Injectable Nut Cap for Lightning Strike Protection
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Solution Overview
Problem
Existing fastener caps fail to provide a reliable and quick seal around fasteners to prevent sparking and out-gassing during lightning strikes, and they are not suitable for use with quick-cure sealing materials due to air gaps and leakage issues.
Innovation Solution
A cap design featuring an inner and outer cap member with an annular sealing cavity, a sealing material inlet for injecting curable sealing material, and a flow restriction feature to ensure even distribution, providing a strong and reliable bond while minimizing the risk of air gaps and leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sealing material is applied manually before cap installation, then the seal is formed, but air gaps and leakage occur compromising seal reliability
Solution Approach 1:
The sealing cavity is prepared in advance during cap manufacturing, and the sealing material injection system is pre-positioned. The cap is installed on the fastener first, then sealing material is injected through the inlet into the pre-formed cavity, ensuring proper distribution and eliminating air gaps through controlled injection pressure and flow paths.
Solution Approach 2:
A sealing material injection device uses fluid pressure to inject curable sealing material through the sealing material inlet into the annular sealing cavity. The hydraulic/pneumatic pressure ensures complete filling of the cavity and proper bonding between the cap and structure without manual application errors.
2Productivity
If quick-cure sealing material is used, then bonding speed increases, but handling time decreases making application difficult
Solution Approach 1:
The cap with sealing cavity and inlet is manufactured and prepared in advance. The fastener assembly is completed first, then the cap is installed, and only then is the quick-cure sealing material injected. This sequence ensures the material is applied at the optimal moment when the structure is ready, maximizing the brief working life of quick-cure materials.
Solution Approach 2:
The sealing material injection device can mix and apply the sealing material automatically on-demand. The system self-regulates the injection process, eliminating manual mixing and application steps that would be difficult with quick-cure materials, while still achieving rapid bonding.
3Ease of manufacture
If cap is installed without sealed cavity, then installation is simpler, but spark suppression and out-gassing containment fail
Solution Approach 1:
The cap is divided into functional segments: the outer cap structure provides mechanical protection and defines the sealed cavity shape, while the injected sealing material provides the actual seal and bonding. This segmentation allows the cavity structure to be simple and easy to install, while the sealing function is added separately through injection, ensuring both simplicity and effectiveness.
Solution Approach 2:
The sealing material acts as an intermediary substance that fills the annular sealing cavity and creates the actual seal between the cap and structure. This intermediary provides the necessary sealing properties for spark suppression and out-gassing containment, while the cap structure itself remains relatively simple for easy installation.
4Loss of time
If sealing material is injected after cap positioning, then working life of material is maximized, but injection complexity increases
Solution Approach 1:
The sealing cavity and inlet are pre-formed during cap manufacturing. The cap is positioned on the fastener first, establishing the injection pathway in advance. This preliminary preparation ensures that when the sealing material is injected, the pathway is already optimized, reducing the complexity of the injection process while maximizing material working life.
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
The cap design achieves a stable and quick seal, capable of withstanding accidental knocks and preventing fuel leakage, while ensuring a secure bond between the cap and structure, effectively containing out-gassing and sparking events during lightning strikes.
Implementation Method 1
The sealing material can be injected after positioning of the cap onto an end of a fastener... The sealing material can be mixed in the sealing material injection device on application... Quick cure sealing materials have the advantage of providing a stable bond very quickly.
Implementation Method 2
A volume of gas is enclosed by a cap around the fastener. The gas provides spark suppression for arcing that may occur between the composite structure and the metal fastener during any lightning strike.
Data Source
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AI summary
The present invention proposes a cap for forming a sealed cavity around one end of a fastener to thereby contain out-gassing and sparking events in the event of a lightning strike to the fastener. The invention also proposes a joint comprising such a cap, and a kit of parts and method for installing such a cap. A cap according to the invention comprises: an inner cap member having an annular base terminating at an edge which surrounds an opening into an air cavity for enclosing the one end of a fastener; and an outer cap member having an annular skirt or flange which extends radially outwardly away from the annular base, the annular skirt or flange and annular base between them defining an annular sealing cavity. The cap also comprises a sealing material inlet comprising an opening in the outer cap member that is in fluid communication with the annular sealing cavity, the opening being arranged to interconnect with a sealing material injection device to provide a flow of curable sealing material from the sealing material inlet into the annular sealing cavity.