Patent Application
20070251660
1. Field of the Invention
The present invention relates to a paper machine, and, more particularly, to a dewatering tissue press fabric used in a belt press in a paper machine. The present invention also relates to a dewatering tissue press fabric for use in a high tension extended nip around a rotating roll or a stationary shoe and/or which is used in a papermaking device/process. The present invention also relates to a press fabric for the manufacture of tissue or towel grades utilizing a through-air drying (TAD) system that is engineered to provide a very flat, even surface yet with a high level of resilience and resistance to compaction. The fabric has key parameters which include permeability, weight and caliper,
2. Discussion of Background Information
The manufacture of tissue utilizes an improved technology called TAD, i.e., through air drying process. This process increases paper quality due to the higher bulk of the tissue paper. As a result, TAD sets the standard for high grade tissue.
In a wet pressing operation, a fibrous web sheet is compressed at a press nip to the point where hydraulic pressure drives water out of the fibrous web. It has been recognized that conventional wet pressing methods are inefficient in that only a small portion of a roll's circumference is used to process the paper web. To overcome this limitation, some attempts have been made to adapt a solid impermeable belt to an extended nip for pressing the paper web and dewater the paper web. A problem with such an approach is that the impermeable belt prevents the flow of a drying fluid, such as air through the paper web. Extended nip press (ENP) belts are used throughout the paper industry as a way of increasing the actual pressing dwell time in a press nip. A shoe press is the apparatus that provides the ability of the ENP belt to have pressure applied therethrough, by having a stationary shoe that is configured to the curvature of the hard surface being pressed, for example, a solid press roll. In this way, the nip can be extended 120 mm for tissue, and up to 250 mm for flap papers beyond the limit of the contact between the press rolls themselves. An ENP belt serves as a roll cover on the shoe press. This flexible belt is lubricated by an oil shower on the inside to prevent frictional damage. The belt and shoe press are non-permeable members, and dewatering of the fibrous web is accomplished almost exclusively by the mechanical pressing thereof.
WO 03/062528 (whose disclosure is hereby expressly incorporated by reference in its entirety), for example, discloses a method of making a three dimensional surface structured web wherein the web exhibits improved caliper and absorbency. This document discusses the need to improve dewatering with a specially designed advanced dewatering system. The system uses a Belt Press which applies a load to the back side of the structured fabric during dewatering. The belt and the structured fabric are permeable. The belt can be a spiral link fabric and can be a permeable ENP belt in order to promote vacuum and pressing dewatering simultaneously. The nip can be extended well beyond the shoe press apparatus. However, such a system with the ENP belt has disadvantages, such as a limited open area.
It is also known in the prior art to utilize a through air drying process (TAD) for drying webs, especially tissue webs. Huge TAD-cylinders are necessary, however, and as well as a complex air supply and heating system. This system also requires a high operating expense to reach the necessary dryness of the web before it is transferred to a Yankee Cylinder, which drying cylinder dries the web to its end dryness of approximately 97%. On the Yankee surface, also the creping takes place through a creping doctor.
The machinery of the TAD system is very expensive and costs roughly double that of a conventional tissue machine. Also, the operational costs are high, because with the TAD process it is necessary to dry the web to a higher dryness level than it would be appropriate with the through air system in respect of the drying efficiency. The reason is the poor CD moisture profile produced by the TAD system at low dryness level. The moisture CD profile is only acceptable at high dryness levels up to 60%. At over 30%, the impingement drying by the hood of the Yankee is much more efficient.
The max web quality of a conventional tissue manufacturing process are as follows: the bulk of the produced tissue web is less than 9 cm3/g. The water holding capacity (measured by the basket method) of the produced tissue web is less than 9 (g H20/g fiber).
The advantage of the TAD system, however, results in a very high web quality especially with regard to high bulk, water holding capacity.
What is needed in the art is a belt, which provides enhanced dewatering of a continuous web.
WO 2005/075732, the disclosure of which is hereby expressly incorporated by reference in its entirety, discloses a belt press utilizing a permeable belt in a paper machine which manufactures tissue or toweling. According to this document, the web is dried in a more efficient manner than has been the case in prior art machines such as TAD machines. The formed web is passed through similarly open fabrics and hot air is blown from one side of the sheet through the web to the other side of the sheet. A dewatering fabric is also utilized.
WO20051075736, the disclosure of which is hereby expressly incorporated by reference in its entirety, discloses an ATMOS system which uses a belt press. A dewatering fabric is disclosed as an important feature of the system.
The use of a press fabric is well known in standard tissue-making systems. In such systems, the fabric acts to dewater the sheet by acting as a way to move the water from the sheet to one or more dewatering devices. Known systems include a press formed by a smooth non-perforated roll and a grooved or drilled counter roll.
Rather than relying on a mechanical shoe for pressing, the invention allows for the use a permeable belt as the pressing element. The belt is tensioned against a suction roll so as to form a Belt Press. This allows for a much longer press nip, e.g., ten times longer than a shoe press and twenty times longer than a conventional press, which results in much lower peak pressures, i.e., 1 bar instead of 30 bar for a conventional press and 15 bar for a shoe press, all for tissue. It also has the desired advantage of allowing air flow through the web, and into the press nip itself, which is not the case with typical Shoe Presses or a conventional press like the suction press roll against a solid Yankee dryer. The preferred permeable belt is a spiral link fabric.
There is a limit on vacuum dewatering (approximately 25% solids on a TAD fabric and 30% on a dewatering fabric) and the secret to reaching 35% or more in solids with this concept while maintaining TAD like quality, is to use a very long press nip formed by a permeable belt. This can be 10 times longer than a shoe press and 20 times longer than a conventional press. The pick pressure should also be very low, i.e., 20 times lower than a shore press and 40 times lower than a conventional press. It is also very important to provide air flow through the nip. The efficiency of the arrangement of the invention is very high because it utilizes a very long nip combined with air flow through the nip. This is superior to a shoe press arrangement or to an arrangement which uses a suction press roll against a Yankee dryer wherein there is no air flow through the nip. The permeable belt can be pressed over a hard structured fabric (e.g., a TAD fabric) and over a soft, thick and resilient dewatering fabric while the paper sheet is arranged therebetween. This sandwich arrangement of the fabrics is important. The invention also takes advantage of the fact that the mass of fibers remain protected within the body (valleys) of the structured fabric and there is only a slightly pressing which occurs between the prominent points of the structured fabric (valleys). These valleys are not too deep so as to avoid deforming the fibers of the sheet plastically and to avoid negatively impacting the quality of the paper sheet, but not so shallow so as to take-up the excess water out of the mass of fibers. Of course, this is dependent on the softness, compressibility and resilience of the dewatering fabric.
The present invention also provides for a specially designed permeable ENP belt which can be used on a Belt Press in an advanced dewatering system or in an arrangement wherein the web is formed over a structured fabric. The permeable ENP belt can also be used in a No Press/Low press Tissue Flex process.
The present invention also provides a high strength permeable press belt with open areas and contact areas on a side of the belt.
The invention comprises, in one form thereof, a belt press including a roll having an exterior surface and a permeable belt having a side in pressing contact over a portion of the exterior surface of the roll. The permeable belt has a tension of at least approximately 30 KN/m applied thereto. The side of the permeable belt has an open area of at least approximately 25%, and a contact area of at least approximately 10%, and preferably approximately 50% open area and approximately 50% contact area, wherein the open area comprises a total area which is encompassed by the openings and grooves (i.e., that portion of the surface which is not designed to compress the web to same extent as the contact areas) and wherein the contact area is defined by the land areas of the surface of the belt, i.e., the total area of the surface of the belt between the openings and/or the grooves. With an ENP belt, it is not possible to use a 50% open area and a 50% contact area. On the other hand, this is possible with, e.g., a link fabric.
An advantage of the present invention is that it allows substantial airflow therethrough to reach the fibrous web for the removal of water by way of a vacuum, particularly during a pressing operation.
Another advantage is that the permeable belt allows a significant tension to be applied thereto.
Yet another advantage is that the permeable belt has substantial open areas adjacent to contact areas along one side of the belt.
Still yet another advantage of the present invention is that the permeable belt is capable of applying a line force over an extremely long nip, thereby ensuring a long dwell time in which pressure is applied against the web as compared to a standard shoe press.
The invention also provides for a belt press for a paper machine, wherein the belt press comprises a roll comprising an exterior surface. A permeable belt comprises a first side and is guided over a portion of the exterior surface of the roll. The permeable belt has a tension of at least approximately 30 KN/m. The first side has an open area of at least approximately 25% a contact area of at least approximately 10%.
The first side may face the exterior surface and the permeable belt may exert a pressing force on the roll. The permeable belt may comprise through openings. The permeable belt may comprise through openings arranged in a generally regular symmetrical pattern. The permeable belt may comprises generally parallel rows of through openings, whereby the rows are oriented along a machine direction. The permeable belt may exert a pressing force on the roll in the range of between approximately 30 KPa and approximately 300 KPa (approximately 0.3 bar to approximately 1.5 bar and preferably approximately 0.07 to approximately 1 bar). The permeable belt may comprise through openings and a plurality of grooves, each groove intersecting a different set of through openings. The first side may face the exterior surface and the permeable belt may exert a pressing force on the roll. The plurality of grooves may be arranged on the first side. Each of the plurality of grooves may comprise a width, and each of the through openings may comprise a diameter, and wherein the diameter is greater than the width.
The tension of the belt is greater than approximately 30 KN/m, and preferably 50 KN/m. The roll may comprise a vacuum roll. The roll may comprise a vacuum roll having an interior circumferential portion. The vacuum roll may comprise at least one vacuum zone arranged within said interior circumferential portion. The roll may comprise a vacuum roll having a suction zone. The suction zone may comprise a circumferential length of between approximately 200 mm and approximately 2500 mm. The circumferential length may be in the range of between approximately 800 mm and approximately 1800 mm. The circumferential length may be in the range of between approximately 1200 mm and approximately 1600 mm. The permeable belt may comprise at least one of a polyurethane extended nip belt or a spiral link fabric. The permeable belt may comprise a polyurethane extended nip belt which includes a plurality of reinforcing yarns embedded therein. The plurality of reinforcing yarns may comprise a plurality of machine direction yarns and a plurality of cross direction yarns. The permeable belt may comprise a polyurethane extended nip belt having a plurality of reinforcing yarns embedded therein, said plurality of reinforcing yarns being woven in a spiral link manner. The permeable belt may comprise a spiral link fabric (which importantly produces good results) or two or more spiral link fabrics.
