Abstract:
A malleable gasket suitable for high purity fluid delivery systems has flat axial end surface sealing regions on opposing sides, and further includes a raised inner lip on a first side and a raised outer lip on a second side. The raised lips align the gasket within a fluid delivery conduit by engaging features in the face of one or more fluid delivery elements joined together, and simultaneously provide protection to the sealing regions during normal handling and fluid delivery system assembly.

Description:
This application claims the benefit under 35 U.S.C. 119(e) of the filing date of Provisional U.S. Application Ser. No. 61/687,105, entitled EZ-Seal Gasket for Joining Fluid Pathway, filed on Apr. 18, 2012, which is commonly owned and expressly incorporated herein by reference, in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention is related to malleable metallic gaskets for sealing joints between portions of a fluid pathway. 
     BACKGROUND OF THE INVENTION 
     Many combinations of interface structures and associated gaskets are well known in the design of fluid delivery systems. These structures include flanges, glands, component connections, and other elements that enable mechanical assembly of various system elements forming an arrangement of interconnected fluid pathways. 
     Representative fluid delivery systems are found among industrial equipment producing fine chemicals, petroleum products, or semiconductors, for example, and may be subjected to vacuum or pressure or purity requirements and/or combinations thereof. Fluid pathways among elements intended for manipulating process materials within semiconductor manufacturing equipment usually require attention to maintaining high purity of the delivered reactants, and also typically have a much smaller cross-section than fluid pathways used in petrochemical plants, for example. In many cases, practitioners have found that metallic gaskets provide superior performance, particularly regarding diffusion of process fluid or contaminants through the gasket and consequent resistance to undesirable leakage, in preference over polymer materials. 
     One known type of fluid pathway joint uses a ring-shaped flat metallic gasket compressed between nominally identical shaped annular projections that surround circular conduit openings of opposing apparatus elements. The annular projections are urged axially toward one another, causing permanent plastic deformation of the ductile metallic gasket to create a seal that will resist leakage of even difficult-to-contain fluids such as helium. Representative examples of such joints may be seen, for example, in U.S. Pat. No. 3,208,758 issued to Carlson and Wheeler (familiarly known as the Varian® Conflat® flange), in U.S. Pat. No. 3,521,910 issued to Callahan and Wennerstrom (familiarly known as the Swagelok® VCR® fitting), and in U.S. Pat. No. 4,303,251, issued to Harra and Nystrom. 
     Another known type of fluid pathway joint uses a ring-shaped metallic gasket of complex shape compressed between nominally identical shaped annular projections that surround circular conduit openings of opposing apparatus elements. Representative examples of such joints are disclosed in U.S. Pat. No. 4,854,597 to Leigh, in U.S. Pat. No. 5,505,464 to McGarvey, and in U.S. Pat. No. 6,135,155 to Ohmi et al. (an early version of the W-seal joint type well known now in the industry). The &#39;155 patent additionally provides a separate retainer for holding and centering the gasket during assembly of the joint. Such separate retainer structures may also be seen in U.S. Pat. No. 5,673,946 and U.S. Pat. No. 5,758,910, both issued to Barber and Aldridge, and in U.S. Pat. No. 7,140,647 to Ohmi et al. 
     Yet another known type of fluid pathway joint, familiarly known in the industry as the C-seal joint type, uses a ring-shaped metallic gasket of complex shape which is compressed between opposing apparatus elements, wherein the face of at least one element has a circular counterbore depression to receive the gasket. Representative examples of such joints are disclosed in, for example, U.S. Pat. No. 5,354,072 to Nicholson, U.S. Pat. No. 6,042,121, to Ma et al., U.S. Pat. No. 6,357,760 and U.S. Pat. No. 6,688,608, both issued to Doyle, and U.S. Pat. No. 6,409,180 issued to Spence and Felber. The &#39;180 patent to Spence and Felber additionally discloses a separate retainer for holding and centering the gasket during joint assembly. Such separate retainer structures may also be seen in U.S. Pat. No. 5,730,448 to Swensen et al., U.S. Pat. No. 5,984,318 to Kojima and Aoyama, U.S. Pat. No. 6,845,984 to Doyle, and U.S. Pat. No. 6,945,539 to Whitlow et al. 
