Blind fastener

Abstract

A blind fastener assembly includes, in one embodiment a pin, an expander and a sleeve. The pin and expander may include, in one configuration, mating threads for drawing the sleeve axially over the expander toward the blind side of a workpiece, or the pin may be a pull-type wherein the portion of the pin opposite from the blind side end has pull grooves which are adapted to be gripped by a conventional pull gun. The sleeve is a tubular member with a portion of its length having a normal radial thickness and a portion having reduced radial thickness comprising a reduced outer diameter over a portion of its axial length and a counter-bore along the same axial length adjacent one end of the sleeve. The expander extends through aligned holes in the workpieces and has a tapered nose surface proximate the reduced thickness portion of the sleeve. When an axial force is exerted on the pin, the reduced thickness portion of the sleeve is forced over the tapered nose surface on the expander toward the blind side of the workpiece and is expanded in diameter. The tapered surface of the expander also deforms and expands the inner diameter of the normal thickness portion of the sleeve where it meets the counter-bore, and when the leading edge of the sleeve contacts the blindside workpiece surface, an optimum shaped, maximum diameter bulb forms in the reduced thickness portion of the sleeve against the blindside workpiece surface. When the bulb is fully formed, a reduced diameter breakneck portion of the pin fractures at a predetermined torque or load, leaving a properly tensioned joint.