SEAL ASSEMBLY FOR A FASTENER

Abstract: A self-centering seal for a threaded fastener comprising a rigid, annular load-bearing retainer (11) with an elastomeric seal (12) moulded in place at its inner periphery. The seal (12) is of tear drop shape in section having a portion (24) which projects axially beyond the respective surfaces (14, 15) of the retainer (11), adjacent set back portions (25, 26) and an inner tip portion (28) with a relatively large radius of curvature (29). The diameter of the tip portion is sized to be an interference fit on the threaded fastener shank so that the seal may be preassembled with the threaded fastener.

Description: The invention relates to a seal for a fastener. Sealing fasteners against leakage can pose a serious challenge where excessively large clearance holes are involved, typically where there is greater than 0.8mm (1/32") diametral clearance. An oil drain plug is one example of this situation while pressurized structural assembly is another. It is necessary to ensure in these instances that the sealing member accommodates the tolerance range of both the opening to be sealed and the fastener involved in order to avoid a leak path. This problem is accentuated if it is necessary to keep the fastener in tight engagement, this is, where there is no torque loss over a period of time. This requirement rules out the use of a plain rubber or composition flat washer which relaxes and takes a set over a period of time. Still other problems inherent in devices of this kind are requirements that the sealing device be preassembled with the fastener to facilitate handling and to avoid the risk of inadvertent omission, and from the functional standpoint, the requirement that the sealing device retain its resilience over its intended service life. According to the invention there is provided a self-centering seal assembly for a fastener, comprising an annular retainer having generally parallel upper and lower surfaces and a central opening therein, and an annular elastomeric seal means disposed in the central opening of the retainer and secured thereto, the seal means being of tear drop shape in cross section and comprising a projecting seal portion, adjacent inner and outer set back seal portions and an inner circular tip portion, the projecting seal portion extending axially outwardly of the retainer beyond the upper and lower surfaces thereof, the inner and outer set back seal portions being set back axially from the upper and lower surfaces of the retainer, the tip portion extending radially inwardly of the inner set back seal portion and terminating in a smoothly rounded edge of convex curvature, the diameter of the tip portion at the edge being less than the diameter of a shank of the fastener with which the seal assembly is to be used, thereby to provide an interference fit thereon for support of the entire seal assembly, and the radius of curvature of the edge being less than one-half the dimension between the upper and lower surfaces of the retainer. Such a seal assembly can be self centering and may be preassembled and retained on the fastener to facilitate assembly procedures. In such a combination of an elastomeric tear drop shaped sealing bulb moulded in place within a metal (or suitable plastics) retainer of annular configuration, the retainer serves as a load bearing structure so that the fastener may be torqued against a rigid member to provide a long term connection. The projecting portion of the sealing bulb interposed between adjacent recessed portions can provide a controlled deflection or squeeze of the elastomeric material, typically, of about 25% which is considered near optimum static sealing practice. Providing the tip of the sealing bulb to converge to a smooth, convex edge of relatively large radius, with the diameter of the opening at the top edge being slightly smaller than the diameter of the fastener shank to provide an interference fit, can permit the seal assembly to be preassembled on the fstener and retained there for assembly in a threaded opening. Further, the seal assembly can be self-centering to locate the projecting portion of the sealing bulb at a position to accommodate the variations of size of the opening to be sealed. The tear drop shape can be effective to place the projecting portion of the seal at a relatively large spacing from the shank of the fastener as well as to provide the centering function. Since deflection of the seal is limited by the rigid retainer, the elastomeric sealing bulb can retain its resilience and sealing characteristics for a long period of time. The invention is diagrammatically illustrated by way of example with reference to the accompanying drawing, in which:- Figure 1 is a plan view of one embodiment of a seal assembly according to the invention; Figure 2 is a sectional view of the seal assembly of Figure 1; Figure 3 is an enlarged partial sectional view of the seal assembly of Figure 1; Figure 4 is a sectional view of the seal assembly of Figure 1 shown preassembled to a fastener, partially threaded at a joint to be sealed; Figure 5 is an enlarged partial sectional view of the fastener and seal assembly of Figure 4 after the fastener has been fully threaded to make a sealed joint; and Figure 6 is an enlarged partial sectional view of an alternative embodiment of seal