Aircraft Cable Arc Resistance via Heat-Treated Mica and PTFE Layers
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Solution Overview
Problem
Aircraft electrical cables fail to meet the standard for resistance to electric arc propagation as per NF EN 3475-604 and EN 2346-005 standards, despite satisfying other safety criteria such as fire resistance and operational continuity at high temperatures.
Innovation Solution
The electrical cable design includes an electrical conductor wrapped with a mica ribbon layer treated at 400°C, a polyimide ribbon layer, and a PTFE ribbon layer, with a specific ratio of PTFE to polymeric binder and polyimide masses, optimized for arc resistance and fire safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cable structure with mica ribbon, polyimide layer, and PTFE layer is used to meet fire resistance and operational continuity requirements, then fire resistance and high-temperature operation are improved, but resistance to electric arc propagation is insufficient
Solution Approach 1:
The patent applies parameter changes by heat-treating the mica ribbon layer at temperatures of at least 400°C for specific durations. This thermal treatment modifies the physical and chemical properties of the mica ribbon, transforming it from a state that does not resist electric arc propagation to one that provides effective protection. The heat treatment activates the mica particles and optimizes their arrangement, enabling the cable to achieve over 75% resistance to dry electric arc propagation while maintaining its fire resistance properties.
Solution Approach 2:
The patent utilizes a composite structure consisting of multiple layers with different materials: mica ribbon (with polymeric binder), polyimide ribbon, and PTFE ribbon. Each material contributes specific properties - the mica provides heat resistance and arc propagation resistance after treatment, the polyimide provides thermal stability and mechanical strength, and the PTFE provides electrical insulation and chemical resistance. The synergistic combination of these composite materials achieves both fire resistance and electric arc propagation resistance that individual materials cannot provide alone.
2Object-affected harmful factors
If the cable insulation is strengthened to resist electric arc propagation, then arc resistance is improved, but cable weight and diameter increase
Solution Approach 1:
The patent applies preliminary action by performing heat treatment on the mica ribbon layer during the manufacturing process, before the cable is installed and put into service. This pre-treatment ensures that the mica particles are activated and optimally positioned to resist electric arc propagation from the outset. By preparing the protective layer in advance rather than relying on thicker insulation, the cable achieves arc resistance without excessive weight gain.
Solution Approach 2:
The heat treatment parameter (temperature of at least 400°C and specific duration) transforms the mica ribbon's properties, enabling it to provide effective arc propagation resistance with minimal thickness. This parameter change allows the use of a thin but highly effective protective layer rather than a thick layer of conventional insulation material, thereby minimizing the increase in cable weight and diameter while achieving the required arc resistance performance.
3Object-affected harmful factors
If the cable insulation is strengthened to resist electric arc propagation, then arc resistance is improved, but cable diameter increases
Solution Approach 1:
The heat treatment of the mica ribbon layer is performed as a preliminary step during manufacturing, activating the protective properties of the mica particles before the cable is assembled and installed. This preliminary activation allows the use of a compact insulation structure that provides effective arc resistance without requiring excessive diameter, as the treated mica layer achieves maximum protective efficiency at minimal thickness.
Solution Approach 2:
The multi-layer composite structure (mica ribbon, polyimide, PTFE) provides electric arc propagation resistance through the synergistic properties of its components rather than through increased overall thickness. The mica ribbon (activated by heat treatment) provides arc resistance, the polyimide provides thermal and mechanical support, and the PTFE provides electrical insulation. This composite approach achieves effective protection with minimal diameter increase compared to using a single thick insulation layer.
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 cable achieves over 75% resistance to dry electric arc propagation and maintains excellent fire resistance and electrical continuity while minimizing weight and diameter, adhering to stringent aeronautical standards.
Implementation Method 1
The first layer is heat treated in a first step at a temperature of at least 400°C for a duration t which is greater than at least 30% than a duration t0 necessary for degassing the first layer
Implementation Method 2
a duration t which is greater than at least 30% than a duration t0 necessary for degassing the first layer
Implementation Method 3
a third layer comprising at least one winding of a polytetrafluoroethylene (PTFE) ribbon
Implementation Method 4
said mica ribbon being composed of mica particles deposited via a polymeric binder on a support
Data Source
Figure 1
AI summary
The present invention relates to an electrical cable comprising: - an electrical conductor surrounded by a first layer comprising at least one winding of a mica ribbon, said mica ribbon being composed of mica particles deposited by means of a polymeric binder onto a support, - a second layer comprising at least one winding of a polyimide ribbon, and - a third layer comprising at least one winding of a polytetrafluoroethylene (PTFE) ribbon, the first layer being heat-treated at a temperature of at least 400°C, and the ratio R of the linear mass density of PTFE to the sum of the linear masses of the polymeric binder and the polyimide being such that: ○ R is greater than or equal to 2 when the cross-section of the electrical conductor is at most 0.2 mm², preferably between 0.1 and 0.2 mm², ○ R is greater than or equal to 4 when the cross-section of the electrical conductor is strictly greater than 0.2 mm² and strictly less than 0.6 mm2,• R is greater than or equal to 6 when the cross-section of the electrical conductor is equal to 0.6 mm², • R is greater than or equal to 12 when the cross-section of the electrical conductor is strictly greater than 0.6 mm², preferably at most 3 mm².