METHOD AND DEVICE FOR CROSS-CUTTING OF PULP WEB

Abstract

 The invention relates to a method for the cross-cutting of a pulp web (W) using a cross-cutting device (11), in which method the pulp web is fed to the cross-cutting device at a web speed (V_w) set by means of feeding means (20) driven by drive means (17), a cutting roll (12) equipped with multiple elongated cutting knives (22.1 - 22.3) arranged on a roll shell (14) is rotated at a circumferential speed (V_r) set by means of drive means (13) of the cutting roll, and the pulp web is cross-cut between the cutting roll and a stationary counter knife (15) arranged in connection with it, forming pulp sheets (S) from the pulp web. The pulp web is cross-cut in accordance with the method so that three or more cutting knives are used in the cutting roll, and the cutting roll is rotated at such circumferential speed that its ratio to the web speed of the pulp web is 0.7 - 1.8 times as high, preferably 1.1 - 1.5 times as high. The invention also relates to a corresponding device for the cross-cutting of pulp web.

Description

[0001] The invention relates to a method for the cross-cutting of pulp web using a cross-cutting device, where:

• pulp web is fed to a cross-cutting device at a web speed set by means of feeding means driven by drive means,
• a cutting roll equipped with multiple elongated cutting knives arranged on a roll shell is rotated at a circumferential speed set by means of the drive means of the cutting roll,
• the pulp web is cross-cut between the cutting roll and a stationary counter knife arranged in connection with it, forming pulp sheets from the pulp web.

[0002] The invention also relates to a device for the cross-cutting of pulp web.

[0003] A dried pulp web is cut in connection with a pulp drying machine, and even more specifically after it, by means of a sheet cutter both in the longitudinal direction of the pulp web and also in the cross direction in order to form pulp sheets of a desired size. A full-width pulp web is first cut in the longitudinal direction in order to form sub-webs of a desired width from the web. The cross-directional cutting of the pulp web, in other words of said sub-webs, in other words the actual sheet formation, takes place on a cross-cutting device, to which the formed sub-webs are taken in parallel after the longitudinal cutting.

[0004] In the cross-cutting device, the pulp web is run through it, where it travels between a cutting roll, which belongs to the cross-cutting device, and its counter piece. When the cutting roll of the cross-cutting device revolves around its axis, the cutting roll cuts the pulp web when the cutting knife, which belongs to the cutting roll, coincides with the pulp web, which is against the stationary counter piece of the cross-cutting device. Prior art includes, for example, a cutting roll known by the name Valmet Cross Cutter^™, which includes two cutting knives. Such two-knife cutting roll has represented established technology in pulp cutting machines for at least 40 years.

[0005] The web width of pulp drying machines has increased in recent years, which, in turn, has led to an increased diameter of the cutting roll in order to accomplish sufficient rigidity in the cutting roll. However, the length of the pulp sheet to be cut has remained the same. The result of this is that it has been necessary to increase the circumferential speed of the cutting roll, the diameter of which has grown, in relation to the speed of the pulp web in order to achieve the same sheet dimension.

[0006] The above causes several problems. When the circumferential speed of a revolving cutting roll is considerably higher, sometimes even twice as high as the speed of the pulp web that travels through the cross-cutting device, it causes instability especially in the travel of a cut sheet. The cutting knife of a cutting roll may throw a sheet after its cutting, which causes problems in the travel of the web. A cut pulp sheet should be pulled out of cutting right away so that the travel of the cutting knife would not disturb the travel of the sheet. Moreover, the adjustment of the knife is also essentially complicated, when the diameter of the roll is great.

[0007] The objective of the present invention is to accomplish a method and device for the cross-cutting of a pulp web to improve the runnability of the cross-cutting device and the reliability of production. The characteristic features of the method according to the invention will be more fully understood from claim 1, and the characteristic features of the device according to the invention will be more fully understood from claim 6.

