METHOD AND DEVICE FOR WASHING THE DRYING WIRE IN A PAPER OR BOARD MACHINE

Abstract: The invention concerns a method for washing the drying wire in a paper or board machine, in which method the drying wire is washed and/or dried by means of a liquid and/or air jet (V, I) when the drying wire (F) runs in a dryer group in the dryer section of a paper machine while guided by drying cylinders (10), reversing rolls (11) or equivalent and by guide rolls (12). In the method, a washing liquid jet (V) is applied to the drying wire (F) when the drying wire (F) runs substantially downwards from a drying cylinder (10) and/or when the drying wire (F) runs towards the next reversing roll (11) or equivalent or towards a guide roll (12). Further, the invention concerns a device for washing the drying wire in a paper machine, which device (14, 16, 17, 18, 20, 21, 22, 23, 24, 25) is placed in a dryer group in the dryer section in the paper machine and which device comprises means for producing a liquid jet and/or an air jet (V, I) so as to wash and/or to dry the drying wire (F), respectively. The device is placed in the dryer section in the paper machine in the vicinity of the drying wire (F) so that the means for producing the liquid jet (V) direct the liquid jet towards the drying wire (F) when the wire runs substantially downwards from a drying cylinder and/or substantially before the drying wire (F) runs onto the next reversing roll (11) or guide roll (12) or equivalent.

Description: Method and device for washing the drying wire in a paper or board machine The invention concerns a method for washing the drying wire in a paper or board machine, in which method the drying wire is washed and/or dried by means of a liquid and/or air jet when the drying wire runs in a dryer group in the dryer section of a paper machine while guided by drying cylinders, reversing rolls or equivalent and by guide rolls. Further, the invention concerns a device for washing the drying wire in a paper or board machine, which device is placed in a dryer group in the dryer section in the paper machine and which device comprises means for producing a liquid jet and/or an air jet so as to wash and/or to dry the drying wire, respectively. As is known from the prior art, in multi-cylinder dryers in paper machines twin-wire draw and/or single-wire draw are/is employed. In twin-wire draw the groups of drying cylinders include two wires, which press the web, one from above and the other one from below, against the heated cylinder faces. Between the rows of drying cylinders, which are usually horizontal rows, the web has free and unsupported draws, which are susceptible of fluttering, which may result in web breaks, in particular as the web is still relatively moist and, therefore, of low strength. This is why, recently, increasing use has been made of said single- wire draw, in which there is just one drying wire in each group of drying cylinders, the web running on the support of said wire through the whole group so that the drying wire presses the web on the drying cylinders against heated cylinder faces and, on the reversing cylinders or rolls between the drying cylinders, the web remains at the side of the outside curve. Thus, in single-wire draw, the drying cylinders are placed outside the wire loop, and the reversing cylinders or rolls inside the wire loop. As is well known, in the dryer sections in paper machines, both dryer groups with single-wire draw and dryer groups with twin-wire draw are frequently employed. The properties required from the drying wires, which are usually made of textile fabric, are different depending on the mode of operation concerned, i.e. single-wire or twin- wire draw. Thus, in single-wire draw, the function of the wire is to support the paper web as a what is called closed draw. Also, the wire supports the paper against the face of the drying cylinder. In order that the paper could be kept in contact with the wire in single- wire draw, various grooved and/or suction rolls can be used as well as blow- suction boxes which produce a vacuum between the cylinders and rolls, such as the stabilizers marketed by the applicant with the trade mark "Uno-Run" . Owing to the above, a permeability within certain limits is required from the wire. When a new wire is acquired, it is possible to choose the permeability, but it is often problematic to make the permeability remain within certain limits, because the wire is contaminated during operation. Since the mechanical service life of a wire is long (about one year), the wire is expensive, and the replacement of the wire always requires a standstill, various wire washing devices are used in order to maintain the permeability of the wire. In the prior-art applications, the washing devices are placed on a free, so-called returning portion of the wire. This is why the washing liquid can spread over a wide area onto the machine, in which case a wide area can be contaminated and become wet by the effect of splashing, and the washing device can be employed at a very low running speed of the machine only. Moreover, the prior-art wire washing devices wash just a part of the wire width at a time. Also, frequently the spacing/oscillation of the nozzles in the washing device is so slow that the device would have to be operated in normal paper running, which is difficult to arrange because of the splashing of liquid. In twin-wire draw, besides good support on the cylinders, a function of the wire is to take care of the ventilation of the so-called pocket space, i.e. to carry away the evaporating liquid out of the closed space formed by the paper and the wire. As is the case also in single- wire draw, this function requires that the permeability of the wire is retained as long as possible. The problems of the prior-art