The belt press may further comprise a first fabric and a second fabric traveling between the permeable belt and the roll. The first fabric has a first side and a second side. The first side of the first fabric is in at least partial contact with the exterior surface of the roil. The second side of the first fabric is in at least partial contact with a first side of a fibrous web. The second fabric has a first side and a second side. The first side of the second fabric is in at least partial contact with the first side of the permeable belt. The second side of the second fabric is in at least partial contact with a second side of the fibrous web. It is also possible to have a second permeable belt on top of the first fabric
The first fabric may comprise a permeable dewatering belt. The second fabric may comprise a structured fabric. The fibrous web may comprise a tissue web or hygiene web. The invention also provides for a fibrous material drying arrangement comprising an endlessly circulating permeable extended nip press (ENP) belt guided over a roll. The ENP belt is subjected to a tension of at least approximately 30 KN/m. The ENP belt comprises a side having an open area of at least approximately 25% and a contact area of at least approximately 10%.
The invention also provides for a permeable extended nip press (ENP) belt which is capable of being subjected to a tension of at least approximately 30 KN/m, wherein the permeable ENP belt comprises at least one side comprising an open area of at least approximately 25% and a contact area of at least approximately 10%.
The open area may be defined by through openings and the contact area is defined by a planar surface. The open area may be defined by through openings and the contact area is defined by a planar surface without openings, recesses, or grooves. The open area may be defined by through openings and grooves, and the contact area is defined by a planar surface without openings, recesses, or grooves. The open area may be between approximately 15% and approximately 50%, and the contact area may be between approximately 50% and approximately 85%. The open area may be between approximately 30% and approximately 85%, and the contact area may be between approximately 15% and approximately 70%. The open area may be between approximately 45% and approximately 85%, and the contact area may be between approximately 15% and approximately 55%. The open area may be between approximately 50% and approximately 65%, and the contact area may be between approximately 35% and approximately 50%. The permeable ENP belt may comprise a spiral link fabric. The open area may be between approximately 10% and approximately 40%, and the contact area is between approximately 60% and approximately 90%. The permeable ENP belt may comprise through openings arranged in a generally symmetrical pattern. The permeable ENP belt may comprise through openings arranged in generally parallel rows relative to a machine direction. The permeable ENP belt may comprise an endless circulating belt.
The permeable ENP belt may comprise through openings and the at least one side of the permeable ENP belt may comprise a plurality of grooves, each of the plurality of grooves intersects a different set of through hole. Each of the plurality of grooves may comprise a width, and each of the through openings may comprise a diameter, and wherein the diameter is greater than the width. Each of the plurality of grooves extend into the permeable ENP belt by an amount which is less than a thickness of the permeable belt.
The tension may be greater than approximately 30 KN/m and is preferably greater than approximately 50 KN/m, or greater than approximately 60 KN/m, or greater than approximately 80 KN/m. The permeable ENP belt may comprise a flexible reinforced polyurethane member. The permeable ENP belt may comprise a flexible spiral link fabric. The permeable ENP belt may comprise a flexible polyurethane member having a plurality of reinforcing yarns embedded therein. The plurality of reinforcing yarns may comprise a plurality of machine direction yarns and a plurality of cross direction yarns. The permeable ENP belt may comprise a flexible polyurethane material and a plurality of reinforcing yarns embedded therein, said plurality of reinforcing yarns being woven in a spiral link manner.
The invention also provides for a method of subjecting a fibrous web to pressing in a paper machine, wherein the method comprises applying pressure against a contact area of the fibrous web with a portion of a permeable belt, wherein the contact area is at least approximately 10% of an area of said portion and moving a fluid through an open area of said permeable belt and through the fibrous web, wherein said open area is at least approximately 25% of said portion, wherein, during the applying and the moving, said permeable belt has a tension of at least approximately 30 KN/m.
The contact area of the fibrous web may comprise areas which are pressed more by the portion than non-contact areas of the fibrous web. The portion of the permeable belt may comprise a generally planar surface which includes no openings, recesses, or grooves and which is guided over a roll. The fluid may comprises air. The open area of the permeable belt may comprise through openings and grooves. The tension may be greater than approximately 50 KN/m.
The method may further comprise rotating a roll in a machine direction, wherein said permeable belt moves in concert with and is guided over or by said roll. The permeable belt may comprise a plurality of grooves and through openings, each of said plurality of grooves being arranged on a side of the permeable belt and intersecting with a different set of through openings. The applying and the moving may occur for a dwell time which is sufficient to produce a fibrous web solids level in the range of between approximately 25% and approximately 55%. Preferably, the solids level may be greater than approximately 30%, and most preferably it is greater than approximately 40%. These solids levels may be obtained whether the permeable belt is used on a belt press or on a No Press/Low Press arrangement. The permeable belt may comprises a spiral link fabric.
The invention also provides for a method of pressing a fibrous web in a paper machine, wherein the method comprises applying a first pressure against first portions of the fibrous web with a permeable belt and a second greater pressure against second portions of the fibrous web with a pressing portion of the permeable belt, wherein an area of the second portions is at least approximately 25% of an area of the first portions and moving air through open portions of said permeable belt, wherein an area of the open portions is at least approximately 25% of the pressing portion of the permeable belt which applies the first and second pressures, wherein, during the applying and the moving, the permeable belt has a tension of at least approximately 30 KN/m.
The tension may be greater than approximately 50 KN/m or may be greater than approximately 60 KN/m or may be greater than approximately 80 KN/m. The method may further comprise rotating a roll in a machine direction, said permeable belt moving in concert with said roll. The area of the open portions may be at least approximately 50%. The area of the open portions may be at least approximately 70%. The second greater pressure may be in the range of between approximately 30 KPa and approximately 150 KPa. The moving and the applying may occur substantially simultaneously.
The method may further comprise moving the air through the fibrous web for a dwell time which is sufficient to produce a fibrous web solids in the range of between approximately 25% and approximately 55%. The dwell time may be equal to or greater than approximately 40 ms and is preferably equal to or greater than approximately 50 ms. Air flow can be approximately 150 m3/min per meter machine width.
The invention also provides for a method of drying a fibrous web in a belt press which includes a roll and a permeable belt comprising through openings, wherein an area of the through openings is at least approximately 25% of an area of a pressing portion of the permeable belt, and wherein the permeable belt is tensioned to at least approximately 30 KN/m, wherein the method comprises guiding at least the pressing portion of the permeable belt over the roll, moving the fibrous web between the roll and the pressing portion of the permeable belt, subjecting at least approximately 25% of the fibrous web to a pressure produced by portions of the permeable belt which are adjacent to the through openings, and moving a fluid through the through openings of the permeable belt and the fibrous web.
The invention also provides for a method of drying a fibrous web in a belt press which includes a roll and a permeable belt comprising through openings and grooves, wherein an area of the through openings is at least approximately 25% of an area of a pressing portion of the permeable belt, and wherein the permeable belt is tensioned to at least approximately 30 KN/m, wherein the method comprises guiding at least the pressing portion of the permeable belt over the roll, moving the fibrous web between the roll and the pressing portion of the permeable belt, subjecting at least approximately 10% of the fibrous web to a pressure produced by portions of the permeable belt which are adjacent to the through openings and the grooves, and moving a fluid through the through openings and the grooves of the permeable belt and the fibrous web.
According to another aspect of the invention, there is provided a more efficient dewatering process, preferably for the tissue manufacturing process, wherein the web achieves a dryness in the range of up to about 40% dryness. The process according to the invention is less expensive in machinery and in operational costs, and provides the same web quality as the TAD process. The bulk of the produced tissue web according to the invention is greater than approximately 10 g/cm3, up to the range of between approximately 14 g/cm3 and approximately 16 g/cm3. The water holding capacity (measured by the basket method) of the produced tissue web according to the invention is greater than approximately 10 (g H20/g fiber), and up to the range of between approximately 14 (g H20/g fiber) and approximately 16 (g H20/g fiber).
The invention thus provides for a new dewatering process, for thin paper webs, with a basis weight less than approximately 42 g/m2, preferably for tissue paper grades. The invention also provides for an apparatus which utilizes this process and also provides for elements with a key function for this process.
A main aspect of the invention is a press system which includes a package of at least one upper (or first), at least one lower (or second) fabric and a paper web disposed therebetween. A first surface of a pressure producing element is in contact with the at least one upper fabric. A second surface of a supporting structure is in contact with the at least one lower fabric and is permeable. A differential pressure field is provided between the first and the second surface, acting on the package of at least one upper and at least one lower fabric, and the paper web therebetween, in order to produce a mechanical pressure on the package and therefore on the paper web. This mechanical pressure produces a predetermined hydraulic pressure in the web, whereby the contained water is drained. The upper fabric has a bigger roughness and/or compressibility than the lower fabric. An airflow is caused in the direction from the at least one upper to the at least one lower fabric through the package of at least one upper and at least one lower fabric and the paper web therebetween.
Different possible modes and additional features are also provided. For example, the upper fabric may be permeable, and/or a so-called “structured fabric”. By way of non-limiting examples, the upper fabric can be e.g., a TAD fabric, a membrane or fabric which includes a permeable base fabric and a lattice grid attached thereto and which is made of polymer such as polyurethane. The lattice grid side of the fabric can be in contact with a suction roll while the opposite side contacts the paper web. The lattice grid can also be oriented at an angle relative to machine direction yarns and cross-direction yarns. The base fabric is permeable and the lattice grid can be a anti-rewet layer. The lattice can also be made of a composite material, such as an elastomeric material. The lattice grid can itself include machine direction yarns with the composite material being formed around these yarns. With a fabric of the above mentioned type it is possible to form or create a surface structure that is independent of the weave patterns. At least for tissue, an important consideration is to provide a soft layer in contact with the sheet.
