Device for cleaning a screen in a papermaking plant

Abstract

A device for cleaning the at least one screen in a papermaking plant enables cleaning of the screen that is guided over rollers. The cleaning device has at least one vacuum chamber which bears against the screen. At least one spray nozzle is arranged in the vacuum chamber to transport a cleaning liquid, in particular water, to the screen. The at least one vacuum chamber is arranged radially outside one of the rollers and the screen, in the area of the vacuum chamber, bears on the roller at least over a major part of its length.

Description

BACKGROUND OF THE INVENTION

[0001] Field of the Invention

[0002] The present invention lies in the papermaking field. More specifically, the invention relates to a device for cleaning the at least one screen in a papermaking plant, wherein the screen is guided over rollers, comprising at least one vacuum chamber which bears against the screen and at least one spray nozzle arranged in the vacuum chamber, through which a cleaning liquid, in particular water, can be applied to the screen.

[0003] In plants for producing paper, a fibrous suspension is applied to an intrinsically closed screen (also referred to as a wire, or a forming fabric) that is guided over rollers. Plants are also known wherein two screens are provided, between which the paper web is produced. In all the plants there is the requirement for the at least one screen, in an area wherein it is lifted off the paper web and led back to the start of the plant, to be cleaned from components remaining in and on it, in particular pulp fibers, and to be dried.

[0004] U.S. Pat. No. 6,099,691 to Clarke et al. discloses a device for cleaning the screen (referred to as a forming fabric) of a papermaking plant. There, the device comprises four vacuum chambers, of which in each case two are arranged on both sides of a screen and wherein there are spray nozzles, through which water is sprayed onto both surfaces of the screen, as a result of which the latter is cleaned. The water applied through the spray nozzles is fed from the vacuum chambers to a separator. In addition, the screen is acted on by air in one of the vacuum chambers in order to dry it.

[0005] Such prior art devices for cleaning a screen are, however, afflicted by a number of disadvantages:

[0006] Since vacuum chambers are provided on both sides of the screen, a very great amount of space is necessitated by this device. Since the screen is led through between at least two vacuum chambers, coming into contact with the edges of their entry and exit slots, there is additionally the risk that it will be damaged by the movement over these edges. In addition, there is the requirement to connect the vacuum chambers arranged on both sides of the screen to separate vacuum sources and, in addition, to assign water separators in each case to these. Furthermore, the water applied to the screen by the spray nozzles passes through the screen, carrying the contaminates with it. However, since the predominant proportion of the contaminants is located on that side of the screen on which the paper web rests, this necessitates the water applied to this side of the screen carrying the contaminants through the screen into the vacuum chamber arranged on the other side of the screen. As a result, this cleaning device has a very poor efficiency and/or is relatively expensive in operation.

SUMMARY OF THE INVENTION

[0007] It is accordingly an object of the invention to provide a device for cleaning a screen in a papermaking plant which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type.

[0008] With the foregoing and other objects in view there is provided, in accordance with the invention, a cleaning device for cleaning the at least one screen in a papermaking plant, wherein the at least one screen is guided over a plurality of rollers. The device for cleaning the screen comprises:

[0009] a vacuum device adjoining the screen;

[0010] at least one spray nozzle disposed in the vacuum device and configured to apply a cleaning liquid (e.g., water) to the screen;

[0011] wherein the vacuum device is disposed radially outside one of the rollers, and the screen bears on the one roller in an area of the vacuum chamber at least over a major portion of a length thereof.

[0012] According to the invention, this is achieved in that the at least one vacuum chamber is arranged radially outside one of the rollers, over which the screen is led back to the start of the plant, the screen in the effective area of the vacuum chamber bearing on this roller at least over a major part of its length.

