GASKETS

Abstract: A gasket (10; 50) comprises at least one metal sheet (12; 52) which extends generally parallel to sealing surfaces (11a, 13a) of the gasket. The metal sheet has deposited metal (20; 54) thereon forming a functional projection, e.g. to limit compression of the gasket. The metal is deposited on the surface (12a, 12b; 52a) of the sheet by electroplating.

Description: GASKETS This invention is concerned with gaskets which comprise at least one metal sheet having at least one functional projection therefrom. The term "functional projection" is used herein to mean a projection which has a mechanical function. Such a projection may serve to concentrate stress to enhance sealing or may serve as a compression-limiting stop to prevent excessive compression of the gasket. This invention is also concerned with methods of manufacturing such gaskets. Gaskets for automotive and other applications often incorporate metal sheets which have functional projections therefrom. Such projections may be in the form of elongated ridges which serve to concentrate stress. Such ridges are conventionally formed by embossing the metal sheet which results in an undesirable groove in the opposite surface of the metal sheet. Furthermore, embossed ridges cannot be provided at the same locations on opposite sides of the same sheet. Functional projections from metal sheets may also provide compression-limiting stops to prevent the gasket from being compressed beyond a predetermined limit. Three methods of providing such compression stops are known to the applicants. Firstly, they can be provided around holes through the gasket or at edges thereof by metal sheets bent over another sheet of the gasket, for example the stops may be formed by eyelets in holes through the gasket. Compression stops formed in this way can, however, only be provided at certain locations, have to have a certain minimum thickness to allow for bending, and may be subject to cracking. Secondly, such compression stops may be provided by foil cut into the required pattern and laser-welded to another sheet of the gasket. This method is complex especially where a narrow stop is required. Thirdly, an extra sheet can be incorporated in the gasket and folded over to provided compression stops. Thus, one type of conventional gasket comprises four overlying sheets of steel, upper and lower functional sheets which are embossed to form stress- concentrating ridges, and two intermediate sheets which are a planar distance or spacing sheet and a thin stopper sheet which is folded to form compression stops. This method can provide thinner stops than the first-mentioned method since the stops only occur on one side of the sheet but the thickness must still be sufficient to allow for folding and cracking can be a problem. Furthermore, compression stops following intricate paths across the gasket are difficult to provide and the use of the additional sheet increases inter-sheet sealing problems. It is also known for the head movements in an internal combustion engine to cause said additional sheet to move relative to the rest of the gasket. It is an object of the present invention to provide an improved gasket in which a functional projection from a metal sheet is provided in an improved manner which avoids the disadvantages referred to above. The invention provides a gasket having upper and lower sealing surfaces, the gasket comprising at least one metal sheet extending generally parallel to said sealing surfaces, characterised in that the metal sheet has metal deposited on an area of the surface thereof by electroplating, said deposited metal forming at least one functional projection from said surface. In a gasket in accordance with the invention, a functional projection can be provided at any point of the gasket whether or not said point is on the opposite surface to another projection and whether the point is adjacent to a hole or to an edge. Furthermore, there is no significant limitation on the thickness or width of the projection since the metal can be deposited to any desired thickness or width. The projection can follow an intricate path and is not subject to cracking. Where the gasket comprises overlying sheets of steel, one less sheet can be used, since a layer to provide a compression stop is not required. Another advantage is that, if desired, the thickness, hardness or height of a projection can be varied along the projection. In a gasket in accordance with the invention, the deposited metal may extend over an edge of the metal sheet and form functional projections from both surfaces of the sheet. This is advantageous where said edge bounds a hole through the metal sheet and said projections extend around said hole. The projection may be in the form of an elongated ridge which may have a width of 1.0mm to 4.0mm. The deposited metal may have a thickness of up to 150 microns, 50 microns being suitable in some cases. The deposited metal is preferably nickel or an alloy thereof, this being advantageous as nickel is not attacked by fluids commonly encountered in engines. Other metals and alloys may, however, be used. Resilient or hard, eg ceramic, particles may be included in the deposited metal to alter the properties of the projection. The metal to form the compression stop may be deposited by conventional electroplating or by jet or brush electroplating. The invention also provides a method of providing at least one functional projection on a selected area of a surface of a metal sheet of a gasket, characterised in that the method comprises depositing metal on said selected area by electroplating. In a method in accordance with the invention, the deposition may be by jet electroplating, ie a process in which a jet of electroplating solution containing metallic ions (eg of nickel) is directed on to the selected area while an electrical potential difference is