Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Headed fastener element with nut – washer – securing means or cap – Headed bolt or screw with threads and complementary nut
Reexamination Certificate
1999-11-02
2001-01-09
Wilson, Neill (Department: 3627)
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Headed fastener element with nut, washer, securing means or cap
Headed bolt or screw with threads and complementary nut
C411S180000, C411S424000, C411S903000, C411S908000
Reexamination Certificate
active
06171041
ABSTRACT:
TECHNICAL FIELD
This invention relates to the technology of applying screw fasteners to plastic bosses, and more particularly to metal screws that are self-tapping to create threads in plastic bosses.
BACKGROUND OF THE INVENTION
Plastic components, particularly automotive dashboards or trim assemblies having bosses that receive self-tapping metal screws to apply a clamping load to a support that secures the component in position. In virgin plastic bosses which have the screws applied for the first time, the interfacial friction between the screw threads and the tapped grooves of the plastic boss sometimes may not be sufficiently high to prevent loosening of the screws over long periods of vibration.
More significantly, when the screws are improperly torqued during installation, the tapped grooves within the plastic may be stripped so that there is little holding power for providing the desired clamping load. Since the plastic component usually has bosses which are tubular with a wall thickness generally in the range of 1.5-2.0 mm, there is little mass left to either install a larger self-tapping screw that would create new and larger thread grooves, or install an expandable anchor insert in the stripped hole with sufficient boss stiffness to promote gripping by the screw.
SUMMARY OF THE INVENTION
A primary object of this invention is to provide an improved screw retaining mechanism that creates a threaded interference fit between the screw and receiving object.
It is also an object to provide a method to more effectively secure a screw in a plastic object, particularly objects having plastic bosses of controlled wall thickness that risk having their holes stripped of threaded grooves.
The invention, in a first aspect, is an article of manufacture in the form of a screw retaining mechanism for assembling a pair of objects. Such mechanism comprises: (a) a tubular wall of given thickness defining a plastic boss on one object; (b) a screw having a threaded shank secured in the boss by grooves complementary to the screw threads, the screw having a head clamping the other object to the first object; and (c) a heat shrunk sheath residing on the screw threads and shank to act as a threaded interference fit film between the screw threads and the boss grooves, the sheath having metal wires weavingly embedded into the sheath to extend at least generally parallel to the axis of the tubular wall.
The invention, in a second aspect, is a method of securing a screw in a plastic object, comprising: (a) providing the plastic object with an integral tubular wall to define a plastic boss, the tubular wall having an interior diameter; (b) providing a metallic screw having a shank with threads extending from the shank to define a thread diameter greater than the tubular wall interior diameter; (c) heat shrinking a polyethylene film containing moldable, hard wires onto said screw shank and threads; and (d) torquing the screw shank containing the heat shrunk film into the boss to create a threaded interference fit with the tubular wall whereby the screw is ready to apply a clamping load.
REFERENCES:
patent: 3477337 (1969-11-01), Racki
patent: 3687493 (1972-08-01), Lock et al.
patent: 4154276 (1979-05-01), Wesner
patent: 4928451 (1990-05-01), Reigstad et al.
patent: 4987714 (1991-01-01), Lemke
patent: 5133630 (1992-07-01), Hughes
Bazinski Stephen Norman
Dapoz Albert James
Shelton Larry I.
Visteon Global Technologies Inc.
Wilson Neill
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