Method and device in drying of a coating on a paper web or equivalent

Abstract: The invention concerns a method in drying of a coating on a paper web or equivalent. In the method, the direction of running of the paper web (W) is turned free of contact by means of blowings produced by means of a turning device (20), and the coating on the paper web (W) is dried free of contact by means of the blowings of the drying devices (30,40) placed at both sides of the paper web (W). In the method, the direction of running of the paper web (W) or equivalent is turned by means of drying blowings. The exhaust air of the turning device (20) and of the drying device (30) placed at the side of the turning device is removed from direct vicinity of the paper web or equivalent by means of a common exhaust device (34). The turning device (20) and the drying device (30) placed at the side of the turning device (20) are placed under a common box construction (25), whereby access of the exhaust air into the surrounding space is prevented. Further, the invention concerns a device in drying of a coating on a paper web or equivalent, which device comprises a turning device (20) for turning the running direction of the paper web (W) or equivalent free of contact and a drying device (30,40) for contact-free drying of the coating on the paper web (W) or equivalent, said turning device (20) and drying device (30,40) comprising nozzles for producing blowings and an exhaust-air device for removing the exhaust air from the vicinity of the paper web (W) or equivalent. The turning device (20) of the paper web (W) or equivalent and the drying device (30) that is placed at the same side of the paper web (W) or equivalent as the turning device (20) are placed under a common box construction (25). The device comprises means for producing drying blowings at the turning device (20). The turning device and the drying device (30) placed under the common box construction (25) with the turning device (20) have common exhaust-air members.

Description: The invention concerns a method in drying of a coating on a paper web or equivalent, in which method the direction of running of the paper web is turned free of contact by means of blowings produced by means of a turning device, and in which method the coating on the paper web is dried free of contact by means of the blowings of the drying devices placed at both sides of the paper web, and the turning device and the drying device placed at the side of the turning device are placed under a common box construction, whereby access of exhaust air into the surrounding space is prevented. Further, the invention concerns a device in drying of a coating on a paper web or equivalent, which device comprises a turning device for turning the running direction of the paper web or equivalent free of contact and a drying device for contact-free drying of the coating on the paper web or equivalent, said turning device and drying device comprising nozzles for producing blowings and an exhaust-air device for removing the exhaust air from the vicinity of the paper web or equivalent, said turning device of the paper web or equivalent and said drying device that is placed at the same side of the paper web or equivalent as the turning device are placed under a common box construction. As is well known, in some coating processes it must be possible to turn the running direction of the web free of contact after the coating has been applied to the web face but, however, before the coating has solidified. In these processes it is often, at the same time, necessary to dry the web quickly and efficiently to contact dryness, both out of reasons of quality and out of reasons of layout. However, at the same time, the runnability of the web must remain good. As is well known, the processes of this type are often carried out by making use of a turning device and of infrared dryers and possibly air dryers. In such a case, however, the drying layout will involve some limitations affecting the machine length and required by the process and by the equipment, and at the same time the runnability of the layout suffers. As an example of a problem of this type can be mentioned the free draw of at least about 0.5 metre between the turning device and the following dryer, which free draw is usually applied in the solutions currently in use. With respect to the prior art related to turning and drying arrangements of the type described above, reference is made to the FI-A- 943657 (priority from DE 44 00 158 and EP 93 112 695 ), corresponding to EP-A-0 643 167, in which a device is described for colouring a paper web by means of two rolls, which have been arranged as parallel to one another and which form a gap between the rolls so as to pass the paper through this gap. The device is provided with at least one jet printing device in order to apply a colour layer onto the mantle faces of the rolls so as to transfer the colour layer in the gap between the rolls from the roll mantle face onto one side of the paper web. The device also includes carrier air beams, which produce a carrier air cushion between the paper web and the face of the carrier air beam turned towards the paper web, said carrier air beams being fitted so that the direction of the paper web is changed at least once after the gap between the rolls. In this prior-art solution, at least one carrier air beam is connected directly after the gap between the rolls, and it is fitted at a distance from the gap formed by the two rolls. With respect to the prior art, reference can also be made to the EP-A- 0 507 218, wherein a dryer section is described in which the web is turned free of contact by means of a web turning device, which web turning device is followed by dryer devices and the turning device and the drying device are placed under a common box construction. Also, with respect to the