Patent Grant
11220785
This application is a National Stage Application, filed under 35 U.S.C. 371, of International Application No. PCT/SE2019/050822, filed Sep. 3, 2019, which international application claims priority to and the benefit of Swedish (SE) Application No. 1851245-9, filed Oct. 12, 2018; the contents of both of which as are hereby incorporated by reference in their entireties.
The present invention relates to a tissue paper making machine and to a method of operating a tissue paper making machine.
In tissue paper making machines, a fibrous web formed in the forming section is typically carried by a carrier fabric to a Yankee drying cylinder where the fibrous web is transferred to the surface of the Yankee drying cylinder. The transfer to the Yankee drying cylinder is typically made in a transfer nip which often also serves as a dewatering nip. An example of such a tissue paper making machine is disclosed in U.S. Pat. No. 6,998,022. It has also been proposed that a shoe roll be used in the transfer nip such that the web is transferred to the Yankee drying cylinder in a nip between a shoe roll and the Yankee drying cylinder. An example of such a tissue paper making machine is disclosed in, for example, U.S. Pat. No. 5,393,384. With reference to FIG. 7 of U.S. Pat. No. 5,393,384, an embodiment is disclosed in which a water-impermeable belt 2 carries a paper web to a nip formed between a “shoe press” and a “tissue drying cylinder” 20. Another example of such a machine is disclosed in European patent No. 926 296 which discloses how a fibrous web is transported by a felt 5 to a nip between a shoe press unit 2 and a tissue drying cylinder 3. The nip between the shoe press unit and the tissue drying cylinder is preceded by a suction roll 6 that is said to remove water from the felt and possibly also from the fibrous web. It is further stated that, thanks to the action of the suction roll, the ability of the felt to receive water is increased significantly such that it can receive water in the press nip. It is stated that this has the effect that the dewatering becomes so much intense that only one press nip is sufficient.
While the use of a suction roll prior to the nip against the Yankee drying cylinder may increase dewatering to such an extent that only one dewatering press nip is sufficient, the use of a suction roll also has some disadvantages. A suction roll requires energy and increases the cost of operating the machine. Moreover, a suction roll contributes to generating noise.
Another example of a tissue paper making machine with a shoe press nip against a tissue drying cylinder is disclosed in U.S. Pat. No. 6,004,429. That patent discloses a machine in which a press roll 28 that is embodied as a shoe press roll is arranged to form a main press 30 with a drying cylinder 60. The main press 30 is preceded by a pre-press formed by a grooved bottom roll 38 and a shoe press roll 40 with a press shoe and a smooth, impermeable flexible press jacket. A felt 12 travels via the pre-press to the main press 30. It is stated that, with this arrangement, a suction roll becomes unnecessary. In the FIG. 1 and FIG. 4 of U.S. Pat. No. 6,004,429, the felt that passes through the pre-press is shown as going directly to the main press 30 without first passing a suction roll. It is stated that the felt 12 winds around the shoe press roll 28 of the main press 30 by more than 45°. It is furthermore stated that the press jacket should be supported from the inside. To provide support from the inside of the press jacket, U.S. Pat. No. 6,004,429 suggests that the press jacket be supported from the inside by small support rolls 86 and FIG. 4 of the '429 patent shows how support rolls 86 are placed on the inside of the press jacket 84. It is stated that it is advantageous if the angular distance between the support rolls in the circumferential direction lies in the range from approximately 7.5 degrees to approximately 15 degrees.
It is an object of the present invention to provide a tissue paper making machine which uses a shoe roll to form a transfer nip against a Yankee drying cylinder and which can operate effectively and achieve a reliable web transfer to the Yankee drying cylinder.
