TECHNICAL FIELD OF THE INVENTION

The object of the invention is an arrangement and a method in connection with an impingement dryer of a fiber web according to the preambles of the independent claims presented further below. The invention relates especially to a new way of keeping clean an impingement dryer in a paper machine or the like and for enhancing tail threading in connection with an impingement dryer.

BACKGROUND OF THE INVENTION

An impingement dryer according to prior art comprises a web run arrangement supporting a fiber web, and a blow chamber, which on the side towards the web is provided with blowing means for blowing air or another gas towards the fiber web. In, general, a web run arrangement comprises several subsequent rolls and cylinders, which are mainly fixed in their place, but arranged to rotate around their, longitudinal axis, a support fabric, such as a wire, which is arranged to move in relation to the rolls and cylinders, and runnability components, such as blow boxes. The fiber web is typically arranged to travel past the blowing means of the impingement dryer, supported by the rolls, cylinders, wire and runnability components, along a so-called machine direction web run. The blowing means generally comprise a blow surface provided with blow openings from which the blown air is directed towards the fiber web. The impingement dryer also usually comprises air exhaust means for removing air from the dryer. The air exhaust means can, for example, be suction openings arranged in the blow surface, through which openings air is suctioned.

Impingement dryers can be divided into vertical and horizontal ones, according to the position of their web run arrangement and thus also to the main position of the fiber web conveyed in them. In vertical impingement dryers air is blown into the fiber web while the web travels in a mainly vertical position. In horizontal impingement dryers air is blown into the fiber web while the web travels in a mainly horizontal position. Vertical and horizontal must be understood widely, comprising up to a 45° deviation from the vertical or horizontal direction. The deviation can also be 0-35°, 0-20°, 0-10° or 0-5 degrees. The position of the web run arrangement and of the fiber web can be, within one impingement dryer, mainly straight or slightly curved. The blown air is usually warmer than the fiber web towards which air is blown. The blown air is usually hot. For example, when drying a paper web the temperature of the blown gas can be for example 200-400 °C.

Also other kinds of impingement dryers exist. For example, an impingement dryer can be placed on a single roll or cylinder in order to dry a fiber web travelling supported by it.

Impingement dryers are presented for example in the patent publications WO 97/13031 , WO 02/36880, WO 2005/068713, and WO 2009/130380.

Pieces of the fiber web, for example of the paper web, to be dried often get onto the impingement dryer. The outer surface of the dryer is usually warm or even hot, whereby a humid piece of fiber hitting it dries and sticks quickly to the surface of the dryer. A piece of fiber stuck to the dryer can impede production, for example trash can come loose from it into the fiber web being produced. Fiber material stuck to the outer surface of the dryer can raise the risk of a fire. Fouling is common especially during a web break. One of the places, which is most easily fouled, is the upper edge of a vertical dryer. Also, for example, when placed on a single roll or cylinder, the dryer has the same fouling tendency.

It is known in paper machines during web break situations to remove dirt or to prevent dirt from sticking to some parts of the paper machine by blowing air to the areas that are most easily fouled. The air flow grabs the pieces of fiber, which then fall for example on the machine room floor. In spite of this, in some cases and for example with some paper grades, pieces of fiber may remain on the dryer. During tail threading, the fiber web may be carried into a direction different from what was meant to, for example, the fiber web coming out from the impingement dryer may tend to be guided via the wrong side of the first roll after the dryer. OBJECT OF THE INVENTION

It is an object of the present invention to reduce or even eliminate the above- mentioned problems appearing in prior art.

It is especially an object of the present invention to provide a solution for enhancing tail threading of a fiber web in connection with an impingement dryer of a paper machine, a board machine or a pulp dryer. It is especially an object to guide the fiber web in a more reliable manner than before into a desired direction during tail threading. It is especially an object of the present invention to provide a solution for keeping clean the impingement dryer of a paper machine, a board machine or a pulp dryer.

It is especially an object of the present invention to provide a solution for keeping clean the impingement dryer of a paper machine, a board machine or a pulp dryer in situations diverging from normal running situation, such as during a web break or tail threading.

It is an object of the present invention to provide a solution for keeping clean the first end of the impingement dryer, i.e. the location in which the fiber web and the support fabric supporting it enter the impingement dryer.

It is an object of the present invention to enhance tail threading of the fiber web at the location of the first end of the impingement dryer.

It is an object of the present invention to provide a solution for keeping clean the second end of the impingement dryer, i.e. the location in which the fiber web and the support fabric supporting it come out of the impingement dryer. It is an object of the present invention to enhance tail threading of the fiber web at the location of the second end of the impingement dryer. It is an object of the present invention to provide a solution with which the upper edge of a vertical impingement dryer is kept clean.

