Method for preventing vibration of a calender and a calender with an arrangement for preventing vibration

Abstract

 The present invention relates to a method for preventing vibration of a calender comprising at least one fly roll (15) and a calender roll stack with at least three calender rolls (12, 13, 14) forming at least two calendering nips (N), in which method position (P) of the at least one fly roll (15) is adjusted relative to the calender roll stack to prevent fiber web induced nip vibration, or barring. The position (P) of the at least one fly roll (15) is calculated based on frequency of nip vibration, length (L) of travel distance of a fiber web (W) from one calendering nip (N) to the next calendering nip (N) and running speed of the calender (10). The position (P) of the at least one fly roll (15) is defined by a control device (20) automatically on basis of measurements of vibration and/or noise and/or fiber web caliber to prevent the nip vibration, or barring, and the position of the at least one fly roll (15) is defined in 0,5 s - 5 min. The invention also relates to a calender with an arrangement for preventing vibration, which calender comprises a calender roll stack with at least three calender rolls (12, 13, 14) forming at least two calendering nips (N) and at least one fly roll (15) position-adjustable relative to the calender roll stack to prevent fiber web induced nip vibration, or barring. The arrangement for preventing vibration comprises a sensor (21) for measuring vibration in the calender (10) and/or a sensor (24) for measuring noise at the calender (10) and/or a measurement device (23) for measuring caliber of the fiber web (W) and a control device (20) that based on the measurement information calculates the position (P) for the at least one fly roll (15) to prevent the barring and the position (P) of the at least one fly roll (15) is defined in 0,5 s - 5 min by the control de-vice.

Description

[0001] The invention relates to a method for preventing vibration of a calender. The invention also relates to a calender with an arrangement preventing vibration. Particularly the invention relates to a method according to the preamble of claim 1 and to a calender according to the preamble of claim 7.

[0002] In fiber web machines the fiber web is produced and treated in an assembly formed by a number of apparatuses arranged consecutively in a process line. A typical production and treatment line comprises a head box, a wire section and a press section as well as a subsequent drying section and a reel-up. The production and treatment line can further comprise other devices and sections for finishing the fiber web, for example, a sizer, a calender, a coating section. The production and treatment line also comprises at least one winder for forming customer rolls as well as a roll packaging apparatus. In this description and the following claims by fiber webs are meant for example a paper, board, tissue webs. In each section and device vibrations may occur in several different components. For example vibrations may occur in a nip, which is formed in between two elements, typically between two rolls but also the nip can be formed with a roll, a belt, a shoe or corresponding element and a counter-element of corresponding or different kind, often at least one of the nip forming elements is a roll. In the nip the fiber web is pressed in order to remove water from the web or to effect to the properties of the web and by the deflection compensated roll the nip pressure is controlled in cross-direction or the fiber web i.e. in the longitudinal direction of the roll.

[0003] Calendering is generally carried out in order to improve the properties, like smoothness and gloss, of a fiber web, such as a paper or board web. In calendering the web is passed into a nip, i.e. calendering nip, formed between rolls that are pressed against each other, in which nip the web becomes deformed as by the action of temperature, moisture and nip pressure. In the calender the nips are formed between two rolls, typically between a smooth-surfaced press roll such as metal roll and a roll coated with resilient material such as a polymer roll. The resilient-surfaced roll adjusts itself to the forms of the web surface and presses the opposite side of the web evenly against the smooth-surfaced press roll. Multinip, or multiroll calendering is calendering in a calendering unit, in which the nips are formed between a smooth-surfaced press roll such as metal roll and a roll coated with resilient material such as a polymer roll and the linear load increases in multinip calenders from the upper nip to the lower nip due to gravitation, unless roll relief systems are used. From prior art multiroll calenders are known, in which the set of rolls of which is formed of two stacks of rolls, each stack of rolls comprising at least two calender rolls. Multinip or multiroll calenders are known in which the fiber web to be calendered is passed through nips formed by a deflection-compensated upper roll and a deflection-compensated lower roll, and by two or more intermediate rolls arranged between the upper and lower roll. The rolls are arranged as a vertical or inclined stack of rolls.

