CN108505383B

CN108505383B - Press section of a web forming machine

Info

Publication number: CN108505383B
Application number: CN201810165540.3A
Authority: CN
Inventors: 里卡·安蒂凯宁; V·许珀宁; J·翁内拉; 亚里·萨韦拉; T·西洛玛; 米卡·托斯卡拉
Original assignee: Metso Paper Oy
Current assignee: Valmet Technologies Oy
Priority date: 2017-02-28
Filing date: 2018-02-28
Publication date: 2020-02-18
Anticipated expiration: 2038-02-28
Also published as: FI20175187L; FI128994B; CN108505383A; EP3366836A1

Abstract

The invention relates to a press section of a web forming machine, which press section comprises a press nip (10). A press nip (10) is formed between a roll (11) and a counter roll (12). Of these rolls, the roll (11) is a hollow-surface press roll (13). The counter roller (12) is an elastic roller (12'). Furthermore, the resilient roll (12') is adapted to be equipped with a flexible roll shell (22), inside which is a resilient loading element (23) against the press roll (13).

Description

Press section of a web forming machine

Technical Field

The present invention relates to a press section of a web forming machine, which press section comprises a press nip formed between a roll and a counter roll, of which rolls the roll is a hollow-faced press roll.

Background

Figure 2 of european patent application No. 0799932 shows the concept of a shoe press without a central roll of the first press nip. Figure 3 of us patent No. 5759355 shows an application that achieves several production records and is still sold under the trade name SymPress B of vimard. The press section comprises three successive press nips, of which two first press nips are roll nips and the third press nip is a so-called extended nip. The first press nip is formed between a hollow-surface press roll and a tube roll serving as a counter roll. In the press section in question, the fibre web is under good control even at high production speeds, while a continuously efficient press activity (event) achieves a high dewatering capacity. Furthermore, the press section is compact, which facilitates its adaptation to the use in a fibrous web machine for modernization.

The press rolls in the press section, which are close to each other, have to be positioned accurately, most of them being special rolls, which require a structure with dimensional accuracy and a support roll for each roll. Moreover, removing one roll also requires removing at least one adjacent roll. Accordingly, supporting the movable roll by means of the moving arm increases the sensitivity to vibrations and the roll nip is susceptible to e.g. break build-up in the web.

Disclosure of Invention

The object of the invention is to achieve a new press section of a fiber web machine, which press section is simpler than before, but more efficient and easier to modify. The press section according to the invention is characterized in what is set forth in the appended claims. In the press section according to the invention, the pressing action is started in a novel and surprising manner. In this case dewatering is started in a controlled manner without destroying the structure of the fibre web. The dewatering is still effective. Furthermore, the pressing activity can be adjusted, in which case the change of stock and grade can be performed without changing the structure of the press section. In other respects the structure of the press section is also simpler than before and the support of the rolls can be made easier than before, for example. The existing press section can easily be retrofitted with minor structural modifications in accordance with the present invention. In this case, the capacity of the fiber web machine can be easily increased. The new press device is very suitable for use in a press having a grammage of over 100g/m²High gram weight variety of (2). At the same time, the quality of the final product may be affected.

Drawings

The present invention is described in detail below with reference to the attached drawings showing some embodiments of the invention, wherein:

figure 1 shows a press section of a prior art fiber web machine,

figure 2 shows a first application of the press section of a fiber web machine according to the invention,

figure 3 shows a press nip according to the invention in cross-section of a loading element,

fig. 4 shows a second application of the press section of a fiber web machine according to the invention.

Detailed Description

Figure 1 shows a prior art press section comprising three successive functional press nips. In the first press nip 10 the fibrous web is located between two different fabrics, and the press nip 10 is formed between a roll 11 and a counter roll 12. In the known solution, the rolls 11 are press rolls 13 and the counter rolls 12 are tube rolls. The upper fabric 14 is typically a press felt. Accordingly, the lower fabric 15 is typically a press felt. After the first press nip 10, the fibre web follows the upper fabric 14 to a second press nip 17 formed by a press roll 13 and a so-called central roll 16, and further to a third press nip 18 on the surface of the central roll 16, which press nip 18 is formed between a shoe press roll 19 and the central roll 16. In the second and third press nips, the fabric is brought to bear against one side of the fibrous web only. The third fabric 20 is also a press felt into which water is transferred from the fibrous web. From the central roll 16 the fibre web is transferred to and supported by a drying wire 21 and further to the dryer section. In addition to fig. 3, the drying wire itself is not shown. Fiber web machines are for example paper, board and pulp machines.