prior art, reference can be made to the published DE-A- 44 15 581, in which contact-free air dryers are described which are fitted outside the turning sector of a turning roll. The object of the present invention is to provide a method and a device in drying of a coating on a paper web or equivalent, in which method and device most of the drawbacks involved in the prior art have been eliminated or the detrimental effects of said drawbacks have at least been minimized. In view of achieving the objectives stated above and those that will come out later, the method in accordance with the present invention as described in claim 1 is mainly characterized in that, in the method, the direction of running of the paper web or equivalent is turned by means of drying blowings of hot air, and that, in the method, the exhaust air of the turning device and of the drying device placed at the side of the turning device is removed from direct vicinity of the paper web or equivalent by means of a common exhaust device. On the other hand, the turning device in accordance with the invention as described in claim 18 is characterized in that the device comprises means for producing and conducting drying blowings of hot air at the turning device, and that the turning device and the drying device placed under the common box construction with the turning device have common exhaust-air members. According to the invention, the drying is carried out most commonly by means of a turning device and an air dryer, and the devices have been constructed physically together as a single unit, and in this way it is possible to eliminate a part of the free draws present in the prior-art layouts. which free draws produce risks of runnability in prior-art arrangements. In the solution in accordance with the present invention, both the length of the turning device and the length of the free draw that was present in the prior-art solutions are utilized for drying, in which situation the drying can be started about 1.2 to 1.5 metres earlier than in the prior art. The solution in accordance with the invention also permits the use of hot circulation air in the turning devices, because the exhaust air of the turning device is recovered together with the exhaust air of the airborne dryer. In the prior-art solutions, in the turning devices, as a rule, cold air taken from the hall has been employed, in which case the drying effect of the turning device has been negligible. The use of hot air in a conventional turning device results in heat and moisture loads in the hall, it is uneconomical from the point of view of consumption of energy, and it can also be experienced as a risk in view of safety at work. According to the invention, the web turning and drying devices have been combined so that, out of reasons of runnability and reasons of controllability of air, the common return air zone has been divided into zones, which are provided with a possibility of regulation of the return air. The combination of turning and drying has been accomplished either by including the turning function in a conventional airborne dryer box or by providing separate devices with a common, insulated housing, out of which the return air is absorbed. Since, in the device in accordance with the invention, the turning and drying devices have been combined inside the box of one device, it is possible to use a high temperature in the feed air of the turning device. Preferably, the temperature of the feed air of the turning device is about 100 to 300°C. Since the air discharged out of the turning device is absorbed away as return air into the air system, a large quantity of high-temperature air can be removed from the area under control without risking the runnability. At the same time, any risk for safety at work has been eliminated, which risk would have been produced by said hot air if discharged freely into the machine hall. The drying portion of the device in accordance with the present invention can follow substantially directly after the turning portion, or after a certain distance, out of reasons of runnability or layout, as necessary. A suitable distance in an arrangement in accordance with the present invention is typically about 100 to 700 mm. In this area, according to the invention, functions that promote runnability and/or drying can be fitted, for example drying and/or exhaust-air devices and/or profiling devices or any other, similar devices. The airborne portion used in connection with the arrangement in accordance with the invention can be accomplished either as a conventional solution in itself known or by means of the high-capacity principle, in which latter case the temperature can be up to 450°C and the velocity 100 metres per second. In the other respects the airborne portion is in itself known from the prior art to a person skilled in the art. In the arrangement in accordance with the invention, the joint return air of the dryer portion and the turning portion is used as the feed air for the turning device or as a part of said feed air. Part of the feed air for the turning device can also be taken from the machine hall or from outdoor air, or as air that has been pre-heated in the recovery of heat. This air that is taken from outside, at the same time, operates as the common replacement air for the whole dryer. In connection with the arrangement in accordance with the invention, the temperature of the feed air for the turning device can be measured and regulated automatically. At the same time it is possible to verify the air quantity of the turning device and to regulate the quantity of air that is used in the turning device. Also, the extent of vacuum in the combination box can be measured and regulated automatically. During tail threading, the combination is operated preferably so that the turning-device portion is in operation so as to secure contact-free turning of the web, but the drying portion has been switched off or switched on to a short circulation. During threading, as the feed air for the turning device, it is possible to use either circulation air or air from the machine hall or outdoor air, or a suitable combination of circulation air and machine-hall/outdoor air. 