[0013] Therefore, at least one vacuum chamber is provided only on that side of the screen on which the paper web has come to rest and on which the major part of the contaminants is found. By means of the at least one spray nozzle located in this vacuum chamber, the cleaning liquid is sprayed onto the screen resting on the roller, and emerges from the screen again on this side, carrying the contaminants with it. By reducing the number of vacuum chambers provided and the vacuum sources associated with the latter, a decisive constructional simplification is achieved, although the effectiveness of the cleaning is increased. In addition, the operating costs are decisively reduced by this means. Since, in addition, the screen is led over a roller in the area of the at least one vacuum chamber, its movement path is defined, as a result of which the side edges of the vacuum chambers are at a defined distance with respect to that side of the screen on which the paper web comes to rest. By this means, any damage to the screen resulting from the edges of the entry and exit openings of the at least one vacuum chamber is ruled out.

[0014] The at least one vacuum chamber is preferably sealed off with respect to the screen led over the roller by means of sealing strips aligned transversely with respect to the direction of movement of the screen. Furthermore, the screen in the area of the first vacuum chamber preferably bears on the roller over the length of this vacuum chamber. In addition, the angle of the jet direction of the at least one spray nozzle arranged on a spray pipe in the first vacuum chamber is preferably adjustable in the direction of movement of the screen.

[0015] According to a preferred embodiment, at least one second vacuum chamber is provided radially outside the roller in the direction of movement of the screen, in addition to the at least one vacuum chamber. In this case, the screen in the area of the first vacuum chamber can bear on the roller over its entire length, and the area of the screen in the effective area of the at least one second vacuum chamber can bear on the roller over part of its length and be lifted off the roller over a further part of its length.

[0016] The at least one first vacuum chamber and the at least one second vacuum chamber are preferably connected to a common vacuum source via an extraction duct, and, furthermore, control devices are arranged between the at least one first vacuum chamber and the at least one second vacuum chamber and the vacuum source and, for example, are formed as flaps which can be pivoted about axes aligned approximately at right angles, and at least part of the at least one second vacuum chamber is formed with a cross section which increases in size transversely with respect to the direction of movement of the screen. The at least one second vacuum chamber is preferably formed with a height which increases in size transversely with respect to the direction of movement of the screen, at least some of the edges of the walls of the vacuum chambers, assigned to the screen and aligned transversely with respect to the direction of movement of the latter, are sealed off with respect to the screen by means of sealing strips, on their sides associated with the edges of the walls of the vacuum chambers, the sealing strips are formed with preferably T-shaped profiled grooves, by means of which they are pushed onto the edges of the sidewalls of the vacuum chambers, and at least some of the sealing strips are asymmetrical.

[0017] Finally, the spray pipe is preferably formed with needle-jet nozzles and with flat-jet nozzles.

[0018] In further summary, and with the above and other objects in view there is also provided, in accordance with the invention, a papermaking plant, comprising:

[0019] at least one screen for forming a web from fiber pulp;

[0020] a plurality of guide rollers guiding the at least one screen, the guide rollers including a given deflection roller; and

[0021] a cleaning device for cleaning the screen, sead cleaning device including at least one vacuum chamber and at least one spray nozzle disposed in the vacuum chamber and configured to spray a cleaning liquid onto the screen;

[0022] the vacuum chamber being disposed radially outside the given deflection roller, and the screen bearing on the given deflection roller in a vicinity of the vacuum chamber at least over a major portion of a length thereof.

[0023] Other features which are considered as characteristic for the invention are set forth in the appended claims.

[0024] Although the invention is illustrated and described herein as embodied in a device for cleaning the at least one screen in a papermaking plant, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

[0025] The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG. 1 is a schematic illustration of a papermaking plant;

[0027] FIG. 2 is a vertical section, taken along a direction of movement of the screen, through a device according to the invention;

[0028] FIG. 3 is a section taken along the line III-III in FIG. 2 showing the device;

[0029] FIG. 4 is a section of the device taken along the line IV-IV in FIG. 2 and illustrated on a scale that is reduced with respect to FIG. 2;

[0030] FIG. 5 is a magnified view of the detail A diagrammatically indicated in FIG. 2;

[0031] FIG. 6 is a magnified-view of the detail B diagrammatically indicated in FIG. 2;

[0032] FIG. 6A is the detail B in a design variant of the invention; and

[0033] FIG. 7 is a side view of a component of the device;

