EP4603638A2

EP4603638A2 - An applicator for a machine for producing a fibrous web

Info

Publication number: EP4603638A2
Application number: EP25187115.8A
Authority: EP
Inventors: Negra Paolo Della; Michele DURISOTTI; Klavdij Lasic; Paolo ESTRELLI; Luca UNGARO
Original assignee: Valmet Oy; Valmet AB
Current assignee: Valmet Technologies Oy; Valmet AB
Priority date: 2023-12-20
Filing date: 2024-12-18
Publication date: 2025-08-20
Anticipated expiration: 2044-12-18
Also published as: SE547758C2; EP4575082B1; PL4575082T3; EP4575082A1; EP4603638B1; EP4603638A3; WO2025132536A3; WO2025132536A2; SE2330584A1

Abstract

The invention relates to a machine for producing a fibrous web, the machine comprising an applicator (7) for applying process air to a moving fibrous web manufactured by the machine, the applicator comprising an envelope (701) forming a cavity (702) adapted to receive the process air, the envelope being adapted to extend, with an envelope main extension, in a web width direction which is transverse to a direction of movement of the web, wherein the envelope comprises a distribution plate (703) presenting a plurality of distribution holes (704) to distribute the process air along the width of the web.

Description

TECHNICAL FIELD

The invention relates to an applicator for a machine for producing a fibrous web, for applying process air to a moving fibrous web manufactured by the machine, and to a machine for producing a fibrous web.

BACKGROUND

In tissue manufacturing technology, there is a desire to increase the productivity of machines for producing fibrous webs, and/or reduce the energy consumption of such machines. For reducing the energy consumption, hot process air from one stage of the machine process may be used in another stage of the machine process.
US9702084B2 describes a machine for making a tissue paper web. A first hood is arranged opposite a suction roll. A Yankee drying cylinder is covered by a second hood, and hot exhaust air from the second hood is fed through a conduit to the first hood and used to supply the first hood with moist hot air. The moist air is then sucked through the tissue paper web by the suction roll such that moisture condensates on the tissue paper web and thereby raises the temperature of the tissue paper web before it passes through an extended nip. Thereby water in the web may be less viscous and thereby more easily removed by the suction roll.
In process air heat reuse applications, there is a desire to avoid excessive build-up of particles, such as fibers, on equipment used for the heat reuse. Upon such build-up, the operator may have to retract some equipment and clean it manually. For this, the machine may have to be shut down, which of course decreases productivity.
WO2021063563A1 describes an applicator for applying process air to a running fiber web. A diffuser can be removed from the applicator for maintenance purposes, and a replacement diffuser can be inserted into the applicator after the dirty diffuser has been removed.
There is nevertheless a desire to provide a system to secure the cleanliness of an applicator for applying process air to a fibrous web, which is simple to operate.

