WO2005005723A1

WO2005005723A1 - A method for guiding an endless belt in a paper/board machine and a device for applying the method

Info

Publication number: WO2005005723A1
Application number: PCT/FI2004/050093
Authority: WO
Inventors: Jani Hakola
Original assignee: Metso Paper, Inc.
Priority date: 2003-07-09
Filing date: 2004-06-15
Publication date: 2005-01-20
Also published as: DE112004001111T5; FI20035124A0; FI114936B

Abstract

The present invention relates to a method for guiding an endless belt (6) in a paper/board machine (1) which comprises a soft-surface roll (2) and at least one guide roll (4) or the like, around which the endless belt (6) is arranged to rotate. To guide the endless belt (6), the endless belt (6) is tensioned evenly over its total width by a force (f1) by exerting equal forces (F1A) and (F1B) on the ends of the guide roll (4). The tensile stress formed on the belt (6) by the tensioning force (f1) generates a counterforce (f2) to the said first force (F1A) and second force (F1B). The movement of the belt (6) shifts the counterforce (f2) and thus inclines the guide roll (4), which brings about an automatic reaction for moving the belt (6) in the axial direction of the rolls (2, 4) and thus maintains the belt (6) essentially in position in the axial direction of the rolls (2, 4). The invention further relates to a device applying the method.

Description

A method for guiding an endless belt in a paper/board machine and a device for applying the method

The present invention relates to a method for guiding an endless belt in a paper/board machine which comprises one or more rolls and at least one guide roll or the like, around which the endless belt is arranged to rotate, and which comprises a backing roll that presses the endless belt against the roll, thus forming a processing zone between the endless belt and the backing roll, through which zone the web material is led.

The present invention further relates to a device applying the method for guiding an endless belt in a paper/board machine which comprises one or more rolls and at least one guide roll or the like, around which the endless belt is arranged to rotate, and which comprises a backing roll by means of which the endless belt can be pressed against the roll, thus forming a nip zone between the endless belt and the backing roll, through which zone the web material may be led.

From the applicant's earlier patent publication FI 110882 is known an arrangement for guiding a belt, where a belt arranged to rotate around two rolls is guided by adjusting the difference in tension between the belt edges. This is accomplished by arranging cylinders tensioning the edges at both ends of the guide roll, and a separate control cylinder at one end, to accomplish a difference in tension between the edges of the belt corresponding to the desired guiding movement. This arrangement requires a complex control system which is difficult to set and unreliable in use.

From patent application no. 971342 is previously known a belt calender, in which an endless belt is led around at least a soft-surface roll forming a second nip and a third so-called guide roll. In the said application are disclosed solutions for lengthening the nip zone by means of a guide roll and for changing the material web heating time by means of a guide roll in a belt calender. The said cited reference makes no comment on the transverse movement of the belt, especially not on guiding it. From patent application no. 931021 is known a belt calender, in which the position of the guide roll with respect to the nip is adjustable, which means that the entering angle of the web material to the nip changes. This in turn affects the distance over which the material web is in contact with the backing roll (the roll to be heated) before the nip. This publication makes no mention of the axial guiding of the belt roll either, but instead discusses adjustments relating to the nip and roll contact of the material web, which are carried out by means of the guide roll.

In the application, a belt refers to a metal belt, a polymer belt and/or their combinations (metal coating on a polymer belt, polymer coating on a metal belt, metal- or fibre-reinforced polymer belt, etc.).

What is problematic about using, for example, a steel belt is its precise tension adjustment around a soft-surface roll and a guide roll, because the elastic strain forming in the steel belt is extremely low compared with, for example, the wires or belts of a paper machine. Due to the low strain, differences in tension are formed in the axial direction of the rolls, and it is not possible to guide the belt by the same methods as the wires and belts of a paper machine. For example, on the edge of the front side belt of a paper/board machine, the tension, that is, tensile stress may be lower than on the backside belt side of the paper/board machine. Because of this, the belt may slide in the axial direction of the roll in the direction in which the belt tension is lower, that is, in the case of the example, in the direction of the front side.

