WO1993008420A1

WO1993008420A1 - Embossed composite gasket

Info

Publication number: WO1993008420A1
Application number: PCT/GB1992/001924
Authority: WO
Inventors: Richard Dinneen Dishaw; Lane Noble
Original assignee: Mccord Payen Incorporated; T&N Plc
Priority date: 1991-10-21
Filing date: 1992-10-20
Publication date: 1993-04-29

Abstract

A laminated gasket assembly (10) including a gasket core (114) having upper and lower core layers (117, 119) formed with embossments (120, 121) providing a sealing force to the gasket assembly. A thin flexible graphite facing (124, 126) is laminated to the gasket core and extends in substantial conformity over the embossments. When mounted between mating surfaces for sealing mechanical components, the embossments of the gasket core provide a spring or sealing force to the gasket assembly while the graphite facings provide a surface having conformable characteristics which enable the gasket to seal surface defects and microfinishes in excess of 2.0νm Ra, and up to 5.0νm, without additional surface coatings.

Description

EMBOSSED COMPOSITE GASKET

BACKGROUND AND SUMMARY OF THE INVENTION

This invention generally relates to a gasket and particularly to a sealing gasket adapted for use as head gasket for motor vehicle internal combustion engines.

Conventional internal combustion engines for automotive applications require a head gasket between the engine block and the cylinder head for purposes of sealing against the leading of combustion gases from within the cylinder. The head gasket further prevents the leaking of coolant from the cooling jacket passages and the leaking of oil from the engine crankcase. While head gaskets have been used from earliest days of internal combustion engines, designers are constantly striving to improve the performance and reliability of these gaskets while reducing production costs.

Previously, gaskets have been constructed from a variety of individual materials and combinations of materials. An inexhaustive list of examples is as follows: metals; multi- layered metals; embossed metals; metals in combination with rubber beads; metals coated with layers of_.sealing materials such as nitrile rubber; and inorganic powders, such as asbestos, bonded into sheets.

Previous embossed metal gaskets, typically steel, used a surface coating of acrylic paint to enhance their sealing characteristics. Often, a supplementary surface coating of silicone or nitrile rubber was used to improve the cold static sealing of the gasket against the surface of the cylinder head or engine block. Embossed gaskets of this type have also been seen to include multiple layers of metal to further supplement the sealing capabilities of the gasket.

While the embossed metal gasket exhibits increased sealing characteristics over a flat metal gasket, leakage through the embossed gasket has remained a problem, particularly where machine components have rough surface finishes or contain surface defects. In internal combustion engines, these problems can be particularly pronounced around the peripheries of the combustion cylinders.

Presently, another variety of gasket includes a metal core over which compressed expanded graphite facings are laminated. These gaskets are presently being used for a number of purposes including head gaskets and exhaust system gaskets where high temperatures are a consideration. Together, the core and laminae define the main body of the gasket. Formed in the main body of the gasket may be a number of openings. Such openings include combustion openings corresponding to the cylinders of the engine, as well as bolt holes, which are used to secure the gasket between the mated mechanical components of the engine.

Graphite itself is a laminated structure of carbon and consists of superposed layers being joined together by weak bonding forces. Two directions or axes of the graphite structure are generally noted. The direction generally parallel with the carbon layers will hereinafter be considered as the x direction, while the y direction will be considered generally perpendicular to the x direction and the carbon layers.

In producing flexible graphite sheets, graphite particles are first subjected to an oxidising environment for a period of time at a suitable temperature. Common oxidising media include both sulphuric acid and nitric acid. After being subjected to oxidising conditions, expansion of the graphite particles is brought about by activating an expanding agent by chemical interaction or heat thereby generating a fluid pressure which causes expansion of the graphite particles in the y direction. Typical expanding agents include water, volatile liquids and the like which change their physical state during the expansion process. The expanded graphite particles are unitary, laminar structures having a vermiform or worm-like appearance. The expanded graphite particles are then compressed or compacted under a predetermined load to form a graphite sheet. Once compressed, the expanded graphite sheet maintains its compression set and is flexible. Expanded graphite sheets can also be combined with a binder material, such as nitrile rubber, and the resulting combination compressed and moulded into various forms.

