Patent Application
20050187324
This invention relates to gasket compositions. In particular, the present invention relates to compositions comprising certain silicone polymers for coating a gasket substrate.
Gaskets provide a seal between two mating components. Typically, the two components have respective (essentially coplanar or flat) mating surfaces essentially adjacently disposed except for the intervening gasket. In this regard and in the absence of the gasket, the mating surfaces frequently do not press together ideally without some voids being created between the two surfaces, and these voids can establish undesired leakage pathways between the two components. The gasket compensates for this by providing a reasonably flexible interface to fill any voids between the surfaces and also, in many cases, to provide a compressed mechanical spring between the two mating surfaces. Bolts or similar fasteners compressively connect (mate) the two components together and compress the gasket (to form a compressed spring seal) between the mating surfaces.
One common application for gaskets is to provide the interface in mating an engine block to a cylinder head of an internal combustion (IC) engine; this is considered to be one of the most difficult gasket applications because of the temperatures and pressures created on the gasket during engine operation. An exhaust manifold is another example of a component mated to an engine with a gasket. IC engine manifold gaskets are typically formed with ports for accommodating flow of fluids between the cylinder head and the exhaust manifold. In cylinder head gasket use during engine operation, combustion and exhaust gases are a source for lateral stress conditions to the gasket of greater than 1,000 lbs per square inch at a temperature of 600° Fahrenheit or greater. These high temperatures and high pressures define the performance environment for the gasket, which is compressed between the engine block and head with a force of at least 10,000 pounds per square inch to contain the hot gases.
Hot oil defines a further source of chemical solvent stress to gasket materials used in IC gaskets. When the engine ceases operating, the materials cool substantially, especially in winter environments, with attendant contractive stresses within the materials and expansive stresses from embedded frozen moisture at low temperatures. Thus, internal combustion engine gaskets are frequently exposed to a wide range of temperatures, pressures, and corrosive materials during normal use.
Cylinder head gaskets are also frequently provided with an embossed bead, for providing an essentially leak-proof seal. Another common feature of these gaskets is a stopper—a stiff metal strip providing a primary thickness offset in the gasket, which both provides a primary seal and also frequently protects softer auxiliary bead seals from over compression between the two mating surfaces.
While many gaskets are made of several different pieces stacked in a multilayer orientation, minimization of the number of parts needed for an engine is an ongoing goal. Single piece gaskets are therefore desirable. Many gaskets require seals applied as coatings rather than as separate gasket-form layers. In highly stressful operational environments, a gasket coating's ability to provide satisfactory adhesion to a (usually metal) substrate and also to persevere in robust condition during use is, therefore, most important. Conformable coatings, however, lose their adhesion over time under their operational high loading and vibration, and an improved gasket is needed to provide a long-term robust interface between the engine block and cylinder head.
The invention provides a gasket coating comprising:
In further aspects of the invention, the gasket coating composition additionally comprises such materials as microspheres, soft (ground) rubber and/or PTFE particulates, fiberglass particulate, carbon fiber particulate, and inorganic fiber particulates. The present invention also provides single component gaskets comprising the compositions of this invention.
It has been found that the compositions of this invention afford advantages over gasket compositions among those known in the art, including one or more of good high temperature robustness (up to at least 900° Fahrenheit), excellent resistance to oil and moisture attack, strength with resiliency, abrasion resistance, solvent resistance, reduced cost, and adhesion to metals, graphite, composites, and other materials having a high surface tension.
Further areas of applicability will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating embodiments of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
The present invention will become more fully understood from the detailed description and the accompanying drawings of FIGS. 1 to 13.
a and 10b illustrate a partial perspective view and a partial cross-sectional view, respectively, of another alternate embodiment of the present invention, wherein the inner sealing portion of the carrier is substantially separated from the remainder of the carrier member but interconnected and held in place by two or more connecting struts.
a and 11b are similar to those of
It should be noted that the figures set forth herein are intended to exemplify the general characteristics of an apparatus, materials and methods among those of this invention, for the purpose of the description of such embodiments herein. These figures may not precisely reflect the characteristics of any given embodiment, and are not necessarily intended to define or limit specific embodiments within the scope of this invention.
In use, a gasket represents an intersection of considerations in both mechanical design and in materials design. In this regard, improvements in materials frequently are intertwined with improvements in mechanical design. When a component, such as a gasket, is made of a basic material coated with at least one additional material, the process of joining the materials together is also of interest. The following discussion will begin with a focus on some new silicone polymeric materials, shift in focus to a consideration of mechanical design considerations benefiting from the new silicone polymeric materials, and then focus on process considerations related to the production of the new silicone polymeric materials and their use.
The following definitions and non-limiting guidelines must be considered in reviewing the description of this invention set forth herein.