SUMMARY

An object of the invention is to provide, in a machine for producing a fibrous web, a way to secure the cleanliness of an applicator for applying process air to the fibrous web, which is simple to operate.
The object is reached with an applicator for a machine for producing a fibrous web, for applying process air to a moving fibrous web manufactured by the machine. The applicator comprises an envelope forming a cavity adapted to receive the process air, the envelope being adapted to extend, with an envelope main extension, in a web width direction which is transverse to a direction of movement of the web, preferably along the entire width of the web. The envelope comprises a distribution plate presenting a plurality of distribution holes to distribute the process air along the width of the web. The applicator comprises a cleaning device extending along the envelope main extension, and being adapted to apply a liquid onto the distribution plate.
By the cleaning device it is possible to clean the distribution plate. By the liquid cleaning, fibers accumulated and stuck on the distribution plate surfaces may be effectively removed. This cleaning may be provided automatically, without any manual process steps. Thereby, cleaning operations may be kept simple, and without the need to shut down the machine. Thereby, a reduction of the productivity of the machine can be avoided.
The liquid which the cleaning device is adapted to apply may be water, or a liquid comprising water.
Preferably, the cleaning device is provided externally of the envelope. The cleaning device may present a slot for the liquid application. Thereby, the slot may be provided at an upper edge of distribution plate.
In some embodiment, the cleaning device comprises a spray bar.
In some embodiments, the cleaning device is provided internally in the envelope.
Thereby, even if the plate is tilted so that the internal surface to be cleaned is facing partly downwards, liquid may run over the surface. Thereby the liquid can remain attached due to cohesive forces.
In some embodiments, the cleaning device is provided externally of the envelope. Thereby, the applicator may comprise an additional cleaning device extending along the envelope main extension, and being adapted to apply a liquid onto the distribution plate, wherein the additional cleaning device is provided internally in the envelope.
In some embodiments, the distribution plate is curved, so as to follow a roll, such as a suction roll. In some embodiments, the distribution plate is planar, so as to follow a planar part of the web path. Regardless whether the distribution plate is curved or planar, there may be an external cleaning device, and also an additional internal cleaning device which may present a slot for the liquid application. The slot may be provided at an upper edge of distribution plate.
In some embodiments, the applicator comprises a retraction actuation assembly by means of which the envelope is adapted to be, when mounted in the machine, retracted away from the web. Thereby, the distribution plate may be kept at a distance from the web such that an external cleaning device may be used to clean the external surface of the plate. When the cleaning action is completed, the envelope may be moved back to its working position.
In some embodiments, the cleaning device is movable in relation to the envelope, so as to be moved along the distribution plate. The movability may be provided by one or more actuators, which may be in any suitable form, e.g. pneumatic or hydraulic cylinders. Thereby, the cleaning device may be moved in a direction which is transverse to the width direction of the web. Guide device, e.g. tracks, may be provided to guide this movement. If the distribution plate is curved, the guide devices may be curved so as for the cleaning device to following the curvature of the plate.
Preferably, the extension of the distribution plate transversely to the envelope main extension is such that when the applicator applies the process air to the web, the distribution plate extends no more than 500 mm, preferably no more than 400 mm, preferably no more than 300 mm, along the web in the web movement direction. Thereby, a more effective cleaning by cleaning device is possible.
Preferably, the respective areas of the distribution holes is at least 28 mm^2, preferably at least 50 mm^2, preferably at least 78 mm^2. For example, if circular, the diameter of the distribution holes is preferably at least 6 mm, preferably at least 8 mm, preferably at least 10 mm. Thereby, there is a decreased possibility of particles clogging the holes.
Preferably, the distribution plate comprises a coating of a low friction material. The coating is preferably provided on both external and internal sides the distribution plate. The material may be PTFE (Polytetrafluoroethylene), e.g. Teflon^®. For example, the material may be AR105 Teflon^® or AR620 MicroCoat^®. Thereby, particle sticking problems are reduced, and easier removal of particles with the liquid from the cleaning device is possible. The coating may be provided on the internal and/or the external surface of the distribution plate.
It has been found that with the cleaning device provided externally of the envelope, the distribution plate extending, where planar no more than 400 mm in the web movement direction, and where curved no more than 300 mm in the web movement direction, and the distribution plate comprising a low friction material coating, a surprising improvement of the cleanliness of the applicator is obtained.
The machine may comprise a drying cylinder, for example a Yankee cylinder, to which a drying hood is assigned. Thereby, an air inlet for the reception of the process air in the envelope may be connected or connectable to an air outlet of the drying hood. In alternative embodiments, the drying cylinder is a cylinder of a through air dryer machine (TAD). Advantageous embodiments of the machine are described below and defined in the dependent claims.

DESCRIPTION OF THE DRAWINGS

Below embodiments of the invention will be described with reference to the drawings, in which

figs. 1A and B show schematically a part of a machine for producing a fibrous web,
fig. 2 shows schematically an applicator to be used with the machine of fig. 1 provided with a first embodiment of a cleaning device,
fig. 3 shows schematically an applicator with a second embodiment of a cleaning device,
fig. 4 shows schematically an applicator with a third embodiment of a cleaning device,
fig. 5 shows schematically an applicator with a fourth embodiment of a cleaning device,
figs. 6 and 7 show schematically an arrangement for moving a cleaning device in relation to an applicator,
figs. 8 and 9 show schematically a variant of an applicator to be used with the machine of fig. 1B and
figs. 10 to 13 show different combinations of the embodiments.

DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 shows a part of a machine for making a tissue paper web W. Parts of the machine may be as described in US9702084B2 incorporated by reference. The tissue web W has first been formed in a former such as a crescent former where a fibrous stock suspension is injected by a head box into a gap between two fabrics. Since this is a well-known procedure, it will not be described further here. The newly formed tissue paper web is carried forward for pressing and drying. For example, it may be carried forward on the lower side of a felt 3 which, in many practical embodiments, may be one of the fabrics between which the tissue paper web has originally been formed.
The tissue paper web W may travel at speeds of 1500 m/min-2500 m/min or 1700 m/min-2500 m/min and preferably 1800 m/min-2400 m/min. Embodiments are conceivable in which the web W travels at a speed of 1800 m/min-2000 m/min.
The tissue paper web W is carried by the felt and passed together with the felt 3 through an extended nip N formed between an extended nip unit 2 and a Yankee drying cylinder 1.
The extended nip unit 2 is preferably an enclosed roll having a flexible tubular jacket 18 (such as a shoe press belt) which can be made of polyurethane or a material that comprises polyurethane or has similar properties. The extended nip unit may also have a press body 17 which may be a concave shoe of metal, for example steel. The press body 17 could also be an elastically deformable body and the extended nip unit could be designed according to, for example, European patent No. 1678374 . The extended nip unit could also be designed in other ways. For example, the extended nip unit 2 could be designed in the way disclosed in EP 2085513 but other known extended nip units could also be used.
As can be seen in FIG. 1, the tissue paper web W is carried on the felt 3 through the extended nip N in such a way that, in the extended nip N, the tissue paper web W contacts the outer surface 4 of the Yankee drying cylinder 1. The web W is separated from the felt 3 when passing through the nip N, and transferred to the Yankee drying cylinder. The web W and the felt 3 are led over a suction roll 5 prior to the extended nip N. Thereby, the felt 3 contacts the suction roll 5, and the felt 3 is located between the tissue paper web W and the suction roll 5. The suction roll 5 is used to drain partly the water from the web W. The suction roll 5 has a suction zone 6 over which the felt 3 and the tissue paper web W pass together. An applicator 7 is arranged opposite the suction roll 5 and partially surrounds the suction roll 5 and the applicator 7 has such an extension around the suction roll that the applicator 7 covers the entire suction zone 6. The applicator 7 comprises an envelope 701, Fig. 2, forming a cavity 702 adapted to receive process air. The envelope 701 is adapted to extend, with an envelope main direction in web width direction which is transverse to a direction of movement of the fibrous web W. The envelope 701 further comprises a distribution plate 703 that is provided with a plurality of orifices or distribution holes 704, wherein the distribution plate 703 is facing the suction roll 5.
The suction roll 5 may have a diameter of 0.50-2.00 meters, e.g. 1.20 meters. The suction zone may have an extension in the axial direction of 3.00-12.00 metres, e.g. 5.70 m. The suction zone 6 may extend for 45°-180° in the circumferential direction, e.g. 120° (a third of the total circumference of the suction roll). The total area of the suction zone may thereby be about 0.6-37.7 m2, e.g. about 7.16 m2.
Moist hot process air is fed from the applicator 7 through the plurality of distribution holes 704 and sucked through the tissue paper web and the felt 3 by the suction roll 5. During this, the tissue paper web W is directly exposed to the applicator 7 such that the moist hot air reaches the tissue paper web W without having to pass through any fabric before reaching the tissue paper web. The total air flow from the applicator 7 through the tissue paper web and into the suction roll may vary typically, depending on the width of the machine, from 0.5 to 3.0 kgDA/s (kilograms dry air per second).
The Yankee drying cylinder 1 is covered by a drying hood 8 which is a Yankee hood which has an air heating and distribution system 9. The heating and air distribution system 9 may comprise one or several heaters 15 and conduits 16 through which hot air can be fed to the drying hood 8, i.e. the Yankee hood. This hot air is blown onto the tissue paper web and contributes to the evaporation of water from the tissue paper web.