In the gaskets having laminated expanded graphite facings, the expanded graphite facing was provided with a thickness that allowed utilization of the resiliency and compressibility of the facing to produce a sealing force or pressure and to provide the actual sealing characteristics. Sealing pressure was achieved by compressing the expanded graphite layers between the cylinder head and the engine block. While gaskets incorporating expanded graphite sheets possess good sealing characteristics, nothing in these gaskets positively acts upon the expanded graphite sheet to actively induce or force the graphite to conform with the surface to be sealed.

A principal object of this invention is to enhance the sealability of an embossed gasket against less than optimum surface finishes. Previous embossed gaskets have exhibited sealability limitations with surface defects such as milling marks, scratches, broach marks, etcetera and with surface finishes of greater than 2.0μm Ra. Without excessive surface coating thicknesses, these rough surface -finishes and surface defects have not been effectively sealed by embossed gaskets. When an excessive coating thickness is used, the coating thickness tends to compromise the integrity of the cylinder combustion seal and is further disadvantageous.

It is a further aim of the present invention to provide a gasket which, while overcoming the disadvantages of the gaskets discussed above, maintains excellent thermal stability and which is inexpensive and easy to manufacture.

In accordance with the present invention a laminated gasket assembly for sealing rough surface finishes between adjacent surfaces of mating mechanical components to prevent fluid leaks therebetween, comprises a core having first and second main faces on opposing outboard sides thereof and a plurality of layers including at least upper and lower cores providing said main faces, and characterised by at least one of said upper and lower cores including at least one embossment formed therein, operable to provide an area of enhanced sealing force at said embossment when the gasket assembly is incorporated between said adjacent surfaces of mating mechanical components, and by a facing of expanded graphite laminated onto a main face of at least one of said upper and lower cores having an embossment therein, each facing being relatively thin with respect to the core on which laminated and extending over said embossment thereof to provide, in response to said enhanced sealing force provided by the embossment, an enhanced conformable surface characteristic to the gasket assembly.

The gasket exhibits improved cold static sealing against both rough surface finishes and surface defects.

The embossments of the gasket are preferably configured around the openings to be sealed by the gasket and the embossments provide a spring or sealing force to the gasket. Unlike previous uses of expanded graphite, the expanded graphite used with the present invention does not itself provide the sealing force. Rather, the expanded graphite provides a necessary conformable surface characteristic which in co-operation with the embossments, enables the gasket to conform with and seal against surface roughnesses up to and greater than 2.0μm Ra, and to also seal against milling marks, scratches, broach marks and the like. Thus, the sealing force provided by the embossments causes the expanded graphite to conform with the surface irregularities and thereby establish a seal.

Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims, taking in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a plan view of a gasket embodying the principles of the present invention;

Figure 2 is a cross-sectional view taken substantially along line 2-2 in Figure 1 illustrating a gasket constructed according to the principles, of the present invention; and

Figure 3 is a cross-sectional view similar to Figure 2 illustrating yet another multi-layered embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now with reference to the drawing, a head gasket incorporating the principles of the present invention is shown in Figure 1 and generally designated by reference number 10. The head gasket 10, as shown, is intended for use in sealing one of two heads onto the cylinder block of a six cylinder V-type engine (not shown) . With reference to the orientation of the head gasket 10 shown in Figure 1, the upper edge 11 is intended to be oriented toward the inboard centreline of the engine (i.e. toward the intake manifold) . The head gasket 10 is comprised of a main body 12 having defined therein are a plurality of openings. These openings include combustion openings 16 and a plurality of other openings 18 which may operate as coolant passages, oil passages or bolt holes for securing the gasket 10 between the cylinder head and the engine block. For the sake of clarity, only a selective number of the openings 18 are being designated in the Figures.