maintained between the jet and the metal sheet. Relative movement between the jet and the metal sheet allows the jet to track along a path on the surface to deposit an elongated ridge of metal to form the projection. If desired, the jet can track along the path several times, or a plurality of jets can follow one another along the path, so that the projection is deposited as a plurality of overlying layers. The projection can be given variable thickness by varying speeds or electrical potentials and variable hardness by varying additives to the jet. Alternatively, conventional electroplating can be used. In this case, areas of the metal sheet other than said selected area may be masked and the metal sheet be immersed or partly immersed in an electroplating solution. Plastics such as PVC and polypropylene are suitable materials for the mask and sheets of the masking material can be clamped to opposite surfaces of the metal sheet. Alternatively, the mask material can be applied by screen printing, by a photoresist technique, or by laminating the sheet with film. For example, a stack may be formed of metal sheets (for use in a plurality of gaskets of the same type) with masking sheets interleaved between the metal sheets. The stack is then immersed or partly immersed in the electroplating solution so that compression stops are formed simultaneously on each metal sheet. There now follow detailed descriptions, to be read with reference to the accompanying drawings, of two gaskets which are illustrative of the invention and of a method of manufacturing which is illustrative of the invention in its method aspects. In the drawings: Figure 1 is a diagrammatic cross-sectional view taken through a portion of a first illustrative gasket; Figure 2 is a diagrammatic view showing the formation of projections on a metal sheet of the first illustrative gasket and on a plurality of similar sheets for use in other similar gaskets; and Figure 3 is a view similar to Figure 1 but of a second illustrative gasket. The first illustrative gasket 10 shown in Figure 1 is of the multi-layer steel type and comprises three generally parallel sheets of stainless steel which are arranged one- above-the-other in a stack. The sheets are numbered 11, 12 and 13. The top sheet 11 has an upper surface Ila which provides an upper sealing surface of the gasket 10. The top sheet 11 is embossed so that it has downwardly projecting stress-concentrating ridges 18 formed therein. The crests of these ridges 18 engage an upper surface 12a of the middle sheet 12 in the stack. The sheet 12 is generally flat except that it has metal 20 deposited on an area of the surface thereof by electroplating. The metal 20 forms a compression-limiting stop of the gasket 10 which is described in more detail below. The sheet 12 overlies the bottom sheet 13 which is a mirror-image of the top sheet 11 having upwardly-projecting stress-concentrating ridges 22 whose crests engage the sheet 12. The sheet 13 has a lower surface 13a which provides a lower sealing surface of the gasket 10. Thus, the sheets 11 to 13 of the gasket 10 extend generally parallel to the sealing surfaces Ila and 13a. The gasket 10 has holes 30 (one visible in Figure 1) therethrough. These holes 30 extend through all three of the sheets 11 to 13 and are positioned to correspond to the positions of cylinders in the engine block of an engine in which the gasket 10 is used. The deposited metal 20 is provided on an area of the metal sheet 12 surrounding the hole 30. Specifically, the deposited metal 20 extends as a functional projection in the shape of an elongated ridge on the surface 12a around the hole 30 and as a further similar projection on a lower surface 12b also around the hole 30. These projections are connected by deposited metal 20 which extends over the edge of the sheet 12 surrounding the hole 30. The compression stop formed by the deposited metal 20, thus, has the shape of an eyelet formed in the hole 30. The elongated ridge projections provide compression-limiting stops on both surfaces 12a and 12b around the hole 30. The ridges extend 2.8mm from the hole 30 and have a thickness of 0.05mm, ie they stand proud of the surfaces 12a and 12b of the sheet 12 by 0.05mm. The deposited metal 20 is nickel deposited on the metal sheet 12 by electroplating. The illustrative method of providing the functional projections on a selected area of the sheet 12 comprises depositing nickel on said area by electroplating. To achieve this, a stack 40 (Figure 2) is prepared. The stack 40 consists of the sheet 12 and a plurality of similar sheets 12c for use in further gaskets. Also in the stack 40 are masking sheets 42 of PVC which are interleaved between the metal sheets so that metal sheets and masking sheets alternate in the stack 40. The PVC sheets 42 have holes 44 therein in positions which correspond to the positions of the holes 30 in the metal sheets. The holes 42 are, however, of greater diameter than the holes 30 so that, adjacent to each hole 30, an edge portion of the metal sheet is left unmasked. The stack 40 is clamped together so that the masking sheets 42 are pressed into intimate contact with the metal sheets 12 and 12c. The stack 40 is immersed in an electroplating solution (not shown) containing nickel ions and is connected to a source of electrical potential so that the metal sheets 12 and 12c are the cathode. Anodes are provided by nickel rods 46 which are inserted in the holes 30 and 44. These rods 46 may be shaped to concentrate plated nickel at desired locations. Plating is then allowed to proceed until deposited metal 20 as described above has been built up on the unmasked areas of each sheet 12 and 12c. Figure 3 shows the second illustrative gasket 50 which comprises a single sheet 52 of embossed steel having deposited metal 54 electroplated on to one surface 52a of the sheet 52 at an edge thereof.