washing devices in connection with twin-wire draw are the same as in connection with single-wire draw applications. With respect to different devices for washing of drying wires and related arrangements, which are in themselves known, reference can be made, for example, to the Patents FI-67,593, FI-60,045, and US-3, 910,815. Thus, the object of the present invention is to provide a system for washing of drying wires that is free from the problems discussed above. In view of achieving the objectives stated above and those that will come out later, the method in accordance with the invention is mainly characterized in that, in the method, a washing liquid jet is applied to the drying wire when the drying wire runs substantially downwards from a drying cylinder and/or when the drying wire runs towards the next reversing roll or equivalent or towards a guide roll. On the other hand, the device in accordance with the invention is mainly character¬ ized in that the device is placed in the dryer section in the paper machine in the vicinity of the drying wire so that the means for producing the liquid jet direct the liquid jet towards the drying wire when the wire runs substantially downwards from a drying cylinder and/or substantially before the drying wire runs onto the next reversing roll or guide roll or equivalent. One of the essential features of the arrangement of the present invention is, for example, the location of the washing device so that the washing liquid can be separated from the wire as quickly and efficiently as possible, i.e. the device is placed in a location in which the wire runs downwards and in which the centrifugal force produced by a reversing roll or equivalent can be utilized. Further, the device is preferably placed as near the well of the machine as possible, in which case possible splashes, if any, do not wet the machine over a wide area or do not wet the machine at all. According to d e invention, the washing device can operate in combination with a runnability, air-conditioning or any other device (for example a doctor). The device may also be placed on the rising side of the wire if lack of space or any other reason requires that. According to the invention, in applications with single-wire draw, the washing device is placed so that, preferably, the run of the wire at the time at which the washing liquid is applied to the wire is downwards towards the bottom, and the centrifugal force of the revolving reversing roll facilitates the separation of the liquid from the wire. The washing device is preferably placed in the beginning of the drying group, whereby the time of drying of the wire on the cylinders is maximized. The dimensioning and the construction of the washing device are arranged such that, besides at a crawling speed, the device can expressly also be used at a normal running speed of the paper machine when running without paper. In such a case, it is possible to use short break standstills for washing, and the washing area of the device is chosen as covering the whole width of the wire or as oscillating with a certain spacing over the entire wire width. The best result is often obtained when die washing of the wire takes place from the paper side. In such a case, the washing device is preferably placed below a cylinder between the rolls. In this location, as a rule, there is a doctor of the cylinder and/or an air-conditioning pipe that blows fresh air to underneath the machine, or equival- ent. The washing device can be constructed as a separate device or by attaching it to a doctor/air-conditioning pipe, or by constructing it in their interior. In such a case, for example, oscillating direct pressure washing can be used. Moreover, cleaning and/or drying of the drying wire by means of compressed air can be placed in this area. The location most suitable for washing the rear side is the portions between a cylinder and a roll. As a rule, the portion arriving from a cylinder onto a roll is used, because in such a case, e.g., the following advantages are obtained: — the wire pumps the liquid down, — the centrifugal force of the revolving roll facilitates the removal of the liquid downwards right on the first roll, — the nip formed by the wire and by the roll forces any liquid that remains at the side of the device to pass through the wire. The washing can be inten¬ sified or the removal of the liquid out of the wire be promoted by means of blowing of air, by blowing air before the nip, into the nip, or to the opposite (i.e. rising) side, — this mode of washing can also be used for cleaning a grooved or perforated roll, or for cleaning a grooved or perforated roll it is possible to use a separate device provided for the rolls. In a suitable location of the washing device, there is often a blow-suction box that stabilizes the run of the web. In such a case, the washing device is constructed in connection with it either separately or as attached to it or as built-in. The blowing air generated by the blow-suction boxes can be used for said nip blowing. If the geometry of the machine is so congested that the washing device cannot be placed near the nip of the roll, the device is placed higher at a suitable location before the wire meets the cylinder. Various combinations of the paper-side and rear-side wire washing and drying devices described above are also included in the scope of the present invention. In groups with twin- wire draw, the preferred location of the device for washing the upper wire is at the beginning of the drying group before the first upper cylinder or at the end of the dryer group after the last cylinder when the last cylinder is an upper cylinder. If there is a stabilizer or equivalent in said location, the washer is constructed by attaching the washer to it or by constructing them