WO2008099053A1

WO2008099053A1 - Calender

Info

Publication number: WO2008099053A1
Application number: PCT/FI2008/050002
Authority: WO
Inventors: Juha Kuismin; Hannu Pullinen
Original assignee: Metso Paper, Inc.
Priority date: 2007-01-11
Filing date: 2008-01-08
Publication date: 2008-08-21
Also published as: AT506853B1; AT506853A3; FI20075010A0; FI119066B; AT506853A2; DE112008000058T5

Abstract

A calender includes at least one stack of rolls in which there are a lower (25B) and an upper roll (21B) and at least one intermediate roll (22B-24B) the bearing cups of which are supported on the driving and tending side to a pivoting arm (32B-34B) and which pivoting arm (32B-34B) is further supported to a relief cylinder (42B-44B). It is characteristic of the calender that each relief cylinder (42B-44B) is provided with a pQ valve (A) and a linear sensor (B).

Description

Calender

FIELD OF INVENTION

The invention relates to a method according to the preamble of claim 1

The invention also relates to a calender according to the pieamble of claim 2

PRIOR ART

Calendering is generally carried out in order to improve the properties, such as smoothness and gloss, of a web-like material, such as a paper or board web In calendering, the web is passed into a nip, i e a calendering nip, formed between rolls being pressed against each other, in which nip the web becomes deformed from the effect of temperature, moisture and nip pressure In a calender, nips are formed between a smooth-surfaced press roll, such as a metal roll, and a roll cov- eied with flexible cover, such as a polymer roll The ioll with a flexible surface accommodates to the shapes of the web surface and evenly presses the opposite side of the web against the smooth-surfaced press roll Here, calender rolls refer to rolls forming a calendering nip, an upper roll refers to the uppermost roll of a stack of rolls, a lower roll refers to the undermost roll of a stack of rolls, and an intermediate roll refers to one or moie rolls between the upper roll and the lower i oil An upper nip refers to the uppermost calendering nip which is formed be- tv\ een the upper roll and the calender roll below the upper roll, a lower nip refers to the undermost calendering nip of the stack of rolls which is formed between the lower roll and the calender roll above the lower roll, and intermediate nips refer to the calendering nips formed by means of the intermediate rolls between the upper nip and the lower nip of the calender Finnish patent specification 96334 discloses a method for calendering paper or equivalent web material in a calender. In the method, the web material 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 rolls. The rolls are arranged as a substantially vertical stack of rolls. Such rolls in which the form of the natural deflection line produced by their dead weight is substantially equal are used as intermediate rolls. The nip load produced by the masses of the intermediate rolls and the auxiliary devices related to them is substantially completely relieved in the method, and an adjustable load is applied to the calendering nips by means of the deflection- compensated upper or lower roll and/or by means of an external load applying to the upper or lower roll.

Typically, compression is provided in a multi-roll calender by fastening the upper or lower roll of the stack of rolls in place and by pressing the stack of rolls against the roll fastened in place. Alternatively, it is possible to press both the upper and the lower roll towards each other either so that none of the intermediate rolls is fixedly locked in place or so that at least one of the intermediate rolls is fixedly locked in place. It is possible to compensate for the deflections of the rolls by means of deflection-compensating devices located in the upper and lower rolls so that the roll nips acquire a linear form.

The relief of moving intermediate rolls is performed in prior-art arrangements by means of so-called UNIX computing. UNIX computing is based on mechanics in which the roll and parts connected to it, such as bearing cups, support arms and relief cylinders, are modelled into a moving mass system. It is fairly complicated computing which requires its own HP workstation and a person highly specialised in intermediate roll computing. SUMMARY OF INVENTION

In the arrangement according to the invention, UNIX computing is replaced by automatic weighing. Automatic weighing is accomplished by providing the relief cylinder of each intermediate roll on both the tending and driving side with a pQ valve and a linear sensor. Each intermediate roll is slowly lifted programmatically starting from the uppermost intermediate roll with the Q command of the valve and observing the reading of the linear sensor to the normal operating position. Close to the operating position, pressure values are read during movement directing upwards and downwards, and the average of the readings is used as relief pressure in which possible excess and under reliefs are added.

The principal characteristic features of the method according to the invention are presented in the characterising part of claim 1.

The principal characteristic features of the calender according to the invention are presented in the characterising part of claim 2.

Automatic weighing considers changes in the masses of intermediate rolls occurring after commissioning, which can be caused e.g. from the fact that the client decommissions a doctor blade connected to an intermediate roll after many years.

In automatic weighing, it is possible to take the creeping of relief pressure sensors into account. Furthermore, the mass difference of the driving and tending side can be automatically compensated which in prior-art arrangements required manual adjustment.

Automatic weighing takes into consideration frictions related to the support systems of the intermediate roll and automatic weighing can be used as assistance in fault diagnostics. Automatic weighing also considers the change of the centre of mass caused by an offset device. Today, this is not taken into account in prior-art arrangements.

The arrangement according to the invention can be utilised in all multi-roll calenders which include at least one intermediate roll. The multi-roll calender can consist of one set of rolls or many sets of rolls in which the rolls form a stack of rolls. The stack of rolls can be vertical or it can form an angle with the vertical plane.