The present invention relates to a press section of a web forming machine, which press section comprises a press nip 10 (fig. 2 and 4). In the press nip, water is removed from the fibrous web between the two rolls. More specifically, a press nip 10 is formed between a roll 11 and a counter roll 12, of which roll 11 is a hollow-surface press roll 13. In the present invention, the press roll 13 is a press suction roll (fig. 2) or a grooved roll (fig. 3). The suction effect produced by the press suction roll enhances the dewatering effect while guiding the fibre web to the direction determined by the press suction roll. In this case the fibre web is still under good control. In the present invention, the counter roll 12 is an elastic roll 12 ', and the elastic roll 12' is suitably equipped with a flexible roll shell 22, inside which flexible roll shell 22 is an elastic loading element 23 (fig. 3) abutting against the press roll 13. In this case, the pressing action is started gradually, instead of giving the fiber web a sudden pulse. Furthermore, the pressing action continues beyond the roll nip. However, the loading achieves a significant loading of the press nip with which effective dewatering from the fibre web is possible. In this case the dewatering capacity of the press section can be increased without compromising the properties of the fibre web. In practice, the properties of the final product are even improved and may have a greater influence on the properties of the fibre web than earlier.

The press nip 10 is advantageously the first press nip of a press section. In this case, the first pressing action of the fiber web is gradually started and very gentle due to the elastic loading elements, in which case the structure of the fiber web remains unbroken. At the same time, the adjustment of the pressure medium of the loading element can be used to influence the intensity of the pressing action. In this way, the loading of the first press nip can be adjusted as desired, depending on the type, without changing the structure.

Fig. 3 shows a spring-loaded element 23 according to the invention, which spring-loaded element 23 is suitable for use in a spring roller 12'. The shaft 24 of the resilient roller 12' includes a suitable support structure 28, which support structure 28 holds the resilient loading element 23 in place even if the sleeve is loaded and rotated. The support structure forms a support for the spring-loaded element on five sides, leaving only the freedom of the loading direction. In this case, the deformation of the loading element is controlled and deformation in the other direction is prevented.

The spring-loading element 23 is advantageously non-metallic. In which case it gives way, for example, at the accumulation of damages in the web (yield), while on the other hand it adapts to the shape of the press roll. At the same time, potential small alignment differences between the press roll and the resilient roll are leveled out by the yielding of the loading element. Secondly, the loading element achieves the required loading in the press nip in addition to the elasticity. Moreover, the structure is simple and easy to adjust. Here, the broken line is also used to indicate the fibre web 25 which, together with the upper press fabric 14, enters the press nip 10. On the sides of the resilient roll 12' there are lower press fabrics 15, in addition to which there are flexible roll jackets 22. After press nip 10, fibrous web 25 follows press roll 13 and upper press fabric 14 on its surface. In this case, the fibre web is guided naturally into the correct direction despite the high production speed.

In the application example of fig. 3, there are three pressure chambers 26 in the spring-loaded element 23. According to the invention, the spring-loaded element comprises at least one pressure chamber 26, the loading effect being produced by means of a pressure medium by varying the dimensions of the spring-loaded element. The dimensions of the spring-loaded element adapted to be used in the spring roll change when the pressure chamber is pressurized. In this way the surface of the loading element rises with the flexible jacket and the press felt against the surface of the roll 11. In this case, the loading element is loaded against the press roll by increasing the pressure, thereby creating a nip load. The pressure chamber may comprise a reinforcement corresponding to the shape of the pressure chamber, the reinforcement comprising an opening towards the loading direction. In this way, when the reinforcement is installed in at least the pressure chamber of lower pressure, the pressure chamber of higher pressure does not affect the loading of the adjacent pressure chamber. Surprisingly, the roll of the first press nip has no loading cylinder of the set and the press roll has no loading element. The pressure medium used is advantageously oil, in which case the loading element is hydraulic. In this way, sufficient nip load and pressure are achieved with the loading element. At the same time, the hydraulic loading can easily be adjusted to the desired level. The achievable nip load can be up to 200kN/m, but typically the nip load is 100kN/m-150 kN/m. Since the loading element is elastic, the pressure distribution in the press nip is also uniform.

