Method and device in the cutting of the leader of a paper web

Abstract: A method and a device in the cutting and diagonal cutting of the leader of a paper web (W). The method and the device are applied in a group of drying cylinders provided with single-wire draw (13) in a paper machine or a finishing machine. The drying wire (13) is separated from the paper web (W) by means of a guide roll, guide rolls (14a,14b) or equivalent static airborne means, an open draw (W₀) being thereby obtained for the web (W). The cutting and diagonal cutting of the leader of the paper web (W) are carried out on the open draw (W₀) of the web (W). After the open draw (W₀), the drying wire (13) and the web (W) are brought together on the subsequent leading or drying cylinder (11). It is preferable to employ two guide rolls (14a,14b), whereof the first roll is placed so that the drying wire (13) supports the web (W) up to the location of said guide roll (14a), which is followed by an open draw (W₀) of the web. By means of the second guide roll (14b), the drying wire (13) is returned onto the subsequent leading or drying cylinder (11).

Description: The invention concerns a method in the cutting and diagonal cutting of the leader of a paper web, which method is applied in a group of drying cylinders provided with single-wire draw in a paper machine or a finishing machine. Further, the invention concerns a device intended for carrying out the method, comprising a transverse beam placed underneath a drying cylinder in a group of single-wire draw, on which beam a carriage is arranged to traverse, in connection with which carriage a web cutting blade is fitted, such as a rotary blade or a pin-shaped or knife-shaped cutting blade. In prior art, a number of different so-called diagonal cutters are known, which are fitted in the drying section of a paper machine, in particular at the final end (dry end) of the drying section. In the prior-art diagonal cutters, as the part that cuts-off the leader out of the web, a pin fixed to a mechanical traverse has been used, said pin acting against the drying cylinder and the diagonal shearing (cutting) being carried out by means of said pin. It is a drawback of this solution that the pin scratches the cylinder and becomes soon dull, whereby the cut quality is deteriorated. In prior art, as a diagonal cutter, it is also known to use a device similar to a circular saw and mounted on a traversing carriage or to carry out the diagonal cutting manually by means of a knife. In respect of prior art, reference is made to the applicant's FI Patent 63,800 (corresp. US Pat. 4,566,944), from which a leader cutter is known. This device comprises a traversing beam which is fitted on, or in connection with, a multi-cylinder dryer of a paper machine in a direction transverse to the paper machine. On said beam, a traversing carriage is provided, which is provided with a web-cutting blade. Said device is characterized in that on said carriage, in connection with its cutting blade, a substantially plane carrier face is provided in connection with which there are air-blowing means. The blow means are provided with a nozzle slot or with opposite nozzle slots or with corresponding nozzle holes. With the prior-art methods and devices, a problem has been how to apply them to the area of single-wire draw in a multi-cylinder dryer of a paper machine or a finishing machine. As is known in prior art, a multi-cylinder dryer provided with single-wire draw comprises two rows of heated drying cylinders, one row above the other, or one row of heated drying cylinders and one row of leading rolls or cylinders. Between said rows of cylinders and/or rolls, in each group of single-wire draw, the web is supported by one drying wire so that the cylinders in one row of cylinders, as a rule the upper cylinders, are placed outside the loop of drying wire and the lower cylinders or lead rolls inside the loop of the drying wire. Thus, in single-wire draw, the web is also supported on the, usually straight, runs between the rows of cylinders. On the latter runs, in the case of twin-wire draw, the web has free, unsupported runs, on which the prior-art diagonal cutters can be used, as is shown in Fig. 1 in the applicant's FI Patent 63,800 mentioned above. Since, in the case of single-wire draw, on said runs between the rows of cylinders, the web is supported by the drying wire on the face of the wire, the prior-art diagonal cutters cannot be applied on these runs. This has constituted a substantial obstacle and limitation for installation of diagonal cutters in the positions that are most purposeful in view of their operation and functioning. An object of the present invention is to provide novel solutions for the problems discussed above. An object of the present invention is to provide such a method and device for cutting of the leader of a paper web wherein no excessively long free unsupported draws are formed for the web, which might cause breaks and other disturbance, mainly resulting from fluttering. It is a non-indispensable further object of the present invention to provide such a method and device in the