APPARATUS FOR CLEANING A FELT IN A SYSTEM FOR PRODUCING A PAPER WEB

Abstract

An apparatus for cleaning a felt in a system for producing a paper web has a device for introducing a cleaning liquid into the felt and at least one following suction device in the direction of movement of the felt and having a vacuum duct, through which the cleaning liquid is suctioned out of the felt. The suction device between the vacuum duct and the felt is formed with suction ducts, through which the cleaning liquid in the felt is suctioned away. At least one of the suction ducts is assigned an inflatable valve element. In the inflated state of the valve element the suction duct is closed and in its ventilated state the suction duct is opened.

Claims

1. An apparatus for cleaning a felt in a system for producing a paper web, the apparatus comprising: a device for introducing a cleaning liquid into the felt; at least one suction device disposed downstream of said device in a direction of movement of the felt, said suction device having a vacuum duct, through which the cleaning liquid is suctioned out of the felt; said suction device having suction ducts formed therein between said vacuum duct and the felt for suctioning the cleaning liquid away from the felt; and an inflatable valve element assigned to at least one of said suction ducts, said inflatable valve element having an inflated state wherein said at least one suction duct is closed and a ventilated state wherein said at least one suction duct is opened.

2. The apparatus according to claim 1, wherein said at least one suction duct is at least one slot oriented transversely with respect to the direction of movement of the felt, and said valve element is an inflatable hose.

3. The apparatus according to claim 2, wherein said at least one suction duct extends over a width of the felt.

4. The apparatus according to claim 3, wherein said at least one suction duct is a plurality of slots oriented transversely with respect to the felt and adjoining one another.

5. The apparatus according to claim 1, wherein said suction ducts are individual openings.

6. The apparatus according to claim 5, wherein said suction ducts are bore holes.

7. The apparatus according to claim 1, which comprises at least one suction plate affixed to said suction device, said at least one suction plate having said suction ducts formed therein and extending transversely with respect to the felt.

8. The apparatus according to claim 7, wherein said at least one valve element is formed with a projecting strip that is clamped between a housing of said vacuum duct and said suction plate.

9. The apparatus according to claim 8, wherein said at least one valve element is a hose.

10. The apparatus according to claim 7, which comprises at least one supporting strip for said at least one valve element disposed between a housing of said vacuum duct and said suction plate, wherein said valve element is fixed to said supporting strip.

11. The apparatus according to claim 10, wherein said at least one valve element is a hose.

12. The apparatus according to claim 10, wherein said at least one valve element is fixed to said supporting strip by adhesive bonding.

13. The apparatus according to claim 10, which comprises at least one valve plate supported on said supporting strip and having said valve element affixed thereto, said at least one valve plate being adjustable by said valve element to be pivoted by said inflatable valve element into the position closing the associated said suction opening.

14. The apparatus according to claim 10, wherein said supporting strip is screwed to a housing of said vacuum duct, and wherein said suction plate and said supporting strips are formed with grooves and tongues assigned to one another and affixing said suction plate and said supporting strip to each other.

15. The apparatus according to claim 14, wherein said grooves and said tongues are oriented transversely with respect to the felt, and wherein said suction plate is displaceable transversely with respect to the felt.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0026] FIG. 1 shows a schematic illustration of a system for producing a paper web;

[0027] FIG. 2 shows a device, located in the system according to FIG. 1, for introducing a cleaning liquid into felts and a suction device, on a scale enlarged with respect to FIG. 1 and in cross section;

[0028] FIG. 2A shows the suction device according to FIG. 2 on a scale enlarged with respect to FIG. 2 and having a control system assigned thereto;

[0029] FIG. 3, FIG. 3A, FIG. 3B show vertical sections taken through a first embodiment of the suction device according to FIG. 2A on a scale reduced with respect to FIG. 2A and in three different operating positions;

[0030] FIG. 4, FIG. 4A, FIG. 4B show vertical sections taken through a second embodiment of the suction device according to FIG. 2A on a scale reduced with respect to FIG. 2A and in three different operating positions;

[0031] FIG. 5, FIG. 5A, FIG. 5B show vertical sections taken through a third embodiment of the suction device according to FIG. 2A on a scale reduced with respect to FIG. 2A and in three different operating positions.

