Patent Grant
9951471
Generally, the invention relates to a method and machine for dewatering paper webs. More specifically, the invention is a process and machine which produces paper having more uniform fiber orientation, sheet structure and improved paper strength characteristics. The improved method and machine includes devices that are arranged in the forming or wet section of a Fourdrinier machine, hereinafter referred to as “Fourdrinier.” The devices are adjusted manually or through a computer and associated drive mechanisms.
An improved method of forming paper using a Fourdrinier is composed of a plurality of foil and vacuum assisted drainage elements that are equipped with on-the-run adjustable angle and/or height dewatering foil blades starting from a paper dryness of 0.1% and extending all the way to 5% dryness within the forming section of a Fourdrinier. The foil blade angle, height, and vacuum level are adjusted as applicable along the entire length of the Fourdrinier dewatering table until a paper dryness of 5% is achieved. These adjustments allow for control of the dewatering rate and turbulence (shear) produced from a paper dryness of 0.1% to 5% on the Fourdrinier dewatering table. Controlling drainage and shear along this entire range of dryness has a direct influence on paper fiber orientation. This has a significant influence on paper strength.
The claimed invention works in unison with the paper machine headbox shear forces to promote maximum fiber orientation in either the cross-machine or machine direction orientation of the paper. The headbox controls fiber orientation through a speed difference between its stock jet speed and the dewatering fabric speed. Once the stock jet lands on the dewatering fabric, it is operated at an overspeed compared to the dewatering fabric “rush” or the same speed “square” or an underspeed “drag” to control the orientation of the fibers during the sheet forming process. Operating the headbox in a rush or drag mode will align fibers in the machine direction which is beneficial for machine direction related strength properties in the finished paper product. Operating in a square mode will produce a maximum cross-machine direction fiber orientation of the fibers in the finished paper product which is beneficial for paper strength properties in the cross-machine direction.
The claimed invention provides control of drainage and turbulence anisoptropic shear after the headbox stock jet lands on the dewatering fabric. After the stock lands, the claimed invention is adjusted to preserve or amplify the fiber orientation characteristics produced by the headbox. In this manner, a higher quality of paper is produced with the instant process and machine. Moreover, existing machines may be retrofitted with various devices and operated in the manner disclosed herein to achieve a superior quality of paper stock.
For example, if machine direction fiber orientation is desired, the headbox jet speed is operated in a rush or drag mode to promote an initial strong machine direction alignment of the paper fibers. From here, the foil blade angles and height, along with the vacuum levels on the vacuum assisted dewatering units are adjusted to produce a high early drainage rate in the initial sheet dewatering zone (0.1% to 2% paper dryness) to immediately freeze the machine direction fiber orientation produced by the headbox. In addition to this, the foil blade angles, heights and vacuum levels are also adjusted to produce a high amount of turbulence in this paper dryness zone (0.1% to 2%). This keeps the fibers mobile and prevents entanglement allowing the headbox shear to become more effective in orientating fibers in the machine direction. After 2% paper dryness, the angle and height and vacuum levels are adjusted to gradually achieve a paper dryness of 5%. However, the foil angle and height are adjusted to achieve only moderate turbulence levels to prevent disruption of the machine direction fiber orientation achieved earlier in the sheet dewatering and forming process.
For cross-machine direction fiber alignment, the process is completely reversed. The headbox stock jet is adjusted to produce a speed difference close to zero (square mode) to promote the highest possible cross-machine direction fiber orientation. However, due to contraction created within the headbox nozzle, a certain unavoidable degree of machine direction fiber alignment is still always present in the fiber slurry when it lands on the dewatering fabric that cannot be reversed through normal Fourdrinier dewatering equipment. To break this natural machine direction fiber orientation up and produce the most random fiber orientation and highest amount of cross-machine direction fiber orientation, the claimed invention is operated as follows. First, the foil blade angles and heights along with the vacuum levels of the vacuum assisted dewatering elements are adjusted to significantly retard drainage in the early sheet forming zone (0.1% to 2% dryness). This is completely opposite of the previously described process for machine direction fiber orientation. In addition to this, the angle and height of the foil blades are adjusted to produce a very high degree of turbulence to prevent fiber entanglement and generate the most random fiber orientation possible for the highest level of cross-machine direction fiber alignment. After a dryness of 2% is achieved, the foil angle and height is adjusted to maintain this high level of turbulence all the way until a paper dryness of 5% is achieved. A very gentle early drainage along with high turbulence all the way until a dryness of 5% will create the most random fiber network resulting in the highest amount of cross-machine direction fiber alignment.
