This application is a U.S. national stage application of International Application No. PCT/FI02/00687, filed Aug. 22, 2002, and claims priority on Finnish Application No. FI 20015023, Filed Aug. 22, 2001.
Not applicable.
The present invention relates to apparatus for leading a web threading tail over an empty space, which empty space is formed between two surfaces and the apparatus is arranged between the surfaces to lead the web threading tail from the surface preceding the empty space, over the empty space to the surface following the empty space, which apparatus includes a belt loop permeable by air, which is arranged to rotate in the direction of travel of the web threading tail and is supported by turnover rolls, and within which belt loop at least one foil strip is arranged to create a vacuum effect in the part of the belt loop that transports the web threading tail.
Empty spaces according to the introduction occur particularly in the dryer sections of twin-wire paper and board machines. The dryer section includes one or more cylinder groups, with drying cylinders set on two levels. In order to lead the web through the cylinders, each level has a separate wire running through it. This arrangement is termed a twin-wire dryer section. The web is guided by means of turnover rolls placed between the drying cylinders, in such a way that both the web and the wire travel for the longest possible distance on the surface of the drying cylinders. In practice, the web is lead over alternate drying cylinders on the different levels. Thus the web travels unsupported from one level to the other, over the empty space between the two levels. There are also similar empty spaces elsewhere in paper machines, for example, in the press section.
During normal operation, an empty space has little effect on the travel of the web in a twin-wire dryer section. However, when starting up production, the web is taken through the dryer section with the aid of a web threading tail cut from the web. This web threading tail that runs between the drying cylinder and the wire tends to catch on the surface of the drying cylinder, though it should move over the empty space into the closing throat formed by a drying cylinder and the wire on the other level. Because of this, special apparatuses are used to carry the web threading tail over the empty space from the opening throat to the closing throat.
Usually the web threading tail is carried by ropeways, but nowadays these are being removed, due to their unreliable and even dangerous operation. Cable-less apparatuses have therefore been developed, in which the web threading tail is lead over empty spaces with the aid of various guide plates with associated air jets. In addition, particularly in dryer sections, doctors are used to transfer the web threading tail from the drying cylinder to the guide plate. In the doctor, a blade or an air jet can be used. The doctors, guide plates, and air jets can also be separate.
The doctoring result achieved using an air jet is generally poor, which leads to breaks when leading the web threading tail. Frequently, attempts are made to improve the doctoring result by increasing the power of the air jet, but the jet then often interferes with the movement of the web threading tail. As air jets have mainly only a guiding effect, they cannot be used to tension the web threading tail. In addition, the nozzles used to create the jet are sensitive to variations in conditions and can only be imprecisely controlled. Doctor blades in contact with the surface of the drying cylinder wear in use and have a complex construction. In practice, threading must be assisted with manually-operated jet pipes, or even by hand, which substantially impairs work safety.
For long empty spaces, apparatuses based on a belt loop have also been developed. In it, the web threading tail, which is lead onto the belt loop, is propelled forwards by the rotation of the belt loop and a vacuum arranged inside it. WO publication number 0019013 discloses such an apparatus. However, the known devices are long, making it impossible to apply them, for example, to empty spaces in a dryer section. In addition, the apparatus requires special devices to detach the web threading tail and guide it on to the belt loop.
The invention is intended to create a new apparatus for leading a web threading tail over an empty space, which is smaller and more reliable than previously, and by means of which the drawbacks of the state of the art are eliminated. The apparatus according to the invention is small in size and can be easily located between structures. By means of the apparatus according to the invention, the web threading tail can be reliably detached from the surface preceding the empty space and transferred in a controlled manner to the surface following the empty space. In addition, the apparatus requires little power and its operation is easy to control.
In the following, the invention is examined in detail with reference to the accompanying drawings showing some embodiments of the invention.
a and 3b show side views of an apparatus according to the invention, turned to the rest position.
a and 5b show one apparatus according to the invention in the operating and rest positions, seen in the machine direction.
a shows a schematic diagram of the apparatus of
b-8d show partial cross-sections of a variation of the apparatus of
For threading to succeed, an apparatus must be fitted in each empty space. After the opening throat 14, the web threading tail 16 travelling between the drying cylinder 11.1 and the wire 13.1 tends to adhere to the surface of the hot drying cylinder 11.1 (
The drum is fitted away from the surface of the drying cylinder, so that it does not wear and has no effect on the drying cylinder. The gap is usually 2-10 mm, preferably 3-6 mm. Thus, there are then fewer restrictions than previously on the placing of the drum and greater tolerances in its location. Thus, the web threading tail is detached by means of the rotating drum, in connection with which a vacuum is arranged. As the gap is small, only a small vacuum is required. On the other hand, the detaching of the web threading tail can be ensured by using a greater vacuum, without, however, this disturbing the movement of the web threading tail. The construction of the drum 18, which incorporates a perforated jacket 19, is described in greater detail in connection with
The apparatus is used specifically for leading and guiding a web threading tail. During the normal operation of the dryer section, the apparatuses according to the invention can be turned to the rest position. For this purpose, an articulated arm is used to create a swivelling support for the apparatus on the structure of the dryer section. In the apparatuses shown in the figures, the articulated arm 20 is attached at one point by bearings to the structure of the dryer section. Correspondingly, the drum 18 is attached to one branch of the articulated arm 20 and the operating device 21 to the other branch. In this case, the operating device 21 is a compressed-air cylinder, which is also attached to the structure of the dryer section. By suitable dimensioning, the apparatus can be moved simply to a sufficient distance from the drying cylinders and the web. In addition, the apparatus can be easily and rapidly swivelled from the rest position to the operating position and back again.
