WO2003046280A1

WO2003046280A1 - Soft calender

Info

Publication number: WO2003046280A1
Application number: PCT/FI2002/000946
Authority: WO
Inventors: Kari Hasanen; Harri Kuosa
Original assignee: Metso Paper Inc.
Priority date: 2001-11-30
Filing date: 2002-11-25
Publication date: 2003-06-05
Also published as: AU2002365470A1; FI116733B; FI20012363A0; DE10297485T5; FI20012363A

Abstract

A soft calender contains two roll groups (A, B) of three rolls, each forming two successive soft calendering nips (N) while the rolls are located on top of each other in the groups. The roll groups (A, B) are positioned in separate vertical frames (R1, R2). In both roll groups (A, B) the bearing housing (2) of the roll (1) in the middle is fastened to the vertical frame (R1, R2) and the upper and lower roll (1) on both sides of the same are fastened by their bearing housings (2) to the bearing housing (2) of the middle roll.

Description

Soft calender

The invention relates to a soft calender containing two groups of three rolls, each forming two successive calendering nips, as the rolls are located on top of each other in the groups.

Different kinds of calenders are used for increasing the smoothness and evenness of the paper or paperboard surface. The calender can be placed inside (such as a precalender) a machine producing paper or paperboard web in the same manufacturing line (on-line) or after it, or the paper web can be calendered in a separate off-line process after unwinding. In the soft calender at least one of the rolls forming the calender nip has a soft surface. Typically, the nip is formed by means of superimposed soft and hard-faced rolls, of which the soft roll is typically polymer-covered, and the hard-faced roll is a heated metal roll, a so-called thermoroll.

There are numerous different types of soft calenders, depending on the application. To perform a two-sided treatment of the paper web to be calendered, there is a known calender containing groups forming two separate roll pairs in the calender frame in such a manner that in successive groups the soft roll and the hard-faced roll are in a reverse order. There is also a known "Optigloss" soft calender in which two groups of three rolls are placed successively in the calender frame, in which groups the roll in the middle is a hard-faced thermoroll, and above and below the same there is a soft-faced roll, wherein a total of four successive nips are formed in the calender, through which nips it is possible to pass the web in such a manner that it is treated on both sides (both sides of the web are positioned against the thermoroll, in the first group of rolls the first side of the web, and in the second group of rolls the second side of the web).

The calender constitutes one section of the paper or paperboard machine that increases the machine length. In the placement of the rolls in the frame, the change and maintenance of the rolls must also be taken into account, for which reason it is not always possible to minimize the length of the calender in the desired manner. An Optigloss-type soft calender is conventionally placed in calender frames that are open forward and backward, i.e. in frames having the shape of two C-letters whose backs are positioned against each other. The roll change takes place in the machine direction at the front or the at the back of the frame by means of cranes.

In four-nip soft calenders the upper and lower rolls are loaded in both roll groups against the middle roll by fastening the bearing housings of the upper and lower rolls to arms that are connected to loading cylinders. In wide machines the forces transmitted from the bearing housings to the frame become substantial.

It is an aim of the invention to present such a four-nip calender containing two groups of three rolls in which the frame structure is lighter and less complicated. To attain this purpose, the calender according to the invention is characterized in that the roll groups are placed in separate vertical frames, and at least in one vertical frame the bearing housings of the rolls are fastened to each other.

Between the separate vertical frames there remains a space for various maintenance operations and auxiliary devices. When the bearing housings of the rolls are attached to each other, only a small amount of forces resulting from the nip pressures will be transferred to the calender frame. The nip forces can be adjusted by adjusting the shell of the upper roll and the lower roll of the roll group in the radial direction. Structurally this can be conducted in such a manner that a deflection compensated roll is used as a upper roll and a lower roll in the group of rolls, the motion of the shell of the deflection compensated roll in the radial direction being produced by means of loading elements inside the roll that are supported by a stationary shaft.

According to a preferred embodiment, the bearing housing of the roll in the middle of the roll group is fastened to the vertical frame and the rolls on both sides of the middle roll are attached at their bearing housings to the bearing housing of the middle roll. When compared to the old Optigloss-type soft calender, it is an advantage of the invention that the tensions of the linear loads are transmitted directly to the bearing housings by means of attachment means such as fastening bolts. The bearing housings only experience compression stress as a result of the pretensioning force of the fastening bolts. When the bearing housings are rigidly attached to each other, problems relating to vibration do not occur.

As the vertical frame of the calender has the shape of the letter U when seen from the side, and it forms a ring with the bearing housing of the middle roll that is attached on top of said vertical frame, the frame becomes more rigid than a frame that has a profile with the shape of letter C and is open in the machine direction.

In the following, the invention will be described in more detail with reference to the appended drawings, in which

Fig. 1 shows a side view of a calender,

Fig. 2 shows a calender according to another embodiment in a side-view, and

Fig. 3 shows an alternative way of leading the web in a calender according to Fig. 1.