     Still another known type of fluid pathway joint, known in the industry as the Z-Seal type, uses a ring-shaped flat metallic gasket compressed between opposing apparatus elements wherein mating features surrounding circular conduit openings create corners that shear into the gasket. This type of corner-shear joint is illustrated in U.S. Pat. No. 5,803,507 and U.S. Pat. No. 6,394,138, both issued to the present inventor, Kim Ngoc Vu, and it also utilizes a retainer structure. All of the foregoing patents are herein expressly incorporated by reference, in their entirety. 
     In the majority of the preceding design examples, there is considerable risk of adversely scratching a face of the gasket prior to joint assembly and such damage thereby making a joint free of leaks unachievable. Gasket centering by a separate retainer provides a desirable consistency of alignment between the fluid pathway conduit ports and the central passageway through the gasket, but incurs undesirable added expense. Within some fluid delivery systems used for semiconductor manufacturing processes, there are situations using multiple types of pathway joints simultaneously, and that situation requires equipment maintenance personnel to stock and have available an undesirably large inventory of various kinds of spare gaskets. 
     SUMMARY OF THE INVENTION 
     In consideration of the foregoing, the present invention addresses the issues noted above, by providing an easily made single-piece malleable metallic gasket, incorporating protection of the sealing regions, that is also self-centering. The inventive gasket is a ring-shaped part which may be described as a torus generated by rotating a cross-sectional profile having specific characteristics about the central axis of the ring. The gasket form may be conveniently machined from solid stock or tubing using a lathe or screw machine, but other manufacturing processes, such as stamping or coining in conjunction with appropriate annealing, are also contemplated. It will be apparent to practitioners that the benefits of sealing region protection and self-centering may also be obtained with gaskets made by molding or machining polymer materials such as PFA, but the resistance to diffusion of process fluid or contaminants will be reduced. 
     The gasket torus typically has an inner diameter corresponding to roughly the inner diameter of the fluid pathway conduits, and an outer diameter proscribed by constraints of the mating apparatus elements. The gasket torus has a first axial end surface sealing region that is orthogonal to the axis of the gasket central fluid pathway hole, and is generally flat. The gasket torus also has a second axial end surface sealing region, opposite the first axial end surface sealing region, that is orthogonal to the axis of the gasket central fluid pathway hole and is also generally flat. The first axial end surface sealing region surrounds an inner raised lip of sufficient axial extent to protect the first end surface sealing region, and has a diameter smaller than the first sealing region. The second axial end surface sealing region is surrounded by an outer raised lip of sufficient axial extent to protect the second end surface sealing region, and has a diameter greater than the second sealing region. The inner raised lip and outer raised lip may each extend axially a convenient distance (such as 0.010 inch) beyond the corresponding adjacent sealing region. The inner raised lip and outer raised lip may have most any convex profile, but a smoothly curved outermost portion with tapering sides is easily machined, and minimizes the chances for snagging or scraping the gasket during fluid delivery assembly in clean room conditions typically used for semiconductor equipment. The gasket form may be conveniently machined from solid stock, such as round bar stock, or tubing using a lathe or screw machine, but other manufacturing processes, such as stamping or coining in conjunction with appropriate annealing, are also contemplated. It will be apparent to practitioners that the benefits of sealing region protection and self-centering may also be obtained with gaskets made by molding or machining polymer materials such as PFA, but the resistance to diffusion of process fluid or contaminants will be reduced. The round bar stock, when used, may be stainless steel or other suitable material, such as Hastelloy C276 or C22. 
     Gaskets intended for use with corner-shear joint types will usually have the inner diameter of the flat first axial end surface sealing region be nominally the same as the outer diameter of the flat second axial end surface sealing region. Another embodiment of the gasket may have the inner diameter of the flat first axial end surface sealing region be nominally the same as the outer diameter of the flat second axial end surface sealing region. Another embodiment of the gasket may have the inner diameter of the first sealing surface be less than the outer diameter of the second sealing surface to ease use with VCR® joint types. A useful variation of the inventive gasket lacks any hole piercing the material of the gasket and thus may function as a blank-off closure that prevents flow through a fluid conduit as is known in the art. A further variation of the inventive gasket has one or more small holes piercing the material of the gasket, rather than a large central hole, and thus may function to reduce or limit flow through a fluid conduit as is also known in the art (see U.S. Pat. No. 7,874,208 for an example application of this function using a corner-shear joint type). 
