阅读说明：本技术 用于制造绵纸的机器和方法 (Machine and method for making tissue paper ) 是由 A·菲利皮 D·迪·维塔 于 2019-01-10 设计创作，主要内容包括：一种机器(10)包括扬克式烘缸(35),所述扬克式烘缸(35)具有围绕其轴线(35A)旋转的圆柱形侧表面(35S)；以及连续的柔性构件(17),所述连续的柔性构件(17)包括第一表面(17A)以及与所述第一表面(17A)相对的第二表面(17B),所述第一表面(17A)适合于接收包括纤维素纤维和水的纤维素纸浆层(S)。还设置引导辊(31),所述连续的柔性构件(17)被围绕所述引导辊(31)驱动。所述连续的柔性构件(17)的第二表面(17B)与所述第一引导辊(31)接触。所述机器进一步包括相对于所述纤维素纸浆层(S)的进给方向布置于所述引导辊(31)的下游的第一压力辊(33),所述连续的柔性构件(17)被围绕所述第一压力辊(33)驱动。所述第一压力辊(33)和所述扬克式烘缸(35)限定第一压力辊隙(34),在所述第一压力辊隙(34)内部,通过所述第一压力辊(33)将所述连续的柔性构件(17)压靠在所述扬克式烘缸(35)的圆柱形表面(35S)上,以便通过所述连续的柔性构件(17)从所述纤维素纸浆层(S)移除水。(A machine (10) comprising a yankee cylinder (35), said yankee cylinder (35) having a cylindrical lateral surface (35S) rotating about its axis (35A); and a continuous flexible member (17), the continuous flexible member (17) comprising a first surface (17A) and a second surface (17B) opposite the first surface (17A), the first surface (17A) being adapted to receive a cellulose pulp layer (S) comprising cellulose fibres and water. A guide roller (31) is also provided, the continuous flexible member (17) being driven around the guide roller (31). The second surface (17B) of the continuous flexible member (17) is in contact with the first guide roller (31). The machine further comprises a first pressure roller (33) arranged downstream of the guide roller (31) with respect to the feeding direction of the layer (S) of cellulose pulp, the continuous flexible member (17) being driven around the first pressure roller (33). The first pressure roller (33) and the yankee dryer (35) define a first pressure nip (34), inside which first pressure nip (34) the continuous flexible member (17) is pressed against the cylindrical surface (35S) of the yankee dryer (35) by the first pressure roller (33) in order to remove water from the cellulose pulp layer (S) by the continuous flexible member (17).)

1. A machine (10) for the wet-laid manufacture of tissue paper comprising, in combination:

-a yankee cylinder (35), said yankee cylinder (35) comprising a cylindrical lateral surface (35S) rotating about its axis (35A);

a continuous flexible member (17), said continuous flexible member (17) comprising a first surface (17A) and a second surface (17B) opposite to said first surface (17A), said first surface (17A) being adapted to receive a cellulose pulp layer (S) comprising cellulose fibres and water;

a guide roller (31), the continuous flexible member (17) being driven around the guide roller (31); wherein a second surface (17B) of the continuous flexible member (17) is in contact with the first guide roller (31); wherein a first surface (17A) of the continuous flexible member (17) is spaced from the Yankee dryer (35) in an area guided around the guide roll (31); and the guide roll (31) is adapted to remove water from the layer (S) of cellulose pulp by means of the continuous flexible member (17);

-a first pressure roller (33) arranged downstream of said guide roller (31) with respect to the feeding direction of the cellulose pulp layer (S), said continuous flexible member (17) being driven around said first pressure roller (33); wherein the first pressure roller (33) and the Yankee dryer (35) define a first pressure nip (34), inside which first pressure nip (34) the continuous flexible member (17) is pressed by the first pressure roller (33) against the cylindrical surface (35S) of the Yankee dryer (35); and said first pressure roller (33) is adapted to remove water from said layer (S) of cellulose pulp by means of said continuous flexible member (17).

2. Machine (10) according to claim 1, characterized in that said guide roll (31) is a suction roll.

3. Machine (10) according to claim 2, characterized in that said guide roller (31) comprises an outer cylindrical skirt (39), said outer cylindrical skirt (39) being provided with a plurality of through holes (51), said through holes (51) connecting the outer surface of said guide roller and the inner suction chamber (43.2) of said guide roller (31).

4. Machine (10) according to claim 3, characterized in that said suction chamber (43.2) extends for a portion of the circumferential extension of said suction roller (31) and is arranged in a fixed position with respect to the rotation axis (31A) of said guide roller (31) so as to generate a suction zone through the through holes (51) of said cylindrical skirt (39), said suction zone being fixed with respect to the path of said continuous flexible member.

5. Machine (10) according to claim 4, characterized in that said suction chamber (43.2) is arranged in the area of said guide roller (31) in contact with said continuous flexible member (17) so as to generate suction of the water contained in said layer (S) of cellulose pulp in said through hole by said flexible member (17).