Waste air from the Yankee hood can then be exhausted from the Yankee hood and this exhaust air (waste air) is moist and hot. Hot exhaust air is taken from the drying hood 8 and fed through a conduit 10 to the applicator 7 and used to supply the applicator 7 with the moist hot process air. The moist hot process air has a temperature in the range of 100° C.-350° C. and preferably in the range of 150° C.-300° C. The moist hot process air has a moisture content of 150 g water/kg dry air-1000 g water/kg dry air (i.e. 150 grams of water per kilogram dry air-1000 grams of water per kilogram dry air). The pressure of the moist hot process air coming from the drying hood 8 (the Yankee hood) will normally be at about normal atmospheric pressure or slightly higher, i.e. at about 101,325 KPa. When the moist hot process air reaches the applicator 7, the overpressure of the moist hot process air may normally be 0.3 KPa-2 KPa but in some cases an overpressure of up to 3 KPa or even higher can be considered.
The conduit 10 can be equipped with an inlet fresh air stack 10A with a damper 10B, that is used to control the temperature of the moist hot air delivered to the applicator. Another way to control the temperature is by injection of a controlled amount of water or a mixture of water and compressed air or by injection of steam. Typically the air delivered to the applicator has to be in the range of 90°C-180°C.
Moreover, the conduit 10 is equipped with a filter 10C used to clean the air before delivery to the applicator. The filter can be mechanical means or water means or any other effective solution.
A further characteristic of the system is that the conduit 10 is normally equipped with a flow meter 10D with the purpose to continuously measure and control (with a feedback to the fan 11) the air flow to the applicator.
With the above features the possibility to have unexpected accumulation of dust in the blowing surfaces of the applicator has been decreased, helping the cleaning processes that is the main purpose of this invention. Also, the safety aspects are improved with the described features.
This hot moist process air is then sucked through the tissue paper web W by the suction roll 5. When the hot moist process air is sucked through the tissue paper web W, moisture in the air condensates on the tissue paper web W and thereby raises the temperature of the tissue paper web W before the tissue paper web W passes through the extended nip N. The temperature of the tissue paper web would be raised also by hot air that contained no moisture at all but condensation produces a better heating effect, even if only a part of the water in the moist hot process air condensates.
In a different configuration of the tissue machine, the suction roll 5 and the extended nip unit 2 are combined in a single component (called suction press roll). In such configuration (Figure 1B) the applicator 7 is configured with a flat distribution plate 703 and positioned just before the suction press roll, as reported at Figures 8 and 9. The purpose is the same, the moist hot air being sent from the applicator 7 towards the web W and felt 3, and then sucked by the suction press roll with the same result.
The applicator 7 may be moved away from the suction roll 5 in the direction of arrow A with a retraction actuation assembly (not shown in Fig. 1A), in order to facilitate cleaning of the suction roll 5 and the applicator 7. Optionally, the applicator may be disconnected from the conduit 11 for such occasions. Alternatively, the suction roll may be movable away from the applicator 7. Embodiments are conceivable in which both the suction roll 5 and the applicator 7 are movable away from each other.
In order to improve or maintain the function of the applicator 7 and to avoid possible shutdowns, the applicator 7 is provided with a cleaning device designed to remove any particles and debris that may stick on the distribution plate 703 and clog or block the distribution holes 704.
According to a first embodiment of a cleaning device 705, it is positioned outside of the envelope 701 at an upper edge of the distribution plate 703, as seen in Fig. 2, and connected to a fluid source 707 via suitable conduits and pipes 708. The cleaning device 705 is provided with a nozzle 706 in the form of a slot that extends generally the main extension of the distribution plate 703. Fluid from the fluid source 707, for instance water possibly added with detergents, is transported via suitable pumping elements and conduits to the slot-shaped nozzle 706, wherein the fluid will flow along the outer surface of the distribution plate 703, thereby removing any particles and debris that block the distribution holes 704.
As a further second embodiment and an alternative to cleaning the outer surface of the distribution plate, it is positioned inside the envelope 701 of the applicator 7, i.e. in the cavity 702. The cleaning device 709 is attached to and provided at an upper edge of the distribution plate 703, Fig. 3. The cleaning device 709 is provided with a nozzle 710 in the shape of a slot that extends generally the main extension of the distribution plate. The nozzle 710 is connected to the fluid source 707 via suitable conduits or pipes 708.