The invention relates to a tissue paper making machine. The inventive tissue paper making machine comprises a forming section and a Yankee drying cylinder A shoe roll is arranged to form a nip with the Yankee drying cylinder. The nip between the shoe roll and the Yankee drying cylinder may be a dewatering nip but it may also be arranged to function as substantially only a pure transfer nip in which a fibrous web is transferred to the outer surface of the Yankee drying cylinder. The shoe roll has a shoe arranged to act against the Yankee drying cylinder in the nip formed between the shoe roll and the Yankee drying cylinder. The shoe roll further comprises a flexible tubular belt that forms a loop around the shoe and which also forms an outer circumference of the shoe roll. The nip between the shoe roll and the Yankee drying cylinder has a maximum extension from an entry point of the nip to an exit point of the nip. A carrier fabric is arranged to be capable of carrying a fibrous web from the forming section to the nip formed between the Yankee drying cylinder and the shoe roll and pass through the nip between the Yankee drying cylinder and the shoe roll together with the fibrous web. The carrier fabric is arranged to reach the outer circumference of the shoe roll at a first contact point such that the carrier fabric will wrap a part of the outer circumference of the shoe roll over an area stretching from the first contact point to the nip. The shoe roll further comprises a mechanical support located inside the loop of the flexible tubular belt and the mechanical support is placed to support the flexible tubular belt in at least a part of the area between the first contact point and the nip between the Yankee drying cylinder and the shoe roll. According to the invention, the carrier fabric wraps the outer circumference of the shoe roll in the area stretching from the first contact point by an angle which is greater than 80°. The shoe roll that forms a nip with the Yankee drying cylinder has axial ends connected to end walls such that the end walls and the flexible tubular belt define an enclosed space such that the shoe roll is an enclosed shoe roll. The paper making machine also comprises a source of pressurized air that can communicate with the enclosed space such that the enclosed space can be filled with pressurized air from the source of pressurized air. The carrier fabric is under tension and the tension in the carrier fabric lies in the range of 3.0 kN/m-5.0 kN/m, preferably in the range of 3.2 kN/m-5.0 kN/m and even more preferred in the range of 3.5 kN/m-5.0 kN/m. Furthermore, the mechanical support is arranged to support the flexible tubular belt in the area from the first contact point to the nip over an angle that is more than 90° and in the mechanical support ends at a point which, in the circumferential direction of the shoe roll, is closer to the entry point of the nip than to the exit point of the nip. At the maximum extension of the nip, the point at which the mechanical support ends is at an angular distance from the entry point of the nip which is at least 8° and preferably 10°-20°.
In preferred embodiments of the invention, the carrier fabric wraps the outer circumference of the shoe roll in an area stretching from the first contact point by an angle which is in the range of 100°-280° and preferably by an angle which is in the range of 100°-200° and even more preferred by an angle which is in the range of 120°-180°. However, embodiments are conceivable in which the wrap angle has other values. For example, embodiments are conceivable in which the wrap angle is only 95°.
In advantageous embodiments of the invention, the shoe is deformable such that the shape of a surface of the shoe that faces the Yankee drying cylinder in the nip between the Yankee drying cylinder and the shoe roll can adapt to match the outer surface of the Yankee drying cylinder. However, embodiments of the invention are conceivable in which the shoe is a substantially rigid element that cannot deform to adapt itself to the outer surface of the Yankee drying surface.
In preferred embodiments of the invention, at least one applicator for a lubricant, for example lubricant oil, is located inside the flexible tubular belt and arranged to be capable of applying a lubricant to an interior surface of the flexible tubular belt. Embodiments without a lubricant applicator are conceivable, for example if the interior surface are coated with a coating selected to reduce friction or if it is decided that a high degree of wear is acceptable, but the preferred solution is to use a lubricant applicator.
If an applicator for a lubricant is used, a trough may optionally be placed adjacent the shoe in an area which, in the circumferential direction of the shoe roll, lies between the entry point of the nip and the mechanical support such that lubricant fluid that enters the nip and is pressed backwards out of the nip can be collected in the trough.
