WO1998053136A1

WO1998053136A1 - Method and device for improving the efficiency of the paper manufacturing process

Info

Publication number: WO1998053136A1
Application number: PCT/FI1998/000422
Authority: WO
Inventors: Pekka Koskinen; Jari Ristola; Mikko Lakanen
Original assignee: Ev Group Oy
Priority date: 1997-05-23
Filing date: 1998-05-19
Publication date: 1998-11-26
Also published as: FI972195A; AU7530998A; FI972195A0; FI111653B

Abstract

Method for improving the efficiency of the paper manufacturing process, in which method, to cleanse the wire used in the wire section of the paper machine, at least one sudden differential pressure impulse is applied across the wire, said differential pressure impulse being applied to an area of the wire where the web has already been released from the wire, and the interstices in the wire structure are substantially filled with a cleansing medium. The invention also relates to a device for improving the efficiency of the paper manufacturing process, said device being fitted near the wire used in the wire section of a paper machine so that at least one sudden differential pressure impulse is generated across the wire, said device comprising a cleansing strip having a suitable profile, fitted e.g. near the wire surface so that it either touches the wire or bends it, and elements for supplying a cleansing medium to the wire, fitted before the strip, preferably very close to the strip.

Description

METHOD AND DEVICE FOR IMPROVING THE EFFICIENCY OF THE PAPER MANUFACTURING PROCESS

The present invention relates to a method as defined in the preamble of claim 1 that can be used to improve the efficiency of the paper manufacturing process.

By this method, the efficiency of the paper manufacturing process as well as the quality of the paper produced can be improved. By this method, the operation of the wire section of a paper machine can be significantly improved. The method makes it possible to minimise the tendency of the wet wires used in the paper machine to get blocked, maintain an optimal permeability of the wet wires, minimise the amount of noil left on the wire and thereby also to considerably improve the overall efficiency and runnability of the paper machine.

The invention also relates to a device as defined in the preamble of claim 10 for improving the efficiency of the paper manufacturing process.

In prior art, several methods and devices designed for cleansing the wires of a paper machine are known. An example of these is a commonly used solution in which a jet pipe provided with nozzles is fitted transversely over the wire section. The nozzles are typically mounted at distances of 10 cm from each other on the pipe and the pipe is moved transversely by means of an oscillating system to ensure that every part of the wire will get washed with time. The high-pressure jet is generally implemented using needle type nozzles.

Finnish patent application FI 943764 presents a wire cleanser comprising a blast washer extending across the wire transversely to its direction of motion and having two parallel strips extending across the wire transversely to its direction of motion, an anterior strip and a posterior strip, each of which touches the surface of the re- volving endless wire, and between the strips a blast aperture connected to a source of pressurised air, and further a wedge-shaped recess formed between the anterior strip and the wire and tapering in the direction of motion of the wire, into which wedge- shaped recess the water spraying device directs a water jet, the blowing device and the water spraying device being placed on opposite sides of the wire.

Finnish patent application FI 924175 presents a wire cleanser comprising a blast washer with two parallel strips extending across the wire transversely to its direction of motion and forming a leading strip and a trailing strip, both of which touch the surface of the wire, and between the strips a blast gap connected to a source of pressurised air, and a wedge-shaped recess formed between the leading strip and the wire and tapering in the direction of motion of the wire, a water jet being directed into said wedge-shaped recess.

However, there are considerable problems and drawbacks associated with the prior- art solutions. Prior-art washers consume plenty of energy (e.g. pressurised air) and they are often incapable of cleansing the wire sufficiently, leaving between the wire fabrics e.g. noil, which cannot be removed by a high-pressure jet. This may lead e.g. to changes in the permeability of the wire, which means that the paper web is no longer uniformly dehydrated. It has also been established that the power needed to run the wire is increased due to this phenomenon. Results of the same nature have been observed in the wet wire sections of several paper machines. Because of its op- erating principle, a high-pressure jet may also produce grain-direction irregularity in the wet wire.

