WO2008090259A1

WO2008090259A1 - A system in a web forming machine for guiding the web in connection with a grooved roll

Info

Publication number: WO2008090259A1
Application number: PCT/FI2008/050021
Authority: WO
Inventors: Kari Juppi; Pasi Kekko; Antti Komulainen; Matti Kurki; Markku Lummila; Pekka Martikainen; Jukka-Pekka Multasuo
Original assignee: Metso Paper, Inc.
Priority date: 2007-01-22
Filing date: 2008-01-21
Publication date: 2008-07-31
Also published as: FI119560B; FI20075038A0; FI20075038A; CN101589195B; CN101589195A; EP2126204A1

Abstract

The invention relates to a system in a web forming machine for guiding a web (28) in connection with a grooved roll (12). The grooved roll (12) includes a surface structure (16) with grooves (56) said grooves (56) being open only to the outer surface of the grooved roll (12). A runnability component (18) is included in connection with the grooved roll (12). In addition, the runnability component ( 18 ) includes at least one passive zone (22) in the cross direction (20) of the web forming machine.

Description

A SYSTEM IN A WEB FORMING MACHINE FOR GUIDING THE WEB IN CONNECTION WITH A GROOVED ROLL

The invention relates to a system in a web forming machine for guiding the web in connection with a grooved roll, said grooved roll including a surface structure with grooves where the grooves are open only to the outer surface of the grooved roll and a runnability component is included in connection with said grooved roll .

Many different dryer sections of web forming machines, i.e. fiber web forming machines, are known in prior art, of which some utilize a double-fabric run arrangement and/or some utilize a single-fabric run arrangement. Open draws of the double- fabric run arrangement are vulnerable to flutter, which causes runnability problems particularly when the paper is still relatively moist and thus weak in strength. In recent years there has been an increasing tendency to use single-fabric run arrangements, in which the web is supported with a dryer fabric within the range of a dryer group. The fabric presses the web against the heated surfaces of the dryer cylinders. At the turning cylinders, the fabric is against the turning cylinder surfaces, and the web is on the other side of the fabric.

In single-fabric run arrangements known in prior art, the fabric and the web arrive from a dryer cylinder to a turning cylinder as a continuous straight run whereupon a closing gap is formed between the dryer cylinder and the turning cylinder. The web and the cylinder surface moving towards this gap gener- ate an overpressure in the gap via the boundary layer flows conveyed by them. The overpressure in the gap causes a pressure difference over the web supported by the fabric, which creates runnability problems . Increasing web speeds increase the overpressure problems of the closing gap even more. From the turning cylinder, the web is transferred to the dryer cylinder, whereupon an opening gap is formed. In connection with the single-fabric run arrangement, a pocket condition occurs, which refers to a pocket-like space defined by parallel dryer cylinders, the turning cylinder between them, and the dryer fabric.

Attempts have been made in prior art to eliminate problems related to the closing gap using a suction roll, various vacuum boxes, as well as combinations of rolls and suction boxes. In old slow machines with the speed below 800 m/min, when shifting to the single-fabric run arrangement, runnability problems were first reduced by grooving the bottom cylinder surface with about 5 mm narrow and about 4 mm deep grooves . When the speeds increased close to 1000 m/min, a runnability component was added to the bottom cylinder or to a corresponding traditionally grooved roll striving to extend its suction to the grooves and, through these, to the fabric wrap area in the roll circumference. Publication WO 8202938 is mentioned here as the prior art technique for such a grooved bottom cylinder with a depressurized runnability component. A figure in this publication shows a bottom cylinder together with the depressurizable runnability component. On page 16 it is stated that higher vacuums are typically created through openings 44 for vacuum zones 32, 34, when a lower vacuum is present in vacuum zones 31 and 33. Figures 4 - 8 show various embodiments of the runnability component. Figures 10 and 11 show how several pressure zones are created in the cross direction of the bottom cylinder by applying vacuums of different magnitude in different positions of the bottom cylinder in the cross direction of a fiber web forming machine .