The aim of the present invention is to provide a method, and a device for applying the method, by means of which the disadvantages of the prior art solutions with respect to belt tensioning and guidance are eliminated or substantially reduced.

To achieve the aims of the invention, the method according to the invention is mainly characterised in that in order to guide the endless belt in the axial direction of the rolls, in the endless belt is generated a force that tensions the belt evenly over its total width by exerting a first force by means of first actuators at the first end of the guide roll, and by exerting a second force equalling that exerted on the first end on the second end of the guide roll by means of second actuators, whereby the tensile stress formed on the belt by the tensioning force generates a counterforce to the said first force and second force; and that the movement of the belt in the axial direction of the rolls shifts the counterforce in the axial direction of the rolls and thus inclines the guide roll, which brings about an automatic reaction for moving the belt in the axial direction of the rolls, and thus maintains the belt essentially in position in the axial direction of the rolls.

Furthermore, to achieve the aims of the invention, the device applying the method is mainly characterised in that in order to guide the endless belt in the axial direction of the rolls, at the first end of the endless belt are arranged first actuators for exerting a first force on the first end of the guide roll, and at the second end of the guide roll are arranged second actuators for exerting a second force equalling that exerted on the first end on the second end of the guide roll, by means of which first force and second force can be generated a force that tensions the belt evenly over its total width, whereby the tensile stress formed on the belt by the tensioning force generates a counterforce to the said first force and second force, and that the movement of the belt in the axial direction of the rolls shifts the counterforce in the axial direction of the rolls and thus inclines the guide roll, which brings about an automatic reaction for moving the belt in the axial direction of the rolls, and thus maintains the belt essentially in position in the axial direction of the rolls.

Preferred embodiments of the invention are disclosed in the dependent claims.

The invention is described in greater detail in the following, with reference to the accompanying drawings, in which:

Figure 1 shows a part of a calender as an axonometric view,

Figure 2 shows the calender part of Figure 1 from the front,

Figure 2A shows the calender part of Figure 2 from the side,

Figure 3 shows the calender part of Figure 2 with the belt moved, Figure 4A shows a diagrammatic view of a second embodiment of the invention,

Figure 4B shows a diagrammatic view of a third embodiment of the invention, and

Figure 4C shows a diagrammatic view of a fourth embodiment of the invention.

Figures 1, 2, 2A show an embodiment of the invention for guiding an endless belt 6 in a belt calender 1. Figures 1 and 2 thus show a part of the belt calender 1 with a soft-surface roll 2, the roll mantle of which is coated with, for example, a polymer. This polymer roll 2 is supported by its shaft on bearings arranged in bearing blocks 10 and 11. The polymer roll 2 may have a fixed shaft or the shaft may rotate with the roll mantle. In the vicinity of the polymer roll 2, axially parallel with the polymer roll 2, is arranged a guide roll 4 which is supported at the ends of the shaft on bearing blocks 12 and 13. The roll 4 may conceivably also be realised internally as a roll fitted in bearings in the centre.

An endless belt 6, preferably made of steel, is fitted to travel at least partly around the mantles of the polymer roll 2 and the guide roll 4. The belt 6 rotates at least with the roll mantles of rolls 2 and 4 along a closed loop-like track in its set position in the axial direction of the rolls. The belt 6 track is arranged to travel, for example, by means of additional rolls or guide shoes (not shown) via the guide roll 4 mantle in such a way that the belt 6 is supported on the guide roll 4 mantle over a distance that preferably corresponds to 1/6 - 1/3 of the overall length of the circumference of the mantle. In the embodiment shown, this distance equals about 1/4 of the length of the circumference of the mantle. In addition, at least between the guide roll mantle 4 and the belt 6 surface are formed friction surfaces or another construction by means of which sliding between the mantle and the belt 6 is prevented.

The belt calender 1 also comprises a backing roll 3, which is arranged in nip N forming contact with the polymer roll 2. In this case, the so-called nip zone is formed between the endless belt 6 and the backing roll 3, the backing roll 3 pressing the belt 6 against the roll mantle of the polymer roll 2. The material web 9 is led through the nip zone N for calendering, and forward, for example, through a second nip (not shown) or for further processing.