[0008] In the invention, three or more cutting knives are used in a cutting roll against a stationary counter knife, and in addition to this, the cutting roll is rotated at such circumferential speed that the ratio of the circumferential speed to the web speed of the pulp web taken through the cross-cutting device is 0.7 - 1.8 times as high, preferably 1.1 - 1.5 times as high.

[0009] As a result of the invention, when using three or more cutting knives in the cutting roll, the circumferential speed of the cutting knives can be lowered closer to the speed of the pulp web. According to one embodiment, the circumferential speed decreases by 50%. The travel of the web improves with a knife speed that is closer to the web speed. In other words, the invention has a positive impact on the travel of the pulp web and especially of the travel of the sheets formed from it after cross-cutting, which hence improves the runnability of the device and the reliability of production. As a result of the invention, a smaller circumferential speed of the cutting roll makes it possible that the pulp sheets formed have more time to exit after the counter knife, and the cutting knife of the cutting roll does not have time to influence the travel of a pulp sheet in a disturbing manner.

[0010] According to one embodiment, it is possible to use three or more cutting knives in the cutting roll and to use the differential speed setting of the cutting roll and pulp web according to the invention, when the diameter of the cutting roll is greater than the dimension (in its direction of travel) of the pulp sheet to be cut. The device and method according to the invention give the cut sheet time to become released from the cutting knife, in which case it is possible to avoid issues such as the overlapping of the sheets after cutting and resulting blockage problems. The other additional advantages to be achieved with the invention are disclosed in the description of the invention, and the characteristics are disclosed in the claims.

[0011] The invention, which is not restricted to the embodiments presented below, is described in more detail by making reference to the enclosed drawings, in which:

Figure 1

shows the principle of one example of a pulp web cross-cutting device as a layout image viewed from a side, and

Figure 2

shows the principle of one example of a pulp web cross-cutting device as a cross-section of the device, viewed from a side.

[0012] Figure 1 shows one example of a cross-cutting device 11 of pulp web W as a layout image in the machine direction viewed from a side. The device 11 can also be referred to as a sheet cutter of a pulp drying machine, because the cross-cutting device 11 according to Figure 1 can be part of a pulp drying machine. Figure 1 only shows a part of this pulp drying machine, more specifically the push press section 110, cutting section 112 and sheet S layer section 114 of the dryer, listed in the order on the machine.

[0013] A fibre web formed from cellulose pulp by forming and drying on a pulp drying machine arrives at a longitudinal cutting device 122 following the push press 110 as a uniform and full-width pulp web W_FW. On it, it is cut in the direction of travel of the fibre web, in other words in the longitudinal direction, into several separate and parallel pulp webs W for their cross-cutting, in other words for sheet formation. After this, these parallel pulp webs W are cut in the cross direction of the web into pulp sheets using the cross-cutting device 11 according to the invention. The pulp sheets are piled into pulp sheet stacks on a sheet layer section 114, and the sheets are then baled into bales. In accordance with Figure 1, the device 11 according to the invention for the cross-cutting of the pulp web W includes the following main parts: revolving cutting roll 12 and its stationary counter piece 104. The counter piece 104 can be, for example, a counter knife beam equipped with a stationary counter knife 15, or equivalent.

[0014] In the embodiment presented, a roll nip 118, more generally feeding means 20, that precedes the cross-cutting device 11, feeds the pulp web W to the cross-cutting device 11, pushing it there. A drive pulley 120 that follows the cross-cutting device 11, in turn, tensions the pulp web W, which is cut using the cross-cutting device 11, through which the pulp web W is run to be cut into sheets. Moreover, the drive pulley 120 pulls the cut sheets S away from the cross-cutting device 11. More generally, these two, especially the roll nip 118 that precedes the device 11 and the even drive pulley 120, can be referred to as pulp web W feeding means 20, which impact the travel of the pulp web W through the cross-cutting device 11.

