Abstract:
A multi-layered composite gasket ( 10 ) includes three, preferably metallic cores ( 12, 14 ). A solid center core ( 12 ) is flanked on both sides by bonded paper layers ( 30 ). Perforated cores ( 14 ) mechanically interlock with each paper layer ( 30 ) through inwardly directed tangs ( 22 ). Graphite layers ( 26 ) are disposed outside of each perforated core ( 14 ) and are mechanically interlocked thereto by outwardly directed tangs ( 20 ) extending from the perforated cores ( 14 ). When using the gasket ( 10 ) material for sealing cylinder heads in internal combustion engines, a fire ring ( 46 ) may be affixed with a fire ring holder ( 48 ). The gasket ( 10 ) can be manufactured by making first and second preform sheets ( 32 ) comprised of one perforated core ( 14 ) sided with one paper layer ( 30 ) and one graphite layer ( 26 ). The preform sheets ( 32 ) are then bonded to a center core ( 12 ) using a heat activated adhesive. Combining rollers ( 42 ) compress and densify the layers to form the completed material set which can be stored on a coil ( 44 ) or cut into sheets.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to Provisional Patent Application No. 61/152,456 filed Feb. 13, 2009, the entire disclosure of which is hereby incorporated by reference and relied upon. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates to a multi-layered composite gasket and method of making a gasket. 
         [0004]    2. Related Art 
         [0005]    Gaskets are used in many applications to perfect a fluid-tight seal between two mating members. The gasket is typically clamped between the mating members and held there in compression. In the case of internal combustion engines, many gaskets are used in various capacities. As one example, the head gasket is one which is positioned between the cylinder block and cylinder head of an engine to prevent the leakage of combustion gases from the combustion chambers during use of the engine. However, the head gasket in this application not only seals the combustion chambers, but also various coolant and lubrication flow passages that extend between the cylinder block and head. 
         [0006]    An example of a prior art head gasket is illustrated in  FIG. 1 , with four large, generally circular openings representing the periphery of four side-by-side combustion chambers. A plurality of smaller openings are shown dispersed about a gasket for conducting coolant, lubrication and accommodating bolts used to establish clamping pressure. It will be readily apparent that a gasket, such as the exemplary head gasket, must be capable of maintaining a fluid-tight seal for various fluid mediums, including high temperature/high pressure gases, water or ethylene glycol-based coolants, lubricating oils and the like all operating at different temperatures, different pressures, and having different chemical compositions. 
         [0007]    Accordingly, designing a gasket to function satisfactorily over an extended duty range can be quite difficult. The prior art has developed numerous gasket styles and compositions for these purposes, some of which are better suited to certain applications. One such gasket construction known in the prior art consists of a multi-layered composite gasket like that shown in  FIGS. 2 and 3 , and which correspond, generally, to the gasket described in U.S. Pat. No. 5,468,003 to Staab et al., issued Nov. 21, 1995, the disclosure of which is incorporated here by reference. This patent describes a cylinder head gasket used predominantly in high performance diesel engine applications. The gasket is composed of five layers, including a steel center layer to which is bonded a flanking perforated steel layer on each side. The perforated steel layers have outwardly extending tangs which establish a mechanically interlocking engagement with outer graphite layers. These five layers—center, two perforated, and two graphite—comprise the body of the gasket assembly. Combustion openings are rimmed with fire rings dressed with a thin sheet metal fire ring holder which directly engages the multi-layered composite gasket body. 
         [0008]    While the prior art gasket construction depicted in  FIGS. 2 and 3  is known to be moderately effective in certain applications, there are aspects of the construction that could be improved to gain better performance. In particular, the solid core center layer is affixed directly to the two facing perforated steel layers by an adhesive compound for the purpose of resisting combustion pressures. The outer graphite facing layers are mechanically bonded to the perforated metal layers to provide a fluid seal against the clamping faces of the cylinder head and block (shown in simplified fashion in  FIG. 2 ). The rigid adhesive glue joint provides a sealing function between the perforated and center metal layers. 