6. Machine (10) according to claim 5, characterized in that inside said cylindrical skirt (39) there is arranged an annular volume (43) fluidly connected to said through hole (51), said annular volume (43) being subdivided into said suction chamber (43.2) and a non-suction zone (43.1), so that the water is temporarily sucked in said through hole (51) when said through hole (51) passes in front of said suction chamber (43.2) and is removed from the through hole (51) due to centrifugal action when said through hole passes along the non-suction zone (43.1) of said annular volume (43).

7. Machine (10) according to one or more of the preceding claims, characterized by the fact that said first pressure roller (33) is a pressure roller with blind holes (57).

8. Machine (10) according to one or more of claims 1 to 6, characterized in that said first pressure roller comprises an external cylindrical skirt provided with a plurality of through holes connecting the external surface of said first pressure roller with the internal suction chamber of said first pressure roller; wherein preferably said suction chamber extends for a portion of the circumferential extension of said first pressure roller and is arranged in a fixed position with respect to the axis of said first pressure roller, so as to generate a suction area through the through hole of said cylindrical skirt, said suction area being fixed with respect to the path of said continuous flexible member (17); and wherein preferably said suction chamber is arranged in the region of said first pressure roller in contact with said continuous flexible member (17) so as to generate suction of the water contained in said layer (S) of cellulose pulp in said through hole by said flexible member (17); and wherein preferably inside said cylindrical skirt there is arranged an annular volume fluidly connected to said through holes, said annular volume being subdivided into said suction chamber and a non-suction zone, so that water is temporarily sucked in said through holes when they pass in front of said suction chamber and is removed from said through holes due to centrifugal action when they pass along the non-suction zone of said annular volume.

9. The machine (10) according to one or more of the preceding claims, further comprising a second pressure roller (61) arranged downstream of said first pressure roller (33) with respect to the direction of feed of the layer (S) of cellulose pulp, said continuous flexible member (17) being driven around said second pressure roller (61); wherein the second pressure roller (61) and the Yankee dryer (35) define a second pressure nip (63), inside the second pressure nip (63), the continuous flexible member (17) being pressed against the cylindrical surface (35S) of the Yankee dryer (35) by the second pressure roller (61); and wherein the second pressure roller (61) is adapted to remove water from the layer (S) of cellulose pulp by means of the continuous flexible member (17).

10. Machine (10) according to claim 9, characterized in that said second pressure roller (61) has the same structure as said first pressure roller.

11. Machine (10) according to claim 9, characterized in that said second pressure roller has a different structure than said first pressure roller, and in particular one of the two pressure rollers has a blind hole configuration and the other of the two pressure rollers has a through hole configuration.

12. Machine (10) according to one or more of the preceding claims, comprising heating means adapted to act on said continuous flexible member (17) and arranged between said guide roller (31) and said first pressure roller (33).

13. Machine (10) according to claim 12, characterized in that said heating means face said first surface (17A) carrying said layer (S) of cellulose pulp.

14. Machine (10) according to claim 12 or 13, characterized in that said heating means are steam heating means and/or infrared heating means and/or microwave heating means and/or electric heating means, such as means for heating by electric resistance and/or electric induction.

15. Machine (10) according to one or more of claims 12-14, characterized in that said heating means comprise a steam box adapted to blow steam directly onto said continuous flexible member (17) carrying said layer (S) of cellulose pulp.

16. Machine (10) according to one or more of claims 12 to 15, characterized by the fact that said heating means comprise a heat radiating plate facing said continuous flexible member (17) carrying said layer (S) of cellulose pulp.

17. The machine (10) according to one or more of the preceding claims, further comprising a forming wire (15), said forming wire (15) being adapted to receive said layer (S) of cellulose pulp from a headbox (11) and being configured to transfer said layer (S) of cellulose pulp directly or indirectly to said continuous flexible member (17).

18. The machine (10) according to one or more of claims 1 to 11, comprising a forming wire (15), said forming wire (15) being driven around a forming cylinder (19), said continuous flexible member (17) also being driven around said forming cylinder (19) to form a volume between said continuous flexible member (17) and said forming wire (15) for receiving the cellulose pulp coming from the headbox.

19. Machine (10) according to one or more of claims 12 to 15 and one of claims 16 and 17, characterized in that said guide roller (31) and said heating means are arranged downstream of the zone where said forming wire (15) is separated from said continuous flexible member (17).

20. Machine (10) according to one or more of the preceding claims, characterized by the fact that said heating means comprise an air suction module, preferably arranged at the opposite side to said continuous flexible member and facing it.

21. Machine (10) according to one or more of the preceding claims, comprising a further heating device arranged immediately upstream of said guide roller.