cutting of the leader of a paper web as, for its part, makes it possible to accomplish threading of a web without guiding by means of ropes. In view of achieving the objectives stated above and those that will come out later, the invention in accordance with the invention is mainly characterized in that the drying wire is separated from the paper web by means of a guide roll, guide rolls or equivalent means, an open draw being thereby obtained for the web, that the cutting and diagonal cutting of the leader of the paper web are carried out on the open draw of the web, and that, after said open draw, the drying wire and the web are brought together on the subsequent leading or drying cylinder. Above, the means equivalent to guide rolls are understood as meaning, for example, static leading devices based on contact-free airborne support. On the other hand, the device in accordance with the invention is mainly characterized in that, above said beam, two guide rolls for the drying wire are placed, whereof the first roll is placed in a position in which the drying wire and the web, which arrive together from the upper cylinder, are separated from each other and the drying wire is guided further on the first guide roll, and that the second guide roll guides the drying wire back again to meet the web, after its open draw, on the lower cylinder, said traversing beam and its cutting blade being placed at the proximity of the free run of the web. As to its construction, the cutter applied in the invention may be, for example, a device similar to that described in the applicant's said FI patent, provided with a rotatory or fixed blade, or some other, corresponding prior-art diagonal cutter, such as a device that cuts the web by means of a water jet. As a rule, the method of the invention is applied in the rear end of a drying group provided with single-wire draw in a paper machine or board machine, preferably before the upper drying cylinder from whose lower circumference the rest of the paper web, from which the leader has been cut apart, is guided into the pulper placed underneath, having been detached by a doctor. The invention may also be applied to various multi-cylinder dryers provided with a cylinder group with single-wire draw in paper or board finishing machines. The method and the device in accordance with the invention can contribute to a rope-free threading of the web and be used for cutting of the leader in geometries of multi-cylinder dryers of the type of the applicant's "Sym-Run" (trade mark) dryer or equivalent. In the following, the invention will be described in detail with reference to some exemplifying embodiments of the invention illustrated in the figures in the accompanying drawing, the invention being by no means strictly confined to the details of said embodiments. Figure 1 illustrates the invention as applied to such a cylinder group with single-wire draw in a paper machine as is followed by a size press in itself known or by some other finishing machine. Figure 2 is a schematic side view, on a scale enlarged from Fig. 1, of a more detailed embodiment of the invention. As is shown in Fig. 1, the last group of cylinders at the dry end of a multi-cylinder dryer is provided with single-wire draw, which is accomplished by the loop 13 of drying wire. The cylinder group is provided with a row of upper cylinders 10, 12 heated from inside, and the lower cylinders consist of leading cylinders 11, which are not heated. The drying wire 13 runs meandering from an upper cylinder 10 onto a leading cylinder 11 and the other way round, so that on the upper cylinders 10 the paper web W reaches direct contact with the heated faces of the upper cylinders 10,12, and on the lower cylinders 11 the web W remains on the outside face of the wire. The last two upper cylinders 10,12 in the group of cylinders are placed at a somewhat higher level (difference in height Δ H) than the preceding cylinders 10 in the row. The leading cylinders 11 are placed in a row in the same horizontal level. According to the invention, after the first upper cylinder 10 placed at a higher level, the drying wire 13 is separated from the cylinder 10 face and from the web W on the first guide roll 14a, whereupon the drying wire 13 is guided by the second guide roll 14b placed at a somewhat higher level. From the second guide roll 14b, the drying wire 13 is returned onto the lower cylinder 11, on which it meets the web W. Thus, the web W runs the run between the first guide roll 14a and the leading cylinder 11 or an equivalent drying cylinder placed below said guide roll 14a as an unsupported draw W₀ free from wire 13. The embodiment of the invention illustrated in the figures is also advantageous in the respect that, owing to the location of the first guide roll 14a, the free draw W₀ of the web becomes relatively short, so that, on the draw W₀, fluttering of the web and resulting drawbacks, such as susceptibility of breaks in the web, do not occur to a detrimental extent. At the free draw W₀ described above, underneath the drying cylinder 10 and between the adjoining leading cylinders 11, a diagonal cutter 20 