The upper fabric may transport the web to and from the press system. The web can lie in the three-dimensional structure of the upper fabric, and therefore it is not flat but has also a three-dimensional structure, which produces a high bulky web. The lower fabric is also permeable. The design of the lower fabric is made to be capable of storing water. The lower fabric also has a smooth surface. The lower fabric is preferably a felt with a batt layer. The diameter of the batt fibers of the lower fabric are equal to or less than approximately 11 dtex, and can preferably be equal to or lower than approximately 4.2 dtex, or more preferably be equal to or less than approximately 3.3 dtex. The batt fibers can also be a blend of fibers. The lower fabric can also contain a vector layer which contains fibers from approximately 67 dtex, and can also contain even courser fibers such as, e.g., approximately 100 dtex, approximately 140 dtex, or even higher dtex numbers. This is important for the good absorption of water. The wetted surface of the batt layer of the lower fabric and/or of the lower fabric itself can be equal to or greater than approximately 35 m2/m2 felt area, and can preferably be equal to or greater than approximately 65 m2/m2 felt area, and can most preferably be equal to or greater than approximately 100 m2/m2 felt area. The specific surface of the lower fabric should be equal to or greater than approximately 0.04 m2/g felt weight, and can preferably be equal to or greater than approximately 0.065 m2/g felt weight, and can most preferably be equal to or greater than approximately 0.075 m2/g felt weight. This is important for the good absorption of water. The dynamic stiffness K* [N/mm] as a value for the compressibility is acceptable if less than or equal to 100,000 N/mm, preferable compressibility is less than or equal to 90,000 N/mm, and most preferably the compressibility is less than or equal to 70,000 N/mm. The compressibility (thickness change by force in mm/N) of the lower fabric should be considered. This is important in order to dewater the web efficiently to a high dryness level. A hard surface would not press the web between the prominent points of the structured surface of the upper fabric. On the other hand, the felt should not be pressed too deep into the three-dimensional structure to avoid loosing bulk and therefore quality, e.g., water holding capacity.
The compressibility (thickness change by force in mm/N) of the upper fabric is lower than that of the lower fabric. The dynamic stiffness K* [N/mm] as a value for the compressibility of the upper fabric can be more than or equal to 3,000 N/mm and lower than the lower fabric. This is important in order to maintain the three-dimensional structure of the web, i.e., to ensure that the upper belt is a stiff structure.
The resilience of the lower fabric should be considered. The dynamic modulus for compressibility G* [N/mm2] as a value for the resilience of the lower fabric is acceptable if more than or equal to 0.5 N/mm2, preferable resilience is more than or equal to 2 N/mm2, and most preferably the resilience is more than or equal to 4 N/mm2. The density of the lower fabric should be equal to or higher than approximately 0.4 g/cm3, and is preferably equal to or higher than approximately 0.5 g/cm3, and is ideally equal to or higher than approximately 0.53 g/cm3. This can be advantageous at web speeds of greater than approximately 1200 m/min. A reduced felt volume makes it easier to take the water away from the felt by the air flow, i.e.1 to get the water through the felt. Therefore the dewatering effect is smaller. The permeability of the lower fabric can be lower than approximately 80 cfm, preferably lower than approximately 40 cfm, and ideally equal to or lower than approximately 25 cfm. A reduced permeability makes it easier to take the water away from the felt by the air flow, i.e., to get the water through the felt. As a result, the re-wetting effect is smaller. A too high permeability, however, would lead to a too high air flow, less vacuum level for a given vacuum pump, and less dewatering of the felt because of the too open structure.
The second surface of the supporting structure can be flat and/or planar. In this regard, the second surface of the supporting structure can be formed by a flat suction box. The second surface of the supporting structure can preferably be curved. For example, the second surface of the supporting structure can be formed or run over a suction roll or cylinder whose diameter is, e.g., approximately 1 m or more or approximately 1.2 m or more. For example, for a production machine with a 200 inch width, the diameter can be in the range of approximately 1.5 m or more. The suction device or cylinder may comprise at least one suction zone. It may also comprise two suction zones. The suction cylinder may also include at least one suction box with at least one suction arc. At least one mechanical pressure zone can be produced by at least one pressure field (i.e., by the tension of a belt) or through the first surface by, e.g., a press element. The first surface can be an impermeable belt, but with an open surface toward the first fabric, e.g., a grooved or a blind drilled and grooved open surface, so that air can flow from outside into the suction arc. The first surface can be a permeable belt. The belt may have an open area of at least approximately 25%, preferably greater than approximately 35%, most preferably greater than approximately 50%. The belt may have a contact area of at least approximately 10%, at least approximately 25%, and preferably between approximately 50% and approximately 85% in order to have a good pressing contact.
In addition, the pressure field can be produced by a pressure element, such as a shoe press or a roll press. This has the following advantage: If a very high bulky web is not required, this option can be used to increase dryness and therefore production to a desired value, by adjusting carefully the mechanical pressure load. Due to the softer second fabric the web is also pressed at least partly between the prominent points (valleys) of the three-dimensional structure. The additional pressure field can be arranged preferably before (no re-wetting), after or between the suction area. The upper permeable belt is designed to resist a high tension of more than approximately 30 KN/m, and preferably approximately 50 KN/m, or higher e.g., approximately 80 KN/m. By utilizing this tension, a pressure is produced of greater than approximately 0.3 bar, and preferably approximately 1 bar, or higher, may be e.g., approximately 1.5 bar. The pressure “p” depends on the tension “S” and the radius “R” of the suction roll according to the well known equation, p=S/R. As can be seen from the equation, the greater the roll diameter the greater the tension need to be to achieve the required pressure. The upper belt can also be a stainless steel and/or a metal band and/or a polymeric band. The permeable upper belt can be made of a reinforced plastic or synthetic material. It can also be a spiral linked fabric. Preferably, the belt can be driven to avoid shear forces between the first and second fabrics and the web. The suction roll can also be driven. Both of these can also be driven independently.
The first surface can be a permeable belt supported by a perforated shoe for the pressure load.
The air flow can be caused by a non-mechanical pressure field alone or in combination as follows: with an underpressure in a suction box of the suction roll or with a flat suction box, or with an overpressure above the first surface of the pressure producing element, e.g., by a hood, supplied with air, e.g., hot air of between approximately 50 degrees C. and approximately 180 degrees C., and preferably between approximately 120 degrees C. and approximately 150 degrees C., or also preferably steam. Such a higher temperature is especially important and preferred if the pulp temperature out of the headbox is less than about 35 degrees C. This is the case for manufacturing processes without or with less stock refining. Of course, all or some of the above-noted features can be combined.
The pressure in the hood can be less than approximately 0.2 bar, preferably less than approximately 0.1, most preferably less than approximately 0.05 bar. The supplied air flow to the hood can be less or preferable equal to the flow rate sucked out of the suction roll by vacuum pumps. A desired air flow is approximately 140 m3/min per meter of machine width. Supplied air flow to the hood at atmospheric pressure can be equal to approximately 500 m3/min per meter of machine width. The flow rate sucked out of the suction roll by a vacuum pump can have a vacuum level of approximately 0.6 bar at approximately 25 degrees C.
The suction roll can be wrapped partly by the package of fabrics and the pressure producing element, e.g., the belt, whereby the second fabric has the biggest wrapping arc “a1” and leaves the arc zone lastly. The web together with the first fabric leaves secondly, and the pressure producing element leaves firstly. The arc of the pressure producing element is bigger than arc of the suction box. This is important, because at low dryness, the mechanical dewatering is more efficient than dewatering by airflow. The smaller suction arc “a2” should be big enough to ensure a sufficient dwell time for the air flow to reach a maximum dryness. The dwell time “T” should be greater than approximately 40 ms, and preferably is greater than approximately 50 ms. For a roll diameter of approximately 1.2 m and a machine speed of approximately 1200 m/min, the arc “a2” should be greater than approximately 76 degrees, and preferably greater than approximately 95 degrees. The formula is a2=[dwell time*speed*360/circumference of the roll].
The second fabric can be heated e.g., by steam or process water added to the flooded nip shower to improve the dewatering behavior. With a higher temperature, it is easier to get the water through the felt. The belt could also be heated by a heater or by the hood or steam box. The TAD-fabric can be heated especially in the case when the former of the tissue machine is a double wire former. This is because, if it is a crescent former, the TAD fabric will wrap the forming roll and will therefore be heated by the stock which is injected by the headbox.
There are a number of advantages of this process describe herein. In the prior art TAD process, ten vacuum pumps are needed to dry the web to approximately 25% dryness. On the other hand, with the advanced dewatering system of the invention, only six vacuum pumps are needed to dry the web to approximately 35%. Also, with the prior art TAD process, the web should preferably be dried up to a high dryness level of between about 60% and about 75%, otherwise a poor moisture cross profile would be created. This way a lot of energy is wasted and the Yankee and hood capacity is only used marginally. The system of the instant invention makes it possible to dry the web in a first step up to a certain dryness level of between approximately 30 and approximately 40%, with a good moisture cross profile. In a second stage, the dryness can be increased to an end dryness of more than approximately 90% using a conventional Yankee/hood (impingement) dryer combined the inventive system. One way to produce this dryness level, can include more efficient impingement drying via the hood on the Yankee.
With the system according to the invention, there is no need for through air drying. A paper having the same quality as produced on a TAD machine is generated with the inventive system utilizing the whole capability of impingement drying which is more efficient in drying the sheet from 35% to more than 90% solids.
The invention also provides for a belt press for a paper machine, wherein the belt press comprises a vacuum roll comprising an exterior surface and at least one suction zone. A permeable belt comprises a first side and is guided over a portion of the exterior surface of the vacuum roll. The permeable belt has a tension of at least approximately 30 KN/m. The first side has an open area of at least approximately 25% a contact area of at least approximately 10%.
