Textiles: spinning – twisting – and twining – Strand structure
Reexamination Certificate
1999-06-28
2002-05-14
Calvert, John J. (Department: 3765)
Textiles: spinning, twisting, and twining
Strand structure
C057S0010UN, C057S258000, C057S295000, C428S357000, C428S358000, C428S362000, C428S363000, C428S364000, C428S369000
Reexamination Certificate
active
06385956
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a packing yarn including at least two bands joined to one another by a yarn manufacturing method and formed of a laminate having at least two mutually joined and alternately disposed layers of two laminar materials, including firstly at least one layer of flexible graphite and secondly at least one layer of a reinforcing agent or medium, wherein both outer flat sides of top and bottom layers of the laminate are formed of flexible graphite or only one of the flat sides is formed of flexible graphite or none of the flat sides is formed of flexible graphite. An example of such a packing yarn is formed of at least two twisted-together bands of a laminate of only one layer of flexible graphite, which is joined at least at one of its two flat sides to at least one reinforcing agent.
Packing yarns of the type described above are used to manufacture seals and, in particular, packings for sealing shaft and spindle glands. According to a known method, two or more packing yarns are combined for that purpose, using a textile processing method such as, for example, braiding, into a cord or plait and then portions of such cords or plaits that are cut to a specific, predetermined length are compressed in a suitable pressing mould to form a packing ring. A plurality of such packing rings produce a stuffing-box packing, once they have been inserted into the appropriate packing space of a stuffing-box. According to another known method, portions of a cord or plait made from the packing yarns, which have been cut to length and correspond to the dimensions of a specific packing space, are inserted directly into the packing space and the packing which is thus produced and is still highly compressible, is tightened up by the gland until tightness of the packing configuration is achieved. According to a third method, the packing yarns or packing cords or plaits manufactured from them may be wound directly around a shaft or spindle having a gland which is to be sealed, until the quantity of packing yarn or packing plait necessary for producing the required packing has been wound on. Then the winding which is thus produced may be tightened up with the aid of the gland, after embedding in the packing space, until tightness of the packing configuration is achieved.
Packing yarns of the type described above are manufactured i.e. by using flexible graphite or expanded graphite. Expanded graphite is obtained by briefly heating graphite salts or intercalation compounds of graphite in the form of an open vermicular material. The flexible graphite is obtained by compressing the expanded graphite which is thus obtained. That is generally produced in the form of graphite foils or graphite plates (see, for example, U.S. Pat. No. 3,404,061). In order to manufacture packing yarns or packing cords or plaits through the use of e.g. braiding, knitting or twisting processes, the graphite foils are cut into strips or bands of a specific width and those strips are then further processed into cords, plaits or strands. Despite a specific flexibility, the strips or bands of flexible graphite tear and/or break during such processing methods because their tensile strength, in particular, is too low. For that reason, a great many possible ways of overcoming the previously mentioned problems associated with manufacturing packing materials from flexible graphite have been indicated.
In one group of solutions to the problem, a substrate of a sufficiently high tensile strength is used, which is finished with a coupling agent, e.g. an adhesive. The substrate is covered with expanded graphite and the expanded graphite and the substrate are pressed together. It is possible to use metal wires, synthetic or natural fibers or yarns, woven fabrics and foils of various types as the substrates. The ropes or bands which are thus obtained are then optionally once more additionally reinforced with yarns, fibers or wires, e.g. by being surrounded by a knitted or braided fabric, or in some other manner, and further processed by using the known processing methods such as braiding into initial products for packings (European Patent Application 0 388 481 A1, corresponding to U.S. Pat. No. 4,961,988; and European Patent 0 466 923 B1, corresponding to U.S. Pat. No. 5,370,405).
According to another group of solutions, use is made of graphite foils which have been cut into strips. In that regard, European Patent 0 253 031 B1, corresponding to U.S. Pat. No. 4,705,722, describes the superimposition of bands of flexible graphite having a width of at most 5 mm, which are then surrounded by a braided or knitted fabric made from a fibrous material. The strands which are thus obtained are then further braided into plaits, which are suitable as an initial material for the manufacture of packings. According to European Patent 0 466 923 B1, corresponding to U.S. Pat. No. 5,370,405, graphite foil strips having a width of at most 5 mm are joined through the use of adhesives to reinforcing organic, inorganic or metal filaments. The reinforced foil strips are processed by braiding, etc. into plaits and the plaits are once more surrounded by a reinforcing fiber braided fabric before being further processed into packings. European Patent Application 0 681 125 A1 discloses the cutting of wide rolls of graphite foils into rolls of reduced width. Foil bands which are thus obtained are provided with a transversely extending embossing or fluting, the fluted foil bands are cut into comparatively narrow strips around 2 mm in width, and the narrow, fluted strips are combined into a rope and surrounded with a reinforced fiber braided fabric. According to European Patent 0 340 303 B1, corresponding to U.S. Pat. No. 5,240,769 and U.S. Pat. No. 5,134,030, strips of graphite foil cut to a width of at most 5 mm are covered with organic, inorganic or metal yarns, fibers or foils and thereby reinforced. The reinforced graphite foil strips are additionally equipped with a further reinforcement of fibers, in the course of further processing into braidable or twistable packing yarns. With that technical solution, a plurality of strips of graphite foil may also be superimposed and processed. According to European Patent Application EP 0 794 367 A2, graphite foil bands having a width of more than 6 mm may be reinforced with a plurality of agents, such as wires, bands, yarns of inorganic, metal or organic agents, and then braided into packing cords or plaits. In that case as well, the graphite foils may be reinforced by a surface coating of plastic material or by laminating with a plastic material. However, a width of the graphite foal bands, which are provided for braiding or knitting, of more than 5 mm is disadvantageous, as is evident from the disclosures of European Patent 0 253 031 B1 or European Patent 0 340 303 B1. Such foils are difficult to process and produce packing cords of a less dense structure.
For that reason, folding techniques are preferentially used when processing wider bands and layers of graphite foils. For instance, European Patent Application 0 444 456 A1 teaches that individual foil bands or a plurality of superimposed foil bands are folded at right angles to their longitudinal direction and a packing ring may be obtained from the folded formed body either directly or after the folded formed body has been surrounded by a braided fabric of yarns, fibers or wires. Prior to folding, for reinforcing purposes, the foil bands may additionally be combined with yarns, fibers or woven fabrics or such reinforcing agents may be placed between the foil layers prior to folding. An insertion of corrosion-resistant plastic foils which preferably additionally have sliding properties, such as e.g. polytetrafluoroethylene foils, is also described. However, such plastic foils are not used for reinforcement purposes. According to U.S. Pat. No. 5,605,341 and U.S. Pat. No. 5,549,306, wide graphite foil bands are folded along their longitudinal direction into the shape of an S or a spiral, with it being possib
Öttinger Oswin
Schellenberger Bernd
Calvert John J.
Greenberg Laurence A.
Hurley Shaun R
Mayback Gregory L.
SGL Technik GmbH
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