Injectable Cap with Snap-Fit Sealing for Fastener Spark Containment
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Solution Overview
Problem
Existing methods for providing spark suppression around fasteners, such as those described in EP-A-0334011, are inadequate in ensuring a reliable and quick seal to prevent fuel leakage and contain out-gassing and sparking during lightning strikes, particularly in aircraft applications where composite structures and metal fasteners are involved.
Innovation Solution
A cap system comprising an inner and outer cap member forming a snap-fit joint with an annular sealing cavity, allowing for the injection and curing of sealing material within the cavity to create a strong, reliable bond and seal, utilizing a curable sealing material like epoxy-based adhesives or polysulphide sealants to ensure a secure and rapid seal around fasteners.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cap system with snap-fit joint is used to enclose the fastener end, then the reliability of spark suppression is improved, but the device complexity increases due to multiple cap members and locking features
Solution Approach 1:
The cap is divided into an inner cap member and an outer cap member that can be assembled separately. The inner cap member encloses the fastener end while the outer cap member provides additional sealing and protection. This segmentation allows for more reliable spark suppression by creating a multi-layer enclosure system.
Solution Approach 2:
The inner cap member is nested within the outer cap member, with the inner cap member fitting into the outer cap member's internal cavity. This nested structure provides reliable spark suppression by creating concentric protective layers around the fastener end, ensuring that sparks are contained even if one layer fails.
2Reliability
If curable sealing material is injected into the annular sealing cavity, then the seal reliability is improved, but the manufacturing complexity increases due to injection channels and curing process
Solution Approach 1:
The sealing material is injected into the annular sealing cavity before the cap is fully assembled and installed on the fastener. This preliminary action allows the sealing material to be properly distributed and cured in place, ensuring reliable sealing while simplifying the final installation process.
Solution Approach 2:
A sealing material injection device uses hydraulic or pneumatic pressure to inject curable sealing material through injection channels into the annular sealing cavity. This ensures uniform distribution of the sealing material and complete filling of the cavity, achieving reliable seals.
3Strength
If multiple locking features are provided between cap members, then the joint strength is improved, but the device complexity increases due to multiple snap-fit joints
Solution Approach 1:
The locking features between the inner and outer cap members are designed with asymmetrical geometries, including angled ramps and undercuts. This asymmetry creates strong mechanical interlocking that resists separation forces from multiple directions, providing high joint strength.
Solution Approach 2:
The locking features incorporate curved surfaces and rounded transitions instead of sharp angles. This curvature distributes stress more evenly across the joint interface, increasing the overall strength and durability of the connection between cap members.
4Manufacturing precision
If flow channels are provided between snap-fit joints, then the sealing material distribution is improved, but the device complexity increases due to additional internal channels
Solution Approach 1:
Flow channels are strategically positioned in specific locations within the cap structure, particularly in regions where sealing material needs to be distributed. The channels are localized to critical areas rather than being distributed uniformly throughout the entire cap, achieving good material distribution while minimizing added complexity.
Solution Approach 2:
The flow channels are designed to extend in multiple dimensions within the cap structure, creating a three-dimensional distribution network. This multi-dimensional channel arrangement ensures that sealing material reaches all areas of the annular sealing cavity uniformly, including hard-to-reach regions.
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 system effectively prevents fuel leakage and contains out-gassing and sparking events by providing a strong, reliable seal around fasteners, even under accidental knocks, with the sealing material curing quickly to withstand operational stresses and ensuring a void-free bond, thus enhancing the safety and integrity of aircraft structures.
Implementation Method 1
injecting curable sealing material into the annular sealing cavity via the sealing material inlet so that the curable sealing material contacts the structure; and curing the curable sealing material to seal the air cavity
Implementation Method 2
The outer cap member has an inner surface formed with a first locking feature, and the inner cap member has an outer surface formed with a second locking feature which forms a snap-fit joint with the first locking feature
Data Source
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. The outer cap member has an inner surface formed with a first locking feature, and the inner cap member has an outer surface formed with a second locking feature which forms a snap-fit joint with the first locking feature.