Dimensions introduced with the grooved bottom cylinder are still used with traditionally grooved rolls and Vac rolls, in which the grooves are 5 mm narrow and 4 mm low. The necks between the grooves are typically about 14 mm wide. With Vac rolls, the runnability of the fiber web forming machine can have been improved. However, it has been difficult to solve the problems in an energy-efficient way. In addition, the need of energy us ed for web stabilization has increa s ed remarkably along with rising machine speeds .

One solution for removing problems is proposed in the appli- cant ' s patent application FI20031461 , in which a grooved roll of a paper or board machine is proposed compri sing a center j ournal and a groove-like surface structure around it . A contact exists between the surface structure and the center j ournal so that a substantially closed construction is formed . A runnability component can be used with the roll , where the effect of the opening gap is intensified, for example , with an aspiration on the trailing side or , on the other hand, the collision and flow effect is intensified, on the side of the closing gap, with an airflow directed to the closing gap .

The object of the invention is to provide a system which can reduce the amount of energy used for generating a vacuum in a web forming machine. The characteristic features of this invention are that the runnability component includes at least one passive zone in the cross direction of a web forming machine.

A web forming machine, i.e. a fiber web forming machine, which refers in this connection to paper, board, tissue and pulp machines, has several grooved rolls via which the web travels. The web can travel via the grooved rolls unsupported or supported by a fabric. Grooved rolls which are used to guide the web have a surface structure provided with grooves . The grooves in the surface structure are open only to the outer surface of the grooved roll. It is known as such that the grooved roll can be provided with a journal using journal pins, a center journal, or a stationary journal, the grooved shell of which is adapted to rotate. Thus, by utilizing the boundary layer flow conveyed by the roll and the web/fabric, a vacuum is generated which keeps the web attached in connection with the grooved roll. A groove-like surface structure creates a vacuum directed to the web as the result of controlling the radial forces . Advantageously, the grooves measure the grooved roll circumference, but a pitched groove is also possible to implement. A pitched groove can be implemented as extending continuously over the entire dimension of the grooved roll. On the other hand, there may be even several pitched grooves; for example, pitched grooves extending from the center of the grooved roll to the edges . A runnability component is included in connection with the grooved roll. Surprisingly, the runnability component includes at least one passive zone in the cross direction of the web forming machine. A passive zone is such that air is not aspirated from it or blown to it. As used herein, air refers more extensively to gas-like mediums moving in a paper machine, such as air containing water as steam. The passive zone intensifies the vacuum, i.e. the pressure difference over the web, created by the grooved roll, by guiding the flows and by creating surfaces that restrict the distribution of pressure. In other words, the passive zone enables generating a vacuum without external suction or blow means. The passive zone is thus passive all the time, in which case a suction or blow flow is not led to it at any time. The effect of a runnability component including a passive zone in improving the operation of a grooved roll is remarkable. When the runnability component is passive, its manufacture is also economically more advantageous than before. In addition, a notable reduction in energy consumption is essential. A runnability component according to the invention including a passive zone enables positioning the grooved roll in new locations as well.

In one embodiment, the runnability component consists of sev- eral zones in the lateral direction of the web forming machine, to some of which an external vacuum is directed. In other words, air is aspirated from part of the zones for creating a vacuum. It is also possible to blow air to these active zones for creating a vacuum by means of an ejector effect. In this case, too, an external vacuum is directed to the active zones.

Part of the zones are passive, in contrast. With actively depressurized zones, higher vacuums are achieved for a part of the grooved roll. These zones with higher vacuums can be used for assisting the transfer of a threading tail, for example. Such a zone can be located in any position of the grooved roll, since a threading tail can be formed at the machine edge or at the center in the lateral direction of the web forming machine . Advantageously, the zones to which external pressure is directed, are located at the edges of the web forming machine, because in this case they can be used, in addition to the tail threading taking place at the edges, also for preventing edge flutter.

In another embodiment the grooved roll is a turning cylinder. When the grooved roll is a turning cylinder, a passive runnability component can be located in a pocket, where the removal of the overpressure present on the side of the closing gap of the turning cylinder has required considerable air removal with runnability components .

