Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Headed fastener element with nut – washer – securing means or cap – Sealing-type washer compressed by head
Reexamination Certificate
1999-04-28
2001-09-04
Barrett, Suzanne Dino (Department: 3627)
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Headed fastener element with nut, washer, securing means or cap
Sealing-type washer compressed by head
C411S542000
Reexamination Certificate
active
06283691
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention is directed generally to the fastener arts, but specifically to sealing fasteners having an undercut groove or channel in the underside of a fastener head for accommodating a sealing element, (specifically an o'ring type elastomer) to accomplish sealing engagement with a workpiece having a threaded or unthreaded aperture.
In general sealing fasteners are well known in the art, spurred on by the space age when finding new ways to seal fasteners became a primary focus. Outdated methods such as copper washers, rtv sealant, etc. are still used to seal fasteners in some applications; however, as the sophistication our world increases, the need for reliable methods of sealing fasteners also becomes increasingly more crucial. That is why many of these inferior methods of sealing are gradually being phased out and replaced with more reliable sealing methods. One of the best ways to accomplish this task is to provide a formed groove or channel in a normally flat undersurface of the fastener head to accommodate a sealing element that is held captive in the fastener head, also achieving metal to metal contact with the workpiece and the outer rim of the fastener head. However, all previous designs have not properly calculated the groove in the fastener head. This causes sealing element failure. In static sealing threaded fastener designs, it is crucial that the groove be precisely calculated in depth, volume, angle, and configuration if one hopes to maintain a positive “seal line” between the sealed surfaces. Without a precisely calculated groove design, the sealing element will either compress too much or not compress enough. For example, by using too large a sealing element it will not have enough volumetric space to accommodate it and will, therefore, force the excess volume of the sealing element beyond the groove area, causing the sealing element to extrude and pinch between the screw and the workpiece in a process known as extruding “on the take down face”. Another problem associated with previous designs is a process known as compression set. A sealing element must maintain a continuous “seal line” between the sealed surfaces. The establishment of this “seal line” is a function of groove design and sealing element cross section which determines the proper amount of squeeze (compression) on the sealing element. When a sealing element volume is larger than the area sealed, it causes excessive squeeze on the sealing element. This excessive squeeze causes sealing element deformation and loss of seal integrity, therefore rendering the sealing element ineffective. A third problem with previous designs is a process known as installation damage. As the fastener is being assembled to the workpiece, the excessive compression of the sealing element causes it to stick between the end wall surface of the groove in the fastener head and the workpiece, thereby twisting and deforming the sealing element and/or causing sealing element extrusion as previously mentioned. When too small a sealing element is used, there is not enough compression on the sealing element to maintain a continuous “seal line” between the sealed surfaces rendering its sealing capabilities useless. As an additional matter, it is vital that fasteners of this type be cold formed without removal of material from the shank or head portion of the fastener since an alteration of this type weakens the grain flow structure of the fastener in a high stress area and greatly increases the chances of head separation either before or after the fastener is tightened to its proper torque specification. It is extremely important that these fasteners maintain the ability to withstand the stress involved when tightened to normal torque values. The main reason for a modification of this type is that during cold forming or roll forming threading operations there is generally an external screw thread of up to one and one half thread pitches of incomplete thread between the undersurface of the fastener head to where the thread begins on the fastener shank. This unthreaded portion would normally keep the mating surfaces from achieving adequate metal to metal contact thus preventing a positive seal. However, using a smaller diameter cold forming wire than is normally used when manufacturing similar products of the same diameter affords the flexibility necessary to maintain high quality while forming the fastener to the minimum pitch diameter. This in conjunction with limiting the unthreaded length from the head to a maximum of
1
incomplete thread assures a complete metal to metal engagement with a workpiece having a standard size threaded or unthreaded aperture. This eliminates the need for any alterations to the fastener as mentioned above and thereby maintains fastener integrity.
BRIEF SUMMARY OF THE INVENTION
It therefore an object of this invention to provide a novel fastener having a formed groove or channel precisely calculated in depth, volume, angle and configuration to greatly improve reliability and substantially eliminate the problems associated with prior art design.
A more specific object is to provide a fastener with a formed annular groove or channel having a sealing element completely captive in said groove and maintaining a continuous positive “seal line” between the fastener and the workpiece while maintaining a stable metal to metal contact between fastener head and the workpiece.
Another object is to provide a fastener with a formed groove or channel in the shape of a trapezoid precisely calculated in depth, volume, and angle to achieve a predetermined percentage of compression on the sealing element preventing sealing element deformation and assuring sealing element reliability and reusability.
It is another object to provide a fastener with a formed groove or channel in the shape of a parallelogram precisely calculated in depth, angle, and volume like the trapezoidal shaped groove to assures a continuous positive “seal line” in larger clearance hole applications.
It is another object to manufacture a fastener with a formed groove or channel in such a way that assures complete mating of the fastener with the workpiece in metal to metal contact without materially altering the physical dimensions of the fastener, thereby retaining the shear and tension characteristics of the said fastener. This prevents head separation by maintaining the necessary strength to withstand the stress involved with using standard torque values.
It is a related object to provide a fastener with a formed groove or channel of the highest quality, reliability of material, and performance. Our design has eliminated the guess work by precisely designing the fastener to assure confidence in aerospace applications, but at the same time, keeping the manufacturing costs down to make it affordable for all industries.
It is another object to have a design method that is versatile enough to use in similar applications such as nuts & rivets and special product configurations. This allows the flexibility necessary to design new products quickly and easily without excessive cost to the customer and at the same time assuring fastener sealing reliability.
Toward the fulfillment of these and other objects, according to the present invention an annular groove or channel is formed in the undersurface of a threaded or unthreaded fastener head and combined there with a sealing element (o'ring). The fastener is comprised of a vertically disposed externally threaded elongate shank extending from an enlarged fastener head that contains an annular groove or channel substantially similar to the shape of a trapezoid formed in the essentially flat undersurface of the fastener head and combined there with a sealing element (specifically an o'ring type elastomer). The said fastener shank is designed to enter into complete engagement with a mating workpiece having an internally threaded or unthreaded aperture. When threaded the shank of the fastener has a screw thread profile that defines a minimum major or thread crest diam
Bogatz Diana S.
Bogatz Larry J.
B & B Hardware, Inc.
Barrett Suzanne Dino
Rogers Mark A.
Speed Gary N.
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