Therefore, the object of the present invention is to minimise the problems of prior-art technology. It is also an object of the present invention to eliminate the drawbacks of prior-art technology and to create a completely new type of solution for keeping the wet wire of a paper machine clean.

In this application, 'interstices in the wire structure' refers to a portion of the wire structure that does not contain its structural material.

The invention is based on the idea of generating at least one sudden differential pressure impulse across the wire during its motion while at the same time the interstices in the wire structure are substantially filled with a cleansing medium, preferably over a sufficient width simultaneously.

In more precise terms, the invention is mainly characterised by what is presented in the characterisation part of claim 1.

The device of the invention is mainly characterised by what is presented in the characterisation part of claim 10. According to a preferred embodiment of the invention, a device as provided by the invention is fitted in a portion of the wire section of the paper machine where the web being produced has already been released and, by means of said device, at least one sudden differential pressure impulse is generated across the wire during its mo- tion while at the same time the interstices in the structural material of the wire are substantially filled with a cleansing medium, preferably simultaneously over a sufficient width along a given line. Such a differential pressure impulse is preferably a negative pressure impulse on the paper side of the wire. According to the present state of knowledge, an advantageous arrangement regarding the equipment is one in which a so-called cleansing strip having an appropriate profile is fitted near the paper side surface of the wire so that it comes close enough to the wire for the wire motion to produce a negative pressure impulse, and in which the elements for supplying water to the wire are disposed before the strip in the direction of wire motion, preferably very close to the strip. According to the invention, the cleansing effect can be enhanced if two successive sudden differential pressure impulses in opposite directions are generated across the wire during its motion while at the same time the interstices between the structural material of the wire are substantially filled with cleansing medium, preferably over the entire width of the wire. In this case, the differential pressure impulses are produced by first generating a positive pressure impulse and immediately thereupon a negative pressure impulse. By the agency of these differential pressure impulses, the solids between the fabrics of the wire structure can be sort of agitated by subjecting them to successive force impulses acting in opposite directions, thus contributing towards releasing the solids. The time interval between the differential pressure impulses must be very short to produce a sufficient effect. This interval between the differential pressure impulses is about 0.05 - 2 ms, preferably 0.05 - 0.75 ms.

According to a preferred embodiment of the invention, the interstices in the wire structure are filled with a cleansing medium mainly consisting of water via nozzles, which preferably produce a fan-shaped flow pattern, while the machine is running and when cleansing is needed or desired, and the wire is so sprayed with the cleansing medium that substantially all the interstices and other free spaces in it are filled with the cleansing medium, such as water or other desired liquid, the jet of cleansing medium being so regulated that some of the jet, but not all of it, passes through the wire. In this manner, the cleansing effect can be optimised and applied to both surfaces of the wire, but with a higher power on that side where the negative pressure impulse is applied. The mechanical arrangement of the invention producing a rela- tively short negative pressure impulse, such as a strip, may be shorter in the transverse direction of the machine than the width of the wire, in which case it is provided with a traversing system that moves the mechanical arrangement or a part of it across the wire in its transverse direction. Preferably, however, the strip is substantially of the same width with the wire, so the cleansing effect extends across the whole width of the wire at the same time.

The cleansing strip is preferably so designed and fitted that the motion of the wire moving in close proximity to it produces on its trailing side between the wire and the strip a negative pressure proportional to the wire speed. According to the invention, cleansing medium, such as water or other desired liquid or a mixture of these, is applied to the wire so that at least the side of the wire facing the strip is saturated with water to a sufficient depth in the thickness direction of the wire to allow a differential pressure impulse as provided by the invention to be generated. The wire is preferably so treated with cleansing medium that substantially all interstices and other free spaces in it are filled with the cleansing medium.

