Suspension arrangement for a roll

Abstract

A vibration-minimizing suspension mechanism for a press roll is provided. The press roll and an opposing roll each having a rotational axis and cooperate to form a press nip for imparting a linear load on a web passing therethrough. The linear load is oriented through the rotational axes of the press and opposing rolls. The suspension mechanism comprises a suspension arm having opposed ends and a medially-disposed pivot, wherein the rotational axis of the press roll is rotatably engaged with one of the opposed ends. The suspension arm is pivotably and adjustably mounted at the pivot to allow the pivot to be adjusted in substantially parallel relation to the linear load. The adjustable pivot thereby allowing a mounting line, defined by the pivot and the rotational axis of the press roll, to be maintained in substantially perpendicular orientation to the linear load to thereby minimize vibration in the press roll.

Description

FIELD OF THE INVENTION

[0002] The present invention relates to paper making machines and, more particularly, to a vibration-minimizing suspension mechanism for a press roll component of a press nip configured to apply a pressure treatment to a fiber web in a wet section and/or a calender of a paper making machine.

BACKGROUND OF THE INVENTION

[0003] 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, smoothing 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.

[0004] A roll conventionally comprises an annular roll shell which rotates about a central axis. The roll is normally suspended on a shaft, the shaft extending out of the roll at both ends thereof and being mounted in bearings on a suspension arm at each end. Such a suspension arm may comprise a straight-armed lever, wherein the roll shaft is mounted in bearings at a first location on said suspension arm, about a first end of the arm. The suspension arm itself may be mounted in bearings on a support structure at a second, intermediate location of the arm. Finally, a balancing force may be applied to the suspension arm at a third location thereof, about a second end of the arm. Typically, the suspension arm is suspended in the support at said second location, between said first and third location, somewhere 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 typically calculated from the length of the two lever arms, the weight of the roll, and the linear load in the nip.

[0005] However, a standard design, such as the above, often 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 break down of the machine. The vibrations are produced for 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 to determine the configuration of the nip is not a true representation of the actual forces in the system.

[0006] There have been many suggestions as to how the vibration problems in connection with the operation of such rolls could be solved. Most of the suggestions relate to different devices which are directed to damping the vibrations. Such devices are for example shown in U.S. Pat. No. 3,512,475; U.S. Pat. No. 5,730,692; U.S. Pat. No. 4,910,842; U.S. Pat. No. 5,081,759; DE 196 52 769 and EP-B1-0 268 769.

[0007] DE 42 32 920 discloses a method directed to avoiding the formation of vibrations, rather than damping the vibrations. However, this method does not primarily relate to eliminating vibrations in relation to rolls for producing a paper web, wherein such paper webs are extremely thin, e.g. 0.1-3.0 mm. Moreover, this method does not focus on the suspension of the rolls.

SUMMARY OF THE INVENTION

[0008] One embodiment of the present invention provides a suspension arrangement for a roll in a paper making machine, wherein the suspension arrangement is arranged to avoid or at least minimize generation of vibrations during operation of the roll. More particularly, a suspension arrangement for a press roll is provided, the roll forming a pressure nip for a fiber web with at least one other roll and being rotatably mounted in bearings on a suspension arm at a first location on said suspension arm, said suspension arm being mounted on a support structure at a second location on the arm, wherein said suspension arm is configured such that a line passing through said first location and said second location of the suspension arm is substantially perpendicular to the direction of the linear load.

[0009] According to one aspect of the invention, the second location of the suspension arm is attached to said support structure in such a manner that the suspension arm is adjustable in a direction parallel to the direction of the linear load.

[0010] According to another aspect of the invention, the 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.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The present invention will be further described with reference to the drawings, which are not necessarily drawn to scale, wherein:

[0012] FIG. 1 is a side view of a first roll suspended on a suspension arm according to a prior art configuration, the first roll and a second roll forming a nip at the contact surface between the two rolls;

[0013] FIG. 2 is a diagram showing the forces acting on a prior art suspension arm;

[0014] FIG. 3 is a diagram showing the forces acting on the press roll mounted on a prior art suspension arm; and

[0015] FIG. 4 is a side view of a first roll suspended on a suspension arm according to one embodiment of the present invention, the first roll and a second roll forming a nip at the contact surface between the two rolls.

DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.

[0017] FIG. 1 shows a prior art first roll 1 such as, e.g. a calender roll, bearing against a second roll 2 to thereby form a pressure nip 3. The first roll 1 is mounted on bearings at a first location 4 within a support structure 9, which is intermediately mounted on a prior art suspension arm 5, which suspension arm 5 is of conventional design. The suspension arm 5 itself is mounted on bearings at a second location 6, e.g. an axis of rotation, which is positioned at a first end of the suspension arm 5. The suspension arm 5 may thus pivot about said second location 6 in a structure, e.g. framework (not shown), in which it is suspended. At a third location 7 on the suspension arm 5, a force FC is applied, such as by a hydraulic assembly (not shown), to counteract the force M due to the mass of the first roll 1 and the force FL due to the pressure in the pressure nip 3 where, e.g. FL is a counterforce created by the load applied by FC, wherein the force FL is directed along a line 10 passing through the nip 3 and the first location 4. In such a prior art system, as shown, the second location 6 is arranged at a second end of the suspension arm 5. Conventionally, the system, such as shown in FIG. 1, is balanced by applying a force FC, which is calculated according to a balancing of forces, where:

F C ×B=A (FL+M),  (a)

[0018] B is the length of the lever arm between the axis of rotation at the second location 6 of the suspension arm 5 and the third location, while A is the length of the lever arm between the axis of rotation at the second location 6 of the suspension arm 5 and the first location. Note that the roll 1 is normally rotatably mounted on two suspension arms, one at each end of the roll 1. As such, it will be appreciated that the illustrated forces shown acting on one suspension arm 5 are shown as such for analysis purposes, wherein the actual magnitude of the forces must be appropriately adjusted to account for the second suspension arm also supporting the roll 1.

[0019] When forces are balanced in the illustrated system, according to equation (a) above, problems with vibrations in the roll 1 are often experienced during operation, that is during the rotation of the roll 1. It has now surprisingly been found that by performing a more detailed equilibrium analysis or balancing of forces, and by designing the suspension arm 5 to avoid the influence of certain forces, the system can be balanced to avoid or minimize vibration and vibration-related problems.

[0020] Due to minor deficiencies such as, 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 treated in the pressure nip 3 may result in a force FT in the nip 3, wherein the force FT is directed along a tangent to the first roll 1. The force FT has a lever arm which corresponds to half the diameter (e.g. the radius) of the first roll 1. Thus, taking the force FT into account, the balancing of forces becomes:

[0021] FIG. 3

→ −FT−LH=0  (1)

↑ LV−M−FL=0  (2)

M V −F T ·r =0  (3)

[0022] FIG. 2

→ RH+LH=0  (4)

↑ RV−LV+FC=0  (5)

L V ·A−F C ·B+L H ·C =0  (6)

[0023] Thus, equation (2) gives FL=LV−M

[0024] and equation (6) gives 1$L_V=F_C\frac{B}{A}-L_H\frac{C}{A}$

[0025] while equation (1) gives LH=−FT

[0026] Thus, 2$\begin{array}{cc}{F}_L=F_C\frac{B}{A}+F_T\frac{C}{A}-M& \left(7\right)\end{array}$

[0027] Definitions:

[0028] FL and FT are a linear load and a tangential force in the pressure nip, respectively.

[0029] FC is the applied force on the system, e.g. by a hydraulic cylinder or the like.

[0030] RH and Rv are reaction forces in the pivot axle.

[0031] LH and Lv are reaction forces in the bearing of the roll.

[0032] MV is the torsional moment.

[0033] M is the force of the weight of the roll.

[0034] A, B, and C are geometric distances.

[0035] It is now realised that if FC and M are constant and FT varies, then FL must also vary, the variances in FT and FL therefore resulting in vibrations. Such variances may be apparent where there are variations in the speed of the driving roll and/or the gear box, which transmits the rotational force to the roll, since only forces acting in a tangential direction FT will be affected. However, though the tangential force FT may vary due to irregularities, e.g. of the web, there will generally be an insignificant influence on FL due to inertial forces, e.g. FT will have the major influence with respect to being the cause of vibrations, since FC remains essentially constant.