In one advantageous embodiment of the inventive tissue paper making machine, the layout of the machine may be as follows. The forming section comprises a first forming fabric that is arranged to run in a loop supported by guide elements. The carrier fabric is a water-receiving felt which is used in the forming section as a second forming fabric that is arranged to run in a loop supported by guide elements and to carry the fibrous web from the forming section to the nip formed between the shoe roll and the Yankee drying cylinder. In this embodiment, the first forming fabric and the carrier fabric are so arranged in relation to each other that the two fabrics converge towards each other to form an inlet gap into which stock can be injected. The forming section comprises a head box that is arranged to inject stock into the inlet gap. A forming roll is arranged within the loop of the carrier fabric and is arranged to guide the carrier fabric into the inlet gap. The forming roll is also arranged to guide the carrier fabric and the first forming fabric along a part of their path which is common to both the carrier fabric and the first forming fabric and which begins at the inlet gap. In this embodiment of the invention, the forming roll comprises a flexible sleeve which is arranged to run in a loop around an axis of rotation that extends in a direction perpendicular to the direction in which the carrier fabric and the first forming fabric are arranged to run. The forming roll further comprises a support ledge located inside the loop of the flexible sleeve and extending in a direction parallel to the axis of rotation of the flexible sleeve. The support ledge is arranged to be capable of pressing the flexible sleeve in a direction outwards away from the axis of rotation of the flexible sleeve in an area along the loop in which the flexible sleeve is arranged to run such that, in the area in which the flexible sleeve is pressed outwards by the support ledge, the flexible sleeve is caused to follow a path with a radius of curvature which is smaller than the radius of curvature of the flexible sleeve outside the area in which the support ledge contacts the flexible sleeve.
In embodiments using a forming roll with a flexible sleeve and a support ledge, the radius of the forming roll in areas not in contact with the support ledge may be in the range of 500 mm-1600 mm and the smallest radius of the support ledge may be in the range of 40 mm-100 mm, preferably in the range of 45-80 mm and even more preferred in the range of 50 mm-75 mm.
In an alternative embodiment of the inventive tissue paper making machine, the layout of the machine may be as follows. The forming section comprises a first forming fabric arranged to run in a loop supported by guide elements and a second forming fabric which is likewise arranged to run in a loop supported by guide elements. In this embodiment, the carrier fabric is not used as a forming fabric but a fabric separate from the carrier fabric us used as a second forming fabric. The second forming fabric in this embodiment is a water-receiving felt and arranged so in relation to the first forming fabric that the two forming fabrics converge towards each other to form an inlet gap into which stock can be injected. A head box is arranged to inject stock into the inlet gap and a forming roll is arranged within the loop of the second forming fabric. In this embodiment of the invention, the tissue paper making machine comprises a pre-press that has an extended nip roll and a counter roll that forms a dewatering nip with the extended nip roll. The extended nip roll comprises a pressure shoe and a flexible jacket that loops the pressure shoe. The second forming fabric is arranged carry the fibrous web to the dewatering nip that is formed between the extended nip roll and the counter roll and to pass through the dewatering nip together with the fibrous web. The carrier fabric is arranged to pass through the dewatering nip and to carry the fibrous web from the dewatering nip to the nip formed between the shoe roll and the Yankee drying cylinder such that the fibrous web is transferred to the surface of the Yankee drying cylinder. In this embodiment, it is also so that the carrier fabric is a fabric that does not absorb water such that the nip between the shoe roll and the Yankee drying cylinder is a non-dewatering nip.
In the embodiment using a pre-press, the carrier fabric may be a water permeable structured fabric capable of imparting a three-dimensional structure onto the fibrous web as the carrier fabric passes through a nip. Alternatively, it may be a water impermeable belt which has a structured surface arranged to face the fibrous web such that a three-dimensional structure can be imparted onto the fibrous web as the carrier fabric passes through a nip. However, if the carrier fabric is a water impermeable belt, it may alternatively have a smooth surface that is arranged to face the fibrous web.
The invention also relates to a method of operating the inventive tissue paper making machine. According to the inventive method, the carrier fabric is caused to run at a speed in the range of 1500 m/s-2300 m/s.
The method may also comprise the step of feeding pressurized air to the enclosed space such that the enclosed space is kept at an overpressure in the range of 60 millibar-140 millibar, preferably in the range of 60 millibar-100 millibar.
Reference will first be made to
The suction roll 54 thus serves two important function. However, suction rolls consume much energy and contribute to increasing the noise around the paper making machine. Moreover, the suction roll 54 also requires extra space, especially if it is used for guiding the path of the carrier fabric 10 since it must be placed at a suitable distance from the nip N between the shoe roll 4 and the Yankee drying cylinder 3. Therefore, it would be desirable to be able to use a layout without such a suction roll 54 before the nip N against the Yankee drying cylinder. In an alternative layout, without the suction roll 54, the carrier fabric would instead wrap a significant part of the circumference of the shoe roll 4.