[0015] Figure 2 shows the principle of one example of a pulp web W cross-cutting device 11 as a cross-section of the device, in other words viewed from a side. The revolving cutting roll 12, in turn, has a knife arrangement 10 for the cross-cutting of the pulp web W. When the cutting roll 12 revolves around its axis, the cutting knives 22.1 - 22.3 of the knife arrangement 10 coincide in turn with a stationary counter piece 104 on each revolution. In this case, when a cutting knife 22.1 - 22.3 and the counter piece 104 are against each other, the pulp web W that remains between them is cut in the cross direction of the web. The cutting can take place when the cutting knife 22.1 - 22.3 is in contact with the counter piece 104 or when the cutting knife 22.1 - 22.3 is sufficiently close to the counter piece 104 without a contact between these. The correct distance depends on issues such as the properties of the fibre web W to be cut, such as grammage, raw material and running speed.

[0016] The device 11 includes, as mentioned above, a cutting roll 12 equipped with multiple elongated cutting knives 22.1 - 22.3, more generally, with a knife arrangement 10 in the longitudinal direction of the cutting roll 12. The cutting roll 12 includes a body 44 and two ends, from which the cutting roll 12 is supported to the frame 60 of the cutting section 112 of the pulp drying machine by means of bearing housings. The cutting roll 12 includes a roll shell 14 formed around the body 44, in which roll shell 14 a recess 16 has been formed for the knife arrangement 10, in other words now for the cutting knives 22.1 - 22.3. The recess 16 can be a structure cast in the roll shell 14, or it can also be formed by fastening a separate fastenable piece to the roll shell 14. The cutting knives 22.1 - 22.3 are arranged on the roll shell 14 of the cutting roll 12 in these recesses, in other words the cutting knives 22.1 - 22.3 are in the circumferential direction of the cutting roll 12, and the distances of the cutting knives 22.1 - 22.3 from each other are equally long in the circumferential direction of the cutting roll 12. The cutting knife 22.1 - 22.3 can be a part made up of one or more pieces.

[0017] Furthermore, the device 11 also includes a stationary counter knife 15, more generally a counter piece 104, referred to above. The counter knife 15 is arranged in connection with the cutting roll 12 so that the pulp web W is adapted to be cut in the cross direction between the cutting knives 22.1 - 22.3 and the counter knife 15 when the pulp web W is fed between them. The counter knife 15 or, more generally, the counter piece 104, can be, for example, a prior art entity arranged in a stationary, in other words non-moving, manner.

[0018] The transfer means of the pulp web W, more specifically the primary feeding means of the cross-cutting device 11 can be, for example, a roll nip 118 formed by a pair of rolls 26.1, 26.2 and adapted before the cross-cutting device 11. The roll nip 118 is used for feeding the longitudinally-cut pulp web W into the cross-cutting device 11.

[0019] The cutting roll 12 is equipped with drive means 13 in order to rotate the cutting roll 12 at a set circumferential speed V_r. Similarly, the feeding means 20 are equipped with drive means 17 in order to run the pulp web W at a set web speed V_w past the counter knife 15. The drive means 17, 13 include in a manner known per se, for example, electric motors and their gears and transmissions connected, for example, to the roll bodies 44 in order to rotate them around their axis. It is also possible to rotate the roll shell, depending on the position and execution of the roll (in the case of a transfer roll, for example). As an example, only one roll or even both rolls 26.1, 26.2 in the roll nip 118 can be equipped with drives. For the drive means 13, 17, there are also control means 18, 19 adapted to impact the drive means 13, 17 in order to set the circumferential speed V_r of the cutting roll 12 and the web speed V_w of the pulp web W, which web speed is accomplished with the feeding means 20, through the cross-cutting device 11.