A first embodiment of the 10 of this invention is illustrated in Figure 2. The main body 112 of the gasket 10 includes a metal core 114 of multi-layered construction. The core 114 of this embodiment includes tnree metal layers, hereinafter designated as centre core 115, upper core 117 and lower core 119. The upper and lower cores 117 and 119 are in registry with the centre core 115 and a sub-layer or sealing layer 130, of conventional sealing material such as nitrile rubber, is provided between the adjacent metal surfaces of the cores 115, 117 and 119. The sealing layers 130 enhance the sealing characteristics of the gasket 10 by preventing fluid from leaking through the gasket 10. While the inner surfaces of the upper and lower cores 117 and 119 are illustrated as being provided with the sealing layers 130, it is apparent that the upper and lower surfaces of the centre core 115 could alternatively be provided with the sealing layers 130.

Cores 117 and 119 are preferably constructed from cold rolled or stainless steel of a spring quality grade and are respectively provided with outwardly directed sealing beads or embossments 120 and 121. The embossments 120 and 121 are substantially vertically aligned with one another and are configured to encircle the openings 16 and 18 being sealed. The centre core 115 is also preferably constructed from cold rolled or stainless steel. However, not being embossed, the centre core 115 need not be constructed from a spring quality grade.

The outboard sides of the upper and lower cores 117 and 119 each respectively define main faces, designated as 122 and 124, to which are laminated thin, flexible graphite facings 126 and 128. The graphite facings 126 and 128 are thin relative to the thicknesses of the cores 115, 117 and 119 and are layers of expanded graphite having thicknesses of approximately 0.05mm to 0.15mm. Extending contiguously with core 114, the graphite facings 126 and 128 extend over and correspond with the embossments 120 and 121.

The graphite facings 122 and 124 are provided so as to contact the mating surfaces of the engine block and cylinder head and therefore terminate at the combustion and other openings 16 and 18 and to prevent fluid from entering between the individual cores 115, 117 and 119 of the core 114, the openings 16 and 18 may be provided with grommets (not shown) of a type presently used in industry.

The embossments 120 and 121 of the centre core 114 provide the gasket 10 with lines or areas of increased sealing force. The graphite facings 122 and 124 provide the gasket 10 with surfaces having conformable characteristics and, in conjunction with the embossments 120 and 121, enable the gasket 10 to seal surface finishes having surface roughnesses of 2.0 μm Ra and greater, even in excess of 5 μm Ra, while also sealing surface defects such as milling marks, scratches, broach marks, etc, without the need for supplemental seal coatings or excessive thicknesses.

Figure 4 illustrates a second embodiment of a gasket 10 incorporating the principles of the present invention. The gasket 10 of the second embodiment includes main body 212 having a multi-layer core 214 which is generally comprised of three metal layers of a spring quality grade, hereinafter designated as upper core 217, inboard core 218, and lower core 219, and a centre core 215 which is not embossed and therefore need not be constructed from a metal having a spring quality grade. The multiple layers of the core 214 are positioned in registry with one another and adjacent metal surfaces of the cores 215, 217, 218 and 219 are provided with a sub-layer or surface coating 230 of sealing material, such as silicone, nitrile rubber or other suitable material.

The upper core 217, inboard core 218 and lower core 219 are each provided with at least one sealing bead or embossment. For illustrative purposes, the inboard core 218 is shown as having two embossments. The embossments are respectively designated as 220, 232 and 234, and are configured around the specific openings 16 and 18 of the gasket 10 being sealed. As with the previous embodiments, the embossments 220, 232 and 234 co-operate and provide the sealing force exhibited by the gasket 10 when positioned between the mating surfaces of the mechanical components of the engine. To further amplify the sealing force derived from each embossment 220, 232 and 234, the embossments 220, 232 and 234 are substantially vertically aligned relative to one another. When adjacent cores exhibit embossments, the embossments are generally directed opposite one another relative to the centre core 215. In the present embodiment, embossments 220 and 232 are directed outward while embossment 234 is directed toward the centre core 215.

