Gasket, especially flat gasket made of graphite

Abstract

Graphite gasket consisting of a graphite sealing plate made of flexible, expanded graphite foils, with / or without stainless steel sheet insert or stainless steel spiky sheet carrier, or of a reinforced, multi-layer graphite sealing plate in adhesive-free bond with stainless steel foils, or of flexible expanded graphite in mechanical bond with a three-dimensional expanded sheet insert made of chromium-nickel steel, characterized in that the gasket punched or cut from a graphite sealing plate is coated with a carbon layer consisting of a hard diamond-like carbon layer and a soft and sealing carbon layer applied to the hard diamond-like carbon layer.

Description

[0001] The invention relates to a seal, in particular a flat seal made of graphite with a carbon coating.

[0002] According to the state of the art, coatings of flat gaskets with • PTFE • Molybdenum disulfide • Elastomeric coatings • Mixture of boron nitride and a polytetrafluoroethylene resin • foamable coating material • electrochemical metal deposition • Sintered bronze alloy made from a copper-tin base alloy is known.

[0003] DE 3905922A1 describes a flat gasket, in particular a cylinder head gasket, which is coated on the edging leg at the opening edge on the side facing the engine block and / or the cylinder head with an applied sliding coating made of a polyamide-imide or polyimide synthetic resin with a solid lubricant additive made of a mixture of polytetrafluoroethylene and molybdenum disulfide.

[0004] DE 4332346 A1 discloses a flat gasket made of graphite material, in particular a cylinder head gasket or an exhaust flange gasket for internal combustion engines, which is provided with an epoxy resin coating on one or both sides.

[0005] In DE 000010209538 A1, a seal for a high-temperature connection is described, wherein the seal for a high-temperature connection of this invention consists of a seal base body formed by filling gaps in a reinforcement part designed as a metallic mesh with a heat-resistant filler material composed mainly of diatomaceous earth, and a cover made of a heat-resistant antifriction material composed mainly of a mixture of boron nitride and a polytetrafluoroethylene resin for covering a surface of the seal base body.

[0006] A method for coating a flat gasket material, a flat gasket layer, or a flat gasket on one or both sides is described in DE 197 32 144 C1. The flat gasket material, or a flat gasket layer, or a flat gasket consists of metal or a soft material, in which a coating material is applied at least partially to the flat gasket material, the flat gasket system, or the flat gasket according to an inkjet printing principle from one or more nozzles.

[0007] A laminated sealing material and a method for its production are described in the invention according to DE 102004041043 B3, wherein the laminated sealing material consists of at least two interconnected layers, of which at least one first layer is a graphite foil connected to a second layer of graphite foil, fluoropolymer or paper, and wherein the first and second layers are bonded together by means of a fluoropolymer layer applied via an aqueous dispersion.

[0008] DE 102004062790 A1 describes a foamable coating material for a metallic flat gasket and a method for coating a metallic flat gasket, wherein

[0009] The foamable coating material is based on a fluoropolymer matrix and contains microspheres with a thermoplastic shell. The metallic flat gasket for internal combustion engines consists of at least one metallic layer, on which such a coating is applied, at least in some areas, for sealing purposes.

[0010] A high-pressure connection and a method for producing a high-pressure connection with two adjacent sealing surfaces, and a method for producing such a high-pressure connection, are disclosed in DE 102005060667 A1. To improve the tightness of such a high-pressure connection, at least one of the sealing surfaces is provided with a partial coating. The partial coating is produced by electrochemical metal deposition using electroforming.

[0011] The invention according to DE 102012010603 B4 relates to a coated sealing article comprising an elastomeric base body which is at least partially provided with a coating, wherein the base body in the uncoated state has a surface energy of less than 50 mN / m and the coating has a surface energy of more than 50 mN / m.

[0012] A flat gasket and a method for its manufacture are described in DE 102008056150 A1, wherein the flat gasket comprises a sealing plate to be clamped between sealing surfaces of machine components, with at least one layer of steel sheet, which is provided on at least one of its two main surfaces, which, when the gasket is installed, bears against one of the sealing surfaces of the machine component, with a surface coating exhibiting micro-sealing and sliding properties. The surface coating is designed as a bronze alloy of a copper-tin base alloy sintered onto the steel sheet layer.

[0013] The CN 204 610 822 U describes a metal flat gasket with a PTFE coating.

[0014] The invention according to CN203431157 U relates to the technical field of sealing elements and a seal coated with aluminum foil. The seal comprises a sealing element, wherein an aluminum foil layer with a longitudinally and transversely raised structure is arranged on the outside of the sealing element, the distance between the raised structures being 0.5 to 0.7 cm. US 5,667,227 A describes a formulation for an elastic sealing coating that can be cured by ultraviolet radiation emitting without fumes into the environment. Different parts of the coating are cured by successive exposure to two different wavelengths of UV radiation during a continuous in-line process. The first wavelength cures an inner section of the coating and bonds the coating to the substrate.The second wavelength hardens a coating surface. The formulation enables thicker, more pigmented coatings that can be cured using ultraviolet light than previously possible.

[0015] A method for producing a seal with a high-temperature coating is disclosed in US 2014 / 0217679A1, wherein a substrate consists of a metallic material and is designed in the form of a seal, containing a nanoparticle suspension over the outer surfaces of the substrate, and a primer layer of a self-protecting oxide coating is formed by heating the substrate to a first elevated temperature.

