ARRANGEMENT IN TAIL THREADING OF A WEB-FORMING MACHINE

The present invention relates to an arrangement in tail threading of a web-forming machine, which arrangement includes at least one belt conveyor for threading the threading tail, which belt conveyor includes

- a frame structure and at least two return rolls in it,

- an air-permeable belt loop, which is arranged around the return rolls, - vacuum means for creating a vacuum in the belt loop, and

- a drive connected to one of the return rolls for rotating the belt loop and thus for threading the threading tail in the web-forming machine.

Finnish patent application number 20045068 discloses a belt conveyor according to the introduction, in which the motor forming the drive is arranged inside a return roll, in order to create a compact belt conveyor. In addition, it has been attempt to make the changing of the belt loop as easy as possible. If necessary, a vacuum can also be created in the belt conveyor, in order to make the threading tail adhere to the surface of the belt loop.

The motor inside the return roll demands the use of a return roll with an unnecessarily large diameter. In addition, the motor and shell of the return roll account for a considerable proportion of the weight of the belt conveyor while servicing the motor requires the belt conveyor to be removed from the web-forming machine. Though the motor is well protected inside the return roll, particularly in hot conditions the cooling of the motor may require special measures . In known belt conveyors, the changing of the belt is already relatively easy, but changes in the properties of the belt loop and/or in the operating conditions will stress the belt loop. In addition, on account of support, the position of the belt conveyor will have to be checked after each change of the belt loop, particularly

if the first return roll is fitted close to a moving surface. The motor of each belt conveyor will also have to be controlled separately, even though belt conveyors that are placed consecutively should rotate at essentially the same speed.

The invention is intended to create a new type of arrangement in tail threading of a web-forming machine, in which the construction of the belt conveyors in the arrangement is simpler than previously and in which it is easier than previ- ously to operate the belt conveyors. The characteristics features of the present invention are stated in the accompanying Claims. In the belt conveyor according to the invention, the drive is situated in a new and surprising manner. Thus the structure of the belt conveyor can be made simpler and consid- erably lighter than previously. In addition, the drive can be placed in favourable conditions, or at least it will be easily protected. At the same time, the use of special motors will be avoided in belt conveyors. By means of the new type of placing of the drive and of the transmission the position of the belt conveyor can be freely altered. In addition, a single drive can be used to rotate more than one belt loop. Further, the positioning of the belt conveyor can be defined more precisely than before without repeated adjustments, while the tension in the belt loop will remain continuously as desired. The use of the drive according to the invention will also reduce the energy consumption of the arrangement .

In the following, the invention is examined in detail with reference to the accompanying drawings showing some applica- tions of the invention, in which

Figure 1 shows a side view of part of the drying section of a web-forming machine, equipped with belt conveyors according to the invention,

Figure 2a shows a side view of the finishing section of a web- forming machine, equipped with belt conveyors according to the invention,

Figure 2b shows one of the belt conveyors of Figure 2a, seen in the machine direction,

Figure 3 shows a top view in partial cross section of the belt conveyor according to the invention, Figure 4 shows a side view in partial cross section of the belt conveyor according to the invention, Figure 5a shows a side view of part of the drying section of a web-forming machine, equipped with a belt conveyor according to the invention, Figure 5b shows the arrangement according to Figure 5a, seen in the machine direction.

Figure 1 shows five belt conveyors 10 according to the invention, for threading the threading tail over an open gap in a two-wire drying section. The belt conveyors form part of the arrangement according to the invention, which is used particu- larly for threading and guiding the threading tail in paper, board, and other similar web-forming machines. In Figure 1, the belt conveyors 10 are shown in their operating positions. During the normal operation of the drying section, the conveyors according to the invention are turned to their rest positions (not shown) . In the known manner, the drying cylinders 11.1 and 11.2 are arranged on two levels. However, the figure does not show the frame structures of the drying section, or the bearing arrangements of the drying cylinders. In addition, on each level there are auxiliary rolls 12.1 and 12.2 between the drying cylinders 11.1 and 11.2, by means of which the wires 13.1 and 13.2 are guided to travel through the consecutive drying cylinders 11.1 and 11.2. However, during operation the web travels alternately from one level to the other. Thus, when starting production, the threading tail 22 must first of all be taken from an opening throat 14 on one level, over the open gap, to a closing throat 15 on the other

level. In Figure 1, the threading tail in the open gap is shown by a broken line. Each throat is formed at any one time between a drying cylinder on the same level and the wire. In practice, for successful threading a belt conveyor according to the invention, or some other threading device must be fitted to each open gap. For example, in a drying section there can be 20 - 30 belt conveyors.

