FI81634C - Method and apparatus for cooling the casing surface of the rollers in a calender, in particular a soft calender - Google Patents

Description

81 634

Method and apparatus for cooling the mantle surface of rollers of a calendar, in particular a soft calender Förfarande och anordning för avkylning av mantelytan av en calander, speciellt en soft-kalander 5

The invention relates to a method for cooling a calendar, in particular a soft calender, rolls, preferably soft rolls, the envelope surface, in particular in areas outside the paper web close to the ends of the rolls.

The invention also relates to a device for cooling a calendar, in particular soft calender rolls, preferably soft rolls, in the envelope surface, in particular in areas outside the paper web near the ends of the rolls, which device comprises a plurality of axially parallel compressed air nozzles and a roll-shaped wall.

An important step in finishing the paper is its calendering, which affects the surface smoothness and gloss of the paper as well as the thickness and density of the paper. The calendering takes place by passing a continuous web of paper through the pressing or nip points between the calendar rolls acting against each other.

As is already known, the calendering of paper is carried out by means of a so-called with a machine calender, the processing of which is supplemented, if necessary, in a separate so-called by supercalendering in a supercalender, which gives the paper more gloss.

The rollers used in the calenders are either hard or elastic rollers.

30 Hard rolls in this context refer to rolls whose casing material is, for example, die-casting or steel and whose hard contact surface on the paper is smoothly ground. A conventional machine calender has only hard rollers and the nip points between them are so-called. hard nips.

35 Elastic rollers are hereinafter referred to as rollers whose contact surface on the web is a flexible material. Such rolls, which are used in supercalender rolls, form a so-called roll with hard rolls. soft nips.

As the sheath material of the elastic rolls, paper 5 is generally used, which is layered on the roll shaft in layers and pressed in the axial direction into a uniform, dense and rather thick roll coating. Various plastic-based coatings are also currently used, which are generally relatively thin, allowing the roll body to be provided with internal deflection compensation devices without the diameter of the roll 10 becoming unreasonably large.

As is already known, machine calendering can also take place with a calendar formed by a single nip, i.e. a single pair of rollers, depending on the type of paper to be processed and the requirements imposed on it. However, the most common 15-minute machine calender comprises 4-8 rolls, which thus form 3 ... 7 hard nips. As a result of machine calendering, any thick points in the web are smoothed and the desired thickness, i.e. the so-called caliber.

20 As is known, a supercalender with only soft nips generally aims to obtain an equal gloss on both sides of the web. Therefore, there must be at least two soft nips and, in addition, generally arranged so that each side of the web will be in the same number of nips against the surface of the hard roll, which actually gives the web a shine. Separate supercalenders have up to 10 pairs of nips. Supercalendering generally results in both uniform density and smoothness for the web.

In order to increase the efficiency of the production of a paper machine, it has proved necessary to strive to provide a calender unit directly connected to the paper machine, which combines the functions of both a machine calender and a supercalender. Such calenders have been presented e.g. F1 Patent Publication Nos. 58,801, 62,874 and 65,106.

35 Although 8-10 nips are generally used in machine and supercalenders, it has been found that only two soft nips can impart sufficient gloss and smoothness and / or other properties to the 3,81634 papers produced for most purposes. This is due to the fact that the paper coming from the paper machine to the calendering process is generally much more uniform in shape and fiber distribution and thus easier to calender than the paper produced by the technology of about 20 years ago, thanks to the currently used web-forming technology and control systems used therein. Also, the development in flexible coating materials on the one hand and in the surface properties of the self-polishing paper on the other, which can be influenced by "brushing" a suitable paste thinly on the paper surface, i.e. "folding" the semi-finished web, e.g. possible the use of different and simpler calender structures.