Reference will now be made to
In the layout according to
To ensure that the flexible tubular belt 9 of a shoe press retains a correct form, shoe rolls may be designed such that the flexible tubular belt 9 has axial ends that are connected to end walls such that the end walls and the flexible tubular belt define an enclosed space. A source of pressurized air can then be connected to the shoe roll 4 and communicate with the enclosed space such that such that the enclosed space can be filled with pressurized air. In this way, the shoe roll 4 can be kept inflated in a way similar to how a balloon is inflated. An example of such a solution is disclosed in, for example, U.S. Pat. No. 5,084,137 and it is suggested in that document that the overpressure should be kept in the range of about 0.03-0.1 bars. Shoe rolls using the same or substantially the same solution for pressurizing the enclosed space as disclosed in U.S. Pat. No. 5,084,137 have also been sold to and used by many paper mills.
Keeping an enclosed space inside the shoe roll 4 can thus contribute to keeping the flexible tubular belt 9 in shape as is known by those skilled in the art of paper making.
However, in order to achieve a correct pressing procedure, it is also desirable that the carrier fabric 10 is kept at a certain level of tension. If the carrier fabric 10 that carries the fibrous web W to the nip N between the shoe roll 4 and the Yankee drying cylinder 3 is not under sufficient tension, there is a risk that the small wrinkles are formed on carrier fabric 10 and the fibrous web W pass through the nip N in a wrinkled state. The wrinkles do not have to be very large to produce adverse effects both on the actual pressing and on the transfer of the fibrous web W to the surface of the Yankee drying cylinder 3.
The inventors of the present invention have found that, in order to achieve a good transfer to the surface of the Yankee drying cylinder 3, the carrier fabric 10 needs to be kept at a tension of at least 3.0 kN/m and preferably at least 3.2 kN/m. Generally, tension levels higher than 3.0 kN/m are advantageous but tension levels higher than 5.0 kN/m are less desirable since most fabrics used in paper machinery tend to be worn out too quickly at levels higher than 5.0 kN/m are used. A suitable tension for the carrier fabric 10 will then normally be restricted to the range of 3.0 kN/m-5.0 kN/m.
The inventors have also found that, at tension levels in the range of 3.0 kN/m-5.0 kN/m, inflation of the shoe roll 4 is insufficient to prevent substantial deformation of the flexible tubular belt 9 that loops the shoe 6. In theory, it would be possible to simply increase the internal pressure inside the shoe roll 4 by feeding more compressed air into the enclosed space inside the shoe roll 4 and thereby preserve the shape of the shoe roll 4. However, increasing the internal pressure inside the shoe roll 4 above a certain level would lead to other undesirable effects. For example, the attachment/securement of the axial ends of the flexible tubular belt 9 to the end walls may give way such that the flexible tubular belt 9 was detached from the end walls which would cause the shoe roll 4 to collapse. The inventors have found that the internal overpressure in the enclosed space of the shoe roll 4 should be kept in the range of 0.04-0.12 bars, preferably in the range of 0.06-0.10 bars. If the overpressure in the enclosed space is lower than 0.04 bars, evacuation of lubricant fluid from the shoe roll 4 becomes more difficult (the overpressure in the enclosed space assists in evacuating lubricants from the enclosed space of the shoe roll). If the overpressure exceeds 0.12 bars, the risk that the flexible tubular belt 9 will come loose from its attachment to the end walls becomes too large.
The inventors have found that, when the carrier fabric 10 is kept at a tension of 3.0 kN or more, an internal overpressure in the shoe roll 4 of 0.12 bars is insufficient to retain a desired shape of the flexible tubular belt 9. Therefore, the inventors have concluded that an internal support is necessary in the region where the carrier fabric 10 wraps the outer circumference of the shoe roll 4.
One embodiment of the inventive tissue paper making machine 1 will now be explained with reference to
As can be seen in
Optionally, the paper making machine 1 is provided with a Yankee drying hood 47. The Yankee drying hood 47—if one is used—may be of such a design as disclosed in, for example, WO 2016/169915 A1 or U.S. Pat. No. 5,416,979 but many other designs of a Yankee drying hood 47 are conceivable.