DETAILED DESCRIPTION OF THE INVENTION

[0032] Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is shown system for producing a paper web. The apparatus has a first system part 1, in which an intrinsically closed wire 11 is guided over deflection rolls 12 and suction boxes 13 that are assigned to the wire 11. On the wire 11 there is a stock material, or pulp, for producing a paper web 10. Water is extracted from the stock material through the suction boxes 13.

[0033] Since the system part 1 is not critical for the present invention, only its end region is illustrated in the drawing. The first system part 1 is adjoined by a second system part 2, 2a, 2b, to which the paper web 10 is transferred.

[0034] Felts 21, 21a, 21b are located in the second system part 2, 2a, 2b. The felts 21, 21a, 21b are guided over deflection rolls 22, 22a, 22b in the direction of the arrows. Each of the felts is intrinsically closed, or endless. In addition, press rolls 23, 23a, 23b, 23c, which are each assigned to one another in pairs, are provided in the system part 2, 2a, 2b. Also provided are tensioning rolls 24, 24a, 24b, over which the felts 21, 21a, 21b are guided and by means of which the felts can be tensioned.

[0035] From the first system part, the paper web 10 is transferred to the felt 21 in the second system part 2, 2a, 2b. Next, the paper web 10 arrives between the felts 21, 21a, with which it is pressed by means of the press rolls 23, 23a, as a result of which moisture in the paper web 10 is given up to the felts 21, 21a. Thereupon, the paper web 10 with the felt 21 passes between the press rolls 23, 23b, by means of which it is pressed with the felt 21. Furthermore, the paper web 10 with the felt 21b passes between the two press rolls 23b, 23c. Thus, moisture from the paper web 10 is given up to the felts 21, 21a, 21b.

[0036] The second system part 2, 2a and 2b is followed by a third system part 3, in which there is a plurality of drying rolls 31, over which the paper web 10 is led, by means of which it is dried further.

[0037] The paper web 10 located on the wire 11 has a dryness of about 20% at the end of the first system part 1. At the end of the second system part 2, 2a, 2b, the paper web 10 has a dryness of about 50% to 55%. In the third system part 3, the paper web 10 is brought to a dryness of about 93%.

[0038] Since it is not only moisture but also foreign materials found in the paper web 10, such as pulp fibers and other paper constituents such as fillers, resins, ash, printer's ink, that are transferred from the paper web 10 into the felts 21, 21a, 21b, there is the need to assign the felts 21, 21a, 21b apparatuses 4, 5 for cleaning the same. The structure and functionality of the cleaning apparatuses 4 and 5 is explained in the following.

[0039] As illustrated in FIG. 2, an apparatus of this type for cleaning a felt 21, 21a, 21b has at least one spraying device 4, 4a for introducing a cleaning liquid into the felt 21, 21a, 21b and, following in the direction of movement of the felt 21, 21a, 21b, at least one suction device 5. In FIG. 2, a first spraying device 4, by means of which a wide jet 41a is applied to the felt 21, 21a, 21b, and a second spraying device 4a, by means of which a narrow jet 41a is applied to the felt 21, 21a, 21b, are illustrated. The application to the felt 21, 21a, 21b is carried out in each case over the entire width of the felt 21, 21a, 21b. The cleaning liquid is composed of water, which is possibly provided with additives such as solvents.

[0040] The suction device 5 has a housing 51 with a vacuum duct 52, in which a negative pressure of −200 millibar to −600 millibar is produced. An opening 53 is provided on the top of the housing 51 which is enclosed by a frame 60 and which is sealed off by a suction plate 54 formed with suction ducts 55, 56, 57. The felt 21, 21a, 21b is moved along the top of the suction plate 54. The suction ducts 56, 57 are assigned valve elements 58, 59, by means of which these two suction ducts 56, 57 can be closed.