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 of said illustrations. Figure 1 is a schematic illustration of an exemplifying embodiment of the device in accordance with the invention. Figure 2 shows a second exemplifying embodiment of the device in accordance with the invention. Figure 3 is a schematic illustration of a third exemplifying embodiment of the device in accordance with the invention. Figure 4 shows an exemplifying embodiment of a PI diagram of the equipment in accordance with the invention. Figures 5A to 5D are schematic illustrations of some exemplifying embodiments of opening of the device of the present invention for the time of threading of the web. As is shown in Fig. 1, above the paper web W, an equipment unit 10 is placed, in which, inside the box 25, there is the turning device 20 and the dryer 30, following after the turning device substantially directly. The turning device 20 comprises nozzles 21, out of which air is blown for contact-free turning of the web W. The dryer 30 comprises nozzles 31, out of which air is blown for drying the coating on the web W. In the dryer 30, between the nozzles 31, there are exhaust openings, through which the moist air is removed from between the web W and the dryer 30. The air fed by the turning device 20 is also removed from the area of the nozzles 31 of the dryer 30, preferably through the exhaust openings in the initial end. Below the paper web W, there is a drying device 40, which is provided with nozzles 41 and, between them, with exhaust openings for removal of the moist air. Out of the nozzles 41, hot air is blown in order to dry the coating on the paper web W. The lower dryer is also enclosed inside a box construction 45. The lower dryer 40 extends to the area of the upper dryer 30 and partly or fully also to the area of the turning device. Air is passed into the turning device 20 out of the duct 22 by means of a blower 23. Air can be passed into the turning device 20 from outside the system along the duct 26, whose regulation plate is denoted with the reference numeral 27. At the turning device 20, combined return air of the drying device and the turning device is used, which return air is passed along the duct 24 through the regulation plate 29. To the dryers 30 and 40, drying air is passed through the ducts 32 and 42. The dryer-specific latticework gates for the air feed are denoted with the reference numerals 33 and 43. Air is passed into the burner system through a combustion-air blower 63, and the gas flow to the burner unit 62 is regulated by means of a regulation valve 64. From the burner unit the air is passed further along the duct 51 to the dryers 30 and 40. Hot drying air can also be passed through the duct 55 to a short circulation by opening the closing latticework gate 56 and by at the same time closing the closing latticework gates 54 and 53. The short circulation is used during such interruptions in production during which it is not justified to run down the whole system. The return air from the upper and lower dryer 30 and 40 is passed from the ducts 44 and 34 through the regulating latticework gates 35 and 46 into the duct 52, from which it can be passed to the turning device through the regulation gate 29 or, as exhaust air, through the regulation gate 57 into the exhaust duct 58 or, as return circulation, through a guide blade regulator 59, to the blower 61, which passes the return air back to circulation. By means of the regulating latticework gates 37 and 38 it is possible to regulate the balance between the exhaust airs of the dryer 30 and the turning device 20, by means of which balance it is possible to influence the runnability of the web in the area between the dryer and the turning device. In the feed of air to the turning device 20, before the blower 23, a regulating latticework gate 28 is fitted. The exemplifying embodiment shown in Fig. 2 is substantially similar to that shown in Fig. 1, and the same reference numerals refer to corresponding parts. Compared with the exemplifying embodiment shown in Fig. 1, it is a difference in the exemplifying embodiment shown in Fig. 2 that a gap 16 has been arranged between the turning device 20 and the dryer 30, through which gap exhaust air is passed from the turning device 20 to the outlet 34 of the dryer 30. The turning device 20 and the dryer 30 are placed inside the same box 25, and between the turning device portion 20 and the dryer portion 30 a partition wall 12 is fitted, which is provided with an opening 15 through which exhaust air is passed, in order to enhance the arrangements of runnability and in order to control the exhaust arrangements. By passing part of the exhaust air of the turning device through the gap 15, air flows detrimental in view of the runnability are avoided. The lower dryer 40 corresponds to that shown in Fig. 1, except that it extends to the area of the upper dryer 30 only, even though it can also extend up to the area of the turning device. The gap between the turning device 20 and the dryer 30 can be covered with a perforated plate, net, or equivalent 17 in order to prevent passage of pieces of paper along with the return air into said gap. The exemplifying embodiment shown in Fig. 3 corresponds to those shown in Figs. 1 and 2, and the same reference numerals refer to corresponding parts. Compared with the exemplifying embodiment shown in Fig. 2, in this exemplifying embodiment an additional dryer 13 is fitted in the space 16 between the turning device 20 and the dryer device 30, which additional dryer dries the