22. A method for removing water from a cellulose pulp layer (S) comprising water and cellulose fibres, the method comprising the steps of:

forming a layer (S) of cellulose pulp comprising water and cellulose fibres on a first surface (17A) of a continuous flexible member (17);

-feeding the cellulose pulp layer (S) towards a yankee dryer (35);

-driving the continuous flexible member (17) around a guide roll (31), the continuous flexible member (17) having a second surface (17B) in contact with the guide roll (31), and-removing water from the cellulose pulp layer (S) by means of the guide roll (31) through the continuous flexible member (17) without contact between the cellulose pulp layer (S) and the yankee dryer (35);

-feeding the layer (S) of cellulose pulp, downstream of the guide roll (31), in a first pressure nip (34) defined by the yankee dryer (35) and a first pressure roll (33), -the continuous flexible member (17) being driven around the first pressure roll (33) in such a way that the second surface (17B) is in contact with the first pressure roll (33), and-removing water from the layer (S) of cellulose pulp by means of the first pressure roll (33) through the continuous flexible member (17).

23. The method of claim 22, further comprising the steps of: -feeding the layer (S) of cellulose pulp, downstream of the first pressure roller (33), in a second pressure nip (63) defined by the yankee dryer (35) and a second pressure roller (61), the continuous flexible member (17) being driven around the second pressure roller (61) in such a way that the second surface (17B) is in contact with the second pressure roller (61), and-removing water from the layer (S) of cellulose pulp by means of the second pressure roller (61) through the continuous flexible member (17).

24. A method according to claim 22 or 23, further comprising a drying step by heating the layer (S) of cellulose pulp between a zone where the continuous flexible member (17) is driven around the guide roll (31) and the first pressure nip (34).

25. The method according to claim 24, characterized in that the drying step takes place by heating generated by means of steam sprayed onto the layer (S) of cellulose pulp or by thermal radiation.

Technical Field

A machine and a method for wet-laid manufacture of cellulose sheets or webs, in particular tissue paper, are disclosed.

Background

Paper is typically made using a wet production process. For example, to make tissue paper (from which kitchen towels, toilet paper, napkins, handkerchiefs and the like are produced), a pulp is formed comprising an aqueous suspension of cellulose fibres and, if desired, other ingredients such as moisture-resistant resins and the like. Pulp having a low dry matter content, e.g. about 0.2% wt (0.2% wt fibres, 99.8% wt water) is distributed by means of a headbox onto a forming wire or into a space between a forming wire forming a closed path and a continuous flexible member, e.g. a felt. The pulp forms a layer from which water is gradually removed in order to increase the percentage of solids content, in order to have a web made of cellulose fibres and other components, the web having a solids content of, for example, about 6% wt.

The partially dewatered layer of cellulose pulp is moved from a continuous flexible member to a yankee dryer where heating is applied inside the yankee dryer and the cellulose web is driven around the yankee dryer to be dried. The air hood surrounding the yankee cylinder circulates hot air outside the yankee cylinder in the area along which the cellulose pulp layer is driven in order to accelerate the drying process, i.e. the dewatering process. The dried web is then separated from the yankee cylinder by means of doctor blades and wound in a reel.

The production process requires a large amount of energy. Typically, about 71% of the energy required is the thermal energy required for heating the yankee cylinder, which is typically heated by a steam and air hood. Generally, the required energy is obtained by burning a fuel such as gas. The remaining 29% of the energy required is the electrical power required to move the various components of the production facility. Therefore, it is very important to reduce the consumption of heat energy required for drying.

For this purpose, systems are used which: the system mechanically removes a portion of the water from the pulp by pressing the cellulosic fiber layer before it reaches the yankee dryer. These systems usually comprise suction presses or presses with blind holes, in which a roll having a structure suitable for dewatering a layer of cellulose fibres forms a pressure nip with the yankee cylinder. In some cases, a press is used that: these presses have rollers with imperforate cylindrical surfaces. A continuous flexible member, typically a felt, to which a layer of cellulose pulp is attached, passes through the pressure nip. The pressure dewaters the cellulose layer and attaches the cellulose layer to a surface of the yankee dryer. The press increases the dry matter content in the cellulose pulp from about 6% to about 40% before the cellulose layer moves to the yankee dryer.

Another key parameter in paper manufacturing, particularly tissue manufacturing, is the caliper (bulk) which should be maximized in order to have a better quality, a greater absorption capacity and a greater softness of the final product. Increasing the paper thickness is also useful to optimize production yield: the greater the thickness of the paper, the greater the volumetric production, given the same fiber weight.

The thickness of the cellulose layer is affected by two parameters: an effective thickness of fiber agglomerates forming the cellulosic web; the degree of creping obtained by the doctor blade, which separates the web from the yankee cylinder. Given the same effective thickness of the fiber agglomerates, the apparent web thickness can be increased by increasing creping.

The use of a pressing system to dewater the cellulose pulp layer before moving it to the yankee dryer allows to save heat energy, since the percentage of water to be evaporated by the heat generated by the yankee dryer and the air hood is reduced. However, the pressing system has a negative impact on the production process in terms of the final thickness of the cellulose web: given the same conditions, the greater the pressure applied, the greater the amount of water that is mechanically removed and, therefore, the less thermal energy required for drying. However, given the same conditions, the greater the pressure applied to the cellulosic layer, the lower its final thickness.

