Method of using a web cutting device

Abstract: The invention concerns a web cutting device (10), which includes a cutter blade (11) and an actuator (12), which is fitted to act upon the cutter blade (11) so as to produce the cutting stroke. The actuator (12) consists of a number of cylinders (13) placed inside a container (17) or of a number of cylinders placed each of them in a container of its own, each of which cylinders includes a piston (14) and a piston rod (15), and said piston rods (15) have been attached to the cutter blade (11) with a certain spacing.

Description: The invention concerns a web cutting device according to the preamble of claim 1. In devices for treatment of a paper web, such as, for example, in paper machines and coating machines, cutting devices are used, whose function is to cut off the web at a number of positions when some failure takes place in the operation of the machine, such as an uncontrolled web break. The function of said cutting is to protect such items as might be damaged when the paper web proceeds as wrinkled and having lost its tension inside the machine, for example, through a coating station or through a calender with soft calender rolls. Further, cutting devices are used in a reel-up as a part of the machine-reel change equipment. When the running speeds of the machines used in the manufacture and finishing of paper (for example, coating, calendering, slitting) are increased even to levels higher than 2500 metres per minute, requirements are also imposed on the operation of the web cutting devices, which require both shorter reaction time, smaller size, and higher speed of movement of the blade at the moment of cutting. WO 92/00169 A discloses a web cutting device, according to the preamble of claim 1, which includes a cutter blade and an actuator, which is fitted to act upon the cutter blade so as to produce the cutting stroke, whereby the actuator consists of a number of cylinders, each of which cylinders includes a piston and a piston rod, and whereby said piston rods have been attached to the cutter blade. The prior-art paper web cutting devices have such a construction that a number of pneumatic cylinders fitted at a distance from one another are fitted to act upon the cutter blade of the cutting device. After cutting, the pneumatic cylinders return the cutter blade back to the initial position. However, by means of this prior-art solution, the cutter blade cannot be given a sufficiently high speed, for which reason an excessively long time delay occurs in the cutting, which results in an incorrect cutting point, i.e. the cutting is too inaccurate in respect of the location. An excessively slow movement of the cutter blade also results in an inferior cutting result in the paper web. At present, an accuracy of about 0.3 metre is commonly required from a paper web cutting device. This means that, from the cutting command, the time delay must be such that the cutting error is less than the required limit of accuracy of 0.3 m. In the prior-art solution, in which a number of pneumatic cylinders placed at a distance from one another are used, the time delay is of an order of 0.25 second. With the present-day web speeds, this corresponds to a distance of about 5 metres in the web. If an error of 10 % is permitted in the cutting, it results from this that the accuracy of this prior-art cutting device is just of an order of 0.5 metre. In the Finnish Patent Application No. 860797 , a paper web cutting device is described, which includes a frame part and a blade device fitted on the frame part and fitted to cut off the paper web, as well as an actuator for producing the power necessary for the blade device for cutting off the paper web. The actuator for producing the power necessary for the blade device to cut off the paper web is a spring device, in which the cutting energy has been stored. The cutting device is provided with at least one charging device, which is fitted to charge the spring device. The charging devices are hoses expandable by means of compressed air. In the German Utility Model Application G-9413363.8 , a paper web cutting device is described, which is fitted to operate so that it cuts off a paper web moving in a space between two rolls. The cutting device includes a toothed cutter blade and an actuator, which actuator is fitted to bring the cutter blade, which is attached to a lever arm, into a cutting movement by the intermediate of said lever arm. The actuator can be pneumatic, hydraulic, electric, piezoelectric, magnetic or inductive. Even though, by means of this prior-art cutting device, a quick cutting is aimed at, this prior-art solution involves a number of remarkable drawbacks. The cutting device requires an abundant space and, moreover, its operation is bad in view of safety at work and can cause risky situations, for example, for people working at paper and coating machines. A further drawback of this prior-art solution is the long delay in accelerating the blade beam to the cutting speed. The prior-art cutting devices are massive, and a great power is required to produce the necessary stroke speed. Also, stopping of the massive cutter blade is problematic, and the massive cutter blade produces high dynamic loads in the cutting device, because of which the constructions must be robust and of large size. This is why the prior-art cutting devices are spacious and, moreover, the high dynamic loads applied to the cutting device are also effective in the environment in direct vicinity of the cutting device. In the FI Patent Application No. 944816 , a web cutting device is described, which includes a frame part and a blade device fitted in the frame part and