Textiles: weaving – Fabrics – Drier felts
Reexamination Certificate
1998-12-15
2001-05-08
Falik, Andy (Department: 3741)
Textiles: weaving
Fabrics
Drier felts
C139S206000
Reexamination Certificate
active
06227255
ABSTRACT:
FIELD OF THE INVENTION
This invention concerns a woven fabric for use in a paper machine, board machine or the like. The invention is especially developed for the forming section, but can also be used in other positions.
BACKGROUND ART
Dewatering in a paper machine is normally made in three different steps, and the earlier in the machine the dewatering is made, the more cost-effective it is:
1. The forming section removes water by drainage from a web by means of suction boxes, by vacuum, table rolls, foils, etc. In older machines of the Fourdrinier type, such dewatering takes place on one side through the so-called extended wire. In modern wire sections, it has been possible to increase the dewatering by injecting the stock between a pair of wires, which permits the water to be drained from both the upper and the lower side. This entails that the wire section can generally be made shorter and more compact. The web is here still weak and is normally passed to the press via a pick-up felt. The purpose of the latter development was to improve the paper characteristics, inter alia, by making it possible to reduce the twosidedness of the web. This is also a condition for running in a stable way at high speeds.
2. In the press section, the web is drained by being subjected to pressure in press nips between one or, alternatively, two felts. The felt covering removes the water and is reconditioned. To make it possible to increase the efficiency in this section, the number of press nips have in many cases been increased to four. Another solution for increasing the capacity has been to replace traditional press nips with so-called extended nips, where the pressing takes place with a shoe as support. In this type of presses, use is made of flexible belts which constitute the roll coating around the shoe. The demands placed on this type of polymer-coated process belts are that they should have a smooth surface and yield a uniform distribution of pressure when passing over the shoe. After the press section, the paper web has such a strength and dry solids content that it may be exposed to a certain amount of tension in the next transfer to the dryer section. In the future, machine concepts will be available, where the web is supported via various belts, etc., through the entire machine.
3. The dryer section dewaters by the web being pressed against steam-heated drying cylinders. There are a number of different solutions to the arrangement of these cylinders and the orientation thereof in order to increase the efficiency in the dryer section.
In wire sections of the twin-wire type, as stated under 1 above, it is possible to have new options regarding the design of suitable fabrics. This depends on the facts that both fabrics work supported by different machine elements in the wire loop, and that these are placed close to each other. The fabric is subjected to a more constant load around the wire loop than in the older wire sections of the Fourdrinier type. In these, a very high stability was required in, e.g., the machine direction for the fabric to resist the pulsating strains that may occur around the revolution.
Known fabrics exist in both single-layered and multilayered design. These include one or more thread systems in the machine direction (MD) and the cross direction (CD), respectively. In order to achieve wear resistance, it is common to choose coarse threads in the CD in the fabric bottom, which is turned to the supporting parts of the machine. Regarding these reinforcements in known fabrics, the reinforcing threads are generally coarse and have higher wear resistance than other threads. It is common to use PA in the bottom. This material does not have higher modulus than PET.
Older single-layered fabrics of metal (bronze alloys) had the disadvantage that their running time was too short. In the 1970's, fabrics made of polymeric material made a breakthrough. Single-layered fabrics with 2-shed surface were, however, not stable enough, so multi-shed patterns (5-shed and above) were run with some success. These single-layered fabrics had too low a stability and too short a running time. To a large extent, they were replaced by multilayered designs of the type double-layered and triple-layered fabrics. Single-layered fabrics have almost completely disappeared from the market.
The drawbacks of today's multilayered fabrics are, among other things, that they do not cope with the high machine speeds that are desired and that they drag too much water. Water currents and pulsations may occur in the fabric. Prior-art single-layered fabrics with a 2-shed pattern especially suffer from the drawback that they are unstable due to a high degree of waviness (crimp) in the individual threads.
The object of the present invention is to provide a thin and stable fabric that especially functions in a twin-wire section and that produces good dewatering also at high machine speeds, above 2000 m/min. The fabric should be easy to keep clean and should drag a minimum amount of water. This results in a better production economy while retaining the paper quality. If the fabric is to be used in the dryer section, a minimum of air friction and thin boundary layers around the fabric are desirable.
SUMMARY OF THE INVENTION
In the light of that stated above, a woven fabric for a paper machine, board machine or the like is provided according to the invention, said fabric, in operation, having a defined machine direction (MD) and a defined cross direction (CD) and said fabric comprising a single-layered structure composed of threads in the machine direction (MD threads) interwoven with threads in the cross direction (CD threads) in a 2-shed repeated pattern in order to form a 2-shed top surface for carrying a web of material, and one reinforcement arranged on the opposite surface (bottom surface) of the single-layered structure and being in the form of reinforcing threads in the machine direction (MDF threads), which bind only with the CD threads in an n-shed repeated pattern, where n≧5, and thus create reinforcing flotations in the machine direction on the bottom surface of the single-layered structure, said MDF threads binding only with one CD thread per repeat and are as fine as or finer than the MD threads, the MD threads and the CD threads as well as the MDF threads being made of polymeric material.
It should be noted that the fabric according to the invention has reinforcing threads in the machine direction MD only. There are no reinforcing threads in the bottom transversely of the machine direction. It should also be noted that the flotations on the bottom surface, which are provided by the MDF threads, are between themselves equally long since the MDF threads bind with the CD threads only once per repeat.
The MD threads, CD threads and MDF threads included in the fabric can individually be chosen with a circular or non-circular cross-section. The above expression “as fine as or finer” concerns the relationship between the cross-sectional areas of the threads. For threads having a circular cross-section, the MDF threads are, according to the invention, not allowed to have a larger diameter than the MD threads. As an example, it is possible to choose thread diameters in the order of 0.15 mm in the bottom for the MDF threads and 0.17 mm for the MD and CD threads of the single-layered structure.
According to the invention, the reinforcing threads (MDF threads) are oriented in the machine direction (MD) of the fabric. If the fabric is manufactured as flat-woven fabric, both the MD threads of the single-layered structure and the MDF threads are warp threads, and the fabric is warp-reinforced. If, instead, one chooses to manufacture the fabric as round-woven fabric, which may be advantageous since no seam is required, the reinforcement will be made by shute wires, and the fabric will be shute-reinforced. Independently of the weaving technique, the fabric has, however, a defined machine direction and the reinforcing threads are oriented in this machine direction.
According to the invention, the reinfor
Nilsson Goran
Osterberg Lars
Albany International Corp.
Falik Andy
Pitney Hardin Kipp & Szuch LLP
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