Method and assembly for cutting a web

Abstract: The present invention relates to a method and assembly for cutting a paper or paperboard web particularly in a winder comprising at least one support roll (2) on which a roll (1) being wound is rotated. The invention is based on bringing a curved, tensioned cutting blade (6) into the nip between the support roll (2) and the roll (1), whereby the sharpened and possibly toothed edge (9) of the blade cuts the web (4) being wound onto the roll (1) at a desired point.

Description: The present invention relates to a method according to the preamble of claim 1 for cutting a paper or paperboard web in a winder. The invention also concerns an assembly suited for implementing the method. In conjunction with paper and board manufacture, the webs must be reeled into mill rolls, which are unwound and rewound back into rolls. Equipment employed for reeling up the web into a roll at the end of the papermaking line is called a winder. Conventionally, the winder is located at the end of the papermaking line. If web finishing is performed on-machine with the paper machine, the number of required winders is only one, while off-machine finishing of the web in a separate finishing station requires a winder at the ends of both the papermaking line and the finishing line. A winder is also required at slitter stations. The winder typically has one or two support rolls on which the roll to be wound is rotated. Furthermore, the equipment comprises arrangements for leading the web onto the support roll and devices for removing a full roll and placing a core for the new roll onto the support roll. In winders having two support rolls, the web is cut after the roll is finished by means of a knife located between the support rolls through actuating the knife to cut the web prior to the nip between the support roll and the roll. The knife may have a length extending over the entire cross-machine width of the web, or alternatively, a short knife can be used that is moved cross-directionally across the web. While a long knife extending over the entire width of the web is difficult to move between the support rolls due to the limited space available, the crosswise moved short knife has disadvantages in being slow and cutting the web obliquely unless the winder is stopped for the duration of web cutting. In equipment having only one support roll, this cutting method is not applicable, because the tail of the cut web cannot be reliably lead into the nip between the support roll and the roll core. Hence, the web is cut on the surface of the finished roll in equipment having a single support roll, whereby the web tail becomes long and must be further cut shorter. Furthermore, the topmost plies of the finished roll may easily become damaged during the cutting of the web. To avoid the shortcomings of the above-described cutting methods, a cord cutting device as disclosed in FR-A-2547802 and corresponding to the preamble of claims 1 and 5, has been developed based on cutting the web by virtue of taking a cord into the nip between the support roll and the paper roll, whereby the cord cuts and severs the web. The cord is arranged to move into the nip between the support roll and the paper roll so that the cord will be trapped between the topmost ply of the roll and next ply underneath, whereby the topmost ply of the roll remains between the support roll and the cutting cord. After the cord has passed the nip and is moved away from the nip on the other side of the nip, the cord tensions the topmost ply of the roll thus cutting it off. After the web is cut, the full roll is removed from above the support roll and a new roll core is brought in the gap between the support rolls. After the web is cut, the rotation of the support roll is braked down to full stop and a new core is brought for the new roll. Prior to cutting the web, glue can be sprayed onto that web surface which will face the next to last ply of the roll in order to secure one end of the web to the roll and the other to the core, respectively. Some of the most serious problems of the cord cutting device are the ill-defined cutting result and torn cut edge. When the cord is taken through the nip, it remains curved, whereby the cord cuts the edges of the web first. Moreover, the cutting point cannot be controlled accurately, because the cutting action is based on severing the web through tightening the cord, whereby the cutting point varies depending on web qualities and web tension. As the web is cut by pulling a relatively thick cord or equivalent noncutting member across the web, the cutting occurs not by neat cutting, but rather, by tearing. For the same reason, the cutting line must be curved, because the web is easiest torn along a line starting from the web edge. Furthermore, it is obvious that this cutting method is ill suited for heavier grades of paper and paperboard. It is an object of the present invention to achieve a method capable of cutting a web at the reel/winder neatly and without causing damage to the paper roll. The goal of the invention is achieved by a method according to claim 1 and by an assembly according to claim 5. The invention offers significant benefits. The most important advantage of the invention is that it provides positive and reliable cutting of the web independently from paper grade and qualities. The end of the cut web remains stable on the support roll and the cutting point is always in the same position relative to the support roll. This helps securing the web end onto a new core and starting the winding of a new roll. With the help of the blade, also thick paper grades and paperboard can be cut readily without the risk of tearing the web, and obviously, the straight edge of the blade renders a straight cut. As the blade is sideways curved, it conforms well to the circumferential shape of the support roll, and pulled by the roll, easily enters the nip without causing damage to a full roll. The blade makes cutting action fast, because the blade can be taken into the nip at the full rotational speed of the support roll and it can be withdrawn extremely rapidly. In the following the invention will be examined in greater detail with reference to the appended drawings in which Figure 1 is a diagrammatic side view of an embodiment according to the invention; Figure 2 is a diagram illustrating the function of the assembly according to the invention as seen from direction A marked in Fig. 1; Figures 3 - 5 are diagrammatic side view illustrations of another embodiment of the assembly according to the invention in the different steps of the web cutting