Claims: CLAIMS A gasket (10; 50) having upper (Ila; 52a) and lower (13a) sealing surfaces, the gasket comprising at least one metal sheet (12; 52) extending generally parallel to said sealing surfaces, characterised in that the metal sheet has metal (20; 54) deposited on an area of the surface (12a, 12b; 52a) thereof by electroplating, said deposited metal forming at least one functional projection from said surface. A gasket according to claim l, characterised in that the deposited metal (20) extends over a edge of the metal sheet (12) and forms functional projections from both surfaces (12a, 12b) of the sheet. A gasket according to claim 2, characterised in that said edge bounds a hole (30) through the metal sheet (12) and said projections extend around said hole. A gasket according to any one of claims 1 to 3, characterised in that the projection is in the form of an elongated ridge. A gasket according to claim 4, characterised in that the elongated ridge has a width of 1.0mm to 4.0mm. A gasket according to any one of claims 1 to 5, characterised in that the deposited metal (20; 54) has a thickness of up to 150 microns. A gasket according to any one of claims 1 to 6, characterised in that the deposited metal is nickel or an alloy thereof. A gasket according to any one of claims 1 to 7, characterised in that the deposited metal contains ceramic particles. A method of providing at least one functional projection on a selected area of a surface (12a, 12b; 52a) of a metal sheet (12; 52) of a gasket (10; 50), characterised in that the method comprises depositing metal (20; 54) on said selected area by electroplating. A method according to claim 9, characterised in that the metal (20; 54) is deposited by jet electroplating. A method according to claim 9, characterised in that areas of said metal sheet (12) other than said selected area are masked and the metal sheet is immersed or partly immersed in an electroplating solution. A method according to claim 11, characterised in that the method comprises forming a stack (40) of metal sheets (12, 12c) with masking sheets (42) interleaved between said metal sheets, and immersing or partly immersing said stack in an electroplating solution. A method according to claim 9, characterised in that the metal (20; 54) is deposited by brush electroplating.

Inventors: EASTHAM DAVID RAYMOND, HARLAND CHRISTOPHER ROBIN, JOHAL CHARAN PREET SINGH, PERCIVAL PAUL REUBEN, EASTHAM, DAVID, RAYMOND, HARLAND, CHRISTOPHER, ROBIN, JOHAL, CHARAN, PREET, SINGH, PERCIVAL, PAUL, REUBEN
Applicants: EASTHAM DAVID RAYMOND, HARLAND CHRISTOPHER ROBIN, JOHAL CHARAN PREET SINGH, PERCIVAL PAUL REUBEN, T & N TECHNOLOGY LTD, EASTHAM, DAVID, RAYMOND, HARLAND, CHRISTOPHER, ROBIN, JOHAL, CHARAN, PREET, SINGH, PERCIVAL, PAUL, REUBEN, T & N TECHNOLOGY LIMITED
Application year: 1995
Main classification: F16J15
IPC codes: C25D7, F16J15