together. In order to obtain economies of time, the washing device in each dryer group can be operated at the same time. On the other hand, in order to minimize the cost of equipment, it is possible to wash the wires one after the other. Also, it is possible to make the operation of the equipment fully automatic, and, if necessary, the device can be connected to the logic system of the machine. Further, it is possible to arrange the desired timing of the washing process of each individual wire, i.e. the sequence and the duration, for example pre- washing - chemical washing - rinsing. The use of chemicals can be arranged to the washing liquid, or the chemicals can be applied directly to the wire by means of a separate device. Compressed-air blowing can be used as an aid for the liquid and/or for wire drying. In the following, the invention will be described in more detail with reference to the figures in the accompanying drawing, the invention being, however, not supposed to be strictly confined to the details in said illustrations. Figures 1 and 2 are schematic illustrations of exemplifying embodiments of a drying- wire washing arrangement in accordance with the invention, wherein the washing device is placed in connection with an air-conditioning device. Figures 3, 4 and 5 are schematic illustrations of some exemplifying embodiments of an arrangement in accordance with the invention, wherein the washing device is placed in connection with a blow-suction box. Figure 6 is a schematic illustration of an exemplifying embodiment wherein the machine has a compact geometry, in which case the washing device is placed in a location before the wire reaches contact with the cylinder. Figure 7 is a schematic illustration of an exemplifying embodiment in which, in a dryer group that makes use of twin- wire draw, the washing device is fitted in connection with the upper wire on the wire portion after the last drying cylinder in the group. Figure 8 is a schematic illustration of an exemplifying embodiment in which, in a dryer group that makes use of single- wire draw, air drying has been employed in addition to the washing device. Figure 9 is a schematic illustration of an exemplifying embodiment in which a water collecting trough has been provided in connection with the washing device. Fig. 1 shows an exemplifying embodiment of the invention in a dryer group with normal single- wire draw in the dryer section of a paper machine, wherein the wire F runs from the reversing roll 11 onto the drying cylinder 10 and further onto the next reversing roll or equivalent 11. The sense of rotation of the drying cylinder 10 is denoted with the reference arrow S. The situation shown in the figure is taken from the washing stage, in which no paper web runs on support of the wire F. In the opening nip of the first reversing roll 11, a blow box 15 is placed, from which compressed air I is blown into the opening nip. Below the drying cylinder 10, in connection with the air-conditioning device 13, a washing device 14 is placed, from which pressurized liquid (arrow V) is sprayed towards the wire F that runs over the latter reversing roll 11 , and air (arrow I) is blown towards the wire F that runs over the former reversing roll 11. The exemplifying embodiment shown in Fig. 2 is similar to that shown in Fig. 1, except that in this exemplifying embodiment, out of the blow box 15 placed in the opening nip, besides into the nip, air is also blown perpendicularly against the wire F (arrows I). The washing device 14 placed in connection with the air-conditioning device 13 sprays liquid in the way indicated by the arrow V towards the wire F that runs over the following reversing roll 11 and air in the way indicated by the arrow I towards the wire F that runs over the preceding reversing roll 11. A blow box 15 is also placed in connection with the latter reversing roll 11 , by means of which blow box air I is blown into the closing nip. In the exemplifying embodiment shown in Fig. 3, likewise, a dryer group is con¬ cerned which makes use of normal single-wire draw and in which the drying cylin- ders are denoted with the reference numeral 10 and they revolve in the sense indicated by the arrows S. In this arrangement, the wire F is cleaned from its rear side, and the washing device is combined wim a blow-suction box 16. In accordance with the arrow V, towards the wire F, on its run from the drying cylinder onto the reversing roll 11, liquid is sprayed, and into the nip closing at the reversing roll 11, both liquid and air are sprayed (arrow V;I). In Fig. 4 an exemplifying embodiment similar to Fig. 3 is shown for washing the rear side of the wire F, wherein the washing device has been combined with a blow- suction box 17. Onto the wire arriving on the reversing roll 11 liquid is sprayed peφendicularly to its run from the drying cylinder 10 onto the reversing roll 11 and into the nip closing at the reversing roll 11. From the washing device 17, air is blown into the nip that opens from the reversing roll 11 as well as peφendicularly to the run of the wire F from the reversing roll 11 onto the drying cylinder 10. In the exemplifying embodiment shown in Fig. 5, likewise, washing of the rear side of the wire F is concerned, and in this arrangement the washing device 18 has been arranged as a separate unit 18 in connection with the blow-suction box 19. The pressure-liquid jets are denoted with the arrows V, and the air blowing with the arrow I. The exemplifying embodiment shown in Fig. 6 is related to a dryer group with a compact geometry in the dryer section of a paper machine, in which case the nip of the roll cannot be used as the location of the washing device, but the device is placed at a higher location before the wire F reaches contact with the cylinder. From the washing device 