Abstract
A curtain application unit for applying a liquid or pasty application medium to at least one surface of a moving material web, in particular a fibrous web, includes an application head having at least one separation edge extending substantially over the width of the application head. The application medium exits the application head in the form of a free-falling curtain at the separation edge. At least one rinsing device is used to apply a flowing gaseous rinsing medium to the at least one separation edge, and at least one blocking device is suitable for keeping air movements of the ambient air away from the curtain. A method for coating a moving material web is also provided.
Claims
1. A curtain application unit for applying a liquid or pasty application medium to at least one surface of a moving material web or fibrous web, the curtain application unit comprising: an application head having a width, an exterior cladding, a nozzle gap for guiding the application medium and at least one separation edge extending over said width of said application head, said at least one separation edge configured to permit the application medium from said nozzle gap to exit said application head at said separation edge as a free falling curtain; at least one rinsing supply disposed within said application head between said exterior cladding and said nozzle gap for applying a flowing gaseous rinsing medium to said at least one separation edge; and at least one blocking air nozzle configured to generate an air shield for keeping air movements of ambient air away from said curtain, said air shield having an air flow direction with at least one of a component pointing away from said application head or a component pointing away from the material web.
2. The curtain application unit according to claim 1, wherein said application head includes a housing block, a cross distribution chamber disposed in said housing block, and a thermally insulating layer surrounding at least a portion of said housing block and coming into contact with the surroundings.
3. The curtain application unit according to claim 2, wherein said housing block is made of a metallic material.
4. The curtain application unit according to claim 2, wherein said thermally insulating layer thermally decouples at least a portion of said exterior cladding from said housing block.
5. The curtain application unit according to claim 1, wherein said at least one blocking air nozzle is disposed at least one of before or after said application head in a direction of travel of the material web.
6. The curtain application unit according to claim 5, wherein said at least one blocking air nozzle and said application head are spaced apart by a distance of less than 100 cm.
7. The curtain application unit according to claim 5, wherein said at least one blocking air nozzle and said application head are spaced apart by a distance of less than 50 cm.
8. The curtain application unit according to claim 5, wherein said at least one blocking air nozzle and said application head are spaced apart by a distance of between 20 cm and 50 cm.
9. The curtain application unit according to claim 5, wherein said rinsing supply and said at least one blocking air nozzle are configured to be connected to a common air supply.
10. The curtain application unit according to claim 1, wherein at least one of the gaseous rinsing medium or the application medium has an adjusting temperature.
11. The curtain application unit according to claim 10, wherein the temperature of the rinsing medium is in a range of 0.4 times to 1.5 times the temperature of at least one of the surroundings or the application medium.
12. The curtain application unit according to claim 1, which further comprises a dehumidifier for reducing a moisture content of the rinsing medium.
13. A method for coating at least one surface of a moving material web or fibrous web with at least one liquid or pasty application medium, the method comprising the following steps: providing a curtain application unit including an application head having a width, an exterior cladding, a nozzle gap for guiding the application medium and at least one separation edge extending over the width of the application head; using the application head to emit the application medium from the nozzle gap past the at least one separation edge as a free falling single or multilayered curtain impinging on the material web; using at least one rinsing supply disposed within the application head between the exterior cladding and the nozzle gap to apply a flowing gaseous rinsing medium to a region of the at least one separation edge; and using at least one blocking air nozzle to generate an air shield at a velocity of between 15 m/s and 60 m/s for keeping air movements of ambient air away from the single or multilayered curtain.
14. The method according to claim 13, which further comprises carrying out the emitting step by applying the application medium at a flow rate of less than 10 l/min*m.
15. The method according to claim 13, which further comprises carrying out the emitting step by applying the application medium at a flow rate of less than 6 l/min*m.
16. The method according to claim 13, which further comprises carrying out the emitting step by applying the application medium at a flow rate of between 2 l/min*m and 5 I/min*m.
17. The method according to claim 13, which further comprises setting a relative humidity of the rinsing medium to be less than 100 RH %.
