows: CLAIMS

1. Apparatus for guiding the wires of a twin wire forming section of a paper or cardboard machine, having at least one forming board, such as a dewatering box or the like, over which the wires run, and a wire track opposite the forming board on the other side of the wire, which consists of elements connected to one another, and which can be moved in the direction perpendicular to the wire plane, characterised in that the track (24; 34; 54) is formed of strips (23; 40; 50) which are flexibly fixed, lie close to one another and extend over the wire width, on whose side, turned away form the wire, of a deflection of the strips act resistance-producing members (21; 31), the pressure on the strips of which can be adjusted individually and/or in groups.

2. Apparatus according to Claim 1, characterised in that each strip (50) has a recess (52) along one longitudinal side (51), in which a projection (55) of the adjacent strip engages, the projection coming to rest in the recess on the wire side, if the side (56) of the strips turned towards the wire lie at least approximately in one plane (Figure 5).

3. Apparatus according to Claim 1, characterised in that the strips (23) sit at the top on pressureexerting members in the form of floats (21), which are guided in a water tank (18), one float being assigned to each strip. (Figures 1 and 2).

4. Apparatus according to Claim 3, characterised in that the water tank (18) has chambers (20) separated from one another for the floats (21) (Figures 1 and 2).

5. Apparatus according to Claim 1, characterised in that the pressure-exerting members are formed by cushions (31) or the like, which can be acted upon by a pressure medium (Figure 3).

6. Apparatus according to Claim 5, characterised in that the pressure cushion (31) has chambers extending at right angles to the direction of travel of the wire (Figure 3).

7. Apparatus according to one of Claims 1 to 3, characterised in that the strips (40) are constructed hollow and have suction slits (42) open against the wire (Figure 4).

8. Apparatus according to Claim 1, characterised in that between the wires (13, 14) of the twin wire forming section (60) and the track (34) a flexible belt, wire (61) or the like rotates in the direction of travel of the wire (Figure 6).