To implement a method whereby two successive sudden differential pressure impulses in opposite directions are produced across the wire, the strip is so designed that it will first produce a positive pressure impulse and then a negative pressure impulse as the wire is moving over it. To produce such an effect, the edge of the cleansing strip is preferably somewhat rounded or otherwise shaped in a corresponding manner so that, as the wire is passing over it, a positive pressure impulse is created in the wire, and, furthermore, the strip is provided with an appropriate clear- ance angle. It has been established that a suitable clearance angle is about 0.5 - 1.5°. In addition to this or alternatively, the strip may also be provided with a stepped profile change.

The cleansing medium, such as an aqueous liquid, can be supplied e.g. via nozzles known in themselves, disposed forward of the strip. However, an arrangement deemed preferable at present is to provide a basin-like structure just before the strip, from where a continuous layer/mat of water is passed to the wire. With such a solution, a controlled flow regulation and dosage and handling of the cleansing medium can be accomplished.

By applying the invention, significant advantages can be achieved. By such a method, the operation of the wire section of a paper machine can be significantly im- proved. The method makes it possible to maintain an optimal permeability of wet wires, minimise the retention of noil in the wire and thus also to considerably improve the efficiency and runnability of the paper machine. The invention can be applied directly to replace the currently used high-pressure jets or in parallel with high- pressure jets to remove the noil concentrated in the wire circulation, which cannot be removed from the wire by using high-pressure jets alone.

In the following, the invention will be described in greater detail by the aid the attached drawings, in which Fig. 1 presents a preferred embodiment of the invention, in which a device according to the invention has been fitted in conjunction with the wire section of a paper machine,

Fig. 2 presents a preferred embodiment of the invention, Fig. 3 presents another preferred embodiment of the invention, Fig. 4 presents yet another preferred embodiment of the invention,

Fig. 5 presents a another preferred embodiment of the invention, Fig. 6 presents yet another preferred embodiment of the invention, Fig. 7 presents yet another preferred embodiment of the invention, Fig. 8 presents yet another preferred embodiment of the invention, Fig. 9 presents yet another preferred embodiment of the invention,

Fig. 10 presents another preferred embodiment of the cleansing strip.

Fig. 1 presents a diagram representing the wire section 10 of a paper machine. If consists of a so-called lower wire unit 11 and an upper wire unit 12. Of course, the con- struction of the wire section of a paper machine may vary considerably, and the apparatus and method of the invention can be applied to any type of paper machine. In the wire section of a paper machine as illustrated by Fig. 1, a web is formed from stock supplied from the head box 13 to the paper side of the wire in the lower wire unit. In this type of wire section, the paper side is the upper side of the wire.

In paper manufacture, the web is formed in the wire section by distributing the stock uniformly over the wire surface. In the wire section, water is drained from the web mechanically through the wire by various known means. An inevitable result of this manner of dehydration is that some of the paper raw material is separated from the web itself, and this material is either completely removed with the water or some of it is left sticking to the wire. The material remaining in the wire is naturally harmful to the manufacturing process, which is why various methods are applied to remove it from the wire and to keep the wire clean. A common solution is to use an oscillating high-pressure water jet 14 to cleanse the wire. However, this solution has recently been found to be inefficient and it has been established that its use may even produce harmful effects. The example in Fig. 1 shows a wire cleanser 500 according to the invention for cleansing the wire, fitted in conjunction with the so-called lower wire unit 1 1 to cleanse the wire. In this case, the wire cleanser has been fitted on the paper side of the lower wire unit so that it touches the wire at a point in its return path, i.e. after the web has been released from the wire and passed on to the press section. In this example, the wire cleanser of the invention has been adjustably mounted on the supporting structures of the machine or on a base rail. The adjustment may be implemented as manual adjustment, in which case it is of a single-operation type nature. The adjustment can also be implemented as an automatic system controlled by a suitable control quantity. Such a control quantity might consist of e.g. one or more of the following: wire tension, so-called wire retention, wire permeability, machine speed, service life of the wire, distance of the device.