The at least one suction zone may comprises a circumferential length of between approximately 200 mm and approximately 2,500 mm. The circumferential length may define an arc of between approximately 80 degrees and approximately 180 degrees. The circumferential length may define an arc of between approximately 80 degrees and approximately 130 degrees. The at least one suction zone may be adapted to apply vacuum for a dwell time which is equal to or greater than approximately 40 ms. The dwell time may be equal to or greater than approximately 50 ms. The permeable belt may exert a pressing force on the vacuum roll for a first dwell time which is equal to or greater than approximately 40 ms. The at least one suction zone may be adapted to apply vacuum for a second dwell time which is equal to or greater than approximately 40 ms. The second dwell time may be equal to or greater than approximately 50 ms. The first dwell time may be equal to or greater than approximately 50 ms. The permeable belt may comprise at least one spiral link fabric. The at least one spiral link fabric may comprise a synthetic, a plastic, a reinforced plastic, and/or a polymeric material. The at least one spiral link fabric may comprise stainless steel. The at least one spiral link fabric may comprise a tension which is between approximately 30 KN/m and approximately 80 KN/m. The tension may be between approximately 35 KN/m and approximately 70 KN/m.
The invention also provides for a method of pressing and drying a paper web, wherein the method comprises pressing, with a pressure producing element, the paper web between at least one first fabric and at least one second fabric and simultaneously moving a fluid through the paper web and the at least one first and second fabrics.
The pressing may occur for a dwell time which is equal to or greater than approximately 40 ms. The dwell time may be equal to or greater than approximately 50 ms. The simultaneously moving may occur for a dwell time which is equal to or greater than approximately 40 ms. This dwell time may be equal to or greater than approximately 50 ms. The pressure producing element may comprise a device which applies a vacuum. The vacuum may be greater than approximately 0.5 bar. The vacuum may be greater than approximately 1 bar. The vacuum may be greater than approximately 1.5 bar.
TAD technology developed as a completely new set up for tissue machinery because older machines could not be rebuilt due to the immense costs involved in doing so and because this older technology had very high energy consumption.
The assignee company of the instant patent application developed a technology which would allow existing machines to be rebuilt and also developed new machines that made tissue with increased paper quality and to the highest standards. Such machines, however, require different fabrics and one main aim of the invention is to provide such fabrics For example, such fabrics should has a very high resilience and/or softness in order to react properly in an environment where it experiences pressure provided by a tension belt. Such fabrics should also have very good pressure transfer characteristics in order to achieve uniform dewatering, especially when the pressure is provided by a tension belt of a system such as, e.g., an ATMOS system. The fabric should also have high temperature stability so that it performs well in the temperature environments which result from the use of hot air blow boxes. A certain range of air permeability is also needed for the fabric so that when hot air is blown from above the fabric and vacuum pressure is applied to the vacuum side of the fabric (or the paper package which includes the same), the mixture of water and air (i.e., hot air) will pass through the fabric and/or package containing the fabric.
The dewatering fabric should also be capable of applying pressure to the paper sheet without loosing bulk which can occur when the fabric steels some of the paper from the TAD fabric as the paper is separated from the fabric. Additionally, the dewatering fabric should have excellent anti-rewetting properties, especially in an environment where the paper is subjected to low pressure dewatering which can occur in a vacuum/pressure/high temperature zone.
The fabric should preferably have a base substrate portion and a fibrous portion. The base substrate portion should be responsible for dewatering of the paper/tissue sheet as well as for ensuring that the paper/tissue sheet has good bulk quality.
The base substrate can be a conventional felt material, a felt that incorporates ATMOS technology, or a combination thereof. In this regard, the dewatering fabric should be a porous media which contains a mainly stress absorbing structure which has machine direction (md) strength and cross direction (cd) strength as well as a certain void volume. This structure can be a woven structure which is made from substantially equal sized yarns as well as yarns that are different. The yarns can also be woven in a variety of weave patterns from single to several layer weave types including those which are weft bound warp bound. Different filler yarns could also be used. Additionally, weave types can also be utilized. Combinations of different available structures (e.g., woven, membranes, films, leno, yarn layered systems and so on) are also possible and such a fabric can have certain specific beneficial properties such as, e.g., resiliency and tensile strength. Such structures could also be either endless or seamable. If the fabric is seamable, it can be provided with different types of seams. The advantage of a seamable structure is that it can be utilized on rebuilt machines as in the case of machines which do not have any cantilever arrangements that allow for the use of endless fabrics. The yarns used for the dewatering fabric can also have different shapes, e.g., flat yarns or elliptical yarns, but are preferably round yarns. The yarns can also be mono yarns or twisted yarns or different combinations thereof. The yarns can additionally also be multifilament yarns of mainly polyamid (e.g., PA 6; PA 6.6; PA 6.12; and so on). Other different polymeric materials, whether natural or artificial, can also be used in specific circumstances. The yarns can further also be one or more component yarns in order to provide certain properties. For example, a two component yarn utilizing PA 6 and sheath PU can be advantageous because both materials can provide unique benefits. In this case, the PA will provide strength in the yarn direction and the PU will provide additional void volume and, due to the material properties, a higher resilience.
Nano particles can be added to the materials in the yarns and/or to other parts of the structure such as the fibers and membranes. Membrane materials (such as spectra) can be used in the fabric as in the case in conventional felts. Such structures can provide good void volume and permeability in all paper grades. Based on the high amount of highly resilient material (when using e.g. PU), the overall resilience is much higher than needed on most conventional arrangements. Such membranes can have very different properties with regard to materials, open areas, caliper, substructures, strength, form, amount and size of pores, and so on. It is also possible for the structure to utilize the combination of a membrane and a laminated non-woven portion.
Non-woven structures can also be utilized. In this regard, the structure can utilize Vector technology, wherein a course non-woven substrate is used having a wide weight range from between approximately 100 g/m2 to approximately 500 g/m2. This structure can also contain fibers which can be greater than approximately 140 dtex or less than approximately 140 dtex. The non-woven structure can also be in the form of a single component or several components. Moreover, even if a single component is utilized, it can utilize different materials, shapes, and so on.
Other structures can also be utilized for the base substrate such as a link fabric or a compound link fabric on which, for example, a porous media can be three-dimensionally extruded, sintered, and so on. Such a structure would allow the use of other available technologies like click systems (father—mother systems).
The fibrous portion of the structure is a porous structure arranged on the base substrate and on one or both sides of the fabric. This portion contacts the paper sheet unlike the base structure which, in most cases, does not directly contact the paper sheet. One appropriate form of the fibrous portion would include fibers such as polymeric (natural and/or artificial) fibers. The fibrous portion can utilize one component fibers as well as a two or more component fibers. The fibers can be in the range of between approximately 1.0 dtex and approximately 350 dtex, and are preferably between approximately 1.7 dtex and approximately 100 dtex, and most preferably between approximately 2.2 dtex and approximately 40 dtex. Of course, other fibers types and sizes can be utilized which are outside these ranges. The fibers can have a shape such as round, oval, flat, and can also be either uniform or irregular in shape (e.g., crocodile fibers). The fibers can also be made from materials which allow for splitting of the fibers either in during the manufacturing process or during the run on the paper machine. Materials which can be used for the fibers (whether splitable or nonsplitable) can be, e.g., PA, PES, PET and PU. The fibers can also be core sheath or side by side structures, and so on. The fibers can also, of course, be any type and shape which is utilized in the prior art and can be utilized based on the benefits they provide.
The fibers can be used as batt and/or can be arranged in pre-processed layers. Such fibers can also be treated chemically to achieve a certain surface energy (i.e., they can be hydrophilic or hydrophobic). The treatment can take place for one or more layers. Alternatively, the entire dewatering fabric can be so treated chemically. One or more of the layers of a multi-layered fibrous portion can even be treated differently depending on their properties or depending on the desired properties of the layers. The use of different fibers in different layers can lead to distinctive and very different partial densities in the dewatering fabric over a width of the structure. Preferably, the fabric utilizes fibers in at least one later of batt on at least one side of the dewatering fabric.
Another way to make the porous media portion of the fibrous portion utilizes soluble materials which are mixed with unsoluble materials. The process can ensure that the soluble material is dissolved in order to create specific permeability. This can be combined with the use, for example, of one or more types of fibrous systems.
Particle technology can also be utilized wherein particles are deposited and connected (using e.g., sintering, e-process, etc.) in order to form or modify the porous media. Specific modifications of the two sides of the dewatering fabric can increase and/or improve the runability. The paper contacting side of the dewatering fabric can have a surface which is configured to match the pattern of the TAD fabric. Furthermore, the opposite side of the fabric can have a surface that is configured to match the shape/surface of the tension belt.
The use of thermoplastic materials can also be utilized on one of more surfaces of the fabric as well as within the internal structure of the fabric. Such materials can improve certain properties of the fabric such as abrasion resistance and resilience. Certain properties of the dewatering fabric can be achieved using different processes. For example, the fabric can be subjected to processes which remove material (e.g., grinding) as well as processes which add material (e.g., sintering, printing, etc.) and so on. The use of physical or chemical processes allow both the surfaces of the dewatering fabric as well as the interior thereof to be modified as desired.
The fibrous portion and substrate base can be connected and/or laminated together by either physical or chemical connection systems. Such connections can be utilized between different materials and between layers of the fabric.
The following are non-limiting characteristics and/or properties of the dewatering fabric; the caliper can be between approximately 0.1 mm and approximately 15 mm, are preferably between approximately 1.0 mm and approximately 10 mm, and most preferably between approximately 1.5 mm and approximately 2.5 mm; the permeability can be between approximately 1 cfm and approximately 500 cfm, is preferably between approximately 5 cfm and approximately 100 cfm, is most preferably between approximately 10 cfm and approximately 50 cfm, and is still most preferably between approximately 15 cfm and approximately 25 cfm; the overall density can be between approximately 0.2 g/cm3 and approximately 1.10 g/cm3, is preferably between approximately 0.3 g/Cm3 and approximately 0.8 g/cm3, and is most preferably between approximately 0.4 g/cm3 and approximately 0.7 g/cm3; the product weight range can be between approximately 100 g/m2 and approximately 3000 g/m2, is preferably between approximately 800 g/m2 and approximately 2200 g/m2, is most preferably between approximately 1000 g/m2 and approximately 1750 g/m2, is still more preferably between approximately 1000 g/m2 and approximately 1400 g/m2. The dewatering fabric can also comprise at least one layer that is polar and/or at least one layer that is non-polar, and/or at least one layer that is hydrophobic, and/or at least one layer that is hydrophilic.