action. As is evident from the diagrams, the assembly has an extremely simple construction. Referring to Fig. 1, a two-roll winder is shown therein with the cutting assembly according to the invention adapted thereto. In the illustrated winder, the roll 1 is wound resting on two parallel, adjacent support rolls 2, 3. The web 4 being wound is passed onto the roll 1 from below the support rolls 2, 3 via the gap between the support rolls, and in the embodiment shown in Fig. 1, is then passed over the left-side support roll 2 to wind onto the roll 1. A web cutting assembly is adapted in conjunction with the left-side support roll 2. The cutting assembly comprises a cutting blade rotating device 7 placed to both ends of the support roll 2, whereby a blade holder 5 is connected to the rotating device on the side facing the end of the support roll 2. The blade holder 5 and the blade rotating device 7 are aligned relative to the end of the support roll 2 so that the rotational center 8 of the blade holder 5 is concentric with the center axis of the support roll 2. The blade holder 5 extends radially in the direction of the radius of the support roll 2 approximately to the circumference of the support roll 2, where a web cutting blade 6 is attached to the end of the blade holder 5. The cutting blade 6 is a thin, sideways curved blade. The sideways curvature of the blade 6 is made equal to the curvature of the circumference of the support roll 2, and the blade 6 is placed as close as possible to the surface of the support roll 2. Advantageously, the gap between the support roll 2 and the cutting blade 6 is so narrow that only the web being wound can pass through the gap. Further advantageously, the blade should conform to the radius of curvature of the support roll as closely as possible. This is because of the requirement that the blade entering the nip between the roll 1 and the support roll 2 may not damage the roll 1. In fact, a thin and properly shaped blade 6 enters the nip without complications and causes no damaging blows on the roll. Advantageously, the blade 6 is provided with the shape of a segment of a circle having a curvature slightly larger than that of a circle corresponding to the radius of the support roll, whereby the shape of the blade in practice is equivalent to a portion sectioned from the envelope of virtual cylinder tightly enclosing the support roll. To permit making the blade 6 sufficiently thin and yet stiff, the blade is tensioned tightly between the blade holders 5. As the blade 6 is also curved and relatively wide, it also is extremely stiff in the direction of the cutting edge 9 of the blade 6. Moreover, the blade 6 must be stiff perpendicularly to the blade side, that is, in the direction of the radius of the support roll 2 and the roll 1, because the blade may not become deformed when the weight of the roll 1 is imposed onto the blade 6. As a thin blade cannot be made sufficiently stiff by other means, the blade must be tensioned with a high force between the blade holders 5. The cutting edge of the blade may be toothed in the fashion of the blade 6 shown in Fig. 2. The cutting action according to the invention is readily explained with the help of the examples illustrated in Figs. 3 - 5. In these diagrams is shown a winder of the single support roll construction in which the cutting blade 6 is adapted in conjunction with the only support roll 2. In such a winder the web 4 is passed onto the support roll 2 from below the roll and is next turned over the support roll to pass into the nip between the support roll 2 and the roll 1. The roll 1 being wound is supported on the support roll 2 with the help of roll change equipment which also serve for removing the full roll and bringing the core of the new roll onto the support roll. When the control system of the winder finds the diameter of the roll 1 grown sufficiently large, the web cutting assembly 5, 6, 7 is given a command to cut the web 4. Then, the rotary actuators 7 rotate the cutting blade 6 into the nip between the roll 1 and the support roll 2, whereupon, when caught by the nip, the blade 6 is taken between the support roll 2 and the roll 1 due to their rotational movements. Hence, no major force is required for the rotation of the blade. After entering the nip, the cutting blade 6 forces the web 4 being wound onto the roll 1 off from the surface of the roll and cuts the web rapidly after the nip. After the web is cut, the full roll is elevated off from the support roll 2 and the rotational movement of the support roll 2 is braked down to full stop. The end of the web 4 is held adhering to the surface of the support roll by means of, e.g., a vacuum applied to the inside of the support roll, and additionally, the blade riding on the web 4 in its part assures the adherence of the web 4 to the support roll 2. Immediately after the full roll 1 is removed from above the support roll 2, the cutting blade 6 is returned to its home position, a new core is brought onto the support roll, the web end is adhered to the core, and the support roll 2 is accelerated to the winding speed. The ends of the web can be attached to the roll 1 and to the new core, respectively, by means of glueing, for instance. The amplitude of the cutting blade swing must be at least so large as to bring the blade past the nip. A wider-amplitude movement is not preferable, and in the most advantageous case, the trailing edge of the blade remains on the ingoing side of the blade into the nip. In the equipment illustrated in Figs. 1 and 2, the roll is rotated freely on the support rolls without auxiliary support by any support devices, and the new core 10 is brought into the gap between the support rolls. The cutting action takes place in a similar fashion as in the equipment provided with a single support roll. While the rotary actuator of the cutting blade is advantageously implemented in the above-described fashion, it is also feasible to replace the rotary actuator operating with the center axis of the support roll as its center of rotation by, e.g., a transfer device driven along a controlled trajectory that moves the cutting blade tangentially close to the roll surface. The actuator of the blade can be driven by an electric motor, hydraulic or pneumatic rotary actuator, cylinder or bellows. The blade can be made from, e.g., steel, or alternatively, from a variety of different composite materials and plastics, as well. Then, the cutting edge of the blade can be made as required from a harder material, whereby longer life against wear is achieved. The cutting edge of the blade may be straight or toothed.