As constructed, the core 214 generally defines an upper face 222 and a lower face 224 to which are laminated flexible graphite sheets or facings 226 and 228. The graphite facings 226 and 228 are coextensive with the core 214 and correspondingly extend over the embossments 220 and 234 of upper core 217 and lower core 219. Each graphite facing 226 and 228 is approximately 0.05mm to 0.15mm in thickness and thin relative to the core 214.

As the gasket 10 is compressed between the mating surfaces of the cylinder head and engine block, the spring-like quality of the embossments 220, 232 and 234 operate to provide the gasket 10 with a positive sealing force. This force co-operates with the facings 126 and 128 of expanded graphite to provide the gasket 10 with a conformable surface characteristic which will conform to rough surface finishes and surface defects, as previously described, without requiring supplemental surface coatings or excessive thicknesses in the facing itself.

While the above description constitutes the preferred embodiments of the present invention, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the accompanying claims.

In particular, and for the avoidance of doubt, whereas the above embodiments show both upper and lower cores to be embossed, embossment may be restricted to one upper or lower core only, the other core being substantially flat. Similarly, said expanded graphite facing may be laminated to one only of the upper or lower cores, provided that such facing is laminated to one embossed core and notwithstanding that it may in addition be laminated to an upper or lower core that is not embossed. Furthermore, where an inboard core layer is provided it may be disposed between said centre core and upper core. Also, although the multilayer gasket core has been described herein in detail with respect to embodiments having three and four layers respectively, including said upper and lower cores, the gasket core may comprise more inboard cores or only said upper and lower gasket cores, that is, omitting said central and inboard cores. The following examples of experiments performed demonstrate the degree of enhancement provided by the combination of conformable expanded graphite facings and core layer embossments over which said facings extend.

EXAMPLE 1

An embossed steel gasket having rubber facings (produced by McCord Payen Inc under the tradename SUNART) was placed between the surfaces of mated mechanical components to simulate the use of the gasket as a head gasket in an automotive engine. The gasket was then subjected to a nitrogen atmosphere at 414 KPa to simulate the internal pressure of a combustion cylinder. Measurements were taken to determine the leak rate in cubic centimetres per hour (cc/hr) through the gasket. The tests were repeated for surface finishes of increasing roughness.

At surface finishes of about 1.Oμm the gasket exhibited a leak rate of about 93 cc/hr; at surface finishes of about 1.8μm a leak rate of about 105 cc/hr; and at surface finishes of about 2.Oμm a leakage rate unsuitable for use in an automotive engine.

EXAMPLE 2

A flat steel gasket having expanded graphite facings (produced by McCord Payen Inc under the tradename GRAFPAK) was disposed and tested according to the same conditions as given in Example 1.

At surface finishes of about l.Oμm, 1.8μm and 3.6μm the gasket exhibited a leak rate of about 15 cc/hr; at surface finish of about 5.4μm a leak rate of about 30 cc/hr.

EXAMPLE 3

An embossed stainless steel gasket having expanded graphite facings in accordance with the invention was also disposed and tested according to the conditions of Examples 1 and 2.

At surface finishes of abour l.Oμm, 1.8μm and 3.6μm the gasket exhibited a leak rate of about l cc/hr; at surface finish of about 5.4μm a leak rate of about 2 cc/hr.

Thus at surface finishes of about l.Oμm, the embossed gasket having graphite facings exhibits at least a ten-fold increase in sealability over the flat gasket facings and approximately a ninety-fold increase in sealability over the embossed gasket having rubber facings; at surface finishes of about 1.8μm, the embossed gasket having expanded graphite facings exhibited approximately a ten-fold increase in sealability over the flat gasket having graphite facings and approximately a one hundred¬ fold increase in sealability over the embossed gasket having rubber facings; at a surface finish of about 3.6μm, the embossed gasket having expanded graphite facings exhibited at least a ten¬ fold in sealability over the flat gasket having graphite facings; and at surface finishes of about 5.4μm, the embossed gasket having expanded graphite facings exhibited approximately a fifteen-fold increase in sealability over a flat gasket having expanded graphite facings.

