CN102165117A - Forming section with metal belt - Google Patents

Abstract

A forming section forming a fibrous web is described, which forming section comprises a forming wire loop (1) for forming the fibrous web from a fiber containing suspension which is injected to the forming wire by a head box. A metal belt loop (2) is arranged- to press the web and the forming wire (11) between the metal belt (21) of that loop and a support surface (12), which can be a roll. Using a metal belt allows the generation of a long nip using appropriate metal belt arrangement and belt tension. The metal belt maybe arranged to contact the fibrous web, and the forming wire is arranged to contact the support surface. In other words, the web is sandwiched between the metal belt and forming wire, wherein the metal belt can be arranged to press the fibrous web from above pressing the liquid of the suspension towards the forming wire which is arranged below the web. In this way, gravity can be used to support water removal, and a more symmetric web can finally be obtained.

Description

Forming section with metal strip

technical field

The invention relates to a forming section which forms a web consisting of fibers.

Background technique

The forming section is used in machines such as paper machines, where a suspension comprising fibers and a suspension, usually water, is injected between two forming wires, followed by removal of most of the liquid to form a wet web from the fibers. The web then travels via a pre-nip to a press section and further into a dryer section where it is further processed to obtain desired properties such as dryness, web bulk, density, thickness, surface properties etc.

In the pre-nip, the web is usually supported on one side of the web by one of the forming wires, since the web in this part of the paper machine is not strong enough to be transported alone. However, forming fabrics are easily damaged by pressure so that their lifespan is reduced by pressing. Furthermore, the forming wire creates surface impressions on the adjacent web surface, thereby reducing the smoothness of the surface and thus the quality of the paper itself.

Additionally, in order to achieve rapid water removal, there is a tendency to use increased pressure in the pre-press zone. However, higher pressures reduce the bulk of the web and at the same time reduce the bending stiffness of the later paper or paperboard product. To avoid this problem, long nips with lower pressure and increased nip length can be used, but long press rolls with felt rings are very expensive.

Contents of the invention

In view of the above, it is an object of the present invention to provide a forming section which allows rapid and energy-efficient dewatering of a formed web while maintaining the desired web properties, and a method of forming a web, In this method, the formed web is dewatered quickly and efficiently.

With respect to the device, the above-mentioned object is solved by a forming section according to claim 1 , and with regard to the method, the above-mentioned object is solved by a method according to claim 12 .

It should be noted that in this specification the terms "fibrous web" and "web" include paper, cardboard and other web types made from fiber-containing suspensions. Although for ease of explanation only a paper machine has been described, the invention also relates to paper machines, board machines etc.; this seems sufficient to keep the description clear. So, when a claim refers to a fibrous web or web, it refers to any of the web types mentioned above.

According to the invention, the forming section forming the fibrous web comprises a forming wire loop for forming a fibrous web from a fiber-containing suspension as described above. In addition, the metal belt loops are arranged to compress the web and the forming wire between the metal belt and the supporting surface.

Long nips can be created by using metal belts simply by using the proper metal belt configuration and belt tension. Preferably, in the nip the metal belt is arranged in contact with the fibrous web and the forming wire is arranged in contact with the support surface. In other words, the web is sandwiched between the metal belt and the forming wire.

Advantageously, the metal belt is arranged to press the fibrous web from above, thereby pressing the liquid of the suspension towards a forming wire arranged below the web. In this way, gravity can be used to enhance water removal.

Preferably, the metal belt is impermeable to fluid so that the suspension cannot pass through the belt. Furthermore, preferably, the surface of the metal belt contacting the web is smooth so that a web with improved surface quality can be obtained after the web has contacted the metal belt.

Preferably, heating means are provided at the metal strip loop for heating the metal strip. Such a heating means may comprise a steam heater which utilizes steam condensation to have a very high heat transfer effect on the metal strip and create a uniform temperature distribution in the heated zone where the strip travels. Additionally, temperature control in steam heating is a well known and inexpensive process.