18. The method according to claim 13, which further comprises setting an outflow velocity of the rinsing medium to be between 6 m/min and 40 m/min.
19. The method according to claim 13, which further comprises setting an outflow velocity of the rinsing medium to be between 12 m/min and 20 m/min.
20. The method according to claim 13, which further comprises setting an exit velocity of the application medium from the application head to be between 10 m/min and 100 m/min.
21. The method according to claim 13, which further comprises setting an exit velocity of the application medium from the application head to be between 16 m/min and 66 m/min.
22. The method according to claim 13, which further comprises carrying out the step of generating the air shield by using between 2.4 m.sup.3/min/m and 12 m.sup.3/min/m of air.
Description
(1) In the following, the invention will be explained more closely with the aid of schematic figures, not true to scale.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
(2) FIG. 1 shows schematically a curtain application unit of the prior art.
(3) FIG. 2 shows a curtain application unit according to one aspect of the invention.
(4) FIGS. 3 and 4 show schematically a portion of a curtain application unit according to further aspects of the invention.
(5) FIGS. 5 to 11 show possible realizations of an application head according to various aspects of the invention.
DETAILED DESCRIPTION OF THE INVENTION
(6) FIG. 1 shows a curtain application unit as is known in the prior art. Material web 4 is led through a slot into an enclosure 30. Supported by two rolls 3, it is led through beneath an application head 1, while a curtain 2 of application medium is deposited on material web 4. After the coating has been done, material web 4 is led out once more from the enclosure through another slot. In order to remove the entrained air, an air stripper 5 is provided, especially an air-cut. To prevent condensation, enclosure 30 is conditioned by means of a climate control 31. Such an encapsulated curtain application unit cannot be operated with stability without a suitable climate control. After exiting enclosure 30, material web 4 is usually deflected by a noncontact deflecting element 32, also known as an air-turn 32, and taken on for a drying, if needed.
(7) This enclosure 30 requires a relatively large design space. Furthermore, the needed climate control entails considerable costs in its acquisition and operation.
(8) FIG. 2, on the contrary, shows a curtain application unit according to one aspect of the invention. An application head 1 is provided in the curtain application unit, from which curtain 2 is deposited on moving material web 4. Application head 1 comprises at least one rinsing device, by means of which at least one separation edge can be subjected to a flowing gaseous rinsing medium, such as air. The exterior cladding in many embodiments is at least partly thermally decoupled from the housing block by a thermally insulating layer. This is very advantageous; however, such an insulation may also be omitted.
(9) Material web 4 moves in the machine direction MD from left to right. The application is done here by two idler rolls 3, over which the material web is led. But this is not essential to the invention. For example, the application can also be done on one roll. A stripping device 5 is provided in front of curtain 2, looking in the running direction of material web 4. This may be designed as a so-called air-cut, for example. Alternatively, it may also be provided, for example, that stripping device 5 comprises or consists of a brush, a film, or a lip, which can be placed against material web 4. Both embodiments can provide the important function of stripping device 5, namely, to reduce or remove the air boundary layer entrained by material web 4.
(10) The curtain application unit in FIG. 2 furthermore shows two blocking devices 9, where one blocking device 9 is arranged before application head 1, and another blocking device 9 is arranged after application head 1. A respective nozzle arrangement 6 is provided. These air nozzles 6 respectively generate an air shield 9, which achieves the desired blocking action, namely, to keep air movements of the ambient air away from curtain 2. The air shield here is oriented in both blocking devices 9 so that the air flow velocity has one component which points away from application head 1 and furthermore one component which points away from material web 4. In this way, an interfering influence of the air shield on the web movement or the curtain stability can be avoided most effectively.
(11) An enclosure of the curtain application unit is not needed here, nor is a climate control for the surroundings of the application head necessary. In this way, the acquisition costs as well as the operating costs can be reduced.
