APPARATUS AND METHOD FOR PREVENTING THE DIRECTION OF A HARMFUL JET FROM A SPRAYING NOZZLE ON A WEB

Abstract: The present invention relates to an assembly and a method for preventing the spray emitted by a spraying nozzle (1) from reaching the surface of a paper web, said nozzle (1) being disposed at a distance from the surface of the paper web to be coated and further being directed toward said web surface to be coated. To in front of the spray emitted by the nozzle (1), between the spray and the paper web, there is adapted a movable baffle (2, 6) serving to prevent the spray from reaching the surface of the paper web.

Description: Apparatus and method for preventing the direction of a harmful jet from a spraying nozzle on a web The present invention relates to an assembly according to the preamble of claim 1 and a method according to the preamble of claim 9 for preventing the detrimental spray emitted by a spraying nozzle from from reaching the surface of a paper web. Coating a paper sheet with a pigment slurry is performed by applying a coat of uniform quantity and quality to the surface of a paper web, after which excess water is removed from the web by means of dryers. The coating process steps can be divided into the application step, which comprises spreading of the coating mix onto the surface of the moving web, the control of the final coat weight and the smoothing of the coat surface. A technique suitable for use in coating a paper web is the so-called spray-coating method that is described, e.g., in the international patent application publication WO 97/13035. In the spray-coating technique, the coating mix is administered to the paper sheet surface by appli- cation from spraying nozzles in which the coating mix is atomized into small droplets prior to spraying onto the moving paper web. The atomization of the coating mix in the spraying nozzle may be based on, e.g., a rotary motion, high-pressure atomization of a liquid coating or high-pressure air-assist/blast nozzles. The coat quality can be controlled by adjusting the distance between the spraying nozzle and the web, the spray-jet velocity and the mass rate of spraying. Generally, there must be disposed a number of spraying nozzles in the cross- machine direction to the web travel, because the coverage of the spraying jet emitted by a single nozzle is usually narrower than the web width. Typically, there is disposed a number of staggered nozzle rows across the web, perpendicular to the web travel, since a single row of nozzles extending across the web usually fails to provide a coating of a sufficiently high quality. In order to collect the coating mist occurring in the coating process and to recover the same from the air, the spraying nozzles are located in a closed space sealed from the environment, such as an enclosing hood having an exit opening made thereto for coating mist removal . The maintenance of spraying nozzles and coating mix feed lines includes washing. Conventionally, the washing operation is carried out by injecting washing liquid into the feed line and spraying nozzles to be washed. Desiredly, the washing operation should be arranged be feasible also in a running paperma ing machine in a manner not causing disturbance to the coating process of the paper web. Currently, this is possible if only a small quantity of the nozzles is washed at a time, whereby the deteriora- tion of the coat quality remains essentially negligible. Moreover, the washing liquid emitted from the spraying nozzles must be prevented from reaching the surface of the paper web being coated. It is an object of the present invention to provide a novel type of assembly and method for preventing a washing liquid spray or other detrimental spray from being directed toward the paper web. The goal of the invention is attained by inserting during the washing operation to in front of the spray emitted by the nozzle a baffle that prevents the washing liquid passed via the nozzles from reaching the paper web. More specifically, the assembly according to the invention is characterized by what is stated in the characterizing part of claim 1. Furthermore, the method according to the invention is characterized by what is stated in the characterizing part of claim 9. The invention offers significant benefits. By virtue of the invention, the spraying nozzles employed in the coating process of a paper web can be washed also in a running papermaking machine without causing disturbance to the coating process. Moreover, the embodiment according to the invention is uncomplicated and cost- advantageous to implement as well as easy to automate. In the following, the invention will be examined in greater detail by making reference to exemplifying embodiments illustrated in the appended drawings in which Fig. 1 shows a side view of an embodiment of an assembly according to the invention in its different operating positions A and B; and Fig. 2 shows a side view of another embodiment of an assembly according to the invention in its different operating positions A and B. In detail A of Fig. 1, a spraying nozzle 1 is shown in its normal operating position, wherein it sprays coating mix onto a paper web running above the nozzle 1. Herein, a baffle 2 is rotated away from in front of the spray emitted by the nozzle 1 and the coating mix can reach the surface of the paper web unobstructedly . In detail B of Fig. 1, the nozzle 1 is shown in its washing position, wherein the baffle 2 is rotated by an actuator means 4 such as a cylinder or a motor about a pivot point 3 to in front of the washing liquid spray emitted from the spraying nozzle 1. Herein, the baffle 2 prevents the washing liquid spray emitted by the nozzle 1 from reaching the paper web. The embodiment shown in Fig. 2 comprises a stationary baffle 5 and a movable baffle 6 adapted to be moved by means of an actuator 4. The stationary baffle 5 has an opening that coincides with the spray emitted by the spraying nozzle 1 and, correspondingly, the movable baffle 6 has an opening or openings made thereto. The second baffle 6 can be arranged to move supported by, e.g., a rail connected to the first baffle 5. In detail A of Fig. 2, the nozzle 1 is shown in its normal operating position, wherein the openings of the stationary baffle 5 and the movable baffle 6 coincide so as to permit the coating spray to reach via the openings of the baffles 5, 6 the surface of the web running above the nozzle 1. Furthermore, the opening of the stationary baffle 5 delineates accurately the margin of the coating spray emitted by the spraying nozzle 1 before the spray im- pinges on the paper web. In detail B of Fig. 2, the nozzle 1 is shown in its washing position, wherein the movable baffle 6 is first moved by means of the actuator 4 into a position that offsets the coincidence of the openings of the stationary baffle 5 and the movable baffle 6. Herein, the washing liquid pumped through the nozzle 1 cannot reach the surface of the paper web. In both of the above-described embodiments, it is advan- tageous to dispose the baffle 2, 6 so that it is in its washing position as close as possible to the tip of the nozzle 1, in front of the spray emitted by the nozzle 1, because the width of the spray pattern in this position is narrow thus allowing the baffle 2, 6 to be constructed with a small shadowing area. The invention may also be contemplated to have embodi- ments and applications different from those described above. The above-described exemplifying embodiments can be modified by locating the nozzles 1 above the paper web. The embodiment shown in Fig. 2 may also be imple- mented without the stationary baffle 5, whereby the baffle shadowing the spray emitted by the nozzle 1 comprises only a single movable plate having an opening or openings made thereto. With a suitable actuator design of the plate motion, the spray emitted by the nozzle 1 can be arranged to pass through the openings toward the paper web. The embodiment may also be implemented so that each nozzle 1 has a separate baffle adapted to rotate in front of the spray emitted by the nozzle 1, whereby the spray of the nozzle 1 toward the paper web can be controlled on and off by varying the rotation angle of the baffle. The baffle arranged to move to in front of the nozzle 1 may also be designed to have a curved shape at the hitting point of the washing- liquid spray on the baffle, whereby the baffle will more effectively deflect the spray of the nozzle 1 away from the nozzle 1. Functions different from those described above may be found for the assembly and method according to the invention. For instance, the embodiment according to the invention is usable for cutting off the coating mix application from the nozzles 1 to the paper web during a quick shutdown of the papermaking machine operation.