The head box 32 used in the inventive machine may be, for example, such a head box as disclosed in EP 0 719 360 B1 but any kind of head box suitable for a tissue paper making machine may be used.
As can be seen in
With reference to
Embodiments are conceivable in which the shoe 6 of the shoe roll 4 is a substantially rigid shoe that can be made of a metallic material such as, for example, steel, aluminum or bronze. Such a shoe has a surface which, in the nip N against the Yankee drying cylinder 3, faces the Yankee drying cylinder 3 and is concave such that its shape matches the convex outer surface 48 of the Yankee drying cylinder (taking into account the thickness of the flexible tubular belt 9, the thickness of the carrier fabric 10 and the thickness of the fibrous web W). However, in preferred embodiments of the invention, the shoe 6 is deformable such that the shape of a surface of the shoe that faces the Yankee drying cylinder in the nip between the Yankee drying cylinder and the shoe roll can adapt to match the outer surface of the Yankee drying cylinder. Shoe rolls with such a shoe that can deform to match its shape to a counter roll (such as a Yankee drying cylinder) have been disclosed in, for example, U.S. Pat. No. 7,527,708. The shoe 6 and the means for pressing the shoe against a counter roll such as a Yankee drying cylinder may be designed as disclosed in U.S. Pat. No. 7,527,708 but other solutions are also possible. Another possible design of a shoe and means for pressing the shoe against a counter roll such as a Yankee drying cylinder is also disclosed in EP 2085513 B1 and such a solution could be used also in the present invention.
A carrier fabric 10 is arranged to be capable of carrying a fibrous web W from the forming section 2 to the nip formed between the Yankee drying cylinder 3 and the shoe roll 4 and pass through the nip between the Yankee drying cylinder 3 and the shoe roll 4 together with the fibrous web W. In the embodiment shown in
The carrier fabric 10 is kept at a tension that lies in the range of 3.0 kN/m-5.0 kN/m in order to secure a reliable web transfer to the outer surface 48 of the Yankee drying cylinder 3. Preferably the carrier fabric 10 is kept at a tension that lies in the range of 3.2 kN/m-5.0 kN/m and even more preferred in the range of 3.5 kN/m-5.0 kN/m.
With reference to
The shoe roll 4 further comprises a mechanical support 12 located inside the loop of the flexible tubular belt 9 which mechanical support 12 is placed to support the flexible tubular belt 9 in at least a part of the area between the first contact point 11 and the nip N between the Yankee drying cylinder 3 and the shoe roll 4. According to the invention, the carrier fabric 11 wraps the outer circumference of the shoe roll 4 in the area stretching from the first contact point 11 by an angle which is greater than 80°. The inventors have found that, in order to ensure that the flexible tubular belt retains its shape even when the carrier fabric is kept at a tension which is 3.0 kN/m or higher, the mechanical support 12 must give support to the flexible tubular belt 9 in the area from the first contact point 11 to the nip N over an angle that is more than 90 and the mechanical support is thus arranged to do this. However, the inventors have also determined that the mechanical support 12 should end at a certain distance from the entry to the nip N in order to ensure that the flexible tubular belt 9 is free to adapt to the change of geometry at the entry to the nip N. Therefore, the mechanical support 12 is shaped such that it ends at a point 13 which, in the circumferential direction of the shoe roll 4, is closer to the entry point 7 of the nip than to the exit point 8 of the nip and which, for the maximum extension of the nip, is at an angular distance from the entry point 7 of the nip which is at least 8° and preferably 10°-20° but not more than 30°, preferably not more than 25°.
Depending on where the entry point 11 is located, i.e. the point at which the carrier fabric 10 first reaches the shoe roll 4, the mechanical support 12 may be so designed and so placed within the shoe roll 4 that it supports the flexible tubular belt 9 over an angle that is much larger than 80°. For example, it may be designed such that it supports the flexible tubular belt 9 over an angle that is 110°, 120° or even 180°. However, it may often be desirable that the layout of the machine 1 is such that the carrier fabric 10 travels along a substantially horizontal path to the shoe roll 4. The first contact point 11 will then be located at the vertically lowest point on the circumference of the shoe roll 4. In many realistic embodiments, the mechanical support 12 may then be designed and arranged to support the flexible tubular belt 9 over an angle in the range of 95°-120° or 100°-115°.