fitted to perform the cutting of the web. The first frame part and the second frame part of the frame part are curved faces, between which there is an annular space. At least one of the curved faces is displaceable, the cutter blade being fitted to be charged in said annular space. At least in one of the frame parts, there is an opening for the striking opening of the cutter blade. The object of the present invention is to provide an improvement over the prior-art web cutting devices. It is a more specific object of the invention to provide a web cutting device whose cutting result is as short as possible in the direction of progress of the web. It is a further object of the invention to provide a web cutting device which is suitable both for paper web and for board web and by whose means the web can be cut off at once across the entire width of the web. It is a further object of the invention to provide a cutting device which permits a cutting stroke as rapid as possible and which also permits to make the construction of the cutting device of a size as small as possible. The objectives of the present invention are achieved by means of a cutting device according to claim 1. By means of the cutting device in accordance with the present invention, a number of remarkable advantages are obtained. The stroke of the cutting device is very quick, and the size of the cutting device is as little as possible. By means of the cutting device it is possible to cut off the paper or board web at once across the entire width of the web so that the cutting result is as short as possible in the direction of progress of the web, as a result of which, the "tail" produced, for example, in connection with splicing can be made considerably shorter than by means of the prior-art cutting devices. Fitting of a small-size cutting device in different environments is far easier than fitting of the prior-art cutting devices. With a cutting device in accordance with the present invention, a high stroke speed of about 15 metres per second of the cutter blade can be achieved with a very good reproducibility. The quick stroke of the cutter blade of the cutting device is produced by means of large-area, quickly opening, pressure-controlled control valves of cylinders attached to the cutter blade as well as by placing the cylinders in the interior of the pressure container so that the passage of the compressed air from the pressure container to the cylinders is as short as possible. The moving parts of the cutting device in accordance with the invention consist of the cutter blade and of piston rods and pistons attached to the cutter blade with a certain spacing. The proportion of the weight of the cutter blade to the total weight of all the moving parts is optimally about 70 %. The invention will be described in detail with reference to some preferred embodiments of the invention illustrated in the figures in the accompanying drawings, the invention being, however, not supposed to be confined to said embodiments alone. Figure 1 is a schematic sectional view of a preferred embodiment of the cutting device in accordance with the invention. Figure 2 is a schematic sectional view of the cutter device shown in Fig. 1 in a situation in which the cutter blade has carried out the cutting movement. In the embodiment shown in Figs. 1 and 2, the cutting device in accordance with the invention is denoted generally with the reference numeral 10. The cutting device 10 includes a cutter blade 11 and an actuator 12, which is fitted to act upon the cutter blade 11 to produce the cutting stroke. In this embodiment the actuator 12 consists of a number of cylinders 13, in each of which there are a piston 14 and a piston rod 15. The piston rods 15 have been attached to the cutter blade 11 with a certain spacing. The spacing of the attaching of the piston rods 15 to the cutter blade 11 depends on the number of the cylinders 13. The number of the cylinders 13 is preferably 6...14, and a number that is recommended in particular is 8...10, depending on the width of the cutter blade 11. The cylinders 13 are placed in the interior of a container 17, and the pressure present in the container 17 is denoted with the letter P s . Each cylinder 13 can also have a container 17 of its own. The movement of the piston 14 can be stopped by means of a stop cushion 16. The operation of the pistons 14 is controlled by means of control valves 18. The control pressure is denoted with the letter P o and the back pressure with the letter P v . The magnitude of the control pressure P o is preferably about 80 % of the pressure P s in the container 17. The guide of the cutter blade 11 is denoted with the reference numeral 19. The piston 14 can be returned either by means of the back pressure P v or by passing a pressure present in a separate pipe system to below the piston 14. In the cutting device 10 in accordance with the invention, the control valves 18 are opened highly efficiently, because, when the slide of the control valve 18 starts moving, the pressure P s in the container 17 can act upon the slide of the control valve 18 on an area that is multiple in comparison with a situation in which the control valve 18 is fully closed. Thus, in the cutting device 10 in accordance with the invention, the rapid stroke of the cutter blade 11 is produced by means of the large-area, rapidly opening, pressure-controlled control valves 18 of the cylinders 13 attached to the cutter blade 11 as well as by placing the cylinders 13 in the interior of the pressure container 17 so that the passage of the compressed air from the pressure container 17 into the cylinders 13 is as short as possible. Thus, in the cutting