This invention is concerned with forming eyelets in gaskets.

Gaskets which comprise a sheet of resilient material adhered to a surface of a reinforcing sheet or two sheets of resilient material adhered to opposite surfaces of a reinforcing sheet are well-known. Such gaskets are used, for example, as the head gaskets of internal combustion engines. It is also well-known to provide such gaskets with so-called eyelets which bend around a hole in the gasket to protect the edge of the resilient sheet or sheets. Thus, in the case of a head gasket, the holes where the engine cylinders are located are protected by eyelets so that the hot and abrasive combustion gases do not come into contact with the edge of the resilient sheet or sheets around said hole. Such an eyelet comprises a first head portion which is substantially flat and extends parallel to one face of the gasket, e.g. that which engages the cylinder block, a second head portion which is substantially flat and extends parallel to the opposite face of the gasket, e.g. that which engages the head of the engine, and a shank portion which joins said first and second head portions by passing through the hole in the gasket. The shank portion extends around the periphery of said hole and is U-shaped when viewed in cross-section.

In order to form the eyelet of a gasket, a piece of sheet metal is pierced with a hole of a smaller size than the hole in the gasket. The periphery of the hole in the sheet metal is then pressed out of the plane of the sheet to form an upstanding cylinder whose outer surface is a tight fit in the hole in the gasket. This cylinder is joined to the remainder of the sheet by a 90° turn made by

a smooth curve of low radius. Next, the sheet is cut around an annulus around the cylinder leaving a flange which will form one of the head portions. The cylinder is then inserted into the hole in the gasket so that the flange engages one surface of the gasket and part of the cylinder projects beyond the other surface of the gasket. Finally, a closure operation is performed in which the flange is held against the gasket while the projecting portion of the cylinder is deformed to form the other head portion of the eyelet by making a 90° turn by a further smooth curve of low radius and a flat portion parallel to the flange. The two 90° curves normally merge with one another to give a smooth 180° curve. It is also known to subsequently flatten this curve adjacent one or both sides of the gasket to alter the resilience of the eyelet. This is achieved by a pressing operation after the closing operation.

The eyelets described above sometimes fail in service because cracks arise therein. In the case of a head gasket, such cracks arise more frequently on the side of the gasket which engages the head. It is considered that this cracking is due to a combination of vertical and horizontal movements between the head and the block. The incidence of cracking is approximately equal whether the initial head portion or the closure head portion engages the head.

It is an object of the present invention to provide a method of forming a reinforcing eyelet around a hole in a gasket which results in a less crack-prone eyelet.

The invention provides a method of forming a reinforcing eyelet around a hole in a gasket, the method comprising forming a 90° bend in a sheet material around a hole therein to provide an upstanding generally cylindrical projection projecting from a substantially flat initial

head portion, inserting said projection in the hole in the gasket, and forming a 90° bend in said projection to form a substantially flat closure head portion on the opposite side of the gasket to said initial head portion, characterised in that at least one of said 90° bends is formed by a bending operation which forms said bend as two curves separated by a substantially straight portion.

It is found that, when an eyelet is formed by a method according to the invention, the eyelet is considerably less prone to cracking. In the case of a head gasket, the tendency towards cracking is particularly reduced if the 90° bend formed as two separated curves is adjacent to the head.

It is considered that an eyelet formed according to the invention is less likely to crack because the metal, usually steel, of the eyelet is subjected to less stress during the bending operation than a conventional eyelet formed as a continuous 90° bend of constant radius. An eyelet formed into a continuous 90° bend in a first bending operation which is then flattened in a second bending operation may be formed into a similar shape as an eyelet formed according to the invention, but such an eyelet having been subjected to greater stress is more likely to crack.

Preferably, the curve of said two curves which is nearer to one of said head portions turns through an angle of between 7° and 23°, more preferably the angle is between 10° and 20°, e.g. 15°. The straight portion is preferably 0.75mm to 2mm long.

Preferably, said at least one of said 90° bends is formed by a closure bending operation. This is found to reduce the forming stress below that reached when said 90° bend is formed by the initial bending operation.

There now follows a detailed description, to be read with reference to the accompanying drawings, of a method of forming an eyelet which is illustrative of the invention.

In the drawings:

Figure 1 is a plan view of a portion of a gasket which is provided with eyelets by the illustrative method;

Figure 2 is a plan view of a portion of a sheet used to form the eyelets showing holes punched therein;

Figures 3 to 10 are diagrammatic cross-sectional views showing successive stages of an initial bending operation of the illustrative method; and

Figures 11 to 14 are diagrammatic cross-sectional views showing successive stages of a closure bending operation of the illustrative method.

