SUSPENSION ARRANGEMENT FOR A PRESS ROLL

Abstract: Suspension arrangement for a press roll (1), which roll is forming a pressure nip (3) with a line load (FL) for a fibre web with at least one other roll (2) and is rotatably mounted in bearings on a suspension arm at a first location (4) of said suspension arm, said suspension arm being mounted in a support structure at a second location (6) of the arm, characterised in that said suspension arm (5) is arranged such that the line (11) passing through the first location (4) and the second location (6) of the suspension arm is essentially perpendicular to the direction (10) of the line load (FL).

Description: SUSPENSION ARRANGEMENT FOR A PRESS ROLL TECHNICAL FIELD The present invention relates to a suspension arrangement for a roll, which roll preferably is used for pressure treatment of web-shaped materials, in particular used in the wet section of a paper-making machine. The suspension arrangement according to the invention is arranged to avoid vibration during operation of the roll. BACKGROUND OF THE DNTvΕNΗON In the pressure treatment of web-shaped materials, e.g. paper or cardboard, there is often used a rotatable roll which bears against another rotatable roll, whereby a pressure is created in the nip between the two rolls. The pressure nip is used for example for dewatering a web material or for pressing two or more layers of a composite web material together. Examples of such arrangements of rolls are calender rolls and roll presses. A roll conventionally comprises an annular roll shell which rotates about a central axis. The roll is normally suspended in a shaft, which extends out of the roll at both ends thereof, by being mounted in bearings on a suspension arm. The suspension arm could thereby be of straight two-armed lever type, the roll shaft being mounted in bearings at a first location of said suspension arm, in connection with a first end of the arm, the suspension arm itself being mounted in bearings in a support structure at a second, intermediate location of the arm and finally a balancing force being applied to the suspension arm at a third location thereof, in connection with a second end of the arm. Typically, the suspension arm is suspended in the support at said second location somewhere between said first and third location along the arm. The purpose of the balancing force which is applied at the third location is to press the roll against an adjacent roll, in order to form a pressure nip. The size of the balancing force which is needed is calculated from the length of the two lever arms in the two-armed lever, the weight of the roll, and the liniear load in the nip. However, a standard design, such as the above, not rarely exhibits problems due to vibrations in the roll during operation, which can lead to quality deficiencies of the web being produced or even premature wear or brake down of the machine. The vibrations can be produced by a variety of reasons, e.g. speed variations of the driving roll or the gear box, a non-round surface of the roll, varying hardness/thickness of the coating of a rubber coated roll, varying liquid content of a "press felt" passing through the nip, varying thickness of the paper web, etc. This implies that the theoretical force balancing system which is used is not a true representation of the actual forces in the system. There have been many suggestions over the years as to how the vibration problems in connection with the operation of rolls could be solved. Most of the suggestions relate to different devices which have the object of damping the vibrations. Such devices are for example shown in US 3 512 475; US 5 730 692; US 4 910 842; US 5 081 759; DE 196 52 769 and EP-Bl-0 268 769. From DE 42 32 920 there is known a method, which appears to have the object of avoiding the formation of vibrations, rather than damping the vibration. However, this latter method does not primarily relate to eliminating vibrations in relation to rolls for producing paper web, which are extremely thin, e.g. 0.1-3 mm. Moreover, this known method does not focus on the suspension of the rolls. SHORT DESCRIPTION OF THE INVENTION By the present invention there is provided a suspension arrangement for paper roll, which suspension arrangement is arranged to avoid or at least minimise generation of vibrations during operation of the roll, which is achieved by a suspension arrangement for a press roll, which roll is forming a pressure nip for a fibre web with at least one other roll and is rotatably mounted in bearings on a suspension arm at a first location of said suspension arm, said suspension arm being mounted in a support structure at a second location of the arm, wherein said suspension arm is arranged that the line passing through said first location and said second location of the suspension arm is essentially perpendicular to the direction of the