Thus the arrangement according to the invention includes at least one belt conveyor 10 for threading the threading tail. In a practical arrangement, there are numerous belt conveyors, by means of which the threading tail is taken through the web- forming machine when production starts . An individual conveyor includes at least two return rolls 16 and 17, which are supported on a frame structure 31 (Figure 3) . The frame structure 31 is formed of side plates 18 and 19, which are supported on each other by suitable transverse structures . In addition, the conveyor 10 includes a belt loop 20, which is fitted around the return rolls 16 and 17. The belt loop 20 is, in addition, arranged to rotate in the direction of travel of the threading tail, supported on the return rolls 16 and 17. In addition, a drive 21 is connected to one of the return rolls 16 and 17, in order to rotate the belt loop 20 and thus to thread the threading tail 22 in the web-forming machine.

Inside the belt loop, in the area between the return rolls, a vacuum can be produced, for example, with the aid of a suction box, coanda blasts, or foil strips (not shown) . Thus the belt loop is usually an air-permeable wire. Also one of the return rolls, preferably the first roll, can have a vacuum. Thus, for example, the threading tail can be detached from the surface of the drying cylinder, according to the applications of Figures 1 and 5a. After detaching, the threading tail is moved forward, carried by the belt loop. In practice, the belt loop is off the surface of the drying cylinder.

The drive 21 according to the invention is arranged separately from the belt conveyor 10. In other words, the drive 21 is entirely separate from the frame structure 33 and detached from it. In addition, the drive 21 is connected to one of the return 5 rolls 16, 17, by means of a flexible transmission element 23. It is thus possible to use as the drive, for example, a standard motor, the purchasing and operating costs of which are considerably cheaper than those of a known drum motor. In addition, the total weight of the belt conveyor is clearly

10 reduced. Thus the construction of the belt conveyor and its supports can be lightened. In addition, the installation and maintenance of the belt conveyor are easy, thanks to its lightness. A known belt conveyor weighs 70 kilograms, whereas a corresponding belt conveyor according to the invention weighs

15 30 kilograms. According to the invention, a flexible transmission element is used, allowing the position and alignment of the belt conveyor to be altered while the drive remains stationary. Indeed the drive motor is preferably fitted immovably to the web-forming machine. Thus, for example, the

20 electrical cabling can be made permanent and the drive motor can be supported optimally against vibration. Particularly in drying-cylinder applications, the belt conveyor is continuously in hot conditions. According to the invention, the drive motor can be fitted, for example, to the side away from the web-

25 forming machine and at a sufficient distance from the hot areas. In addition, the drive motor can be easily shielded using simple structures. Figure 1 uses broken lines to show schematically the protective cases 24 of the drive motors 43 used as drives 21.

30

Induction motors, which have a simple but durable construction, are preferably used as the drive motors. In addition, induction motors can be controlled precisely, for example, using a frequency converter. Indeed Figure 1 shows that the electricity

35 supply for the belt conveyors 10 of the entire cylinder group is controlled using a frequency converter 25. In practice, the

induction motors used have an output of less than five kilowatts. In addition, the masses being rotated in the belt conveyor are relatively small . Thus the drive motors can even be started without the frequency converter, especially if the motor is fitted with a soft starter. In addition, the consecutive belt conveyors can be started in stages, thus avoiding loading peaks in the power network. Similarly, the starting and stopping of each belt conveyor can be arranged to suit its position.

Figure 2b shows one belt conveyor 10 arranged in connection with a drying cylinder 11.2, as well as the drive motor 43 that forms its drive 21, which in this case is situated laterally farther away from the drying cylinder 11.2. Thus the drive motor can be attached, for example, to the frame structures of the web-forming machine. This simplifies the construction of the arrangement and permits easy servicing of the drive motor. According to the invention, the transmission element 23 is preferably mechanical and mainly consists of a cable 26, which is arranged between the drive motor 43 and the return roll 16, 17. A suitably dimension cable will permit movements in the belt conveyor. In other words, the belt conveyor can be turned between the operating and rest positions and the position and alignment of the belt conveyor can be otherwise altered, without altering the transmission. In addition, the cable is easy to change and the cables can even be several metres in length. In Figure 2b, the broken line shows also a second location for the second drive motor 43. In other words, the drive motor can be situated at a point at which the operating conditions are suitable for the drive motor. Thus standard motors can be used, even though the belt conveyor may be placed in demanding operating conditions, such as in a drying section.