The illustrative method is a method of forming a reinforcing eyelet E around a hole H in a gasket G. The gasket G is a head gasket for a four cylinder internal combustion engine and the hole H is one of four similar holes which correspond to the cylinders of the engine, all four holes being provided with eyelets in the illustrative method. The gasket G also has other holes h which, in this case, are not provided with eyelets. The gasket G comprises a metal reinforcing sheet S made of sheet steel (aluminium is an alternative) having a layer of adhesive (not shown) on each surface thereof. The gasket G also comprises two layers of resilient sealing material M secured to the reinforcing sheet S by the adhesive. The material M is, in this case, nitrile rubber but other materials, such as expanded graphite, are possible.

In the illustrative method, the eyelets E are formed as a unit with connecting tags T between them from a piece of sheet material 10 which is, in this case, steel. The method comprises piercing four holes 12 through the sheet 10 by a conventional punching operation. The holes 12 are

smaller than the holes H but have their centres spaced at the same intervals as those of the holes H.

Next, in the illustrative method, the annular portions 13, 14 and 15 of the sheet 10 which bound the holes 12 are each formed into the eyelets E. The annular portion 13 which immediately bounds the hole 12 and the annular portion 14 between the portions 13 and 15 are bent through into a 90° bend to provide an upstanding generally cylindrical projection 16 projecting from the portion 15 of the sheet 10 which will provide a substantially flat head portion 18 of the eyelet E. The portions 13, 14 and 15 are indicated by broken lines in Figure 2. This bending is referred to herein as the initial bending operation.

The initial bending operation forms said 90° bend as two curves 25 and 26 separated by a substantially straight portion 28. The first curve 25 adjoins the portion 15 which has remained flat and turns through an angle of 15°. The straight portion 28 is 1mm long and joins the two curves 25 and 26. The straight portion is, thus, inclined at 15° to the flat head portion 18. The curve 26 completes the turn through 90°, i.e. it turns through an angle of 75°. The curves 25 and 26 are both of constant radius throughout.

Figures 3 to 10 illustrate the initial bending operation. In Figure 3, the formation of the first curve 25 is illustrated. The sheet 10 is gripped at the portion 15 between a flat upper surface 20a of a first lower die 20 and a flat lower surface 21a of an upper die 21. A portion 21b of the upper die 21 extends beyond the lower die 20 (to the left viewing Figure 3) . The portion 21b has a lower surface 21c which is the same shape as that of the 90° bend to be formed, i.e. the surface 21c has a 15° curve, a flat portion 1mm long, and 75° curve. The sheet 10 is bent against the surface 21c by a further lower die 22 which has

an inclined upper surface 22a disposed opposite the surface 21c. The die 22 is moved upwardly past the die 20 to bend the sheet upwardly.

Figure 4 illustrates the next stage of the initial bending operation. A third lower die 24 is moved upwardly in a cylindrical vertical passage defined by vertical aligned surfaces 21d and 22b of the dies 21 and 22. The die 24 has a flat top 24a bounded by an edge surface 24b which, in cross-section, is in the shape of a 90° arc. The die 24 engages the sheet 10 within the vertical passage and presses it upwardly into the projection 16 during which the sheet 10 is bent against the surfaces 21c and 2Id and adopting their shape. Figures 5 to 10 illustrate successive further stages of the initial bending operation, Figure 10 illustrating that an end portion of the projection 16 springs back slightly after withdrawal of the die 24.

Next, in the illustrative method, the sheet 10 with its projections 16 is cut to the outline shape required for the flat head portions 18, i.e. the unwanted part of the sheet 10 is removed. This is achieved by a punching operation which cuts along the outer edge of the sheet portions 15 except where the tags T are located. Then the projections 16 are inserted into the holes H until the head portions 18 engage one of the sheets M.

Next, in the illustrative method, a 90° bend in each projection 16 is formed to form a substantially flat closure head portion 50 on the opposite side of the gasket G to the initial head portion 18. This 90° bend is achieved, in a closure bending operation, by pressing between an upper die 52 and the lower dies 20 and 22, to form the 90° bend as a continuous curve 56. The upper die 52 has a substantially planar lower surface 52a which leads

to a vertical surface 52b which leads in turn to a concave surface 52c which is complementary to the 90° bend.

Figures 11 to 14 illustrate successive steps of the closure bending operation, Figure 14 showing the die 52 withdrawing from the gasket G. The illustrative method is then completed by pressing the head portion 50 flat with a planar die (not shown) .

An eyelet formed according to the illustrative method was found to have been subjected to significantly less stress, in regions where cracking is expected to occur than a comparable eyelet make conventionally.