Fig. 2 presents a preferred embodiment of the invention. The wire cleanser 500 shown in Fig. 2 comprises a supporting beam 501 extending across the whole width of the wire and is further mounted e.g. on the supporting structures of the paper ma- chine, preferably adjustably as stated above. The wire cleanser presented here comprises a cleansing strip 502 similarly extending substantially across the whole width of the wire 503. The device is fitted in the immediate vicinity of the wire 503. It may be so fitted that the cleansing strip 502 only touches the wire 503, or in some cases, if necessary or desired, the cleansing strip 502 may also bend the wire 503 at a desired angle. Provided in conjunction with the supporting beam is a first space 504, into which a cleansing medium can be supplied via a connection 505 while the machine is in operation and when cleansing is needed or desired. The cleansing medium, which preferably contains at least water, can be passed from the first space into a second space 506 via flow equaliser elements 507 connecting the first and second spaces. In the case of Fig. 2, the flow equaliser elements consist of one or more apertures of suitable size. Placed ahead of the cleansing strip 502 as seen in the direction of wire motion is a stopper strip 508 for stopping the cleansing medium. The stopper strip is so disposed that the cleansing medium surface in the second space 506 between the cleansing strip and the stopper strip can be brought to a suitable level to allow the wire to be thoroughly filled with cleansing medium as provided by the invention. This second space, delimited by the stopper strip and the cleansing strip and other parts, forms a basin-like structure through which cleansing medium can be applied to the wire. The stopper strip is preferably separated from the wire by a clearance of 0.5 - 10 mm, most appropriately 1 - 5 mm, whereas the cleansing strip preferably touches the wire.

In the solution presented in Fig. 2, the stopper strip consists of a strip having a suitable rounded profile, with a T bar inserted into it. The stopper strip may also be adjustably mounted, in which case the distance of the stopper strip can be adjusted e.g. according to the pressure of the cleansing medium used or e.g. according to the running speed of the machine, such adjustment being indicated by the arrow shown in the figure. As the wire is moving past the stopper and cleansing strips, cleansing medium will penetrate into it. When a given part of the wire meets the cleansing strip, the solid material in its interstices is subjected to forces due to a momentary increase in the pressure of the cleansing medium (positive pressure impulse), and further, when this part passes the cleansing strip, the solid material in the interstices of the wire is subjected to substantially opposite forces due to a momentary decrease in the pressure of the cleansing medium (negative pressure impulse). Thus, this solid material undergoes a kind of rapping treatment and is released from the wire as a result of the momentary pressure decrease, the negative pressure impulse. The negative pressure impulse has a duration at least equal to the positive pressure impulse, but pref- erably 1 -2 times as long.

Fig. 3 presents a wire cleanser 500 corresponding to the solution in Fig. 2. For the sake of clarity, reference numbers corresponding to Fig. 2 are used in Fig. 3 as well. The stopper strip 508 in Fig. 3 has been made of a tubular element extending through the length of the cleansing strip in the same direction with the device. In this case the supporting beam is also somewhat differently constructed than in the solution presented in Fig. 2. In principle, the solution in Fig. 3 works like the one in Fig. 2.

Fig. 4 presents a slightly different solution according to the invention. In Fig. 4, too, reference numbers corresponding to those in Fig. 2 are used for the sake of clarity. In Fig. 4, the stopper strip 508 has been made of a tubular element extending through the length of the cleansing strip in the same direction with the device. In the embodiment illustrated by the figure, disposed in conjunction with the stopper strip is a first space 504, into which a cleansing medium can be supplied via a connection 505 while the machine is in operation and when cleansing is needed or desired. The cleansing medium, which preferably contains at least water, can be passed from the first space into a second space 506 via flow equaliser elements 507 connecting the first and second spaces. In the case of Fig. 4, the flow equaliser elements consist of one or more apertures of suitable size in the stopper strip structure. In this solution, it is possible to use a supporting beam of a lighter construction than e.g. in the solution according to Fig. 2.