In a third embodiment, a closing gap is present on the first side of the turning cylinder from where the web arrives to the turning cylinder. On the second side of the turning cylinder from where the web leaves the turning cylinder, an opening gap is present. The runnability component is adapted to be so designed that the channel extending to the opening gap is substantially opening to the direction away from the turning roll, over the entire range tangential to the runnability component. Such a design creates flow conditions which facilitate stabilizing the fabric and the web in the opening gap.

In a fourth embodiment, dryer cylinders are placed on both sides of the turning cylinder, sloping downwards or upwards, through which the fabric is adapted to be transferred as a single-fabric run. The web is transferred from the dryer cylin- der to the turning cylinder as a short transfer having a length of 80 - 600 mm, advantageously of 100 - 350 mm. In a short β trans fer , dryer cylinders and turning cylinders are placed close to each other, which enables to make the dryer section of a web forming machine more compact than before . Thi s short trans fer requires efficient vacuum generation means , because the pressure difference can equalize over the web and the fabric only at a very short distance . When a runnability component including a pas s ive zone is used in connection with a short transfer, the pressure level required in connection with a short transfer can be implemented with reduced energy and thus economically as regards costs .

In a fifth embodiment the web touches the grooved roll for less than 120° , advantageously less than 30° . The angle can vary in different grooved rolls such that larger contact angles can be used in transfers with fewer rolls and smaller contact angles are used in long trans fers with several rolls (more than 3 ) when using grooved roll s . Thi s contact angl e i s us ed, f or example, in an impingement section, and the tangential angles- of success ive grooved rolls can vary significantly from each other .

In a sixth embodiment, the passive zone of the runnability component in the pocket space of the single-fabric run has a vacuum of at least 500 Pa, advantageously 800 Pa. Lower vacuums are suitable for the last dryer groups of the dryer section. In other words, a higher pocket space vacuum is needed at the beginning of the dryer section than at the end of the dryer section. Generating this vacuum with suction means requires large investments in suction means. In addition, the suction means require a considerable amount of energy. In systems according to prior art, pocket spaces have a vacuum of 100 - 300 Pa. Furthermore, in prior art it has been possible to divide from the pocket space a separate zone with a higher vacuum in which aspiration is directed to a gap with a width of a few centimeters only for increasing the vacuum in the gap area. The system according to the invention thus simultaneously enables saving energy and providing higher vacuums than before in the pocket space of the single-fabric run provided with a runnability component, compared to prior art runnability compo- nents, which direct a high vacuum only to the opening gap of the cylinder. Vacuums higher than before in the entire pocket space area, for their part, enable better runnability and control of web properties, such as shrink.

The invention is described below in detail by making reference to the enclosed drawings, which illustrate some of the embodiments of the invention, in which

Figure 1 shows the system according to the invention for guiding a web in a web forming machine in connection with a grooved roll,

Figure 2a shows a sealing means used in the system according to the invention, which is a comb, seen from the front of a grooved roll, Figure 2b shows a sealing means used in the system according to the invention, which is a two-row comb, seen from the front of a grooved roll,

Figure 3 shows the system according to the invention in connection with a single-fabric run arrangement,

Figure 4a shows the system according to the invention provided with a runnability component,

Figure 4b shows the system according to the invention provided with a runnability component,

Figure 4c shows the system according to the invention provided with a runnability component,

Figure 5 shows the system according to the invention in a vertical impingement unit.

Figure 6 shows a grooved roll including several groove zones and

Figure 7 shows the system with a runnability component which includes vacuum discharge means. Figure 1 shows the system 10 according to the invention for guiding a web 28 in a web forming machine in connection with a grooved roll 12. The grooved roll 12 includes a center journal 14 and a groove-like surface structure 16 with a contact between them forming a substantially closed construction in which the grooves are open only to the outside of the grooved roll. A runnability component 18 is included in connection with the grooved roll 12 with at least one passive zone 22 in the cross direction, i.e. in the lateral direction 20 of the web forming machine. Aspiration or blow is not brought to the passive zone from outside. The suction effect of the passive zone of the runnability component is based on the co-operation between the passive zone of the runnability component and the grooved roll. The passive zone is thus passive all the time, in which case a suction/blow flow is not led to it at any time.