[0034] FIG. 7A is a plan view thereof; and

[0035] FIG. 7B is a sectional end view of the component.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is shown a plant according to the invention for producing paper. The plant is illustrated with a first screen 1 and a second screen 2. These two screens 1 and 2, which are intrinsically closed (i.e., they are endless belt screens) are moved over a plurality of guide and deflection rollers 11 and 21 associated with them at the same speed of, for example, about 40 m/sec, being led on each other in the area of the rollers 11a and 21a and separately from each other in the area of the rollers 11b and 21b. In the region wherein the two screens 1 and 2 are moved resting on each other, there is provided a spray nozzle 3. Furthermore, a plurality of suction boxes 4 are provided on both sides of the screens 1 and 2. In addition, a further spray nozzle 3a and a suction box 4a are arranged in the further course of the first screen 1. Finally, cleaning device for the two screens 1 and 2 are arranged in the area of the guide rollers 11c and 21c.

[0037] Additional cleaning devices of this kind may be assigned to the first screen and the second screen 2.

[0038] During the operation of the papermaking plant 1, in the area of the two rollers 11a and 21a, the pulp prepared for the production of a paper web is introduced uniformly over the width of the two screens 1 and 2 in the direction of the arrow C between the two screens 1 and 2. By means of the suction boxes 4 that are provided along the two screens 1 and 2, the liquid contained in the pulp is extracted, as a result of which a paper web 6 is formed which, after the second screen 2 has been lifted off the first screen 1, remains on the latter, being dried further by the further suction box 4a. Finally, in the area of a deflection roller 16, it is lifted off the first screen 1 and fed to further processing.

[0039] The spray nozzles 3 and 3a are used to wet the screens 1 and 2 when no pulp is resting on them.

[0040] Since the two screens 1 and 2 have to be cleaned of cellulose fibers and the like adhering to them, the cleaning devices 5 are provided in their further movement paths, and are explained as follows:

[0041] As can be seen from FIG. 2, radially outside the guide roller l1c and at that point of the screen 1 on which the paper web 6 is laid, there are two vacuum chambers 51 and 52 following one after the other in the direction of movement of the screen 1, whose suction openings are sealed off with respect to the screen 1 by means of sealing strips 53, 54 and 55. Inside the first vacuum chamber 51 there is a spray pipe 56 constructed with nozzles 57, via which water can be sprayed onto the associated side of the screen 1. Furthermore, control flaps 62 and 63 are assigned to the vacuum chambers 51 and 52.

[0042] As can further be seen from FIG. 3, a common suction duct 61 is connected to the two vacuum chambers 51 and 52, which leads to a water separator and to a vacuum source. The control flaps 62 and 63 are located at the connection between the suction duct 5 and the two vacuum chambers 51 and 52, it being possible for the control flap 62 to be pivoted about the axis 62a and the control flap 63 to be pivoted about the axis 63a at right angles to the axis 62a. By means of the control flaps 62 and 63, the vacuum prevailing in the chambers 51 and 52 can be controllered. As is additionally indicated by a double arrow D, the spray pipe 56 can be displaced to and fro in an oscillatory manner, the amplitude of the oscillatory movement being approximately equal to the spacing from one another of the spray nozzles 57 provided in the spray pipe 56.

[0043] As can further be seen from FIG. 4, the second vacuum chamber 52 is constructed with a base 52a running obliquely. This ensures that the suction action of the second vacuum chamber 52 is approximately the same over the width of the screen 1.

[0044] As FIG. 5 shows, the screen 1 bears on the roller 11c over its entire length in the suction area of the first vacuum chamber 51. Since, in addition, the spray pipe 56 can be rotated about its longitudinal axis, the direction of the water jets emerging from said spray pipe can be adjusted over the angular range of about &agr;=30° in the direction of movement of the screen 1.