Figure 2a shows a second application of the arrangement according to the invention. In this case, the belt conveyors 10 are principally permanently in place, but mainly their length

varies. In the prior art, there is an expensive and heavy drum motor in each belt conveyor. According to the invention, the number of drive motors can be reduced by connecting one and the same drive motor to two or more return rolls of the belt conveyor. Suitable means are used to attach the cables. On the other hand, the return rolls of a single belt conveyor can be connected to two different drive motors belonging to the arrangement. Thus in different situations the belt conveyor can be run in different ways. On the other hand, the use of two drive motors permits a further reduction in the size of the drive motors, or the use of differently sized drive motors, for example, during starting. In Figure 2a, the third drive motor 43 from the right rotates two belt conveyors 10, both of which have two return rolls 16 and 17. In addition, both return rolls 16 and 17 of the longer belt conveyor 10 are connected by a transmission element 23 to one and the same motor 43. In addition, the drive motor in question also rotates the following, considerably short belt conveyor. Thus the arrangement can be dimensioned case-specifically, so that at the same time the size and number of the drive motors can be optimized. The same reference numbers are used for functionally similar components . Thus, in general the arrangement includes several drive motors, which are preferably arranged outside the web-forming machine. Figure 2a shows the finishing section of a web-forming machine, to which the threading tail is transferred from the final drying cylinder 11.2. From it, the threading tail 22 is taken, generally using eight belt conveyors through two soft calenders 27 and 28, to the reeler 29. In Figure 2a, the path of the web is shown by a dot-and-dash line. However, the threading tail travels in a slightly wavy path from one belt conveyor to the next. The end result is reliable and fast threading.

Figure 3 shows one belt conveyor 10 according to the invention, the belt loop 20 being shown by a broken line. According to the invention, the belt conveyor 10 includes two return rolls 16, 17, both of which are essentially similar grooved rolls. A

grooved roll can be used for, among other things, creating a vacuum effect in the return roll to detach the threading tail. The means for creating the vacuum are not shown here. In addition, a grooved roll formed of disc-like ridges is light. Thanks to the separate drive, the diameters of both return rolls can now be selected freely. It is preferable to use similar grooved rolls, which will reduce the number of different components required.

The belt conveyor 10 of Figure 3 also includes moving elements 30 for adjusting the tension of the belt loop 20 by altering the mutual positions of the return rolls 16 and 17. In addition, the moving elements 30 are arranged to be operated from one side of the frame structure 31. Thus the changing of the belt loop is as easy as possible and the ends of the return rolls will move by the same amount relative to each other. The construction and operation of the moving elements are disclosed in detail in Finnish patent application number 20045068. According to the invention, loading elements 32 are combined with the moving elements, in order to maintain the desired tension in the belt loop 20. In other words, the loading elements are used to create a continuous loading in the moving elements, which will maintain the tension in the belt loop in different situations .

In Figure 3, the loading elements 32 are spring elements 33, which are fitted around the connecting shaft 35 forming part of the moving elements 30 and extending from one edge of the frame structure 31 to the other. In practice, the connecting shaft 35 is used to operate the moving elements 30, by means of which the side plates 18 and 19 and the carriers 36 of the return roll 17 are moved relative to each other. The spring elements 33 are arranged in such a way that they load the connecting shaft 35 in the same direction. The direction of the rotation created in the connecting shaft 35 by the spring elements 33 is shown by an arrow in Figure 3. In this situation, the connect-

ing shaft 35 attempts to rotate clockwise, so that the return ' rolls 16 and 17 move away from each other. Thus the belt loop 20 is tightened. In addition, the binder ^' bolts 37 binding the side plates 18 and 19 are arranged in such a way that they permit the movement of the carriers 36 in question even during operation. Particularly in hot conditions, the belt loop shrinks in operation, when without the adjustment elements according to the invention the tension would become too great. On the other hand, if the belt loop possibly stretches, the adjustment elements loaded by the spring elements will reimpose the target tension. The spring elements also facilitate the changing of the belt loop. When removing the belt loop, the return rolls are first of all moved toward each other by rotating the connecting shaft, so that the belt loop slackens. At the same time, the components of the side plates are locked, for example, using a locking pin (not shown) . The old belt loop can then be removed and a new one set in place. After this, when the locking pin is removed the spring elements rotate the connecting shaft and the belt loop tightens automatically. The construction of the loading elements can vary in different applications and they can be implemented in other ways . On the other hand, it is easy to add spring elements, the tension of which can be adjusted case-specifically, to connecting shafts that are already in use.