         [0009]    In use, a gasket in an engine is subjected to varying loads from the forces of combustion and heating cycles which impart sheer stresses to the gasket as the head and block expand and contract at different rates or otherwise move relative to one another due to dynamic forces. Sheer loads are thus created in the body of the gasket, which can weaken and possibly break the rigid glue layers between the perforated metal layers and the central metal core. It has been observed that sheer loads resisted within the body of the gasket can weaken and possibly break the rigid glue layers and thereby present a possible leak path for fluids through the gasket body. If the glue layers do not break under sheer loading, then the sheer loads are borne almost entirely by the graphite layers, putting these layers under undue sheer stresses which can, over time, compromise their ability to maintain a good seal against the mating members. Thus, prior art gasket constructions like that depicted in  FIGS. 2 and 3  suffer from shortened service life because of failure modes resulting from undue sheer stresses. 
         [0010]    Accordingly, there is a need in the art for an improved multi-layer composite gasket construction of the type to be clamped between mating members for perfecting a fluid-tight seal therebetween. 
       SUMMARY OF THE INVENTION 
       [0011]    According to this invention, a multi-layered composite gasket is provided of the type to be clamped between mating members so that a fluid-tight seal can be established therebetween. The gasket comprises a center core layer having oppositely facing sides. A pair of perforated core layers are arranged on opposite sides of the center core. Each perforated core has a proximal surface facing toward the center core and a distal surface facing away from the center core. A pair of outer graphite layers are provided. Each graphite layer is mechanically interlocked with the distal surface of a respective one of the perforated cores. A pair of paper layers are provided. Each paper layer is disposed between one of the perforated cores and the center core. Each paper layer is mechanically interlocked with the proximal surface of its respective perforated core and affixed to the center core layer. 
         [0012]    A gasket assembled according to the techniques of this invention reduces the buildup of sheer loads caused by relative movement between the mating members. The paper layers disposed between the respective perforated cores and the center core can function as slip planes to enable slight lateral shifting of the perforated cores relative to the center core which thereby relieve sheer loads in use without detracting from the sealing function of the gasket. The graphite layers are able to maintain their seals against the mating members even during adverse, dynamic conditions. Accordingly, the gasket manufactured according to this invention is able to accommodate dynamically changing compressive and sheer forces placed on the gasket in use, while maintaining excellent sealing capabilities over an extended duty range. 
         [0013]    According to another aspect of this invention, a method is provided for forming a multi-layer composite gasket of the type clamped between mating members. The method comprises the steps of making a first preformed sheet according to the following steps: providing a perforated core layer having a proximal surface and a distal surface, providing an outer graphite layer, mechanically interlocking the graphite layer to the distal surface of the perforated core, providing a paper layer and mechanically interlocking the paper layer to the proximal surface of the perforated core. A second preformed sheet is made according to the same steps used to make the first preformed sheet. A center core layer is provided having oppositely facing sides. The paper layer from the first preformed sheet is bonded to one side of the center core, while the paper layer from the second preformed sheet is bonded to the opposite side of the center core. As a result, the center core is sandwiched between the first and second preformed sheets, with the paper layers thereof bonded directly to the center core. By this method, a multi-layered composite gasket can be manufactured which overcomes the shortcomings and deficiencies inherent in prior art gasket designs. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a plan view showing a standard prior art gasket such as may be used in sealing a cylinder head to a block in an internal combustion engine; 