In the system according to the invention shown in Figure 1, the runnability component 18 consists of several zones 24 in the lateral direction of the web forming machine. To part of the zones, a vacuum is directed from outside. Active zones 26, i.e. the zones to which a vacuum generated with external means is directed, are at the edges of the grooved roll 12 for preventing flutter of the edges 30 of the web 28 supported by a fabric 29 in connection with the grooved roll 12. The widths a of the active zones 26 are typically 10 - 100 cm, advantageously 20 - 60 cm. When the web forming machine itself is, for example, 10 m wide, an externally created vacuum is directed only to a small portion of the lateral range of the web forming machine. In the width direction of the web forming machine, 75 - 99%, advantageously 90 - 98%, of the web forming machine is covered with a passive zone. In addition, the vacuum generated in the active zones with external vacuum generation means can be disabled when the machine can operate without. However, in case flut- ter appears at the web edges, the active zones can be kept in operation. In addition, the active zones located at the edges can be used during tail threading for transporting the tail. A zone used for transporting a tail can exist in the center part of the machine as well. In fact, a passive zone can also be composed of more than one part. Several zones enable optimum vacuum utilization in each position in the lateral direction of the web forming machine.

In the system according to the invention shown in Figure 1, a sealing element 32 is included between the runnability component 18 and the grooved roll 12. The runnability component 18 is open towards the grooved roll 12 and the dryer cylinder 36. The grooved roll 12 and the fabric 29 meet at the broken line 21. With a grooved roll with pitched grooves, the sealing element can be, for example, a mechanical counter thread or a sealing shower. A sealing shower can be present in the passive part of the runnability component as well. A sealing shower does not create a pressure difference between the runnability component and its exterior, but it seals the runnability component to the grooved roll. The airflow coming from the sealing means is 5 - 100 m³/h/m, advantageously 10 -

50 m³/h/m. For creating a vacuum effect with an ejector effect, on the other hand, the flow should be in a class of 500 - 2000 m³/h/m. The flow used in the sealing means is thus notably smaller than the flow that is required for creating a vacuum via the ejector mechanism. Advantageously, the sealing means is mechanical in which case it does not need an airflow to operate, which simplifies the manufacture of the sealing means. In addition, using a sealing means that operates without an airflow is more economical.

Figure 2a shows a sealing element 32 used in the system according to the invention in connection with a grooved roll, which is a comb 50, seen from the front of the grooved roll 12. The grooved roll 12 and the sealing element 32 are not completely shown but only a part thereof is shown. A bottom slot 60 exists between the tip 54 of the tooth 52 of the comb 50 and the bottom 58 of the groove 56 of the grooved roll 12. The height c of the bottom slot 60 is 0,5 - 2,5 mm, advanta- geously 0,8 - 1,5 mm. A wall slot 60' exists between the tooth 52 of the comb 50 and the wall 62 of the groove 56 of the grooved roll 12. The width d of the wall slot 60' is 0,5 - 2,5 mm, advantageously 0,8 - 1,5 mm. A frame slot 60'' exists between the frame part 64 of the comb 50 and the neck 66 of the grooved roll 12. The height e of the frame slot 60'' is 1,0 - 3,0 mm, advantageously 1,3 - 2,0 mm.

Figure 2b shows, in the system according to the invention, a sealing element 32 used in connection with a grooved roll 12 as seen from the end of the grooved roll 12. The sealing element 32 is a comb 50, in which teeth 52 are set in more than one row 68. Advantageously the teeth 52 of the comb 50 are in two rows 68. Such a labyrinth seal of successive combs efficiently restricts the flow to the runnability component at very high operating speeds, for example.

Figure 3 shows the system 10 according to the invention in which the grooved roll 12 is a turning roll 34. In connection with a turning cylinder 34, energy saving provided by the grooved roll 12 and the runnability component 18 including a passive zone, is huge. This is because for creating a vacuum in runnability components, in modern paper machines, in a machine over 10 m wide, power is used about 1-2 MW in the dryer section in connection with a grooved roll according to prior art.