The applicator 7 may comprise a cleaning device 711 in the form of a spray bar which is provided outside the envelope. For example, as a third embodiment and as an alternative to an external cleaning device with slot-shaped external nozzle, the cleaning device 711 in the form of a spray bar may be provided outside the envelope, Fig.4, which spray bar 711 is designed and arranged such that fluid sprayed from the spray bar will cover the outer surface of the distribution plate 703. The spray bar 711 comprises several nozzle outlets that are positioned along the main extension of the distribution plate 703 in order to be able to cover the whole outer surface of the distribution plate 703. As seen in Fig. 4, the spray bar 711 may be positioned above the outer surface of the distribution plate 703 and arranged such that fluid sprayed from the spray bar 711 will hit an upper area of the distribution plate 703 and flow downwards. With this solution, the spray bar 711 may be attached to a suitable support provided with conduits and pipes for distribution of fluid from the fluid source. The spray bar 711 of the applicator 7 may be mounted to the envelope 701, or to any other suitable part of the tissue paper making machine.
As an alternative to an internal cleaning device with slot-shaped nozzle, a fourth embodiment comprises a cleaning device 712 in the form of a spray bar that is provided inside the envelope, Fig. 5, i.e. in the cavity 702, which spray bar 712 is designed and arranged such that fluid sprayed from the spray bar 712 will cover the inner surface of the distribution plate 703. In this regard, the spray bar 712 comprises several nozzle outlets 713 that are positioned along the main extension of the distribution plate 703 in order to be able to cover the whole inner surface of the distribution plate 703.
As an alternative to an external spray bar that is fixed or stationary in relation to the outer surface of the distribution plate, the external spray bar may be arranged to be movable in relation to the distribution plate. Figs. 6 and 7 show one feasible solution. The spray bar 711 is provided with guide elements 714 at both ends as seen in the main extension of the distribution plate 703. The guide elements 714 fit into elongated tracks 715 and the spray bar 711 is connected to movement elements 716. The movement elements 716 may comprise pneumatically or hydraulically driven pistons that when actuated can move the spray bar 711 along the tracks 715 in order to cover the whole outer surface of the distribution plate with fluid, Fig. 7. As seen in Figs. 6 and 7, the tracks 715 may have a curvature that corresponds to the curvature of the distribution plate 703 so that the nozzle outlets of the spray bar 711 are positioned at generally the same distance in relation to the distribution plate 703 during movement and cleaning with the spray bar 711. The tracks 715 and the movement elements 716 of the applicator 7 may be mounted to the envelope 701, or to any other suitable part of the tissue paper making machine. The tracks may be stationary, or movable together with the rest of the applicator, e.g. away from the suction roll, as exemplified below.
The embodiments above show an applicator 7 that is positioned such that the distribution plate 703 is facing the suction roll 5, whereby the distribution plate 703 is provided with a curvature generally corresponding to the curvature of the suction roll 5. However, an applicator 7' may be placed "upstream" or before the suction roll 5 as seen in the feeding direction of the web, as seen in Fig. 7. In this position, the distribution plate 703' is flat since the fibrous web W passing the applicator 7' here is flat. The applicator 7' with a flat distribution plate 703' may have the same types of cleaning devices as mentioned above.
With any of the above embodiments, the applicator has to be moved away from the suction roll and/or the web W with a retraction actuation assembly 717 when a cleaning operation is to be performed. The retraction actuation assembly 717 may be designed in many ways with appropriate mechanisms that can provide translational movement, as seen with arrow T1 in Fig. 4, or tilting movement, as seen with arrow T2 in Fig. 7, of the applicator 7 in relation to the suction roll 5 and/or the web W. The mechanisms may of course be designed to perform both translational and tilting movement for changing the position of the applicator 7. The person skilled in the art is capable of designing several solutions within his/her technical ability and these will not be discussed in detail here.
The embodiments described above may be combined in several ways. For instance, cleaning may be performed both internally and externally with cleaning devices that are positioned both inside and outside of the envelope. In that regard, the internal cleaning may be performed by a cleaning device 709 with a slot-shaped nozzle 710 and the external cleaning performed with a cleaning device 705 with a slot-shaped nozzle 706 as seen in Fig. 10. As an alternative the internal cleaning may instead be performed with a spray bar 712 as seen in Fig. 11. Moreover, the external cleaning may be performed by a spray bar 711 that may be stationary or movable. The internal cleaning may then be performed with a slot-shaped nozzle 710 as seen in Fig. 12 or with a spray bar 712 as seen in Fig. 13. In this manner, both the inner surface and the outer surface of the distribution plate are cleaned.
Examples according to the following clauses are also disclosed:

1. An applicator (7) for a machine for producing a fibrous web, for applying process air to a moving fibrous web manufactured by the machine, comprising
- an envelope (701) forming a cavity (702) adapted to receive the process air, the envelope being adapted to extend, with an envelope main extension, in a web width direction which is transverse to a direction of movement of the web,
- wherein the envelope comprises a distribution plate (703) presenting a plurality of distribution holes (704) to distribute the process air along the width of the web,
- wherein the applicator comprises a cleaning device (705, 709, 711, 712) extending along the envelope main extension, and being adapted to apply a liquid onto the distribution plate (703).
2. An applicator according to clause 1, wherein the cleaning device (705, 711) is provided externally of the envelope (701).
3. An applicator according to any one of the preceding clauses, wherein the cleaning device (705, 709) presents a slot (706, 710) for the liquid application.
4. An applicator according to clause 3, wherein the slot (706, 710) is provided at an upper edge of distributor plate (703).
5. An applicator according to any one of the preceding clauses, wherein the cleaning device (711, 712) comprises a spray bar.
6. An applicator according to any one of the preceding clauses, wherein the cleaning device (709, 712) is provided internally in the envelope (702).
7. An applicator according to any one of clauses 1-5, wherein the cleaning device (705, 711) is provided externally of the envelope (701), wherein the applicator comprises an additional cleaning device (709, 712) extending along the envelope main extension, and being adapted to apply a liquid onto the distribution plate (703), wherein the additional cleaning device (709, 712) is provided internally in the envelope (701).
8. An applicator according to any one of the preceding clauses, wherein the applicator comprises a retraction actuation assembly (717) by means of which the envelope (701) is adapted to be, when mounted in the machine, retracted away from the web.
9. An applicator according to any one of the preceding clauses, wherein the cleaning device (711) is movable in relation to the envelope, so as to be moved along the distribution plate.
10. An applicator according to any one of the preceding clauses, wherein the extension of the distribution plate (703) transversely to the envelope main extension is such that when the applicator (7) applies the process air to the web, the distribution plate (703) extends no more than 500 mm, preferably no more than 400 mm, preferably no more than 300 mm, along the web in the web movement direction.
11. An applicator according to any one of the preceding clauses, wherein the respective areas of the distribution holes (704) is at least 28 mm^2, preferably at least 50 mm^2, preferably at least 78 mm^2.
12. An applicator according to any one of the preceding clauses, wherein the distribution plate (703) comprises a coating of a low friction material.
13. An applicator (7) for a paper machine, for applying process air to a moving fibrous web manufactured by the machine, comprising
- an envelope (701) forming a cavity adapted to receive the process air, the envelope being adapted to extend, with an envelope main extension, in a web width direction which is transverse to a direction of movement of the web,
- wherein the envelope comprises a distribution plate (703) presenting a plurality of distribution holes (704) to distribute the process air along the width of the web,
- wherein the extension of the distribution plate (703) transversely to the envelope main extension is such that when the applicator (7) applies the process air to the web, the distribution plate (703) extends no more than 500 mm, preferably no more than 400 mm, preferably no more than 300 mm, along the web in the web movement direction.
14. An applicator (7) for a paper machine, for applying process air to a moving fibrous web manufactured by the machine, comprising
- an envelope (701) forming a cavity adapted to receive the process air, the envelope being adapted to extend, with an envelope main extension, in a web width direction which is transverse to a direction of movement of the web,
- wherein the envelope comprises a distribution plate (703) presenting a plurality of distribution holes (704) to distribute the process air along the width of the web,
- wherein the respective areas of the distribution holes (704) is at least 28 mm^2, preferably at least 50 mm^2, preferably at least 78 mm^2.
15. An applicator (7) for a paper machine, for applying process air to a moving fibrous web manufactured by the machine, comprising
- an envelope (701) forming a cavity adapted to receive the process air, the envelope being adapted to extend, with an envelope main extension, in a web width direction which is transverse to a direction of movement of the web,
- wherein the envelope comprises a distribution plate (703) presenting a plurality of distribution holes (704) to distribute the process air along the width of the web,
- wherein the distribution plate (703) comprises a coating of a low friction material.
16. A machine for producing a fibrous web, such as for tissue, for example paper tissue, comprising an applicator according to any one of the preceding clauses.
17. A machine according to clause 16, wherein the machine comprises a drying cylinder (1), for example a Yankee cylinder, to which a drying hood (8) is assigned, and wherein an air inlet for the reception of the process air in the envelope (701) is connected or connectable to an air outlet of the drying hood via a conduit (10).
18. A machine according to clause 17, wherein the conduit (10) is equipped with means (10A, 10B) to control the temperature of the moist hot air delivered to the applicator.
19. A machine according to clause 18, wherein the means to control the temperature are a fresh air stack (10A) with a damper (10B).
20. A machine according to clause 18, wherein the means to control the temperature are a water or water/air compressed injectors.
21. A machine according to clause 18, wherein the means to control the temperature are a steam injector.
22. A machine according to any one of clauses 17-21, wherein the conduit (10) is equipped with a filter (10C) for cleaning the air before delivery to the applicator.
23. A machine according to clause 22, wherein the filter (10C) is a mechanical filter.
24. A machine according to clause 22, wherein the filter (10C) is a filter using water.
25. A machine according to any one of clauses 17-24, wherein the conduit (10) is equipped with a flow meter (10D) with the purpose to continuously measure and control the air flow to the applicator.