Claims: What is claimed is: 1. Assembly for preventing the spray emitted by a spraying nozzle (1) from reaching the surface of a paper web, said nozzle (1) being disposed at a distance from the surface of the paper web to be coated and further being directed toward said web surface to be coated, c h a r a c t e r i z e d by a baffle (2, 6) adapted to be movable to in front of the spray emitted by the nozzle (1) , between the spray and the paper web, so as to prevent the spray from reaching the surface of the paper web. 2. Assembly according to claim 1, c h a r a c t e r - i z e d in that said baffle is provided separately for each nozzle (1) and is formed by an element (2) adapted rotatable to in front of the nozzle (1) . 3. Assembly according to claim 1, c h a r a c t e r - i z e d in that said baffle is formed by a pair of plates (5, 6) having openings made thereto and being adapted to move in a superimposed manner in regard to each other. 4. Assembly according to claim 1, c h a r a c t e r i z e d in that said baffle is formed by a single plate having openings made thereto. 5. Assembly according to claim 1, c h a r a c t e r - i z e d in that said baffle is provided separately for each nozzle (1) and is formed by an element adapted to be rotatable in front of the nozzle. 6. Assembly according to any of foregoing claims, c h a r a c t e r i z e d in that said baffle has a curved shape . 7. Assembly according to any of foregoing claims 1-5, c h a r a c t e r i z e d in that said assembly includes an actuator means (4) such as a cylinder or a motor suitable for moving said baffle (2, 6) . 8. Assembly according to claim 1, c h a r a c t e r i z e d in that the spraying nozzles (1) are disposed above or below the paper web being coated, advantageously below the same. 9. Method for preventing the spray emitted by a spraying nozzle (1) from reaching the surface of a paper web, c h a r a c t e r i z e d in there is disposed a baffle (2, 6) to in front of the spray emitted by the nozzle (1) , between the spray and the paper web, so as to prevent the spray from reaching the surface of the paper web . 10. Method according to claim 9, c h a r a c t e r - i z e d in that said baffle (2, 6) is moved by an actuator means (4) .

Inventors: NISSINEN VILHO, VAEHAEKUOPUS MIKA, NISSINEN, VILHO, VAEHAEKUOPUS, MIKA
Applicants: NISSINEN VILHO, VAEHAEKUOPUS MIKA, VALMET CORP, NISSINEN, VILHO, VAEHAEKUOPUS, MIKA, VALMET CORPORATION
Application year: 1999
Main classification: D21H23
IPC codes: B05B1, B05B15, B05D1, B05D7, D21H23