In the system according to the invention shown in Figure 3, the runnability component 18 is in the pocket space 37 of the single-fabric run. The vacuum in the passive zone of the runnability component 18 is at least 500 Pa, advantageously at least 800 Pa. The system according to the invention enables thus simultaneously saving energy and providing higher vacuums than before in the pocket space of the single-fabric run provided with a runnability component. Consequently, runnability and the control of web properties improve.

In the system 10 according to the invention shown in Figure 3, a closing gap 40 exists on the first side 38 of the turning cylinder 34 from where the web 28 and the fabric 29 come to the turning cylinder 34. On the second side 42 of the turning cylinder from where the web 28 and the fabric 29 leave the turning cylinder 34, an opening gap 44 is present. In addition, the runnability component 18 is adapted to be so designed that the channel 46 extending to the opening gap 44 is opening to the direction away from the turning roll 34 over the entire range tangential to the runnability component 18.

In the system 10 according to the invention shown in Figure 3, dryer cylinders 36 are located on both sides of the turning cylinder 34, sloping upwards. The web 28 and the fabric 29 supporting it are adapted to be transferred as a single- fabric run via the dryer cylinders 36 and the turning cylinder 34. In addition, the web is transferred from the dryer cylinder 36 to the turning cylinder 34 as a short transfer, having a length b of 80 - 600 mm, advantageously 100 - 350 mm. When the web is transferred as a short transfer from the dryer cylinder to the turning cylinder, the dryer section can be made more compact than before.

Figures 4a - 4c and 5 show systems 10 according to the inven- tion in which the web 28 touches the grooved roll 12 for 1 -

120°, advantageously for 4 - 30°, very advantageously for

5 - 9°. The grooved roll is in an impingement section, which has a hood of which a section of the hood edge 41 is shown in Figure 4a. Between the hood edges, in Figure 4a, only two rolls are located, but the hood edges could also be remarkably further away from each other. The system 10 includes a runnability component 18 between two grooved rolls 12, which are on the same side of the fabric 29. Flows directed to the runnability component 18 result from the operation of the two grooved rolls 12 and the supported fabric 29. In addition, the runnability component 18 includes at least one passive zone in the cross direction of the web forming machine.

In the systems 10 according to the invention shown in Figures 4a - 4c and 5, the runnability component 18 is in a pocket space 47 of an impingement section. The vacuum in the passive zone of the runnability component 18 is 50 - 500 Pa, advantageously 100 - 300 Pa. At this vacuum level, the web control is functional in the impingement section. Moreover, this pressure level can be well implemented with a passive runnability component.

In Figures 4a - 4c, the runnability components 18 in connection with the grooved rolls 12 are advantageously passive. The edges of passive runnability components can be mechanically sealed, for example, with a flat wear-resistant edge or a doctor-like labyrinth seal. Sealing can also be accomplished with a combination of these such that the doctor-like seal extends best to the gap and there is more freedom for the sealing of the other edges . When the runnability component is passive, the volume of the space defined by the runnability component and the fabric, i.e. the box, is advantageously small. The design is opening towards the following grooved roll, as in Figures 4a and 4c. When the design is opening towards the following grooved roll, the extension of the roll's suction effect area improves, and the above travelling fabric can depressurize the runnability component and partly the opening gap, formed by the runnability component and the fabric, on the side of the roll preceding its gap seal. In Figures 4a - 4c, sealing on the side of the runnability component 18, which is passive, and the closing gap 40 of the following grooved roll 12 also influences the vacuum generating in the runnability component 18. At its simplest, the seal is directly against the grooved roll, when the contact angle does not form a closing gap between the seal and the grooved roll, and even in other cases, when it is desired to reduce the vacuum present in the runnability component. When more efficient sealing is desired, or when a closing gap is formed between the runnability component and the grooved roll, it is possible to intensify the vacuum of the runnability component and the grooved roll by extending the sealing against the roll' s rotation direction, whereupon access of air along with the grooved roll is restricted the more, the longer the seal is.