15 The most commonly accepted notion of the effect of supercalendering on the web to be treated is that a stronger gloss is created on the surface that is in the nip against the hard roll. However, the formation of gloss and smoothness is influenced by several factors together, e.g. nip load, the possible difference between the rotational speeds 20 of the elastic roll and the hard roll, and the material of the elastic coating as an important factor. With regard to the latter factor in particular, development work continues and new and / or emerging coatings may warrant a revision of calendering theories.

25 One previously known solution belonging to on-machine calenders, i.e. machine supercalenders, is the so-called soft calender. Such a calender is disclosed, for example, in F1 patent application 871871.

The temperature used in soft calendering is higher than that used in superka-30 calendering. In addition, in soft calendering, there are usually fewer nips, but usually at least two. The roll material of the elastic roll used in soft calendering is usually plastic-based. The line pressure obtained in soft calendering is also generally slightly lower than that obtained in supercalendering in time-35.

4,81634

The soft calender is usually connected directly to the paper machine or may be located directly behind the coating device. The soft calender can also be used as an off-machine device.

5 Problems in soft calendering have been caused by excessive overheating of the off-paper area of the soft roll jacket surface near the roll ends due to pressing a hot steel roll over 130 ° C against the soft roll jacket surface, in the off-paper area near the roll ends, especially when calibrating a.

It is known from the prior art to solve this problem by grinding the diameter of the soft roll in a smaller area outside the paper web near the ends of the roll. This narrows down the problem area, but does not completely eliminate the problem. In addition, when driving paper paths of different widths, it is problematic to determine the extent of the area to be sanded.

Another previously known solution to this problem is the use of compressed air blowing by means of nozzles perpendicular to the shell surface of the roll. The efficiency of these 20 methods is modest and the noise generated is high. In addition, the soft roll wears heavily when compressed air is blown perpendicular to the roll shell surface. In addition, efforts have been made to solve the problem by using low pressure blowing. However, the effectiveness of this solution has proven to be poor.

25

The object of the invention is to provide a method and a device by means of which overheating of the jacket surface of the soft rollers of a soft calender in the area outside the paper web can be prevented. In particular, the object of the invention is to provide a solution which does not place restrictions on the width of the paper web to be calendered and does not cause noise problems.

It is a further object of the invention to provide efficient cooling of the envelope surface of the soft rollers of the soft calender in the region 35 outside the paper web.

Il 5 81634

The cooling method according to the invention is mainly characterized in that the method preferably blows compressed air at room temperature or cooled into an elongate space formed by the roll and the wall adjacent thereto in the opposite direction to the direction of rotation of the roll 5 and that the compressed air is directed along the wall.

The cooling device according to the invention is mainly characterized in that the wall with the roll of the soft calendar forms a long-term intermediate space for the circumferential length of the roll of max. 90%, near the ends of the roll in the axial direction for a small part of the length of the roll.

In addition, other advantageous features of the invention are set out in claims 2-4 and 6-11.

15

By using the method and apparatus according to the invention, excessive overheating of the jacket surface of the soft rolls of the soft calender in the areas outside the paper web near the ends of the roll is prevented. In addition, the efficiency of the method and device according to the invention is so good that the air pressure level can be reduced. The noise caused by using the method according to the invention is clearly lower already when using the same air pressure level used by previously known solutions.

When using the method and device according to the invention, it is not necessary to grind the diameter of the soft rolls close to the ends of the roll to a smaller size, whereby driving paper webs of different widths does not cause any problems.

When using the device according to the invention, no separate fans are required, but it is often possible to utilize a ready-made compressed air network. When using the device according to the invention, it is also not necessary to perform a separate filtration of compressed air, because the compressed air is not directed towards the jacket surface of the roll.

In the following, a method and apparatus according to the invention for cooling the envelope surface of soft rolls of soft calender 35 in areas outside the paper web near roll ends will be described in more detail 6,81634 with reference to the accompanying drawings, in which Figure 1 schematically shows a soft calender and associated cooling devices; schematically shows a cooling device according to the invention, and Fig. 3 shows the compressed air nozzles of the device according to the invention.