[0016] The process also includes applying a liquid over the primer layer, which consists of boron nitride, and drying the boron nitride at a second elevated temperature to form a coating layer.

[0017] An oil-resistant seal and a method for the oil-resistant seal are described in US 6,129,360 A, wherein the seal includes an organic polymeric coating consisting of the group consisting of parylene N, parylene D, parylene C and mixtures thereof, forming a porous, elastomeric seal.

[0018] The invention according to JP 2011-42 769 A describes an expanded graphite foil used as a gasket, which is a simple and easily removable seal from the flange surface. The expanded graphite foil is coated with a PP resin on the surface of the expanded graphite foil to a thickness of 20-40 [µm]. After coating with the PP resin, a heat treatment is carried out such that the PP resin layer is heated to 150-160 °C and held in this heated state for 10 minutes.

[0019] A graphite seal with improved release characteristics is disclosed in US 4 591 166 A, which is embossed and forms a relief pattern from relatively raised areas and is provided with a coating of silicone rubber.

[0020] German patent DE 4441132 A describes a sealing element and a method for its manufacture, particularly for shut-off and control devices. The sealing element consists of a plate-shaped or piston-shaped shut-off body made of a metallic or non-metallic material. For example, it is an aluminum ceramic material. A carbon- and silicon-containing hard coating of approximately 1 to 2 µm is deposited onto a working surface of the shut-off body using a plasma-CVD process. This coating consists of an adhesive layer and a sliding layer, with the silicon content being higher in the adhesive layer than in the sliding layer. To increase the adhesion of the adhesive layer, it is tempered after coating. The tempering is carried out either for 0.5 to 1 minute at 900°C or for 30 to 60 minutes at 500°C.

[0021] The deposition of silicon, especially silicon carbide, as a coating on seals, particularly on flat seals, does not achieve the desired leakage values ​​and leads to leakage losses at high temperatures and high pressures.

[0022] The graphite gaskets used in the prior art tend to stick to flange surfaces at temperatures up to 450°C under the influence of pressure and temperature, causing contamination and adhesions that must be removed before inserting new graphite sealing discs, thus making gasket replacement very time-consuming. The coatings for graphite gaskets described in the prior art also do not achieve the desired result when replacing gaskets.

[0023] The object of the invention is to develop a coating for graphite seals that does not cause sticking on the sealing surfaces at high temperatures and high pressure, thus preventing contamination of the sealing surfaces and exhibiting low leakage rates.

[0024] The object of the invention is achieved by a gasket, in particular a flat gasket made of graphite, which consists of a graphite sealing plate made of flexible, expanded graphite foils, with / or without a stainless steel sheet insert or stainless steel spiky sheet carrier, or of a reinforced, multi-layer graphite sealing plate in an adhesive-free bond with stainless steel foils, or of flexible expanded graphite in a mechanical bond with a three-dimensional expanded sheet insert made of chromium-nickel steel, characterized in that the gasket, in particular a flat gasket, punched or cut out from a graphite sealing plate, is coated with a carbon layer consisting of a hard diamond-like carbon layer and a soft and sealing carbon layer applied to the hard diamond-like carbon layer.

[0025] The invention will now be explained in more detail using an example.

[0026] A flat gasket, die-cut from a graphite gasket sheet for a flange sealing surface, undergoes plasma-enhanced chemical vapor deposition (PECVD) with a deposition voltage of up to 900 V to apply a hard, diamond-like carbon (DLC) layer. The higher the deposition voltage, the harder this layer becomes, which adheres optimally to the graphite surface of the flat gasket and bonds with it.

[0027] These DLC coatings have hardnesses of approximately 2000 to 3000 HV and are particularly distinguished by their very low dry friction coefficients of approximately 0.1 to 0.25 compared to metallic friction partners, which they retain even in inert atmospheres or under vacuum. They are applicable up to approximately 500°C.

[0028] Since the surface structure of graphite is very uneven and the unevenness is further increased by the DLC coatings, a soft carbon sealing layer is applied to this hard diamond-like (DLC) layer.

[0029] Leakage values ​​of less than 0.1 mg / ms were only achieved through the interaction of an applied hard diamond-like carbon (DLC) layer with a soft carbon layer applied to this DLC layer for carbon sealing.

[0030] The coating of the graphite seal with a carbon layer according to the invention can also be carried out using other physical vapor deposition processes, such as evaporation, sputtering, ion plating or ICB technology.

Claims

[1] Graphite gasket consisting of a graphite sealing plate made of flexible expanded graphite foils, with or without stainless steel sheet insert or stainless steel spiky sheet carrier, or of a reinforced multi-layer graphite sealing plate in adhesive-free bond with stainless steel foils, or of flexible expanded graphite in mechanical bond with a three-dimensional expanded sheet insert made of chromium-nickel steel, characterized by , that the gasket punched or cut from a graphite gasket sheet is coated with a carbon layer consisting of a hard diamond-like carbon layer and a soft and sealing carbon layer applied to the hard diamond-like carbon layer. [2] Seal according to claim 1, characterized by , the seal is designed as a flat seal.