     More particularly, there is provided in a disclosed inventive embodiment a malleable gasket suitable for high purity fluid delivery systems. The gasket comprises a first side, an opposed second side, and an outer circumference, and further comprises a raised inner lip on the first side and a raised outer lip on the second side, wherein the raised inner lip and the raised outer lip are circumferentially spaced from one another. In the illustrated embodiments, the gasket is round. It may be metallic, or alternatively made from a polymer. A metallic version of the gasket may be machined from a round bar stock, such as stainless steel or hastelloy. 
     The first side of the gasket comprises a flat first sealing region disposed outwardly of the raised inner lip, while the second side of the gasket comprises a flat second sealing region disposed inwardly of the raised outer lip. As illustrated, the first side of the gasket is a mirror image of the second side of the gasket. The first side of the gasket further comprises a circular sector forming a part of the raised inner lip, an outward tapering portion extending from the circular sector, and a smooth curve extending outwardly from the tapering portion and joining the flat first sealing region. The second side of the gasket further comprises a circular sector forming a part of the raised outer lip, an inwardly tapering portion extending from the circular sector, and a smooth curve extending inwardly from the tapering portion and joining the flat second sealing region. The gasket comprises a torus having an inner circumference defining a central axial bore, and each of the flat first sealing region and the flat second sealing region are substantially orthogonal to the axis of the central axial bore. 
     The gasket is disposed in a sealing arrangement within a fluid passageway formed by assembled members having a joint comprising each of a joint counterbore portion and a joint groove portion, a counterbore corner extending from the joint counterbore portion and a groove portion corner extending from the joint groove portion, and further wherein the inner raised lip aligns the gasket with the joint counterbore portion and the outer raised lip aligns the gasket with the joint groove portion, such that when the joint is completely assembled, the counterbore corner shears into the gasket first sealing region and the groove portion corner shears into the gasket second sealing region. 
     The invention, together with additional features and advantages thereof, may be best understood by reference to the following description taken in conjunction with the accompanying illustrative drawings. In these accompanying drawings, like reference numerals designate like parts throughout the figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1   a  is a top view of a gasket constructed in accordance with one embodiment of the present invention; 
         FIG. 1   b  is a cross-sectional view taken along line A-A of the gasket shown in  FIG. 1   a;    
         FIG. 1   c  is an isometric view of a portion of the gasket of  FIGS. 1   a  and  1   b;    
         FIG. 2  is an enlarged detail of the portion of  FIG. 1   b  identified by the letter “B”; 
         FIG. 3   a  is a top view of a portion of a fluid delivery system having planar corner-shear fluid delivery elements and using the gasket of the present invention; 
         FIG. 3   b  is a cross-sectional view of the system of  FIG. 3   a , taken along line A-A; 
         FIG. 3   c  is an isometric cross-sectional view of the system of  FIGS. 3   a  and  3   b;    
         FIG. 3   d  is an enlarged cross-sectional view of the portion of  FIG. 3   b  denoted by the letter “C”; 
         FIG. 4   a  is a top view of a portion of a fluid delivery system having a combination of recessed and planar corner-shear joint fluid delivery elements and using the gasket of the present invention; 
         FIG. 4   b  is a cross-sectional view of the system of  FIG. 4   a , taken along line A-A; 
         FIG. 4   c  is an isometric cross-sectional view of the system of  FIGS. 4   a  and  4   b;    
         FIG. 4   d  is an enlarged cross-sectional view of the portion of  FIG. 4   b  denoted by the letter “D”; 
         FIG. 5   a  is a top view of a portion of a fluid delivery system with yet other recessed corner-shear joint fluid delivery elements and using the gasket of the present invention; 
         FIG. 5   b  is a cross-sectional view of the system of  FIG. 5   a , taken along line A-A; 
         FIG. 5   c  is an isometric cross-sectional view of the system of  FIGS. 5   a  and  5   b ; and 