Advantageously, when the support surface is a roll having surface portions at which moisture leaves the forming wire, a rapid removal of moisture is facilitated. This can be achieved, for example, by means of grooved rolls or suction rolls. Additionally, a suction box may be provided at the forming wire downstream of the support surface, the suction pressure being set to hold the web on the forming wire. Here, the suction box can have a curved cover.

Preferably, the metal belt is a steel belt coated with a low-viscosity coating so that sticking of the web to the steel belt is avoided, especially when the metal belt is heated. By using such a coating, the metal strip can be heated to a higher temperature so that the increase in temperature can be used to facilitate the removal of moisture.

Significant energy savings can be achieved when the hood is arranged over or around the metal belt so that, for example, hot air drawn by the suction box can increase the temperature of the web before it is directed to the press section of the paper machine The web is preheated.

The invention also proposes a method for forming a fibrous web from a fiber-containing suspension, using a step of pressing the web and the forming wire between a metal belt and a supporting surface. In this way, the suspension is already hydraulicized out of the fiber web in the forming section, so that the water removal in the subsequent press section is simplified or made more efficient. Tests have shown that, especially for webs with a higher basis weight, very good dewatering results can be achieved, while at the same time significant energy savings can be achieved compared to the prior art solutions described above.

In this method, a metal belt is heated and then brought into contact with the fiber web. Here, the metal belt may be heated to a temperature below the boiling point of the suspension when it contacts the fiber web. By heating the web through the metal belt, the viscosity of the suspension is reduced, allowing the suspension to flow through the pores and mesh at a reduced pressure differential, thus resulting in more liquid being removed with the same available pressure differential . Therefore, the efficiency of removing liquid is improved.

Alternatively, the metal belt may be heated to a temperature higher than the boiling point of the suspension when it contacts the fibrous web. In this case, the liquid at the surface of the web where the metal belt is in contact with the web evaporates at or near the surface of the liquid. Here, the liquid generates a vapor pressure which enhances the liquid removal from the web by additionally pressing the liquid against the forming wire.

Liquid removal may be further enhanced by applying suction pressure to the forming wire at and/or downstream of the support surface.

Description of drawings

The invention is explained below by way of example of a preferred embodiment, which is shown in the drawings:

Figure 1 shows a first embodiment of the application of the invention to the forming section of a paper machine;

Figure 2 shows another embodiment of the application of the invention to the forming section of a paper machine;

Figure 3 shows a detailed view of the metal band ring configuration used in Figures 1 and 2;

Figure 4 shows a modification of the metal band ring of Figure 3;

Figure 5 shows another modification of the metal band loop of Figure 3; and

Fig. 6 shows an enlarged schematic cross-sectional view for illustrating the liquid removal mechanism.

Detailed ways

FIG. 1 shows the forming section of a paper machine with two forming wire rings 1 , 3 and a metal belt ring 2 .

Furthermore, on the right hand side in Fig. 1 is shown a transfer ring 4, this transfer fabric ring is used to transfer the web from the forming section further to a subsequent section of the paper machine, eg the press section. The transfer fabric loop 4 may comprise a felt or a belt as transfer fabric.

The forming wire loop 3 is shown on the left hand side in FIG. 1 , wherein the forming wire 31 travels past a set of guide rollers 35 in a counterclockwise direction. The forming wire 31 also passes through a forming roll 32 which is a suction roll, a suction box 33 and a blow box 34 . On the right-hand side in FIG. 1 , the forming wire ring 1 has a forming wire 11 passing in clockwise direction through several guide rolls 14 , transfer rolls 13 (which are usually suction rolls), suction rolls 12 and The suction box 15 travels. A fibrous suspension containing fibers which are later formed into paper is injected from the head box into the gap between the two forming wires 11 and 31 , as indicated by arrow 10 at the bottom of FIG. 1 . In the initial stage, the moisture in the suspension is quickly transferred to the forming roll 32 and the suction box 33 . In order to ensure that the web which has been formed on the forming wire remains on the forming wire 11, a blow box 34 is provided cooperating with the transfer roll 13, so that a pressure differential is used to ensure that the web follows the desired section (i.e. with the forming wire 11) March.