Fig. 1 shows a calender according to the invention in a side view. The calender contains two roll groups A, B, each composed of three calender rolls and positioned successively in the machine direction. Both roll groups form a so-called calender stack in which two calendering nips N successive in the travel direction of the web are formed between superimposed calender rolls 1. In both calendering nips one of the calendering elements is the roll in the middle of the roll group, which is a heated so-called thermoroll with a metal surface. The other calendering elements of the nips are composed of soft-faced rolls 1 on both sides of the middle roll, said soft-faced rolls being typically equipped with a polymer cover. These upper and lower rolls are also deflection compensated rolls in which the motion of the roll shell is attained by means of loading elements which are placed on a stationary shaft inside the roll and which can be adjusted independently.

Both groups A, B are placed in a vertical frame R1 , R2 of their own in such a manner that free space remains between the frames. Thus, the central part of the calender is open upward. The vertical frame is composed of supporting structures located at the ends of the rolls. The supporting structures have U-shaped side profiles (when seen in the direction of the axes of the calender rolls). The bearing housings 2 of the calender rolls 1 are attached to each other in both vertical frames R1 , R2. As a result of this, forces caused by the nip pressure required by the calendering process are not transmitted to the calender frame. In practice, the calender rolls 1 are attached to the frame by means of their bearing housings 2 in such a manner that the bearing housing 2 of the calender roll in the middle (thermoroll) is fastened to the frame R1 by means of fastening elements producing pretensioning force, such as bolts 3 tightened by means of nuts 3a, and the bearing housings 2 of the calender rolls 1 above and below the middle roll are also fastened to the bearing housing 2 of the middle roll by means of fastening elements producing pretensioning force, such as bolts 4 tightened by means of nuts 4a.

On both sides of the web the bearing housing 2 of the roll in the middle is fastened on top of the vertical frame, in the upper ends of the branches (posts) of the U-shape. The bearing housing 2 of the lower roll is positioned between the posts, inside the U-shape. The bearing housings 2 of the upper and lower roll are fastened to the bearing housing of the roll in the middle by means of fastening elements shared by the upper and the lower bearing housing 2, said fastening elements extending in the vertical direction through all three superimposed bearing housings 2. There are two fastening elements, one on both sides of the line formed by the roll axes. The fastening of the bearing housings 2 to the frame and to each other is similar in both vertical frames R1 , R2. The fastening elements are long bolts 4 that are so- called stud bolts, i.e. threaded rods, both ends of which contain nuts 4a screwed thereon. The bearing housings of the rolls are secured to each other by tightening said nuts to form a "packet" composed of three bearing housings 2. The nuts 4a existing in the upper ends of the threaded rods are positioned against the upper bearing housing 2, and the nuts 4a in the lower ends of the same are positioned against the lower bearing housing 2. Thus, the tightening of the fastening elements shared by the bearing housings takes place in relation to the upper bearing housing 2 and the lower bearing housing 2 that become tightened against the bearing housing 2 in the middle by means of the fastening elements.

Fig. 1 also shows how it is possible to place rolls used before the nip or between nips for guiding the paper or paperboard web to be calendered in the ends of the posts of the frame R1 , R2. In Fig. 1 , the paper web W to be calendered enters the first calender roll group A via a spreading roll 5 that is positioned in the end of the post of the frame R1 , travels through a calendering nip N between the lower calendering roll 1 and the middle calendering roll 1 to a web guiding roll 6 in the end of another post in the same frame, and thereafter via a spreading roll 5 through the calendering nip N between the middle roll 1 and the upper roll 1 to a web guiding roll 6 on the inlet side of the web, whereafter the paper web travels over the roll group A under the guidance of two web guiding rolls 6 located on different sides of the roll stack, and then under the guidance of a spreading roll 5 located between the roll groups A, B to the upper nip N in the second roll group B, said nip being formed between the middle calender roll 1 and the upper calender roll 1. After this nip the web W travels under the guidance of a web guiding roll 6 and a spreading roll 5 located in the end of the post of the frame R2 to the lower calender nip N that is formed between the middle calender roll 1 and the lower calender roll 1 , whereafter it travels under the guidance of two web guiding rolls 6 located between the roll groups A, B from underneath the roll group A to a web guiding roll 6 located on the outlet side of the web, and then out of the calender.

This way it is possible to calender the web W on both sides in a similar manner, because both sides are alternately in contact with a thermoroll 1 in the middle in successive calendering nips N, the upper side in the first roll group A and the lower side in the second roll group B. When the web is to be calendered only in two nips in the entire calender with a similar treatment on both sides, the web W is passed along a path marked with broken lines, said path 6 passing the posterior (upper) calendering nip in the first roll group A and the posterior (lower) calendering nip N in the second roll group B.