(12) It may also be seen from FIG. 2 that the curtain application unit is very flexible, and can also be easily integrated in existing layouts. On the one hand, it may have a very compact design—especially when there is no enclosure. The curtain application unit requires only a relatively small design space in the machine transverse direction. Furthermore, it is also possible to adapt the guidance of the material web 4. In the case of an enclosed curtain application unit, the web is led into and out from the enclosure through a slot. This slot is predefined. Furthermore, it is also usually very narrow, in order to ensure an adequate climate control of the enclosure. This leads to relatively strong restrictions on the web guidance. FIG. 2 shows, as an example, that such restrictions are largely eliminated in the case of curtain application units according to the invention. The broken lines 4a and 4b show two possible runs of material web 4, 4a, 4b prior to the application process. Idler rolls 3a and 3b here can also be positioned relatively close to the application unit.
(13) The curtain application unit shown in FIG. 3 comprises an application head 1, from which a curtain 2 is deposited under the influence of gravity onto a material web 4, such as a paper or carton web. Material web 4 is diverted by means of an idler roll 3, such that its run beneath curtain 2 is largely horizontal. The point of impact of the curtain here is somewhat behind idler roll 3, looking in the running direction of material web 4. The entrained air moving along with material web 4 is kept away from curtain 2 with a stripping device 5. Suitable stripping devices 5 are so-called air knifes, for example, known in the industry as air-cuts. Often stripping device 5 ends just before the point of impact of the curtain.
(14) In FIG. 3, the at least one blocking device 9, 9a, 9b according to the invention is realized in the form of two plates 9a and 9b. The two plates 9a, 9b here are fastened directly to the application head. While it is basically also possible for the plates to be fastened otherwise, the fastening directly to application head 1 has the benefit that the distance between plates 9a, 9b and curtain 2 is extremely short. Distances of less than 100 mm, and even less than 50 mm, can be realized here. This results in a very compact design. Moreover, the area around the application head, such as idler roll 3 or stripping device 5, is freely accessible for maintenance work or the like during operation, without interfering with curtain 2 by resulting movement of the ambient air.
(15) FIG. 4 shows a curtain application unit according to one preferred aspect of the invention. The at least one blocking device 9, 9a, 9b here is realized by an air shield 9. The air emerges from an air nozzle 6, or a row of nozzles 6, to generate air shield 9. The flow direction of the air, and thus the orientation of air shield 9, may be vertically upward, or also slightly slanted to this direction. Advantageously, this slanting is directed away from application head 1, and thus also away from curtain 2, in order to avoid an influencing of curtain 2 by air shield 9. Advantageously, air shield 9 may extend at least across the entire width of curtain 2 in the machine transverse direction.
(16) In the embodiment shown in FIG. 4, air nozzle 6, or row of nozzles 6, is fastened directly to a stripping device 5. This may be advantageous, yet other possibilities of the fastening are also possible and advisable, depending on the situation.
(17) Advantageously, the distance of the air shield from the application head is less than 150 cm, especially less than 100 cm, especially preferably less than 50 cm. As shown in FIG. 2, a further deflecting device is usually also provided after curtain 2, such as an idler roll 3a. The distance of this deflecting device 3a from the curtain 3 may vary in different installations.
(18) FIG. 5 shows—in a cross sectional representation in a plane parallel to the web running direction MD and perpendicular to the web transverse direction CD (CD extends perpendicular to the drawing layer of FIGS. 5-11)—a first embodiment of an application head 1 according to the invention for producing a single-layer free falling curtain 2 of a liquid or pasty application medium for the coating of a moving material web.
(19) Application head 1 has a cross distribution chamber 23 and a nozzle gap 24, connected to it, with an exit opening 25, such that the application medium coming from the cross distribution chamber 23 via the nozzle gap 24 toward the exit opening 25 exits the application head 1 at the exit opening 25.
(20) In the present case, exit opening 25 provides a front separation edge 26, looking in the web running direction MD, as well as a rear separation edge 27 looking in the web running direction MD.
