Tools – Wrench – screwdriver – or driver therefor – Having work engaging and force exerting portion inserted...
Reexamination Certificate
1999-04-28
2001-05-29
Hail, III, Joseph J. (Department: 3723)
Tools
Wrench, screwdriver, or driver therefor
Having work engaging and force exerting portion inserted...
C081S460000
Reexamination Certificate
active
06237450
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to fastener systems, and more particularly, to a fastener system comprising a threaded fastener having a spline-drive recess for receiving a mating tool during application of a nut on the fastener.
BACKGROUND OF THE INVENTION
Threaded fasteners typically consist of a nut and a bolt. The nut has an internal thread that screws onto an external thread of the bolt. Wrenching surfaces on the nut and/or bolt accept wrenches that tightly join the fasteners and one or more workpieces together. The fastener secures workpieces together to form a joint by compressive engagement between the nut on one side of the workpiece, and the head of the bolt on the opposite side.
U.S. Pat. No. 4,260,005 describes a particular type of threaded fastener having a self-locking nut that uses external lobes to accept a driver having a generally triangular or deltoid shaped socket to tighten the nut on a cooperating pin. The teachings of this patent necessary for an understanding of the present invention are incorporated herein by this reference. The nut is preferably used with a pin having a plurality of grooves or flutes extending longitudinally along the pin. Once a predetermined axial load exists in the joint being made, the lobes plastically deform and the driver can no longer turn the nut. Deformation of the lobes displaces material positioned radially inward from them into the flutes of the cooperating pin to produce a mechanical thread lock. The thread lock results from material deforming into and across the pin flutes.
There are numerous applications where it is advantageous to provide a fastener which may be held against rotation from its leading edge while a nut is torqued upon the pin. For example, as is often the case in the aerospace industry, there are many requirements for “blind” bolt applications, where the head of the bolt cannot be conveniently reached, or is perhaps altogether unreachable for wrenching purposes. For these applications, a holding bit or tool is often provided with the driver. The bit engages a recess in the threaded end of the pin to facilitate application of the nut by the driver. The bit remains stationary, thus holding the pin against rotation, while the driver turns to torque the nut. U.S. Pat. Nos. 4,583,483 and 5,044,225 describe the use of such a bit or tool in connection with power tools developed for the rapid installation of fasteners.
Generally, a hexagonal recess is provided in the threaded end of bolts for receiving a matching hexagonal bit. Existing hexagonal bits, however, have experienced unacceptable failure rates when used during installation of bolts in certain wet-sealant applications. In these applications, sealant often surrounds the head of the bolt and is present between the bolt and the workpiece. As a result, all of the torque required to apply the nut to the pin is transferred directly to the bit, rather than being partially absorbed by the friction normally present between the head of the bolt and the workpiece. When the above induced torque exceeds the strength of the hexagonal bit, application of the nut becomes impossible.
Initial attempts at solving this problem included varying the cross-section and material of the hexagonal bit. However, these attempts have been largely unsuccessful due to radial loading for hexagonal recesses. Spline keys and drivers are known and have been used in many applications. When used in connection with fasteners, standard spline recesses and wrenching tools result in the splines in the fastener being sheared by the tool. Torque is transmitted from the mating spline of the tool to the spline of the recess. When resistance is achieved after seating the fastener, additional torquing can result in the shearing of the splined socket. Shearing results because standard spline design results in the wrenching drive tool being fabricated from a material that is usually stronger than the material of the fastener. Standard configurations results in the spline surface area of the wrenching tool being 7.9% to 38.5% greater than the spline surface area of the fastener socket's spline surface area. This coupled with the tool having a greater shear strength than the fastener's socket results in an unacceptable failure rate.
Consequently, a need exists for a spline drive socket/tool arrangement for fasteners that prevent unacceptable failure.
SUMMARY OF THE INVENTION
The present invention, therefore, provides an improved fastener system that minimizes the disadvantages identified with respect to the prior art fastener systems described above. The fastener system according to the present invention generally includes a threaded pin having a recess in an end face on the threaded portion of the pin for receiving a tool when a nut is torqued onto the pin. In a presently preferred embodiment, the recess comprises a newly designed spline socket extending into the end face. Additionally the tool comprises a plurality of mating splines extending from at least an end of the tool configured to match the recess such that the tool may be received in the recess to prevent the pin from rotating when the nut is torqued onto the pin.
The pin preferably includes a plurality of flutes extending in an axial direction across the threaded portion of the pin. Preferably, the nut includes at least one external, axially extending lobe. As a result, when the nut is torqued onto the pin, some of the material positioned radially inward from the lobe is displaced into the flutes of the pin.
In a presently preferred embodiment, the recess is a spline recess comprising six splines extending around the circumference of the recess. To engage the recess during torquing of the nut onto the pin, the tool is formed as a shaft with six splines extending around the circumference of the shaft and sized to cooperate with the recess splines. The tool prevents the pin of the fastener from rotating during application of the nut. The spline widths and shear areas of both the recess and the tool are formed so that torsional loading is equal for both the tool and the recess. An advantage of this design is that the strength of the recess is significantly enhanced which is particularly important in aerospace fasteners. This result is accomplished by forming the width of the splines to be larger in the socket than on the tool. By increasing the spline width on the recess (which is made from lower strength material) the shear area is increased. The shear area of the splines of the driving tool (which is made from higher strength material) is reduced so that it is in close balance strengthwise with that of the socket. The net result is a substantial increase in torsional performance since the tool will not overpower the socket.
The tool has also been designed to include a curved minor diameter. Typically the spline drivers included a minor diameter with a machined flat surface which results in loss of valuable torsional strength because of the removed material.
REFERENCES:
patent: 1075710 (1913-10-01), Goodwin
patent: 3285119 (1966-11-01), Dean et al.
patent: 3584667 (1971-06-01), Reiland
patent: 4637764 (1987-01-01), Imai
patent: 4809569 (1989-03-01), Erb
patent: 5088869 (1992-02-01), Greenslade
patent: 5279190 (1994-01-01), Goss et al.
patent: 5435680 (1995-07-01), Schuster
patent: 5549431 (1996-08-01), Royle
patent: 5553983 (1996-09-01), Shinjo
Christie Parker & Hale LLP
Fairchild Holding Corp.
Hail III Joseph J.
Ojini Anthony
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