Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Having separate expander means – Bulged by axially contracting ends
Reexamination Certificate
2000-04-06
2001-04-10
Wilson, Neill (Department: 3627)
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Having separate expander means
Bulged by axially contracting ends
C411S043000, C411S055000
Reexamination Certificate
active
06213698
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to blind fasteners for securing sheet material together and, in particular to a blind bolt having improved shear, bending and tension values.
Blind fasteners have become particularly useful in securing sheet materials where it is impossible to access the underside of the material. Typically, such fasteners are inserted into an aperture through the material and include a threaded stem for engaging a fastener. Rotation of the stem draws an expansion member into engagement with the underside of the material. Expansion may be aided by a nut body which forces the expansion member radially outward to engage the underside. Upon complete expansion to fully clamp the sheet material, the exterior end of threaded stem may be broken away to eliminate any protrusions from the exterior surface.
Such fasteners have wide application in aircraft and space vehicle assembly. However, the vibrations and sonic fatigue such vehicles are subject to causes loosening of the fasteners.
Previously available blind bolts comprise an externally threaded core bolt which is positioned within a hollow bolt and an internally threaded collar is threaded onto the core bolt. The core bolt also includes a breakneck along its length. The blind bolt is installed by placing the hollow bolt within an aperture in one or more workpieces and rotating the core bolt with respect to the collar. Rotation of the core bolt moves the collar up the hollow bolt causing it to expand radially. Further rotation of the core bolt continues to move the collar towards the head of the hollow bolt until it abuts the underside of the structure. The collar then stops moving axially and begins to expand radially wherein continued rotation causes the collar to reach a maximum diameter and an increasing compressive load on the structure. The resistence increases until it reaches a point when the breakneck on the core bolt shaft fractures in torsional loading.
A problem with previously available blind bolt designs is that they require a slight deformation in the grip area of the hollow bolt in order to captivate or offer rotational resistence to their core bolt design. The purpose of crimping or deformation is to prevent unloosening or separation of the components. This added friction often complicates the range of acceptable breakneck fracture levels. Another problem with currently available blind bolt designs is that if during installation should there be a tensile load sufficient enough to fail the core bolt, the collar would be free to fall from the hollow bolt, thus causing a structural weakness.
Consequently, a need exists for an improved blind bolt design with improved shear bending and tension values and which eliminates the problems associated with previously available blind bolt designs.
SUMMARY OF THE INVENTION
The present invention is directed to a structural blind bolt assembly with improved shear, bending and tension values and which has been designed to overcome the disadvantages of previous blind bolt designs. A blind bolt of the present invention includes a hollow bolt having a head portion, a grip section and a threaded portion located at an end opposite of the head portion. A cylindrical hole or aperture extends through the center of the bolt throughout its entire length. A cross-slot is imbedded into the surface of the head portion to accommodate a driving tool to prevent rotation of the hollow bolt during installation of the blind bolt assembly.
A core bolt having a long cylindrical shaft having a diameter slightly smaller than the internal diameter of the hollow bolt is positioned in the hollow bolt. Positioned on one end of the shaft of the core bolt is a head portion having an external spline drive configuration. Also positioned along the cylindrical shaft away from the head portion is a reduced diameter groove commonly referred to as a “breakneck”. Extending above the breakneck along the cylindrical shaft are two parallel flat surfaces which extend to the end of shaft opposite of the head portion. The parallel flats function as a driver for rotating the core bolt during the assembly process.
The blind bolt assembly also includes a collar having a hollow cylindrical configuration. A portion of the internal diameter of the collar includes a smooth bore for a given length which leads into an internally threaded section. The internal threaded section is designed to mate with the threads on the end of the hollow bolt. Also positioned on the internal diameter of the collar is a splined section which is adjacent the threaded section and opposite the smooth bore section. The spline section has a mating configuration with the spline configuration of the core bolt. The spline section of the collar is slightly longer than the length of the mating splines of the core bolt to captivate the core bolt to the collar during final assembly.
Other objects, features and advantages of the invention will be apparent from the following detailed description taken in connection with the accompanying drawings.
REFERENCES:
patent: 2282711 (1942-05-01), Eklund
patent: 3521521 (1970-07-01), King, Jr. et al.
patent: 3596948 (1971-08-01), Spoehr
patent: 4659271 (1987-04-01), Pratt et al.
patent: 4900205 (1990-02-01), Sadri
Christie Parker & Hale LLP
Fairchild Holding Corp.
Wilson Neill
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