assembly of the invention. Referring to the drawing, a seal assembly 10 is shown in plan and cross sectional views in Figures 1 and 2. The seal assembly 10 comprises a rigid retainer 11 and an elastomeric sealing bulb 12, both being generally annular with the sealing bulb 12 secured within the retainer 11. As more apparent in the enlarged partial view of Figure 3, the retainer 11 is a ring having substantially flat and parallel upper and lower circular surfaces 14, 15, respectively and outer and inner peripheral cylindrical surfaces 18, 19. A ring-like ledge 20 projects inwardly of the inner cylindrical surface 19, being stepped inwardly of the upper and lower surfaces 14, 15 to provide one form of interlocking support for the sealing bulb 12. The upper and lower surfaces 14, 15 are spaced by a dimension indicated by arrow 21, defining the thickness of the retainer 11. The sealing bulb 12 is also best seen in the enlarged partial sectional view of Figure 3 as comprising an integral ring of elastomeric material secured at the ledge 20 and the inner peripheral surface 19 of the retainer 11 and having a projecting portion 24, adjacent outer and inner set back portions 25, 26, respectively, and a tip portion 28 inwardly of the inner set back portion 26. The sealing bulb 12 is preferably symmetrical so that a further projection portion 24 and adjacent set back portions 25, 26 are provided at an opposite face of the sealing bulb 12 to said one face. The sealing bulb 12 is generally of tear drop shape as seen in section in Figure 3 with the projecting portion 24, the adjacent set back portions 25, 26 and the tip portion 28 blended into one another to form a continuous, smooth surface. The thickness of the sealing bulb at the projecting portion 24 is greater than the dimension 21 of the retainer 11 such that the sealing bulb projects axially beyond the upper and lower surfaces 14, 15 of the retainer 11. The outer set back portion 25 is such that in that region the sealing bulb faces are recessed below the upper and lower surfaces 14, 15 of the retainer 11. Preferably, the faces in the outer recessed portion 25 are of concave curvature, blended into the faces of the convexly curved projecting portion 24, in turn blended into the faces of the adjacent inner set back portion 26. The faces of the inner set back portion 26 comprises a pair of conical surfaces which taper linearly inwardly, converging into the tip portion 28 which is smoothly rounded into a convex curve of a radius as depicted by arrow 29 and forming an inner tip edge 30. The radius 29 is preferably less than half the dimension 21 between the upper and lower surfaces 14, 15 of the retainer 11 and forms an inner tip edge 30 diameter indicated by arrow 34 in Figure 2, which is also preferably less than one-half the diameter, indicated by arrow 35 at the projecting portion 24, as measured at its peak. By such dimensioning it will be seen that the projecting portion 24 and the retainer 11 are positioned a considerable distance from the tip portion 28 which arrangement can be utilized advantageously to place the projecting portion 24 outside a range of the tolerance of an opening to be sealed. The configuration of the projecting portion 24 of the sealing bulb 12 and the adjacent set back portions 25, 26 is a sealing configuration which is generally well known in the art. In such an arrangement, the amount of elastomeric material in the projecting portion 24 is arranged to be slightly less than or equal to the void volumes formed by the adjacent set back portions 25, 26 and the adjacent structure to be sealed, so that the voids are substantially filled when the sealing bulb 12 is deflected or deformed under pressure. Preferably, such deformation of the cross section of the sealing bulb 12 is limited to about 25% to provide an optimum sealing arrangement which will retain its sealing characteristics over a long interval of time. Such deformation of the elastomeric sealing bulb 12 is limited by the rigid retainer structure 11 where the sealing assembly 10 is placed between sealing surfaces. One example of this arrangement is depicted in Figures 4 and 5 wherein sealing assembly 10 is shown positioned on a fastener 40 respectively, in preassembled and assembled conditions. The fastener 40 may be a conventional bolt having a threaded shank 41 and a cap with a flat, annular sealing surface 42. The object to be sealed is, for example, a housing 45, having a flat sealing surface 46 with an opening 48 therein. A threaded stud 49 is depicted rigidly mounted within the housing 45 to receive the fastener 40 and to draw the cap sealing surface 42 into close proximity with the housing sealing surface 46. The seal assembly 10 is shown preassembled on the fastener 40 in Figure 4 with the upper and lower surfaces 14, 15 interposed between the cap sealing surface 42 and the housing surface 46. The seal assembly 10 is fully supported on the fastener 40 solely by the tip portion 28 in engagement with the shank 41. The diameter 34 of the tip edge 30 is smaller than the diameter of the shank 41, providing an interference fit while the radius 29 of the tip portion 28 is sufficiently large to avoid substantial penetration of the tip portion 28 between the threads of the fastener 28 which might affect the positioning of the seal assembly 10. As