Claims

1. A laminated gasket assembly (10) for sealing rough surface finishes between adjacent surfaces of mating mechanical components to prevent fluid leaks therebetween, said gasket assembly comprising a core (114, 214) having first and second main faces (122, 124, 222, 224) on opposing outboard sides thereof and a plurality of layers including at least upper and lower cores (117, 119, 217, 219) providing said main faces, and characterised by at least one of said upper and lower cores including at least one embossment (120, 121, 220, 234) formed therein, operable to provide an area of enhanced sealing force at said embossment when the gasket assembly is incorporated between said adjacent surfaces of mating mechanical components, and by a facing (126, 128, 226, 228) of expanded graphite laminated onto a main face of at least one of said upper and lower cores having an embossment therein, each facing being relatively thin with respect to the core on which laminated and extending over said embossment thereof to provide, in response to said enhanced sealing force provided by the embossment, an enhanced conformable surface characteristic to the gasket assembly.

2. A gasket assembly as claimed in claim 1 characterised by embossments (120, 121, 220, 234) in the upper and lower cores substantially vertically aligned.

3. A gasket arrangement as claimed in claim l or claim 2 characterised in that the core (114, 214) includes between said upper and lower cores (117, 119, 217, 219) a centre core (115, 215) .

4. A gasket arrangement as claimed in claim 3 characterised in that the embossments (120, 121) of said first and second cores extend outwardly away from said centre core.

5. A gasket arrangement as claimed in claim 3 when dependant on claim 2 characterised by an inboard core layer (218) disposed between the centre core (215) and one of said upper and lower cores (217, 219) and having at least one embossment (232) formed therein substantially vertically aligned with said embossments (220, 234) of the upper and lower cores.

6. A gasket arrangement as claimed in claim 5 characterised in that said inboard core layer (218) is disposed adjacent the lower core (219) .

7. A gasket arrangement as claimed in claim 5 or claim 6 characterised in that the embossments (232, 220, 234) in the inboard core layer and adjacent core layer are generally directed oppositely to each other with respect to the centre core (215) and the embossments (220, 234) in the upper and lower cores (217, 228) are generally directed oppositely to each other with respect to the centre core (215) .

8. A gasket arrangement as claimed in any one of the preceding claims characterised by a layer of sealing material (130, 230) between each upper and lower core layer and an adjacent layer of the core.

9. A gasket arrangement as claimed in claim 8 characterised in that the sealing material (130, 230) is rubber.

10. A gasket arrangement as claimed in any one of the preceding claims characterised in that said layers (115, 117, 119, 215, 217, 218, 219) of the core (114, 214) are metal.

11. A gasket arrangement as claimed in claim 10 characterised in that each embossed core layer (117, 119, 217, 218, 219) is of sprung steel.

12. A gasket arrangement as claimed in any one of the preceding claims characterised in that each thin facing of expanded graphite (126, 128, 226, 228) extends continuously across its supporting core layer (117, 119, 217, 219) .

13. A gasket arrangement as claimed in any one of the preceding claims characterised in that each facing 126, 128, 226, 228) of expanded graphite has a thickness in the range 0.05mm — 0.15mm.

14. A gasket arrangement as claimed in any one of the preceding claims characterised in that said embossments (120, 121, 220, 232, 234) and facing (126, 128, 226, 228) permit sealing of adjacent surfaces of mating mechanical components having surface roughness of about 2.Oμm Ra.

15. A gasket arrangement as claimed in any one of the preceding claims characterised in that said embossments (120, 121, 220, 232, 234) and facing (126, 128, 226, 228) permit sealing of adjacent surfaces of mating mechanical components having surface roughness up to 5.Oμm Ra.