The headings (such as “Introduction” and “Summary”) used herein are intended only for general organization of topics within the disclosure of the invention, and are not intended to limit the disclosure of the invention or any aspect thereof. In particular, subject matter disclosed in the “Introduction” may include aspects of technology within the scope of the invention, and may not constitute a recitation of prior art. Subject matter disclosed in the “Summary” is not an exhaustive or complete disclosure of the entire scope of the invention or any embodiments thereof.
The citation of references herein does not constitute an admission that those references are prior art or have any relevance to the patentability of the invention disclosed herein. All references cited in the Description section of this specification are hereby incorporated by reference in their entirety.
The description and specific examples, while indicating embodiments of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. Moreover, recitation of multiple embodiments having stated features is not intended to exclude other embodiments having additional features, or other embodiments incorporating different combinations the stated of features.
As used herein, the words “preferred” and “preferably” refer to embodiments of the invention that afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the invention.
As used herein, the word “include,” and its variants, is intended to be non-limiting, such that recitation of items in a list is not to the exclusion of other like items that may also be useful in the materials, compositions, devices, and methods of this invention.
The present invention provides a gasket silicone polymeric material, comprising a silicone polymer blend of diphenyl polysiloxane silanol polymer and methylsiloxane polymer, where the diphyenyl polysiloxane silanol polymer is from about 45 to about 95 weight percent of the silicone polymer blend, and the methylsiloxane polymer is comparably from about 55 to about 5 weight percent of the blend. An example of diphenyl polysiloxane silanol resin is GE-TPR178 made by General Electric Corporation. An example of methylsiloxane resin is GE-TPR179.
Powdered particulate of aluminum, graphite, or a mixture thereof is dispersed in the silicone polymer blend in a quantity from about 30 to about 115 parts per 100 parts by weight of the silicone polymer blend. The powdered particulate has a maximum particle size of about 325 mesh (that is, the particles will pass through a 325 mesh screen).
The composition also comprises a curing agent of zirconium acetate in a concentration from about 0.02 to about 1.5 parts per 100 parts by weight of the silicone polymer blend.
The new silicone polymer blend composition provides handling benefits similar to coatings based upon organic polymers. Very beneficially, however, the new composition provides properties, when cured, which are comparable to metallic coatings. In this regard, the new cured silicone polymer composition appears to be robust at 900° Fahrenheit and to survive at peaking temperatures of 1200° Fahrenheit without visual change. The new coatings have good strength and bond well to stainless steel without benefit of a primer.
In one embodiment, the composition comprises soft filler particulate of less than about 35 parts per 100 parts by weight of the silicone polymer blend. This soft filler particulate has a mean particle size from about 5 to about 50 microns. Ground rubber and polytetrafluorinated ethylene (PTFE) are two preferred soft filler particulates for the composition. The soft filler particulate is preferably dispersed within the continuous cured silicone polymer, so that at least a two phase polymeric coating is provided. The PTFE particles help to reduce wear on the gasket from engine vibration, and they also augment release of the gasket during engine disassembly.
The compositions optionally comprise microspheres preferably having a mean particle size from about 20 to about 120 microns and preferably at a concentration of from about 0.5 to about 20 parts per 100 parts by weight of the silicone polymer blend. The microspheres have shells of any of fiberglass, ceramic, glass, and combinations thereof.
The microspheres establish dispersed and sealed gaseous phases within the continuous cured silicone polymer blend, so that a foamed polymeric coating is provided. In this regard, localized regions of the coating can be engineered to have a foam attribute, and a designed coating is therefore enabled with differentiated regions interbonded with a continuous silicone polymer phase. In such embodiments, the microspheres thereby enable degrees of freedom (in concentration, size, and microsphere compositional specifics) for balancing properties related to flexibility, conformability, resiliency, and toughness in the cured coating.
The compositions of this invention optionally comprise filler particulates of fiberglass, inorganic fiber, carbon fiber, or a mixture thereof, preferably at a concentration of up to about 35 parts per 100 parts by weight of the silicone polymer blend. The filler particulates preferably have a mean particle size from about 10 to about 50 microns. In one embodiment, filler particulate is added to create a rigid region in a gasket comprising a plurality of gasket layers or regions. In one such embodiment, silicone polymer blend composition of this invention without filler particulates is first deposited on a metal substrate. Silicone polymer blend admixture with filler particulates (preferably having the same silicone polymer blend as used in the first layer) is then deposited on the first layer. Both layers are then cured. During the curing process, crosslinking occurs across the boundary between the two deposited layers so that a continuum of crosslinked silicone polymer blend is established in the cured coating. This approach enables a multi-region gasket seal having a very rigid region integrated via continuously crosslinked silicone polymer into a somewhat less rigid and metallically adhesive region. As will be further described herein, such a region enables a raised rigid bead (which, in one embodiment, provides an integrated stopper) to be provided in the derived gasket.