The ability of the claimed process and machine improvement to be adjusted in conjunction with shear significantly increases paper sheet strength properties such as Mullen, Burst, Bending Stiffness, or Concora (machine direction strength properties) and Ring Crush, S.T.F.I, SCT (cross machine direction strength properties) and all other strength properties associated with paper manufacturing.
In addition to this, the claimed invention and sheet forming process also improves other paper properties such as formation, smoothness, uniformity, printability, ply bond strength, and the like.
The forming or wet section of a Fourdrinier consists mainly of the head box and forming wire. Its main purpose is to generate consistent slurry, or paper pulp, for the forming wire. Several foil, suction boxes, a couch roll, and a breast roll commonly make up the rest of the forming section. The press section and dryer section follow the forming section to further remove water from the stock.
Historically, the main tools used to control paper strength have been fiber species and fiber refining energy along with the orientating shear generated by the speed difference between the headbox jet speed and the dewatering (forming) fabric speed. The first method of continuous sheet forming and dewatering was the Fourdrinier dewatering table which is still the dominant tool used for paper manufacturing today. Since the time of its invention, its impact on sheet strength has been misunderstood or vaguely understood. Also, the ability to directly influence sheet strength through changing the drainage or shear rates produced during the Fourdrinier dewatering and forming process have also been misunderstood. Past technologies such as the VID, Deltaflo or Vibrefoil have been able to adjust drainage and turbulence on the Fourdrinier table. However, these technologies have been used prior to a sheet consistency on the Fourdrinier table of 1.5% or less. The impetus behind their design was simply to generate turbulence in a very short area in an effort to improve paper uniformity (formation) which was claimed to influence sheet strength.
It has been discovered through the use of the claimed improved Fourdrinier papermaking process that controlling drainage and turbulence from a paper dryness of 0.1% to 5% on a dewatering table has a far more significant impact of fiber orientation and paper strength. In addition, the previously described methods of adjusting the headbox shear in conjunction with adjusting drainage and turbulence in this zone to control fiber orientation and paper strength up to this point been has been unknown to anyone other than the inventors of the claimed improved process.
An improved process of Fourdrinier papermaking is used for dewatering and paper quality control and achieved in the forming end of the Fourdrinier. The process uses a plurality of gravity and vacuum assisted drainage elements that are equipped with on-the-run adjustable angle and height dewatering foil blades starting from a paper dryness of 0.1% and extending all the way to 5% dryness. The foil blade angles and heights along with vacuum level are adjusted manually or automatically along the entire length of the Fourdrinier dewatering table until paper dryness of 5% is achieved.
The claimed invention uses a series of gravity assisted drainage elements in the beginning of the Fourdrinier dewatering table. These units are the forming board and hydrofoil section that are equipped with a combination of static and adjustable angle foil blades, as well as foil blades which are height adjustable depending on the paper grade being produced. A low-vacuum section is arranged on the dewatering table after the hydrofoil section. The low-vacuum section includes vacuum assisted drainage elements which are equipped with vacuum control valves, fixed angle and angle adjustable foil blades, as well as foil blades which are height adjustable depending on the paper grade being produced. A high-vacuum section is arranged between the low-vacuum section and a couch roll.
Adjusting the angle and height of the dewatering foil blades along with the vacuum level allows for control of the dewatering rate and turbulence (shear) produced from a paper dryness of 0.1% to 5% on the Fourdrinier dewatering table. Controlling drainage and shear along this entire range of dryness in conjunction with fiber orientation shear produced by the headbox has a direct influence on paper fiber orientation. This has a significant influence on paper strength.
Adjustable dewatering technologies are typically used on the Fourdrinier table in an area directly after the forming board or within a short distance of the forming board and dry the stock to a dryness content of 3.5%. Previously, the design and operation of a Fourdrinier has been focused on fiber orientation control to improve sheet strength.
Other technologies such as the dandy roll or top dewatering machines have been used at a dryness content of 1.5% or greater. However, their purpose has simply been water removal or paper formation improvement, not fiber orientation control liked the claimed invention. Moreover, none of the existing technologies are directed towards precisely controlling fiber orientation as in the disclosed manner.
It is an object of the invention to disclose an improved process for controlling the fiber orientation of paper stock to achieve a better quality paper than is currently produced on a Fourdrinier.
It is a further object of the invention to teach a Fourdrinier having adjustable on-the-run mechanisms for adjusting the height and angle of foils or blades to easily switch over operation of the Fourdrinier to produce paper of higher quality through controlling the orientation of the fibers.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned from practicing the invention. The objects and advantages of the invention will be obtained by means of instrumentalities in combinations particularly pointed out in the appended claims.