         FIG. 5   d  is an enlarged cross-sectional view of the portion of  FIG. 5   b  denoted by the letter “E”. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now more particularly to the drawing figures, wherein like reference numerals designate identical or corresponding parts throughout the several views and embodiments, there is shown in  FIGS. 1   a - 1   c  and  FIG. 2  one embodiment of a gasket  10  constructed in accordance with the principles of the present invention. The gasket  10  has an inner raised lip  20  and a smooth straight central axial bore  40 , wherein the inner raised lip  20  begins as a nominally 30 degree outward taper  21  therefrom. Upon reaching an axial extent of approximately 0.007″, the outward taper  21  turns into a smooth curve directed outwardly with a radius of approximately 0.006″ to form a circular sector  22  of approximately 90 degrees extent, and then begins a further outward taper  23  of nominally 45 degrees in the reverse axial direction. Upon nearly reaching the same axial location as the start of the outward taper  21 , the further outward taper  23  turns into a smooth curve  24 , which is directed further outward with a radius of approximately 0.004″, and joints a flat first axial end surface region  30  that is orthogonal to the axis of the gasket central axial bore  40  which defines the fluid pathway hole. The flat first sealing region  30  extends radially approximately 0.005″ outward, then turns into a smooth curve directed outwardly with a radius of approximately 0.020″, forming a circular sector  26  of approximately 90 degrees extent, whereupon the straight wall of a gasket outside diameter  50  is formed parallel to the central axis. 
     In the foregoing embodiment, the profile of an outer raised lip  60  and flat second sealing region  70  transition from the gasket outside diameter  50  are mirror images of the corresponding inner raised lip  20  and flat first sealing region  30 . The gasket  10  has a smooth straight outside diameter  50  and an outer raised lip  60 , beginning as a nominally 30 degree inward taper  61  therefrom. Upon reaching an axial extent of approximately 0.007″, the inward taper  61  turns into a smooth curve, directed inwardly with a radius of approximately 0.006″, forming a circular sector  62  of approximately 90 degrees extent, and then begins a further inward taper  63  of nominally 45 degrees in the reverse axial direction. Upon nearly reaching the same axial location as the start of the 30 degree taper  61 , the further inward taper  63  turns into a smooth curve  64  directed further inwardly with a radius of approximately 0.004″ and joins the flat axial second end surface sealing region  70  that is orthogonal to the axis of the gasket central axial bore  40  which defines the fluid pathway hole. The flat second sealing region  70  extends radially approximately 0.005″ inwardly, then turns into a smooth curve directed inwardly with a radius of approximately 0.020″ forming a circular sector  66  of approximately 90 degrees extend, whereupon the straight wall of the gasket smooth central axial bore  40  is formed parallel to the central axis. 
     The axial spacing between the first sealing region  30  and the second sealing region  70  may be chosen for convenience according to particular dimensions of the corresponding apparatus elements wherein the gasket will be used. In the illustrated embodiment, an axial spacing of approximately 0.058″ allows the gasket to be used with planar corner-shear joint types intended to provide a nominal gasket compression of 0.012″ when completely assembled. It should be appreciated that the corner-shear joint mating features may be located at various recessed axial depths within the corresponding apparatus elements, and the same one embodiment may be used with these different combinations. 
     The gasket  10  may be conveniently machined from solid stock, such as round bar stock, or tubing using a lathe or screw machine, but other manufacturing processes, such as stamping or coining in conjunction with appropriate annealing, are also contemplated. It will be apparent to practitioners that the benefits of sealing region protection and self-centering may also be obtained with gaskets made by molding or machining polymer materials such as PFA, but the resistance to diffusion of process fluid or contaminants will be reduced. The round bar stock, when used, as presently preferred, may be stainless steel or other suitable material, such as Hastelloy C276 or C22. 