It is an object of the present invention to provide a retrofittable cleaning solution and/or tail threading enhancing solution for an impingement dryer.

It is an object of the present invention to reduce spreading of hot and humid air from the dryer into the surroundings, especially during tail threading or a fault situation, such as a web break.

It is an object of the present invention to reduce the risk of a fire.

It is an object of the present invention to efficiently extinguish an eventual fire.

DESCRIPTION OF THE INVENTION

In order to realise i.a. the objects mentioned above, the arrangement and method according to the invention are characterized by what is presented in the characterizing parts of the enclosed independent claims.

The embodiments and advantages mentioned in this text are in suitable parts applicable to both the arrangements and methods according to the invention, even if this is not always specifically mentioned.

In this text a fiber web stands for a paper web, a board web or a pulp web. Thus, the invention is particularly well suitable to be used in connection with a paper machine, a board machine or a pulp dryer.

The present invention can be applied in connection with a prior art impingement dryer. In a typical impingement dryer: - The fiber web to be dried is supported with a support fabric, such as a wire.

- The support fabric and the fiber web to be dried are moved in the machine direction supported by several rolls or cylinders, which rotate around machine cross direction axes:

a) in via a first end of the impingement dryer,

b) inside the impingement dryer past blowing means and exhaust means, and c) out via a second end of the impingement dryer.

- Gas, for example air, is blown from the blowing means towards the fiber web to be dried. The blown gas is usually hot. Usually the gas is warmer than the fiber web to be dried. For example, when drying a paper web, the temperature of the blown gas can be for example 200-400 °C.

- Gas is removed from the vicinity of the fiber web into the exhaust means.

In a typical method according to the invention in connection with an impingement dryer of a fiber web:

- the fiber web (50) is guided into the impingement dryer (10, 20, 30) via its first end (11 , 21 , 31), ,

- the fiber web is guided inside the impingement dryer past blowing means (104) and exhaust means (105), and

- the fiber web is guided out via a second end (12, 22, 32) of the impingement dryer,

- during a web break or tail threading, the fiber web is guided into a desired direction by means of a guiding form (304) arranged in the first end (11 , 21 , 31) or the second end (12, 22, 32) of the impingement dryer, on an outer surface (303) of the impingement dryer, and the guiding form having, in the machine cross direction, at least the width of mainly the entire dryer.

A typical prior art impingement dryer is used to dry a continuous fiber web, such as a paper web, a board web or a pulp web. The web is supported by a support fabric, such as a wire. Both the support fabric and the web supported by it are moved through the impingement dryer in its machine direction. A typical impingement dryer comprises: - A first end and a second end of the impingement dryer, which are mainly transversal with respect to the machine direction, and edges mainly in the machine direction.

- Gas blowing means and gas exhaust means arranged inside the impingement dryer. The blown gas is typically heated air. A part of the gas can be brought from the outside of the impingement dryer and a part can be circulated inside the device from the exhaust means back to the blowing means.

- Several rolls or cylinders arranged to rotate around their longitudinal axis arranged in the machine cross direction, i.e. transversal with respect to the machine direction, on which rolls or cylinders the support fabric and the fiber web to be dried are arranged to move. The rolls or cylinders are arranged to define the path along which the support fabric and the fiber web are arranged to travel:

a) into the impingement dryer via its first end,

b) inside the impingement dryer past the blowing means and the exhaust means, and

c) out via the second end of the impingement dryer.

A typical arrangement according to the invention in connection with an impingement dryer of a fiber web comprises

- an impingement dryer in which the fiber web is arranged to travel into the impingement dryer via its first end, inside the impingement dryer past the blowing means and the exhaust means, and out via the second end of the impingement dryer.

In the first end or the second end of the impingement dryer, on the outer surface of the impingement dryer, is arranged a guiding form, which is at least of the width of mainly the entire dryer in the machine cross direction. The guiding form is arranged to guide the fiber web into a desired direction during a web break or tail threading.

The guiding form can be a separate formed part fixed to the outer surface of the dryer. The guiding form can also be formed of the outer surface of the dryer by shaping a form in the machine cross direction in it. One dryer can be provided with several guiding forms.

One of the main advantages of the invention is that, by means of the guiding form, the fiber web to be dried can be guided into a desired direction. The guiding form works in a guiding manner during normal use of the impingement dryer, but the advantages come up especially in exceptional situations, such as during tail threading or a web break. For example, during tail threading the fiber web may have the tendency to follow the support fabric that has supported it, even in locations where the fiber web and the support fabric should move into different directions.

