BLIND FASTENER

摘要

BLIND FASTENER WARREN F. DAHL AND RICHARD C. LANDT A blind fastener assembly included, 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. In another embodiment of the invention, the blind fastener comprises a pin and an integral sleeve/expander combination which is designed to fracture at the expander/sleeve interface and form an optimum diameter bulb upon axial movement of the pin. The formed bulb advances along a tapered nose portion of the expander and bears against the blind side of the workpiece clamping the joint together. In yet another embodiment of the invention, a grip accommodating feature is provided by a second varying reduced thickness portion in the sleeve, located in the normal thickness portion between the first reduced thickness portion and the blindside end of the sleeve adjacent a pulling head on the pin. Once the bulb is optimally formed and bears against the blind side of the workpiece, additional axial force exerted on the pin causes a second outwardly bulbed portion to form on the sleeve at the second reduced thickness portion to accommodate variations in workpiece thickness in the joint. The diameter of the second bulb is dependent on the overall joint thickness, with a larger diameter bulb forming for a maximum joint thickness and a smaller diameter bulb being formed for a minimum joint thickness.