     As shown in  FIGS. 3   a - 3   d , the inventive gasket  10  may be used with planar corner-shear joint mating features similar to those disclosed in U.S. Pat. Nos. 5,803,507 or 6,394,138 wherein the inner raised lip  20  aligns the gasket  10  with a joint counterbore portion  320  and the outer raised lip  60  aligns the gasket  10  with a joint groove portion  360 . When the joint is completely assembled, a counterbore corner  322  shears into the gasket first sealing region  30  and a groove portion corner  362  shears into the gasket second sealing region  70 . The gasket central axial bore  40  has approximately the same diameter as an upper element conduit port  364 , which usually also has the same diameter as a lower element conduit port  324 . In this design, the upper and lower device conduit ports  364 ,  324  usually have the corner features  362 ,  322  sharpened by lapping the flat surface of the joined elements, which necessarily places the corner features  362 ,  322  at opposing interface surfaces  365 ,  325 . The joint is best assembled by interposing a thick shim  310  between the opposing interface surfaces  365 ,  325  to ensure the desired compression (typically 0.012″) of the gasket  10  is achieved and also to provide a hard stop when the full fastener force is applied. 
     As shown in  FIGS. 4   a - 4   d , the inventive gasket  10  may be used with corner-shear joint mating features, wherein some element features have been recessed. As before, the inner raised lip  20  aligns the gasket  10  with a joint counterbore portion  420  and the outer raised lip  60  aligns the gasket  10  with a joint groove portion  460 . When the joint is completely assembled, a counterbore corner  422  will shear into the gasket first sealing region  30  and a groove portion corner  462  will shear into the gasket second sealing region  70 . The gasket central axial bore  40  has approximately the same diameter as an upper element conduit port  464 , which usually also has the same diameter as a lower element conduit port  424 . In this alternate apparatus design, the lower device conduit port  424  has a joint counterbore portion  420  and its corner feature  422  placed within a slightly larger counterbore  423  and recessed below a lower element surface  425 . Within the included planar upper element design, the joint groove portion  460  corner feature  462  may optionally be sharpened by lapping the flat surface of the upper element. The joint is assembled without any shim between the opposing interface surfaces  465 ,  425 , since the desired compression (typically 0.012″) of the gasket  10  is achieved by selecting the depth of the larger counterbore  423 , and a hard stop still occurs when the full fastener force is applied. A similar combination of planar lower element design and recessed upper element design can also be implemented, but is not illustrated in the interest of brevity. 
     As shown in  FIGS. 5   a - 5   d , the inventive gasket  10  may be used with corner-shear joint mating features wherein element features have been symmetrically recessed. As before, the inner raised lip  20  aligns the gasket  10  with a joint counterbore portion  520  and the outer raised lip  60  aligns the gasket  10  with a joint groove portion  560 . When the joint is completely assembled, a counterbore corner  522  will shear into the gasket first sealing region  30  and a groove portion corner  562  will shear into the gasket second sealing region  70 . The gasket central axial bore  40  has approximately the same diameter as an upper element conduit port  564 , which usually also has the same diameter as a lower element conduit port  524 . In this other alternative apparatus design, the lower device conduit port  524  has the joint counterbore portion  520  and its corner feature  522  placed within a slightly larger additional counterbore  523  and recessed below an element surface  525 . Likewise, the upper device conduit port  564  has the joint groove portion  560  and its corner feature  562  placed within a deeper additional counterbore  563  and recessed above an element surface  565 . The joint is assembled without any shim between the opposing interface surfaces  525 ,  565  since the desired compression (typically 0.012″) of the gasket  10  is achieved by selecting the depth of the matching additional counterbores  523 ,  563  and a hard stop still occurs when the full fastener force is applied. 
     Practitioners skilled in the art may further appreciate that the inner raised lip  20  and the outer raised lip  60  are radially displaced with respect to one another (as may be seen in  FIG. 2 ) in all embodiments of the inventive gasket  10 , because they originate from opposing edges of the sealing regions  30 ,  70 . Inadvertent virtual leaks and contamination traps within the fluid pathway are avoided by the smooth open form of the inward circular sector  66  adjacent to the axial bore  40  and also the smooth form of the inner raised lip  20  beginning as the nominally 30 degree outward taper  21 . 
     While this application examples and embodiments, it is to be understood that various modifications may be made without departing from the scope thereof. Therefore, the above description should not be construed as limiting the invention, but merely as an exemplification of preferred embodiments thereof and that the invention can be variously practiced within the scope of the following claims.