The part of the belt 6 remaining between rolls 2 and 4 is tensioned by means of the guide roll 4, especially in conjunction with the ends of the guide roll 4, preferably by means of the belt 6 tensioning means 14, 16 and 15, 17 located on the bearing blocks 12 and 13. As a part of the tensioning means are here included identical hydraulic cylinders 14 and 15 located in conjunction with the bearing blocks 12 and 13 at the ends of the guide roll 4, by means of which cylinders are exerted forces on the ends of the guide roll 4. Pneumatic cylinders or other known devices for exerting force may alternatively be used. In addition, the bearing blocks 12 and 13 are supported, for example, by means of slide bearings or linear guides 16 and 17 in such a way that the guide roll 4 will be able to move essentially in the direction of the plane determined by the directions of travel or loads of either one, or both, of the cylinders 14 or 15. The slide bearings or linear guides 16 and 17, therefore, receive forces exerted on the belt 6 roll 4, and other forces exerted on the guide roll 4 and the bearing blocks 12 and 13, which potentially also tend to move the guide roll 4 in the transverse direction with respect to the said plane.

By means of the first cylinder 14, a force F_iA is exerted on the corresponding end of the guide roll 4, whereby the belt 6 tensions due to the effect of the force F_XA against the roll mantle of the guide roll 4. The desired tension is generated by supplying the cylinder 14 with hydraulic pressure adjusted through the decompression valve comprised in the hydraulic circuit 18 of the cylinder 14, and further through the supply line 20, 20a. Correspondingly, by means of the second cylinder 15, a force Fι_B is exerted on the corresponding end of the guide roll 4, whereby the belt 6 tensions due to the effect of the force Fι_B against the roll mantle of the guide roll 4. To the cylinder 15 is supplied hydraulic pressure adjusted through the decompression valve comprised in the hydraulic circuit 18 of the cylinder 15, and further through the supply line 20, 20a. The hydraulic pressure may be adjusted here between about 0-200 bars, but it may deviate from this if necessary. As can be seen in Figures 2 and 3, the cylinders 14 and 15 are connected to the same pressure medium source, whereby the pressure chambers of the cylinders 14 and 15 are in flow communication with one another. Therefore, the forces F_iA and F_IB exerted on both ends of the roll 4 are of essentially the same magnitude. Due to the equal forces, a tensioning force fi distributed evenly over the total width of the belt 6 is exerted on the belt 6. As a result of the tensioning force f_x, tensile stress is formed on the belt 6. The tensile stress generates an essentially opposite counterforce f₂ distributed evenly over the total width of the belt 6 with respect to the tensioning force f_u the said counterforce being exerted on the roll 4. In this case, the belt 6 is in a position of equilibrium with respect to all the above- mentioned forces.

In the foregoing is disclosed a simplified example of setting the forces Fι_A and Fι_B that tension the belt 6. The setting of the tensioning forces F_iA and F_1B may be realised in many ways, for example, by supplying the desired hydraulic pressure to the control cylinders 14 and 15 through a pressure-compensated pump. The forces F_iA and F_iB generated by the above-mentioned tensioning means, and thus the tightness of the belt, remain essentially unchanged in the actual guiding operation of the belt 6.

In addition to these forces, due to structural and functional factors relating to the belt 6 and the guide roll 4, also other forces are in reality exerted on them which the linear guides 16 and 17 receive for their part. Despite this, due to these other forces, an imbalance may be formed in the lateral direction of the belt 6 on the force fi tensioning the belt 6, which will result in a difference in tension between the areas of the edges 6a and 6b. As a result of the difference in tension, the belt 6 for its part tends to move from its set position in the axial direction of the rolls 2 and 4.