The direction of the dimensional change of the spring-loaded element is adapted primarily to the radial direction of the spring roller, in which case the distance of the running surface of the spring-loaded element with respect to the axis of the spring roller changes. In this case, the spring-loaded element can be pressed against the press roll by varying the pressure of the pressure medium, whereby a suitable nip load can be defined. According to this structure there is a roll jacket and one or more press fabrics and a real fibrous web between them. The spring-loaded element thus has a certain stroke length of the same magnitude as the dimensional change, which stroke length can also be used for so-called nip openings. In this case, the opening of the nip and the formation of the nip load are accomplished using a single loading element. In this case, the resilient roller may be rigidly supported without the known loading arm and loading cylinder.

In addition to the adjustable loading, the spring-loaded element also achieves other advantages. Now, the resilient roll can be rigidly supported to the web forming machine when the necessary load is generated by the loading element inside the resilient roll. In this case, the prior art loading arm and external loading means are not necessary. Similarly, a conventional loading cylinder inside the nip roll may be omitted entirely. At the same time, the press nip is less sensitive to vibrations and the spring-loaded element also partly acts as a damper. Furthermore, the press roll and the resilient roll are supported independently of each other, in which case they can be removed without the need to remove the other roll.

The dimensional change of the spring-loaded element according to the invention in the loading direction is 1mm to 40mm, more advantageously 5mm to 30 mm. In this case, the loading element can be used, in addition to the loading, for example to open the press nip for the duration of a fabric change. At the same time, the resilient roll can be supported rigidly on the fiber web machine, which simplifies the structure of the press section and reduces the vibrations of the structure. As the structure becomes simpler, the cost is also reduced. In practice, the press roll is the only roll that is movably supported by means of loading arms connected to the three press nips.

The various dimensions of the spring-loaded element may vary from application to application. In general, the length of the elastic press nip according to the invention in the running direction of the web is 60mm to 150mm, advantageously 75mm to 125 mm. In this case the length of the pressing action is much longer than in a normal roll nip, in which case there is time to remove more water than previously. For example, the nip length formed by a loading element with one pressure chamber may be 60mm, whereas a nip length of 150mm is achieved by three consecutive pressure chambers. By means of two or more pressure chambers, it is also possible to adjust the desired nip pressure profile in the machine direction. In this case, in practice, there is a small nip load at the beginning of the press nip, which nip load increases at the location of the next pressure chamber. By adjusting the pressure of the pressure chamber, the position of the spring-loaded element can also be changed to adjust the pressing action. This change corresponds to an adjustment of the shoe press roll, which requires opening of the shoe press roll plus mechanical changes. By means of the spring-loaded element, it is possible to adjust by varying the pressure without opening the spring roller. It is even possible to make the adjustment during the run without stopping the fiber web machine.

The support of the resilient roll also simplifies the structure of the press section. In the present invention, the roller 11 and the elastic roller 12' are supported independently of each other. In this case, for example, the roller can be replaced without the need to remove another roller, which simplifies maintenance measures.

Figure 2 shows an application of the press section according to the invention. Here, the central roll 16 is arranged in nip contact with the press roll 13 to form a second press nip 17. Furthermore, an extended nip roll 19 is also arranged in nip contact with the central roll 16 to form a third press nip 18. The structure is compact and the press section according to the invention can be formed simply by replacing the resilient roll. In this case, more dewatering capacity and various adjustment possibilities for the press section are obtained.

Figure 4 shows a second application of the press section according to the invention. Here, after the press nip 10, there is a separate press nip 27. In other words, there are two successive but separate press nips in the press section in question. According to the invention, in the first press nip 10, the counter roll 12 is an elastic roll 12 ', which elastic roll 12' comprises an elastic loading element 23 against the press roll 13. In this case, the above-mentioned advantages are also achieved in this application. Unlike the first application, the press roll 13 is here in a lower position, which helps to collect the removed water. The separate press nip 27 has a shoe press roll 19. The counter roll of the shoe press roll 19 is a variable crown roll having a structure similar to the above-described center roll.

