Paper making and fiber liberation – Apparatus – Running or indefinite length product forming and/or treating...
Reexamination Certificate
2002-02-19
2003-05-27
Griffin, Steven P. (Department: 1731)
Paper making and fiber liberation
Apparatus
Running or indefinite length product forming and/or treating...
C162S358200, C162S900000, C162S902000, C034S660000, C428S101000, C428S134000, C428S137000
Reexamination Certificate
active
06569290
ABSTRACT:
BACKGROUND
The present invention relates to papermaking fabrics, especially dryer fabrics. More specifically it relates to fabrics made from interconnected modular subassemblies. Most specifically it relates to pre-molded, bi-component subassembly links used to make a modular fabric.
A papermaking fabric is used in the form of an endless belt which is supported by and advanced through the papermaking machine by various machine rolls. The process and the various sections of the machine, forming, press and dryer, will be known to those skilled in the art.
Traditionally, fabrics have been made either through endless or flat weaving techniques. More recently, spiral fabrics have been made by connecting spiral coils with pintles to create a fabric. The spiral fabrics allow for greater flexibility in making fabrics of various dimensions because, unlike flat or endless woven fabrics whose dimensions must be known ahead of time, they are not limited by loom design. Spiral fabric, however, lacks adaptability with regard to desired changes in drainage, permeability and surface characteristics.
Papermaking fabrics, especially dryer fabrics, commonly comprise woven monofilament yarns. The monofilaments have traditionally been extruded from materials such as nylon, polyester, etc. Unfortunately, the extrusion process renders many plastics unsuitable for use in the harsh dryer section environment. Therefore, the choice of materials suitable for use in forming the monofilament has been limited. Many more plastics would become available if a dryer fabric could be made with molding techniques. To date, few practical mechanisms exist for constructing fabrics from molded parts.
One prior attempt at forming a dryer fabric for a paper machine from molded components is described in DE 37 35 709 A1. This reference discloses flat plastic elements which are interconnected by pintles or articulated joints, with the spacing of the elements and the size of the apertures therethrough being selected to provide a desired air permeability for the fabric. However, each of the molded components extends across an entire width of the fabric and there is no teaching of the necessary features to successfully practice the invention in connection with commercial papermaking dryer fabrics, which typically have a width of 10 meters (30 feet). There is also no suggestion as to how such molded components, which extend across an entire fabric could be economically manufactured and assembled, or of molded subassemblies having a width smaller than the entire fabric width or a manufacturable aspect ratio and thicknesses for such subassemblies which can be assembled together to form a dryer fabric. Additionally, this references teaches punched or stamped through openings which are formed in the flat elements or in the fabric after it is assembled. Therefore, if fabrics having different permeabilities are desired, a different number or size of openings would have to be punched or stamped in the flat elements because there is no suggestion of a bi-component assembly wherein the base and surface components are linked together through the plane of the fabric and the air permeability of the resulting fabric is determined by the overlapping alignment of the apertures in the first layer relative to the second layer such that the same components can be assembled to produce different permeability fabrics. Punching or stamping the openings also introduces additional processing cost as well as increased potential for damage to the pintles.
U.S. Pat. No. 4,579,771 discloses a laminated spiral mesh papermakers fabric having a base layer formed from a plurality of intermeshed monofilament spiral coils which are joined together with pintles. An upper layer, such as a felt batt or a molded sheet of plastic having apertures cut or punched therethrough, is attached to the base layer using an adhesive.
Present dryer fabrics form endless belts passing around rollers having diameters from 18 to 60 in. (45.7 to 152.4 cm). While flexibility is an important requirement, fabrics also must be strong enough to support the paper web along its path under a variety of conditions and temperatures. Suggested load capacities have been fifteen pounds per linear inch (PLI) (267.9 kg/m). The fabric must also withstand traveling at speeds greater than 4,000 feet per minute (1219.2 m/min).
Damage and dirt accumulation are also major factors which typically limit the maximum useful life of the fabric. Fabric edges are particularly vulnerable because of a tendency of the yarns to unravel and shift. Once damaged, the entire fabric must be replaced. Although traditional woven fabrics have been limited in size by loom construction, they have still reached as much as thirty feet wide by three hundred feet long. Damage to even a small area of the fabric necessitates costly replacement of the entire fabric.
Even minor marring of the surface may deteriorate fabric quality because the paper contact surface characteristics greatly affect the final paper product. Traditional fabrics adjust these characteristics through choice of materials and the type of weave used. Often, a compromise between the best material or the best weave and final product quality must be made. Batting or other material has been affixed to the paper support surface to gain benefits not available from standard materials and weaves. A molded fabric also offers greater flexibility in this regard, as surface characteristics may be incorporated directly into the mold and repeated consistently throughout the fabric. Even more flexibility is added when a separate molded surface plate is attached to a molded base fabric. A removable and replaceable surface plate opens up new flexibility in choosing and maintaining surface characteristics.
The use of molded fabrics will benefit the art in many ways. A more direct process, avoiding additional storage and coiling requirements of monofilament yarns, as well as reducing trimming time and eliminating sealing will be enjoyed by using molded fabrics. More choices of less expensive material will become available, including lower molecular weight materials and gels having less stringent filtration requirements. The molding process also allows the use of composite materials to achieve more beneficial physical properties while maintaining cost effectiveness. A molded fabric allows greater flexibility and efficiency in design when creating fabric patterns (i.e., weave patterns and fabric dimensions). A fabric assembled from pre-molded subassemblies is strong, dimensionally stable, thermally stable, easy to join, distortion free, and has tough finished edges. Furthermore, use of a molded fabric limits fabric stretch, reduces costs, facilitates repair and generally benefits the papermakers art.
SUMMARY
The present invention is a pre-molded, bi-component subassembly for constructing papermaking fabrics. A surface component may be attached to a base component for combined effects on the final paper product. A plurality of the subassemblies are interconnected to create an endless fabric. The completed fabric operates as a papermaking carrier surface in any of the known machine positions.
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AstenJohnson, Inc.
Griffin Steven P.
Hug Eric J
Volpe and Koenig P.C.
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