noted, the seal assembly is then positioned with the projecting portion 24 outwardly of the opening 48 in the housing 45 and beyond any combination of the range of misalignment of the stud 49 with respect to the opening 48, the tolerance of the opening 48 itself, and the tolerance of the shank 41 of the fastener 40. In the enlarged view of Figure 5, the fastener 40 is shown fully threaded into the stud 49 so that the cap sealing surface 42, the retainer 11 and the housing sealing surface 46 are in firm contact, limiting further engagement of the fastener 40 into the stud 49. The fastener 40 may be torqued to any desired level and it will be noted that the retainer 11 prevents any further distortion of the seal assembly 10 beyond that depicted, resulting in a known, controlled distortion thereof, well within its range of sealing capabilities. The sealing bulb 12 is distorted in Figure 5 into engagement with and between the cap sealing surface 42 and the housing sealing surface 46 as well as the upper portionof the stud 49 to provide an enhanced seal. The projecting portion 24 has been deformed into the adjacent set back portions 25, 26 substantially completely filling the voids thereby and creating an expansive sealing area of predeterminable characteristics. In the embodiment of Figure 6, a circular retainer 50 and a sealing bulb 51 of tear drop shape are shown. The sealing bulb 51 includes a projecting portion 52 and adjacent outer and inner set back portions 54, 55, being similarly smoothly contoured and culminating in a tip portion 56, but in this instance, the faces of the inner set back portion 55 converge at a sharper angle. This results in the positioning of the tip portion 56 closer to the projecting portion 52 and modification of the radially extended tear drop shape to a more compact form, however, the same attributes of this embodiment result as described with respect ot that shown in Figures 1-5. Dashed line 58 indicates that the inner periphery of the retainer 11 may be formed as an alternate series of axially extending ribs and grooves to enhance the bond between the sealing bulb 51 and the retainer 50 while still retaining a radially projecting ledge 59. In both embodiments of the invention, the sealing bulb 12, 51 is preferably moulded in place to the respective retainer 11, 50, however, these elements may be formed separately and bonded together by adhesives or by other manufacturing techniques. Preferably, the retainers 11, 50 are metal, however, rigid plastics would serve as well in many instances. The sealing bulbs 12, 51 may be natural rubber or any one of many different forms of synthetic elastomers, such as nitrile, which are well known as sealing materials for devices of this kind.

Claims: 1. A self-centering seal assembly for a fastener, comprising an annular retainer (11, 50) having generally parallel upper and lower surfaces (14, 15) and a central opening therein, and an annular elastomeric seal means (12, 51) disposed in the central opening of the retainer (11, 50) and secured therto, the seal means (12, 51) being of tear drop shape in cross section and comprising a projecting seal portion (24, 52), adjacent inner and outer set back seal portions (25, 54, 26, 55) and an inner circular tip portion (28, 56), the projecting seal portion (24, 52) extending axially outwardly of the retainer (11, 50) beyond the upper and lower surfaces (14, 15) thereof, the inner and outer set back seal portions (25, 54, 26, 55) being set back axially from the upper and lower surfaces (14, 15) of the retainer, the tip portion (28, 56) extending radially inwardly of the inner set back seal portion (26, 55) and terminating in a smoothly rounded edge (30) of convex curvature, the diameter of the tip portion (28, 56) at the edge being les than the diameter of a shank of the fastener with which the seal assembly is to be used, thereby to provide an interference fit thereon for support of the entire seal assembly, and the radius of curvature of the edge (30) being less than one-half the dimension between the upper and lower surfaces (14, 15) of the retainer (11, 50). 2. A seal assembly acording to claim 1, wherein the retainer is a rigid member for load-bearing placement between a surface (46) defining an opening (48) in a device (45) to be sealed and a conforming sealing surface (42) of a fastener (40). 3. A seal assembly according to claim 2, wherein the diameter of the projecting portion (24) of the seal means (12), is greater than the diameter of the opening(48) in the device (45) to be sealed for any range of tolerance in the size of the opening(48). 4. A seal assembly according to any one of claims 1 to 3, wherein the retainer (11) further comprises an inner annular ledge (20, 59) in the retainer opening, the ledge extending beneath the outer set back portion (25, 54) and the projecting portion (24, 52) of the seal means (11). 5. A seal assembly according to any one of claims 1 to 4, wherein the retainer (11, 50) is metal and the seal means (12, 51) is bonded to the retainer (11, 50). 6. A seal asembly according to any one of claims 1 to 4, wherein the seal means (12, 51) is moulded in place to the retainer (11, 50).

Inventors: JELINEK, JERRY G.
Applicants: PARKER HANNIFIN CORPORATION
Application year: 1987
Main classification: F16B43
IPC codes: F16J15, F16B43