During its further travel, the web reaches the nip formed between the suction roll 12 and the metal belt 21 of the metal belt ring 2 , in particular formed between the metal belt 21 and the suction roll 12 . The metal strip 21 itself is guided by guide rollers 22 , 23 , 24 so as to run counterclockwise in FIG. 1 . A heating device 25 may be provided to heat the metal strip. The guide roll 22 is arranged to be movable inside the metal belt loop 2 in order to adjust the tension of the metal belt and thereby control the nip formed between the metal belt 21 and the suction roll 12 . Immediately after the suction roll 12 a suction box 15 is arranged.

A web (not shown) traveling on the forming wire 11 enters from the left in Figure 1 into the nip formed between the metal belt 21 and the forming wire 11, which presses the web against the forming wire. As the suction roll 12 is approached, the pressure in the nip increases, where moisture pressed from the web is quickly removed by the suction pressure applied to the web through the forming wire 11 . Arranged immediately after the suction roll 12 is a suction box 15 which exerts a negative pressure on the forming wire 11 in order to enhance the removal of moisture. The web, now prepressed, travels further with the forming wire 11 to the nip formed between the forming wire and the transfer fabric of the transfer ring 4 at the suction transfer roll 41 of the transfer ring 4 . The web is then transferred with the transfer fabric of this transfer ring 4 to subsequent parts of the paper machine.

The rectangle 25 drawn with dashed lines in FIG. 1 represents a heating device arranged together with the metal strip 21 for heating the metal strip. The heating of the metal belt 21 basically has two different possibilities; the metal belt is heated to a temperature below the boiling point of the water forming the suspension, or the metal belt is heated to a suspension (water) of the suspension used for papermaking temperature above the boiling point. In the former case, the metal belt temperature is set such that the web and the water in the web will be sufficiently heated, but the water will not be evaporated to a large extent. When the web and the suspension contained therein are heated, the viscosity of the suspension decreases. Consequently, the suspension will flow more easily through the pores of the web and of course through the openings of the forming wire, thereby enabling accelerated liquid removal. If the removal of liquid is made easier by reducing the viscosity of the suspension, then naturally a greater amount of suspension can be removed in a given time with the same pressure difference.

A special additional effect is brought about if the metal strip 21 is heated to a temperature such that the surface of the suspension boils, as will be explained with reference to FIG. 6 . It should be noted that boiling occurs only at or near the contact surface between the metal strip and the suspension; that is, the boiling of the suspension occurs only at the liquid surface.

A cross-sectional view through the nip formed between the metal belt 21 and the forming wire 11 is shown in FIG. between. The forming wire has apertures or meshes 111 through which the suspension 5 is expelled when the web W is compressed between the metal belt 21 and the forming wire 11 . The metal strip 21 has no pores and is airtight. When the metal belt is sufficiently heated in contact with the wet web W, the suspension 5 evaporates rapidly at its surface, forming a vapor cushion 6 between the web W and the metal belt 21 . The pressure of this steam pad 6 is added to the nip pressure between the metal belt 21 and the forming wire 11 , which thus provides an additional boost for the discharge of the suspension from the web W.

As can be seen in FIG. 6 , the steam cushion 6 formed between the web and the belt helps to separate the metal belt from the web, making it easier for the web to follow the further course of the forming wire 11 . In addition, this effect can be further enhanced by a coating of the metal belt 21 which prevents the web W from sticking to the belt 21 .

Returning to Figure 1, a suction box 15 arranged in the forming wire ring 1 is used to draw warm air through the web to achieve preheating of the web which improves the quality of the web in the subsequent press section. Status and processability in .