One of the main advantages of the invention is that, by means of the guiding form, fouling of the impingement dryer is prevented during the normal use of the dryer, but especially in exceptional situations, such as during tail threading and a web break.

By means of the invention, building up of the tail end into a wrong place can be prevented.

One of the main advantages of the invention is that keeping of the dryer clean can be performed by guiding the web and by closing wrong paths from the web by means of a simple and reliable mechanical form. One of the main advantages of the invention is the diminution of the risk of a fire and the minimization of the damages caused by an eventual fire. By means of the invention, the web can be guided in tail threading and/or during web breaks. In this manner, gathering of pieces of web, harmful in view of fire safety, on the hot surfaces of the dryer can be reduced. Fiber material stuck on the outer surface of the hot dryer can raise the risk of a fire. Enhancing of tail threading, more efficient guiding of the web in a break situation, and keeping the dryer clean, achieved by means of the invention, all serve, for their part, the fire protection. In an embodiment of the invention, a guiding form according to the invention is placed near the first end of the impingement dryer. In an embodiment of the invention, a guiding form according to the invention is placed near the second end of the impingement dryer. These places, where the fiber web to be dried enters the dryer or comes out of it, are critical in view of the quality of the fiber web to be dried.

In an embodiment of the invention, the impingement dryer is vertical. In a vertical dryer especially its upper edge is fouled. In an embodiment of the invention, a guiding form according to the invention is placed in connection with the upper edge of a vertical impingement dryer.

In an embodiment of the invention, the impingement dryer is horizontal. A horizontal dryer is often provided with a long horizontal upper surface, i.e. with a lot of possibly fouling surface, for the cleaning of which the invention can be utilized.

In an embodiment of the invention, the upper surface of the guiding form is in an angle in view of the horizontal plane in the machine direction. In an embodiment of the invention, the upper surface of the guiding form is mainly horizontal in the machine cross direction. An inclined surface remains clean and is easy to clean.

In an embodiment of the invention, the upper surface of the guiding form is formed into a ridge in the machine cross direction. The ridge angle can be for example 45- 135 degrees or 80-135 degrees. In an embodiment of the invention, the upper surface of the guiding form is formed by two substantially planar surfaces, which are placed in an angle with respect to each other.

An embodiment of the invention comprises

- blowing means and a pressurized air pipe for bringing pressurized air into the vicinity of the impingement dryer;

- a blow nozzle for guiding the pressurized air out of the pressurized air pipe. In an embodiment of the invention, the blow nozzle is arranged to guide the pressurized air towards the upper surface of the guiding form in order to keep it clean. Air can also be guided towards other surfaces of the dryer and the guiding form in order to keep them clean.

In an embodiment of the invention, the blow nozzles are arranged so that air is blown to both sides of the upper edge of the guiding nozzle or of the said ridge. In an embodiment of the invention, the blow nozzles are placed so that air is blown mainly downwards from said ridge.

In an embodiment of the invention, the blow nozzles comprise only openings formed in the pressurized air pipe.

In an embodiment of the invention, there are several blow nozzles, by intervals of for example 2-35 cm, 5-20 cm, 5-15 cm or 10-20 cm along the entire guiding form.

In an embodiment of the invention, the pressurized air pipe and the blow nozzles are separate from the guiding form. They can be fixed for example to a suitable beam or other structure, from which the blows can be guided into desired directions. The pressurized air pipe and the blow nozzles can be fixed also to the one and same impingement dryer which is provided with the guiding form.

In an embodiment of the invention, the pressurized air pipe is integrated to the guiding form. The pressurized air pipe can be arranged to travel inside the guiding form on the width of the entire dryer. The pressurized air pipe can be a separate pipe mounted in connection with the impingement dryer. In an embodiment, it is possible to form the structures of the guiding form to be pipe-like, hollow, as such.

Thereby the structures of the guiding form, as such, can work as an air pipe. On the other hand, it is easy to mount a separate pressurized air pipe inside a hollow guiding form. A pressurized air pipe travelling inside the guiding form is protected against fouling, for example. In an embodiment of the invention, the blow nozzle comprises an opening arranged in the upper surface of the guiding form via which opening air is arranged to the outside of the upper surface of the guiding form via a pressurized air pipe provided inside the guiding form. Separate blow nozzles can be mounted in the opening, or the opening can function as a blow nozzle as such.

In an embodiment of the invention, the blow nozzle is arranged to guide pressurized air towards the fiber web to be dried in order to guide the fiber web into a desired direction. In this manner, the fiber web guiding effect produced by the guiding form itself can be enhanced.