[0041] The modes of action of the spraying devices 4, 4a and of the suction device 5 are as follows:

[0042] The felt 21, 21a, 21b is moved past the spraying devices 4, 4a and then past the suction device 5. By means of the spraying devices 4, 4a, a cleaning liquid, which penetrates into the felt 21, 21a, 21b, is applied to the felt 21, 21a, 21b. By means of the at least one suction device 5, this cleaning liquid is drawn out of the felt 21, 21a, 21b to thereby remove foreign materials from the felt 21, 21a, 21b. However, as the operating time increases, more and more proportions of foreign materials remain in the felt 21, 21a, 21b, as a result of which the latter becomes less and less permeable. For this reason, the area of the felt 21, 21a, 21b on which a suction force is exerted by the suction device 5 must be enlarged, in order to be able to carry out effective cleaning of the felt 21, 21a, 21b by means of the cleaning liquid.

[0043] This need is met in that, for the cleaning of a new and thus still very permeable felt 21, 21a, 21b, the suction ducts 56, 57 are closed by means of the valve elements 58, 59, as illustrated in FIG. 2. This ensures that the vacuum which is produced in the vacuum duct 52 and which is required to achieve the necessary suction force can be maintained. However, as soon as the permeability of the felt 21, 21a, 21b decreases on account of the foreign materials remaining in the same, which means that the cleaning force affected by the extracted cleaning liquid is reduced, the area of the suction force acting on the felt 21, 21a, 21b must be enlarged. For this purpose, the valve elements 58, 59 assigned to the suction ducts 56, 57 are brought into the open position thereof, by which means that area of the felt 21, 21a, 21b on which a suction force is exerted is enlarged.

[0044] In the following, by using FIG. 2A, the formation of the suction device 5 and its mode of action are explained further.

[0045] The housing 51 of the suction device 5 is formed on its upper side with the frame 60, which encloses the opening 53. Provided on this frame 60 are supporting strips 61, 62 located at the side of the opening 53, which are fixed to the frame 60 by means of bolts 63. The suction plate 54 and the supporting strips 61, 62 are formed with grooves 54a and tongues 61a, 62a assigned to one another.

[0046] The valve elements 58, 59 are each formed by an inflatable hose, which is rectangular in cross section and which is respectively formed with a laterally projecting flap 58a, 59a, which is located between the frame 60 and the strips 61, 62, by which means the hoses 58, 59 are fixed. The inflatable hoses consist of a rubber or synthetic material, such as ethylene-propylene-diene rubber (EPDM) or of nitrile butadiene rubber (NBR).

[0047] A vacuum pump applies a vacuum to the vacuum duct 52 which is measured by a measuring device 64. The output from the measuring device 64 is led to a control device 65. The hoses 58, 59 can be connected via lines 70, 71 either to a pressurized air pump +P, by which means they are inflatable, or they can be connected to a vacuum pump −P, by means of which they can be vented. For this purpose, two lines 70a, 70b are connected to the line 70, and two lines 71a, 71b are connected to the line 71, the lines 70a, 71a being connected to the compressed air pump and the lines 70b, 71b being connected to the vacuum pump. In the lines 70a, 70b and 71a, 71b there are valves 72a, 72b and 73a, 73b, which are controlled by the control device 65. As soon as the valves 72a, 73a are opened, compressed air is applied to the hoses 58, 59 assigned to the suction ducts 56, 52. As a result, they are inflated, by which means the suction ducts 56, 57 are closed. This is necessary when the permeability of the felt 21, 21a, 21b is still so high that only the suction ducts 55 should be opened to maintain the vacuum in the vacuum duct 52, whereas the suction ducts 56, 57 must be closed.