[0045] As can further be seen from FIGS. 5, 6 and 6A, the upper edges of the sidewalls of the vacuum chambers 51 and 52 are profiled in a T-shape, and the sealing strips 53, 54 and 55 are formed with oppositely profiled grooves. By this means, the sealing strips 53, 54 and 55 can be pushed on to the upper edges of the sidewalls of the vacuum chambers 51 and 52. In order to be able to adjust the width of the effective area of the second vacuum chamber 52, the sealing strip 55 is asymmetrical as compared with its groove. Depending on the position wherein the sealing strip 55 is pushed on to the associated sidewall, the effective width of the area of the second vacuum chamber 52 which is effective with respect to the screen 1 can be adjusted with the values s and s1.

[0046] As illustrated in FIGS. 7, 7a and 7b, according to a further embodiment, the spray pipe 56a is constructed with a first group of needle-jet nozzles 57a and a second group of flat-jet nozzles 57b, which are offset with respect to one another in the longitudinal direction of the spray pipe 56a, and whose jets form an acute angle of about 10° with one another. Furthermore, the planes of the jets of the flat-jet nozzles 57b form an angle of about 5° with the plane formed by the jets of the needle-jet nozzles 57a.

[0047] The operation and functionality of the cleaning device 5 will now be explained with reference to the first screen 1:

[0048] The screen 1, which is constructed as an intrinsically closed belt, or an endless belt, is placed over the guide and deflection rollers, 11, 11a, 11b and 11c, bearing on these rollers with that side which does not come into contact with the paper web 6. The cleaning device 5 assigned to the roller 11c has two vacuum chambers 51 and 52 which follow each other in the direction of movement of the screen 1. In the active area of the first vacuum chamber 51, the screen 1 bears completely on the roller 11c, the vacuum chamber 51 being on that side with which the screen 1 is laid on the paper web 6. This is accordingly that side on which the predominant part of the paper fibers and the like are located. The vacuum chamber 51 is sealed off with respect to the screen 1 by means of the sealing strips 53 and 54. Since the screen 1 is guided by the roller 11c, it is ensured that it does not rub on the sealing strips 53 and 54. This is critical because the screen 1 is very susceptible to mechanical damage.

[0049] By means of the spray pipe 56 in the vacuum chamber 51, a cleaning liquid, in particular water, is sprayed onto this side of the screen 1, but does not pass through the screen 1 but instead, because of the centrifugal force which occurs as a result of the deflection of the screen 1 being moved at high speed, emerges again on the same side and is led away via the vacuum chamber 51 and the extraction line 61. Since the cleaning liquid is applied to that side on which the contaminants are found, a very high efficiency is achieved. In order to achieve an optimum cleaning effect, the direction of the jets of the cleaning liquid with respect to the direction of movement of the screen 1 can be adjusted in the range of the angle &agr;. In addition, the spray pipe 56 executes an oscillating displacement transversely with respect to the direction of movement of the screen 1, as a result of which the screen 1 is covered over its entire width by the cleaning liquid. Contaminants are removed from the screen 1 by the cleaning liquid. The screen 1 then passes into the area of the second vacuum chamber 52, which comes to act on said screen between the sealing strips 54 and 55. In this area, the screen 1 rests on the roller 11c only in a first part, whereas it is lifted off the screen 11c in the second part. In this area, firstly the water in the screen 1 is extracted and, secondly, air is sucked in from the outside, as a result of which the screen 1 is dried.

[0050] The action of the vacuum chambers 51 and 52 is controllered by means of the control flaps 62 and 63. Since the second vacuum chamber 52 is constructed with a cross section that widens in the suction direction, a uniform suction action is achieved over the width of the screen 1.

[0051] By means of the needle-jet nozzles 57a, the surface of the screen 1 is cleaned in the first vacuum chamber 51, dirt particles which have been deposited and dried on to said screen being removed there. By means of the flat-jet nozzles 57b, the cavities in the screen 1 are filled with water. In the second vacuum chamber 52, this water is sucked out and, with the latter, the fine particles out of the screen 1.

[0052] A device is therefore provided which, as compared with known cleaning devices, has a simplified constructional design, as a result of which it is cheaper to produce and also takes up less space, which is far more effective and economic and cheaper in operation and wherein damage to the screen which is very susceptible to damage, is avoided to the greatest possible extent.