Figure 3 shows an example situation where the belt 6 moves in the direction of the longitudinal axis of the guide roll 4 by distance d to the right due to the imbalance caused by the forces exerted on the guide roll 4. Figure 3 shows that also the counterforce f₂ shifts with the belt 6 to the right, closer to the end of the guide roll 4 on which the force F_iA is exerted. Since unchanged forces F_JA and F_1B are exerted on the ends of the guide roll 4, the shifting of the counterforce f₂ brings about a moment in the guide roll 4, as a result of which the guide roll 4 inclines in such a way that the right end rises supported by the linear guides 16 and 17 in the direction of the plane formed by the movement of the cylinders 14 and 15. It should be mentioned here that the distance d and the position of the guide roll 4 when turned are greatly exaggerated in Figure 3 for illustrative purposes. In reality, the distance d is between about 0.1 mm to 1 mm, more often between 0.1 mm to 0.5 mm. This suffices to accomplish the guiding movement described below.

The inclination of the guide roll 4 also changes the direction of travel of the belt 6 between the guide roll 4 and the roll 2. The changed direction of travel is marked by arrow D2 in Figure 3, which is essentially parallel to the tangent of the guide roll 4 mantle at the point where the belt 6 detaches from the guide roll 4 mantle.

The change in the direction of travel, on the other hand, brings about an automatic reaction for moving the belt 6 to the roll 4 in the axial direction. Guided by its changed direction of travel D2, the belt 6 moves in the direction of the longitudinal axis of the roll 4 towards its originally set position. When the belt 6 reaches its set position on the guide roll 4, counterforce f₂ and the inclined end of the roll 4 reach their original positions of equilibrium. In this way, the belt 6 will always be guided in a controlled manner to its correct position and no overdriving, for example, will occur.

Figure 4A shows a second embodiment of the invention. Parts shown in Figure 4A that have the same or a similar function as parts shown in Figures 1 and 2 of the first embodiment are marked with the same reference numerals. Here, the belt 6 is arranged to rotate around the roll 2 and guide roll 4 while the guide roll 4 is in such a position that the web material 9 is in contact with the belt 6 before the nip N formed by the roll 2 and the backing roll 3.

Figure 4B shows a third embodiment of the invention. Here, the guide roll 4 is arranged into a position where the web material 9 is in contact with the belt before the nip N. The backing roll 3 is arranged at a distance from the roll 2, whereby the nip N is formed without support from the roll 2 and the web material 9 is in contact or may be in contact with the belt 6 also after the nip N.

The belt, which is arranged to rotate around two or more rolls, is used also elsewhere in the paper machine than in calenders. For example, in the web material drying section shown diagrammatically in Figure 4C are currently used two belts 6 and 7, between which the web material 9 is fed and between which the web material is dried. It is conceivable for the method and device according to the invention for guiding the belt in the axial direction of the rolls to be applied in such drying sections, where each belt 6 and 7 would rotate around at least two rolls. This arrangement is described diagrammatically in Figure 4C. As guide rolls in these are, for example, the rolls marked with reference numerals 2a and 3a. The method and device according to the invention can also be used in press sections, dryers and coating devices.

Claims

1. A method for guiding an endless belt (6) in a paper or board machine (1) which comprises one or more rolls (2) and at least one guide roll (4) or the like, around which the endless belt (6) is arranged to rotate, and which comprises a backing roll (3) that presses the endless belt (6) against the roll (2), thus forming a processing zone (N) between the endless belt (6) and the backing roll (3), through which zone the web material (9) is led, characterised in that in order to guide the endless belt (6) in the axial direction of the rolls (2, 4), in the endless belt (6) is generated a force (fi) that tensions the belt evenly over its total width by exerting a first force (F_iA) by means of first actuators (14, 16) at the first end of the guide roll (4), and by exerting a second force (F_1B) equalling that exerted on the first end on the second end of the guide roll (4) by means of second actuators (15, 17), whereby the tensile stress formed on the belt (6) by the tensioning force (f_) generates a counterforce (f₂) to the said first force (F_iA) and second force (Fι_B); and that the movement of the belt (6) in the axial direction of the rolls (2, 4) shifts the counterforce (f₂) in the axial direction of the rolls (2, 4) and thus inclines the guide roll (4), which brings about an automatic reaction for moving the belt (6) in the axial direction of the rolls (2, 4) and thus maintains the belt (6) essentially in position in the axial direction of the rolls (2, 4).