web W during this gap, and the dryer can be, for example, an infrared dryer, as is illustrated in the figure. In this embodiment the exhaust airs of the turning device 20 are passed from both sides of the infrared dryer 13 and from behind the partition wall to the outlets of the dryer 30 as well as through the space 14 above the infrared dryer 13, through the gap 15 provided in the partition wall 12, to the outlet of the dryer. The lower dryer 40 is similar to the dryer shown in Fig. 2. The PI diagram shown in Fig. 4 shows one mode of arranging the automation as well as the arrangement of the control of the process and of the dryer. In the figure the same reference numerals are used as are used in Figs. 1...3 for corresponding parts. The quantity of air for the turning device is regulated either by means of the guide blade regulator 28 or by means of regulation 73 of the number of revolutions of the blower. The quantity of air is controlled based on measurements of the pressures of the air cushion 72 and the intake air 71, so that a sufficient and desired pressure and thickness of air cushion are obtained in view of the turning of the web. The quantity of the replacement air coming to the turning device, which air comes from the machine hall, from outdoor air, or which is pre-heated air, is regulated by means of a regulation plate 27. The quantity of the exhaust air of the dryer is regulated by means of the regulation plate 57. By means of regulation of the proportions of these two plates, the air balance of the dryer unit is ensured. The other regulations of the airborne dryer comply with the traditional principle of regulation employed in corresponding conventional airborne dryers. Fig. 5A is a schematic illustration of an arrangement of equipment in accordance with the invention, in which the upper part is denoted with the reference numeral 10 and the lower part with the reference numeral 11. The paper web W runs between the parts free of contact, in which connection the coating on the paper web W is dried and the web is turned. Figs. 5B to 5D show some possibilities of opening the assembly of equipment for the time of threading the tail W I of the web W. In the exemplifying embodiment shown in Fig. 5B, the lower device 11 is shifted as parallel downwards, for example, along guides (not shown) fitted in the frame constructions. In the exemplifying embodiment shown in Fig. 5C, the upper equipment unit 10 is pivoted upwards around the centre point of the turning device portion, in which connection the turning of the web remains correct during the threading, but the dryer does not affect the threading of the web. In the arrangement shown in Fig. 5D, the edge of the lower device 11 either at the driving side or at the tending side is provided with hinges, and the device is pivoted open around this hinge axis for tail threading of the web.

Claims: A method in drying of a coating on a paper web or equivalent, in which method the direction of running of the paper web (W) is turned free of contact by means of blowings produced by means of a turning device (20), and in which method the coating on the paper web (W) is dried free of contact by means of the blowings of drying devices (30,40) placed at both sides of the paper web (W), and the turning device (20) and the drying device (30) placed at the side of the turning device (20) are placed under a common box construction (25), whereby access of the exhaust air into the surrounding space is prevented; characterized in that , in the method, the direction of running of the paper web (W) or equivalent is turned by means of drying blowings of hot air, and that, in the method, the exhaust air of the turning device (20) and of the drying device (30) placed at the side of the turning device is removed from direct vicinity of the paper web or equivalent by means of a common exhaust device (34). A method as claimed in claim 1, characterized in that the feed air for the turning device (20) is taken as a mixture of air taken from the return air duct of the dryer and air taken from the hall or from outdoors or of pre-heated replacement air. A method as claimed in claim 1 or 2, characterized in that the air removed from the turning device is passed under control from the zone between the turning device and the dryer so as to constitute return air of the dryer (30). A method as claimed in any of the claims 1 to 3, characterized in that , in the method, substantially directly after the turning of the web (W) by means of the turning device (20), the web (W) is dried by means of a drying device (30,40). A method as claimed in any of the claims 1 to 3, characterized in that , in the method, after the turning device (20), the web (W) is made to by-pass an intermediate space (16), through which intermediate space at least a part of the exhaust air from the turning device (20) is passed into the box arrangement of the drying device (30) through openings (12) placed between the intermediate space (16) and the box of the drying device (30) and/or through the opening (18) provided for the web. A method as claimed in any of the claims 1 to 5, characterized in that , in the method, the balance between the return airs of the turning device (20) and the drying device (30) is set by means of regulation plates (37 and 38). A method as claimed in any of the claims 1 to 6, characterized in that at least a part of the exhaust air from the turning device (20) is passed through the intermediate space (16) and the opening (12) into the return-air space of the dryer (30), whereby air flows detrimental in view of runnability are reduced in the web opening (18) between the turning device (20) and the dryer (30). A method as claimed in any of the claims 1 to 7, characterized in that , in the method, in the gap between the turning device (20) and the drying device (30,40), the paper web (W) is dried by