(21) As can be seen from the representation of FIG. 5, application head 1 comprises a first rinsing device 28 and a second rinsing device 29, which are arranged and configured such that, when application head 1 is used as intended, and looking in the web running direction of material web 4, first rinsing device 28 applies a flowing rinsing medium 13 (dot and dash line with arrow) to first separation edge 26 from the front and second rinsing device 29 applies a flowing rinsing medium 14 (dot and dash line with arrow) to second separation edge 27 from the rear. In the present exemplary embodiment, the two rinsing devices 28, 29 are arranged outside nozzle gap 24. In the present case, each of the two rinsing devices provides a rinsing medium in the form of air.
(22) Application head 1 comprises a housing block made from a metallic material, advantageously a steel, in which cross distribution chamber 23 and nozzle gap 24 are arranged. The housing block comprises a first housing block part 10 (in the present embodiment, front housing block part 10) and a second housing block part 11 (in the present embodiment, rear housing block part 11), wherein cross distribution chamber 23 and nozzle gap 24 are formed by a cavity formed between the two housing block parts 10, 11. As can be seen from the representation of FIG. 5, first housing block part 10 comprises a first nozzle lip 10.1, which provides first separation edge 26 in the area of exit opening 25 of nozzle gap 24. Moreover, second housing block part 11 comprises a second nozzle lip 11.1, which provides second separation edge 27 in the area of exit opening 25 of nozzle gap 24. The two nozzle lips 10.1 and 11.1 can be moved relative to each other, so that the width of nozzle gap 24 can be individually adjusted in the area of exit opening 25 in the transverse direction of application head 1.
(23) In the present exemplary embodiment, the housing block is surrounded for a portion by an exterior cladding 12.1, 12.2, which comes into contact with the surroundings. Exterior cladding 12.1, 12.2 here comprises a front part of the exterior cladding 12.1 in the form of a curved metal sheet, looking in the web running direction MD, and a rear part of exterior cladding 12.2 in the form of a curved metal sheet, looking in the web running direction MD. As can further be recognized, the exterior cladding 12.1, 12.2 is arranged and configured in the area of separation edges 26, 27 such that it does not affect the free fall of curtain 2.
(24) Exterior cladding 12 is thermally decoupled from housing block 10, 11 at least for a portion by a thermally insulating layer.
(25) In the present case, the thermally insulating layer is formed by a gaseous insulating medium between the front part of exterior cladding 12.1 and front housing block part 10, which is channeled in a gap between the front housing block part 10 and the front part of the exterior cladding 12.1 and which is provided by flowing gaseous rinsing medium 13 from first rinsing device 28. Moreover, in the present case, the upper part of the gap in FIG. 5 between rear housing block part 11 and the rear part of exterior cladding 12.2 is formed by a foam material. Moreover, one can see that the lower part of the gap in FIG. 5 between rear housing block part 11 and the rear part of the exterior cladding 12.2, adjacent to the upper part, is formed by a gaseous insulating medium, which is provided by flowing gaseous rinsing medium 14 from second rinsing device 29.
(26) In both cases, i.e., in regard to first rinsing device 28 and second rinsing device 29, the rinsing medium flows in a direction from the top to the bottom toward the two separation edges 26, 27.
(27) For the following discussion of FIGS. 6 to 11 it should be noted that only the differences from the explicitly mentioned embodiment (e.g., the one of FIG. 5) will be discussed and that the same or similar technical objects or features will be denoted by the same reference numbers.
(28) FIG. 6 shows a variant of application head 1 shown in FIG. 5. Both rinsing devices 28, 29 here are arranged in the lower area of application head 1. Both the upper part of the gap between the rear housing block part 11 and the rear part of exterior cladding, 12.2, as well as the upper part of the gap between front housing block part 10 and the front part of exterior cladding 12.1, are filled here entirely or at least partly by a foam material.
(29) FIG. 7 shows a second embodiment of an application head 1 according to the invention for generating a single-layer free falling curtain 2.