device 10 in accordance with the present invention, it has been successfully possible to make the cutter blade 11 and the devices that move it as of a weight as low as possible. The moving parts consist of the cutter blade 11 and of piston rods 15 and pistons 14 attached to the cutter blade 11 with a certain spacing. The proportion of the weight of the cutter blade 11 to the total weight of all the moving parts is optimally about 70 %. In the cutting device 10 in accordance with the invention, the operation of the control valves 18 has been made very accurate, and the speed of opening of the control valves 18 is very high. This has been achieved by reducing the weight of the slide in the control valve 18 and the proportions of the areas so that the control valve 18 is opened with a very high control pressure P o , preferably with a pressure that is of an order of 2.3...7 bar if the pressure P s in the container 17 is of an order of 3...10 bar. Preferably, the pressure P s in the container 17 is about 4 bar. The high level of the control pressure P o makes the operation of the control valve 18 very accurate, because the discharging of the control valve 18 takes place so that the control pressure P o of the control valve 18 is eliminated at the same time from all the control chambers. The more rapidly the pressure P o in the control chambers 20 is lowered, the more quickly is the pressure range bypassed in which all the control valves 18 are opened. The pressure level has a substantial effect on the speed of lowering of pressure. With a cutting device in accordance with the present invention, a high stroke speed of about 15 metres per second of the cutter blade 11 can be achieved with a very good reproducibility. This is why, by means of the cutting device 10 in accordance with the invention, it is possible to cut off the web at once across the entire width of the web so that the cutting result is as short as possible in the direction of progress of the web, and thus, the "tail" produced, for example, in connection with splicing can be made considerably shorter than by means of the prior-art cutting devices. The cutting device 10 in accordance with the invention is also of small size, so that its fitting in different environments is very easy. From the point of view of the speed of the cutter blade 11 of the cutting device 10 in accordance with the invention, it is important that the cylinders 13 should operate at the same time, i.e. as synchronized. Also, in view of the service life of the blade 11, it is important that the pistons 14 collide against their stop cushions 16 as precisely at the same time as possible. The timing can be affected by means of regulation of the flow resistances in the system of control pressure pipes 21. This is why the control pressure pipes of all the control valves 18 should preferably be made equally long, and the control pipes should be provided with an equal number of elbows. All the cylinders 13 of the cutting device 10 in accordance with the invention can be easily made to operate within one millisecond. During one millisecond, the piston 14 proceeds a distance of about 1 mm from its starting point. This maximal phase difference is, in fact, theoretical, for the rigidity of the cutter blade 11 in the direction of the force of the piston 14 is high enough so that the cutter blade 11 can equalize differences of this magnitude. Above, just one preferred embodiment of the invention has been described, and it is obvious to a person skilled in the art that numerous modifications can be made to said embodiment within the scope of the accompanying patent claims.

Claims: Method of using a web cutting device (10) which includes a cutter blade (11) and an actuator (12), which is fitted to act upon the cutter blade (11) so as to produce a cutting stroke, whereby the actuator (12) comprises a number of cylinders (13), each of which cylinders (13) includes a piston (14) and a piston rod (15), and whereby said piston rods have been attached to the cutter blade (11) with a certain spacing, characterized in that the cylinders (13) are placed inside a pressure container (17) or each of the cylinders (13) is placed in a pressure container of its own, and that in use the pressure container (17) has a pressure (P s ) of 3 to 10 bar, favourably 4 bar, that control valves (18) are arranged to control the operation of the pistons (14) so that each cylinder chamber on the piston side opposite to the piston rod (15) is, by means of the control valve (18), selectively brought into fluid communication with the pressure container (17) in which the cylinder is disposed, and that the control valves (18) are large-area, quickly opening, and pressure-controlled and whereby in use each of the control valves (18) is opened with a very high control pressure (Po) of 2.3 to 7 bar. Method of use claimed in claim 1, characterized in that stop cushions (16) have been fitted to stop the movements of the pistons (14). Method of use as claimed in any of the claims 1 or 2, characterized in that the number of the cylinders (13) is 6...14, preferably 8...10, depending on the width of the cutter blade (11). Method of use as claimed in any of the claims 1 to 3, characterized in that the proportion of the weight of the cutter blade (11) to the total weight of all the moving parts is of an order of about 70 %. Method of use as claimed in any of the claims 1 to 4, characterized in that the stroke speed of the cutter blade (11) is of an order of 15 metres per second.

Inventors: MANNIO AARON, MANNIO, AARON
Applicants: METSO PAPER INC, METSO PAPER, INC.
Application year: 1996
Main classification: B26D5
IPC codes: D06H7, D21F7, B26D5, B26D1, D21G9