In an embodiment of the invention, the arrangement comprises a control unit, which is arranged to observe the fiber web production process in which the impingement dryer is used. Thereby the control unit is arranged to detect a web break or tail threading taking place in the production process. After having detected the same, the control unit sends a control signal to the blowing means in order to guide the pressurized air into the pressurized air pipe. The control unit can be arranged to send a control signal to the blowing means for example in the following manner:

- during a normal running situation guiding of the pressurized air into the pressurized air pipe is prevented,

- during a web break or tail threading guiding of the pressurized air into the pressurized air pipe is allowed.

By means of the control signal, it is possible for example to open and to close a pressurized air valve provided in the pressurized air pipe.

In an embodiment of the invention, the guiding form comprises a sealing member arranged between the outer surface of the impingement dryer and some other structure, which sealing member is connected via a first connection to the outer surface of the impingement dryer and via a second connection to the said other structure. The first and the second connection can be movable in such a manner that they allow moving of the outer surface of the impingement dryer with respect to the other structure for example during a web break or tail threading. For example, the first or the second connection can be a hinge and a longitudinal slot of a suitable form into which a counterpart is arranged in a mobile manner. In an embodiment the sealing member as such is made of a flexible material, for example rubber or plastic, so that while the outer surface of the impingement dryer is moving with respect to the other structure, then the sealing member is stretched allowing said movement.

In an embodiment of the invention, the guiding form comprises a fire-extinguishing system, which comprises a water pipe and a nozzle connected to the pipe in order to lead water towards the impingement dryer. The nozzles of the fire-extinguishing system are preferably water mist extinguishing nozzles. A mist extinguishing system uses only little of water. The nozzles according to the invention can easily be placed so that water hits only the fire area, but not for example the hot surfaces of the dryer, such as the nozzle surfaces. Fire-extinguishing water hitting a hot surface can break the dryer. The structures can for example be distorted and thereby deteriorated.

The invention can be realized as an integrated arrangement separately mounted, for example retrofitted, in the impingement dryer. This kind of an integrated arrangement can comprise:

- a guiding form according to the invention,

- fixing means in order to fix the integrated arrangement to the impingement dryer. An integrated, for example retrofitted, arrangement can also be provided with one or more of the following:

- a pressurized air pipe for bringing pressurized air to the cleaning arrangement,

- one or more blow nozzles for guiding the pressurized air out of the pressurized air pipe,

- a fire alarm system, which is arranged to produce an alarm signal in case of a fire, - a fire-extinguishing system comprising a water pipe and a nozzle connected to the pipe in order to lead water towards the impingement dryer on the basis of the alarm signal. In an integrated, for example retrofitted, arrangement the guiding form and the fixing means and other possible parts, such as the pressurized air pipe, blow nozzle, fire-extinguishing water pipe, fire-extinguishing water nozzle are fixed into a one and same piece before mounting to the dryer. Thereby the arrangement can be mounted as a single unit to the impingement dryer. A retrofitted arrangement can comprise also all the other above-mentioned features of the invention, when applicable.

An advantage of an integrated, for example retrofitted, arrangement is that by means of one separated unit easily mountable to the impingement dryer, both an enhanced cleaning and fire safety are easily achieved. The pressurized air blow nozzles and the fire-extinguishing water nozzles can thereby be easily arranged for example to an elevated part, which is separated from the surface of the dryer and located at a distance therefrom. In this manner, both the guiding property of the pressurized air and the directing of the fire-extinguishing water can be enhanced and adjusted.

BRIEF DESCRIPTION OF THE FIGURES

The invention is described in more detail below with reference to the enclosed schematic drawing, in which

Figure 1 shows impingement dryers according to the invention placed in the dryer section of a paper machine,

Figure 2 shows a partial cross section in the machine direction of an impingement dryer according to the invention,

Figure 3 shows the upper end of a vertical impingement dryer according to the invention,

Figure 4 shows the upper end of another vertical impingement dryer according to the invention, Figure 5 shows the upper end of a third vertical impingement dryer according to the invention,

Figure 6 shows the upper end of a fourth vertical impingement dryer according to the invention in the dryer section of a paper machine,

Figure 7 shows the cross section of the guiding form according to the solution of

Figure 6,

Figure 8 shows the guiding form of Figure 6 in a perspective view,

Figure 9 shows the upper end of a fifth vertical impingement dryer according to the invention in the dryer section of a paper machine, and

Figure 10 shows a method according to the invention as a flow chart.