[0004] One type of nip vibration that occurs in calenders is barring, which may cause wear of roll covers, limit running speed of the calender and cause noise disturbance. It is known from prior art, for example US patent publication 6892631 (EP 1275777) and US patent publication 6902691 (EP 1275775) and US patent publication 6851356 (EP 1275776) to eliminate or minimize barring by displacing at least one of the calender rolls relative to the press plane formed by the rolls of the calender roll stack. In the US patent publications it is also disclosed that it is known to arrange a fly roll at alternating distances from the roll stack such that its position can be changed relative to the roll stack to prevent barring.

[0005] In DE patent application publication 102003030684 is disclosed a calender, comprising at least three calender rolls, of which rolls at least one is displaceable such that its center line is off the line passing via the axis of the other rolls. There are also fly rolls arranged in connection with the calender, by which fly rolls the fiber web is transferred from one calendering nip to the next calendering nip. The fly rolls comprise an adjustment possibility for moving their position to control the travel of the fiber web.

[0006] Applicant has found out in practice that the arrangement, in which the fly roll is arranged movable so, that its position in view of the calender roll stack is adjustable, to alternating distances from the calender roll stack, is an effective manner to prevent fiber web induced nip vibration i.e. barring in a multiroll calender. The arrangements known from practice are manually controlled.

[0007] The fiber web induced nip vibrations i.e. barring can arise rapidly to a harmful level and thus the manual control has been in some cases too slow to prevent the barring. It is also known that in some countries there are strict rules limiting the use of control of for example a calender by operating personnel without a permission from a supervisor and thus the time for getting the permission might take too long before the operator can make the needed barring preventing adjustment of the fly roll position.

[0008] An object of the present invention is to provide a method for preventing vibration of a calender and a calender with an arrangement for preventing vibration in which the disadvantages of prior art are eliminated or at least minimized.

[0009] In order to achieve the above objects and those that will be disclosed later the method according to the invention is mainly characterized by the features of claim 1 and the calender with an arrangement for preventing vibration is mainly characterized by the features of claim 7.

[0010] Advantageous aspects and features are presented in dependent claims.

[0011] According to the invention in the method for preventing vibration of a calender comprising at least one fly roll and a calender roll stack with at least three calender rolls forming at least two calendering nips, position of the at least one fly roll is adjusted relative to the calender roll stack to prevent fiber web induced nip vibration, or barring. The position of the at least one fly roll is calculated based on frequency of nip vibration, length of travel distance of a fiber web from one calendering nip to the next calendering nip and running speed of the calender. The position of the fly roll is defined automatically on basis of vibration, noise or fiber web caliber. The position of the fly roll to prevent barring is defined in 0,5 s - 5 min.

[0012] According to the invention the calender with an arrangement for preventing vibration, which calender comprises a calender roll stack with at least three calender rolls forming at least two calendering nips and at least one fly roll position-adjustable relative to the calender roll stack to prevent fiber web induced nip vibration, or barring. The arrangement for preventing vibration comprises a sensor for measuring vibration in the calender and/or a sensor for measuring noise at the calender and/or a measurement device for measuring caliber of the fiber web and a control device that based on the measurement information calculates the position for the at least one fly roll to prevent the barring and that the position of the at least one fly roll is defined in 0,5 s - 5 min by the control device.

[0013] According to an advantageous feature of the invention nip vibration in the calender or noise at the calender or caliber of the fiber web is measured continuously and based on the measurement information the position for the at least one fly roll is calculated and adjusted to prevent barring.

[0014] The position of the at least one fly roll in relation to the calender roll stack is adjustable in position area of 2 mm - 200 mm, advantageously 2 mm - 50 mm.