In order to obtain a better compromise between the two conflicting requirements mentioned above, so-called shoe presses have been implemented which co-act with the yankee cylinder. The shoe press comprises a cylindrical sleeve made of a waterproof flexible material. The cylindrical sleeve rotates around an axis of rotation and is pressed against the yankee cylinder by means of a hydrostatic pad having a concave surface. In this way, a pressure area is provided between the cylindrical sleeve and the yankee cylinder, the extension of which in the circumferential direction of the yankee cylinder is greater than that provided in conventional presses with suction rolls or rolls with blind holes. Thus, the cellulosic fiber layer is subjected to pressure for a longer period of time. In this way, efficient dewatering can be achieved with a relatively low specific pressure compared to the specific pressure used in conventional presses with suction rolls. As a result, water is effectively removed with lower compression of the cellulosic fiber layer.

In this way, a better compromise is obtained between two contradictory requirements: before starting to heat the cellulose web, the cellulose fiber layer is pressed as little as possible and as much water as possible is removed mechanically.

However, while effective in terms of energy consumption and final quality of the cellulosic web, the shoe press has significant drawbacks, including the following.

The construction of the shoe press is very complicated and requires a higher initial investment than the initial investment of other systems for pressing the cellulose web. In practice, a shoe press requires a central support shaft onto which hydrostatic pads (shoes) are mounted, and a system for moving the hydrostatic shoes and a system for supplying pressurized oil to the hydrostatic shoes, including a hydraulic control unit.

The cylindrical sleeve is subjected to stresses and to cyclic deformations and, in particular, to repeated bending due to its concave shape in the region of contact with the boot. Therefore, the sleeve should be replaced frequently with consequent down time. Replacing the cylindrical sleeve requires specialized labor.

Therefore, there is a need to provide a machine and a method for the wet manufacturing of paper that achieve better results in terms of energy consumption and quality of the final product.

Disclosure of Invention

According to a first aspect, a machine for the wet-laid manufacture of tissue paper is disclosed, said machine comprising a yankee cylinder having a cylindrical surface and rotating about an axis of rotation. A separating member, such as a doctor blade or doctor blade, for separating the cellulosic web can co-act with the outer cylindrical surface of the yankee dryer. An air hood may be disposed around the yankee dryer. The machine further comprises a continuous flexible member, typically a felt, comprising a first surface adapted to receive a layer of cellulose pulp comprising cellulose fibres and water. A guide roller is also provided around which the continuous flexible member is driven with its second surface in contact with the first guide roller. The guide roll is positioned relative to the yankee dryer such that the first surface of the continuous flexible member is spaced from the yankee dryer such that in the area of contact with the guide roll, the layer of cellulose pulp adhered to the first surface of the continuous flexible member is spaced from the yankee dryer, i.e., it is not in contact with the yankee dryer.

The guide roll is adapted to dewater the cellulose pulp layer by the continuous flexible member. The guide roller can be configured, for example, as a suction roller.

The machine further comprises a first pressure roller arranged downstream of the guide roller with respect to the direction of feed of the layer of cellulose pulp, around which the continuous flexible member is driven. The pressure roller is in contact with a second surface of the continuous flexible member, i.e. the surface opposite to the surface on which the cellulose pulp layer is applied. The first pressure roll and the yankee cylinder define a first pressure nip inside which the continuous flexible member is pressed against the cylindrical surface of the yankee cylinder by the first pressure roll, the layer of cellulose pulp being positioned between the cylindrical surface of the yankee cylinder and the continuous flexible member.

The first pressure roll is adapted to dewater the cellulose pulp layer by the continuous flexible member. For example, the first pressure roller may, together with the cylindrical surface of the yankee cylinder, constitute a so-called press with blind holes.

Typically, the guide roller and the first pressure roller have an outer cylindrical surface adapted to absorb water from the cellulose pulp layer through the continuous flexible member.

Thus, in contrast to the cylindrical sleeve of the shoe press of the prior art, the pressure roller of the machine disclosed herein absorbs water inside the cylindrical skirt.

In contrast to what happens with shoe presses, the construction of the pressure roller is particularly simple and requires a small amount of maintenance.

In fact, a machine constructed in this way allows an efficient dewatering by mechanical systems before the layer of cellulose pulp is heated and dried by the thermal energy supplied by the yankee cylinder and the air hood. Dewatering is performed by simple and economical means which are easy to maintain and control, contrary to what happens with shoe presses of the prior art. Furthermore, the preliminary removal of water by the guide roll (in which the cellulose pulp layer is not pressed) allows to have a paper layer that: given the same drying energy savings, the paper layer has a thickness greater than that obtained by prior art machines.

In fact, the guide roll removes a part of the water mechanically and/or hydraulically and/or pneumatically without pressing, thus making the subsequent removal by pressing more efficient, so that the cellulose pulp layer, given the same thickness, can have a higher dry matter content than that obtained by conventional machines.