As mentioned above, the metal belt ring 2, which together with the forming wire ring 1 forms the nip through which the web passes, facilitates the removal of water or suspension in the forming section of the paper machine. Compared with known solutions with press rolls or extended nip press (extended nip press) between the web and the forming wire, the special advantage obtained by the present invention is that the nip pressure is reduced. This is especially true in the nip. Thus, the life of the forming wire is increased.

Furthermore, due to the long nip formed between the metal belt at the suction roll 12 and the forming wire, there is a considerable time for removing moisture from the web, enabling the use of less pressure at the nip. This avoids excessive pressure on the web, thereby reducing the bulk of the later paper.

Furthermore, the pressure in the initial forming rolls 32 and in the initial suction box 33 is reduced due to the high water removal capacity of this metal belt loop arrangement. Specifically, compared with the prior art which uses a high vacuum suction box at the end of the forming section which causes considerable sliding resistance between the forming wire and the suction box, when the metal belt ring is used instead of the high vacuum suction box When , the energy used to drive the mesh ring will be significantly reduced. Furthermore, the high vacuum generated by the high-performance suction box is the main energy-consuming factor, and the reduction of the required pressure difference provides a direct benefit in reducing the energy costs of the paper machine.

Figure 2 shows an alternative configuration for the forming section of a paper machine in which a metal belt configuration for moisture removal is used. Since the basic structure of the forming section including the configuration of the metal strips is the same as that of FIG. 1 , repeated descriptions of these components will be omitted here. However, since the same reference numerals denote the same elements, direct reference is made here to the description of FIG. 1 with respect to these elements. Therefore, only the differences are described in more detail.

In the forming section of Figure 2, the wire ring 3 is on the left-hand side and the wire ring 1 is on the right-hand side. The suspension from which the fibrous web is made is injected from a head box (not shown) in the direction indicated by arrow 10 . In this embodiment of the forming section, the wire loop 3 has a further guide roll 36 instead of a suction roll. On the other hand, the wire loop 1 has a suction box 16 installed immediately after the guide roll 14, where the two forming wires 11, 31 are close to each other, in order to form the initial web forming area. After passing the suction box 33 already described in detail with reference to FIG. With configuration 2. In this suction roll 17 moisture can be removed and the suction pressure further ensures that the web follows the forming wire 11 during travel. In FIG. 2 , the wet web, now on top of the forming wire 11 , enters the nip formed between the metal belt 21 and the forming wire 11 . The further progress of the web corresponds to that described in FIG. 1 .

Moreover, since the same heating means 25 are also provided in the metal belt loop 2, the same operations and advantages as previously described with reference to Figures 1 and 6 apply here as well.

Figure 3 shows details of the metal strip configuration. It should be noted that the reference numerals for the same elements are the same as those used in the above description of the forming portion with reference to FIGS. 1 and 2 . Therefore, these elements have the same function and have been explained before. In FIG. 3 , when the forming wire 11 and the metal belt 21 pass through the guide roller 23 , the web W on the forming wire 11 enters the nip formed between the forming wire 11 and the metal belt 21 .

The surface of the metal belt 21 is smooth, and the smoothness Ra is preferably less than 6.3 μm. Furthermore, as mentioned above, the metal strip is impermeable to fluids, especially water and vapour. These requirements can be met by a metal strip made of stainless steel sheet material, which can of course be coated with a suitable coating. Furthermore, surface treatments chemically reacting with the steel material or compatible with the steel on an atomic basis can be used here, as well as coatings applied to the strip surface.

The suction roll 12 is arranged such that its outer diameter crosses the line connecting the outer diameters of the guide rolls 23 , 24 , that is, the suction roll 12 pushes the metal strip 21 into the gap between the guide rolls 23 , 24 . The guide roller 22 can be adjusted as indicated by the double-pointed arrow drawn on the guide roller 22 . Adjustment of the guide rolls 22 controls the tension of the metal belt so that the pressure applied to the web and forming wire can be adjusted as the metal belt presses the web. Clean the metal strip, if necessary, by means of a water shower or a scraper (not shown).

