Conductive Fastener Assembly Counterbore Gap Design
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Solution Overview
Problem
In aerospace applications, sleeved fasteners often experience incidental electrical contact with other structural elements due to the lack of a reliable conductive interface between the fastener and sleeve, despite lubrication efforts to enhance conductivity.
Innovation Solution
A conductive sleeved fastener assembly is designed with a counterbore in the nut to maintain radial and axial gaps between the nut and fastener sleeve, along with a countersink configuration and the omission of lubricant from the interface, to prevent unwanted electrical contact while ensuring conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If lubricant is applied to the fastener shank to enable installation, then the fastener can be inserted into the sleeve, but the lubricant electrically insulates the fastener from the sleeve
Solution Approach 1:
The patent removes the lubricant from the interface between the fastener head and sleeve flare, extracting the insulating element from the critical electrical contact zone. This allows the fastener and sleeve to maintain direct electrical contact while the lubricant is still present on the shank for installation purposes.
Solution Approach 2:
The patent applies different lubrication conditions to different portions of the fastener assembly. The shank retains lubricant for installation, while the interface between the fastener head and sleeve flare is kept free of lubricant to ensure electrical conductivity. This localized differentiation resolves the contradiction between ease of installation and electrical reliability.
2Reliability
If the fastener and sleeve are assembled tightly to ensure conductivity, then electrical contact is achieved, but incidental contact with other structural elements occurs
Solution Approach 1:
The patent introduces a counterbore in the nut as an intermediary feature that creates controlled gaps between the nut and surrounding structural elements. These gaps act as electrical insulators, preventing arcing to adjacent structures while the fastener-sleeve interface maintains direct contact for conductivity.
Solution Approach 2:
The patent segments the electrical pathway by creating distinct zones: a conductive zone at the fastener-sleeve interface and insulating zones at the nut-structure interfaces through the counterbore gaps. This segmentation allows simultaneous achievement of desired conductivity and prevention of harmful electrical contact.
3Ease of operation
If multiple lubricants are applied to enhance installation, then the fastener can be installed reliably, but the electrical insulation increases
Solution Approach 1:
The patent applies lubricants selectively to specific regions - multiple lubricants can be applied to the shank for installation reliability, but the interface between the fastener head and sleeve flare is maintained as a lubricant-free zone to preserve electrical conductivity. This localized quality differentiation resolves the contradiction.
Data Source
AI summary
A conductive fastener assembly, system, and method are described. The fastener assembly includes a nut having a counterbore formed therein. The counterbore is formed to maintain a sufficient gap between the nut and the protruding end of a fastener sleeve. The nut with the counterbore improves the conductive fastener system such that the need for a solid copper grid and a cap seal is reduced or eliminated.