[0015] By the invention the fly roll position for preventing barring is defined and adjusted fast enough even in cases where the barring evolves rapidly. Furthermore usability is improved both in new installation calenders and in calenders already in used as the invention can be installed into already existing calenders, in which the position adjustment of a fly roll is used for preventing barring.

[0016] As the barring is prevented profile of the fiber web in the MD (machine direction) is improved and thus runnability problems in following operations, such as in slitting-winding or in printing, are decreased.

[0017] The invention is in particular utilizable in calenders where the operations of the calender are mainly manually controlled.

[0018] The invention is utilizable in connection of production of all grades of fiber webs.

[0019] Paper and board are available in a wide variety of grades and can be divided according to basis weight in two categories: papers with a single ply and a basis weight of 25 - 300 g/ m² and boards manufactured in multi-ply technology and having a basis weight of 150 - 600 g/ m². It should be noted that the borderline between paper and board is flexible since board grades with lightest basis weights are lighter than the heaviest paper grades. Generally speaking, paper is used for printing and board for packaging. The subsequent descriptions are examples of some values presently applied for fibrous webs, and there may be considerable variations from the disclosed values.

[0020] Mechanical-pulp based, i.e. wood-containing printing papers include newsprint, uncoated magazine and coated magazine paper.

[0021] Newsprint is composed either completely of mechanical pulp or may contain some bleached softwood pulp (0 - 15 %) and/or recycled fiber to replace some of the mechanical pulp. General values for newsprint can be regarded as follows: basis weight 40 - 48,8 g/m², ash content (SCAN-P 5:63) 0 - 20 %, PPS s10 roughness (SCAN-P 76:95) 3,0 - 4,5 µm, Bendtsen roughness (SCAN-P 21:67) 100 - 200 ml/min, density 200 - 750 kg/m³, brightness (ISO 2470:1999) 57 - 63 %, and opacity (ISO 2470:1998) 90 - 96 %.

[0022] Uncoated magazine paper (SC=supercalendered) usually contains mechanical pulp to 50 - 70 %, bleached softwood pulp to 10 - 25 %, and fillers to 15 - 30%. Typical values for calendered SC paper (containing e.g. SC-C, SC-B. SC-A/A+) include basis weight 40 - 60 g/m², ash content (SCAN-P 5:63) 0 - 35 %, Hunter gloss (ISO/DIS 8254/1) < 20 - 50 %, PPS s10 roughness (SCAN-P 76:95) 1,2 - 2,5 µm, Bendtsen roughness (SCAN-P 21:67) 100 - 200 ml/min, density 700 - 1250 kg/m3, brightness (ISO 2470:1999) 62 - 70 %, and opacity (ISO 2470:1998) 90 - 95 %.

[0023] Coated magazine paper (LWC = lightweight coated) contains mechanical pulp to 40 - 60 %, bleached softwood pulp to 25 - 40 %, and fillers and coaters to 20 - 35 %. General values for LWC paper can be regarded as follows: basis weight 40 - 70 g/m², Hunter gloss 50 - 65 %, PPS s10 roughness 0,8 - 1,5 µm (offset), 0,6 - 1,0 µm (roto), density 1100 - 1250 kg/m³, brightness 70 - 75 %, and opacity 89 - 94 %.

[0024] General values for MFC (machine finished coated) can be regarded as follows: basis weight 50 - 70 g/m², Hunter gloss 25 - 70 %, PPS s10 roughness 2,2 - 2,8 µm, density 900 - 950 kg/m³, brightness 70 - 75 %, and opacity 91 - 95 %.

[0025] General values for FCO (film coated offset) can be regarded as follows: basis weight 40 - 70 g/m², Hunter gloss 45 - 55 %, PPS s10 roughness 1,5 - 2,0 µm, density 1000 - 1050 kg/m³, brightness 70 - 75 %, and opacity 91 - 95 %.