In the solution of fig. 4, instead of suction press rolls, it is also possible to use solid press rolls, in other words tube rolls with thick jackets. The sleeve has a thickness of 70mm to 150mm and the diameter of the tube roll is less than 1800mm, typically 1000mm to 1600 mm. The thick casing of a solid press roll carries the loading without the need for internal loading devices and other internal equipment. The solid press roll advantageously comprises a surface structure or coating having spaces, e.g. grooves, for the pressed-out water. In this way, the press arrangement is cheap and easy to arrange in order to function in terms of runnability and geometry. Furthermore, for small diameter rolls, there is more space and easier construction to arrange the vat belonging to the water collection system in response to increased dewatering capacity.

Press applications include strong-walled rolls (strong-walled rolls) for pressing, the surface structure of which always includes space for water when loading removes large amounts of water from a web with a higher grammage. Furthermore, the reasonable diameter of the rolls enables other dewatering equipment to be placed in the immediate vicinity of the nip and in connection with both nip rolls. In this case, the removed water is avoided from getting back into the fabric and the web. Furthermore, the running of the web into the press nip is advantageously rather simple and can thus be easily controlled. Fig. 2 and 4 show a large economizer (saveall) 29 placed below the lower roll, which economizer 29 collects the water removed in the press nip 10. The water circulating with the roll is removed by means of a doctor blade into the economizer. The economizer also prevents water from splashing into the internal circulation of the press felt 15. In fig. 2, there is an economizer 30 around the roller 11. In fig. 4, a corresponding economizer 30 is placed at the exit side of the press nip 10. Corresponding economizers (dashed lines) may also be present on the entry side, in particular when heavy products are produced. These figures also show a small economizer located below the press felt 15. Fig. 4 shows a doctor strip 31 adapted to abut the press felt 15, which doctor strip 31 can be used instead of an economizer on the outlet side.

In the roll nip, there are two hard fixed shell rolls opposite each other, which rolls may have different types of surface structures. The shoe roll nip is a press nip between a crowned roll with a hard jacket and a crowned roll equipped with a shoe and having a flexible jacket. The shoe with a hard surface is concave in structure to match the shape of the counter roll. Furthermore, the shoe is loaded from below the rigid shoe structure by means of a cylinder. The jacket of the hard-jacketed roller is also loaded by means of a cylinder through a skid shoe.

The structure and components of the press section according to the invention may be known, but the resilient loading element is arranged in the resilient roll together with the flexible roll jacket. In this case an extended press nip is achieved, which has a positive effect on the production and the quality of the fibre web. The extended and resilient press nip achieves a greater dewatering capacity than before without interrupting the fibre web just coming out of the web forming section. At the same time a higher bulk than before is obtained and now also the ratio of bulk to dry matter content can be controlled. The strength properties of the fiber web can also be adjusted. The elastic roller itself has a simple and operationally reliable construction, the cost of which is obviously cheaper than other special rollers. Furthermore, the resilient roller requires less alignment than previously.

Claims

1. A press section of a web forming machine, comprising a press nip (10) formed between a roll (11) and a counter roll (12), wherein the roll (11) is a hollow-faced press roll (13), wherein the counter roll (12) is an elastic roll (12') adapted to be equipped with a flexible roll shell (22), the interior of which (22) is an elastic loading element (23) against the press roll (13), the elastic loading element (23) comprising a pressure chamber (26) creating a loading effect by changing the size of the elastic loading element (23) by means of a pressure medium,

wherein the elastic loading element (23) has a dimension variation in the loading direction of 1mm-40mm and the elastic roll (12') is rigidly supported to the web forming machine.

2. The press section according to claim 1, characterized in that the press nip (10) is the first press nip of the press section.

3. Press section according to claim 1 or 2, characterised in that the spring-loaded element (23) is non-metallic.

4. Press section according to claim 1, characterised in that the dimension of the spring loading element (23) in the loading direction varies between 5mm and 30 mm. .

5. A press section according to claim 1 or 2, characterised in that the length of the press nip (10) in the running direction of the web is 60-150 mm.

6. A press section as claimed in claim 5, characterised in that the length of the press nip (10) in the running direction of the web is 75-125 mm.

7. The press section according to claim 1 or 2, characterized in that the roll (11) and the resilient roll (12') are supported to the web forming machine independently of each other.

8. Press section according to claim 1 or 2, characterized in that the press roll (13) is a press suction roll or a grooved roll.

9. A press section as claimed in claim 1 or 2, characterized in that a centre roll (16) is arranged in nip contact with the roll (11) so as to form a second press nip (17), and a shoe roll (19) is arranged in nip contact with the centre roll (16) so as to form a third press nip (18).