Turning now to the Figures and to mechanical design opportunities and considerations affiliated with the new silicone polymer blend coating admixtures,
Referring initially to
Gasket 10 of
Preferably, exemplary flexible stopper 40 (which can be characterized as a “full embossment”) is longitudinally offset to a lesser extent than inner sealing portion 36 (which can similarly be characterized as a “half embossment”). Flexible stopper 40 is spaced away from gasket opening 20 (as well as from mating member openings 16 and 18), with the primary sealing component of the gasket (i.e., inner sealing portion 36) and intermediate portion 38 being between flexible stopper 40 and gasket opening 20. Flexible stopper 40 has a convex side 42 and a concave side 44, either of which can be oriented toward either of members 12 or 14.
Concave side 44 can optionally be coated with a sealing material 32 such as a cured silicone polymer blend having microspheres as previously discussed, or concave side 44 is partially or completely filled with sealing material 32 such as a cured silicone polymer blend having microspheres as previously discussed. Typically, although not necessarily in a given application, inner sealing portion 36 is more flexible than flexible stopper 40.
Examples of materials for carrier 40 can include semi-rigid synthetic or natural materials, metals or non-metals, with one example being composed of 301 stainless spring steel, full-hard, from about 0.15 mm to about 0.35 mm thick. Lower hardnesses of steel or other metals can of course also be used if a reduction in spring force is desired in a particular application. However, such softer materials may, over time, exhibit a decrease in recovery performance during unloading conditions, such as those resulting from relative movement between the mating members. Other metals or metal alloys may also have application in the present invention, such as hardened carbon steel, inconel, titanium, or still others known to those skilled in the art.
Examples of materials for sealing material 32 in the illustrated example include cured silicone polymer blends having optional microspheres as previously discussed. The silicone polymer blend coating (ultimately cured to provide sealing material 32) is, in one embodiment of an application process, applied to the carrier material and cured prior to forming the carrier itself. In an alternative application process, the silicone polymer blend coating is coated onto the carrier after it is formed; or it is coated onto localized areas as appropriate, such as those adjacent gasket opening 20 or other areas adjacent fluid openings (e.g., for lubricant, for cooling, etc.), bolt holes, or the like. Such sealing material 32 is preferably on at least both sides of any or all of inner sealing portion 36, intermediate portion 24, or flexible stopper 40. If desired to be applied only in localized areas of gasket 20, sealing material 32 is applied in a variety of different ways, such as by (in example) screen printing, direct coating, or even decal transfer. In this regard, it should also be noted that concave side 44 of flexible stopper 40 can be merely coated (as in concave side 44 on stopper 40 shown in
In
In one embodiment, the present invention provides machine components covered with a composition of this invention having differentiated regions. In this regard, in one embodiment, a first coating region without admixed microspheres is derived from a first admixture of the crosslinkable silicone polymer and a second coating region has dispersed microspheres derived from a second admixture of the crosslinkable silicone polymer. In one such embodiment, the amount of microspheres (for instance, at least 5 parts per hundred parts of crosslinkable silicone polymer) in the second region enable the second region to be “foamed” and yet smoothly interbonded with the first coating region with the cured continuous silicone polymer phase. The cured continuous silicone polymer phase (interbonding the first region and the second region) is derived from simultaneous curing of the crosslinkable silicone polymer in both regions. In this way, microspheres enable “foam in place” regions within an otherwise non-foamed coating, so that a designed coating is enabled for a component such as a gasket. When positioned at low loading points of the gasket, the somewhat conformable foamed region facilitates an excellent seal; and, when comparably positioned at high load points of the gasket, the non-foamed regions of the coating minimize load loss derived from creep and relaxation in the compressed gasket. In another beneficial aspect, the foam region can be positioned to level and distribute the load on the gasket and thereby minimize undesirable crushing of other regions of the gasket (such as, for example, beaded portions).
In further example of this,
A second silicone polymer blend admixture having essentially the same silicone polymer blend base as the first coating, but with a large number of microspheres (see microsphere 4015), is disposed onto carrier 4006 at region 4003. After curing, region 4003 provides a “stopper” (reference stopper 40) portion in the gasket which is of raised thickness 4010 as compared to thickness 4008 of cured coating at regions 4002a and 4002b.
In one embodiment, the concentration of microspheres in the composition of gasket region 4003 is dependent upon the particular spring force desired when gasket 4000 is used. In this regard, when compressively interfaced to a second surface (as in
In a similar showing of an alternative feature in gasket embodiment 5000 in
It is to be noted that the first and second silicone polymer blend coatings of both embodiments 4000 and 5000 form, during curing, a crosslinked silicone polymer continuum among and throughout, respectively, regions 4002a, 4003, and 4002b and regions 5002a, 5004, and 5002b. This enhances strength and degrees of freedom of the overall conjoined coatings insofar as macroproperties are provided in the gasket seal from the regionally differentiated properties respective to the compositionally differentiated regions.