Other objects and purposes of this invention will be apparent to person acquainted with apparatus of this general type upon reading the following specification and inspecting the accompanying drawings, in which:
The embodiments of the invention and the various features and advantageous details thereof are more fully explained with reference to the non-limiting embodiments and examples that are described and/or illustrated in the accompanying drawings and set forth in the following description. It should be noted that the features illustrated in the drawings are not necessarily drawn to scale, and the features of one embodiment may be employed with the other embodiments as the skilled artisan recognizes, even if not explicitly stated herein. Descriptions of well-known components and techniques may be omitted to avoid obscuring the invention. The examples used herein are intended merely to facilitate an understanding of ways in which the invention may be practiced and to further enable those skilled in the art to practice the invention. Accordingly, the examples and embodiments set forth herein should not be construed as limiting the scope of the invention, which is defined by the appended claims. Moreover, it is noted that like reference numerals represent similar parts throughout the several views of the drawings.
For illustrative purposes only, the invention will be described in conjunction with a Fourdrinier papermaking machine although the invention and concept could also be applied to hybrid and gap formers. The invention is implemented in the wet section of the Fourdrinier and includes a forming board section 10, a hydrofoil section 20, and a low-vacuum section 30. High-vacuum section 40 does not include automatically adjustable height blades or automatically angle adjustable blades. It should be noted that a headbox is known and is therefore not shown in
As shown in
During this stage, some water is drained from the stock and a very thin wet sheet is carried over to various other dewatering devices such as foil blades in hydrofoil section 20, until a sheet paper dryness of around 1% to 1.5% is achieved. Following this, the paper dryness is increased by the foil blades in the Varioline and Vaculine in the low vacuum section 20 to a dryness level of 5%. Next, a paper dryness of 8% to 10% is achieved in the elements of the low-vacuum section 30 and the sheet is transferred to the high-vacuum section 40 to achieve a paper dryness of 18% or greater. Finally, the sheet is transferred over the couch roll where additional dryness level is achieved.
A Fourdrinier composed of the previously described equipment is fitted with a plurality of adjustable angle and height foil blades starting from the forming board section 10 and partially through the low-vacuum section 30. As the stock travels with the forming fabric 105, it encounters the adjustable angle and height foil blades at various points along the dewatering table to manipulate the paper web and orient more fibers in a desired direction. On the forming board section 10 and the hydrofoil or gravity section 20, the adjustable angle foil blades generate a vacuum pulse that dewaters the stock slurry. The amount of drainage produced along each adjustable angle foil blade is determined by the angle setting of the foil blade which can be typically varied between +2 and −4 degrees. A higher angle will produce more drainage.
Also within the forming board section and hydrofoil or gravity section of the papermaking process, the stock encounters adjustable height foil blades. These blades also drain water from the stock slurry. The amount of water drained by the adjustable height foil blades is determined by their height setting in relation to the forming fabric. At a setting of −5 mm, they do not touch the fabric and do not drain any water. At a setting of 0 mm, they are in the same plane as the forming fabric and will drain water. As the adjustable height foil blades are lowered from the fabric, the amount of drainage increases up until a point at which the static and dynamic vacuum forces generated by the adjustable height foil blade are overcome by the tension forces of the forming fabric. When this occurs, the fabric breaks its seal with the adjustable height foil blade and no dewatering, occurs. The setting at which this occurs will vary based on the drainage characteristics of the stock, the stock consistency, and the speed of the forming fabric. As can be understood, changing the height settings will directly influence the fiber orientation.
The wet slurry will leave the hydrofoil section 20 at a consistency of around 1.5% depending on the paper grade and speed. From here, it travels to the initial vacuum assisted foil units in the low-vacuum section 30 which are referred to as the Varioline elements. In addition to natural gravity drainage, these Varioline elements also use a dynamic and an external vacuum source to create a vacuum which is drawn onto the lower side of the forming fabric 105. This further increases drainage within these units. The Varioline elements are equipped with a plurality of stationary and adjustable height foil blades. Similar to the previous section, as the foil blades are lowered from the forming fabric, the drainage rate increases as discussed above.
Following the Varioline table elements, another set of vacuum assisted units is encountered by the underside of the forming fabric 105. These table elements are the Vaculine elements which are equipped with adjustable angle foil blades. Again, as the angle of the foil blades is increased, the drainage rate will increase until a consistency of 5% is achieved.