Fig. 5 shows a slightly different solution according to the invention. However, for the sake clarity, reference numbers corresponding to those in the other figures are used in this case as well. The wire cleanser 500 presented in Fig. 5 comprises a supporting beam 501 which is further mounted e.g. on the supporting structures of the paper machine, preferably adjustably as stated above. The wire cleanser presented here comprises a cleansing strip 502 preferably extending substantially across the whole width of the wire 503. The device is fitted in the immediate vicinity of the wire 503. It may be so fitted that the cleansing strip 502 only touches the wire 503, or in some cases, if necessary or desired, the cleansing strip 502 may also bend the wire 503. Disposed in conjunction with the supporting beam in the immediate vicinity of the cleansing strip (distance preferably <lm) in the direction of wire motion is a cleansing medium distributing system, which in this embodiment is a pipe 510 provided with suitable elements for applying the cleansing medium to the wire. In this embodiment, the pipe 510 is provided with nozzles 511 preferably so fitted that they form a fan-shaped flow pattern. With the machine running and when cleansing is needed or desired, cleansing medium is supplied via the pipe 510 and sprayed into the wire so that substantially all the interstices and other free spaces in it are filled with the cleansing medium, such as water or other desired liquid. Especially in a method of the invention implemented according to the embodiment illustrated by Fig. 5, the jet of cleansing medium is preferably so regulated that some of the jet, but not all of it, penetrates the wire 512.

Fig. 6 presents another preferred embodiment of the invention, in which, however, reference numbers corresponding to those in the other figures are used for the sake clarity. The wire cleanser 500 presented in Fig. 6 likewise comprises a supporting beam 501 which is further mounted e.g. on the supporting structures of the paper machine, preferably adjustably as stated above. The wire cleanser presented here comprises a cleansing strip 502 preferably extending across the whole width of the wire 503. The device is fitted in the immediate vicinity of the wire 503. It may be so fitted that the cleansing strip 502 only touches the wire 503, or in some cases, if necessary or desired, the cleansing strip 502 may also bend the wire 503. This embodiment corresponds to the embodiment in Fig. 5 in operation, but it additionally com- prises a deaeration system fitted in conjunction with the apparatus. The deaeration system comprises a suction beam 521, which in this embodiment surrounds the cleansing strip 502. The verges of the suction beam lie near the wire 503 before and after the cleansing strip 502 and the beam is provided in this area with sealing ele- ments 522, which may be e.g. strips of ceramic or plastic material, preferably extending across the whole width of the suction beam. The suction beam is also provided with a deaeration arrangement 520 for passing the air from the suction beam to further treatment. Fitted in the suction beam are also elements 523 for draining the suction beam of any liquid that may get into it / be condensed in it. With this solu- tion, the aqueous mist that could otherwise gather around the cleanser device can be minimised. The suction beam may also be fitted to draw air and/or mist only from the trailing side of the cleansing strip if so desired or required. This embodiment provides an additional advantage in situations where a high-pressure jet is used.