Both frames R1, R2 contain rails 7 extending in the cross-machine direction, along which rails it is possible to transfer the lowermost calender roll sideways out of the calender on top of a carriage to perform roll change after its bearing housing 2 is released from the bearing housing of the middle roll and lowered down to the carriage located underneath by means of a small hydraulic cylinder positioned in the frame underneath both bearing housings of the lowermost roll. Said hydraulic cylinder is lifted up to support the bearing housing before the lowermost nuts 4a of the fastening bolts 4 are released. Correspondingly, by means of same cylinders it is possible to lift up the bearing housings of the lowermost roll against the bearing housings of the middle roll while the fastening bolts 4 are tightened. The vertical frame of the calender is open to the sides at the location of the lowermost calender roll 1 (the bearing housing 2 of the roll is positioned between the posts). The upper calender roll 1 can be changed through the top by means of a crane after its bearing housing 2 is released from the bearing housing of the middle calender roll 1. The roll change in the calender does not require space in the machine direction.

Fig. 2 shows a calender according to a second embodiment, which contains two roll groups A and B, which contain rolls that correspond to the embodiment of Fig. 1. The attachment of the rolls to each other and to the vertical frames R1 , R2 is also similar. However, the rolls are here connected to each other by means of the bearing housings 2 in such a manner that the nip line formed by the calendering nips N is placed in an inclined position when compared to the completely vertical line, i.e. the roll stack is in an inclined position. The angle α between the vertical line and the nip line is in Fig. 2 approximately 10°, but it may vary. In practice, the upper and lower surface of the bearing housing 2 of the middle roll 1 , against which the bearing housings 2 of the upper and lower roll are positioned, have a corresponding sloping shape in such a manner that the roll stack assumes an inclined position when the bearing housings 2 of the upper roll 1 and the lower roll 1 are fastened to the bearing housing 2 of the middle roll. The inclination of the roll stack (angle α) deviates from the vertical line advantageously 15° at the most. In an inclined roll stack the roller bearings of the thermoroll 1 in the middle never enter the zero load area.

In Fig. 2, the web is conveyed in such a manner that it travels first through the uppermost nip N in the first roll group A. To conduct calendering on both sides, the web W travels downward from an upper level by the first roll group A, and upward from a lower level by the second roll group B, passing by the first roll group A underneath it and the second roll group B above it.

Fig. 3 shows an embodiment in which the nip lines of the roll groups A, B are vertical, i.e. the fastening of the bearing housings 2 is implemented according to Fig. 1 , but the web W is conveyed in a similar manner as in the embodiment of Fig. 2.

All the drawings show the calender from one side. It is obvious that the structure of the calender is similar on the other side in cross direction. Both vertical frames R1 , R2 thus contain two U-shaped supporting structures in the opposite ends of the calender roll, i.e. on different sides of the calender when seen in the machine direction. Both bearing housings of the calender roll in the middle are fastened to the corresponding U-shaped supporting structure.

The runs of the web can be changed by changing the position of the web guiding rolls 6 and the spreading rolls as well as the directions of rotation of the drives of the calender rolls 1. Similarly, the drawings show that in all embodiments it is possible to bypass the second caledering nip in both roll groups A, B to calender the paper web on both sides in a total of two calendering nips instead of four.

Claims

Claims:

1. A soft calender containing two roll groups (A, B) of three rolls, which both form two successive soft calendering nips (N) as the rolls (1) are located on top of each other in the groups, characterized in that the roll groups (A, B) are positioned in separate vertical frames (R1 , R2), and at least in one vertical frame the bearing housings (2) of the rolls (1) are fastened to each other.

2. The soft calender according to claim 1 , characterized in that soft calendering nips (N) are formed between a soft-faced roll and a hard- faced roll.

3. The soft calender according to claim 2, characterized in that the roll (1) in the middle of the roll group (A, B) is a hard-faced roll, advantageously a heated thermoroll.

4. The soft calender according to any of the preceding claims, characterized in that the bearing housing (2) of the roll (1) in the middle of the roll group (A) is attached to the vertical frame (R1 , R2) and the upper and lower roll (1) on both sides of the middle roll are fastened by their bearing housings (2) to the bearing housing (2) of the roll in the middle.

5. The soft calender according to claim 4, characterized in that the bearing housing (2) of the roll in the middle is fastened on top of the vertical frame (R1 , R2).

6. The soft calender according to claim 5, characterized in that the bearing housing (2) of the roll in the middle is fastened on top two successive posts of the vertical frame (R1 , R2).

7. The soft calender according to claim 5 or 6, characterized in that the vertical frame has a side profile with shape of the letter U, and it forms a ring with the bearing housing (2) of the middle roll (1) that is fastened on top of the U-shape.

8. The soft calender according to claim 4, 5, 6 or 7 characterized in that the bearing housings (2) of the upper and lower roll of the roll group are fastened to the bearing housing (2) of the roll in the middle by means of common fastening elements.