[0036] According to the present invention, an embodiment of which is shown in FIG. 4, it is realized that the influence of the force FT on FL can be minimized, or even eliminated in some instances, by choosing the second location 6 so as to make C=0. Accordingly, the suspension arm 5 in FIG. 4 is arranged such that a line 11 passing through the first location 4 and the second location 6 of the suspension arm 5 is perpendicular to the direction 10 of the linear load FL. Accordingly, where C=0, the force FT will have no effect, as shown in equation (7). Thus, the force FL of the pressure nip 3 will be constant when FC and M are constant, thereby avoiding or at least minimizing vibration.

[0037] Thus, the suspension arm 5 according to embodiments of the present invention is configured such that the second location 6, at which the arm 5 is mounted on bearings, is at the same level as the first location 4 such that C=0. Accordingly, as compared to the distance C as shown in FIG. 1, a value of C=0 eliminates the effect of the force FT according to equation (7).

[0038] Further, in the embodiment shown in FIG. 4, the third location 7, e.g. the location of the balancing force FC, is positioned on the opposite side of the pivot point 6, which allows the suspension arm 5 to be straight, in contrast to the prior art suspension arm shown in FIG. 1.

[0039] It is not unusual that rolls, such as those described herein, are treated in some manner, e.g. re-coated, ground, etc., after operation for a certain period. Such treatments will typically alter the diameter of the roll. Accordingly, embodiments of the present invention advantageously comprise an adjustable attachment point 6, i.e. the second location 6, for the suspension arm 5. More particularly, the second location 6 is configured to be adjustable such that, after treatment of the roll 1, the second location 6 may be re-adjusted in order to obtain C=0. This described adjustability of the second location 6 may be achieved in many ways such as, e.g. by providing a slot in either the frame structure or the suspension arm 5 such that the axis of rotation 6 is movable within the slot. The axis of rotation 6 may then be fixed when the line 11 between the first location 4 and the second location 6 is perpendicular to the line 10 indicating the direction of the linear load FL.

[0040] Typically, the design of the suspension arm 5 according to embodiments of the invention is applied to machine configurations having linear loads of between about 0.1 kN/m and about 500 kN/m and, more particularly, between about 80 kN/m and about 100 kN/m, wherein the roll 1 may have a diameter of between about 600 mm and about 2000 mm and, more particularly, between about 800 mm and about 1500 mm. Accordingly, the length of the lever arms A and B according to such embodiments of the invention are typically between about 1000 mm and about 2500 mm and between about 2000 mm and 5000 mm, respectively.

[0041] Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. For instance, the suspension arm may be positioned in many different ways with respect to the support structure. Moreover, the pivot point 6 may be adjustable in directions other than parallel with respect to the linear load such as, e.g. following a curve or a non-parallel line. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

1. A method of minimizing vibration in a press roll forming a press nip only with an opposing roll, each of the rolls having a rotational axis, said method comprising: applying a force to one end of a suspension arm having a medially-disposed pivot and the press roll operably engaged with the other end thereof, the force being configured to act about the pivot so as to cause the suspension arm to impart a linear load through the press roll onto a fiber web passing through the press nip, the linear load being oriented through the rotational axes of the press roll and the opposing roll; and adjusting the pivot in substantially parallel relation to the linear load such that a mounting line defined by the pivot and the rotational axis of the press roll is maintained in substantially perpendicular relation to the linear load to thereby minimize vibration in the press roll.

2. A method according to claim 1 wherein applying a force further comprises applying a force so as to cause the suspension arm to impart a linear load of between about 0.1 kN/m and about 500 kN/m through the press roll onto the fiber web.

3. A method according to claim 1 wherein applying a force further comprises applying a force so as to cause the suspension arm to impart a linear load of between about 80 kN/m and about 100 kN/m through the press roll onto the fiber web.

4. A method according to claim 1 wherein adjusting the pivot further comprises adjusting the pivot such that the mounting line is disposed at an angle of between about eighty-eight degrees and about ninety-two degrees with respect to the linear load.

5. A method according to claim 1 wherein adjusting the pivot further comprises adjusting the pivot such that the mounting line is disposed at an angle of between about eighty-nine degrees and about ninety-one degrees with respect to the linear load.

6. A method according to claim 1 wherein adjusting the pivot further comprises adjusting the pivot such that the mounting line is disposed at an angle of about ninety degrees with respect to the linear load.