is placed in accordance with the invention, by means of which, thus, the web W₀ can be cut without a detrimental effect of the drying wire 13. The diagonal cutter 20, which is fitted in the position in accordance with the invention at the proximity of the web draw W₀ that is arranged free, may be any cutter in itself known, for example a device similar to that described in the applicant's said FI Patent 63,800, in which contact-free airborne support is employed. The diagonal cutter 20 shown in Fig. 2 includes a beam 21, which extends parallel to the axes of the cylinders 10,11,12 from the driving side of the paper machine to the operating side. On the guides 22 on the beam 21, a carriage 23 is fitted to be traversed. On the carriage 23, an electric motor, a pneumatic motor 24, or an equivalent drive gear is fitted, which produces the transverse movement of the carriage 23. Moreover, by means of a rotor 24, a circular cutter blade 25 of the diagonal cutter 20, similar to a circular saw, is rotated if such a blade is used. The cutter blade 25 cuts the web W₀ into two strips, whereof the narrower one, about 10 to 15 cm wide, is the leader, and the wider part, which is denoted with W H in Fig. 1, is detached from the lower face of the last cylinder 12 in the cylinder group by means of a doctor 15, being passed into the pulper (not shown) placed underneath. After the run of the leader has been stabilized, the diagonal cutter 20 is shifted along its traversing beam 21 and the leader is made wider, whereby, correspondingly, the portion W H of the web becomes narrower. After the web W has been widened to full width, the diagonal cutter 20 in accordance with the invention is placed at one side of the web, and its blade 25 is placed outside the width of the web W and/or has been pivoted apart from the web. As is shown in Fig. 1, after the topmost point on the last upper cylinder 12 in the group of cylinders, the drying wire 13 is separated from the cylinder 12 and, being guided by the guide roll 14c and further by the guide rolls 14d, passed onto the first cylinder (not shown in Fig. 1) in the single-wire group. After the cylinder 12 the paper web W of full width or the leader is detached from the cylinder 12 and, being guided by the guide rolls 16, is passed into the following device, which is, in Fig. 1, represented by a size press, which has a sizing nip N between the rolls 17 and 18. In the environment of application shown in Fig. 1, there may be, for example, a Pope-type reel-up or a machine calender in place of the size press. In respect of Fig. 1, it should still be emphasized in this connection that it is meant just to be one example of an environment of application of the invention, and the invention can be applied in a great number of different multi-cylinder geometries. The diameters D₀ of the guide rolls 14a and 14b used in the invention are usually chosen so that the rolls can be fitted partly side by side and partly one above the other between the drying cylinders 10 and 12. The diameter D₀ is, for example, about 0.5 x V₁ (V₁ = shortest horizontal distance between the adjoining cylinders 10,12). As a rule, the rolls are dimensioned in accordance with their deflection and with their conditions of characteristic frequencies, and the gap V₁ between the cylinders is dimensioned on the basis of the roll diameters in accordance with a certain table of selection. If necessary, the horizontal distance V₁ between the cylinders 10 and 12 can be made longer than normal. The difference in height H₀ between the guide rolls 14a and 14b is, for example, somewhat larger than the radius D₀/2 of the rolls 14a,14b. H₀ is chosen so that a gap of about 20...40 mm remains between the returning wire and the roll 14a. The length of the free draw W₀ of the web is about 40...80 %, preferably about 50...70 % of the total length of the draw between the drying cylinder 10 and the leading cylinder 11. The horizontal distance V₀ between the guide rolls 14a and 14b is preferably substantially equal to the diameter D₀ of the guide rolls 14a,14b. The diameter D₁ of the cylinders 10,12 is somewhat larger than the diameter D₂ of the leading cylinders 11 in the lower row. The horizontal distance V₁ is of the same order as the diameter D₂, preferably about 5...30 % smaller than the diameter D₂. If it is desirable to place the subsequent drying cylinders 10,12 closer to one another than in the geometry illustrated in Fig. 2, as the first and the second guide roll 14a and 14b it is possible to use special rolls, for example so-called fragmentary rolls, whose diameter can be made smaller than the diameter D₀ of normal guide rolls. In some applications of the invention, it is possible to use one guide roll 14a/14b only, in which case the guide roll is placed slightly to the side from the straight run of the web W from the upper cylinder 10 to the lower cylinder 11. In such a case the free draw of the web W becomes of full length, which is not always favourable. When one guide roll is used, the wire 13 separated from the web W is returned to the lower cylinder 11 substantially in the same direction as in Fig. 2.

