This invention relates generally to novel gaskets having continuous multiple seals created by utilizing a core of functionally corrugated material encapsulated by a graphite material such that an interaction occurs among the graphite, the functionally corrugated core, and the surfaces to be sealed. Specifically, the present invention relates to fail-safe, ring-type, concentrically corrugated, graphite encapsulated gaskets with continuous, multiple seals creating a multiplicity of parallel, fluid-locked, graphite-densified, barriers for use in the petrochemical industry to seal flange connections. The present invention also relates to fail-safe, concentrically corrugated, graphite encapsulated heat exchanger and internal combustion engine head gaskets with similarly created continuous, multiple seals.
In the petrochemical industry there exists a need for a versatile flange gasket and heat exchanger gasket having the following characteristics: continuous, fail-safe operation thereby avoiding potential damage to human health, plant equipment and the surrounding environment; fire resistance; resistance to temperature differentials across the diameter of the gasket; chemical resistance; field ruggedness; positive sealing even when the gasket is misaligned; positive sealing when the gasket material differs in thermal expansivity with respect to the surface to be sealed; environmentally safe, non-asbestos construction; operability at high pressures and temperatures; resiliency, springiness, memory, and structural integrity particularly during thermal cycling from high temperatures to low temperatures and vice versa, thermal shock, or other thermal excursions; low torque requirements for maintaining a positive seal at all operational or accidental temperatures and pressures to avoid subjecting the flanges (or other surface) and flange bolts to warpage and/or other damage; inhibited gasket creep or cold flow; crash resistance to enhance the potential for gasket reusability; minimized extrusion of the gasket coating; and reduced installation and maintenance time.
Furthermore, it is likewise desirable to have a cylinder head gasket having similar characteristics as those set forth above in order to improve engine performance.
Until the gaskets of the instant application, these desired gasket characteristics, in combination, had not been achieved. Whereas existing gaskets to date have demonstrated a level of utility and selected ones of the characteristics noted, no gasket until the present invention has been able to achieve the desired combination of gasket characteristics.
Graphite has long been known to possess properties generally desired for high temperature packing materials. In particular, an expanded form of graphite material such as the flexible expanded graphite material sold under the names "Grafoil.RTM." (Union Carbide Corporation, U.S. Pat. No. 3,404,061), "Calgraph.RTM." (Polycarbon, Inc.), "Flexicarb.RTM." (Flexicarb, Inc., a Flexitallic Gaskets, Limited Company), or "Sigraflex.RTM." (Sigri GmbH); an inorganic binder-containing expanded graphite material, such as that described in U.S. Pat. No. 4,234,638; or an intercalated graphite material, such as that described in U.S. Pat. No. 4,799,956, have been employed for use in flange gaskets, heat exchanger gaskets, and automobile engine and exhaust gaskets, and the like.
Bare metal corrugated ring gaskets are known in the art for use as flange gaskets for high temperature applications. Bare metal flat gaskets are also known in the art. However, these bare metal gaskets must be precisely aligned, and the flange and gasket surfaces must be virtually flawless (i.e., highly polished and free of scratches and other abrasions) and the flange bolts must be torqued extremely tightly (approximately 150 ft-lbs on a 3", 150 lb flange) to create a positive seal. Therefore, the flange bolts are typically tightened and over-tightened with a relatively high level of torque to achieve positive sealing. Such over-tightening can warp the flanges, damage both the flanges and the bolts, and create the dangerous potential for seal failure. The bare metal corrugated gaskets have spring-like characteristics which give them high memory and structural integrity, in contrast with a flat metal gasket which has no memory or resiliency. However, the memory capability of a bare metal corrugated gasket is limited in extreme temperature or thermal cycling situations. Under conditions such as thermal cycling, thermal excursions, or thermal shock, these bare metal corrugated gaskets, and the other existing gaskets tend to leak. Furthermore, bare metal is highly vulnerable to corrosion, abrasion, scratching or other attack from hostile materials thereby creating potential leak paths and gasket failure.
Spiral-wound gaskets also exist in the art. These gaskets are composed of two materials, for example, a thin profiled metal strip wound into a spiral with an interleaved strip of a sealing material such as Teflon.RTM., paper, asbestos, or graphite. Spiral-wound gaskets have disadvantages. For example, spiral-wound gaskets have inadequate temperature resiliency when subjected to extreme thermal shocking, excursions or temperature cycling. Spiral-wound gaskets are also abusive to the flanges because they are very difficult to seal and require a relatively high level of torque (as much as 150-160 ft-lbs) be applied to the associated flange bolts. Attempts have been made to enhance the elasticity of a spiral-wound gasket, such as by using the gaskets in tandem, or, as suggested in U.S. Pat. No. 4,796,351, by using annealed high tensile strength, precipitation heat-hardenable alloy steel strip and then heat treating such strip prior to interleaving with the sealing material.
Asbestos gaskets have existed in the art. For example, flat metal, grooved-faced gaskets have been utilized with flanges wherein alternating grooves are filled with asbestos. Asbestos has also been used as a filling material between corrugated sheet metal, metal jackets or spirally wound strips. Also, compressed asbestos sheet material utilizing a rubber binder has been employed in the petrochemical industry as a flange gasket. This asbestos sheet material (such as that sold under the name "Durabla.RTM." by Durabla Manufacturing Co.) is cut into the desired gasket shape and placed between the flange surfaces. Asbestos fiber has desirable material characteristics for gaskets in that it is impervious to most chemicals and acids, it is wear-resistant, and it has high, but limited, temperature capacity (up to approximately 1,000.degree. F. depending upon the stability of the binder material). However, asbestos gaskets only have limited springiness or memory, thereby increasing the likelihood of seal failure during temperature cycling. Furthermore, due to the environmental health dangers associated with asbestos, such a material is no longer desirable in the industry. Kevlar is the most common replacement for asbestos as a gasket material, but it has a temperature limit of only approximately 450.degree. F.