           [0015]      FIG. 2  represents a fragmentary view of a prior art gasket clamped between two mating members which, for illustrative purposes, may comprise a cylinder head and a block of the type common in internal combustion engines; 
           [0016]      FIG. 3  is an enlarged, cross-sectional and fragmentary view of the prior art gasket shown in  FIG. 2 ; 
           [0017]      FIG. 4  is a fragmentary, cross-sectional view, shown in perspective, of a multi-layered composite gasket according to this invention; 
           [0018]      FIG. 5  is an exploded view depicting the layered composition of the gasket of  FIG. 4 ; 
           [0019]      FIG. 6  is an enlarged, fragmentary cross-sectional view of the subject gasket; 
           [0020]      FIG. 7  is a fragmentary perspective view of a perforated core layer according to this invention; 
           [0021]      FIG. 8  is a simplified schematic illustrating a first step in the manufacturing process of this invention, wherein a first preform sheet is made by mechanically interlocking a graphite layer and a paper layer to opposite sides of a perforated core; 
           [0022]      FIG. 8A  is an enlarged view of the first preformed sheet indicated at  8 A in  FIG. 8 ; 
           [0023]      FIG. 9  is a simplified schematic view depicting the bonding of a first preformed sheet and a second preformed sheet to opposite sides of a center core layer; and 
           [0024]      FIG. 9A  is an enlarged view of the area indicated at  9 A in  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0025]    Referring to the figures, wherein like numerals indicate like or corresponding parts throughout the several views, a gasket according to this invention is generally shown at  10  in  FIGS. 4-6 . The gasket  10  includes a metallic, preferably steel, center core layer  12  having oppositely facing sides. Preferably, the center core  12  has a generally uniform thickness and is formed without discontinuities or irregularities so as to establish a continuous, uninterrupted barrier throughout the gasket  10 . The center core  12  may be supplied in roll form on a coil  36 , like that shown in  FIG. 9 , or in sheet form. The center core  12  may have a thickness ranging between about 0.13 and about 6.35 millimeters. The center core  12  may be provided with a coarse surface finish if the specifications for a particular application so dictate. 
         [0026]    A pair of substantially identical perforated metal core layers, each generally indicated at  14 , are arranged on opposite sides of the center core  12 . The perforated cores  14  are preferably made from low-carbon or stainless steel, but other compositions including even non-metallic compositions, may be substituted under appropriate circumstances. The perforated cores  14 , in one exemplary embodiment, have a thickness ranging between about 0.15 and about 0.30 millimeters. As perhaps best shown in  FIGS. 5-7 , the perforated cores  14  each include a proximal surface  16  and a distal surface  18 . In each case, the proximal surface  16  is that side which faces toward the center core  12 , whereas the distal surface  18  faces in a direction away from the center core  12 . A plurality of outwardly directed tangs  20  extend away from the distal surface  18  of each perforated core  14 . In a somewhat similar fashion, a plurality of inwardly directed tangs  22  extend from the proximal surface  16  of each perforated core  14 . The tangs  20 ,  22  may take the form of punch tabs or pieces bent integrally from the sheet-like membrane or stock in a roll forming or other type of manufacturing operation. In the preferred embodiment of this invention, the tangs  20 ,  22  are formed simultaneously by passing raw sheet stock through the nip of punch rollers  24 , as shown in  FIG. 8 . Of course, other forming techniques are possible.  FIG. 7  shows one exemplary form taken by the tangs  20 ,  22 . Here, one inwardly directed tang  22  opposes each outwardly directed tang  20 , such that they appear in something of a nose-to-nose fashion. The bending of each tang  20 ,  22  away from the base stock material of the perforated cores  14  creates a void or opening in the stock material, thereby establishing its perforated characteristics. 