Yet another feature in gasket construction is shown in gasket embodiment 6000 of
In an alternative embodiment of gasket embodiment 6000 of
In yet another embodiment, region 13005 is silicone polymer enhanced with filler particulate of fiberglass, inorganic fiber, carbon fiber, or a mixture thereof as previously described and regions 13007 and 13003 are resilient fluoroelastomers. In this embodiment, rigid region 13005 essentially provides a polymeric bead bonded to a portion of the surface of carrier section 13001. The remaining surface of region 13005 (free of bonding connection to the “upper” surface of carrier section 13001) rises to a maximum bead thickness—the greatest distance of the upper surface of rigid region 13005 above the upper surface of carrier 13001. Coating region 13003 has a bead enclosing portion bonded to this remaining exterior surface of polymeric bead 13005 so that polymeric bead 13005 is encapsulated within a peripheral boundary defined by the “upper” surface of carrier 13001 and the “lower surface” of the bead enclosing portion of coating region 13003. The thickness of coating region 13003 at the “crest” or highest point of region 13005 is referenced herein as the crest thickness. When rigid region 13005 and the portion of coating region 13003 covering rigid region 13005 are considered as a unified “bead” (metaphorically, a tough rigid core within a velvet coating when regions 13003 and 13007 are fluoroelastomer-based), a second maximum bead thickness for the unified bead is therefore the sum of the maximum bead thickness and the crest thickness of region 13003. In this regard, the maximum thickness of region 13007 respective to the surface of carrier 13001 is preferably greater than this second maximum bead thickness (per visual comparison of the “high points” of region 13005 as covered by region 13003 and of region 13007). This provides, for example, a gasket in use when pressed against a consistently “horizontal” upper surface (not shown but which should be apparent) where region 13007 is, (a) compressed to seal against fluid (gas or liquid) passage while still (b) precluded from inappropriate compression and distortion by the greater rigidity of region 13005. Region 13005 also provides sealing efficacy in the form of a stopper function and second seal augmented by the moderate compressibility of coating 13003 at the crest of bead 13005.
Turning now to process considerations related to the production of the new silicone polymeric materials and their use, diphenyl polysiloxane silanol polymer and methylsiloxane polymer and powdered aluminum, graphite, or a mixture thereof as previously described are admixed into a blend in a mixer to form a precursor silicone polymer blend. Curing agent of zirconium acetate as previously described herein is then admixed into the silicone polymer blend precursor shortly before use to make the coating admixture for application to a component.
The coating admixture is applied, in one embodiment of a process for using the coating admixture, to an essentially flat surface of a machine component (for example, a gasket). The component is then optionally further formed for final use. In a second embodiment, a component is first formed into a component not having a universally-flat surface of interest for coating (a component having a non-planar coating application surface); and the coating is then applied to the non-planar surface. In this regard, it has been learned that screen printing of coating admixtures onto the non-planar surface is especially facilitated by the use of a very fine screen for passing a finer granularity than at least 60 mesh, preferably about a 110 mesh printing screen, with multiple layers of the coating admixture being deposited (applied) prior to curing as needed to enable a specific coating thickness. In this regard, the thickness of each layer deposited on the non-planar surface is controlled in thickness so that surface tension of the deposited layer on either the carrier or the previously applied layer is such that that flow of the deposited layer essentially is precluded (essentially does not occur) laterally along the surface of interest and that a consistently thick coating is built thereby over the surface of interest.
After the coating admixture has been applied to the component, the component and coating are heated to from about 400° to about 450° Fahrenheit as needed to cure the coating.
The silicone polymer cured admixture is, in some embodiments, further cured and strengthened by increasing the temperature to a level of from about 1000° Fahrenheit to about 1200° Fahrenheit. In this regard, the new silicone polymer blends appear to provide opportunities in high temperature applications such as for disk brakes or for sealants for components such as mufflers, catalytic converters, and their associated piping. A further opportunity for use in surface repair is as a filler to improve surface finishes for components such as cylinder heads, engine blocks, and exhaust manifolds.
A silicone polymeric gasket is prepared from admixing the following ingredients:
The blended ingredients are coated onto a metal carrier and cured to form a tough coating which demonstrate no visible deterioration when tested in an oven capable of 1200° Fahrenheit.
The examples and other embodiments described herein are exemplary and not intended to be limiting in describing the full scope of compositions and methods of this invention. Equivalent changes, modifications and variations of specific embodiments, materials, compositions and methods may be made within the scope of the present invention, with substantially similar results.