18, pressurized liquid V is blown towards the wire F on its run from the guide roll 12 to the reversing roll 11. Fig. 7 shows an exemplifying embodiment for a group with twin- wire draw in the dryer section of a paper machine, wherein the washing device is placed after the last upper cylinder 10 in the group, where the washing device has been constructed as a device 20 combined with a stabilizer device. The pressure-liquid jet is denoted with the reference arrow V and the air jet with the reference arrow I. In the exemplifying embodiment shown in Fig. 8, the wire F washing device 21 has been arranged below an upper cylinder 10 in a dryer group that uses single- wire draw, underneath a doctor 13, and by means of the washing device 21 liquid is sprayed in the way indicated by the arrow V towards the wire F on its run onto the reversing roll 11. The washing device 21 is also provided with blowing of air, which is indicated by the arrow I, which blowing of air I dries the wire F. Fig. 8 also shows alternative or additional drying devices 22,23,24, by whose means air is blown, as is indicated by the arrows I, towards the wire F so as to dry me wire. The drying is preferably arranged as close as possible to the location at which the wire F is subjected to liquid washing, arrow V, but the entire gaps between the cylinders and rolls in the dryer group are available for the location of the drying devices. Fig. 9 is a schematic illustration of an exemplifying embodiment in which a water collecting trough 26 has been provided in connection with the wire F washing device 25, into which trough the major part of the washing liquid that was used can be passed and out of which trough the water can be passed further to the desired drain pipe 28, such as the sewer. The water collecting trough 26 can be shifted for the time of normal running away from the opemng between the washing device 25 and the wire F, for example, by means of a pneumatic cylinder 27 or an equivalent actuator. Above, the invention has been described with reference to some preferred exemplify¬ ing embodiments of same only, the invention being, yet, not supposed to be strictly confined to the details of said embodiments. Many variations and modifications are possible within the scope of the inventive idea defined in the following patent claims.

Claims: Claims 1. A method for washing the drying wire in a paper or board machine, in which method the drying wire is washed and/or dried by means of a liquid and/or air jet (V,I) when the drying wire (F) runs in a dryer group in the dryer section of a paper machine while guided by drying cylinders (10), reversing rolls (11) or equivalent and by guide rolls (12), characterized in that, in the method, a washing liquid jet (V) is applied to the drying wire (F) when the drying wire (F) runs substantially downwards from a drying cylinder (10) and/or when the drying wire (F) runs towards the next reversing roll (11) or equivalent or towards a guide roll (12). 2. A method as claimed in claim 1, characterized in that, in a dryer group that makes use of single-wire draw, a washing liquid jet (V) is applied to the drying wire (F) out of a washing device, which is placed underneath the drying cylinder (10) between the reversing rolls (11). 3. A method as claimed in claim 1 or 2, characterized in that the drying wire (F) is washed from what is called the paper side. 4. A method as claimed in claim 1 or 2, characterized in that the drying wire (F) is washed from the rear side. 5. A method as claimed in any of the preceding claims, characterized in that the drying wire (F) is washed while running without paper. 6. A method as claimed in any of the claims 1 to 5, characterized in that the drying wire (F) is washed while the paper machine runs at a crawling speed. 7. A method as claimed in any of the claims 1 to 5, characterized in that the drying wire (F) is washed while the paper machine runs at a normal speed. 8. A device for washing the drying wire in a paper machine, which device (14,16, 17,18,20,21,22,23,24,25) is placed in a dryer group in the dryer section in the paper machine and which device comprises means for producing a liquid jet and/or an air jet (V,I) so as to wash and/or to dry the drying wire (F), respectively, characterized in that the device is placed in the dryer section in the paper machine in the vicinity of the drying wire (F) so that the means for producing the liquid jet (V) direct the liquid jet towards the drying wire (F) when the wire runs substantially downwards from a drying cylinder and/or substantially before the drying wire (F) runs onto the next reversing roll (11) or guide roll (12) or equivalent. 9. A device as claimed in claim 8, characterized in that, in a dryer group that makes use of single- wire draw, the washing device is placed underneath the drying cylinder (10) between the reversing rolls (11). 10. A device as claimed in claim 8 or 9, characterized in that the washing device (14) has been attached to direct vicinity of an air-conditioning device, which air¬ conditioning device (13) is placed below the drying cylinder (10). 11. A device as claimed in claim 8, characterized in that the washing device (14,16,17,20,21,25) has been constructed as a single unit together with a blow- suction box or an equivalent device. 12. A device as claimed in claim 8, characterized in that the washing device (18) has been attached to a blow-suction box or equivalent. 13. A device as claimed in claim 8, characterized in that the washing device has been constructed in connection with a doctor.

Inventors: EIVOLA ILKKA, VUORINEN VESA, EIVOLA, ILKKA, VUORINEN, VESA
Applicants: EIVOLA ILKKA, VALMET CORP, VUORINEN VESA, EIVOLA, ILKKA, VALMET CORPORATION, VUORINEN, VESA
Application year: 1996
Main classification: D21F1
IPC codes: D21F1