Aircraft are complex, critical systems that need exacting reliability and precision during manufacture. Even ordinary and passive aircraft components have demanding standards and specifications to ensure flightworthiness and the utmost safety.

Wire insulation materials play a critical role in aerospace standards compliance. Aircraft have become more reliant on automated and advanced technologies, increasing the demand for electrical wire assemblies. Modern aircraft contain anywhere from 40 to 350 miles of electrical wiring.

It is a challenge for both aerospace engineers, as they design aircraft wiring harnesses, and assembly technicians, who are tasked with laying or repairing wiring in cramped, dim environments.

To help these engineers and technicians better do their jobs, and keep millions of aviation passengers safe, Saint-Gobain has developed an innovative, high-contrast, laser-markable fluoropolymer wire tape.

Contrast ratio is key

Figure 1. High-contrast materials ensure that engineers and technicians can identify the right wire in crowded aircraft wiring harnesses. Source: Saint-Gobain

The ratio of the luminance of the white part of the tape versus that of the dark, printed text is the contrast ratio. A high contrast ratio helps assembly technicians identify and find the correct wires, even when adjacent wires are of a similar color, when they are in confined, low-light workspaces.

Traditional wire insulation printing techniques, such as the print wheels, are becoming obsolescent. Print wheels require ink refills, maintenance and cleaning, and need to be changed out for different text. However, laser systems require minimal maintenance and print patterns are easy to change. Additionally, the wiring used in modern aircraft is of an increasingly smaller gauge, which is better suited for the precision of a laser. Mechanical printing is more likely to damage wire insulation as well, potentially creating rework or repair.

Fluorowrap high-contrast wire insulation film

To satisfy the needs of wiring vendors, aircraft manufacturers and industry standards, Saint-Gobain has introduced its high-contrast MA wire insulation film. This jacketing material is extremely versatile and suitable for flight control, power delivery and communication and infotainment systems throughout the aircraft.

Performance

The Fluorowrap MA jacketing material is made of premium polytetrafluoroethylene (PTFE) resin. The material exceeds the minimum standard contrast ratio (e.g., 55%) for new wiring, with an industry-leading initial contrast ratio of 65%, and a ratio of 50% after heat aging. This makes it exceptionally easy for technicians to find, check and repair strands of wiring.

Figure 2. An assortment of PTFE colors is available to further demarcate wire types and systems. Source: Saint-GobainFluorowrap MA full-density (1.6 g/cm3) wire insulation is available in a wide range of thicknesses with tight tolerances (3 to 10 mil, ±5%).

Maintaining material integrity while under stress is another important consideration. Technicians will need to pull wiring through conduits, and the wiring must also be able to handle vibration and flex loads. Fluorowrap MA insulation has a minimum tensile strength of 2,900 psi in the machine direction and 247 psi in the transverse direction. It also has a minimum elongation of 800% in the transverse direction and 60% elongation in the machine direction.

PTFE is self-extinguishing; therefore, the wire insulation will not support a flame, nor flame propagation. Fluorowrap MA high-contrast laser-markable insulation passes arc track resistance requirements, driven by strict industry fire standards.

Standards

MA wire insulation film meets the standards for various aircraft manufacturers. Several of these standards call for a specific arc resistance and temperature range (e.g., -65° C to 250° C) for wire sizes from 26 to 4/0 AWG, rated up to 600 V, with tin, nickel or silver-coated conductors composed of copper, copper alloy or aluminum. MA wire insulation film also complies with military standard Mil Spec 22759 and it is also RoHS and REACH compliant.

Fluorowrap medium-contrast wire insulation film

Saint-Gobain fabricates a medium-contrast (mA) PTFE film as well. This option has an initial contrast ratio of 60%, compared to 65% for the high-contrast variety. After heat aging, the contrast ratio is typically 40%. The medium-contrast resin can also be provided in thicknesses of 2.5 mil, ±5%. Otherwise, the performance and physical properties are identical to the high-contrast type.

Why Saint-Gobain?

Saint-Gobain Fluorowrap’s proprietary extrusion process can manufacture joint-free lengths of Fluorowrap PTFE insulation up to 3,600 ft in length. The continuous extrusion process allows for greater material consistency and reduces the potential for weak points in the film.

Saint-Gobain has a rich legacy of materials innovation and aerospace support. No other manufacturer has comparable engineering expertise and equipment. They are also available for consultation on engineering challenges, and when called for, exclusive products and customization.

Contact Saint-Gobain to learn how Fluorowrap high-contrast, laser-markable, PTFE materials can improve the manufacturability and repairability of demanding aerospace applications.