One purpose of the dewatering is to dewater the sheet in a long extended press nip. This allows additional air/steam to act upon the sheet and improves dewatering. The dewatering fabric of the invention should be distinguished from the typical TAD fabric which is very much more open, or a rigid construction, and has distinctly less fine face than the dewatering fabric of the invention.
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:
a is an enlarged cross-sectional view of the permeable belt of
b is an enlarged cross-sectional view of the permeable belt of
c is an enlarged cross-sectional view of the permeable belt of
a-b illustrate one way in which the contact area can be measured;
a illustrates an area of an Ashworth metal belt which can be used in the invention. The portions of the belt which are shown in black represent the contact area whereas the portions of the belt shown in white represent the non-contact area;
b illustrates an area of a Cambridge metal belt which can be used in the invention. The portions of the belt which are shown in black represent the contact area whereas the portions of the belt shown in white represent the non-contact area;
c illustrates an area of a Voith Fabrics link fabric which can be used in the invention. The portions of the belt which are shown in black represent the contact area whereas the portions of the belt shown in white represent the non-contact area;
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplary embodiments set out herein illustrate one or more acceptable or preferred embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description is taken with the drawings making apparent to those skilled in the art how the forms of the present invention may be embodied in practice.
Referring now to the drawings, and more particularly to
Fibrous web 12 is moved by fabric 14 in a machine direction M past one or more guide rolls and then past the suction box 16. At the vacuum box 16, sufficient moisture is removed from web 12 to achieve a solids level of between approximately 15% and approximately 25% on a typical or nominal 20 gram per square meter (gsm) web running. The vacuum at the box 16 provides between approximately −0.2 to approximately −0.8 bar vacuum, with a preferred operating level of between approximately −0.4 to approximately −0.6 bar.
As fibrous web 12 proceeds along the machine direction M, it comes into contact with a dewatering fabric 20. The dewatering fabric 20 can be an endless circulating belt which is guided by a plurality of guide rolls and is also guided around the suction roll 18. The dewatering belt 20 can be a dewatering fabric of the type shown and described in FIGS. 13 or 14 herein. The dewatering fabric 20 can also preferably be a felt. The web 12 then proceeds toward vacuum roll 18 between the fabric 14 and the dewatering fabric 20. The vacuum roll 18 rotates along the machine direction M and is operated at a vacuum level of between approximately −0.2 to approximately −0.8 bar with a preferred operating level of at least approximately −0.4 bar, and most preferably approximately −0.6 bar. By way of non-limiting example, the thickness of the vacuum roll shell of roll 18 may be in the range of between approximately 25 mm and approximately 75 mm. The mean airflow through the web 12 in the area of the suction zone Z can be approximately 150 m3/min per meter of machine width. The fabric 14, web 12 and dewatering fabric 20 are guided through a belt press 22 formed by the vacuum roll 18 and a permeable belt 34. As is shown in
The upper fabric 14 transports the web 12 to and from the belt press system 22. The web 12 lies in the three-dimensional structure of the upper fabric 14, and therefore it is not flat but has also a three-dimensional structure, which produces a high bulky web. The lower fabric 20 is also permeable. The design of the lower fabric 20 is made to be capable of storing water. The lower fabric 20 also has a smooth surface. The lower fabric 20 is preferably a felt with a batt layer. The diameter of the batt fibers of the lower fabric 20 are equal to or less than approximately 11 dtex, and can preferably be equal to or lower than approximately 4.2 dtex, or more preferably be equal to or less than approximately 3.3 dtex. The batt fibers can also be a blend of fibers. The lower fabric 20 can also contain a vector layer which contains fibers from approximately 67 dtex, and can also contain even courser fibers such as, e.g., approximately 100 dtex, approximately 140 dtex, or even higher dtex numbers. This is important for the good absorption of water. The wetted surface of the batt layer of the lower fabric 20 and/or of the lower fabric itself can be equal to or greater than approximately 35 m2/m2 felt area, and can preferably be equal to or greater than approximately 65 m2/m2 felt area, and can most preferably be equal to or greater than approximately 100 m2/m2 felt area. The specific surface of the lower fabric 20 should be equal to or greater than approximately 0.04 m2/g felt weight, and can preferably be equal to or greater than approximately 0.065 m2/g felt weight, and can most preferably be equal to or greater than approximately 0.075 m2/g felt weight. This is important for the good absorption of water. The dynamic stiffness K* [N/mm] as a value for the compressibility is acceptable if less than or equal to 100,000 N/mm, preferable compressibility is less than or equal to 90,000 N/mm, and most preferably the compressibility is less than or equal to 70,000 N/mm. The compressibility (thickness change by force in mm/N) of the lower fabric 20 should be considered. This is important in order to dewater the web efficiently to a high dryness level. A hard surface would not press the web 12 between the prominent points of the structured surface of the upper fabric. On the other hand, the felt should not be pressed too deep into the three-dimensional structure to avoid loosing bulk and therefore quality, e.g., water holding capacity.
The circumferential length of vacuum zone Z can be between approximately 200 mm and approximately 2500 mm, and is preferably between approximately 800 mm and approximately 1800 mm, and an even more preferably between approximately 1200 mm and approximately 1600 mm. The solids content leaving vacuum roll 18 in web 12 will vary between approximately 25% to approximately 55% depending on the vacuum pressures and the tension on permeable belt, as well as the length of vacuum zone Z and the dwell time of web 12 in vacuum zone Z. The dwell time of web 12 in vacuum zone Z is sufficient to result in this solids range of between approximately 25% and approximately 55%.
With reference to
The fabric 20 proceeds past one or more shower units 30. These units 30 apply moisture to the fabric 20 in order to clean the fabric 20. The fabric 20 then proceeds past a Uhle box 28, which removes moisture from fabric 20.
The fabric 14 can be a structured fabric 14, i.e., it can have a three dimensional structure that is reflected in web 12, whereby thicker pillow areas of the web 12 are formed. The structured fabric 14 may have, e.g., approximately 44 mesh, between approximately 30 mesh and approximately 50 mesh for towel paper, and between approximately 50 mesh and approximately 70 mesh for toilet paper. These pillow areas are protected during pressing in the belt press 22 because they are within the body of the structured fabric 14. As such, the pressing imparted by belt press assembly 22 upon the web 12 does not negatively impact web or sheet quality. At the same time, it increases the dewatering rate of vacuum roll 18. If the belt 34 is used in a No Press/Low Press apparatus, the pressure can be transmitted through a dewatering fabric, also known as a press fabric. In this case, the web 12 is not protected with a structured fabric 14. However, the use of the belt 34 is still advantageous because the press nip is much longer than a conventional press, which results in a lower specific pressure and less or reduced sheet compaction of the web 12.
The permeable belt 34 shown in
As is shown in
By way of non-limiting example, the width of the generally parallel grooves 40 shown in
With reference to
By way of non-limiting example, and with reference to the embodiments shown in
As with the previous embodiments, the permeable belt 34 shown in FIGS. 10 and 11 is capable of running at high running tensions of between at least approximately 30 KN/m and at least approximately 50 KN/m or higher and may have a surface contact area of approximately 10% or greater, as well as an open area of approximately 15% or greater. The open area may be approximately 25% or greater. The composition of permeable belt 34 shown in
The process of using the advanced dewatering system (ADS) 10 shown in
The permeable belt 34 of the present invention is capable of applying a line force over an extremely long nip, i.e., 10 times longer than for a shoe press, thereby ensuring a long dwell time in which pressure is applied against web 12 as compared to a standard shoe press. This results in a much lower specific pressure, i.e., 20 times lower than for a shoe press, thereby reducing the sheet compaction and enhancing sheet quality. The present invention further allows for a simultaneous vacuum and pressing dewatering with airflow through the web at the nip itself.
The fibrous web 112 is moved by fabric 114 in a machine direction M past one or more guide rolls. Although it may not be necessary, before reaching the suction roll, the web 112 may have sufficient moisture is removed from web 112 to achieve a solids level of between approximately 15% and approximately 25% on a typical or nominal 20 gram per square meter (gsm) web running. This can be accomplished by vacuum at a box (not shown) of between approximately −0.2 to approximately −0.8 bar vacuum, with a preferred operating level of between approximately −0.4 to approximately −0.6 bar.
As fibrous web 112 proceeds along the machine direction M, it comes into contact with a dewatering fabric 120. The dewatering fabric 120 can be an endless circulating belt which is guided by a plurality of guide rolls and is also guided around a suction roll 118. The web 112 then proceeds toward vacuum roll 118 between the fabric 114 and the dewatering fabric 120. The vacuum roll 118 can be a driven roll which rotates along the machine direction M and is operated at a vacuum level of between approximately −0.2 to approximately −0.8 bar with a preferred operating level of at least approximately −0.4 bar. By way of non-limiting example, the thickness of the vacuum roll shell of roll 118 may be in the range of between 25 mm and 75 mm. The mean airflow through the web 112 in the area of the suction zone Z can be approximately 150 m3/min per meter machine width. The fabric 114, web 112 and dewatering fabric 120 is guided through a belt press 122 formed by the vacuum roll 118 and a permeable belt 134. As is shown in
The circumferential length of vacuum zone Z can be between approximately 200 mm and approximately 2500 mm, and is preferably between approximately 800 mm and approximately 1800 mm, and an even more preferably between approximately 1200 mm and approximately 1600 mm. The solids leaving vacuum roll 118 in web 112 will vary between approximately 25% and approximately 55% depending on the vacuum pressures and the tension on permeable belt as well as the length of vacuum zone Z and the dwell time of web 112 in vacuum zone Z. The dwell time of web 112 in vacuum zone Z is sufficient to result in this solids range of between approximately 25% to approximately 55%.
The press system shown in
The upper fabric 114 can be permeable and/or a so-called “structured fabric”. By way of non-limiting examples, the upper fabric 114 can be e.g., a TAD fabric. The hood 124 can also be replaced with a steam box which has a sectional construction or design in order to influence the moisture or dryness cross-profile of the web.