Between the guide rolls 23 , 24 the web is clamped between the metal belt 21 and the forming wire 11 . The web is pressed continuously ensuring that it travels in a sandwich state, since the metal belt is airtight, the suspension (usually water) is only forced out through the forming wire. The smooth metal belt surface smoothes the web surface. The symmetry of the paper web is improved when the metal belt is on the other side than most of the suction boxes or suction rolls. Also, since in the (subsequent) press section the underside surface of the web is usually smoother than the upper side surface, it is preferred to smooth the upper side surface already in the forming section. As a result, a more symmetrical web can be obtained in the end.

In order to simplify liquid removal, the suction roll 12 may be a suction roll having openings for removing moisture, or may be formed as a grooved roll allowing moisture to be removed from the forming wire 11 .

The suction box 15 shown is arranged facing the part of the forming wire loop 1 where the web and forming wire are about to leave the metal belt, i.e. at the position where the metal belt follows the guide rolls 24, while the web and the forming wire are facing towards The lower guide rollers 14 (see FIGS. 1 and 2 ) travel. The suction boxes 15 provide negative pressure on the web surface facing the forming wire 11 and thus help to separate the web from the metal belt 21 and of course to advance the web towards the transfer belt of the transfer ring 4 .

Furthermore, the reference numeral 26 in FIG. 3 designates a hood or casing which is placed over the metal strip arrangement 2 . The hood is a hood that insulates the metal strip to prevent heat loss, enabling a more energy efficient configuration of the heated metal strip. In addition to reducing suction pressure in the initial forming part of the forming section, reducing negative pressure and reducing frictional losses, the hood 26 also contributes to improving the energy balance of the paper machine. The hot air from this hood can be passed to heat exchangers or other heat consumers in the paper or board machine, if required. Moreover, the hood also has noise reduction and protection functions, thus further improving the forming part. The hood is preferably designed to prevent moisture and/or fiber dust generated by the forming section from entering the interior of the metal belt loop.

Figure 4 shows some modifications at the nip formed between the metal belt and the forming wire. Below the forming wire 11 , a suction box 18 is arranged which overlaps the part where the wet web starts to be sandwiched between the forming wire 11 and the metal belt 21 .

In particular, the suction box 18 is arranged to overlap the position where the metal belt 21 guided by the guide roller 23 contacts the web. At the beginning of the nip, a maximum immediate removal of moisture, which is then carried away by the suction box 18, is observed. Since the suction box 18 only removes free liquid, the suction pressure can be low so that when the suction box contacts the forming wire 11 there is no significant increase in wear and friction losses. Furthermore, opposite the suction zone 125 of the suction roll 12 , a pressure or pressing device 27 is arranged, which may be a hydraulic (water and/or steam) pressing element pressing the metal strip towards the suction roll 12 . The pressing medium, such as hot water or steam, then transfers heat to the web, preferably via the metal belt, thereby further improving the dewatering capacity or efficiency. Alternatively, the pressing arrangement may be a mechanical pressing element, such as a roller. With such a press arrangement, it is possible to control the pressure distribution in the nip, if desired, so as to achieve moisture removal during a predetermined portion of the web travel. Preferably, the pressing device is arranged close to or at the end of the metal strip nip.

Finally, a further suction box 15 is arranged overlapping the opening of the nip, ie at the point where the web separates from the metal belt to remain on the forming wire 11 . With such superimposed suction boxes, it has been possible to generate a negative pressure on one side of the forming wire, so that the web control is more reliable, ie with a lower pressure difference, precise web control has been achieved.

FIG. 5 shows another variant of the nip formed between the metal belt ring 2 , in particular the metal belt, and the forming wire. Below the forming wire 11, a suction roll 12 is arranged, which has a special configuration such as a suction chamber 125 or an effective suction area.