It is also known in the art that graphite can be applied to the edge or center of gaskets to improve the sealing characteristics of the gasket. For example, a strip of expanded graphite tape has been applied around the edge of a flat metal gasket, or has been utilized directly on the flange surface. As described below, the use of a graphite tape is undesirable. Graphite has also been used to encapsulate thin, flat metal gasket reinforcements, such as those described in U.S. Pat. Nos. 4,333,975 and 4,422,894. However, these flat metal-reinforced graphite gaskets have no resiliency or memory, lack a plurality of seals, and do not possess a means of preventing seal loss due to extrusion of the graphite from the metal reinforcement during operation at high temperatures and pressures. Furthermore, the metal is often perforated or tanged thereby creating leak paths.
The use of a strip or strips of narrow graphite tape (i.e., typically less than one inch width) has been employed on corrugated metal pipe flange gaskets typically having larger than an 18" diameter. Application of this tape results in covering only a partial planar surface extending from one corrugation apex to an adjacent corrugation apex on only a portion of the corrugated gasket. Thus, the tape surface generally remains flat and parallel to the flange surface, adhering only to the apex portion of the corrugation, but does not extend into the valley areas between each apex. Furthermore, application of this tape to a circular strip of material creates irregularities or flutes in the tape as the tape is bent or folded to conform to the circular shape. This partial application of tape leaves the metal gasket exposed to corrosion, involves non-uniform, non-unitary, distorted, and overlapping application of the graphite to the gasket face, and does not create a plurality of concentrically spaced, parallel, fluid-locked barrier seals. Furthermore, when the adhesive backing carbonizes at high temperature, and the gasket is placed through a series of temperature cycles, the resulting expansion and contraction of the metal can thereby cause stress and loss of adherence at the graphite/apex points of contact, and/or cause the graphite layer expanse between adjacent corrugation apex points to tear. Furthermore, the expanse of graphite material between adjacent corrugation apex points is vulnerable to puncturing, tearing, and cutting during handling, installation, and use. Thus, the application of this tape creates leak paths, and the potential for extrusion of the graphite material and seal failure.
It has also been suggested that a thin rectilinearly embossed iron sheet could serve as a reinforcement for an inorganically bound graphite material, such as in U.S. Pat. No. 4,234,638. However, this thin rectilinear embossment serves only as a thin reinforcement to a thicker graphite seal, and is not believed to be interactive with the surface to be sealed, nor does it prevent extrusion or channelling of the graphite. This arrangement may experience seal failure at high temperature and pressure.
Graphite has also been used with grooved flat metal pipe flange gaskets, such as described in U.S. Pat. No. 4,121,858. However, the grooves in the gaskets function only to help contain the graphite, and are not believed to give the gasket any memory or resilience.
Furthermore, graphite has been used on heat exchanger head gaskets (for example, as a filler material on a double jacketed heat exchanger gasket as set forth in U.S. Pat. No. 4,118,850 and as a single flat surface coating on a heat exchanger gasket as described in U.S. Pat. No. 4,872,506). However, these heat exchanger head gasket seals also require that a relatively high level of torque (up to approximately 150 ft-lbs) be applied to the head bolts to achieve a positive seal, and these heat exchanger gasket seals have no structural memory or resiliency.
Graphite has also been employed in conjunction with the manufacture of internal combustion engine head gaskets and exhaust manifold gaskets, such as those described in U.S. Pat. Nos. 3,926,539; 4,083,570; 4,423,544; 4,465,287; 4,591,170; 4,705,278; 4,723,783; 4,776,602; 4,810,454; 4,822,062; and 4,911,972. Automotive head gaskets typically require that about 90-100 ft-lbs of torque be applied to the associated bolts to achieve a positive seal and are essentially constructed from a flat, thin (e.g., 7 mil.) metal sheet material which has been perforated and subsequently laminated with a graphite material. The metal has perforations and may further include protrusions (or tangs) extending outwardly on one or both sides of the face of the metal. The graphite material is applied to the surface of this perforated or tanged metal and then the gasket is compressed to close the tangs to affix the graphite in place. Problems exist with these gaskets. For example, the perforations and tangs in the metal substrate may provide leak paths. Additionally, the actual perforated metal is believed to be too thin for welding, thereby, creating size limitations for the gasket. Even if one could weld this very thin (e.g., 7 mil.) material to create a large diameter gasket, the material must then be tanged, which again presents difficulties due to the increased size. Furthermore, these tanged, flat gaskets do not have resilience or memory, thereby reducing their effectiveness in high performance, temperature cycling applications.
Graphite has also been employed in conjunction with the manufacture of valve stem seals or stuffing box seals, such as those described in U.S. Pat. Nos. 4,116,451; 4,160,551; 4,190,257; 4,350,346; 4,394,023; 4,744,572; 4,753,443; and 4,892,320.
As noted above, these existing gasket configurations have limitations and are inadequate to accomplish the desired, combined characteristics for flange, heat exchanger and engine head gaskets as set forth herein.
Therefore, in accordance with the present invention, a fail-safe, multi-sealed, interactive gasket system is provided which overcomes or substantially minimizes these and other disadvantages of the gaskets presently known or used in the art.