Claims

1. In a papermaking plant having at least one screen guided over a plurality of rollers, a device for cleaning the screen, comprising:

a vacuum device adjoining the screen;

at least one spray nozzle disposed in said vacuum device and configured to apply a cleaning liquid to the screen;

wherein said vacuum device is disposed radially outside one of the rollers, and the screen bears on the one roller in an area of said vacuum chamber at least over a major portion of a length thereof.

2. The device according to claim 1, wherein said vacuum device comprises at least one vacuum chamber bearing against the screen.

3. The device according to claim 1, wherein the cleaning fluid is water and said spray nozzle is one of a plurality of spray nozzles configured to spray the water onto the screen.

4. The device according to claim 2, which comprises a plurality of sealing strips aligned transversely with respect to a direction of movement of the screen and disposed to seal said at least one vacuum chamber with respect to the screen guided over the one roller.

5. The device according to claim 2, wherein the screen in an area of said vacuum chamber bears on the one roller over an entire length of said vacuum chamber.

6. The device according to claim 2, wherein said spray nozzle is adjustable in terms of an angle of a jet direction in said vacuum chamber in the direction of movement of the screen.

7. The device according to claim 6, which comprises a spray pipe supporting and communicating with said at least one spray nozzle.

8. The device according to claim 1, wherein said vacuum device comprises at least one first vacuum chamber and at least one second vacuum chamber radially outside the one roller, and wherein said second vacuum chamber is disposed, in the direction of movement of the screen, next to said first vacuum chamber.

9. The device according to claim 8, wherein the screen, in an area of said first vacuum chamber, bears on the one roller over an entire length of said first vacuum chamber, and wherein an area of the screen within an effective area of said at least one second vacuum chamber bears on the roller over part of a length thereof, and is lifted off the roller over a further part of the length thereof.

10. The device according to claim 8, which comprises an extraction duct commonly connecting said at least one first vacuum chamber and said at least one second vacuum chamber to a common vacuum source.

11. The device according to claim 10, which further comprises control devices arranged between said at least one first vacuum chamber and said at least one second vacuum chamber and said vacuum source.

12. The device according to claim 11, wherein said control devices include flaps, pivotally disposed about respective axes aligned approximately at right angles.

13. The device according to claim 2, wherein at least a part of said vacuum chamber is formed with a cross section increasing in size transversely to the direction of movement of the screen.

14. The device according to claim 8, wherein at least a part of said first vacuum chamber is formed with a cross section increasing in size transversely to the direction of movement of the screen.

15. The device according to claim 14, wherein said at least one second vacuum chamber is formed with a height increasing in size transversely to the direction of movement of the screen.

16. The device according to claim 8, wherein said vacuum chambers are formed with edges, and a plurality of sealing strips are aligned transversely with respect to the direction of movement of the screen and disposed to seal at least some of said edges of said vacuum chambers against the screen.

17. The device according to claim 16, wherein, on sides associated with sidewall edges of said vacuum chambers, said sealing strips are formed with profiled grooves, by way of which said sealing strips are pushed onto the sidewall edges of said vacuum chambers.

18. The device according to claim 17, wherein said profiled grooves are T-shaped.

19. The device according to claim 16, wherein at least some of said sealing strips are asymmetrical strips.

20. The device according to claim 1, which comprises a spray pipe supporting and communicating with said at least one spray nozzle, and said at least one spray nozzle includes needle-jet nozzles and flat-jet nozzles.

21. A papermaking plant, comprising:

at least one screen for forming a web from fiber pulp;

a plurality of guide rollers guiding said at least one screen, said guide rollers including a given deflection roller; and

a cleaning device for cleaning said screen, sead cleaning device including at least one vacuum chamber and at least one spray nozzle disposed in said vacuum chamber and configured to spray a cleaning liquid onto said screen;

said vacuum chamber being disposed radially outside said given deflection roller, and said screen bearing on said given deflection roller in a vicinity of said vacuum chamber at least over a major portion of a length thereof.