(30) The application head of FIG. 7 differs from the application head shown in FIG. 5 basically in that both rinsing devices 28, 29 in the application head of FIG. 7 are arranged in the lower area of application head 1, i.e., at the level of nozzle lips 10.1 and 11.1, and exterior cladding 12.1 and 12.2 in front of and behind the curtain protrude beyond the two separation edges 26, 27 at exit opening 25 by up to 100 mm in the direction of free falling curtain 2, so that free falling curtain 2 is shielded from interfering influences of the surroundings, such as air currents. For directing flowing rinsing medium 13 provided by first rinsing device 28 onto first separation edge 26, the front part of exterior cladding 12.1 comprises a baffle 12.1.1. Similarly, the rear part of exterior cladding 12.2 comprises a baffle 12.2.2, by which flowing rinsing medium 14 provided by second rinsing device 29 is directed onto second separation edge 2.
(31) As a further difference from FIG. 5, the thermally insulating layer between the front part of exterior cladding 12.1 and housing block 10, 11 as well as the rear part of exterior cladding 12.2 and housing block 10, 11 are provided each time by air, which is not provided by rinsing medium 13, 14.
(32) However, it may also be provided that a different thermally insulating layer instead of air, such as foam material, mineral wool, etc., can be used.
(33) FIG. 8 shows a third embodiment of an application head 1 according to the invention for generating a single-layer free falling curtain 2.
(34) Application head 1 of FIG. 8 differs from the application head shown in FIG. 5 basically in that the thermally insulating layer between the rear part of exterior cladding 12.2 and rear housing block part 11 is also formed by the gaseous insulating medium, which is channeled in the gap between rear housing block part 11 and the rear part of exterior cladding 12.2 and which is provided by flowing gaseous rinsing medium 14 from second rinsing device 29.
(35) FIG. 9 shows yet another embodiment of an application head 1 according to the invention for generating a single-layer free falling curtain 2.
(36) Application head 1 of FIG. 9 differs from the application head shown in FIG. 8 basically in that no exterior cladding 12.1 and 12.2 is provided. In the present exemplary embodiment, housing block 10, 11 is merely surrounded by the thermally insulating layer, which comes into contact with the surroundings, while the thermally insulating layer surrounding the front housing block part 10 is provided by flowing gaseous rinsing medium 13 from first rinsing device 28 and the thermally insulating layer surrounding rear housing block part 11 is provided by flowing gaseous rinsing medium 14 from second rinsing device 29.
(37) FIG. 10 shows yet another embodiment of an application head 1 according to the invention for generating a single-layer free falling curtain 2.
(38) Application head 1 of FIG. 10 has a cross distribution chamber 23 and, connected to it, a nozzle gap 24 with an exit opening 25, as well as a sliding face 17 adjacent to it, which is in turn adjacent to a separation edge 16 such that the application medium coming from cross distribution chamber 23 via nozzle gap 24 and exit opening 25 flows after exit opening 5 across sliding face 17 toward separation edge 16 and exits application head 1 at separation edge 16. It should be mentioned that sliding face 17 is provided by a sliding face block 15 arranged at front housing block part 10.
(39) Two rinsing devices 28, 29 are provided at separation edge 16, by means of which flowing gaseous rinsing medium 13, 14 can be applied to separation edge 16.
(40) FIG. 11 shows an embodiment of an application head 1 according to the invention for generating a multilayered free falling curtain 2′.
(41) Application head 1 of FIG. 11 differs from the application head shown in FIG. 8 basically in that the housing block has, in addition to a front and rear housing block part 10′, 11′, a housing block middle part 18, and also two cross distribution chambers 23.1 and 23.2 are provided with respective nozzle gap 24.1, 24.2, which meet at exit opening 25 to form a two-layered free falling curtain 2′. The application of medium to two separation edges 26, 27 and the thermal insulation of housing block 10′, 11′, 18 is designed similar to the embodiment of FIG. 8, namely, application of rinsing medium 13 provided by first rinsing device 28 to first separation edge 26 and application of rinsing medium 14 provided by second rinsing device 29 to second separation edge 27, the two rinsing media 13, 14 being channeled from the top part of housing block 10′, 11′, 18 in the gap between exterior cladding 12.1 or 12.2 in a flow direction running from the top to the bottom.