DETAILED DESCRIPTION OF THE EXAMPLES OF THE FIGURES

For the sake of clarity, the same reference numbers are usually used for corresponding parts in different embodiments.

Figure 1 shows both two typical so-called vertical impingement dryers 20, 30 according to the invention, and a so-called horizontal impingement dryer 10. The impingement dryers 10, 20, 30 are mounted in the forward end of a dryer section 41 of a paper machine, before drying cylinders 42-45. The paper web 50 to be dried is, supported by a first wire 51 , guided from a press section 40 with the aid of a runnability component 60 to a roll 61 and to be supported by a second wire 52. Thereafter the paper web 50 is, supported by the second wire 52, led in through a first end 11 of the horizontal impingement dryer 10. Inside the dryer 10 the second wire 52 and the paper web 50 travelling with it are transported substantially horizontally, supported by rotating support rolls 13 and blow boxes 14. When moving horizontally, the paper web 50 is subjected to the drying of the horizontal impingement dryer 10. The second wire 52 and the paper web 50 to be dried are, supported by a roll 19, led out via a second end 12 of the horizontal impingement dryer 10. Thereafter the travel of the second wire 52 and the paper web 50 is turned downwards and further on to a roll 28. On the roll 28, the paper web 50 to be dried is moved to be supported by a third wire 53. From the roll 28 the third wire 53 and the paper web 50 supported by it are led in via a first end 21 of the first vertical impingement dryer 20. Inside the dryer 20, the third wire 53 and the paper web 50 travelling with it are transported substantially vertically downwards, supported by rotating support rolls 23 and blow boxes 24. When moving downwards, the paper web 50 is subjected to the drying of the first vertical impingement dryer 20. The third wire 53 and the paper web 50 are led out via a second end 22 of the first vertical impingement dryer 20 to a turn roll 29 at the bottom end of the dryer 20. With the aid of the roll 29, the travel direction of the third wire 53 and the paper web 50 is turned back upwards, and in via a first end 31 of the second vertical impingement dryer 30. Inside the dryer 30 the third wire 53 and the paper web 50 travelling with it are transported substantially vertically upwards, supported by rotating support rolls 33 and blow boxes 34. When moving upwards, the paper web 50 is subjected to the drying of the second vertical impingement dryer 30. The third wire 53 and the paper web 50 are led out via a second end 32 of the second vertical impingement dryer 30 and via the roll 28 to the first drying cylinder 42 of the dryer section 41 of the paper machine. In Figure 1 , also subsequent drying cylinders 43, 44 and 45 and turn rolls 46, 47 and 48 of the drying section 41 have been drawn.

In the example of Figure 1 , the paper web 50 travels along a somewhat curved path inside both the vertical 20, 30 and the horizontal 10 impingement dryers. The curved path has been achieved by placing the axes of the rolls 13, 23, 33, which support the paper web 50 and the wire 51-53 at the location of the dryer, in a curved line as seen in the machine cross direction. The path of the paper web 50 and the wire 51-53 turns slightly at the location of each of these rolls 13, 23, 33. In the sections between these rolls 13, 23, 33 the wire and the web travel with an unsupported draw, i.e. along an essentially straight path supported by the blow boxes 14, 24, 34.

In Figure 1 , alternative positions 10', 20', 20", 30', 30" of the dryers are drawn with dotted lines, into which positions the dryers can be moved for example for the duration of maintenance work. Typically, when moving the dryer 10, 20, 30 to its alternative position 10', 20', 20", 30', 30", the wire 51-53 and the paper web 50 located by the dryer do not move with it. In the alternative positions 10', 20', 20", 30', 30", the dryer with its blow chambers and blowing means is thus moved further away from the support rolls 13, 23, 33, from the paper web 50 to be dried and from the wire 51-53 than in a normal running situation. In Figure 1 also some support structures 62 of the paper machine and a hood 63 of the dryer section are seen.

In Figure 1 two guiding forms 304 according to the invention are seen. One is placed at the highest point of the outer surface of the horizontal impingement dryer 10. The other guiding form 304 is mounted in the upper edge of the vertical impingement dryer 30, in connection with the second end 32 of the dryer 30. The structure of the different guiding forms is described more in detail in Figures 3 - 9.

Blow chambers 101 of the dryers are provided inside the dryers 10, 20, 30, whereby on the blow chambers' sides towards the paper web 50 blowing means 102 have been arranged for blowing air or another hot gas towards the paper web 50 travelling past them. The structure of a blow chamber 101 is shown in Figure 2. The blowing means 102 comprise a blow surface 103 provided with blow openings 104 from which the hot air is directed towards the paper web 50. Exhaust means for the air, i.e. exhaust openings 105, have also been arranged in the blow surface 103, through which openings air is suctioned out from the dryer 10, 20, 30.