With reference to
With reference to
The belt 120 shown in
The upper fabric 114 can thus transport the web 112 to and away from the press and/or pressing system. The web 112 can lie in the three-dimensional structure of the upper fabric 114, and therefore it is not flat, but instead has also a three-dimensional structure, which produces a high bulky web. The lower fabric 120 is also permeable. The design of the lower fabric 120 is made to be capable of storing water. The lower fabric 120 also has a smooth surface. The lower fabric 120 is preferably a felt with a batt layer. The diameter of the batt fibers of the lower fabric 120 can be equal to or less than approximately 11 dtex, and can preferably be equal to or lower than approximately 4.2 dtex, or more preferably be equal to or less than approximately 3.3 dtex. The batt fibers can also be a blend of fibers. The lower fabric 120 can also contain a vector layer which contains fibers from at least approximately 67 dtex, and can also contain even courser fibers such as, e.g., at least approximately 100 dtex, at least approximately 140 dtex, or even higher dtex numbers. This is important for the good absorption of water. The wetted surface of the batt layer of the lower fabric 120 and/or of the lower fabric 120 itself can be equal to or greater than approximately 35 m2/m2 felt area, and can preferably be equal to or greater than approximately 65 m2/m2 felt area, and can most preferably be equal to or greater than approximately 100 m2/m2 felt area. The specific surface of the lower fabric 120 should be equal to or greater than approximately 0.04 m2/g felt weight, and can preferably be equal to or greater than approximately 0.065 m2/g felt weight, and can most preferably be equal to or greater than approximately 0.075 m2/g felt weight. This is important for the good absorption of water.
The compressibility (thickness change by force in mm/N) of the upper fabric 114 is lower than that of the lower fabric 120. This is important in order to maintain the three-dimensional structure of the web 112, i.e., to ensure that the upper belt 114 is a stiff structure.
The resilience of the lower fabric 120 should be considered. The density of the lower fabric 120 should be equal to or higher than approximately 0.4 g/cm3, and is preferably equal to or higher than approximately 0.5 g/cm3, and is ideally equal to or higher than approximately 0.53 g/cm3. This can be advantageous at web speeds of greater than 1200 m/min. A reduced felt volume makes it easier to take the water away from the felt 120 by the air flow, i.e., to get the water through the felt 120. Therefore the dewatering effect is smaller. The permeability of the lower fabric 120 can be lower than approximately 80 cfm, preferably lower than 40 cfm, and ideally equal to or lower than 25 cfm. A reduced permeability makes it easier to take the water away from the felt 120 by the air flow, i.e., to get the water through the felt 120. As a result, the re-wetting effect is smaller. A too high permeability, however, would lead to a too high air flow, less vacuum level for a given vacuum pump, and less dewatering of the felt because of the too open structure.
The second surface of the supporting structure, i.e., the surface supporting the belt 120, can be flat and/or planar. In this regard, the second surface of the supporting structure SF can be formed by a flat suction box SB. The second surface of the supporting structure SF can also preferably be curved. For example, the second surface of the supporting structure SF can be formed or run over a suction roll 118 or cylinder whose diameter is, e.g., approximately 1 m. The suction device or cylinder 118 may comprise at least one suction zone Z. It may also comprise two suction zones Z1 and Z2 as is shown in
The fibrous web 212 is moved by the fabric 214, which may be a TAD fabric, in a machine direction M past one or more guide rolls. Although it may not be necessary, before reaching the suction roll 218, the web 212 may have sufficient moisture is removed from web 212 to achieve a solids level of between approximately 15% and approximately 25% on a typical or nominal 20 gram per square meter (gsm) web running. This can be accomplished by vacuum at a box (not shown) of between approximately −0.2 to approximately −0.8 bar vacuum, with a preferred operating level of between approximately −0.4 to approximately −0.6 bar.
As fibrous web 212 proceeds along the machine direction M, it comes into contact with a dewatering fabric 220. The dewatering fabric 220 (which can be any type described herein) can be endless circulating belt which is guided by a plurality of guide rolls and is also guided around a suction roll 218. The web 212 then proceeds toward vacuum roll 218 between the fabric 214 and the dewatering fabric 220. The vacuum roll 218 can be a driven roll which rotates along the machine direction M and is operated at a vacuum level of between approximately −0.2 to approximately −0.8 bar with a preferred operating level of at least approximately −0.5 bar. By way of non-limiting example, the thickness of the vacuum roll shell of roll 218 may be in the range of between 25 mm and 75 mm. The mean airflow through the web 212 in the area of the suction zones Z1 and Z2 can be approximately 150 m3/meter of machine width. The fabric 214, web 212 and dewatering fabric 220 are guided through a belt press 222 formed by the vacuum roll 218 and a permeable belt 234. As is shown in
The circumferential length of at least vacuum zone Z2 can be between approximately 200 mm and approximately 2500 mm, and is preferably between approximately 800 mm and approximately 1800 mm, and an even more preferably between approximately 1200 mm and approximately 1600 mm. The solids leaving vacuum roll 218 in web 212 will vary between approximately 25% and approximately 55% depending on the vacuum pressures and the tension on permeable belt 234 and the pressure from the pressing device PS/A/JB as well as the length of vacuum zone Z2, and the dwell time of web 212 in vacuum zone Z2. The dwell time of web 212 in vacuum zone Z2 is sufficient to result in this solids range of approximately 25% and approximately 55%.
The fibrous web 312 is moved by fabric 314, which can be a TAD fabric, in a machine direction M past one or more guide rolls. Although it may not be necessary, before reaching the suction roll 318, the web 212 may have sufficient moisture is removed from web 212 to achieve a solids level of between approximately 15% and approximately 25% on a typical or nominal 20 gram per square meter (gsm) web running. This can be accomplished by vacuum at a box (not shown) of between approximately −0.2 to approximately −0.8 bar vacuum, with a preferred operating level of between approximately −0.4 to approximately −0.6 bar.
As fibrous web 312 proceeds along the machine direction M, it comes into contact with a dewatering fabric 320. The dewatering fabric 320 (which can be any type described herein) can be endless circulating belt which is guided by a plurality of guide rolls and is also guided around a suction roll 318. The web 312 then proceeds toward vacuum roll 318 between the fabric 314 and the dewatering fabric 320. The vacuum roll 318 can be a driven roll which rotates along the machine direction M and is operated at a vacuum level of between approximately −0.2 to approximately −0.8 bar with a preferred operating level of at least approximately −0.5 bar. By way of non-limiting example, the thickness of the vacuum roll shell of roll 318 may be in the range of between 25 mm and 75 mm. The mean airflow through the web 312 in the area of the suction zones Z1 and Z2 can be approximately 150 m3/meter of machine width. The fabric 314, web 312 and dewatering fabric 320 are guided through a belt press 322 formed by the vacuum roll 318 and a permeable belt 334. As is shown in
The circumferential length of at least vacuum zone Z1 can be between approximately 200 mm and approximately 2500 mm, and is preferably between approximately 800 mm and approximately 1800 mm, and an even more preferably between approximately 1200 mm and approximately 1600 mm. The solids leaving vacuum roll 318 in web 312 will vary between approximately 25% and approximately 55% depending on the vacuum pressures and the tension on permeable belt 334 and the pressure from the pressing device RP as well as the length of vacuum zone Z1 and also Z2, and the dwell time of web 312 in vacuum zones Z1 and Z2. The dwell time of web 312 in vacuum zones Z1 and Z2 is sufficient to result in this solids range between approximately 25% and approximately 55%.
The arrangements shown in
The permeable belt 234 or 334 can be supported by a perforated shoe PS for providing the pressure load.
The air flow can be caused by a non-mechanical pressure field as follows: with an underpressure in a suction box of the suction roll (118, 218 or 318) or with a flat suction box SB (see
The pressure in the hood can be less than approximately 0.2 bar, preferably less than approximately 0.1, most preferably less than approximately 0.05 bar. The supplied air flow to the hood can be less or preferable equal to the flow rate sucked out of the suction roll 118, 218, or 318 by vacuum pumps.
The suction roll 118, 218 and 318 can be wrapped partly by the package of fabrics 114, 214, or 314 and 120, 220, or 320, and the pressure producing element, e.g., the belt 134, 234, or 334, whereby the second fabric e.g., 220, has the biggest wrapping arc “a2” and leaves the larger arc zone Z1 lastly (see
The second fabric 120, 220, 320 can be heated e.g., by steam or process water added to the flooded nip shower to improve the dewatering behavior. With a higher temperature, it is easier to get the water through the felt 120, 220, 320. The belt 120, 220, 320 could also be heated by a heater or by the hood, e.g., 124. The TAD-fabric 114, 214, 314 can be heated especially in the case when the former of the tissue machine is a double wire former. This is because, if it is a crescent former, the TAD fabric 114, 214, 314 will wrap the forming roll and will therefore be heated by the stock which is injected by the headbox.
There are a number of advantages of the process using any of the herein disclosed devices such as. In the prior art TAD process, ten vacuum pumps are needed to dry the web to approximately 25% dryness. On the other hand, with the advanced dewatering systems of the invention, only six vacuum pumps are needed to dry the web to approximately 35%. Also, with the prior art TAD process, the web should preferably be dried up to a high dryness level of between about 60% and about 75%, otherwise a poor moisture cross profile would be created. This way a lot of energy is wasted and the Yankee and hood capacity is only used marginally. The systems of the instant invention make it possible to dry the web in a first step up to a certain dryness level of between approximately 30% to approximately 40%, with a good moisture cross profile. In a second stage, the dryness can be increased to an end dryness of more than approximately 90% using a conventional Yankee/hood (impingement) dryer combined the inventive system. One way to produce this dryness level, can include more efficient impingement drying via the hood on the Yankee.
As can be seen in
The entire disclosure of U.S. patent application Ser. No. 10/768,485 filed on Jan. 30, 2004 is hereby expressly incorporated by reference in its entirety. Moreover, the instant application also expressly incorporates by reference the entire disclosures of U.S. patent application Ser. No. 11/276,789 filed on Mar. 14, 2006 entitled HIGH TENSION PERMEABLE BELT FOR AN ATMOS SYSTEM AND PRESS SECTION OF PAPER MACHINE USING THE PERMEABLE BELT in the name of Ademar LIPPI ALVES FERNANDES et al., U.S. patent application Ser. No. 10/972,408 filed on Oct. 26, 2004 entitled ADVANCED DEWATERING SYSTEM in the name of Jeffrey HERMAN et al. and U.S. patent application Ser. No. 10/972,431 filed on Oct. 26, 2004 entitled PRESS SECTION AND PERMEABLE BELT IN A PAPER MACHINE in the name of Jeffrey HERMAN et al.
