Gasket manufacture

An embossed sheet coated at least partially with expanded graphite and suitable for use as a gasket or as a component layer of a gasket is manufactured by positioning a planar metallic sheet between an upper embossing die and a lower embossing die with a layer of particles of expanded graphite between one of said dies and a surface of the sheet. One of the dies has a protuberance to emboss a ridge into the sheet while the other die has a recess to receive the ridge. The method also comprises pressing the dies together to cause the particles to coalesce and form a coating attached to the sheet while simultaneously embossing said ridge into the sheet.

FIELD OF THE INVENTION 
This invention is concerned with a method of manufacturing an embossed 
metallic sheet coated at least partially with expanded graphite and 
suitable for use as a gasket or as a component layer of a gasket. 
DESCRIPTION OF THE PRIOR ART 
Many gaskets for use in industrial and automotive applications comprise a 
metallic sheet, often of steel, coated on one or more surfaces with a 
sealing material. The sealing material is, in some cases, expanded 
graphite which has been compacted. Expanded graphite is also called 
"exfoliated graphite". 
The normal method of coating such a metallic sheet is to make a thin (0.2 
to 1.5 mm thick) self-supporting foil of the expanded graphite and to 
attach the foil to a surface of the reinforcing sheet. This method, 
however, involves making and handling the thin foil which is easily 
damaged and so requires extreme care. 
Instead of applying an already made foil to the reinforcing sheet, it is 
known to position a layer of particles of expanded graphite on a surface 
of the sheet which has been treated with a layer of adhesive, and to press 
the particles so that the coalesce and form a coating in situ on the 
reinforcing sheet. 
It is known to provide rubber coated gaskets with embossed ridges, e.g. a 
generally semi-circular (in cross-section) ridge, around the hole in the 
gasket. These ridges are resilient and cause controlled stress 
concentrations during use of the gasket. 
SUMMARY AND OBJECTS OF THE INVENTION 
It is an object of the present invention to provide an efficient method of 
manufacturing an embossed metallic sheet coated at least partially with 
expanded graphite and suitable for use as a gasket or as a component layer 
of a gasket. 
The invention provides a method of manufacturing an embossed metallic sheet 
coated at least partially with expanded graphite and suitable for use as a 
gasket or as a component layer of a gasket, characterised in that the 
method comprises positioning a substantially planar metallic sheet between 
an upper embossing die and a lower embossing die with a layer of particles 
of expanded graphite between one of said dies and a surface of the sheet, 
one of said dies having at least one protuberance arranged to emboss a 
ridge into the sheet, the method also comprising pressing said dies 
together thereby compressing the particles of expanded graphite, so that 
they coalesce and form a coating attached to said sheet, and 
simultaneously embossing the ridge into the sheet and the coating. 
In a method in accordance with the invention, the expanded graphite is 
applied to the planar sheet and the ridge is embossed into the sheet in 
one operation so that an efficient method of manufacture is provided. 
The other of said dies may have a complementary shape to the die which has 
the protuberance, e.g. it may have a recess to receive the ridge. In some 
sheets, a portion of the embossed sheet may be planar and parallel to 
other portions of the sheet and the ridge may connect said portions. 
Preferably, said layer of particles is positioned by providing a particle 
retaining wall surrounding the lower embossing die and projecting upwardly 
therefrom to a substantially equal extent around the periphery of the 
wall, filling the space defined by the wall above the lower die with 
particles of expanded graphite, and skimming the particle layer level with 
the top of said wall, the planar sheet being positioned on top of the 
layer of particles. This method provides a convenient way in which the 
edges of the layer of particles can be confined and a substantially level 
layer can be formed across the sheet. The presence of the wall also 
assists in locating the sheet relative to the dies. 
Where the sheet is to have expanded graphite coatings on both of the 
surfaces thereof, a further layer of particles may be positioned between 
said sheet and the other of said dies, and two layers are pressed into 
coatings simultaneously. Alternatively, however, the two coatings may be 
applied sequentially with the embossing taking place simultaneously with 
the formation of either coating. Where the afore-mentioned particle 
retaining wall is used, the further layer of particles may be positioned 
by raising said wall relative to the lower die after positioning the 
sheet, filling the space defined by said wall above the planar sheet with 
particles, and skimming the further particle layer level with the top of 
said wall. 
Instead of positioning the layer of particles on top of the lower die, a 
method according to the invention may comprise providing a 
particle-retaining wall surrounding the lower embossing die and projecting 
upwardly therefrom to a substantially equal extent around the periphery of 
the wall, positioning the planar sheet on the lower die within said wall, 
filling the space defined by the wall above the planar sheet with 
particles of expanded graphite, and skimming the particle layer level with 
the top of the wall. 