In the systems 10 according to the invention shown in Figures 4a - 4c, the runnability components 18 between the grooved rolls 12 are different. When sealing the opening gap 44 to the runnability component 18, the most important is to prevent air from flowing out from the grooved roll and, along with the fabric, to between the runnability component and the fabric. For this reason, sealing is extended in the opening gap as deep as possible to the gap. It is true, however, that at a higher speed and vacuum, the deflection of the fabric towards the runnability component can be avoided, preventing thus also seal and fabric wear, by moving the seal slightly further away from the opening gap.

In the systems according to the invention shown in Figures 4a - 4c, control parameters related to the runnability components 18 include the length of the gap seal following the surface of the passive runnability component 18 and the grooved roll 12, and the opening of the gap between the following runnability component and the related grooved roll. The length of the gap seal on the roll surface in its rotat- ing direction influences the extension of produced vacuum.

The gap opening, for its part, influences the vacuum production.

In the systems according to the invention shown in Figures 4a - 4c, at least one grooved roll 12 is non-driven. The grooved roll can be non-driven, since the grooved roll design can be implemented as rotating very slightly. A slightly rotating grooved roll does not need a drive but it receives the movement force required for the rotation from the fabric. Advantageously all grooved rolls located within the fabric loop are non-driven.

In the system according to the invention shown in Figure 4a, the diameter d of the grooved roll 12 is less than 1000 mm. The grooved roll diameter depends as such from the machine's operating speed and width. Grooved rolls are provided with bearings at the ends. In prior art, instead of grooved rolls of this size class, suction rolls are used for generating a vacuum. The airflow needed for generating the suction roll aspiration is brought through the suction roll bearing, in which case the bearings are dimensioned according to the suction flow. When the grooved roll diameter is less than 1000 mm, the bearings included in the grooved roll heads have an inner diameter of less than 300 mm, advantageously less than 150 mm. Using a grooved roll in place of a suction roll of this size class enables significant cost savings as the bearings can be dimensioned according to stresses because it is not necessary to bring a suction flow through them.

Figure 5 shows the system according to the invention provided with a vertical impingement unit 70. Between the grooved rolls 12, runnability components 18 are included, which include at least one passive zone. Runnability components that include a passive zone advantageously enable to maintain a vacuum level in connection with grooved rolls, which is very advantageous in a vertical impingement section. In a vertical impingement section, web drying can be very efficiently carried out. A vacuum is needed in order that an overpressure otherwise generating in the closing gap would not release the web from the fabric support. It is possible to prevent this overpressure also with grooved rolls with deep grooves at least partially by means of passive runnability components. Generating a high vacuum level according to prior art technique requires large suction means, because the benefit provided by a grooved roll without an at least partially passive runnability component is significantly smaller than the benefit provided by a grooved roll with a passive runnability component. A passive runnability component according to the invention enables efficient use of the grooved roll in a vertical impingement section with lower energy consumption than before.

The design of the turning cylinder 72 of a vertical impingement section used in the system according to the invention as shown in Figure 5 depends on the machine speed. A smooth roll can be used in slow machines, whereas in fast machines a grooved roll is used as the turning cylinder, and at least a partially passive runnability component or a suction roll is used. When a smooth roll is used as the turning cylinder, the runnability components in connection with it should be active .

The depth f of the grooves 56 in the grooved roll 12 used in the systems shown in Figures 1 - 5, is 10 - 100 mm, advanta- geously 20 - 50 mm. When the grooves of the grooved roll are so deep, a vacuum is generated during the groove rotation over that portion of the grooved roll which is covered by the web. The groove width in turn is 4 - 10 mm, advantageously 6 - 7 mm. The narrow necks between the grooves are 1 - 8 mm, advantageously 3 - 6 mm wide. Advantageously, the groove volume is considerably high compared to traditionally grooved rolls and Vac rolls, in connection with which an active runnability component is used.

