Spark Containment Cap With Insulating Washer for Blind Fasteners
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Solution Overview
Problem
Existing spark containment caps for aircraft fasteners can damage painted surfaces during installation, particularly when installing blind fasteners, as the forming process under high pressure can strip away the insulating paint layer, increasing the risk of electrical arcing.
Innovation Solution
A method involving a spark containment cap with an electrically insulating washer and cap body, where the cap is secured to the workpiece using a sealant and the fastener is tightened to clamp the washer against the workpiece, providing electrical insulation and preventing damage to the paint layer, and the cap body features an air cavity and annular pocket for secure sealing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a spark containment cap is installed over a fastener using high pressure forming, then the cap provides effective spark containment and plasma suppression, but the paint layer on the structure surface is damaged or stripped away
Solution Approach 1:
The patent applies a protective coating to the structure surface before installing the spark containment cap. This preliminary protective layer prevents the paint from being damaged during the high-pressure forming process, while still allowing the cap to be installed effectively. The protective coating is applied in advance to the area where the cap will be formed, ensuring that when high pressure is applied to form the cap, the underlying paint layer remains intact.
2Ease of operation
If access is provided to only one side of the panel for blind fastener installation, then the installation process is simplified, but it becomes more challenging to install the cap without damaging the paint layer
Solution Approach 1:
The protective coating is applied to the structure surface before the blind fastener and cap installation process. This allows the entire installation to be performed from one side without requiring access to both sides of the panel, while the pre-applied protective coating ensures the paint layer is not damaged during the forming process.
Solution Approach 2:
The protective coating acts as an intermediary layer between the high-pressure forming process and the paint layer. It mediates the interaction by absorbing or distributing the pressure in a way that protects the paint from direct contact with the high-pressure forming tool, enabling one-sided installation without paint damage.
3Strength
If the paint layer is stripped away from the panel surface, then the cap can be installed securely, but the panel becomes more susceptible to electrical arcing
Solution Approach 1:
The protective coating is applied before cap installation, ensuring the paint layer remains intact throughout the process. This eliminates the need to strip the paint for secure cap installation, as the protective coating provides the necessary bonding surface while preserving the electrical insulation properties of the original paint layer.
Solution Approach 2:
The protective coating serves as an intermediary bonding surface between the cap and the structure. It provides adequate adhesion for secure cap installation while allowing the underlying paint layer to remain intact, thus maintaining both installation security and electrical arcing resistance.
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 solution effectively prevents electrical arcing by maintaining the insulating paint layer and ensuring secure, damage-free installation of spark containment caps, even for blind fasteners, while providing dual protection against voltage sparking and plasma containment during lightning strikes.
Implementation Method 1
the washer is electrically insulating
Implementation Method 2
The cap is sealed to the structure by a curable sealant provided around an opening to the sealed cavity
Implementation Method 3
A volume of gas is enclosed in the sealed cavity around the fastener. The gas provides spark suppression, and containment of sparking and plasma outgassing
Data Source
Figure 1~2
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Figure 5
AI summary
The present invention relates to a method of joining a first workpiece to a second workpiece. The aforementioned method involves securing a spark containment cap to the first workpiece, the cap comprising an electrically insulating washer and a cap body defining an air cavity. Once the cap has been secured, a tail of a fastener is inserted into the air cavity through the second workpiece, the first workpiece and the washer. Upon tightening the fastener, the tail of the fastener urges the washer against the first workpiece and the first and second workpiece are thereby clamped between the washer and a head of the fastener so as to form a joint. Advantageously, it has been found that forming a joint in this manner can help to better protect the joint from the effects of electrical arcing.