         [0027]    In practice, the outwardly directed tangs  20  are longer than the inwardly directed tangs  22 , with both being bent away from the general plane of the stock membrane by an equal but opposite acute angle. Of course, other angular orientations are possible, and it is not necessary that the inwardly directed tangs  22  be bent away from the plane of the stock membrane by an equal but opposite angle to that of the outwardly directed tangs  20 . In other words, it is possible that the outwardly directed tangs  20  may be oriented at 90 degrees orthogonally relative to the plane of the core  14 , whereas the inwardly directed tangs  22  are bent at some acute angle less than 90 degrees. Those of skill in the art will envision many alternative configurations for the shapes of the tangs  20 ,  22 , their relationship to the voids or openings in the perforated core  14 , their relative numbers and spacings, and the angles at which they are bent away from their respective proximal  16  and distal  18  surfaces. As perhaps best shown in  FIG. 6 , the orthogonal projection of the outwardly directed tangs  20 , i.e., the distances measured normal to the plane of the stock membrane, is greater than the orthogonal projection of the inwardly directed tangs  22  from the proximal surface  16 . Thus, in the example illustrated wherein the tangs  20 ,  22  project from their respective distal  18  and proximal  16  surfaces by equal but opposite angles, the outwardly directed tangs  20  are formed longer so that their orthogonal projection can be greater. Of course, it would be possible to make the tangs  20 ,  22  equal in length, but maintain the unequal orthogonal projections by altering the angles at which they are bent relative to the plane of the perforated core  14 . 
         [0028]    A pair of outer graphite layers, each generally indicated at  26 , are provided consistent with well-known principles of head gasket construction associated with perforated core structures. The graphite layers  26  are mechanically interlocked with the distal surface  18  of the respective perforated core  14  via the outwardly directed tangs  20 . This can be accomplished by compressing the graphite in sheet form against the distal surface  18  of the perforated core  14  so that the outwardly directed tangs  20  embed themselves within the graphite material. As shown in  FIG. 8 , this can be accomplished by passing graphite material in rolled sheet form together with a perforated core  14  through the nip of a compression roller set  28 . This mechanically interlocking step can be accomplished in-line together with the formation of the tangs  20 ,  22  as illustrated in  FIG. 8 , or can be accomplished in distinct operations or batch processes. The thickness of the graphite layers  26  are somewhat variable, but in the preferred embodiment of this invention, the thickness of each graphite layer  26  is equal to or slightly greater than the orthogonal projection of the outwardly directed tangs  20 , as shown in  FIGS. 4 and 6  where the tips of the outwardly directed tangs  20  do not break the distal outer surface of the respective graphite layers  26 . Those of skill in the art, however, will envision some applications wherein the outermost tips of the outwardly directed tangs  20  can be seen through the graphite layers  26 . 
         [0029]    A pair of paper layers, generally indicated at  30 , is also provided within the gasket  10 . The paper layers  30 , known sometimes as beater sheets, are substantially identical to one another in thickness and composition and are each disposed between a respective one of the perforated cores  14  and the center core  12  as shown in  FIGS. 4-6 . Each paper layer  30  is mechanically interlocked with the proximal surface  16  of one of the perforated cores  14  by way of the inwardly directed tangs  22 . Each paper layer  30  is also affixed with the center core  12 . Thus, as shown in the figures, the center core  12  appears sandwiched between the two paper layers  30 . These paper layers  30  accommodate relative dynamic slippage between the perforated cores  14  and the center core  12  during use of the gasket  10  so as to dissipate sheer stress caused by relative movement between the mating members being sealed. In some cases, it may be desirable to use a bonding agent, e.g., a nitrile phenolic composition, between the paper layers  30  and their respective perforated core  14  to help hold all layers together during manufacturing and installation of a gasket  10 . In such cases, the paper layers  30  are either received from a material supplier with the adhesive pre-applied in an unactivated form, or the adhesive is applied in a subsequent processing step. 
         [0030]    The mechanical interlocking of the paper layers  30  to the perforated cores  14  can be accomplished simultaneously with the mechanical interlocking of a graphite layer  26  by simultaneously passing a paper layer  30  through the same compression roller set  28 . The resulting composition, as shown in  FIG. 8A , represents a preform sheet  32  which is densified and/or sized to specification by the compression roller set  28 . The preform sheet  32  can be cut and collected as sheets, or wound on a spool  34  for future processing. 