Figure 6 shows a grooved roll 12 used in the system according to the invention, in which the adjacent grooves 56 are separate vacuum zones. This grooved roll 12 includes a center journal 14, or a center construction, and a groove-like surface structure 16, or a steel shell, in which the grooves 56 are open only to the outside of the grooved roll 12. The surface structure 16 is attached to an end ring 31.

Figure 6 shows a grooved roll 12 including at least two groove zones 23. The grooves 56 have the same depth within the groove zone 23, but the grooves have a different depth between the groove zones 23. It is also possible to contemplate a situation in which all grooves would have a different depth. In this case the number of the groove zones would be the same as the number of grooves. When the grooved roll includes several groove zones, the manufacturing costs of the grooved roll can be reduced improving at the same time the pressure profile of the grooved roll. With a good pressure profile, the vacuum generated by the grooved roll in connection with the web, i.e. the vacuum directed to the fabric from the grooved roll, can be adjusted with greater freedom than before. The pressure directed to the fabric from the grooved roll refers to the pressure generated by the grooved roll in connection with the fabric. In addition, the mass of the grooved roll compared to the rigidity of the grooved roll can be made smaller. In other words, while the weight of the grooved roll remains the same, the rigidity of the grooved roll increases.

A vacuum is needed in a fiber web forming machine particularly in the web edge areas for the sake of runnability of the fiber web forming machine. In the center part of the grooved roll, in the cross direction of the fiber web forming machine, the vacuum level can be lower. In this case the grooves can be lower in the center part of the grooved roll. The manufacturing costs of the grooved roll reduce when the amount of work required for grooving decreases.

The grooved roll 12 shown in Figure 6 includes three groove zones 23 for a half grooved roll 12. Three groove zones in a half grooved roll is an extremely advantageous embodiment due to the combination of the grooved roll properties and manu- facturing costs. More generally speaking, the number of groove zones 21 is 2 - 6, advantageously 3 - 4, in a half grooved roll 12. Two groove zones for a half of the grooved roll enable different vacuums at the edge and in the center part of the grooved roll .

As shown in Figure 6, the grooves 56 in the grooved roll 12 have a depth f and a width g. In addition, the depth f of the grooves 24 is greater than the width g, which is very essential as regards the vacuum production. Typically, the depth f of the grooves 56 is 2 - 15, advantageously 3 - 8 times the width g of the grooves 56. When the grooved roll 12 is used in applications in which the web touches the grooved roll for

1 - 120°°, the depth f_x of the grooves is 30 mm, f₂ is 25 mm, and f₃ is 20 mm. On the other hand, when the grooved roll is used as a turning roll, the groove depths are typically slightly greater.

Figures 4a - 4c and 5 show systems 10 in which the web 28 touches the grooved rolls 12 for 1 - 120°. Passive runnability components 18 are located between the grooved rolls 12. In such a connection, the target vacuum level is typically advantageously 100 - 300 Pa. However, when the machine speeds rise, remarkably high vacuums are generated at passive runnability components. When the machine speed rises to a level of 1500 m/min, the vacuum can very well rise as high as to 350 Pa or higher. Figure 7 shows the system 10 in which the web touches the grooved rolls with an angle of less than 30°. The passive runnability component 18 present in this system includes means 78 for partially discharging the vacuum. These means enable access of air to the passive runnability component when the vacuum rises too high. The means 78 for partially discharging the vacuum comprise a flow channel 84 of the opening gap, a flow channel 82 of the closing gap, and a flow channel 80 of the box. When the means 78 for partially discharging the vacuum include three flow channels, it is possible to reduce the pressure of the runnability component exactly where the reduction is needed. In other words, the pressure affecting in the runnability component can be pro- filed as desired in the machine direction. In the cross direction of a fiber web forming machine, the vacuum can be profiled as desired, for example, using a pipe with holes between the flow channels. When the holes of the pipe are located at more frequent intervals at the center of the fiber web forming machine, the pressure affecting in the runnability component can be decreased at the center of the web forming machine. The means 78 for partially discharging the vacuum, i.e. flow channels, are passive flow channels in which case they are not blown to. In other words, the flow channels are openings through which air can flow to the runnability component due to the effect of the vacuum present in the runnability component.