Figure 2 shows a partial cross section in the machine direction of a blow chamber 101 of a horizontal impingement dryer 10 according to the invention. In the bottom of the Figure, the paper web 50 to be dried is shown and underneath it the support fabric, i.e. the wire 52, supporting it. Above the web 50, at a distance of for example 10-50 mm or 20-30 mm, there is a blow surface 103, which is parallel to the web 50 and the support fabric 52. Above the blow surface 103 there are air inlet channels 106, from which heated air is blown via the blow openings 104 formed in the blow surface 103 towards the web 50 to be dried in the manner shown by the arrows. Moisture moves from the web 50 to be dried into the air. Between the air inlet channels 106 there are air exhaust channels 107, into which moist air is suctioned from the vicinity of the web 50 to be dried via the exhaust openings 105 formed in the blow surface 103. In Figures 3 - 9 solutions according to the invention are shown mounted in the upper edge 307 of a vertical impingement dryer 20 or 30. It is clear that the solution according to the invention works also, for example, in the first end or the second end of a horizontal impingement dryer. As the structure of an impingement dryer is not an object of this invention as such, several details are shown in a relatively schematic way. For example, the blow surface 103 and its structure with different openings are shown in Figures 3 and 4 only in a schematic way.

Figure 3 shows the upper edge 307 of a vertical impingement dryer 30. The upper edge 307 of the dryer is formed into a sharp guiding form in the machine cross direction, i.e. into a ridge 304, so that it has no mainly horizontal part onto which fiber material, such as paper fiber, could easily stick. The upper surface of the ridge 304 is formed of two planes 305 placed in an angle of about 90 degrees with respect to each other. Both planes 305 are inclined in the machine direction in an angle of about 45 degrees with respect to the horizontal plane. Pressurized air is brought in by a pipe 301 via the end 309 of the ridge. Several openings 302 are arranged in the pipe 301 and in corresponding locations of the surfaces 305, from which openings air is blown along the surfaces 305. Blowing of the air is shown in schematic arrows. The blows can also be arranged towards other outer surfaces 303 of the dryer.

Figure 4 shows the upper edge 307 of a vertical impingement dryer 30. The upper edge 307 of the dryer is formed into a sharp guiding form in the machine cross direction, i.e. into a ridge 304, so that it has no mainly horizontal part onto which fiber material, such as paper fiber, could easily stick. The upper surface of the ridge 304 is formed of two planes 305 placed in an angle of about 30 degrees with respect to each other. Both planes 305 are inclined in the machine direction in an angle of about 75 degrees with respect to the horizontal plane. The planes 305 of the ridge are formed so that fiber material hitting it falls at least mainly away from the surfaces 305 even without an assisting blowing of air. A pressurized air blow arrangement shown in Figure 3 can also be connected to the example of Figure 4, which arrangement is arranged to blow air towards the surfaces 305 in order to keep them clean. The upper surface 305 of the ridge 304 guides, in a web break situation or in another fault situation and during tail threading, the fiber material, for example shredded paper, falling on the dryer 30 so that it does not end up on the dryer 30. According to an embodiment of the invention, in the vicinity of the upper edge 307 of the dryer, there can be arranged a device cleaning it mechanically. In figure 4 there is shown such a structure, a beam 315, parallel with the upper edge 307 of the dryer. The structure 315 could also be, for example, a machine part, such as a blow box or a support structure, located near, for example above the dryer 30. In a fault situation, such as after a web break and during tail threading, the dryer 30 is moved, in a manner known as such, away from the paper web 50 to be dried into positions 30' or 30"shown in Figure 1. In the example of Figure 4 this moving is performed so that the ridge 304 moves past the beam 315 touching it, whereby the edge of the beam 315 sweeps away the trash stuck on the ridge. In other words, when the dryer 30 moves between the positions 30, 30' and 30" in the upper end of the dryer, an extra fiber material can be swept away by means of the structure 315 so that the structure 315 sweeps clean the surface passing by it. The structure 315 can be provided with for example a flexible scraper, a brush or an exhaust fan.