Fig. 7 presents a preferred embodiment of the invention. The wire cleanser .500 presented in Fig. 7 comprises a supporting beam 501 which is further mounted e.g. on the supporting structures of the paper machine, preferably adjustably as stated above. The wire cleanser presented here comprises a cleansing strip 502 preferably extending across the whole width of the wire 503. The device is fitted in the immediate vi- cinity of the wire 503. It may be so fitted that the cleansing strip 502 only touches the wire 503, or in some cases, if necessary or desired, the cleansing strip 502 may also bend the wire 503. As to its basic solution, the embodiment in Fig. 7 corresponds to the one in Fig. 2, but the device additionally comprises elements 530 for changing the direction of the liquid jet coming forth from the cleansing strip and/or for smoothing the flow. In the solution presented in this figure, the elements are placed in the area of cleansing strip action on the trailing side in the direction of wire motion relatively close to the wire. The elements comprise a guide plate preferably of a length corresponding to the cleansing strip, serving to direct the liquid flow downward. In this case this is an advantageous direction, but of course the liquid flow can be directed to some other direction if required or desired. The verge of the guide plate lies near the wire 503 after the cleansing strip 502 and is provided in this area with a sealing element 532, which in this case is a tube with a round surface. The space between the cleansing strip and the stopper strip is preferably sealed at the ends with sealing blocks 531. Although the figure does not show it, this solution can also be provided with a suction system between elements 530 and beam 501, so that the humid air, which may carry some cleansing medium, is removed by suction while at the same time part of the liquid flow is directed downward by elements 530. Fig. 8 presents an embodiment in which the method of the invention is applied using a traversing device. The device has a widthways dimension smaller than the wire width and it is movably fitted near the wire using a so-called traverser system. Fitted near the wire 503 is a supporting beam 510, in whose guidance a wire cleanser 500 comprising a cleansing strip 502 can be moved in a direction transverse to the wire by using a separate gear known in itself. In this solution, one zone of the wire is cleansed at a time, but in the long run the entire wire is cleansed.

Fig. 9 presents a preferred embodiment in which the method of the invention is applied from the top side of the wire to the under side. In Fig. 9, the wire cleanser 500 comprises a supporting beam 501 which is further mounted e.g. on the supporting structures of the paper machine, preferably adjustably as stated above. The wire cleanser presented here comprises a cleansing strip 502 preferably extending across the whole width of the wire 503. The device is fitted in the immediate vicinity of the wire 503. It may be so fitted that the cleansing strip 502 only touches the wire 503, or in some cases, if necessary or desired, the cleansing strip 502 may also bend the wire 503. Disposed in conjunction with the supporting beam in the immediate vicinity of the cleansing strip in the direction of wire motion is a cleansing medium distributing system, which in this embodiment is a pipe 510 provided with suitable elements for applying the cleansing medium to the wire. In this embodiment, the pipe 510 is provided with nozzles 511 preferably so fitted that they form a fan-shaped flow pattern. With the machine running and when cleansing is needed or desired, cleansing medium is supplied via the pipe 510 and sprayed into the wire so that substantially all the interstices and other free spaces in it are filled with cleansing medium, such as water or other desired liquid. In a method of the invention implemented according to the embodiment illustrated by Fig. 9, the jet of cleansing medium is preferably so regulated that some of the jet, but not all of it, penetrates the wire 503. Fitted in conjunction with the apparatus is a deaeration system, which comprises a suction beam 521, which in this embodiment has been arranged to draw air by suction from the trailing side of the cleansing strip 502. The suction beam is so disposed that its verge lies close to the wire 503 after the cleansing strip 502 so that the suction effect of the suction beam is applied to an area close to the cleansing strip. The device also comprises a stopper strip 508 placed before the cleansing strip in the direction of motion of the wire 503. The suction beam is also provided with a deaeration arrangement 520 for passing the air from the suction beam to further treatment. Fitted in the suction beam are also elements 523 for draining the suction beam of any liquid that may get into it / be condensed in it. With this solution, the amount of aqueous mist gathering around the cleanser device can be minimised.

Fig. 10 presents a preferred embodiment of the cleansing strip of the invention, and an example profile of the differential pressure impulses produced by the cleansing strip in the wire being cleansed. The wire 503 touches the cleansing strip 502 or is bent as it passes over it, undergoing, according to the invention, at least one sudden differential pressure impulse in a part of the wire where the web has already been released and the interstices in the wire structure are substantially filled with cleansing medium.

With a cleansing strip as illustrated by Fig. 10, two successive sudden differential pressure impulses in opposite directions are applied to the wire during its motion while at the same time the interstices in its structure are substantially filled with cleansing medium over a sufficient width. The differential pressure impulses are produced by first generating a positive pressure impulse and immediately after it a negative pressure impulse. In this way, by means of the differential pressure impulses, the solids in the interstices of the wire structure can be agitated by subjecting them to successive forces acting in opposite directions, thus contributing towards releasing the solids. The edge 550 of the strip 502 that meets the wire is preferably of a rounded shape, ensuring that the first positive pressure impulse will be effective, and the strip is further provided with a clearance angle 551 or a step 552 (depicted with a broken line). Fig. 10 also shows an adjustably fitted stopper strip 508.