[0026] General values for MWC (medium weight coated) can be regarded as follows: basis weight 70 - 90 g/m², Hunter gloss 65 - 75 %, PPS s10 roughness 0,6 - 1,0 µm, density 1150 - 1250 kg/m³, brightness 70 - 75 %, and opacity 89 - 94 %.

[0027] HWC (heavy weight coated) has a basis weight of 100 - 135 g/m² and can be coated even more than twice.

[0028] Pulp-produced, wood free printing papers or fine papers include uncoated - and coated - pulp-based printing papers, in which the portion of mechanical pulp is less than 10 %.

[0029] Uncoated printing papers (WFU) contain bleached birch wood pulp to 55 - 80 %, bleached softwood pulp 0 - 30 %, and fillers to 10 - 30 %. The values with WFU have a large variation: basis weight 50 - 90 g/m², Bendtsen roughness 250 - 400 ml/min, brightness 86 - 92 %, and opacity 83 - 98 %.

[0030] In coated printing papers (WFC), the amounts of coating vary widely in accordance with requirements and intended application. the following are typical values for once- and twice-coated, pulp-based printing paper: once-coated basis weight 90 g/m2, Hunter gloss 65 - 80 %, PPS s10 roughness 0,75 - 2,2 µm, brightness 80 - 88 %, and opacity 91 - 94 %, and twice-coated basis weight 130 g/m², Hunter gloss 70 - 80 %, PPS s10 roughness 0,65 - 0,95 µm, brightness 83 - 90 %, and opacity 95 - 97 %.

[0031] Release papers have a basis weight within the range of 25 - 150 g/m².

[0032] Other papers include e.g. sackkraft papers and wallpaper bases.

[0033] Board making makes use of chemical pulp, mechanical pulp and/or recycled pulp. Boards can be divided e.g. in the following main groups cartonboards, containerboards and specialty boards. Cartonboards are mainly used for consumer product packaging and they comprise boxboards, used for making boxes, cases, which boxboards include e.g. liquid packaging boards; FBB = folding boxboard, WLC = white-lined chipboard, SBS = solid bleached sulfate board, SUS = solid unbleached sulfate board and LPB = liquid packaging board. Containerboards comprise f. ex. linerboard and fluting board and other corrugated boards and specialty boards comprise wallpaper base, plaster board etc. Graphic boards are used for making e.g. cards, files, folders, cases, covers, etc. and wallpaper bases. Each end use sets its own demands on the mechanical and functional properties of boards. Basically a certain mechanical strength and stiffness, especially bending stiffness is required, and in the optimum structure middle-ply is very bulky, and top and back plies have high modulus of elasticity. Often also purity and cleanliness requirements are very high and also almost all boards have defined printing properties and for example the printing requirements of folding box board are usually very high and also high bulkiness is required of folding box board.

[0034] The calender and the method according to the invention can be utilized in an online-calender or as an offline-calender.

[0035] In the following the invention is described with reference to the accompanying drawing in which

[0036] in figure 1 is schematically shown an example of a calender with a calender control arrangement according to an advantageous example of the invention.

[0037] Figure 1 schematically show an example of multiroll calender 10 with a stack of calender rolls 12, 13, 14, in which a fiber web W is calendered in the calendering nips N between the calender rolls 14, 13; 13,12; 12,13. By reference numerals 13 a calender roll that is a resilient-surfaced calender roll is indicated and by reference numeral 12 a calender roll that is a smooth-surfaced calender roll, for example a thermo roll, is indicated. The upper roll 14 of the calender roll stack is a deflection compensated roll. Resilient-surfaced calender rolls 13 are soft-surfaced, for example polymer-surfaced deflection, rolls and smooth-surfaced rolls 12 are metal rolls, or thermo rolls either heatable and/or coolable thermo rolls. Fly rolls guiding the fiber W web in the calender 10 are indicated by reference numeral 15 and a guide roll 16 guides the fiber web W from the calender 10 to further operations.

