Stock material or miscellaneous articles – Self-sustaining carbon mass or layer with impregnant or...
Reexamination Certificate
2000-01-26
2002-06-04
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Self-sustaining carbon mass or layer with impregnant or...
C252S502000, C277S938000, C277S944000, C428S066400, C428S297400, C428S402000, C428S446000, C428S448000
Reexamination Certificate
active
06399204
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a flexible multi-layer gasketing product having high thermal stability and good sealing properties. More particularly, the present invention relates to an improved multi-layer gasketing product that does not require employment of adhesive between the layers and which comprises a non-expanded graphite layer and a fibrous layer.
2. Background of the Related Art and Information Disclosure Statement
Gasketing products are used in many applications to seal adjacent surfaces so as to prevent fluid leakage. A variety of materials are used in gasket manufacture, the particular materials used in the fabrication being chosen to meet the particular conditions under which the gasketing product is to perform. For example, vegetable fiber-based gasketing is often used to seal hot and cold liquids in applications wherein the pressure is relatively low (less than 300 psi). On the other hand, graphite-based gasketing is frequently used in pumps where the gasket may be exposed to relatively high pressure (up to 10,000 psi) and/or may be exposed to corrosive media. Neoprene-based gaskets are frequently employed in applications wherein compressibility is a factor, such as when two irregular joint flanges are to be joined together to effectuate a seal. Polymeric aromatic polyamide-based gasketing (such as aramid or Kevlar®) with a nitrile or SBR binder, offers good temperature and pressure resistance lending itself to be used for steam, gases and mild caustic sealing.
There are a number of characteristics that are typically desired in a gasketing product: (1) the material comprising the gasket should be relatively inert to prevent reaction of the gasket with its ambient environment and the surfaces it is designed to seal; (2) the material comprising the gasket should not stick to the parts against which the gasket is intended to bear; (3) the material comprising the gasket should have high wear resistance to provide for a gasket with a relatively long service life; (4) the material should be easily handable and not friable in nature; (5) the material should provide for compressibility of the gasket; and the (6) the materials comprising the gasket should be relatively inexpensive.
One particularly useful material for fabricating gaskets is graphite. Graphite is used in gasketing products because of its relative non-reactivity to other chemical compounds, its ability to resist both corrosive and non-corrosive media, its low coefficient of friction, and its excellent thermal stability.
Graphite is made up of substantially flat planes of hexagonally arranged carbon atoms, which are oriented so as to be substantially parallel and equidistant to one another. Natural graphites may be characterized as superposed laminated structures of carbon atoms joined together by weak Van der Waals forces. The laminae are linked together in groups known as crystallites.
In order to be useful in most sealing applications, graphite-based gaskets must be flexible. So-called “flexible graphite” is therefore conventionally used in most graphite containing gaskets. The term “flexible graphite” refers to the exfoliated reaction product of rapidly heated natural graphite particles which have been treated with an agent that intercalates into the crystal-structure of graphite to expand the intercalated particles at least 80 or more times in the direction perpendicular to the carbon layers in the crystal structure. A preferred intercalating agent is a solution of a mixture of sulfuric acid and an oxidizing agent. A conventional process for producing a flexible graphite sheet is described in U.S. Pat. No. 3,404,061 to Shane et al. Such process comprises treating the natural graphite particles with a suitable oxidizing agent, heating the treated particles to permit a natural expansion and then compressing and compacting the heated particles to form a flexible integrated sheet. Typical oxidizing agents include nitric acid, potassium chlorate, hydrogen peroxide, chromic acid, potassium permanganate, potassium chromate, potassium dichromate, and perchloric acid.
Flexible graphite-based gasketing products exhibit excellent temperature resistance, maintaining integrity from cryogenic temperatures to temperatures over 5400° F. in inert or reducing atmospheres, and up to approximately 850° F. in oxidizing atmospheres. Such products further exhibit very low creep relaxation (about 5%), excellent compressibility and conformability, and excellent chemical resistance (except for concentrated highly oxidizing mineral acids). Flexible graphite-based gaskets, however, suffer from a number of disadvantages, including, the adhesion of the graphite to mating surfaces, exhibition of a low resistance to compressive forces in particular after exposure to fluids such as oil or antifreeze, a lack of resiliency after compression, and a lack of inherent tensile strength which results in a tendency of such gaskets to break during handling in particular when bent.
In an attempt to take advantage of the desirable characteristics of graphite as a sealing agent, while avoiding its drawbacks, numerous manufacturers have proposed graphite-based gaskets fabricated from composite blends, and manufactured as laminates.
Gaskets made from composite materials that include graphite portend improved physical properties while generally offering the advantage of ease of manufacture. U.S. Pat. No. 4,282,288 discloses a graphite composite comprising a natural flake graphite bound with a binder such as coal tar or coal pitch which has been heat fixed. U.S. Pat. No. 4,443,517 discloses a fiber-reinforced graphite composition comprising a mass of intermeshed fibers bonded to one-another at points of contact by a binder and graphite distributed throughout the intermeshed fibers in an amount of from about 45% to about 95% of the total weight of the material. U.S. Pat. No. 5,286,574 discloses a composite gasket material, which is said to provide for, improved sealability and thermal stability. Such composite includes a fiber component, elastomeric binder component and a solid filler component that includes as a component a salt formed from a multivalent metal cation and a sterically hindered dicarboxylic acid. U.S. Pat. No. 4,529,653 discloses a non-asbestos flexible sheet material useful as a gasket which comprises graphite along with clay, silicate, cellulose fibers, starch and rubber. Such patent asserts improved flexibility and tensile strength. U.S. Pat. No. 5,902,762 discloses a sheet useful for forming gaskets formed from resin-impregnated flexible material which has embedded ceramic fibers extending from the surface of the sheet into the sheet. The ceramic fibers increase the permeability of the sheet to resin.
U.S. Pat. Nos. 4,977,205 and 5,437,920, both assigned to Frenzelit-Werke GmbH & Co. KG, describe composite sealing materials employing fibrillated organic fibers, flaked graphite and an elastomeric organic binder. U.S. Pat. No. 4,977,205 discloses a composite comprising between about 10% to about 70% by weight flake graphite having a particle size of 50 um to 250 um, between about 5% to about 20% by weight of an elastomer, and between about 5% to about 30% by weight process fiber, which preferably are aramids. U.S. Pat. No. 5,437,920 describes a composite comprising at least about 60% by weight finely divided graphite powder, from about 3% to about 5% elastomeric resin binder, and between about 2.5 to about 5.5% fiber of which about 0.5% to about 1.5% by weight is non-fibrillated fibers, and of which about 2 to about 4% by weight is fibrillated organic fibers.
Flexible graphite laminates have also been proposed for use as gaskets in various sealing applications. Laminates offer the possibility of maximizing the amount of graphite which is exposed to any conjoining surface. Many of these laminates contain metal or plastic sheets bonded between two sheets of flexible graphite material. The interlayer provides for an increase in strength and may improve the ease of handling of the lam
Hill Kenneth L.
Hurley Timothy J.
Shekleton Laura E.
Boss Wendy
Cummings & Lockwood
Garlock Inc.
Jones Deborah
LandOfFree
Flexible multi-layer gasketing product does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Flexible multi-layer gasketing product, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Flexible multi-layer gasketing product will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2899629