Referring now to the embodiment shown in
Fibrous web 412 is moved by fabric 414 in a machine direction M past the suction box 416. At the vacuum box 416, sufficient moisture is removed from web 412 to achieve a solids level of between approximately 15% and approximately 25% on a typical or nominal 20 gram per square meter (gsm) web running. The vacuum at the box 416 provides between approximately −0.2 to approximately −0.8 bar vacuum, with a preferred operating level of between approximately −0.4 to approximately −0.6 bar. As fibrous web 412 proceeds along the machine direction M, it comes into contact with a dewatering fabric 420. The dewatering fabric 420, which is described in detail below, can be an endless circulating belt which is guided by a plurality of guide rolls and is also guided around the suction roll 418. The tension of the dewatering fabric 420 can be adjusted by adjusting guide roll 433. The dewatering fabric 420 can be a dewatering fabric of the type shown and described in FIGS. 13 or 14 herein. The dewatering fabric 420 can also preferably be a felt. The web 412 then proceeds toward vacuum roll 418 between the fabric 414 and the dewatering fabric 420. The vacuum roll 418 rotates along the machine direction M and is operated at a vacuum level of between approximately −0.2 to approximately −0.8 bar with a preferred operating level of at least approximately −0.4 bar, and most preferably approximately −0.6 bar. By way of non-limiting example, the thickness of the vacuum roll shell of roll 418 may be in the range of between approximately 25 mm and approximately 75 mm. The mean airflow through the web 412 in the area of the suction zone Z can be approximately 150 m3/min per meter of machine width. The fabric 414, web 412 and dewatering fabric 420 are guided through a belt press 422 formed by the vacuum roll 418 and a permeable belt 434. As is shown in
The upper fabric 414 is an endless fabric which transports the web 412 to and from the belt press system 422 and from the forming roll 403 to the final drying arrangement which includes a Yankee cylinder 436, a hood 437, one or more coating showers 431 as well as one or more creping devices 432. The web 412 lies in the three-dimensional structure of the upper fabric 414, and therefore it is not flat but has also a three-dimensional structure, which produces a high bulky web. The lower or dewatering fabric 420 is also permeable. The design of the lower fabric 420 is made to be capable of storing water. The lower fabric 420 also has a smooth surface. The lower fabric 420 is preferably a felt with a batt layer. The diameter of the batt fibers of the lower fabric 420 are equal to or less than approximately 140 dtex, and can preferably be equal to or lower than approximately 67 dtex, or more preferably be equal to or less than approximately 17 dtex. The batt fibers can also be a blend of fibers. The lower fabric 420 can also contain a vector layer which contains fibers from approximately 30 dtex to approximately 140 dtex, or from approximately 44 dtex to approximately 67 dtex, and can also contain even courser fibers such as, e.g., approximately 100 dtex, approximately 140 dtex, or even higher dtex numbers. The vector layer can alternatively contain fibers from approximately 67 dtex, and can also contain even courser fibers such as, e.g., approximately 100 dtex, approximately 140 dtex, or even higher dtex numbers. This is important for the good absorption of water. The wetted surface of the batt layer of the lower fabric 420 and/or of the lower fabric itself can be equal to or greater than approximately 35 m2/m2 felt area, and can preferably be equal to or greater than approximately 65 m2/m2 felt area, and can most preferably be equal to or greater than approximately 100 m2/m2 felt area. The specific surface of the lower fabric 420 should be equal to or greater than approximately 0.04 m2/g felt weight, and can preferably be equal to or greater than approximately 0.065 m2/g felt weight, and can most preferably be equal to or greater than approximately 0.075 m2/g felt weight. This is important for the good absorption of water. The dynamic stiffness K* [N/mm] as a value for the compressibility is acceptable if less than or equal to 100,000 N/mm, preferable compressibility is less than or equal to 90,000 N/mm, and most preferably the compressibility is less than or equal to 70,000 N/mm. The compressibility (thickness change by force in mm/N) of the lower fabric 420 should be considered. This is important in order to dewater the web efficiently to a high dryness level. A hard surface would not press the web 412 between the prominent points of the structured surface of the upper fabric 414. On the other hand, the felt should not be pressed too deep into the three-dimensional structure to avoid loosing bulk and therefore quality, e.g., water holding capacity.
The permeable belt 434 can be a single or multi-layer woven fabric which can withstand the high running tensions, high pressures, heat, moisture concentrations and achieve a high level of water removal required by the papermaking process. The fabric 434 should preferably have a high width stability, be able to operate at high running tensions, e.g., between approximately 20 kN/m and approximately 100 kN/m, and preferably greater than or equal to approximately 20 kN/m and less than or equal to approximately 60 kN/m. The fabric 434 should preferably also have a suitable high permeability, and can be made of hydrolysis and/or temperature resistant material. As is apparent from
Referring back to
To enable suitable dewatering, the single or multilayered fabric 434 should preferably have a permeability value of between approximately 100 cfm and approximately 1200 cfm, and is most preferably between approximately 300 cfm and approximately 800 cfm. The nip can also have an angle of wrap that is preferably between 50 degrees and 130 degrees. The single or multi-layered fabric or permeable belt 434 can also be an already formed (i.e., a pre-joined or seamed belt) an endless woven belt. Alternatively, the belt 434 can be a woven belt that has its ends joined together via a pin-seam or can be instead be seamed on the machine. The single or multi-layered fabric or permeable belt 434 can also preferably have a paper surface contact area of between approximately 5% and approximately 70% when not under pressure or tension. The contact surface of the belt should not be altered by subjecting the belt to sanding or grinding. By way of non-limiting example, the belt 434 should have a high open area of between approximately 10% and approximately 85%. The single or multi-layered fabric or permeable belt 434 can also be a woven belt having a paper surface warp count of between approximately 5 yarns/cm and approximately 60 yarns/cm, and is preferably between approximately 8 yarns/cm and approximately 20 yarns/cm, and is most preferably between approximately 10 yarns/cm and approximately 15 yarns/cm. Furthermore, the woven belt 434 can have a paper surface weft count of between approximately 5 yarns/cm and approximately 60 yarns/cm, and is preferably between approximately 8 yarns/cm and approximately 20 yarns/cm, and is most preferably between approximately 11 yarns/cm and approximately 14 yarns/cm.
Due to the high moisture and heat which can be generated in the papermaking process, e.g., in the ATMOS process, the woven single or multi-layered fabric or permeable belt 434 can be made of one or more hydrolysis and/or heat resistant materials. The one or more hydrolysis resistant materials can preferably be a PET monofilament and can ideally have an intrinsic viscosity value normally associated with dryer and TAD fabrics, i.e., in the range of between 0.72 IV and 1.0 IV. These materials can also have a suitable “stabilization package” including carboxyl end group equivalents etc. When considering hydrolysis resistance, one should consider the carboxyl end group equivalents, as the acid groups catalyze hydrolysis, and residual DEG ordi-ethylene glycol as this too can increase the rate of hydrolysis. These factors separate the resin which should be used from the typical PET bottle resin. For hydrolysis, it has been found that the carboxyl equivalent should be as low as possible to begin with and should be less than 12. For DEG level, less than 0.75% should preferably be used. Even that this low level of carboxyl end groups, it is essential that an end capping agent be added. A carbodiimide should be used during extrusion to ensure that at the end of the process there are no free carboxyl groups. There are several classes of chemical that can be used to cap the end groups, such as epoxies, ortho-esters and isocyanates, but, in practice, monomeric and combinations of monomeric with polymeric carbodiimides are the best and most used. Preferably, all end groups are capped by an end capping agent that may be selected from the above-noted classes such that there are no free carboxyl end groups.
PPS can be used for the heat resistant materials. Other single polymer materials such as PEN, PBT, PEEK and PA can also be used to improve properties such as stability, cleanliness and life. Both single polymer yarns as well as copolymer yarns can be used.
The material used for the high tension belt 434 may not necessarily be made from monofilament, and can also be a multifilament, including the core and sheath. Other materials such as non-plastic materials can also be used, e.g., metal materials.
The permeable belt need not be made of a single material and can also be made of two, three or more different materials, i.e., the belt can be a composite belt
The permeable belt 434 can also be formed with an external layer, coating, and/or treatment which is applied by deposition and/or which is a polymeric material that can be cross linked during processing. Preferably, the coating enhances the fabric stability, contamination resistance, drainage, wearability, improved heat and/or hydrolysis resistance. It is also preferable if the coating reduces fabric surface tension to aide sheet release or to reduce drive loads. The treatment or coating can be applied to impart and/or improve one or more of these properties.
Ideally, the permeable belt 434 has good to excellent permeability and surface contact area. The materials and weave of the belt are less important than such considerations.
In such a system, the dewatering fabric must work very efficiently to achieve the necessary dryness, i.e., approximately 32% or better for towel and approximately 35% or better for tissue, prior to the sheet reaching the Yankee.
In order to achieve desirable sheet parameters using an ATMOS system or a typical TAD arrangement, the dewatering fabric should have the following characteristics; a relatively low caliper so as to maximize the press impulse while not absorbing energy from the same during pressing; a high permeability so as to maximize the flow of air/vapor through the fabric and to maximize dewatering efficiency; the highest practicable weight so as to enable the density of the fabric to be optimized for efficient pressing.