[0038] For preventing vibration of the calender 10 position P of the at least one fly roll 15 is adjusted relative to the calender roll stack to prevent fiber web W induced nip vibration, or barring. The position P of the at least one fly roll 15 is calculated based on frequency of nip vibration, length L of travel distance of a fiber web W from one calendering nip N to the next calendering nip N and running speed of the calender 10. The position P of the at least one fly roll 15 is defined by a control device 20 automatically on basis of measurements of vibration and/or noise and/or fiber web caliber to prevent the nip vibration, or barring, and that the position of the at least one fly roll 15 is defined in 0,5 s - 5 min. In connection with the calender 10 is provided a sensor 21 for measuring frequency of nip vibration and/or a device 23 for measuring the caliber of the fiber web W and/or a noise sensor 24 for measuring noise at the calender 10. Measurements from the sensors 21, 24 and from the measurement device 23 are transmitted to a calculating and control device 20. The control device 20 may also receive information and/or measurement results from other part/-s 22 of the fiber web machine. By the control device 20 the position of the at least one position adjustable fly roll 15 is defined automatically on basis of vibration and/or noise and/or fiber web caliber. The position of the at least one position adjustable fly roll 15 to prevent barring is defined in 0,5 s - 5 min. The position P of the at least one position adjustable fly roll 15 in relation to the calender roll stack is adjustable in position distance of 2 mm - 200 mm, advantageously 2 mm - 50 mm.

Claims

1. Method for preventing vibration of a calender comprising at least one fly roll (15) and a calender roll stack with at least three calender rolls (12, 13, 14) forming at least two calendering nips (N), in which method position (P) of the at least one fly roll (15) is adjusted relative to the calender roll stack to prevent fiber web induced nip vibration, or barring, characterized in that the position (P) of the at least one fly roll (15) is calculated based on frequency of nip vibration, length (L) of travel distance of a fiber web (W) from one calendering nip (N) to the next calendering nip (N) and running speed of the calender (10), that the position (P) of the at least one fly roll (15) is defined by a control device (20) automatically on basis of measurements of vibration and/or noise and/or fiber web caliber to prevent the nip vibration, or barring, and that the position of the at least one fly roll (15) is defined in 0,5 s - 5 min.

2. Method according to claim 1, characterized in that nip vibration in the calender (10) is measured by a sensor (21) and/or noise at the calender by a sensor (24) and/or caliber of the fiber web (W) by a measurement device (23) is measured continuously and based on the measurement information the position for the at least one fly roll is calculated by the control device (20) and adjusted to prevent the barring.

3. Method according to claim 1, characterized in that the control device (20) receives information and/or measurement results from other part/-s 22 of the fiber web machine for calculating the position of the at least one fly roll (15) to prevent the barring.

4. Method according to claim 1, characterized in that the position of the at least one fly roll (15) in relation to the calender roll stack is adjustable in position area of 2 mm - 200 mm, advantageously 2 mm - 50 mm.

5. Method according to any of claims 1 - 4, characterized in that the method is utilized in new installation calenders and in modernized calenders.

6. Method according to any of claims 1 - 4, characterized in that the method is utilized in online-calenders and in offline-calenders.

7. Calender with an arrangement for preventing vibration, which calender comprises a calender roll stack with at least three calender rolls (12, 13, 14) forming at least two calendering nips (N) and at least one fly roll (15) position-adjustable relative to the calender roll stack to prevent fiber web induced nip vibration, or barring, characterized in that the arrangement for preventing vibration comprises a sensor (21) for measuring vibration in the calender (10) and/or a sensor (24) for measuring noise at the calender (10) and/or a measurement device (23) for measuring caliber of the fiber web (W) and a control device (20) that based on the measurement information calculates the position (P) for the at least one fly roll (15) to prevent the barring and that the position (P) of the at least one fly roll (15) is defined in 0,5 s - 5 min by the control device.

Drawing