In advantageous embodiments, a trough 24 may optionally be placed adjacent the shoe 6 in an area which, in the circumferential direction of the shoe roll 4, lies between the entry point of the nip 7 and the mechanical support 12 such that lubricant fluid that enters the nip and is pressed backwards out of the nip can be collected in the trough 24. By ending the mechanical support 12 at a certain distance from the nip N, it also becomes easier to fit a trough 25 adjacent the shoe 6 to collect a lubricant (for example a lubricant oil) that has been pressed out of the nip N.
The mechanical support 12 may comprise a guide shoe that is curved to correspond to the radius of curvature of the flexible tubular belt, i.e. to match the curvature of the flexible tubular belt such that the flexible tubular belt 9 can glide on the mechanical support 12. With reference to
With reference to
A mechanical support 12 having one or several curved shoes may be designed such that the shoe (or shoes) has (have) an initial part 14 that is curved away from the inner surface 22 of the flexible tubular belt 9. In this way, the flexible tubular belt 9 can meet the mechanical support 12 gradually such that there is no risk of a sudden impact that might damage the flexible tubular belt.
In preferred embodiments of the invention, the carrier fabric 10 wraps the outer circumference of the shoe roll in an area stretching from the first contact point by an angle which is in the range of 100°-280° and preferably by an angle which is in the range of 100°-200° and even more preferred by an angle which is in the range of 120°-180°.
In preferred embodiments of the invention, at least one applicator 21 for lubricant is located inside the flexible tubular belt 9 and arranged to be capable of applying a lubricant to an interior surface 22 of the flexible tubular belt 9.
In order for the paper making machine 1 to achieve a high dryness without using more heat energy for evaporation, it is desirable that the dryness of the fibrous web W that reaches the nip N between the shoe roll 4 and the Yankee drying cylinder 3 already has a certain dryness, even when a suction roll is not used before the nip N with the shoe roil 4. Therefore, in preferred embodiments of the invention, the machine 1 should be designed such that a reasonably high dryness can be achieved before the nip N between the shoe roll 4 and the Yankee drying cylinder 3 even though no suction roll is used.
A possible embodiment of the inventive machine will now be described with reference to
With reference to
The function of the forming roll 33 according to the embodiment of
Reference will now be made to
In
The support ledge 36 is arranged to be capable of pressing the flexible sleeve 35 in a direction outwards away from the axis of rotation A of the flexible sleeve 35 in an area along the loop in which the flexible sleeve 35 is arranged to run. This has the result that, in the area in which the flexible sleeve 35 is pressed outwards by the support ledge 36, the flexible sleeve 35 is caused to follow a path with a radius of curvature which is smaller than the radius of curvature of the flexible sleeve 35 outside the area in which the support ledge 36 contacts the flexible sleeve 35.
In the embodiment of
The flexible sleeve 35 is preferably impermeable to water but embodiments are conceivable in which the flexible sleeve is permeable to water. If the flexible sleeve 35 is impermeable to water, which it preferably is, this assists in making the water in the stock pass out through the first forming fabric 28.
From the above description, those skilled in the art to which the invention pertains will now understand that the forming roll 33 with the flexible sleeve 35 is substantially similar to a shoe press unit such as a shoe press roll. Such units are sold commercially under such trade names as SymBelt™ shoe press or NipcoFlex shoe press and have been described in many patent publications, for example in U.S. Pat. No. 7,387,710 or 5,662,777. The support ledge 36 could alternatively be termed “shoe” since it is placed in the position where a shoe would be placed in a shoe press unit. However, while the support ledge 36 of the forming roll 33 is used in connection with dewatering while a certain pressure is applied as the first forming fabric 28 and the carrier fabric 10 pass over the support ledge 36, the purpose of the support ledge 36 differs from that of a shoe in a shoe press as will be explained in the following.