Layer BL can be a two layer system or a multi-layered structure which utilizes one or more two-layered structures and can be made up of monofilaments. The base layer or substrate BL is responsible for dewatering of the paper/tissue sheet as well as for ensuring that the paper/tissue sheet has good bulk quality. The base substrate BL can be a conventional felt material, a felt that incorporates ATMOS technology, or a combination thereof. In this regard, the layer BL should be a porous media which contains a mainly stress absorbing structure which has machine direction (md) strength and cross direction (cd) strength as well as a certain void volume. This structure BL can be a woven structure which is made from substantially equal sized yarns as well as yarns that are different. The yarns can also be woven in a variety of weave patterns from single to several layer weave types including those which are weft bound warp bound. Different filler yarns could also be used. Additionally weave types can also be utilized. Combinations of different available structures (e.g., woven, membranes, films, leno, yarn layered systems and so on) are also possible and such a fabric can have certain specific beneficial properties such as, e.g., resiliency and tensile strength. The yarns used for the layer BL can also have different shapes, e.g., flat yarns or elliptical yarns, but are preferably round yarns. The yarns can also be mono yarns or twisted yarns or different combinations thereof. The yarns can additionally also be multifilament yarns of mainly polyamid (e.g., PA 6; PA 6.6; PA 6.12; and so on). Other different polymeric materials, whether natural or artificial, can also be used in specific circumstances. The yarns can further also be one or more component yarns in order to provide certain properties. For example, a two component yarn utilizing PA 6 and sheath PU can be advantageous because both materials can provide unique benefits. In this case, the PA will provide strength in the yarn direction and the PU will provide additional void volume and, due to the material properties, a higher resilience.
Nano particles can be added to the materials in the yarns and/or to other parts of the structure BL such as the fibers and membranes. Membrane materials (such as spectra) can be used in the fabric as in the case in conventional felts. Such structures can provide good void volume and permeability in all paper grades. Based on the high amount of highly resilient material (when using e.g. PU), the overall resilience is much higher than needed on most conventional arrangements. Such membranes can have very different properties with regard to materials, open areas, caliper, substructures, strength, form, amount and size of pores, and so on. It is also possible for the structure BL to utilize the combination of a membrane and a laminated non-woven portion.
Other structures can also be utilized for the base substrate BL such as a link fabric or a compound link fabric on which, for example, a porous media can be three-dimensionally extruded, sintered, and so on. Such a structure would allow the use of other available technologies like click systems (father—mother systems).
By of non-limiting example, the base substrate of the dewatering fabric 420 can include a course non-woven layer having at least one of a weight range of between approximately 200 g/m2 and approximately 480 g/m2 and fibers having between approximately 30 dtex and approximately 140 detx. The base substrate of the dewatering fabric can also have a course non-woven layer having at least one of a weight range of between approximately 120 g/m2 and approximately 300 g/m2 and fibers having between approximately 30 dtex and approximately 140 detx. Additionally, the base substrate of the dewatering fabric 420 can utilize a course non-woven layer having at least one of a weight range of between approximately 120 g/m2 and approximately 300 g/m2, fibers having between approximately 44 dtex and approximately 67 dtex, and a material comprising PA, PU, PPS, PEEK, natural fibers, or man-made fibers. The base substrate of the dewatering fabric 420 can also include a material comprising PA, PU, PPS, PEEK, natural fibers, or man-made fibers.
Layer VL is a non-woven semi-rigid fibrous batt layer which may or may not use low melt fibers. The purpose of layer VL is to enhance compaction resistance and to maintain the openness of the dewatering fabric during its life. The ball fibers of the layer VL may or may not be specifically oriented in the machine direction (depending on a particular application) and effectively replaces or is substituted for the more traditional woven cloth layer typically used in dewatering fabrics. The layer VL can have a weight range that is between approximately 200 g/m2 to approximately 480 g/m2 and can also be between approximately 120 g/m2 and approximately 300 g/m2. The fibers can be between approximately 67 dtex and approximately 140 dtex, and is preferably between approximately 44 dtex and approximately 67 dtex. Alternatively, the layer VA can be a course non-woven substrate having a wide weight range from between approximately 100 g/m2 to approximately 500 g/m2. Other non-limiting examples include layers with between approximately 44 dtex and approximately 100 dtex, and can be approximately 67 dtex. The layer VL can also contain fibers which have an isotropie of between 0 and approximately 1 and can include either unidirectional or random and/or equal fibers. The non-woven layer VL can also be made of PA, PU, PPS, PEEK, or any other natural or man-made fibers. The layer VL can be contoured or smooth, and can be in the form of a single component or several components. Moreover, even if a single component is utilized, it can utilize different materials, shapes, and so on.
The inner and outer fibrous layers IFL and OFL are porous structures arranged on the base substrate BL. The outer layer OFL contacts the paper sheet unlike the base structure BL which, in most cases, does not directly contact the paper sheet. The inner layer IFL contacts the various rolls of the machine. The layer OFL can be between approximately 100 g/m2 and approximately 500 g/m2 and can utilize fibers with approximately 4.2 dtex. The layer OFL can also be between approximately 200 gsm and 600 gsm and can utilize fibers with between approximately 1 dtex and 11 dtex. The layer OFL can also be between approximately 200 gsm and 600 gsm and can utilize fibers with between approximately 3.1 dtex and 6.7 dtex. The layer OFL can also preferably be approximately 100 gsm and can utilize fibers with approximately 4.2 dtex. The fiber shape of layer OFL can be round or flat and the material can be PA or PU. The layer IFL can be between approximately 100 g/m2 and approximately 400 g/m2. The layer IFL can utilize fibers with between approximately 6.7 dtex and 17 dtex. The layer IFL can also be between approximately 100 gsm and 200 gsm and can utilize fibers with approximately 11 dtex. The fiber shape of layer IFL can be round or flat and the material can be PA or PU.
Also by way of non-limiting example, the fibrous portions OFL and IFL can also include fibers such as polymeric (natural and/or artificial) fibers. The fibrous portions OFL and IFL can utilize one component fibers as well as a two or more component fibers. The fibers can be in the range of between approximately 1.0 dtex and approximately 350 dtex, and are preferably between approximately 1.7 dtex and approximately 100 dtex, and most preferably between approximately 2.2 dtex and approximately 40 dtex. Of course, other fibers types and sizes can be utilized which are outside these ranges. The fibers can have a shape such as round, oval, flat, and can also be either uniform or irregular in shape (e.g., crocodile fibers). The fibers can also be made from materials which allow for splitting of the fibers either in during the manufacturing process or during the run on the paper machine. Materials which can be used for the fibers (whether splitable or nonsplitable) can be, e.g., PA, PES, PET and PU. The fibers can also be core sheath or side by side structures, and so on. The fibers can also, of course, be any type and shape which is utilized in the prior art and can be utilized based on the benefits they provide.
The fibers can be used as batt and/or can be arranged in pre-processed layers. Such fibers can also be treated chemically to achieve a certain surface energy (i.e., they can be hydrophilic or hydrophobic). The treatment can take place for one or more layers. Alternatively, the entire dewatering fabric can be so treated chemically. One or more of the layers of a multi-layered fibrous portion can even be treated differently depending on their properties or depending on the desired properties of the layers. The use of different fibers in different layers can lead to distinctive and very different partial densities in the dewatering fabric over a width of the structure. Preferably, the fabric utilizes fibers in at least one later of batt on at least one side of the dewatering fabric.
Another way to make the porous media portion of the fibrous portions OFL and IFL utilizes soluble materials which are mixed with unsoluble materials. The process can ensure that the soluble material is dissolved in order to creates specific permeability. This can be combined with the use, for example, of one or more types of fibrous systems.
Particle technology can also be utilized wherein particles are deposited and connected (using e.g., sintering, e-process, etc.) in order to form or modify the porous media. Specific modifications of the two sides of the dewatering fabric can increase and/or improve the runability. The paper contacting side of the dewatering fabric, i.e., layer OFL, can have a surface which is configured to match the pattern of the TAD fabric. Furthermore, the opposite side of the fabric, i.e., layer IFL, can have a surface that is configured to match the shape/surface of the tension belt.
The use of thermoplastic materials can also be utilized on one of more surfaces of the fabric as well as within the internal structure of the fabric. Such materials can improve certain properties of the fabric such as abrasion resistance and resilience. Certain properties of the dewatering fabric can be achieved using different processes. For example, the fabric can be subjected to processes which remove material (e.g., grinding) as well as processes which add material (e.g., sintering, printing, etc.) and so on. The use of physical or chemical processes allow both the surfaces of the dewatering fabric as well as the interior thereof to be modified as desired.
The fibrous portions OFL and IFL and substrate base BL/VL can be connected and/or laminated together by either physical or chemical connection systems. Such connections can be utilized between different materials and between layers of the fabric.
The following are considerations which should be considered in the dewatering fabric: fiber weight especially of the surface layers and the base structure; fiber fineness; fiber shape; material; isotrophy; surface contour; and base construction. The dewatering fabric can also utilize special options such as; one or more flow control membranes to prevent rewetting and/or high resistance to reverse water flow back into the paper sheet; one or more Spectra™ membranes can be used to add higher long-term resilience which occurs due to the porous polyurethane element and because this material provides more even pressure distribution across the fabric; and surface enhancement which can be produced using particle deposition technology that provides for one or more of the following; higher resilience; flatter surfaces; improved density; and improved fiber anchorage.
The following are non-limiting characteristics and/or properties of the dewatering fabric 420; the caliper can be between approximately 0.1 mm and approximately 15 mm, are preferably between approximately 1.0 mm and approximately 10 mm, and most preferably between approximately 1.5 mm and approximately 2.5 mm; the permeability can be between approximately 1 cfm and approximately 500 cfm, is preferably between approximately 5 cfm and approximately 100 cfm, is more preferably between approximately 10 cfm and approximately 50 cfm, and is most preferably between approximately 15 cfm and approximately 25 cfm; the overall density can be between approximately 0.2 g/cm3 and approximately 1.10 g/cm3, is preferably between approximately 0.3 g/cm3 and approximately 0.8 g/cm3, and is most preferably between approximately 0.4 g/cm3 and approximately 0.7 g/cm3; the product weight range can be between approximately 100 d/m2 and approximately 3000 g/m2, is preferably between approximately 800 g/m2 and approximately 2200 g/m2, is more preferably between approximately 1000 g/m2 and approximately 1750 g/m2, and is most preferably between approximately 1000 g/m2 and approximately 1400 g/m2.
It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to exemplary embodiments, it is understood that the words that have been used are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the invention has been described herein with reference to particular arrangements, materials and embodiments, the invention is not intended to be limited to the particulars disclosed herein. Instead, the invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.