The suction roll chamber 125, or its respective suction zone, is arranged to extend substantially beyond the metal belt, ensuring that the web is retained on the wire surface, the suction chamber also directs removed moisture away from the wire and web. The suction box 15 of Figures 3 and 4 can be used with this arrangement.

The forming section according to the invention can be applied to new paper or board machines, and can also be integrated into existing machines in so-called retooling. Tests have shown that excellent dewatering results can be achieved with the following parameters in a paper machine:

Metal strip temperature: 20°C to 180°C

Metal strip tension: 50kN/m to 200kN/m (bandwidth along CD direction)

Diameter of suction roll (120): 1000mm to 2000mm

Diameter of guide rollers (22, 23, 24): 600mm to 2000mm

Pressure in the pressure zone: 0.05MPa to 0.3MPa

Squeeze configuration (27) increased to 1MPa

It should be noted that the invention is described with reference to a paper machine. Of course, the invention can be applied to board machines, or other machines that make paper webs from fibrous suspensions and require removal of water or suspension from the fibrous suspensions.

Claims (16)

1. forming section that forms fiber web (W), described forming section comprises:

Forming net ring (1) forms fiber web (W) by fibre-bearing suspended matter (10) thereon; And

Ferrule (2), its described fiber web (W) and forming net (11) that is arranged between impermeable metal tape of convection cell (21) and the stayed surface (12) squeezes.

2. forming section according to claim 1, wherein, described metal tape (21) is level and smooth, and is arranged to contact described fiber web (W), and described forming net (11) is arranged to contact described stayed surface (12).

3. according to claim 1 and/or 2 described forming sections, wherein, described metal tape (21) is arranged to squeeze from the top described fiber web (W), thereby the liquid (5) of described suspended matter (10) is pressed to the described forming net (11) of the below that is arranged in described width of cloth material (W).

4. according to claim 1,2 and/or 3 described forming sections, wherein, locate to be furnished with heating tool (25), be used to heat described metal tape (21) at described ferrule (2).

5. according to each described forming section in the claim 1 to 4, wherein, described stayed surface is the roller (12) with surface portion, leaves described forming net (11) from the liquid (5) of described suspended matter (10) in described surface element office.

6. forming section according to claim 5, wherein, described stayed surface is fluted roller or suction roll (12).

7. according to each described forming section in the aforementioned claim, wherein, at the downstream part of described stayed surface (12), on forming net (11), be provided with suction box (15), wherein swabbing pressure is set to described width of cloth material (W) is remained on the described forming net (11).

8. forming section according to claim 7, wherein, described suction box (15) has the arc lid.

9. according to each described forming section in the aforementioned claim, wherein, described metal tape (21) is the steel band that is coated with the low-viscosity coating.

10. according to each described forming section in the aforementioned claim, wherein, in the top of described metal tape (21) or be provided with hood (26) on every side.

11. paper machine or board machine, it comprises according to each described forming section in the aforementioned claim 1 to 10.

12. form the method for fiber web (W) by fibre-bearing suspended matter (10), described method comprises squeezes fiber web (W) between metal tape (21) and the stayed surface (12) and forming net (11), so that suspension (5) is extruded the step of fiber web (W).

13. method according to claim 12 also comprises heating described metal tape (21) and makes heated described metal tape (21) contact the step of described fiber web (W).

14., be included in also that described stayed surface (12) is located and/or the downstream of described stayed surface (12) is applied to swabbing pressure the step of described forming net (11) according to claim 12 or 13 described methods.

15. method according to claim 13, wherein, when described metal tape (21) contacted described fiber web (W), described metal tape (21) was heated to the following temperature of boiling point with described suspension (5).

16. method according to claim 13, wherein, when described metal tape (21) contacted described fiber web (W), described metal tape (21) was heated to the high temperature of boiling point that has than suspension (5).

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