[0020] The control means 18, 19 can comprise a computer 21 and necessary control software 23 saved as program code 24 on recording medium 25, frequency converters and sensors in order to establish response for, for example, feedback speed control and for the comparison and setting of the speeds V_r, V_w. For a person having ordinary skill in the art, the technical execution of the drive means 13, 17 and also of the control means 18, 19 is known per se, and their technical execution does not constitute an essential part of the invention here. Machine control automation can be used as a term more generally instead of computer and software. The actual invention is in the way in which these are used in the manner described in more detail below.

[0021] The cutting roll 12 of the device 11, where the cutting roll 12 is adapted to revolve, is equipped with three or more cutting knives 22.1 - 22.3. In the embodiment presented, there are three cutting knives 22.1 - 22.3, but equally as well there could be also more, such as four or even five. In this case, however, the diameter of the roll increases. Of course, if the length of the sheet to be formed is for some reason shorter than conventionally known, there can be more than three cutting knives.

[0022] In the embodiment presented, the cutting roll 12 includes three recesses 16 as shown in Figure 2. The recesses 16 are adapted at an equal distance from each other on the roll shell 14 of the cutting roll 12 for the knife arrangement 10, in other words now for three cutting knives 22.1 - 22.3. In this case, the angle between the recesses 16 and also between the cutting knives 22.1 - 22.3 arranged in them is 120 degrees. Each recess 16 can include a counter surface as presented, for example, in Finnish utility model publication FI12451, comprising fastening elements, such as counter threads, for the locking of each cutting knife 22.1 - 22.3 in each recess 16. In other respects, too, the fastening and adjustment of the cutting knives 22.1 - 22.3 of the knife arrangement 10 of the cutting roll 12 of the device 11 can be as presented, for example, in the above-mentioned Finnish utility model publication FI12451. This accomplishes easier and faster knife adjustment in connection with a cutting roll 12 that comprises three or more cutting knives 22.1 - 22.3.

[0023] In the device 11 according to the invention, the control means 18, 19 are adapted to control the drive means 13, 17 of the cutting roll 12 and feeding means 20 so that the ratio of the circumferential speed V_r of the cutting roll 12 to the web speed V_w of the pulp web W is 0.7 - 1.8 times as high, preferably 1.1 - 1.5 times as high. This is partly enabled by the greater quantity of the cutting knives 22.1 - 22.3 of the cutting roll 12. A smaller circumferential speed of the cutting roll 12 stabilises sheet cutting, and the sheets S behave in a more controlled manner especially after sheet cutting, more specifically after the counter knife 15, because the cutting roll 12 revolves more slowly and the sheets S have more time to descend calmly into a space 27 below the cutting roll 12 to be pulled away. The cross-cut pulp web W, in other words the pulp sheets S, are guided to the pulling means 120' by means of a guide 28 in the space 27. This reduces the possibility of blockages and production interruptions arising. One example of the absolute values of the speeds V_r, V_w can be said to be, for example, a circumferential speed of V_r = 319 m/min of the cutting roll for a web speed of V_w = 220 m/min. In this case, the ratio is hence 1.45. The running range of the web speed V_w can typically be 100 - 300 m/min, for example. The length of the sheet S in its direction of travel can, in turn, be 700 - 950 mm, for example.

[0024] In addition to the cross-cutting device 11, the invention relates equally to a method for the cross-cutting of the pulp web W using the cross-cutting device 11. In the method, the pulp web W is fed using a web speed V_w set in the cross-cutting device 11 by means of feeding means 20 driven by drive means 17. The cutting roll 12 of the cross-cutting device 11, equipped with multiple elongated cutting knives 22.1 - 22.3 arranged on the roll shell 14 of the cutting roll 12, is rotated at a circumferential speed V_r set by means of the drive means 13 of the cutting roll 12. The drive means 13 are impacted by the control means 18, 19 in order to rotate the cutting roll 12 at the set circumferential speed V_r, and the drive means 17 of the feeding means 20 are impacted by the control means 18, 19 in order to feed the pulp web W at the web speed V_w set for cross-cutting. These adjust the speed of the cutting roll 12 and the feeding speed of the pulp web W in the desired manner.