means of an infrared radiator (13), which is placed under the same box construction (25). A method as claimed in claim 8, characterized in that the infrared radiator (13) is embodied as a profiling unit. A method as claimed in any of the preceding claims, characterized in that , from the turning device (20), air is blown whose temperature is 25 to 300 °C, preferably 100 to 300°C. A method as claimed in any of the preceding claims, characterized in that the temperature of the air blown from the drying devices (30,40) is 100 to 450 °C, and in the method air is blown from the drying device at a velocity of 20 to 100 metres per second, preferably 150 to 400 °C and 40 to 75 metres per second. A method as claimed in any of the preceding claims, characterized in that the air that is used as the feed air to be blown out of the turning device (20) is at least partly circulation air that returns from the drying device (30,40). A method as claimed in any of the preceding claims, characterized in that the air that is used as the air blown from the turning device (20) is a mixture of circulation air returning from the drying devices (30,40) and air taken from the machine hall or from outdoors or of pre-heated replacement air, so that the temperature of the blow air of the turning device is regulated by means of the ratio of these airs. A method as claimed in any of the preceding claims, characterized in that the air that is used as the air blown from the turning device (20) is a mixture of the drying air fed to the drying devices (30,40) and air taken from the machine hall or from outdoor air or of preheated replacement air. A method as claimed in any of the preceding claims 1 to 14, characterized in that , for the time of tail threading (W I ) of the web (W), the drying device (30) that is connected with the turning device and that forms a part of the dryer device (30,40) is pivoted around the centre point of the turning device (20) away from the web (W) (FIG. 5C). A method as claimed in any of the preceding claims 1 to 14, characterized in that , for the time of tail threading (W I ) of the web (W), the drying device (40) that is placed at the side of the web (W) opposite to the turning device (20) and that forms a part of the dryer device (30,40) is shifted away from the web (W) (FIG. 5B). A method as claimed in any of the preceding claims 1 to 14, characterized in that , for the time of tail threading (W I ) of the web (W), the drying device (40) that is placed at the side of the web (W) opposite to the turning device (20) and that forms a part of the dryer device (30,40) is pivoted apart from the web around an edge of the device (40) parallel to the machine direction (FIG. 5D). A device in drying of a coating on a paper web or equivalent, which device comprises a turning device (20) for turning the running direction of the paper web (W) or equivalent free of contact and drying devices (30,40) for contact-free drying of the coating on the paper web (W) or equivalent, said turning device (20) and drying devices (30,40) comprising nozzles for producing blowings and an exhaust-air device for removing the exhaust air from the vicinity of the paper web (W) or equivalent, said turning device (20) of the paper web (W) or equivalent and said drying device (30) that is placed at the same side of the paper web (W) or equivalent as the turning device (20) being placed under a common box construction (25), characterized in that the device comprises means (24,26,34,44,52; 27,29) for producing and conducting drying blowings of hot air to the turning device (20), and that the turning device and the drying device (30) placed under the common box construction (25) with the turning device (20) have common exhaust-air members (34). A device as claimed in claim 18, characterized in that the turning device (20) comprises a duct (22) for feed air for the turning device (20), to which duct (22) are connected return air ducts (34,44) of the dryers and a duct (26) for air taken from the hall or from outdoors or for pre-heated replacement air. A device as claimed in claim 18, characterized in that the turning device (20) has nozzles (21) for passing air from said nozzles under control between the turning device (20) and the dryer (30) and into the return air duct (34) of the dryer (30). A device as claimed in any of the claims 18 to 20, characterized in that the turning device (20) and the drying device (30), which are placed under the box construction (25), are placed directly one after the other in the running direction of the web (W). A device as claimed in any of the claims 18 to 20, characterized in that the turning device (20) and the drying device (30), which are placed under the box construction (25), are placed at a distance from one another. A device as claimed in any of the claims 18 to 20, characterized in that between the turning device (20) and the drying device (30), which are placed under the box construction (25), there is an infrared radiator (13). A device as claimed in claim 23, characterized in that the infrared radiator (13) has been embodied as a profiling unit. A device as claimed in any of the claims 18 to 24, characterized in that the drying device (40) placed at the side of the web (W) opposite to the turning device (20) extends both to the area of the opposite drying device (30) and at least to a part of, possibly to the whole of the area of the turning device (20). A device as claimed in any of the claims 18 to 24, characterized in that the drying device (40) placed at the side of the web (W) opposite to the turning device (20) extends to the area of the opposite drying device (30).

Inventors: HEIKKILAE PERTTI, KARLSTEDT BERTEL, HEIKKILAE, PERTTI, KARLSTEDT, BERTEL, Heikkilä, Pertti
Applicants: METSO PAPER INC, METSO PAPER, INC.
Application year: 1996
Main classification: D21H25
IPC codes: F26B13, D21H25, F26B21