According to an embodiment of the invention, in a fault situation, such as after a web break and during tail threading, the dryer 10, 20, 30 is moved in a manner known as such away from the paper web 50 to be dried. For example in Figure 1 , the outer surface of the dryer 30 is moved to the shown positions 30' or 30". The guiding forms 304 of Figures 3 or 4 are then stopped near some other suitable structure, such as the beam 315 shown in Figure 4, or some of the wires 52 - 54 or the rolls 54, 42 of Figure 1 , or for example some blow box. The guiding form can be stopped at a distance of, for example, 1 - 10 cm or 1 - 3 cm from the said other structure. This moving seals the area so that in a fault situation or during tail threading practically no shredded paper is able to fall on the dryer 30 or on its upper edge 307 from between the ridge 304 and the structure 315. During tail threading, the arrangement guides the fiber web 50 into the right direction and prevents the fiber web from travelling to non-intended places, for example along the wire that has supported it.

Figure 5 shows the upper edge 307 of a vertical impingement dryer 30. Above the upper edge 307 of the dryer in the structure 315 there is fixed, by means of hinges 316, a hinged protective plate 317. The hinges 316 allow the protective plate 317 to turn around a turning axis in the machine cross direction. The structure 315 can also be for example a machine part located above the dryer 30, such as a blow box or a support structure. In the example of Figure 5 the structure 315 is parallel with the upper edge 307 of the dryer. In the situation shown in Figure 5, the dryer 30 is in its normal running position. In case of a web break or during tail threading the dryer is moved to the left in Figure 5, for example to the position 30' or 30" shown in Figure 1. Then the protective plate 317 hangs right downwards, preferably still in contact with the upper edge 307 of the dryer. Thereby the turning protective plate 317 guides the extra fiber material coming towards the upper edge 307 of the dryer away from the upper edge 307 of the dryer. The protective flap 317 thereby prevents the upper edge 307 of the dryer, especially its upper surface 305, from fouling both in normal running situation and during tail threading and in fault situations. During tail threading, the arrangement guides the fiber web 50 into the right direction and prevents the fiber web from travelling to non-intended places, for example along the wire that has supported it. The pressurized air blow arrangement shown in Figure 3 can also be connected to the example of Figure 5, which arrangement is arranged to blow air towards the surfaces 305 of the upper edge 307 of the dryer, the outer surface 303 of the dryer or the protective plate 317 in order to keep them clean. By means of a correctly directed and dimensioned pressurized air blow it is also possible to guide the fiber web 50 into a desired direction. Especially during tail threading it is possible, by means of the blowing, to prevent the fiber web 50 from travelling to non-intended places, for example along with the wire that has supported it.