[0025] By feeding the pulp web W into the cross-cutting device 11 and by rotating the cutting roll 12 against the counter knife 15, the pulp web W is cross-cut between the cutting roll 12 and the stationary counter knife 15 arranged in connection with it, forming pulp sheets S from the pulp web W. In accordance with the method, the pulp web W is cross-cut so that three or more cutting knives 22.1 - 22.3 are used in the cutting roll 12. In this way, a single revolution of the roll forms three or more pulp sheets S. Moreover, the cutting roll 12 is rotated at such circumferential speed V_r that its ratio to the web speed V_w of the pulp web W is 0.7 - 1.8 times as high, preferably 1.1 - 1.5 times as high. Here, both speeds V_r, V_w can be adjusted, and both speeds V_r, V_w can be set to speeds that are in the speed ratio range of the method and device 11 according to the invention. Typically, however, the circumferential speed V_r of the cutting roll 12 is calculated and set on the basis of the web speed V_w of the pulp web W. The web speed of the pulp web W is partially determined by the production speed, in other words the running speed, of the pulp drying machine. In this case, it is therefore the drive means 13 of the cutting roll 12 that are controlled by its control means 18 in order to accomplish a set speed ratio according to the invention and hence in order to rotate the cutting roll 12 in the manner according to the invention.

[0026] In accordance with one embodiment of the method, the diameter of the cutting roll 12, with which diameter the pulp web W is cross-cut, is greater than the longitudinal dimension (in its direction of travel) of the pulp sheet S to be cross-cut. One example of the diameter of the cutting roll 12 used in the method and device 11 is 900 - 1400 mm, as an example in the case of the presented cutting roll 12 with three knives.

[0027] Moreover, in accordance with one embodiment of the method and device 11, the pulp web W to be cross-cut is formed before the cross-cutting device 11 from a full-width pulp web W_FW by longitudinal cutting. This takes place on the longitudinal cutting device 122, which is before the feeding means 20, in other words now before the roll nip 118 formed by the pair of rolls 26.1, 26.2.

[0028] Moreover, in accordance with one embodiment of the method and device 11, the pulp web W is fed to the cross-cutting device 11 into connection with its stationary counter knife 15.

[0029] In the method and device 11, the width of the pulp web W to be cross-cut, both in the cross-cutting device 11 and also before it, as a full-width pulp web W_FW can be, for example, 8000 - 12500 mm, more specifically 9500 - 12500 mm.

[0030] The recess 16 that is formed in the cutting roll 12, the counter surface, cutting knife 22.1 - 22.3 and guide strip can have a slightly spiral shape in the longitudinal direction between the ends of the cutting roll 12. In other words, they have a twist, and there is a pitch between the ends. This means that the plane of the guide strip points to a slightly different direction perpendicularly from the surface of the roll shell 14 of the cutting roll 12 at one end of the cutting roll 12 as compared to the other end. Due to the spirality, when the cutting knives 22.1 - 22.3 of the knife arrangement 10 of the cutting roll 12 coincide with the counter piece 104 while the cutting roll 12 is rotating, the cross-cutting of the pulp web W takes place at a slightly different time at the different ends of the cutting roll 12, like scissors cutting.

[0031] The invention relates to a method for the cross-cutting of a pulp web (W) using a cross-cutting device (11), in which method the pulp web is fed to the cross-cutting device at a web speed (V_w) set by means of feeding means (20) driven by drive means (17), a cutting roll (12) equipped with multiple elongated cutting knives (22.1 - 22.3) arranged on a roll shell (14) is rotated at a circumferential speed (V_r) set by means of drive means (13) of the cutting roll, and the pulp web is cross-cut between the cutting roll and a stationary counter knife (15) arranged in connection with it, forming pulp sheets (S) from the pulp web. The pulp web is cross-cut in accordance with the method so that three or more cutting knives are used in the cutting roll, and the cutting roll is rotated at such circumferential speed that its ratio to the web speed of the pulp web is 0.7 - 1.8 times as high, preferably 1.1 - 1.5 times as high. The invention also relates to a corresponding device for the cross-cutting of pulp web.