In certain embodiments, the guide roll comprises an outer cylindrical skirt provided with a plurality of through holes connecting the outer surface of the guide roll and the inner suction chamber of the guide roll. The suction chamber may, for example, extend for a portion of the circumferential extension of the suction roll and be in a fixed position with respect to the axis of the guide roll, so as to generate a suction zone through the through holes of the cylindrical skirt. The suction zone is fixed relative to the path of the continuous flexible member and is disposed along an arc of contact between the cylindrical skirt and the continuous flexible member. In this way, the suction chamber draws water from the cellulose pulp layer through the continuous flexible member (felt) and water accumulates in the holes of the cylindrical skirt. Due to centrifugal forces, water is then ejected from the holes, which move away from the suction zone due to the continuous rotation of the cylindrical skirt.

The first pressure roller may also be a suction roller similar to the guide roller. However, in order to simplify the overall structure of the machine and also to reduce energy consumption, in some embodiments, said first pressure roller may be a pressure roller with blind holes. The pressure roller with blind holes may have a cylindrical skirt coated with an elastically yielding material, for example a layer of rubber, polyurethane or the like. The coating may be provided with blind, i.e. non-through holes, which connect the coating to the outer surface of the pressure roller. Due to the pressure between the pressure roller and the yankee dryer cylinder (felt-or other continuous flexible member-with which the cellulose pulp layer is attached-passing in between), water is transferred from the cellulose pulp layer to the blind holes through the felt or other continuous flexible member. Due to centrifugal force, water is then ejected from the blind hole downstream of the point where the continuous flexible member (felt) moves away from the pressure roller.

In certain embodiments, the machine may further comprise a second pressure roller disposed along the path of the continuous flexible member (felt) and downstream of the first pressure roller. The continuous flexible member is driven around the second pressure roll and is thereby pressed against the cylindrical surface of the yankee cylinder, defining a second pressure nip.

In certain embodiments, the second pressure roller has the same construction as the first pressure roller. For example, both the first pressure roller and the second pressure roller may have blind holes. In other embodiments, the first pressure roller and the second pressure roller have different configurations. For example, the first pressure roller is a suction roller similar to the guide roller, while the second pressure roller is a roller with blind holes.

In certain embodiments, the machine comprises heating means adapted to act on the continuous flexible member to increase the temperature of the layer of cellulose pulp and thus reduce the viscosity of the water contained in the cellulose pulp. This allows to increase the efficiency of the step of pressing the cellulose pulp between the pressure roll and the yankee cylinder and thus to increase the dry matter content after the pressure nip defined between the pressure roll and the yankee cylinder. In particular, the heating device is arranged between the guide roller and the first pressure roller.

The specific location of the heating means in combination with the guide roll and the first pressure roll is particularly advantageous for better drying of the cellulose pulp. In fact, the presence of the guide roll allows to remove a certain amount of water contained in the cellulose pulp, thus preventing it from being absorbed by the felt. The heating downstream of the guide roll allows for a greater heating of the cellulose pulp than in prior art machines, i.e. because the felt has lost a certain percentage of water through the guide roll. Moreover, the heating means are able to transfer more energy to the cellulose pulp layer, because a portion of the felt comprised between the guide roll and the first pressure roll contains less water.

Advantageously, the heating means may face a first surface of a continuous flexible member carrying the layer of cellulose pulp.

Advantageously, the heating device is a steam heating device and/or an electric heating device and/or an infrared heating device and/or a microwave heating device, or any other heating device.

Advantageously, the heating means comprises a steam box adapted to blow steam directly onto the continuous flexible member carrying the layer of cellulose pulp. Alternatively, the heating means may comprise a heat radiating panel facing a continuous flexible member carrying the layer of cellulose pulp.

Advantageously, the heating device comprises air suction modules, preferably arranged at opposite sides of and facing the continuous flexible member, for removing humid air in the vicinity of the heating device.

The machine may also comprise a further heating device similar to the one described above and arranged directly upstream of the guide roll in order to increase the temperature of the cellulose pulp layer.

The machine may further comprise a forming wire adapted to receive a layer of cellulose pulp from a headbox and to transfer the layer of cellulose pulp directly or indirectly to the continuous flexible member. The guide roll and the heating device are arranged downstream of a separation region of the forming wire from the continuous flexible member.

According to another aspect, a method for removing water from a cellulosic pulp layer comprising water and cellulosic fibers is disclosed. In embodiments described herein, the method comprises the steps of:

forming a layer of cellulose pulp comprising water and cellulose fibers on a first surface of a continuous flexible member;

driving the continuous flexible member around a guide roller, the continuous flexible member having a second surface in contact with the guide roller, and removing water from the layer of cellulose pulp by the continuous flexible member via the guide roller;

downstream of the guide roll, feeding the layer of cellulose pulp into a first pressure nip defined by a yankee dryer and a first pressure roll, around which the continuous flexible member is driven with the second surface in contact with the first pressure roll, and removing water from the layer of cellulose pulp by means of the first pressure roll through the continuous flexible member.

The method may comprise the further step of: -feeding the layer of cellulose pulp into a second pressure nip defined by the yankee dryer and a second pressure roller, around which the continuous flexible member is driven with the second surface in contact with the second pressure roller, and-removing water from the layer of cellulose pulp by means of the second pressure roller through the continuous flexible member.