Claims: A method of cutting a paper or paperboard web (4) in a winder comprising at least one support roll (2) on which a roll (1) being wound is adapted to rotate, with cutting the web (4) being wound onto the roll (1) by bringing into the nip between said support roll (2) and said roll (1) a thin cutting blade (6) extending over the width of the web (4), in such a fashion that the cutting blade (6) is moved tangentially close to the surface of the support roll (2), and bringing the cutting edge (9) of the blade (6) past the nip to the other side of the nip relative to the ingoing side of the blade, thereby the cutting blade (6) forces the web (4) being wound onto the roll (1) off from the surface of the roll and cuts the web rapidly after the nip, characterized in that the cutting blade (6) is sideways curved and relatively wide to become extremely stiff in the direction of the cutting edge (9) of the blade (6) and moreover perpendicularly to the blade side, and that the cutting blade (6) is drawn by the rotational movement of the support roll (2) and the roll (1) so far past the nip as to force the cutting edge (9) to cut the web (4). A method as defined in claim 1, characterized by stopping the movement of the cutting blade (6) before the entire blade (6) has passed the nip. A method as defined in claim 1 or 2, characterized by keeping the cutting blade (6) tensioned along its longitudinal direction between two blade holders (5). A method as defined in any foregoing claim, characterized by moving the cutting blade (6) along such a trajectory that conforms to the surface of a cylinder having a radius larger than that of the support roll (2). An assembly for cutting a paper or paperboard web (4) in a winder comprising at least one support roll (2) on which a roll (1) being wound is adapted to rotate, a thin cutting blade (6) extending over the width of the web (4), and means (5,7) for bringing the blade (6) into the nip between the support roll (2) and the roll (1) so that the blade (6) is moved tangentially close to the surface of the support roll (2), and to bring the cutting edge (9) of the blade (6) past the nip to the other side of the nip relative to the ingoing side of the blade, characterized by a stiff, sideways curved cutting blade (6), which is relatively wide, and which is drawn by the rotational movement of the support roll (2) and the roll (1) into the nip at least so far as to force the cutting edge (9) of the cutting blade (6) to cut the web (4). An assembly as defined in claim 5, characterized by blade holders (5) arranged to both sides of the web (4) to be cut, said blade holders being suited for attaching the blade (6) and tensioning the same in its longitudinal direction. An assembly as defined in claim 5 or 6, characterized in that the width of the blade (6) is larger than the width of the nip between the support roll (2) and the roll (1). An assembly as defined in any of claims 5 - 7, characterized in that the shape of the cutting blade (6) is equivalent to the longitudinal section of a cylindrical envelope and the blade radius of curvature is larger than that of the support roll (2). An assembly as defined in any of claims 5 - 8, characterized in that said means for bringing the blade (6) into the nip comprise rotatable blade holders (5) adapted to both sides of the support roll (2), whereby the center (8) of rotation of said blade holders is concentric with the center axis of the support roll (2) and said blade holders support the blade (6) at a distance from the surface of the support roll (2), and at least one actuator (7) for rotating said blade holders about their centers (8) of rotation.

Inventors: KOUTONEN PAULI, MALMI JARMO, NISKANEN HEIKKI, KOUTONEN, PAULI, MALMI, JARMO, NISKANEN, HEIKKI
Applicants: VALMET CORP, VALMET CORPORATION
Application year: 1995
Main classification: B65H19
IPC codes: B65H18, B65H19