10

According to Figure 1, the soft calender 1 comprises body parts 6 as well as hard rollers 2,3 and soft or elastic rollers 4,5. The hard roll 2 and the soft roll 4 form a nip Nx and the hard roll 3 and the soft roll 5 form a nip N2. A calibrated paper web 15 R is passed through the nips N2 and N2.

Connected to the soft calender structure 1 are cooling devices 10 for areas outside the paper web of the envelope surface of the soft rolls 4.5 near each end of each soft roll 4,5. The cooling device 10 comprises 20 compressed air nozzles 11 and a pressure relief valve 12 connected thereto, by means of which the pressure can be adjusted. Through the pressure relief valve 12, the compressed air nozzles 11 are connected to the compressed air network 13. The cooling device solution 10 also includes a wall 15 near the jacket surface of the roll 4,5 fixed to the soft calender body 6 by the mounting body 25 16. intermediate space K.

The length of the intermediate space K is at most about 90% of the length of the 4.5 circumference of the roll. Alternatively, it is possible to place several separate cooling devices 10 according to the embodiment of the invention shown on the circumference of the roll 4.5. In addition, it is possible to place one long wall 15 which at most forms an intermediate space K covering approximately 90% of the circumferential surface of the roll 4.5. nozzles 11 for blowing compressed air are arranged at certain intervals. The length of the space K is determined by how much temperature is to be lowered / the length of the wall, the number of nozzles 11 in the axial direction of the roll 4.5 and in the circumferential direction.

li 7 81634 The width of the intermediate space K is determined by the axial direction of the roll 4.5 of the area outside the paper path R. For example, the width of the intermediate space K in the axial direction is 2-10% of the length 4.5 of the roll, preferably about 5%.

5

The blowing by the compressed air nozzles 11 is carried out against the direction of rotation S of the soft roll 4,5 into the intermediate space K formed by the wall 15 and the roll 4,5. The wedge-shaped shape of the intermediate space K helps to obtain the correct compressed air flow. A high velocity is obtained for the compressed air in the narrow intermediate space K10, whereby the situation can be compared to the more efficient cooling of the roll caused by the increase in the rotational speed, because the compressed air is blown in the opposite direction to the rotational direction S of the roll 4.5. In addition, the turbulence phenomena generated in the compressed air increase the cooling efficiency. The pressure of the compressed air is determined according to the driving speeds used and the pressure is preferably 0-650 kPa. The temperature of the compressed air is equal to the temperature of the air taken in by the compressor, ie corresponding to room temperature or cooled air.

The compressed air blowing is directed along the wall 15, whereby the wear of the soft roll 4,5 caused by the blowing 20 is reduced and also the removal of compressed air impurities is avoided because the blowing is not directed towards the jacket surface of the roll 4,5.

The pressure relief valve 12 included in the device 10 controls the noise level in addition to the air pressure.

According to Fig. 2, the wall 15 contained in the cooling device 10 can be attached to the body 6 of the soft calender 1 by means of a fixing body 16 (Fig. 1). The fastening body 16 comprises a fastening plate 17 and a fastening hole 18 therein, by means of which the fastening body 16 of the wall 15 is fastened to the frame 6 of the soft calendar 1 by means of conventional fastening means. There are several compressed air nozzles 11 in parallel, as shown in FIG. These nozzles 11 are used one at a time as many times as necessary to cool the jacket surface of the roll 4.5 outside the paper web in the axial direction of the roll. The shape of the wall 15 81634 follows the shape of the roll 4.5 preferably so that the gap KA of the inlet end K between the wall 15 and the roll 4 is larger than the gap KY of the outlet end, the shape K of the gap K being wedge-shaped. The depth of the intermediate space K in the radial direction depends on the diameter of the roll 4. For example, the depth KA of the inlet-5 end KA of the intermediate space K in the radial direction may be 10 * 30 mm, preferably 20 mm and the depth of the outlet end Ky 1-9 mm, preferably 5 mm, depending on the diameter of the roll 4.5.