The method may further comprise a drying step by heating the cellulose pulp layer between a guide of the continuous flexible member around a guide roll and the first pressure nip. Preferably, the drying step by heating takes place by heating generated by means of steam sprayed onto the layer of cellulose pulp or by thermal radiation.

The method may further comprise a further drying step by heating the cellulose pulp layer upstream of the guide roll.

Drawings

The invention will be better understood by following the description and accompanying drawings, which show non-limiting examples of embodiments of the invention. More specifically, in the figure:

figure 1 is a diagram of a first embodiment of a machine according to the invention;

fig. 2 is a schematic enlarged view of the active area of the suction guide roller;

FIG. 3 is an enlarged schematic view of a first pressure nip of the machine of FIG. 1;

FIG. 4 is a diagram of another embodiment of a machine according to the present disclosure; and

fig. 5 is a diagram of a part of a machine according to the invention, which differs from the example of fig. 1 and 4 in that a heating device is interposed between the guide roller and the first pressure roller.

Detailed Description

Example embodiments are described in detail below with reference to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. Moreover, the drawings are not necessarily drawn to scale. The following detailed description does not limit the invention. The scope of protection of the invention is defined by the appended claims.

Reference in the specification to "one embodiment," "the embodiment," or "some embodiments" means that a particular feature, structure, or element described in connection with the embodiment is included in at least one embodiment of the described subject matter. Thus, the phrases "in one embodiment" or "in a described embodiment" or "in some embodiments" in the specification do not necessarily refer to the same embodiment or embodiments. Furthermore, the particular features, structures, or elements may be combined in any suitable manner in one or more embodiments.

Referring initially to fig. 1, in one embodiment, a machine for tissue wet-making, generally designated by the numeral 10, includes a headbox 11 disposed in front of a forming zone defined between a forming wire 15 and a continuous flexible member 17, such as a felt. A continuous flexible member 17 (referred to herein simply as a "felt") is driven around a forming roll 19, and the forming wire 15 is also driven around the forming roll 19.

The forming wire 15 follows a closed path defined by the guide rolls 21, 22, 23, 24 and the forming roll 19. The felt 17 follows a closed path defined by guide rollers 25, 26, 27, 28, forming roller 19, guide roller 31 and first pressure roller 33, as will be described in more detail below.

The machine 10 further comprises a yankee cylinder 35, around which yankee cylinder 35 an air hood 37 is arranged. The yankee dryer 35 rotates about its axis of rotation 35A and has an outer cylindrical surface 35S. The felt 17 passes through a pressure nip 34, said pressure nip 34 being defined between an outer cylindrical surface 35S of a yankee cylinder 35 and a pressure roller 33, said pressure roller 33 being pressed against the cylindrical surface 35S.

A doctor or doctor blade 38 co-acts with the yankee dryer 35, which doctor or doctor blade separates the tissue ply V at the outlet of the yankee dryer 35 after the tissue ply V has been dried.

The headbox 11 feeds a pulp or aqueous suspension of cellulosic fibers to a nip or forming space between a felt 17 and a wire 15. The cellulosic suspension or pulp comprises, for example, about 99.8% water and 0.2% solid matter, in particular cellulose fibers. A portion of the water is removed, i.e. drained, through the forming wire 15 so that at the outlet of the area where the forming wire 15 and the felt 17 are in contact with each other, i.e. in the area of the guide roll 24, a layer of cellulose pulp having a solids content of about 6% is present on the felt 17. The layer of cellulose fibers remains adhered to the outer surface 17A of the felt 17 and is carried by the felt 17 toward the yankee dryer 35.

The layer of cellulose pulp, indicated by the letter S, is carried along the path defined by it by the felt 17, said felt 17 being driven around a guide roller 31 and a pressure roller 33, the felt 17 being in contact with the guide roller 31 and the pressure roller 33 by its inner surface 17B, said inner surface 17B being opposite to the outer surface 17A, the layer S of cellulose pulp being attached to said outer surface 17A. As will be described below, the guide roll 31 and the pressure roll 33 are configured to remove water from the layer S of cellulose pulp before the layer S of cellulose pulp is transferred from the felt 17 to the outer cylindrical surface 35S of the yankee dryer 35.

In a known manner, during contact with the yankee dryer 35, the layer S of cellulose pulp is dried due to the heat supplied by the yankee dryer 35 through its cylindrical wall and the hot air supplied by the air hood 37. Thus, the layer S of cellulose pulp arriving at the yankee dryer 35 with a percentage of water greater than 50% is dried, forming a ply or web V; the web V, after being separated from the yankee cylinder 35 by a doctor or doctor blade 38, is fed to a winder, not shown, to form a reel.

The guide roll 31 may have a structure adapted to remove a portion of the water contained in the layer S of cellulose pulp, which is attached to the felt 17, the felt 17 being driven around the guide roll 31 and in contact with the roll through the inner surface 17B.