BRIEF DESCRIPTION OF FIGURES

Fig. 1 shows a multi-roll calender formed of two sets of rolls in which the arrangement according to the invention can be utilised.

Fig. 2 shows the second set of rolls of the multi-roll calender shown in Fig. 1 and support systems related to the rolls.

Fig. 3 shows a section of a fastening arrangement of an intermediate roll.

DESCRIPTION OF ADVANTAGEOUS EMBODIMENTS

Fig. 1 shows a multi-roll calender in which the arrangement according to the invention can be utilised. The multi-roll calender comprises two sets of rolls 2OA, 2OB in the nips between the calender rolls of which sets of rolls a fibrous web W is calendered. The rolls of a first set of rolls 2OA are designated from above with reference numbers 21 A-25A and the rolls of a second set of rolls 2OB with references 21B-25B. An uppermost and undermost roll 2 IA, 25 A; 2 IB, 25B of both sets of rolls 2OA, 20B are polymer-surfaced deflection-compensated sym rolls. An uppermost and undermost intermediate roll 22A, 24A; 22B, 24B of both sets of rolls 2OA, 20B are, again, steel rolls, either heatable and/or coolable rolls, and middle rolls 23A, 23B are polymer-surfaced rolls. Fig 2 shows the second set of rolls 2OB of the multi-roll calender shown in Fig 1 and support systems related to the rolls The lower roll 25B of the set of rolls 2OB is supported at its bearing cups on both the driving and tending side to a cylinder device 50 and the upper roll 21 B is fixedly supported to the calender frame The intermediate rolls 22B-24B are supported to the calender frame by pivoting arms 32B, 33B, 34B and the pivoting arms are moved around pivot points by relief cylinder devices 42B, 43B, 44B

Each relief cylinder device 42B, 43B, 44B is provided with a pQ valve A and a linear sensor B which are connected to a control unit 100 The intermediate rolls are slowly lifted programmatically starting from the uppermost intermediate roll 22B with the Q command of the pQ valve A and observing the reading of the linear sensor B to the normal operating position Close to the operating position, pressure values are read during movement directing upwards and downwards, and the average of the readings is used as relief pressure in which possible excess and under reliefs are added

As the upper 21 B and lower roll 25B of the set of rolls 20B can be used rolls with a movable shell, whereby the intermediate rolls 22B-24B can be floated between the upper 2 IB and lower roll 25B The nips of the set of rolls 2OB are closed by lifting the lowei roll 25B by the cylinder device 50 upwards, aftei which the nips aie loaded by the shells of the upper 21 B and lower roll 25B

Fig 3 shows a section of a fastening arrangement of an intermediate roll A shaft 22C of the intermediate roll 22B is in a bearing cup 22D which is supported by a pn oting arm 32B The pivoting arm 32B is fastened in the frame R by means of a bolt 32C at the pivot point The relief cylinder is fastened to the pivoting arm 32B at a point 32D The mox ement of the relief cylinder is perpendicular against the plane of the figure The bearing of the pivoting arm 32B in the bolt 32C fastened in the frame R is normally implemented by bronze bearings in which it is difficult to arrange an effective lubrication operating in all conditions. The movements of the set of rolls are small and the movement cycles periodical. Due to the lubrication problem, friction forces increase and this, again, makes controlling nip forces difficult. A separate lubrication system also causes additional costs and service requirement. The bronze sleeves of the intermediate rolls and the slide guides of the lower roll can be replaced by self-lubricating bronze material usually including graphite. Also bearing sleeves of composite material can operate as bearing elements. With such an arrangement, the friction conditions are achieved constant and, due to being maintenance-free, no separate lubrication systems are required.

In the embodiments shown in the figures, the stacks of rolls 20A, 2OB are substantially vertical, but the stacks of rolls 2OA, 2OB can, from the viewpoint of the invention, naturally form also an angle with the vertical plane. A line drawn via the centres of the rolls can form a straight or broken line.

Above were described only some advantageous embodiments of the invention and it is evident to those skilled in the art that several modifications can be made to them within the scope of the enclosed claims.

Claims

1. A method for relieving intermediate rolls of a calender, characterised in that the method comprises the following steps:

- each intermediate roll (22B-24B) is lifted starting from an uppermost intermediate roll (22B) with the Q command of a pQ valve (A) connected to a relief cylinder (42B-44B) of the intermediate roll and observing the reading of a linear sensor (B) to the normal operating position of the intermediate roll (22B- 24B),

- the pressure values of the pQ valve are read during the movement of the intermediate roll (22B-24B) directing upwards and downwards, and the average of the readings is used as the relief pressure of the intermediate roll (22B-24B) in question in which possible excess and under reliefs are added.

2. A calender, which includes at least one stack of rolls (20B), in which there are a lower (25B) and an upper roll (21B) and at least one intermediate roll (22B-24B) the bearing cups of which are supported on the driving and tending side to a pivoting arm (32B-34B) and which pivoting arm (32B-34B) is further supported to a relief cylinder (42B-44B), characterised in that each relief cylinder (42B-44B) is provided with a pQ valve (A) and a linear sensor (B).