MANUFACTURE OF GASKETS

Abstract: A gasket (14) comprising a compression-limiting stop (15) is manufactured by bending an edge portion (10a) of a metal sheet (10) of substantially uniform thickness out of the plane of the sheet and pressing said bent edge portion so that it is formed into the stop (15) which is of greater thickness than the sheet. The sheet (10) with the formed stop (15) is then incorporated into said gasket.

Description: Manufacture of Gaskets This invention is concerned with the manufacture of gaskets for forming a seal between two members, eg the cylinder block and the head of an internal combustion engine. Many gaskets incorporate a compression-limiting stop which is present to limit, in certain areas, the degree by which the gasket may be compressed, eg by tightening bolts which connect the members between which the gasket forms a seal. Where the gasket incorporates a resilient layer to form the seal, the stop acts to prevent the resilient layer from being crushed beyond its elastic limit or to prevent the resilient material from being forced out of the sealed joint. Where the gasket is of the multi-layer steel type (MLS) in which sealing is dependant on embossments in the layers concentrating the sealing force in certain areas, the stop acts to prevent the embossments from being completely crushed. Various methods of providing compression-limiting stops are known. For example, where the gasket incorporates at least one metal sheet, edges of this sheet can be folded over through 180° to provide the stop. EP 0 533 357 Al describes an MLS gasket with this type of stop. This type of stop, however, has the disadvantage that its height above the sheet is of necessity equal to the thickness of the metal sheet, that the metal sheet is severely bent and may be subject to cracking, and that the stop is provided only on one side of the metal sheet. It is an object of the present invention to provide a method of manufacturing a gasket comprising a compression- limiting stop which overcomes the above-mentioned disadvantages. The invention provides a method of manufacturing a gasket comprising a compression-limiting stop, characterised in that the method comprises bending an edge portion of a metal sheet of substantially uniform thickness out of the plane of the sheet, pressing said bent edge portion so that it is formed into a solid stop of greater thickness than the sheet, and incorporating said sheet in a gasket. In a method according to the invention, the stop can be given any desired height above the sheet and can project beyond both the opposite surfaces of the sheet. Although the method does involve bending the edge portion of the sheet, this bending is through 90° or less with a consequently reduced risk of cracking compared with bending through 180°. Preferably, in a method according to the invention, the stop is given substantially planar opposite surfaces extending parallel to the plane of the sheet. This is achieved by pressing the bent edge portion between tools which have opposed flat faces. Where the stop is required only on one side of the sheet, one of said opposite surfaces of the stop is made flush with a surface of said sheet. Alternatively, both opposite surfaces of the stop may stand proud of the sheet, for example, by equal amounts. Said bending may be carried out by clamping said sheet in a clamp with said edge portion projecting beyond said clamp, and bending said projecting edge portion with a forming punch which is moved normally to the plane of said sheet. Said pressing operation may be carried out in two stages. If necessary, said edge portion may be restrained, during pressing, against expansion in the plane of the sheet. The invention also provides a gasket manufactured by a method in accordance with the invention. There now follows a detailed description, to be read with reference to the accompanying drawings, of a method of manufacturing a gasket which is illustrative of the invention and of a gasket made by the illustrative method, said gasket also being illustrative of the invention. In the drawings: Figures 1 to 5 are diagrammatic views illustrating successive stages in the formation, by the illustrative method, of a stop on a distance or stopper layer of a multi-layer steel gasket; and Figure 6 is a diagrammatic view of a portion of a gasket manufactured by the illustrative method. The illustrative method is a method of manufacturing an illustrative gasket 14 (shown in Figure 6) comprising a compression-limiting stop 15 of greater thickness than the steel sheet 10 on which it is integrally formed. The stop 15 is solid, ie it has substantially no spaces within its volume. The stop 15 is annular and extends around the hole 13 forming part of the bordering surface of the hole 13. The stop 15 projects above and below the remainder of the sheet 10 by approximately equal amounts and has planar upper and lower surfaces which extend parallel to the upper and lower surfaces of the remainder of the sheet 10. In the illustrative method, the sheet 10 (which as yet does not have the stop 15 but is of substantially uniform thickness) is provided with holes 12 at positions where the holes 13 are required in the gasket 14. In this case, the holes 12 are positioned at the positions where the cylinders of an internal combustion engine are located. The holes 12 have a smaller diameter than the holes 13 which are required in the gasket 14. In this case, the sheet 10 is 1mm in thickness. As shown in Figure 1, in the illustrative method, the sheet 10 is clamped between an upper clamp 16 and a lower clamp 18. The clamps 16 and 18 are annular so that they surround a generally cylindrical passage 20 which has a diameter greater than that of the holes 12. The sheet 10 is clamped so that an edge portion 10a of the sheet 10 surrounding one of the holes 12 projects into said passage 20. The edge portion 10a may be 2 to 3mm wide. Next, in the illustrative method, the edge portion 10a is bent out of the plane of the sheet 10. This is achieved by moving a punch 22 downwardly in the passage 20 (normally to the plane of the sheet 10) so that it contacts the edge portion 10 and bents it. The punch 22 is a close fit in the portion of the passage 20 which is defined by the upper clamp 16 and has a lower surface which contacts the edge portion 10a and bends it. The lower surface of the punch 22 has a flat central portion 22a joined to a radiused convex edge portion 22b which is in turn joined to a cylindrical surface portion 22c which extends in the direction of the passage 20. The cylindrical portion 22c is joined to a radiused concave edge portion 22d which extends to the wall of the passage 20. The bending results in the edge portion 10a conforming to the shape of the surface portions 22c and 22d as is shown in Figure 2. Next, in the illustrative method, the bent edge portion 10a is pressed in two stages so that it is formed into the stop 15. This operation is illustrated by Figures 3 to 5. The sheet 10 (which has been removed from the clamps 16 and 18) is clamped between an upper clamp 24 and a lower clamp 26. The lower clamp 26 is annular and defines a generally cylindrical passage 28 which has a diameter greater than that of the passage 20. The lower clamp 26 engages the sheet 10 with the bent portion 10a and an annular portion 10b of the sheet 10 surrounding the portion 10a projecting into the passage 28. The portions 10a and 10b project by a total of 3mm beyond the lower clamp 26. The upper clamp 24 is also annular and defines a generally cylindrical passage 30 of smaller diameter than the passage 28. Thus, the upper clamp 24 projects above the portions 10a and 10b of the sheet 10. The upper clamp 24 has a lower surface which engages the sheet 10 opposite to the lower clamp 26 but does not engage the projecting portions 10a and 10b because it has a shallow recess 24a above those portions which has a flat bottom surface extending parallel to the plane of the sheet 10. A tool 32 is inserted into the passage 30, in which it is a close fit, so that it projects past the edge of the portion 10a into the passage 28. The tool 32 has only a small clearance with the edge of the portion 10a and has the purpose of restraining expansion of the portion 10a in the plane of the sheet 10 towards the centre of the passage 28. Next, in the illustrative method, a punch 34 is moved upwardly in the passage 28. The punch 34 has an annular upward projection 34a which is a close fit in the passage 28 and on the outer surface of the tool 32. The projection 34a has an upper surface 34b arranged to engage the portions 10a and 10b. The surface 34b is frustoconical being inclined downwardly in the direction of increasing radius. Figure 3 shows the situation before the surface 34a has engaged the portions 10a and 10b and Figure 4 illustrates the effect of this engagement. As can be seen from Figure 4, the portion 10a is bent round against the portion 10b and both portions are deformed into the recess 24a in the upper clamp 24. The deformed portion of the sheet 10 formed from the portions 10a and 10b is hereafter referred to as 10c. The deformed has metal both above the upper surface of the remainder of the sheet 10 and below the level of the lower surface thereof. Next, in the illustrative method, the punch 34 is removed and replaced by a punch 36. The punch 36 is identical to the punch 34 except that, instead of the surface 34b, it has a surface 36a which extends parallel to the flat bottom of the recess 24a in the upper clamp 24. The punch 36 is moved upwardly in the passage so that the surface 36a engages the deformed portion 10c and deforms it further forming the stop 15 which has substantially planar upper and lower surfaces which extend parallel to the plane of the sheet 10. The sheet 10 is now incorporated in the gasket 14 by forming a stack of steel sheets and connecting them together in a conventional manner. Although the stop 15 has a uniform thickness around the hole 13, this may not be the case. If desired, the recess 24a and for the punch surfaces 34b and 36a may give the stop variable thickness. The illustrative gasket 14 (shown in Figure 6) is of the MLS type and comprises three generally parallel sheets of stainless steel, the sheets being a top sheet 42, the sheet 10 which forms a middle sheet, and a bottom sheet 44. The upper surface 42a of the sheet 42 provides an upper sealing surface of the gasket 14 while a lower surface 44a of the sheet 44 provides a lower sealing surface of the gasket. The sheets 42 and 44 have sealing embossments, 42b and 44b respectively, which extend around the hole 13. These embossments 42b and 44b are in the form of ridges projecting towards and contacting the middle sheet 10.