An embodiment of the guide roller 31 is schematically shown in an enlarged view in fig. 2. In this embodiment, the guide roller 31 comprises a rotating outer cylindrical skirt 39 and a fixed inner core 41. An annular volume 43 is defined between the cylindrical skirt 39, which rotates about the axis of rotation 31A, and the fixed core 41. The annular volume 43 can be subdivided into two parts 43.1 and 43.2. The two portions 43.1 and 43.2 may be defined by a fixed dividing wall 45 mounted on the inner core 41. The portion 43.2 may be connected to a suction line, schematically indicated with numeral 49. The suction pipe may be disposed at either one or both ends of the guide roller 31. In this way, a suction chamber is defined between the partition walls 45.

The cylindrical skirt 39 may be provided with a plurality of through holes 51, the through holes 51 being evenly distributed over the entire extension of the cylindrical skirt 39. In this way, the through hole 51 connects the outer cylindrical surface of the guide roller 31 to the suction chamber 43.2 comprised in the area between the walls 45. A suction effect is thus generated in this region by the through-holes 51 and the felt 17. Due to this suction, water contained in the cellulose pulp layer S is sucked inside the through-hole 51. When the through-holes 51 pass over the suction area defined between the walls 45 as the guide roller 31 rotates, there is no suction anymore and, therefore, the water accumulated in the through-holes 51 is removed by the centrifugal force. The separation wall 45 is positioned relative to the path of the felt 17 such that the suction effect terminates at or downstream of the point where the felt 17 moves away from the outer cylindrical surface of the guide roller 31, so that water in the through holes 51 is removed from the roller 31 due to centrifugal force and does not return into the felt 17.

By means of this mechanism, a portion of the water contained in the layer S of cellulose pulp is removed before said layer reaches the pressure nip 34 defined between the pressure roll 33 and the yankee dryer 35.

In the nip 34, the cellulose pulp layer S is pressed between the outer surface 35S of the yankee dryer 35 and the felt 17 due to the pressure exerted by the pressure roll 33 on the yankee dryer 35. The structure of the pressure roller 33 may be the same as that of the guide roller 31, so that the water contained in the cellulose pulp layer S is collected in the through holes of the rotating cylindrical skirt and then removed due to the centrifugal effect.

In other preferred embodiments, the pressure roller 33 may have a structure shown in more detail in an enlarged view of fig. 3. This structure is a typical structure of a so-called blind-drilled press (blind-drilled press). It comprises a roller with a head, a cylindrical skirt and supporting pins (not shown). On the cylindrical skirt 33.1 a layer of elastic material 33.2, for example rubber or polyurethane, is applied. The elastomeric layer 33.2 is provided with a plurality of blind holes 57. In the area where the inner surface 17B of the felt 17 is in contact with the outer cylindrical surface of the pressure roller 33, the cellulose pulp layer S and the felt 17 are pressed so that a part of the water contained in the cellulose pulp layer S passes through the felt 17 and penetrates into the blind hole 57 by pressure. In the area downstream of the position where the felt 17 separates from the cylindrical surface of the pressure roller 33, the water collected in the blind holes 57 is removed by centrifugal force. In this way, a part of the water is removed from the cellulose pulp layer S.

In certain embodiments, the combined effect of the suction guide roll 31 and the pressure roll 33 reduces the moisture content in the layer S of cellulose pulp to about 42-43%, wherein a linear pressure of about 90-100kN/m is applied in the pressure nip 34. According to the standard TAPPI-T580 tissue, napkin and facial product caliper (caliper) (thick) of towel, tissue, napkin and facial products, a thickness of the cellulose web V of about 95-100 μm can be obtained for ten sheets of paper. It should be understood that the values of linear pressure and thickness applied are given by way of non-limiting example only. This applies generally to all values mentioned in the present description, unless otherwise stated.

Thanks to the combination of the pressure roll 33 and the suction guide roll 31, an effective dewatering is achieved without compressing and pressing the cellulose pulp layer S, i.e. the moisture in the cellulose pulp layer S is significantly reduced before starting drying around the yankee dryer 35 by thermal effect. Since a portion of the water is removed without compressing and without pressing the cellulose pulp layer S, dewatering does not occur to excessively reduce the thickness of the resulting cellulose fibre layer.

Figure 4 shows a second embodiment of the machine according to the invention. The same reference numerals indicate the same or equivalent components as those of fig. 1, which will not be described again. The main difference between the embodiment of fig. 1 and the embodiment of fig. 4 is that the embodiment of fig. 4 has a second pressure roller 61 downstream of the pressure roller 33. The felt 17 is driven around an intermediate roller 64, said intermediate roller 64 being arranged between the first pressure roller 33 and the second pressure roller 61 along a closed path defined by the felt 17. The second pressure roll 61 defines a second pressure nip 63 between the pressure roll 61 and the outer cylindrical surface 35S of the yankee dryer 35.

In some embodiments, the second pressure roller may be provided with a suction structure as described with reference to the guide roller 31. In a preferred embodiment, the second pressure roller 61 has a configuration with blind holes, as in the configuration of the first pressure roller 33 described above (fig. 3).