The following example gives a good idea of the efficiency of the invention. A feature characteristic of the method of the invention is that it makes use of the running speed of the machine, i.e. the velocity of the wire. The table shown above presents a theoretic negative pressure impulse that can be produced in the wire by the method and device of the invention for cleansing the wire. Even at the current running speeds (500 - 750 m/min) of cardboard machines, fairly intensive pressure impulses can be achieved without a separate external energy source. At the running speeds (1000- 1250) of paper machines, a momentary negative pressure as high as over 2 bar can be achieved.

By using the device of the invention, it is possible to produce a differential pressure impulse applied to the wire whose duration of action is preferably about 0.5 - 7 ms, depending on the speed of the machine.

Although the invention has been described here in the light of certain embodiments, it can naturally be applied to other types of solutions. The invention is not to be construed as being limited to the examples presented in this description, but instead all solutions obvious to the person skilled in the art as defined in the following claims are possible.

Claims

1. Method for improving the efficiency of the paper manufacturing process, characterised in that, in the method, cleansing medium is applied to the wire so that interstices in the wire structure are substantially filled with cleansing medium, and to cleanse the wire used in the wire section of the paper machine, at least one sudden differential pressure impulse is generated across the wire, said differential pressure impulse being applied to a wire area where the web has already been released from the wire.

2. Method as defined in claim 1, characterised in that two successive sudden differential pressure impulses in opposite directions are gen- erated across the wire during its motion while at the same time the interstices in its structure are substantially filled with cleansing medium, preferably over a sufficient width simultaneously.

3. Method as defined in claim 2, characterised in that the differential pressure impulses are implemented by first generating a positive pressure impulse and immediately thereafter a negative pressure impulse, said differential pressure impulses serving to agitate the solids between the fabrics of the wire structure by subjecting them to successive forces acting in opposite directions, thus con- tributing towards releasing the solids.

4. Method as defined in claim 3, characterised in that the time interval between the differential pressure impulses is 0.05 - 2 ms, preferably 0.05 - 0.75 ms, and the negative pressure impulse is at least equal to the positive pressure impulse in duration, but preferably 1 - 2 times as long.

5. Method as defined in any one of claims 1 - 3, characterised in that the differential pressure impulse(s) is/are generated on the paper side of the wire.

6. Method as defined in any one of claims 1 - 3, u characterised in that the differential pressure impulse(s) is/are generated on the inner side of the wire.

7. Method for improving the efficiency of the paper manufacturing process as de- fined in claim 1 , characterised in that the interstices in the wire structure are filled with a cleansing medium mainly consisting of water via a basin-like structure fitted just before the strip, from where a continuous layer/mat of water is passed to the wire across its entire width.

8. Method for improving the efficiency of the paper manufacturing process as defined in claim 1 , characterised in that the interstices in the wire structure are filled with a cleansing medium mainly con- sisting of water via nozzles (511), which preferably form a fan-shaped flow pattern, while the machine is running and when cleansing is needed or desired, and the wire is so sprayed with the cleansing medium that substantially all the interstices and other free spaces in it are filled with the cleansing medium, such as water or other desired liquid, and the jet of cleansing medium is preferably so regulated that some of the j et, but not all of it, penetrates the wire (512).

9. Method for improving the efficiency of the paper manufacturing process as defined in claim 1 , characterised in that in conjunction with the generation of the differential pressure impulse or after it, mist produced in conjunction with the generation of the differential pressure impulse is drawn away by suction along with air from the vicinity of the wire.

