Patent Application
20050167068
1. Field of the Invention
The present invention relates to a paper machine, and, more particularly, to a permeable belt used in a belt press in a paper machine.
2. Description of the Related Art
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 rollers circumference is used to process the paper web. To overcome this limitation, some attempts have been made to adapt a solid impermeable belt to form an extended nip for pressing the paper web to 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 presses (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 well 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 on the inside to prevent frictional damage. The belt and shoe press are non-permeable members and dewatering of the fibrous web is accomplished by the mechanical pressing thereof.
What is needed in the art is a belt, which provides enhanced dewatering of a continuous web.
The present invention 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 having a tension of at least 30 KN/m applied thereto. The side of the permeable belt having an open area of at least approximately 25%, and a contact area of at least approximately 25%.
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 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:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one preferred embodiment of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
Referring now to the drawings, and more particularly to
Fibrous web 12 is moved by fabric 14 past suction box 16. At vacuum box 16 sufficient moisture is removed from web 12 to achieve a solids level of between 15% and 25% on a typical 20 gram per square meter web (gsm) running at −0.2 to −0.8 bar vacuum, with a preferred operating level of −0.4 to −0.6 bar.
As fibrous web 12 proceeds in the machine direction it comes into contact with dewatering fabric 20. Web 12 then proceeds toward vacuum roll 18 between fabric 14 and dewatering fabric 20. Vacuum roll 18 is operated at a vacuum level of −0.2 to −0.8 bar with a preferred operating level of at least −0.4 bar. Fabric 14, web 12 and fabric 20 are engaged against vacuum roll 18 by belt press 22.
Now, additionally referring to
Fabric 20 proceeds past showers 30, which apply moisture to fabric 20 to clean fabric 20. Fabric 20 then proceeds past Uhle box 28, which removes moisture from fabric 20.
If fabric 14 is a structured fabric 14, having a three dimensional structure that is reflected in web 12, thicker pillow areas of web 12 are formed. The pillow areas are protected during pressing as they are within the body of structured fabric 14. As such the pressing imparted by belt press assembly 22 upon web 12 does not negatively impact web quality, while it increases the dewatering rate of vacuum roll 18. In a No Press/Low Press apparatus the pressure is transmitted through a dewatering fabric, also known as a press fabric. In such a case web 12 is not protected inside structured fabric 14. This is still advantageous, because the press nip is much longer than a conventional press, which results in a lower specific pressure and less compaction of web 12.
Now, additionally referring to
Permeable belt 34 has a pattern 38 of holes 36 therethrough, which may, for example, be drilled, laser cut, etched formed or woven therein. Permeable belt 34 may be monoplanar without the grooves shown in
In one embodiment of permeable belt 34, as illustrated in
In another embodiment of permeable belt 34, as illustrated in
In yet another embodiment of permeable belt 34, as illustrated in
Permeable belt 34 is capable of running at high running tensions of at least 30 KN/m or 60 KN/m or higher with a surface contact area of 10% or greater and an open area of 15% or greater. The contact may be 25% or greater and the open area of 25% or greater. Preferably permeable belt 34 will have an open area of at least 50%, and even more preferably an open area of at least 70%. More preferably, permeable belt 34 has an open area of between 15% and 50%, and a contact area of between 50% and 85%. The composition of permeable belt 34 may include a thin spiral link having a support layer within permeable belt 34. Further, permeable belt 34 may be a spiral link fabric 34 having a contact area of between 10% and 40%, and an open area of between 60% to 90%.
The circumferential length of vacuum zone Z can be from 200 mm to 2500 mm, with a preferable length of 300 mm-1200 mm, and an even more preferable length of 400 mm-800 mm. The solids leaving vacuum roll 18 in web 12 will vary between 25% to 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 25% to 55%.
Permeable belt 34 is capable of applying a line force over an extremely long nip, 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, 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.
Advanced dewatering system 10 utilizes belt press 22 to remove water from web 12, which is formed prior to reaching belt press 22. Permeable belt 34 is routed in belt press 22 so as to engage a surface of fabric 14 and thereby press fabric 14 further against web 12, and web 12 against fabric 20, which is supported thereunder by vacuum roll 18. The physical pressure applied by belt 34 places some hydraulic pressure on the water in web 12 causing it to migrate toward fabrics 14 and 20. As this coupling of web 12 with fabrics 14 and 20, and belt 34 continues around vacuum roll 18 in machine direction M, it encounters a vacuum zone Z through which air is passed from hood 24 through permeable belt 34, fabric 14, drying web 12 and the moisture picked up by the air flow proceeds further through fabric 20 and through a porous surface of vacuum roll 18. Drying air passes through holes 36 is distributed along grooves 40 before passing through fabric 14. As web 12 leaves belt press 22, belt 34 separates from fabric 14. Shortly thereafter fabric 20 separates from web 12, and web 12 continues with fabric 14 past pick up vacuum 26, which additionally suctions moisture from fabric 14 and web 12.
While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.