The means 78 for partially discharging the vacuum shown in Figure 7 include a control element 88. The control element 88 can be, for example, a control baffle 89 with a very simple operation. A counter force is generated for the control element, more specifically for the control baffle, with a passive loading means, which can be a spring, for example. When the pressure falls too low within the runnability component, the control baffle opens and lets air flow to the runnability component. When the pressure falls too low, the limit force required for opening the control baffle is exceeded. The control baffle opens and closes according to the pressure affecting in the runnability component. The control baffle 89 included in connection with the flow channels 82 and 84 can be simply a baffle hinged on the inner surface of the side wall of the runnability component. When the runnability component does not have a significant vacuum relative to the environment, a spring closes the flow channel with the control baffle. When the vacuum reaches the level required by the limit force, air starts flowing to the runnability component from the flow channel.

Claims

1. A system. in a web forming machine for guiding the web (28) in connection with a grooved roll (12) , said grooved roll (12) including a surface structure (16) with grooves (56) where the grooves (56) are open only to the outer surface of the grooved roll (12) and a runnability component (18) is included in connection with said grooved roll (12), characterized in that the runnability component (18) includes at least one passive zone (22) in the cross direction (20) of the web forming machine.

2. A system according to claim 1, characterized in that the runnability component (18) consists of several zones (24) in the cross direction (20) of the web forming machine, of which part are active zones (26) to which an external vacuum is directed.

3. A system according to claim 1 or 2, charac- terized in that a sealing element (32) is included between the runnability component (18) and the grooved roll (12) .

4. A system according to any of claims 1 - 3, characterized in that the sealing element (32) is a comb (50) .

5. A system according to any of claims 1 - 4, characterized in that the runnability component (18) is in a pocket space (37) of a single-fabric run arrangement, and the passive zone (22) of the runnability component (18) has a vacuum of at least 500, advantageously 800 Pa.

6. A system according to any of claims 1 - 5, characterized in that the grooved roll (12) is a turning cylinder (34) .

7. A system according to claim 6, in which a closing gap (40) is present on the first side (38) of the turning cylinder (34) from where the web (28) arrives to the turning cylinder (34), and an opening gap (44) is present on the second side (42) of the turning cylinder from where the web (28) leaves the turning cylinder (34), characterized in that the runnability component (18) is adapted to be so designed that a channel (46) extending to the opening gap (44) is substantially opening in the direction away from the turning cylinder (34) over the entire range tangential to the runnability component (18).

8. A system according to claim 6 or 7, in which dryer cylinders (36) are located on both sides of the turning cylinder (34), slanting upwards or downwards, via which the web (28) is adapted to be transferred as a single-fabric run, characterized in that the web (28) is transferred from the dryer cylinder (36) to the turning cylinder (34) in a short transfer having a length (b) of 80 - 600 mm, advantageously 100 - 350 mm.

9. A system according to any of claims 1 - 4 , characterized in that the web ( 28 ) touches the grooved roll

( 12 ) for less than 120° , advantageously less than 30°.

10. A system according to claim 9, characterized in that the grooved roll ( 12 ) is located in an impingement section .

11 . A system according to claim 10 , characteri zed in that a runnability component ( 18 ) i s in a pocket space ( 47 ) of an impingement , and a passive zone ( 22 ) of the runnability component ( 18 ) has a vacuum of at least 50 - 500 Pa, advantageously 100 - 300 Pa .

12. A system according to any of claims 1 - 11, characterized in that the depth (f) of the grooves (56) present in the grooved roll (12) is 10 - 100 mm, advantageously 20 - 50 mm.

13. A system according to claims 1 - 12, with the grooves (56) in the grooved roll (12) having a depth (f) and a width (g) , characterized in that the depth (f) of the grooves (24) is greater than the width (g) .

14. A system according to claim 13, characterized in that the depth (f) of the grooves (56) is 2 - 15, advantageously 3 - 8 times the width (g) of the grooves (56) .