Claims: A method of cutting a lead-in strip of a paper web in a dryer provided with single-wire draw comprising the steps of: (a) guiding said paper web (W) along a first joint run with a wire (13) over at least a part of the surface of a first cylinder; (b) moving said first joint run from said first cylinder onto the surface of a relatively smaller diameter second cylinder disposed downstream of said first cylinder; (c) guiding said paper web from said second cylinder along a second joint run around and out of direct contact with the surface of a third cylinder disposed downstream of said second cylinder; characterized by the following steps: (d) defining an open draw (W o ) spanningly between said second and third cylinders and along which said paper web (W) moves in unsupported relation from said second to said third cylinder; and (e) cutting said paper web (W) within said open draw (W o ) between said second and third cylinders; each of said first and second joint runs comprising a combination defined by said single wire (13) and said paper web (W). A method according to claim 1, characterized in that said first cylinder is a drying cylinder. A method according to claim 1 or 2, characterized in that said open draw (W o ) is formed by separating said single wire (13) from said paper web (W) by means of a guide roll, guide rolls (14a, 14b) or equivalent means. A method according to claim 3, characterized in that , after said open draw (W o ), said single wire (13) and said web (W) are brought together on the subsequent leading or drying cylinder. A method as claimed in claim 3 or 4, characterized in that , in the method, said two guide rolls (14a, 14b) are employed, whereof said first guide roll (14a) is placed so that said drying wire (13) supports said web (W) up to the level of this guide roll (14a), whereupon said open draw (W o ) of the web follows, and that on said second guide roll (14b) the direction of running of said drying wire (13) is turned and the wire is returned to the subsequent leading or drying cylinder (11), on which the runs of said drying wire (13) and the web are united after said open draw (W o ). A method as claimed in any of the claims 1 to 5, characterized in that , the method is applied in the dry end of the last cylinder group provided with single-wire draw in the drying section. A method as claimed in any of the claims 3 to 6, characterized in that , in the method, said guide roll or guide rolls (14a, 14b) is/are placed in the space between the last two heated upper cylinders (10, 12) in the cylinder group provided with single-wire draw. A method as claimed in claim 4, characterized in that , said last two drying cylinders (10, 12) are placed at a higher level Δ H than said preceding cylinders (10) in the upper row in the group of cylinders (Fig. 1). A method as claimed in any of the claims 1 to 8, characterized in that , after said open draw (W o ), said web (W) and said drying wire (13) are guided over said leading or drying cylinder (11) and thereupon, as a substantially vertical run, onto said last upper cylinder (12) in the group of cylinders, from which the leader separated from said web (W) is passed further and the rest of the web (W H ) is separated from said cylinder (12) on its lower circumference and is passed into the pulper or equivalent placed underneath. A method as claimed in any of the claims 1 to 9, characterized in that , on said open draw (W o ) of said web (W), the cutting and diagonal cutting of the leader are carried out by means of a circular blade, knife-shaped or pin-shaped blade, or a water jet. A device intended for carrying out the method as claimed in any of the claims 1 to 7, comprising a transverse beam (21) placed underneath a drying cylinder (10) in a group of single-wire draw, on which beam (21) a carriage (23) is arranged to traverse, in connection with which carriage (23) a web cutting blade is fitted, such as a rotary blade or a pin-shaped or knife-shaped cutting blade, characterized in that , above said beam (21), two guide rolls (14a, 14b) for the drying wire (13) are placed, whereof said first roll (14a) is placed in a position in which said drying wire (13) and said web (W), which arrive together from said upper cylinder (10), are separated from each other and said drying wire (13) is guided further on said first guide roll (14a), and that said second guide roll (14b) guides said drying wire (13) back again to meet said web (W), after its open draw (W o ), on said lower cylinder (11), said traversing beam (21) and its cutting blade (25) being placed at the proximity of the free run of the web. A device as claimed in claim 11, characterized in that said second guide roll (14b) is placed at a certain horizontal distance (V o ) and vertical distance (H o ) from said first guide roll (14a), and that said horizontal and vertical distances are of the same order of magnitude as compared with one another and of a magnitude substantially of the same order as the diameters (D o ) of said guide rolls (14a, 14b). A device as claimed in claim 11 or 12, characterized in that said the first guide roll (14a) is placed so that said web (W) runs from said upper cylinder (10) on support of said drying wire (13) onto said first guide roll (14a), whereupon said web (W o ) continues its run, substantially without changing its direction, onto said lower cylinder (11), and that the length of said open draw (W o ) is about 40...80 %, preferably about 50...70 % of the total length of the web draw between said upper cylinder (10) and said lower cylinder (11).

Inventors: AULA JOUKO, LIEDES ALLAN, SAARI AUVO, AULA, JOUKO, LIEDES, ALLAN, SAARI, AUVO
Applicants: VALMET PAPER MACHINERY INC, VALMET PAPER MACHINERY INC.
Application year: 1990
Main classification: D21G9
IPC codes: D21G9, D21F5