Insulating Spark Containment Cap for Paint-Safe Fastener Installation
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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 the paint, leaving the panel more susceptible to 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, preventing damage to the paint and providing electrical insulation.
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 spark containment and sealing, but the paint layer on the structure surface is damaged or stripped
Solution Approach 1:
The patent applies preliminary action by pre-installing the electrically insulating washer onto the fastener shaft before the cap installation process. This ensures the washer is already in position to protect the paint surface during the high-pressure forming operation, preventing the harmful effect of paint stripping while maintaining spark containment functionality.
2Reliability
If an electrically insulating washer is added to the fastener assembly, then electrical insulation and paint protection are improved, but the device complexity increases
Solution Approach 1:
The electrically insulating washer serves multiple functions simultaneously: it provides electrical insulation between the conductive fastener and the composite structure, protects the paint layer during installation, and maintains the sealing interface within the cap assembly. This multi-functionality reduces the need for separate components, thereby limiting the increase in device complexity.
3Manufacturing precision
If the washer is pre-installed on the fastener tail, then alignment accuracy is improved and installation is easier, but the manufacturing process becomes more complex
Solution Approach 1:
The washer is pre-installed onto the fastener tail in a controlled manufacturing environment where precise alignment can be achieved. This preliminary action ensures that during final assembly, the washer is already correctly positioned, improving alignment accuracy and reducing the skill level required for installation, thereby offsetting the increased manufacturing complexity.
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 secures the cap without damaging the paint, provides electrical insulation to prevent arcing, and allows for easy installation of blind fasteners by reducing alignment errors and workload on assembly line workers.
Implementation Method 1
The cap is sealed to the structure by a curable sealant provided around an opening to the sealed cavity
Implementation Method 2
the washer is electrically insulating
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
AI summary
A method of joining a first workpiece to a second workpiece is disclosed including 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.