In addition to controlling drainage, the adjustable angle and height foil blades in the previously described drainage units also control turbulence within the wet slurry. This is accomplished through deflection of the forming fabric from its original plane as it travels along the top surface of the adjustable angle foil blades and adjustable height foil blades. This deflection creates a series of accelerations within the stock slurry that results in turbulence and shear within the stock slurry. This turbulence keeps the fibers fluidized and mobile within the wet slurry so that they can be orientated in the cross-machine or machine direction, depending on what the finish paper property strength requirements are.
For example, if machine direction fiber orientation is desired, the headbox jet speed is operated in a rush or drag mode to promote an initial strong machine direction alignment of the paper fibers. From here, the foil blade angles and height, along with the vacuum levels on the vacuum assisted dewatering units are adjusted to produce a high early drainage rate in the initial sheet dewatering zone (0.1% to 2% paper dryness) to immediately freeze the machine direction fiber orientation produced by the headbox.
In addition to this, the foil blade angles, heights and vacuum levels are adjusted to produce a high amount of turbulence in this paper dryness zone (0.1% to 2%). This keeps the fibers from entangling with each other and allows the headbox shear to become more effective in orientating fibers in the machine direction. After 2% paper dryness, the angle and height and vacuum levels are adjusted to gradually achieve a paper dryness of 5%. However, the foil angle and height are adjusted to achieve only moderate turbulence levels to prevent disruption of the machine direction fiber orientation achieved earlier in the sheet dewatering and forming process.
For cross-machine direction fiber alignment, the process is completely reversed. The headbox stock jet is adjusted to produce a speed difference close to zero (square mode) to promote the highest possible cross-machine direction fiber orientation. However, due to friction created within the headbox nozzle, a certain unavoidable degree of machine direction fiber alignment is still always present in the fiber slurry when it lands on the dewatering fabric that cannot be reversed through normal fourdrinier dewatering equipment.
To break this natural machine direction fiber orientation up and produce the most random fiber orientation and highest amount of cross-machine direction fiber orientation, the claimed invention is operated as follows. First, the foil blade angles and heights along with the vacuum levels of the vacuum assisted dewatering elements are adjusted to significantly retard drainage in the early sheet forming zone (0.1% to 2% dryness). This is completely opposite of the previously described process. In addition to this, the angle height of the foil blades are adjusted to produce a very high degree of turbulence to prevent fiber entanglement and generate the most random fiber orientation possible for the highest level of cross-machine direction fiber alignment. After a dryness of 2% is achieved, the foil angle and height is adjusted to maintain this high level of turbulence all the way until a paper dryness of 5% is achieved. A very gentle early drainage along with high turbulence all the way until a dryness of 5% is achieved will create the most random fiber network resulting in the highest amount of cross-machine direction fiber alignment.
After passing through the forming board section, the paper stock is moved along to pass through a hydrofoil or gravity section 20 equipped with Hydroline elements 21. Each Hydroline element 21 comprises height adjustable blades 13 and angle adjustable blades 22 which are alternately arranged as shown in
Tables 1 and 2 show blade angle and height settings for a paper grade with machine direction fiber alignment and a grade with cross-machine direction fiber alignment. The tables show a variety of angle adjustable and height adjustable blades which may be utilized in the respective regions of the wet end of the Fourdrinier to achieve synergistic results. It should be noted that in this instance seven blades are shown in each section with the abbreviations “H” or “A” indicating that the blade is either height or angle adjustable respectively. Moreover, the gravity units 1-3 correspond to the hydrofoil sections and are three Hydroline elements. Low vacuum units 1-3 correspond to Varioline elements. Low vacuum units 4, 5 correspond to Vaculine elements.
It is to be understood that the invention is not limited to the exact construction illustrated and described above, but that various changes and modifications may be made without departing from the spirit and the scope of the invention as defined in the following claims. While the invention has been described with respect to preferred embodiments, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in limiting sense. From the above disclosure of the general principles of the present invention and the preceding detailed description, those skilled in the art will readily comprehend the various modifications to which the present invention is susceptible. Therefore, the scope of the invention should be limited only by the following claims and equivalents thereof.
The present application relates to U.S. Provisional Patent Application Ser. No. 61/517,613 filed on Apr. 21, 2011 and claims priority therefrom. The present application was not subject to federal research and/or development funding.
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| Parent | 13506470 | Apr 2012 | US |
| Child | 14039236 | US |
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| Parent | 15075502 | Mar 2016 | US |
| Child | 15595229 | US | |
| Parent | 14592104 | Jan 2015 | US |
| Child | 15075502 | US | |
| Parent | 14222958 | Mar 2014 | US |
| Child | 14592104 | US | |
| Parent | 14039236 | Sep 2013 | US |
| Child | 14222958 | US |