         [0031]    The orthogonal projection of the inwardly directed tangs  22  is preferably less than or equal to the thickness of the paper layers  30 , so that the extended tips of the inwardly directed tangs  22  do not pass completely through the paper layers  30 . In other words, as shown in  FIG. 6 , there may remain a slight spacing between the inwardly directed tangs  22  and the center core  12 . However, this specification is subject to alteration depending upon the application and design characteristics needed. Likewise, the relative thicknesses between the paper layers  30  and graphite layers  26  may be such that the paper layers  30  are thinner as shown in the figures, however this is also not an inviolate specification. 
         [0032]      FIG. 9  depicts a method for forming the multi-layered composite gasket  10  using first and second preform sheets  32  carried on respective spools  34 . Raw stock for the center core  12  is carried on a coil  36 . An adhesive material is either applied to or pre-exists on both oppositely facing sides of the center core  12  in substantially equal quantities. The adhesive may take any of the known and suitable forms, including but not limited to a nitrile phenolic composition. As illustrated, the adhesive will have been pre-applied to the center core  12  and reside there in a dormant, inactivate dry form in the wound coil  36 . However, it will be understood that the adhesive can alternatively be applied as the core  12  is unwound from the coil  36  in dry film form or in suspension through a brushing, rolling, spraying or other appropriate application technique. In other words, the coil  36  is either received from a material supplier with the adhesive pre-applied, or the adhesive is applied to both sides of the core material stock at some point after it is unwound from the coil  36 . In cases where an inactive adhesive must be activated, the coated center core material is passed through a heater  40  which melts and/or activates the adhesive film. In one possible variation, the adhesive could be applied directly to the paper layers  30  rather than to the core  12  using either a pre-applied or in-process application technique. This variation may be desirable if both sides of the paper layers  30  are to be coated with adhesive. 
         [0033]    First and second preform sheets  32  meet the center core  12  with melted adhesive in the nip of a combining roller set  42 , as shown in  FIG. 9 . The orientation of the preform sheets  32  as they are carried on their spools  34  is such that the paper layers  30  of each are presented toward the center core  12  and the respective graphite layers  26  are facing to the outside. The combining rollers  42  then compress these layers together, thereby shaping the materials to final specifications of thickness and/or density. The completed gasket material  10  exits the combining roller set  42  and may be either cut into sheets or stored on a coil  44  as shown in  FIG. 9 . The gasket material fed to the coil  44  appears like that shown in  FIG. 9A . 
         [0034]    In the process of transforming the raw gasket material  10  into a finished gasket, cutting, dressing or further operations may be required. For example,  FIGS. 4-6  illustrate fractional cross-sections of a head gasket made from the multi-layered composite material. In this case, as is customary, it is necessary to install a fire ring  46  around the periphery of any combustion chamber openings, covered by a fire ring hold  48  whose edges overlap the graphite layers  26  and provide durability and stopper height adjustment as needed in head gasket applications. It will be appreciated that other uses of the gasket material  10  can be used to make gaskets which are not intended for sealing a cylinder head in an internal combustion engine, and therefore the fire ring  46  and holder  48  may be omitted. Likewise, grommets or other features may be included so that the gasket  10  can be used any suitable application. 
         [0035]    By introducing paper layers  30  between the perforated cores  14  and the center core  12 , the paper layers  30  are able to provide a slip plane so that lateral sheer loads do not build up within the body of the gasket  10  and ultimately lead to fluid leaks. The composition of the adhesive applied between the paper layers  30  and the center core  12  is such that slippage can occur either within the adhesive itself, at the interface between the adhesive and center core  12 , at the interface of the paper layers  30  and perforated cores  14 , or within the body of the paper layers  30 . In other words, the yield strength of the adhesive and/or paper layers  30  and/or interfaces are such that they will give before the sheer loads may build to problematic levels. 
         [0036]    The foregoing invention has been described in accordance with the relevant legal standards, thus the description is exemplary rather than limiting in nature. Variations and modifications to the disclosed embodiment may become apparent to those skilled in the art and fall within the scope of the invention. Accordingly the scope of legal protection afforded this invention can only be determined by studying the following claims.