Claims

1. A method for the cross-cutting of pulp web using a cross-cutting device, where:

- pulp web (W) is fed to a cross-cutting device (11) at a web speed (V_w) set by means of feeding means (20) driven by drive means (17),

- a cutting roll (12) equipped with multiple elongated cutting knives (22.1 - 22.3) arranged on a roll shell (14) is rotated at a circumferential speed (V_r) set by means of drive means (13) of the cutting roll (12),

- the pulp web (W) is cross-cut between the cutting roll (12) and a stationary counter knife (15) arranged in connection with it, forming pulp sheets (S) from the pulp web (W),

characterised in that the pulp web (W) is cross-cut so that

- three or more cutting knives (22.1 - 22.3) are used in the cutting roll (12),

- the cutting roll (12) is rotated at such circumferential speed (V_r) that its ratio to the web speed (V_w) of the pulp web (W) is 0.7 - 1.8 times as high, preferably 1.1 - 1.5 times as high.

2. A method according to claim 1, characterised in that the pulp web (W) is cross-cut by means of a cutting roll (12), the diameter of which is greater than the dimension (in its direction of travel) of the pulp sheet (S) to be cross-cut.

3. A method according to claim 1 or 2, characterised in that the diameter of the cutting roll (12) is 900 - 1400 mm.

4. A method according to any one of the claims 1 - 3, characterised in that the pulp web (W) to be cross-cut is formed before said cross-cutting device (11) by longitudinal cutting from a full-width pulp web (W_FW).

5. A method according to any one of the claims 1 - 4, characterised in that the width of the pulp web (W) to be cross-cut is 8000 - 12500 mm, more specifically 9500 - 12500 mm.

6. A device for the cross-cutting of a pulp web, including:

- a cutting roll (12) equipped with multiple elongated cutting knives (22.1 - 22.3) arranged on a roll shell (14) and rotated at a circumferential speed (V_r) set by means of drive means (13) of the cutting roll (12),

- a stationary counter knife (15) arranged in connection with the cutting roll (12) so that the pulp web (W) is adapted to be cut in the cross direction between the cutting knives (22.1 - 22.3) and the counter knife (15),

- feeding means (20) equipped with drive means (17) in order to run the pulp web (W) at a set web speed (V_w) past the counter knife (15),

- control means (18, 19) adapted to impact said drive means (13, 17) in order to set the circumferential speed (V_r) of the cutting roll (12) and the web speed (V_w) of the pulp web (W), which speed is accomplished with the feeding means (20),

characterised in that

- the cutting roll (12) is equipped with three or more cutting knives (22.1 - 22.3),

- the control means (18, 19) are adapted to control said drive means (13, 17) so that the ratio of the circumferential speed (V_r) of the cutting roll (12) to the web speed (V_w) of the pulp web (W) is 0.7 - 1.8 times as high, preferably 1.1 - 1.5 times as high.

7. A device according to claim 6, characterised in that the pulp web (W) is adapted to be cross-cut by means of the cutting roll (12), the diameter of which is greater than the dimension (in its direction of travel) of the pulp sheet (S) to be cross-cut.

8. A device according to claim 6 or 7, characterised in that the diameter of the cutting roll (12) is 900 - 1400 mm.

9. A device according to any one of the claims 6 - 8, characterised in that the pulp web (W) to be cross-cut is adapted to be formed before said cross-cutting device (11) by longitudinal cutting from a full-width pulp web (W_FW).

10. A device according to any one of the claims 6 - 9, characterised in that the width of the pulp web (W) to be cross-cut is 8000 - 12500 mm, more specifically 9500 - 12500 mm.

Drawing