Since the support ledge 36 is capable of pressing the flexible sleeve 35 outwards, it can achieve the effect that, over a part of the circumference of the flexible sleeve 35, the radius becomes smaller. Over that part of the circumference of the flexible sleeve 35, the pressure to which the stock is subjected will rise and have a peak that it would otherwise not have. The support ledge 36 is arranged to or capable of pressing the flexible sleeve 35 out from the path it follows at those parts of its circumference where it does not pass over the support ledge 36. As the support ledge 36 does this, it forces the flexible sleeve 35, the forming fabric 28 and the carrier fabric 10 to follow a path where the radius over which the fabrics 28, 10 pass is actually smaller than what is the case at other points along the circumference of the flexible sleeve 35. As a result, the pressure to which the stock is subjected increases as the fabrics 28, 10 pass over that part of the forming roll 33 where the support ledge 36 is acting.
With reference to
In some embodiments, the support ledge 36 can be arranged in a fixed position such that the amount to which the flexible sleeve 35 is pressed outwards by the support ledge 36 is constant. For example, the support ledge 36 may be directly supported by or integral with a support beam 50 located inside the loop of the flexible sleeve 35 and remain fixed in position in relation to the support beam 50.
Instead of a support ledge 36 that is held in a fixed position, it could be so that at least a part of the support ledge 36 is arranged to be movable towards or away from the axis of rotation A of the flexible sleeve 35 such that the amount to which the flexible sleeve 35 is pressed outwards by the support ledge 36 can be varied. Possible embodiments of such an arrangement will now be explained with reference to
It should be understood that the actuator (or actuators) 57 of
With continued reference to
Reference will now be made only to
The radius of the forming roll 33 in areas not in contact with the support ledge 36 may be in the range of 500 mm-1600 mm and the smallest radius of the support ledge 36 may be in the range of 40 mm-100 mm, preferably in the range of 45-80 mm and even more preferred in the range of 50 mm-75 mm.
With reference to
An alternative embodiment of the inventive paper making machine 1 will now be explained with reference to
In the embodiment of
The pressure in the pre-press 40 is preferably set to a low level that does not entail any significant risk that the fibrous web W will be crushed. This means that dewatering in the pre-press 40 will not be so large but the dryness of the fibrous web W may still be increased to an acceptable level.
In the embodiment of
Alternatively, the carrier fabric 10 in the embodiment of
In yet another alternative embodiment, the carrier fabric 10 in the embodiment of
The carrier fabric in the embodiment of
In the embodiments of
The invention may also be understood in terms of a method in which the inventive paper making machine is operated to produce tissue paper. In operation, the machine speed is suitably selected such that the carrier fabric 10 is running at a speed in the range of 1500 m/s-2300 m/s. During operation, the tension in the carrier fabric may be monitored and controlled such that the tension in the carrier fabric remain within the range of 3.0 kN/m-5.0 kN/m.
During operation, the method preferably comprises feeding pressurized air to the enclosed space 19 of the shoe rill 4 such that the enclosed space 19 is kept at an overpressure in the range of 60 millibar-100 millibar.
Thanks to the invention, a good transfer to the smooth surface 48 of the Yankee drying cylinder 3 can be achieved since the carrier fabric 10 has a sufficient tension which is possible due to the mechanical support 12 without the use of which the flexible tubular belt 9 would not be able to retain its shape. An added advantage is that, since the carrier fabric can wrap a large angle of the shoe roll 4, it is not necessary to guide the carrier fabric 10 and the fibrous web W over a turning roll (such as a suction turning roll) before the shoe roll 4 in order to guide the carrier fabric to the nep against the Yankee drying cylinder 3. This is of importance where available space is limited.
If other dewatering steps are taken before the fibrous web W reaches the Yankee drying cylinder, for example if more effective dewatering is achieved in the forming section 2, it is possible to avoid using a suction roll before the nipa against the Yankee drying cylinder.
While the invention has been described above in terms of a paper making machine and a method, it should be understood that these categories only reflect different aspects of one and the same invention. The method may thus comprise such steps that would inevitably follow from using various embodiments of the inventive machine, regardless of whether such steps have been mentioned explicitly or not. In the same way, the inventive machine may comprise means for performing any step of the method, regardless of whether such steps have been mentioned explicitly or not.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1851245-9 | Oct 2018 | SE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/SE2019/050822 | 9/3/2019 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2020/076204 | 4/16/2020 | WO | A |
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