Claims: CLAIMS A method of manufacturing a gasket (14) comprising a compression-limiting stop (15) , characterised in that the method comprises bending an edge portion (10a) of a metal sheet (10) of substantially uniform thickness out of the plane of the sheet, pressing said bent edge portion so that it is formed into a solid stop (15) of greater thickness than the sheet (10) , and incorporating said sheet in a gasket. A method according to claim 1, characterised in that the stop (15) is given substantially planar opposite surfaces extending parallel to the plane of the sheet (10). A method according to claim 2, characterised in that one of said opposite surfaces of the stop (15) is made flush with a surface of said sheet. A method according to any one of claims 1 to 3, characterised in that said bending is carried out by clamping said sheet (10) in a clamp (16, 18) with said edge portion (10a) projecting beyond said clamp, and bending said projecting edge portion with a forming punch (22) which is moved normally to the plane of said sheet. A method according to any one of claims 1 to 4, characterised in that said pressing operation is carried in two stages. A method according to claim 5, characterised in that said edge portion (10a) is restrained, during pressing, against expansion in the plane of the sheet. A gasket manufactured by a method according to any one of claims 1 to 6.

Inventors: CUNNINGTON KEITH, PERCIVAL PAUL REUBEN, WRIGHT VINCENT CLIVE, CUNNINGTON, KEITH, PERCIVAL, PAUL, REUBEN, WRIGHT, VINCENT, CLIVE
Applicants: COOPERS PAYEN LTD, CUNNINGTON KEITH, PERCIVAL PAUL REUBEN, WRIGHT VINCENT CLIVE, COOPERS PAYEN LTD., CUNNINGTON, KEITH, PERCIVAL, PAUL, REUBEN, WRIGHT, VINCENT, CLIVE
Application year: 1996
Main classification: F16J15
IPC codes: B21D19, F16J15