The distance between the nozzles 11 is e.g. 30 * 40 mm. If the distance K pi-10 of the intermediate space corresponds to about 90% of the length of the 4.5 circumference of the roll, e.g. 3-4 rows of nozzles are used.

In addition to the application example presented above, it is possible to use the cooling device 10 of the soft rolls 4.5 of the soft calendar 1 according to the invention, e.g. for controlling the temperature profile of a steel roll, e.g. with a paper thickness profile when adjusting with a soft, super or machine calender.

In one example, when cooling the jacket surface of soft roll soft rolls in areas outside the paper web near the ends of the rolls 20, the surface temperature of the steel roll was 200 ° C and the surface temperature of the soft roll without cooling blow was about 140 ° C. In this case, the cooling demand was about 40 ° C. At a speed of 600 m / min, a pressure of 3 bar in the bellows nozzles provided a cooling of 50 ° C and at a speed of 1100 m / min a pressure of 6.5 bar provided a cooling of 50 ° C, respectively. In this use example, the diameters of the rolls 25 were 710 mm, flexible roll, and 1000 mm, steel-la.

The invention has been described above with reference to only one preferred embodiment thereof, which, however, is not intended to limit the invention, but many modifications and variations of the invention are possible within the scope of the inventive idea defined by the following claims.

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Claims (11)

Method for cooling the cant surface of calender, especially soft calender, rolls, most preferably soft rolls, mainly at the outer regions of the paper web near the ends (4,5), characterized in that the process is blown compressed air most preferably Ar at room temperature or cooled to an elongated space (K) formed by the vala (4,5) and a wall (15) placed in the immediate vicinity thereof in the opposite direction relative to the rotational direction of the roller (4,5), and that the compressed air blast is directed along the wall (15). 2. A method according to claim 1, characterized in that the method can be applied for checking the temperature profile of the rollers · when controlling the thickness profile of the paper. Method according to any one of claims 1 * 2, characterized in that the pressure of the compressed air is adjusted according to the running speed used, most preferably to 0-650 kPa. 20 Method according to any one of claims 1-3, characterized in that the pressure of the compressed air is regulated in a manner known per se with a pressure-lowering valve (12) or the like. 6. Apparatus for cooling the casing surface of calender, especially soft calender, rolls, most preferably soft rolls, mainly at the outer areas of the paper web near the roll ends (4,5), which includes in the axial direction several parallel compressed air nozzles (11) and a wall (15) along the shape of the roller (4,5), characterized in that the wall (15) together with the roller (4,5) of the soft calender (1) forms an elongated space (K). ) above max. 90% of the length of the circumference of the roller (4,5) near the roller ends (4,5) in the axial direction to a small part of the length of the roller (4,5). 6. Device according to claim 5, characterized in that the compressed air pieces (11) are connected to a compressed air channel (13) or the like by means of pressure relief valves 12 81 634 (12). 7. Device according to claim 5 or 6, characterized in that the wall (15) is connected by means of a fastening body (16) to the body (6) of the soft calender (1). 8. A device according to claim 6, characterized in that the shape of the space (K) sob is formed by the wall (15) of the roller (4,5). 10 direction is less than the depth of the input end (KA) of the space (K) in the radial direction. Device according to any of claims 5-8, characterized in that the depth of the intermediate space (K) in the radial direction Ar at the input end (KA) 10-30 mm, most suitable 20 frame and the output end (Ky) 1-9 mm, Most suitable 5 mm. Device according to any of claims 5-9, characterized in that the width p in the intermediate space (K) in the axial direction of the roller (4,5) is 2-10%, or more than 5%, of the length of the roller (4,5). 11. Apparatus according to any of claims 5-10, characterized in that the compressed air nozzles (11) are most suitable for the number parallel to the longitudinal direction of the roller (4,5) on the side so that the compressed air blasting is provided at an area of the casing surface of the roller ( 4,5) corresponds to the outer areas of the paper web. II