line load. According to one aspect of the invention the second location is adjustably, fixedly attached to said support structure, in a direction parallel to the direction of the line load. According to another aspect of the invention, said roll is used for pressure treatment of web-shaped materials, for example in the press section of a paper making machine or in a calender. SHORT DESCRIPTION OF THE DRAWINGS The invention will be further described with reference to the drawings, of which: Fig. 1 is showing, from the side, a first roll which is suspended in a suspension arm according to prior art, and a second roll, by which is formed a nip at the contact surface between the two rolls; Fig. 2 is showing the forces acting on the suspension arm; Fig. 3 is showing the forces acting on the press roll; and Fig. 4 is showing, from the side, a first roll which is suspended in a preferred manner in relation to the suspension arm according to the invention, and a second roll, by which is formed a nip at the contact surface between the two rolls. DETAILED DESCRIPTION OF THE INVENTION Detail number 1 in Fig. 1 denotes a prior art first roll, such as e.g. a calender roll, which bears against a second roll 2, whereby a pressure nip 3 is formed. The first roll 1 is mounted in bearings at a first location 4 within a support structure 9 which is mounted adjacent the middle of on a prior art suspension arm 5, which suspension arm 5 is of conventional design. The suspension arm itself is mounted in bearings at a second location 6, i.e. an axis of rotation, which is positioned at a first end of the suspension arm. The suspension arm 5 may thus pivot about said second location in a support structure, e.g. framework, (not shown) in which it is suspended. At a third location 7 on the suspension arm 5, there is applied a force Fc, normally by means of a hydraulic assembly (not shown), which counteracts the force M due to the mass of the first roll 1 and the force F due to the pressure in the pressure nip 3, i.e. F is a counterforce created by the load applied by Fc, which is directed along a line 10, which passes through the nip and the first location 4. In the known system as shown, said second location 6 is arranged at a second end of said suspension arm. Conventionally the system such as shown in Fig. 1 is balanced by applying a force Fc which is calculated according to the equilibrium of forces: F c x B = A (F L + M), (a) where B is the length of the lever arm between the axis of rotation at the second location 6 of the suspension arm 5 and said third location, and A is the length of the lever arm between the axis of rotation at the second location 6 of the suspension arm 5 and said first location. Of course, the roll 1 is normally rotatably mounted in two suspension arms, one at each end of it, why the forces for one suspension arm are strictly half the values of the total forces. When balancing the system according to equation (a) above, there is however often experienced problems with vibrations in the roll 1 during operation, that is during the rotation of the roll 1. It has now surprisingly been found that by performing a more detailed equilibrium of forces and by designing the suspension arm 5 to avoid the influence of certain forces, the system can be balanced to avoid vibration problems. Due to minor deficiencies, e.g. irregularities in the coating of the roll, irregularities in the balancing of the roll itself or speed variations of the driving roll and/or the gear box, variations in the thickness of the web which is treated in the pressure nip 3, i.a. cause a force FT in the nip, which force F T is directed along the tangent of the nip. The force F T has a lever arm which corresponds to half the diameter (i.e. r) of the first roll 1. Taking the force F T into account, the equilibrium of forces, which are shown in Figs. 2 and 3, becomes: → - F T - L H = 0 (1) t L V - M - F L = 0 (2) n M v - FT ' r = 0 (3) → → R R HH ++ LL HH == 00 (4) t Rv - Lv + Fc = 0 (5) n Lv ' A - Fc • B + L H - C = 0 (6) (2) gives F L = L V - M B C (6) gives Lv - Fc — - LH — r A A (1) gives LH = - FT B C FL = Fc — + F τ — - M Definitions: F L and F T are line load and tangential force in the pressure nip, respectively. Fc is the applied force on the system, e.g. by a hydraulic cylinder or the like. RH and Rv are reaction forces in the pivot axle. LH and Lv are reaction forces in the bearing of the roll. My is the torsional moment. M is the force of the weight of the roll. A, B, and C are geometric distances. It is now realised that if F c and M are constant and F T varies, then F must vary too, which results in vibrations. This is especially relevant if there are variations in the speed of the driving roll and/or the gear box, which transmits the rotational force to the roll, since then only forces acting in a tangential direction, F T , will be affected. However, also in