The movement of the return rolls must also be taken into account when positioning the belt conveyor. According to the invention, the belt conveyor 10 is supported by the frame structure of the web-forming machine, in such a way that the position of the first return roll 16 in the direction of travel of the threading tail 22 remains unchanged, despite the operation of the adjustment elements 30. This is significant, especially when the first return roll is place close to a surface, such as, for example, a drying cylinder. In practice, the carrier 38 intended to support the belt conveyor 10 is fitted to the side plate 18 (Figure 3) supporting the first

return roll 16. Thus, independently of the tension in the belt loop, the position of the first return roll always remains the same. Thus, for example after changing the belt loop, it is possible to be certain of the position of the first return roll, even though the mutual positions of the return rolls might have changed after maintenance. In addition, if the belt loop possibly breaks, the sudden movement of the return roll towards the drying cylinder or other structure will be avoided. Only the other return roll moves due to the force of the loading elements, until the adjustment tolerance of the adjustment elements is used up.

In the application of Figure 4 too, the loading elements 32 according to the invention are fitted in connection with the adjustment elements 30. In addition, the carrier 38 of the belt conveyor 10 is attached to the side plate 18, so that the position of the first return roll 16 will remain unchanged. In this case, instead of a conventional drum motor, a synchronized permanent-magnet motor is used as the drive motor. In addition, the permanent-magnet motor 43 is fitted inside the return roll 17 and has a fixed stator 39 inside it, which is shown schematically by a dot-and-dash line. At the same time, the shell 40 of the return roll 17 is arranged as the rotor 41. Thin permanent magnets 42 are glued to the inside surface of the shell 40. In this case, there are six permanent magnets 42. The solution in question is lighter than the massive-rotor drum motors used, and a magnetizing current is unnecessary. In addition, a permanent-magnet motor can be controlled precisely and even several permanent-magnet motors can be controlled using a single frequency converter. Thus, according to the invention the permanent-magnet motor is combined with a frequency converter 25, which is connected to the drive motors 43 of at least two belt conveyors 10. This simplifies the construction of the arrangement and facilitates the operation of the belt conveyor. In addition, the efficiency and power ratio of a permanent-magnet motor are good. Thus little waste

heat is created and the over-dimensioning of the input power to nominal power is unnecessary. In addition, slip is nonexistent in a permanent-magnet motor, so that the speed of rotation of the motor is directly proportional to the frequency of the input current. Also, the nominal torque of a permanent-magnet motor is available immediately from starting, which is advantageous, especially at low rotation speeds. At the same time, gearboxes are unnecessary.

Figures 5a and 5b show application of the arrangement according to the invention, in which the drive 21 is a drive wheel 44. In other words, the belt conveyor 10 entirely lacks its own motor. According to the invention, the drive wheel is arranged to be in contact with a rotating machine component belonging to the web-forming machine. Thus, the energy required to rotate the belt conveyor is taken from some machine component near to the belt conveyor. In Figures 5a and 5b, the machine component in question is an auxiliary roll 12.2, but it can also be, for example, some other roll or drying cylinder. The machine components in question are relatively massive compared to the belt conveyor, so that the drive wheel will have no effect on their rotation. In this application too, the drive wheel 44 forming the drive 21 is connected to the belt conveyor 10 by a flexible power-transmission element 23, thus achieving the advantages referred to above. In the rest position of the belt conveyor, the drive wheel is not in contact with the machine component, so that the belt loop is motionless. Here, the support of the drive wheel is not shown, but when threading starts the drive wheel is brought lightly towards the machine component. This avoids the problems that might be caused by the differences in speed and the belt conveyor starts smoothly. In Figure 5a, a solid line is used to show the drive wheel 44, which contacts with the circumference of the auxiliary roll 12.2. The flexible power-transmission element 23 then forms a sharp bend, but the direction of rotation will already be correct. A broken line is used to show a second drive wheel,

which is arranged to be in contact with the end of the auxiliary roll 12.2. The power-transmission element will then be in only a slight bend and the speed of rotation of the drive wheel can be altered by altering its radial position. On the other hand, the direction of rotation must be changed. For this purpose it is possible to use, for example, a small gearbox fitted to the return roll, by means of which a suitable gear ratio can also be selected (not shown) . If necessary, a suitable coating and/or additional structures can be used to achieve sufficient durability and friction. For example, a groove for the drive wheel can be machined in the machine part . The positioning of the drive wheel will then be facilitated and the friction can be increased if necessary.

The belt conveyor is lighter than before and can be located in even difficult operating conditions. In addition, it can be fitted in different positions and its construction can be altered. Correspondingly, in the arrangement according to the invention drive motors that are simpler than previously can be utilized, the power and number of which can, in addition, be optimized. On the other hand, the use of motors can even be avoided entirely. The control of the belt conveyor is also simpler than before while the changing of the belt loop is faster than previously. At the same time, the adjustment of the position of the belt conveyor after changing the loop is unnecessary, as the tension in the belt loop will nevertheless remain as desired.