At least one hole in the sheet may be cut out therefrom after the expanded 
graphite has been applied. This may be advantageous in that the ridge may 
be more easily formed when it is not close to the edge of an existing 
hole. This can also be achieved by cutting the hole out from the sheet in 
two stages, a first stage performed before the expanded graphite is 
applied to the planar sheet, and a second, hole trimming, stage performed 
on the embossed sheet. In the second stage, the hole created in the first 
stage is enlarged by the removal of material of the metallic sheet and 
expanded graphite adhered thereto. Alternatively, during the application 
of expanded graphite to the planar sheet, a hole may be blanked off by a 
further protuberance from one of said dies which enters a corresponding 
recess in the other die. This saves graphite since graphite is not 
compressed in the area where the hole is positioned. 
Preferably, the particles have their mean dimension in the range 0.2 to 2 
mm, i.e. the average maximum dimension of the particles is in this range. 
They may be milled to this size. If the particles are provided in this 
size range, it is found that they flow better to form the coating or 
coatings. Such particles are substantially smaller than those 
conventionally used for making self-supporting foils, which have mean 
dimensions of 2 to 10 mm. 
Where the gasket is for use with substantially planar surfaces, the 
particle layer or layers may have a thickness of between 2 and 5 mm and 
the coating or coatings created therefrom may have a thickness of between 
20 and 200 microns. However, for some applications, layers up to 100 mm 
thick may be used to give coatings up to 2 mm thick. 
There now follow detailed descriptions, to be read with reference to the 
accompanying drawings of five methods of manufacturing a gasket which are 
illustrative of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The first to the fifth illustrative methods are all methods of 
manufacturing an embossed steel sheet S at least partially coated with 
expanded graphite. The sheet S having at least one hole H there-through, 
the hole H having an embossed ridge R surrounding it. In each of the 
illustrative methods, a substantially planar steel sheet 10 is first cut 
to the outline shape required for the finished gasket G and a layer of 
adhesive 12 is applied to a surface of the sheet 10. It is not, however, 
necessary to apply the adhesive after cutting the sheet 10 to its outline 
shape and the cutting to outline shape can be left until the end of the 
illustrative method. The sheet 10 can be cut out by any of the usual 
methods and the adhesive 12 can also be applied by any of the usual 
methods. The adhesive may be, for example, a nitrile-phenolic adhesive 
which is applied as a solution and, after the expanded graphite has been 
applied thereto, requires heating to cross-link the adhesive. 
The apparatuses used in each of the five illustrative methods are similar 
in many respects and like parts in the five apparatuses are given the same 
reference numerals in the drawings and are only described in detail in 
relation to the first illustrative method. 
The apparatus shown in FIG. 1 is used in the first illustrative method. 
This apparatus comprises an upper embossing die 14 which is mounted on the 
upper platen of a press (not shown). The die 14 has a protuberance 16 
extending downwardly therefrom which is arranged to emboss the ridge R 
into the sheet 10 so that, in the finished sheet S, the ridge R extends 
around the hole H. In this case, the hole H is circular so that the 
protuberance 16 is also circular having a greater diameter than the hole 
H. The protuberance 16 is itself of approximately semi-circular 
cross-section so that it provides a ridge also of approximately 
semi-circular cross-section. However, as shown in FIG. 7, the ridge R may 
be of V-shaped cross-section. The apparatus also comprises a lower 
embossing die 18 which is mounted on a lower platen of the afore-mentioned 
press (not shown) in opposed relationship with the die 14. The lower 
embossing die 18 has a recess 20 therein which is complementary to the 
protuberance 16 and is arranged to receive the ridge embossed in to the 
sheet 10. 
The first illustrative method comprises positioning the upper embossing die 
14, and the lower embossing die 18 on the press in opposed relationship, 
positioning the metallic, planar sheet 10 between the dies 14 and 18, and 
positioning a layer of particles 22 of expanded graphite between the lower 
die 18 and the layer of adhesive 12 on the sheet 10. The method also 
comprises pressing the dies 14 and 18 together by operation of the 
afore-mentioned press thereby compressing the particles of expanded 
graphite in the layer 22, so that they coalesce and form a coating 24 
adhered to the adhesive layer 12, and simultaneously embossing the ridge R 
into the sheet 10 and the coating 24. 
In order to position the layer of particles 22, the apparatus used in the 
first illustrative method also comprises a particle-retaining wall 26. The 
wall 26 forms an enclosed rectangle, open at the top and at the bottom so 
that it can surround the lower embossing die 18 and project upwardly 
therefrom to a substantially equal extent around the periphery of the wall 
26. The upper embossing die 14 can fit into the wall 26 as can the sheet 
10. 