connection with irregularities, e.g. of the web, there will merely be an insignificant influence of Fc due to inertial forces, i.e. F T will have the major influence in relation to the cause of vibrations since Fc remains essentially constant. According to the present invention, an embodiment of which is shown in Fig. 4, it is realised that the influence of the force F T can be eliminated or as good as eliminated by minimising or even eliminating its influence on F L , which is achieved by chosing the second location 6 to make C = 0. Accordingly, the suspension arm 5 in Fig. 4 is arranged so that the line passing through the first location and the second location 6 of the suspension arm is perpendicular to the direction 1 Oof the line load F L . When the lever arms for the force F T is zero, the force F L of the pressure nip will be constant too when Fc and F M are constant, whereby vibration is avoided or at least minimised. Thus, the suspension arm 5 according to the invention is designed so that said second location 6, where the arm is mounted in bearings, is moved upwards the distance C in relation to its position in Fig. 1, whereby the lever arm of the force F T becomes zero. In the shown embodiment shown in Fig. 4, the third location 7, i.e. the location of the balancing force Fc, is positioned on the opposite side of the pivot point 6, which allows the suspension arm to be straight, contrary to the one shown in Fig. 1. It is not unusual that rolls are treated in some manner after a while, e.g. re-coated, grinded, etc. Such a treatment will, of course, alter the diameter of the roll. Accordingly, it is a major advantage if the attachment point of the suspension arm, i.e. the second location 6, is adjustable, such that it can be re-adjusted after treatment of the roll in order to re-arrange C = 0. Said adjustability may be achieved in many known ways, e.g. by having a slot in either the frame structure or the suspension arm within which the axis of rotation 6 may be moved for fixation to make the line 11 exactly perpendicular to the line 10. Typically, the design of the suspension arm 5 according to the invention is related to linear loads of about 80 to about 100 kN/m. The length of the lever arms A and B according to the invention are typically 1000 - 2500 mm and 2000 - 5000 mm, respectively. It is understood that the invention is not limited to what is shown above, but may be varied within the scope of the claims. For instance, it is evident that the suspension arm can be positioned in many different ways to the support structure. Moreover it is understood that the adjustability may be provided in directions other than exactly parallel in relation to the line load, e.g. following a curve or a non-parallel line.

Claims: CLAIMS 1. Suspension arrangement for a press roll (1), which roll is forming a pressure nip (3) with a line load (F L ) for a fibre web with at least one other roll (2) and is rotatably mounted in bearings on a suspension arm at a first location (4) of said suspension arm, said suspension arm being mounted in a support structure at a second location (6) of the arm, characterised in that said suspension arm (5) is arranged such that the line (11) passing through the first location (4) and the second location (6) of the suspension arm is essentially perpendicular to the direction (10) of the line load (F L ). 2. Suspension arrangement according to claim 1, characterised in that the angle (α) between said lines (10,11) is between 88 and 92°, preferably between 89 and 91°, and more preferred about 90°. 3. Suspension arrangement according to claim 1 or 2, characterised in that the second location (6) is adjustably fixedly attached to said support structure, in a direction parallel to the direction of the line load (F L ). 4. Suspension arrangement according to claim 2 or 3, characterised in that the suspension arm (5) is substantially straight. 5. Suspension arrangement according to any one of the preceding claims, characterised in that the suspension arrangement of said roll (1) is balanced by a force (F c ) which is substantially constant during operation. 6. Suspension arrangement according to claim 5, characterised in that Fc is applied at a third location (7) and that said second location (6) is arranged between said first and third locations (4, 7) along the suspension arm (5). 7. Suspension arrangement according to any one of the preceding claims, characterised i a linear load of 0.1 kN/m - 500 kN/m, preferably 80-100 kN/m. 8. Suspension arrangement according to any one of the preceding claims, characte r i s e d in that said roll (1) has a diameter of 600 - 2000 mm, preferably 800 - 1500 mm.

Inventors: GUSTAVSSON TORD, GUSTAVSSON, TORD
Applicants: GUSTAVSSON TORD, VALMET KARLSTAD AKTIEBOLAG, GUSTAVSSON, TORD, VALMET-KARLSTAD AKTIEBOLAG
Application year: 2000
Main classification: D21G1
IPC codes: D21F3, D21G1