[0048] However, as soon as the permeability of the felt 21, 21a, 21b to the cleaning liquid has been reduced as a result of the fact that foreign materials are increasingly located in the latter, for which reason that area of the felt 21, 21a, 21b on which the suction force is exerted must be enlarged, the valves 72b, 73b are opened, by which means the hoses 58, 59 are vented. In this way, the suction ducts 56, 57 are opened, by which means suction force is also applied to the felt 21, 21a, 21b through the suction ducts 56, 57.

[0049] On account of the fact that the valve elements are inflatable, being formed in particular by inflatable hoses, those suction ducts which are assigned these valve elements can be opened at any time during the operation of the system for paper production, which means that the difficulties adhering to the known prior art during the opening of further suction ducts are avoided.

[0050] Since the suction plate 54 is formed with grooves 54a and the supporting strips 61, 62 are formed with tongues 61a, 62a assigned to the grooves 54a, the suction plate 54 can be drawn out laterally, by which means the hoses 58, 59 can be mounted in a simple way.

[0051] In the following, by referring to FIG. 3, FIG. 3A, FIG. 3B, the mode of action of such a suction device 5 is explained by using a first embodiment.

[0052] According to FIG. 3, the two hoses 58, 59 have compressed air applied thereto, by which means they are inflated. In this way, the suction ducts 56, 57 are closed. This is necessary when the felt 21, 21a, 21b contains no or only few foreign materials, so it is very permeable for the extraction of the cleaning liquid.

[0053] However, as soon as the felt 21, 21a, 21b contains more and more foreign materials with increasing operating time, as a result of which its permeability to the cleaning liquid is reduced more and more, firstly the hose 58 is vented, which means the suction duct 56 is opened and a suction force is also exerted on the felt 21, 21a, 21b via said suction duct. This operating position is illustrated in FIG. 3A.

[0054] Next, the hose 59 is also vented, by which means the suction duct 57 is also opened and a suction force is also exerted on the felt 21, 21a, 21b via the suction duct 57. This operating position is illustrated in FIG. 3B.

[0055] A second embodiment, changed with respect to FIG. 3, FIG. 3A, FIG. 3B, is illustrated in FIG. 4, FIG. 4A, FIG. 4B. Here, the supporting strips 61, 62 are formed with extensions 61a, 62a, to which the hoses 58, 59 are fixed, for example by adhesive bonding with an adhesive.

[0056] The mode of action of the hoses 58, 59 and the modes of operation thereof are the same as explained by using FIG. 3, FIG. 3A, FIG. 3B.

[0057] In the following, by using FIG. 5, FIG. 5A, FIG. 5B, a third embodiment in the formation of the hoses acting as valve elements is explained. Here, between the suction plate 54 and the supporting strips 61, 62 there are hinge-like elements 80, 82, each having two plates 81, 81a and 83, 83a, which are mounted on axle bolts 81b, 83b. The plates 81, 83 are located between the suction plate 54 and the supporting strips 61, 62 and are fixed in this way. The plates 81a, 83a are pivotable with respect to the plates 81, 83. Between the plates 81a, 83a and the supporting strips 61, 62 there are hoses 58a, 59a. If the hoses 58a, 59a are inflated, the plates 81a, 83a rest on the suction plate 55, by which means the suction ducts 56, 57 are closed. As soon as the hoses 58a, 59a are vented, the plates 81a, 83a are lifted off the suction plate 55, by which means the suction ducts 56, 57 are opened.

[0058] The suction ducts located in the suction plate 55 can be formed by slots extending over the widths of the felts, by a plurality of slots which, overall, extend over the widths of the felts, or by a plurality or a multiplicity of openings, in particular drilled holes, which are arranged over the widths of the felts. Some of these suction ducts are assigned inflatable valve elements, in particular in the form of hoses, by means of which individual suction ducts can be opened.

[0059] The particular advantage of such an apparatus consists in the fact that, on account of the inflatable and deflatable valve elements which are assigned to the suction ducts located in the suction plate, it is possible to open the suction ducts during the operation of the system, in order to be able to apply suction force to enlarged areas of the felts. In this way, it is not necessary to provide a further suction device which is connected as the loading of the felts with foreign materials rises.