In order to position the layer of particles 22, in the first illustrative 
method, the space defined by the wall 26 above the lower die 18 is filled 
with the particles of expanded graphite and the particle layer 22 is 
skimmed off level with the top of the wall 26. This ensures a 
substantially uniform layer of particles on the lower die 18 which is 
confined at its edges by the wall 26. The wall 26 is then raised relative 
to the lower die 18 and the reinforcing sheet 10 is positioned within the 
wall 26 on top of the layer 22 with the adhesive layer 12 facing 
downwardly and in contact with the layer 22 (this condition is shown in 
FIG. 1). The dies 14 and 18 are then pressed together to compress the 
particles in the layer 22, so that they coalesce and form the coating 24 
adhered to the adhesive layer 12. In this process the upper embossing die 
14 is moved downwardly into the wall 26 and engages the sheet 10 pressing 
it downwardly towards the lower die 18 so that the layer 22 is compressed 
between the sheet 10 and the die 18. The pressing process which is carried 
out by operation of the afore-mentioned press also embosses the ridge R 
into the sheet 10 and the coating 24. 
In the first illustrative method, the hole H is punched through the gasket 
G after the expanded graphite coating 24 has been adhered to the sheet 10. 
This can be achieved by a punching operation of conventional type. 
FIG. 6 illustrates that the sheet S may have further ridges r and holes h 
which can be formed in the same operations as the ridge R and the hole H. 
FIG. 7 shows that the sheet S can be used in a stack-type gasket G. In this 
case, the opposite surface of the sheet S is coated with nitrile rubber, 
by a conventional method, to give a coating 28. The coating 28 engages a 
planar steel sheet 29 of the stack. The stack is completed by an inverted 
version of the sheet S whose coating 28 also engages the sheet 29. 
FIG. 2 illustrates the apparatus used in the second illustrative method. In 
the second illustrative method, a further layer of adhesive 30 is applied 
to an opposite surface of the reinforcing sheet 10 to the adhesive layer 
12 and a further layer of particles 32 is assembled between the layer of 
adhesive 30 and the upper die 14. The second illustrative method is 
otherwise identical to the first illustrative method described above. In 
the pressing operation, the die 14 compresses the layer 32 to form a 
further coating 34 adhered to the layer 30 of adhesive. The further layer 
of particles 32 is positioned by filling the space defined by the wall 26 
above the reinforcing sheet 10 after the latter has been positioned within 
the wall 26 on the layer 22 and the wall 26 has been raised for a second 
time. The further layer 32 is also skimmed level with the top of the wall 
26 before the pressing operation begins. The sheet S produced by the 
second illustrative method is suitable for use as a gasket itself. 
FIG. 3 illustrates the third illustrative method, which is similar to the 
first illustrative method except that the sheet 10 is positioned on the 
lower die 18 within the wall 26 with the layer 12 uppermost without 
previously forming a layer of particles on top of the die 18. Also, the 
protuberance 16 is provided on the lower die 18 and the recess 20 is in 
the upper die 14. The third illustrative method continues by filling the 
space defined by the wall 26 above the sheet 10 with particles of expanded 
graphite to form a layer 40 and skimming the particle layer 40 level with 
the top of the wall 26. The third illustrative method then continues in 
similar fashion to the first illustrative method with the pressing 
operation forming a coating 24 adhered to the adhesive layer 12. 
In the first, second and third illustrative methods, the hole H is cut out 
from the gasket after the expanded graphite has been applied to the sheet 
10. In the fourth illustrative method, however, illustrated by FIG. 4, the 
hole H is cut out from the sheet in two stages. In a first stage, 
performed before the expanded graphite is applied to the sheet 10, a 
smaller hole 50 is punched out of the sheet 10 and the coating 24 is 
applied and the ridge R is embossed as in the first illustrative method. 
In a second, hole trimming stage, performed on the embossed sheet S, the 
hole 50 is enlarged by punching out a ring around it of the metal and of 
graphite adhered thereto. 
In the fifth illustrative method shown in FIG. 5, the hole H is cut through 
the sheet 10 before the sheet 10 is positioned between the dies 14 and 18. 
In this case, the lower die 18 has a further protuberance 60 which is 
generally cylindrical and enters the hole H in the sheet 10 and a 
corresponding recess 62 in the die 14. The protuberance 60 acts to blank 
off the hole H in the sheet 10 so that expanded graphite is not required 
in the area which will form the hole H. 
It will be apparent that various combinations of the five illustrative 
methods can be used. For example, a protuberance similar to the 
protuberance 60 can be utilised in a method similar to the first 
illustrative method.