Application of Fluoroplastics in Aerospace Irradiation Cross-linked Wire and Cable

PublishTime： 2023-10-25 Article Source：Futureway News

As we all know, fluorine-containing plastics and polyimides are very good wire and cable insulation materials. So far, they have occupied a very important position in aerospace cables. However, with the development of aerospace technology, their shortcomings are also more obvious. The most representative typical fluoroplastics, including PTFE, PFA, and FEP, apart from insufficient mechanical strength and high specific gravity, the weakest point is poor radiation resistance. All plastics will produce chain scission under high-energy radiation. As for the amount of chain scission, the degree of chain scission, etc., various plastics have different performances. Under irradiation conditions, PTFE quickly decomposes after a few dosages. Among the fluoroplastics, ETFE and PVDF have high mechanical strength, small specific gravity, and radiation resistance, but they are used at low temperatures. PI, which was once widely used in aviation wires, cannot be used in aerospace because it is not resistant to string arcs, oxygen atoms, moisture, hydrolysis, and poor low-temperature bending properties. While researching and developing new varieties of fluoroplastics, we have modified various existing fluoroplastics in physical and chemical properties, or improved the cable insulation structure, such as the use of a composite insulation structure of PTFE and PI film, which makes their performance complementary in recent years. The general trend of the development of aerospace cables.

Insulation Materials

Cross-linkable ETFE is a copolymer of ethylene-tetrafluoroethylene containing a third monomer together with an appropriate amount of cross-linking agent and appropriate amount of pigments, lubricants, antioxidants, flame retardants, fibers or mineral fibers, Dyes, plasticizers, etc. are mixed together. In order to facilitate marking on the surface of the wire, a small amount of photosensitizer can be added.

Squeeze out

Cross-linked ETFE insulated wires can be single-layer insulation, but more are double-layer insulation. Double-layer insulation can be extruded at one time with a double-layer extruder, or it can be extruded in two layers. There is also a double-layer insulation with PVDF as the inner layer. The extrusion temperature distribution is roughly 200℃, 240℃, 275℃, 290℃, and an insulating layer with an insulation thickness of 0.13mm can be extruded under a reasonable mold configuration.

Crosslink

Radiation can be used for cross-linking at an appropriate dose rate, or the so-called "skin irradiation" technology can be used to control the voltage and dose of the accelerated particles to obtain satisfactory results.

New composite installation line

In order to make the wires have higher reliability, in order to reasonably utilize the advantages of different insulating materials and realize the complementary performance of the insulating materials, the so-called "composite installation line" with double or multilayer insulation is adopted. "Composite installation line" itself is not a new proposition. For example, polyvinyl chloride nylon insulated wires, polyvinyl chloride, polyvinylidene fluoride insulated wires, PTFE and PI composite installation wires, etc., have appeared long ago. Such installation wires, Especially composite installation lines have been widely used in aerospace installation lines. But the insulating layer and the layer can be separated (peelable).

The so-called new composite installation line is that the different insulation layers in the wire and cable are inseparable (non-peelable, or the peeling force is particularly large). The installation wire structure with PTFE insulation wrapped around PI insulation has been widely used, but its shortcomings are also obvious. First of all, it only has low, at best, moderate moisture resistance and cannot be marked with a laser. More serious is that it is not abrasion resistant. Once it is scratched, PTFE is easily scraped off. It has poor moisture resistance and is easily hydrolyzed, which reduces its insulation. In addition, PTFE is not resistant to radiation and is obviously not suitable for use in aerospace. The new installation line adopts coating hot-melt sealing material, and the outer layer adopts cross-linked ETFE, which overcomes the above shortcomings.

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