2. A method as claimed in claim 1, characterised in that the actuators (14, 16; 15, 17) comprise hydraulic or pneumatic cylinders (14, 15).

3. A method as claimed in claim 1, characterised in that the pressure chambers of the cylinders (14, 15) are connected to the same pressure medium source.

4. A method as claimed in any of the above claims 1 to 3, characterised in that the guide roll (4) is supported by support means (16, 17) comprised in the actuator means (14, 16; 15, 17) in a transverse direction to the plane formed by the direction of load of the first force (Fι_A) and/or the second force (Fι_B).

5. A method as claimed in any of the above claims 1 to 4, characterised in that the belt (6) is arranged to travel with the guide roll (4) mantle over a distance corresponding to about 1/6 to 1/3 of the circumferential length of the guide roll (4) mantle.

6. A method as claimed in any of the above claims, characterised in that the belt is a metal belt or a polymer belt or a metal- or fibre-reinforced polymer belt.

7. A method as claimed in any of the above claims, characterised in that the belt is a polymer-coated metal belt or a metal-coated polymer belt.

8. A device applying the method as claimed in any of the above claims for guiding an endless belt (6) in a paper or board machine (1) which comprises one or more rolls (2) and at least one guide roll (4) or the like, around which the endless belt (6) is arranged to rotate, and which comprises a backing roll (3) by means of which the endless belt (6) may be pressed against the roll (2), thus forming a processing zone (N) between the endless belt (6) and the backing roll (3), through which zone the web material (9) may be led, characterised in that in order to guide the endless belt (6) in the axial direction of the rolls (2, 4), at the first end of the guide roll (4) are arranged first actuators (14, 16) for exerting a first force (F_iA) on the first end of the guide roll (4), and at the other end of the guide roll (4) are arranged second actuators (15, 16) for exerting a second force (Fι_B) equalling the force (F_1A) exerted on the first end on the second end of the guide roll (4), by means of which first force (F_iA) and second force (Fι_B) may be generated a force (fi) that tensions the belt (6) evenly over its total width, whereby the tensile stress formed on the belt by the tensioning force (f_t) generates a counterforce (f₂) to the said first force (F_iA) and second force (F_iB), and that the movement of the belt (6) in the axial direction of the rolls (2, 4) shifts the counterforce (f₂) in the axial direction and thus inclines the guide roll (4), which brings about an automatic reaction for moving the belt (6) in the axial direction of the rolls (2, 4) and thus maintains the belt (6) essentially in position in the axial direction of the rolls (2, 4).

9. A device as claimed in claim 8, characterised in that the actuators (14, 16; 15, 17) comprise hydraulic or pneumatic cylinders (14, 15).

10. A device as claimed in claim 9, characterised in that the pressure chambers of the cylinders (14, 15) are connected to the same pressure medium source.

11. A device as claimed in claim 9 or 10, characterised in that the pressure chambers of the cylinders (14, 15) are in flow communication with one another.

12. A device as claimed in any of the above claims 8 to 11, characterised in that the actuator means (14, 16; 15, 17) comprise support means (15, 17) by which the guide roll (4) may be supported in a transverse direction to the plane formed by the direction of load of the first force (F_ω) and/or the second force (Fι_B).

13. A device as claimed in any of the above claims 8 to 12, characterised in that the belt (6) is arranged to travel with the guide roll (4) mantle over a distance corresponding to about 1/6 to 1/3 of the circumferential length of the guide roll (4) mantle.

14. A device as claimed in any of the claims 8 to 13, characterised in that the belt is a metal belt or a polymer belt or a metal- or fibre-reinforced polymer belt.

15. A device as claimed in any of the claims 8 to 13, characterised in that the belt is a polymer-coated metal belt or a metal-coated polymer belt.

16. A use of the device as claimed in any of the claims 8 to 15 in a belt calender or press section or dryer.