US 4,408,936 AGranted

Torque-limited threaded locking fastener, and method for setting the same

AssigneeHi-Shear Corporation

InventorHerman L. Williamson

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Abstract

A torque limited threaded locking fastener and a method for setting it to form an assembly. The fastener comprises an externally threaded shank and an internally threaded collar. At least one convolution of the threads on the shank is non-circular. The collar has a nut section and a drive section. The drive section is shaped to be engaged by a driver. Between these sections there is formed a shear section having the least torque resistance of the sections. The shear section fractures when a predetermined torque is exerted between the two sections. The nut section has an internal thread engageable to the shank thread, and an external rib engageable by a swaging tool. The swaging tool radially inwardly deforms and displaces the rib so as to displace nut section material at the non-circular convolution whereby to lock the nut to the shank after, but only after, the drive section is torqued off. The rib is proportioned and arranged so that the swaging of the rib to a lesser radial dimension does not change the torque level which was applied when the drive section was torqued off.

Claims11

Dependent claims

A torque-limited threaded locking fastener comprising:

a shank member having an axis, a head adjacent to one end, and an external thread adjacent to the other end thereof, said thread having a plurality of convolutions, at least one of said convolutions when viewed axially being non-circular;
a collar member comprising a nut section having an axially extending internal thread and at least one integral external rib projecting beyond the outer wall of said nut section and so disposed and arranged as to be axially aligned with the non-circular thread when said nut is fully engaged to said shank member, a drive section having an internal passage aligned with and larger than said internal thread, and a non-circular driver-engaging surface to receive a driver for applying torque to said drive section, and a shear section joining said nut section and drive section, said shear section having the least resistance to torque of said sections whereby to fracture when a predetermined torque is applied to said drive section;
said rib being so proportioned and arranged that when a swaging tool is applied to displace the rib material radially inward thereby to displace material of which the nut section is made into said non-circular thread to lock said nut section to said thread after it does so, but only after, the drive section has torqued off, and without increasing the torque which existed when said shear section fractured;
the material of said rib and of said nut section being sufficiently ductile to enable said rib to be swaged inwardly.

1 more element

Dependencies are inferred from the claim text.