It is to be understood that the embodiments described above and shown in the drawings are only to be regarded as non-limiting examples of the invention and that it may be modified in many ways within the scope of the patent claims.

Claims

A machine for producing a fibrous web (W), such as for tissue, for example paper tissue, comprising an applicator (7) for applying process air to a moving fibrous web manufactured by the machine, the applicator (7) comprising
- an envelope (701) forming a cavity adapted to receive the process air, the envelope being adapted to extend, with an envelope main extension, in a web width direction which is transverse to a direction of movement of the web (W),

- wherein the envelope (701) comprises a distribution plate (703) presenting a plurality of distribution holes (704) to distribute the process air along the width of the web (W),

- wherein the respective areas of the distribution holes (704) is at least 28 mm^2, preferably at least 50 mm^2, preferably at least 78 mm^2,

- wherein the applicator (7) comprises a retraction actuation assembly (717) by means of which the envelope (701) is adapted to be, when mounted in the machine, retracted away from the web,
wherein the machine comprises a drying cylinder (1), for example a Yankee cylinder, to which a drying hood (8) is assigned, and wherein an air inlet for the reception of process air in the envelope (701) is connected or connectable to an air outlet of the drying hood (8) via a conduit (10) the machine comprising a suction roll and wherein the applicator (7) is positioned upstream the suction roll as seen in the feeding direction of the web (W).
A machine according to claim 1, wherein the extension of the distribution plate (703) transversely to the envelope main extension is such that when the applicator (7) applies the process air to the web, the distribution plate (703) extends no more than 500 mm, preferably no more than 400 mm, preferably no more than 300 mm, along the web in the web movement direction
A machine according to claim 1 or 2, wherein the distribution plate (703) comprises a coating of a low friction material (7).
A machine according to any one of the preceding claims, the applicator (7) comprising a cleaning device (705, 709, 711, 712) extending along the envelope main extension, and being adapted to apply a liquid onto the distribution plate (703).
A machine according to claim 4, wherein the cleaning device (705, 711) is provided externally of the envelope (701).
A machine according to claim 4 or 5, wherein the cleaning device (705, 709) presents a slot (706, 710) for the liquid application.
A machine according to claim 6, wherein the slot (706, 710) is provided at an upper edge of distributor plate (703).
A machine according to any one of claims 4 to 7, wherein the cleaning device (711, 712) comprises a spray bar.
A machine according to any one of claims 4 to 8, wherein the cleaning device (709, 712) is provided internally in the envelope (702).
A machine according to any one of claims 4 to 8, wherein the cleaning device (705, 711) is provided externally of the envelope (701), wherein the applicator comprises an additional cleaning device (709, 712) extending along the envelope main extension, and being adapted to apply a liquid onto the distribution plate (703), wherein the additional cleaning device (709, 712) is provided internally in the envelope (701).
A machine according to any one of the preceding claims, wherein the conduit (10) is equipped with means (10A, 10B) to control the temperature of the moist hot air delivered to the applicator.
A machine according to claim 11, wherein the means to control the temperature are a fresh air stack (10A) with a damper (10B), or a water or water/air compressed injectors, or a steam injector.
A machine according to claim 11 or 12, wherein the conduit (10) is equipped with a filter (10C) for cleaning the air before delivery to the applicator, wherein the filter (10C) is a mechanical filter, or a filter using water.
A machine according to any one of claims 11 to 13, wherein the conduit (10) is equipped with a flow meter (10D) with the purpose to continuously measure and control the air flow to the applicator.