In the example of fig. 4, the water content of the cellulose pulp layer S is reduced in the following three steps: due to the suction by the guide roller 31, due to the pressing by the first pressure roller 33 in the first pressure nip 34, and due to the pressing by the second pressure roller 61 in the second pressure nip 63.

With the configuration of fig. 4, it is possible to have a lower moisture content inside the cellulose pulp layer S than can be obtained in the embodiment of fig. 1, before the drying step on the yankee cylinder, even if the cellulose pulp layer S is pressed slightly more and therefore its final thickness is slightly reduced. For example, in the case of a linear pressure in the pressure nips 34 and 63 of about 90-100kN/m, a solids content of about 44-45% in the layer S of cellulose pulp can be obtained at the outlet of the second pressure nip 63, and a caliper of about 93-95pm can be obtained for ten sheets according to the standard TAPPI-T580 tissue, napkin and facial product caliper (caliper). As mentioned above, the numerical values are given by way of non-limiting example only.

Advantageously, in fig. 5, another machine according to the invention is shown, which is a variant of the example of fig. 1 and 4 and comprises heating means 40, said heating means 40 being adapted to act on the continuous flexible member 17 (felt) in order to increase the temperature of the layer of cellulose pulp and thus to reduce the viscosity of the water contained in the cellulose pulp. This allows to increase the efficiency of the step of pressing the cellulose pulp between the pressure roll and the yankee cylinder and, consequently, the dry matter content after the pressure nip defined between the pressure roll and the yankee cylinder.

In particular, the heating device 40 is arranged between the guide roller 31 and the first pressure roller 33 and faces the first surface 17A of the felt 17, i.e. the surface carrying the layer S of cellulose pulp.

From an operational point of view, it is important that the heating device 40 is not too close to (and never overlaps) the guide roller 31 or the first pressure roller 33, i.e. it is not arranged on the circumference of these rollers. In fact, the rotation of the two rolls 31 and 33 causes the fragments of cellulose pulp to be dispersed in the air. If the heating device 40 overlaps or is arranged on the circumference of one of the two rolls 31 or 33, fragments of cellulose pulp tend to deposit on the heating device, forming a pulp layer thereon, which will reduce the heating capacity of the heating device.

According to a preferred embodiment, the device 40 is heated by steam. In this example, the device is a known steam box which sprays saturated, preferably dry or superheated steam onto the cellulose pulp S present on the felt 17, thereby facilitating the drying thereof.

The steam used to supply the steam box can arrive via a pipe 40A from a heat recovery unit (not shown in the figures) which generates steam, for example using the fumes of the hood 37. In practice, the recovery unit generates high-pressure steam to feed the yankee cylinder and supplies the steam box of the device 40 through a pipe 40A with reduced pressure. In another embodiment, the heat recovery unit may generate low pressure steam only for the steam box.

According to other embodiments, the heating means 40 can be of the type that uses electric power (joule effect), for example a resistive or inductive plate, or of the type that generates infrared rays, such as an infrared lamp or panel, or of the microwave type.

In this example, the heating device 40 also comprises a suction module 40B, said suction module 40B being arranged opposite the steam box with respect to the felt 17 and close to the felt 17, so as to suck the humid air in said area. The sucked air is removed through a tube not shown in the figure.

It is clear that the use of the heating device 40 between the guide roll 31 and the first pressure roll 33 is particularly effective for improving the drying of the cellulose pulp. The guide roll 33 allows removing water contained in the cellulose pulp that is not absorbed by the felt. Thus, the heating device 40 is able to transfer more energy to the cellulose pulp layer and thus perform an optimal drying.

Due to the combined effect of the suction roll 31 and the first pressure roll 33, the dry matter content in the cellulose pulp S increases by a value between at least 2.8% and 3.5% compared to the above described embodiment, due to the heating device 40.

In order to further increase the temperature of the layer S of cellulose pulp, in this example a further heating device 40 'is provided, said heating device 40' being similar to the heating device 40 described above and being arranged immediately upstream of the guide roll. Again, in this case, it may be of the steam type or of the type using electricity, such as a resistance or induction plate, or of the infrared ray generating type, such as an infrared lamp or panel, or of the microwave type. It may also include another suction module 40'. Again, in this case, it is important that the further heating device 40' is not too close to (and never overlaps) the guide roller 31, i.e. it is not arranged on the circumference of the roller.

Although particular embodiments of the invention described above have been illustrated in the accompanying drawings and described in the foregoing description in whole with the features and characteristics relating to the various exemplary embodiments, it will be understood by those skilled in the art that modifications, variations and omissions are possible without departing from the advantages of the inventive concepts, the principles and concepts described above and as described in the appended claims.

For example, at least one or both of the rollers 33, 61 may be non-perforated and have a smooth cylindrical surface.

Accordingly, the scope of the described improvements should be determined only based on the broadest interpretation of the appended claims so as to encompass all modifications, changes, and omissions. Further, the order or sequence of any steps of a method or process may be varied according to alternative embodiments.