Figures 6, 7 and 8 show a guiding form 317 according to the invention. The upper edge 307 of the impingement dryer 30 in Figure 6 is the second end of the dryer, i.e. the fiber web 50 travels upwards from the lower edge of the Figure, past the blow nozzles 102 and away from the dryer 30 supported by the support roll 33. Between the upper edge 307 of the dryer and the support beam 315 of a doctor cleaning the cylinder 42 there is fixed a protective plate 317 acting as a guiding form according to the invention. Lugs 320 are fixed to the upper edge 307 of the dryer. The protective plate is fixed by its lower end 324 in a hinged manner to the openings provided in the lugs 320. Brackets 321 for the protective plate are fixed to the support beam 315, the brackets being provided with longitudinal openings, i.e. slots 322. The upper part 325 of the protective plate is provided with horizontal pins 323, which are fitted in the slots 322 in a hinged manner and movably in the direction of the slot 322. The arrangement hereby allows turning of the protective plate 317 around a turning axis in the machine cross direction, and at the same time moving of the dryer 30 during a web break or tail threading to its second position 30'. The respective second position of the protective plate is shown by dotted lines 317'. In Figure 6 it can be seen how the pins 323 move in the slot 322 while the dryer is moved. The protective plate 317 guides the extra fiber material coming towards the upper edge 307 of the dryer away from the upper edge 307 of the dryer. The protective plate 317 thereby prevents the upper edge 307 of the dryer, especially its upper surface 305, from fouling both in a normal running situation and during tail threading, and in fault situations. During tail threading the protective plate in position 317' guides the fiber web 50 marked with dotted line into the right direction between the roll 28 and the drying cylinder 42. In this manner, the protective plate prevents the fiber web from travelling to non-intended places, such as between the turn roll 46 and the beam 315. The pressurized air blow arrangement shown in Figure 3 can also be connected to the example of Figure 5, which arrangement is arranged to blow air towards the surfaces 305 of the upper edge 307 of the dryer, the outer surface of the dryer or the protective plate 317 in order to keep them clean. By means of a correctly directed and dimensioned pressurized air blow it is also possible to guide the fiber web 50 into a desired direction. Especially during tail threading it is possible to efficiently prevent, by means of the blow, travelling of the fiber web 50 to non-intended places. In Figure 7 the protective plate is shown in its second position 317'. Figure 9 shows the upper edge of a vertical impingement dryer 20, into which edge there is arranged an integrated arrangement 351 , separately mounted in the impingement dryer, and provided with a guiding form 304. The upper edge of the dryer 20 in Figure 9 is the first end of the dryer, i.e. the fiber web 50 travels in the Figure downwards from the roll 28 past the guiding form 304 and into the dryer 20 supported by the support roll 23. The integrated arrangement 351 and its guiding form 304 are fixed with bolts 330 as a retrofit to the original horizontal upper edge 307 of the dryer. Inside the lowest part 331 of the integrated arrangement 351 there travels a fire-extinguishing water pipe 333, into which several fire- extinguishing water nozzles 332 are connected in the machine cross direction. The nozzles 332 can be for example nozzles for the water mist fire-extinguishing system. Water or water mist spurting out into different directions from the nozzle 332 as a sector coming from the fire-extinguishing water nozzle 332 is drawn schematically in the Figure. The arrangement 351 comprises control devices needed for starting up the fire-extinguishing system when needed. The fire- extinguishing systems being known as such, they are not presented here more in detail. Inside the uppermost part 334 of the integrated arrangement 351 there travels a pressurized air pipe 301 into which a blow nozzle 302 is connected. There can be several blow nozzles 302 or it can be a longitudinal slot nozzle in the machine cross direction. An arrow 335 is drawn schematically in Figure 9, which arrow shows the guiding air flow blown from the blow nozzles 302 during tail threading and possibly during a web break. Thus, during tail threading both the blow 335 and the guiding form 304 itself guide the fiber web 50 into the right direction towards the dryer. In this manner, the arrangement prevents the fiber web from travelling to non-intended places such as to the outer surface 303 of the dryer 20. The pressurized air blow arrangement shown in Figure 3 can also be connected to the example of Figure 9, which arrangement is arranged to blow air towards the surface 305 of the guiding nozzle or the outer surface 303 of the dryer in order to keep them clean. An adjustment part 336 is provided between the lowermost part 331 and the uppermost part 334 of the integrated arrangement 351 , by means of the height of which adjustment part the height of the integrated arrangement and/or its guiding form are easily adjustable to suit each retrofitting situation. The fire-extinguishing water nozzle 332 shown in Figure 9 is placed in the slightly downwardly bent surface part 350 of the integrated arrangement 351 in such a manner that fire-extinguishing water is guided upwards and downwards into the desired directions. Thus, the fire-extinguishing water can be guided sufficiently close to the blowing means 102. The nozzle 332 is, however, in a suitable position so that water is not guided to the hot parts of the dryer, such as the blow surface and its blowing means 102, such as the blow nozzles. The solutions presented in the examples of the Figures mechanically sealing the spaces between the upper edge 307 of the dryer and other machine parts, as well as adequately directed air blows, also prevent the hot and moist air from spreading from the dryer into the surroundings, especially during tail threading or a fault situation, such as a web break.

In connection with all presented solutions, it is possible to arrange an automatic fire-extinguishing system with for example its nozzles like the ones shown in Figure 9. The arrangements according to the invention shown in Figures 3 - 9 can be enclosed to the impingement dryers already at the stage of their manufacture. The solutions as presented can also be mounted as a retrofitting to dryers already mounted. The phases of a method according to the invention are shown in a very simplified manner in Figure 10. In phase 401 , the fiber web 50 production process utilizing the impingement dryer 10, 20, 30 is observed by means of a control unit. The control unit is arranged to detect a web break or tail threading taking place in the production process, and to send, on the basis of these observations, a control signal to the blowing means 104 according to the invention. By means of the control signal it is guided whether the pressurized air blow according to the invention is turned on or not. The blow can be a cleaning blow directed towards the impingement dryers 10, 20, 30, or a guiding blow guiding the fiber web into a desired direction during tail threading. If no web break or tail threading are detected in the phase 401 , the control unit will not ask to turn on the blows, but, if the blows are on, they are turned off. If a web break or tail threading is detected in the phase 401 , the control unit will ask to turn on the blows.

The Figures show only a few preferred embodiments according to the invention. The figures do not specifically show matters that are of secondary importance in view of the main idea of the invention, known as such or obvious as such for a person skilled in the art. It is obvious to a person skilled in the art that the invention is not limited merely to the above-described examples, but the invention may vary within the scope of the claims presented below. The dependent claims present some possible embodiments of the invention, and they are as such not to be considered to restrict the scope of protection of the invention.