Braided graphite-foil and method of production

BRAIDED GRAPHITE-FOIL AND METHOD
OF PRODUCTION

CROSS-REFERENCE TO RELATED
APPLICATIONS

This is a continuation application of U.S. patent application Ser. No. 08/324,703, filed Oct. 18, 1994 now abandoned, which is a continuation-in-part application of U.S. patent application Ser. No. 07/987,640, filed Dec. 09, 1992, and now abandoned.

FIELD OF THE INVENTION

The present invention relates to a reinforced vermiculated graphite textile yarn and a method for its production. For a number of years, it has been expected that braided graphitefoil yarns would become commercially viable and available. However, a method of manufacturing a low cost fiber reinforced, vermiculated natural flake graphite textile yarn suitable for braiding, weaving, twisting, and other common textile processing has been elusive, until now.

BACKGROUND OF THE INVENTION

For many years asbestos has played an important role as a mechanical packing material. After centuries of faithful service, asbestos now is shunned because of its toxicity and carcinogenic nature. In high temperature applications, it has been difficult to find a substitute that will work as well as asbestos and still be cost effective.

Cables of braided graphite yarns have shown promise as offering an effective substitute for asbestos. The best of these yarns, however, have not fulfilled their promise. The reason for this is that existing methods of production have compromised the structural integrity of the braided yarn in order to produce a reinforced graphite strand. Reinforced strands of graphite are the key to an effective braided graphite yarn.

Yarns intended for braiding, weaving and other textile processes which may be formed from the reinforcing fibers are jacketed with vermiculated natural flake graphite (vermiculated graphite was first described in Aylsworth Patent numbers: U. S. Pat Nos. 1,137373 of Apr. 27, 1915 and 1,191383 of Jul. 18, 1916) Braiding of graphite yarns is discussed in Shane et al U.S. Pat. No. 3,404382 and 3,494382. Unfortunately, a practical, low cost method of fabricating these yarns from commercially available graphite sheet material had not become commercially practical. The wrapping method described in the above patents was not commercially implemented because it was destructive to the graphite material and therefore it never could be manufactured in the manner in which it was proposed in the patents.

While other references, particularly Ueda U.S. Pat No. 5,134,030 and Leduc U.S. Pat. No. 5,225,262, show a finished end product of similar appearance to the present invention, they are made in a very different manner. Both Ueda and Leduc overknit Iaconel wire about their graphite to keep it together and give it the flexibility to be braided into a final form. This overknitting limits effectiveness at high temperatures in that the overknitted reinforcement degrades leaving passageways through the graphite where vapors may escape. Even when this product is used at lower temperatures, flexing overknitted packing can cause the metal wire to be impressed into the graphite which creates passageways in the graphite through which vapors might escape. Further, overknitting puts metal wire on the outside of the graphite where it has the potential to score expensive machined shafts on which it is used.

DESCRIPTION OF RELATED ART

Applicant is aware of the following U.S. and foreign patents concerning methods of producing long continuous articles employing dies and adhesives, as well as the following listed articles, reports, and sales brochures.

u.s.

Pat. No.

10

Issue Date Inventor Title

1,137,373 04-27-1915 Aylsworth

2,664,374 12-29-1953 Slayter

2,813,051 11-12-1957 MacHenry

3,333,941 08-01-1967 Olstowski

3,404,061 HKI1-1968 Shane

65 4,151,031 04-24-1979 Goad

OTHER PRIOR ART

Crosier, Robert A.; National Engineer, "Braided Graphite Foil: The Asbestos Alternative"; January, 1992; pages 7-11.

Gibson, Sr., Vernon W.; Disclosure Document 083086; "COMPRESSION PACKING AND PROCESS OF FORMING SAME"; Aug. 7, 1979.

A flyer by the Slade Company discloses a fire resistant packing material designated "SLADE FOIL".

A test report by the Southwest Research Institute entitled "Fire Test for Evaluation of Valve Stem Packing"; Jun. 17, 1994.

A test report by the Southwest Research Institute entitled "Fire Test for Evaluation of Valve Stem Packing"; Jul. 21, 1994.

A test report entitled "The Cambridge Report of VOC Valve Emissions".

A test report entitled "The Cambridge Performance Report of VOC Valve Emissions"; May 25, 1994.

Aylsworth U.S. Pat. No. 1,137373 teaches a novel form of graphite and a process for its production. This invention

4

changes the physical orientation of flake graphite so that the flake graphite is greatly expanded in volume after treatment of the myriad of small leaves, which each flake is composed, opened up and separated like leaves of an open or partly

5 open book. These leaves however, are not completely separated from one another. The separation is accomplished by the entrapment of gas or air between the leaves of the expanded flakes, resulting in a graphite of reduced specific gravity and vastly increased bulk or volume.

10 Aylsworth U.S. Pat No. 1,191383 teaches the use of expanded graphite from Aylsworth U.S. Pat. No. 1,137373 compounded with a binder and other substances which can then be molded in various forms.

Crane U.S. Pat. No. 2,072,543 provides an improved

!5 packing fibrous material and method of fluid-tight packing as used in pumps and the like.

Barmack U.S. Pat No. 2,372,645 provides a method for applying insulation to electrical conductors such as wires and cables. The tape form of insulation is applied so as to

20 embrace the conductor as a sheath.

Slayter U.S. Pat No. 2,664,374 teaches a method for the fabrication of strands, cords, tubes and improved products.

Barnes U.S. Pat No. 3,011,933 provides a method of producing a foil-covered elongated member in the form of a

25 wire or tube having an external straight line, longitudinal seam. A plurality of forming rolls is employed to shape the foil sheet into a generally tubular element having a U-shaped cross-section.

Garner U.S. Pat. No. 3332,138 teaches a method and 30 apparatus for making precision sized tubing. This process involves forming the coated metal strip into a longitudinally seamed tube with a lapped seam and extruding a seamless plastic jacket over the outside of the formed tube.

OlstowsM U.S. Pat No. 3,333,941 teaches a method to 35 make a heat expandable composition. The expanded graphite material may be used as a flame retarding agent and is useful as a mulch agent

Garner U.S. Pat No. 3379,821 provides a cable with aluminum or other metal shielding strip pre-coated with 40 special adhesive polyethylene with the outer polyethylene jacket extruded under such temperature and pressure conditions so as to obtain firm adhesion over a portion only of the interface between the extruded jacket and the coated shielding layer.

45 OlstowsM U.S. Pat. No. 3,389,964 teaches a method of producing relatively low density graphite structures from compressed vermicular graphite.

Shane U.S. Pat. No. 3,404,061 teaches a novel form of

50 graphite and a process of producing the same. Shane further shows that threads or yarns can be woven, braided or otherwise worked into the thin, flat, flexible graphic sheet material.

OlstowsM U.S. Pat No. 3,409,563 teaches a process for 55 producing hyperconductive graphite structures by contacting vermicular expanded graphite with a fluid intercalation agent.

OlstowsM U.S. Pat. No. 3,414,381 provides a process for producing graphite structures using low temperature for go reexpanding compressed vermicular graphite.

Sanders U.S. Pat. No. 3,475,244 teaches a process for pressure-bonding compressed vermicular graphite structures to other relatively dense structures. The graphite is treated with a reexpanding agent and heated and pressed to the 65 structure for bonding.

OlstowsM U.S. Pat No. 3,492,197 teaches a method for preparing graphite by compressing expanded vermicular