Sealed Washer Assembly for Lightning Fastener Arcing Containment
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Solution Overview
Problem
Metallic fasteners in composite structures, such as those in aircraft, cause sparking and arcing during lightning strikes, leading to material breakdown and potential ignition of escaped hot gases or particles, which existing solutions like pre-molded caps or conductive coatings are costly and labor-intensive to mitigate.
Innovation Solution
A washer assembly comprising a metallic washer with a high-strength polymer seal, featuring a lower seal portion engaging the fastener and an upper seal portion engaging a counter-bored nut, to reduce the escape of energized particles and prevent arcing, using materials like engineering thermoplastics and dielectric coatings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pre-molded caps are used to guard fastener heads, nuts, and washers, then protection against sparking and arcing is improved, but installation cost and labor time increase substantially
Solution Approach 1:
The patent extracts the protective function from separate pre-molded caps and integrates it into a polymer seal that is already part of the fastener assembly. The polymer seal is molded directly onto the fastener body, eliminating the need for separate protective caps and their associated installation steps.
Solution Approach 2:
The patent combines the protective function with the fastener structure itself by integrating the polymer seal directly onto the fastener body. This merging of functions eliminates separate components and reduces assembly complexity while maintaining protection against sparking and arcing.
2Reliability
If conductive coatings and interference fits are used to reduce contact resistance, then protection against sparking is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent changes the electrical parameter of the fastener interface by using a polymer seal with appropriate electrical properties. Instead of adding conductive coatings to metallic surfaces, the solution uses an inherently insulating polymer material that provides the necessary electrical isolation and contact resistance management.
Solution Approach 2:
The patent employs composite material construction with the polymer seal providing both mechanical sealing and electrical isolation functions. The polymer material combines structural integrity with appropriate electrical properties, eliminating the need for separate conductive coatings while managing contact resistance.
3Strength
If metallic fasteners are used to join structures, then structural strength is improved, but sparking and arcing occur during lightning strikes
Solution Approach 1:
The patent introduces a polymer seal as an intermediary material between metallic fastener components. This polymer layer acts as a mediator that maintains the structural connection while preventing direct metal-to-metal contact that would generate sparks and arcs during lightning strikes.
Solution Approach 2:
The patent uses composite material construction combining metallic fastener components with a polymer seal. This composite approach maintains the structural strength provided by metal while incorporating the insulating properties of polymer to eliminate sparking and arcing hazards.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively seals voids between fasteners and structures, reducing arcing and escape of energized particles, thereby protecting against lightning-induced damage and simplifying installation with a cost-effective and efficient solution.
Implementation Method 1
The lower seal portion is configured to engage, at the counter-bore, a fastener to form a seal to reduce escape of energized particles. The upper seal portion is configured to engage a counter-bore of a counter-bored nut to form a seal inside the counter-bored nut to reduce escape of energized particles.
Implementation Method 2
In certain embodiments, a dielectric coating is applied to the metallic washer to further reduce potential for arcing, sparking, or other electromagnetic effects (EME).
Implementation Method 3
application of torque to the counter-bored nut compresses the lower seal portion against a surface of the conjoined structures and around the sleeve at the counter-bore of the polymer seal, and to compress the upper seal portion of the polymer seal into a counter-bore of the counter-bored nut and around the threaded end of the sleeved fastener
Data Source
AI summary
A washer assembly including a metallic washer and a polymer seal. The metallic washer defines a cylindrical void and an axis therethrough. The polymer seal is attached to the metallic washer and is positioned radially inward thereof. The polymer seal includes a lower seal portion positioned at least partially within the cylindrical void and defining a counter-bore, and an upper seal portion extending axially from the lower seal portion. The lower seal portion is configured to engage, at the counter-bore, a fastener to form a seal to reduce escape of energized particles. The upper seal portion is configured to engage a counter-bore of a counter-bored nut to form a seal inside the counter-bored nut to reduce escape of energized particles.