10. Device for improving the efficiency of the paper manufacturing process, said de- vice being fitted near the wire used in the wire section of a paper machine, characterised in that the device comprises at least one cleansing strip having an appropriate profile and fitted e.g. near the surface of the paper side of the wire so that at least one sudden differential pressure impulse is generated across the wire, and that the device comprises elements for supplying water to the wire, said elements being fitted before the strip, preferably very close to the strip.

11. Device as defined in claim 10 for improving the efficiency of the paper manufacturing process, characterised in that the cleansing strip extends substantially across the whole width of the wire, and it comprises elements for supplying cleansing medium over the entire width of the wire so that the action of the cleansing medium will cover the whole wire width simultaneously.

12. Device as defined in claim 10 for improving the efficiency of the paper manu- facturing process, characterised in that the cleansing strip is preferably so shaped that the strip is provided with a clearance angle or step, said clearance angle being preferably about 0.5 - 1.5┬░, so that the motion of the wire moving past it at close proximity will produce a negative pressure proportional to the velocity of the wire between the wire and the strip on the trailing side of the strip as seen in the direction of wire motion.

13. Device as defined in claim 10 for improving the efficiency of the paper manufacturing process, characterised in that the edge of the cleansing strip is rounded or otherwise appropriately shaped so that the motion of the wire moving past it at close proximity will produce a positive pressure impulse on the entry side of the strip in the direction of wire motion as the wire is passing over it.

14. Device as defined in claim 10 for improving the efficiency of the paper manufacturing process, characterised in that the edge of the cleansing strip is rounded or otherwise appropriately shaped so that, as the wire is moving over it, a positive pressure impulse is applied to the wire, and the strip is provided with a clearance angle or a step, so that the motion of the wire moving past it at close proximity will produce a negative pressure proportional to the velocity of the wire between the wire and the strip on the trailing side of the strip as seen in the direction of wire motion.

15. Device as defined in claim 12 or 14 for improving the efficiency of the paper manufacturing process, characterised in that the height of the step is about 0.5 - 2 mm.

16. Device as defined in claim 13 for improving the efficiency of the paper manu- facturing process, characterised in that the device comprises nozzles for the application of cleansing medium to the wire on the anterior side of the strip.

17. Device as defined in claim 10 for improving the efficiency of the paper manufacturing process, characterised in that the device comprises a basin-like structure disposed just before the strip, from where a continuous layer/mat of water can be passed to the wire, said basin-like structure being delimited preferably on two sides by the cleansing strip and a stopper strip.

18. Device as defined in claim 10 for improving the efficiency of the paper manufacturing process, characterised in that the device (500) comprises a cleansing strip (502) preferably extending across the entire width of the wire (503) and a deaeration system comprising a suction beam (521), the verges of which suction beam lie close to the wire (503) at least after the cleansing strip (502) and are provided in this area with sealing elements (522) fitted close to the wire and preferably consisting of ceramic or plastic strips or equivalent and preferably extending across the entire width of the suction beam, said suction beam being provided with a deaeration system (520) designed to draw air from the suction beam and pass it on to further treatment, as well as elements (523) for draining the suction beam of liquid that may get into it / be condensed in it.

19. Device as defined in claim 10 for improving the efficiency of the paper manufacturing process, characterised in that the device (500) comprises a supporting beam (501) preferably extending across the whole width of the wire and elements (530) for changing the direction of the liquid jet coming forth from the cleansing strip and/or for smoothing the flow, placed in the area of the cleansing strip action on the trailing side in the direction of wire motion relatively close to the wire, preferably comprising at least a guide plate or equivalent of a length corresponding to the cleansing strip, said guide plate serving to change the direction of the liquid flow, e.g. to direct it downward.

20. Device as defined in claim 17 for improving the efficiency of the paper manu- facturing process, characterised in that the stopper strip is adjustably fitted to the cleanser device.

21. Device as defined in claim 10 for improving the efficiency of the paper manu- facturing process, characterised in that the widthways dimension of the device is smaller than the width of the wire and the device is movably fitted near the wire using a so-called traverser system.