a and 5b show the support of the second apparatus from the left in
Generally, the apparatus 10 includes devices 22 arranged after the drum 18 in the direction of travel of the web threading tail, for leading the web threading tail to the next closing throat. This ensures the transfer of the web threading tail over the empty space.
In the second apparatus according to the invention, the devices 22 include a belt loop 28 permeable by air. The belt application is shown in partial cross-section in
In
Both of the apparatuses disclosed according to the invention can also be used to tension the web threading tail. Tensioning is achieved by rotating the drum faster than the web. Especially the drum itself can be rotated at even a much higher speed than the web, as after the detaching of the web threading tail the web threading tail only touches the drum for a short distance. Once the tail threading has succeeded, the web threading tail detaches entirely from the drum (
In the apparatus described, the diameter of the drum itself is about 300 mm. In belt applications, the turnover roll is considerably smaller. According to
a shows a schematic diagram of a belt application of the apparatus according to the invention. A belt loop 28, which moves in the direction shown by the arrow, is supported on the turnover rolls 29 and 30. The web threading tail 16 is lead on top of the belt loop 28. Correspondingly,
The construction of the apparatus is new in other ways too. The vacuum is preferably created using compressed air, making separate blowers unnecessary. In the application described, a venturi pipe 45, with a ring nozzle 46 connected to it, is used. The compressed air blown from the orifice of the ring nozzle creates a flow in the venturi pipe and in turn a sufficient vacuum in the apparatus. The venturi pipe 45 is also connected to an intermediate pipe 47, which is correspondingly connected by means of an angle pipe 48 to the chamber 41. In addition, the force required to rotate the belt loop is created by a drum motor. In other words, the motor 49 is inside one of the turnover rolls 30. In addition, the motor is fitted on the attachment point side, thus bringing the center of gravity of the apparatus close to the attachment point. Further, there is a connection from the motor to the intermediate pipe, so that the airflow removes the heated air from the motor.
Compressed air is also used in connection with the blowing plate. For this purpose there is a transverse feed pipe 44 with swan-neck pipes 50 connected to it, which terminate in the actual blowing pipe 51. In the blowing pipe, the compressed air is distributed evenly over the width of the belt loop and then discharged through the holes in the blowing pipe, creating the aforesaid Coanda blowing (not shown). The foil strip and Coanda blowing create a powerful vacuum soon after the first turnover roll. At the approach to the second turnover roll, the vacuum effect diminishes, so that the web threading tail naturally separates from the surface of the belt loop. The separation can be ensured with the aid of air doctors 52, which are arranged in connection with the second turnover roll 30 (
In addition to the above description, the apparatus according to the invention can also be used elsewhere in a paper machine.
One critical empty space is in the press section, which is shown in
Using the apparatus according to the invention, the web threading tail is first reliably detached from the surface preceding the empty space and then transferred to the surface following the empty space. The use of a vacuum avoids jets and their difficult orientation. In addition, the vacuum required is low, clearly less than 0.1 bar. The apparatus according to the invention is versatile and easily adaptable. In addition, it can be installed in different positions. Retrofitting is also easy. Both members can be rotated appropriately at any time. Usually an electric or pneumatic motor is used, which is preferably fitted in connection with, or even inside a turnover roll. Particularly the exhaust air from a pneumatic motor can be used to create the vacuum inside the drum. Especially in drum applications, the upper limit of the rotation speed is very high, so that a pneumatic motor can be used to rotate the drum at a clearly higher speed in relation to the surface.
Number | Date | Country | Kind |
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20015023 | Aug 2001 | FI | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/FI02/00687 | 8/22/2002 | WO | 00 | 4/9/2004 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO03/018909 | 3/6/2003 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
3355349 | Devlin | Nov 1967 | A |
4698919 | Wedel | Oct 1987 | A |
4881327 | Hauser et al. | Nov 1989 | A |
5037509 | Wedel | Aug 1991 | A |
5918830 | Verajankorva et al. | Jul 1999 | A |
6219934 | Moskowitz | Apr 2001 | B1 |
6290817 | Autio | Sep 2001 | B1 |
6358366 | Hongisto et al. | Mar 2002 | B1 |
6648198 | Demers | Nov 2003 | B2 |
Number | Date | Country |
---|---|---|
36 30 571 | Mar 1987 | DE |
200 19 346 | Feb 2001 | DE |
WO 0019013 | Apr 2000 | WO |
WO 03018909 | Mar 2003 | WO |
Number | Date | Country | |
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20040244217 A1 | Dec 2004 | US |