PATCHwork for frayed wires

Materials World magazine
,
1 Oct 2008
Exposed wires coated in the PATCH solution

A cheap but effective technique to repair damaged aircraft wires and prevent them from sparking and causing an explosion is available, says a chemist at the University of Dayton Research Institute, USA.

The Power-Activated Technology for Coating and Healing (PATCH), created by Robert Kauffman, comes in two forms – a spray and a water-soluble solid material. Both are based on a solution that is 90-98% distilled water and 2-10% polyvinyl alcohol (PVAL).

It follows Kauffman’s investigations into the 1996 crash of TWA flight 800 mid-flight from New York, USA, to Rome, Italy. He and colleagues concluded that frayed-fuel sensor wiring was partially to blame for the explosion.

‘When the [spray] comes in contact with a powered conductor, the water undergoes electrolysis and produces metal ions (the same ions that cause wet wires to short out),’ explains Kauffman. ‘These cross-link with the dissolved PVAL to become water-insoluble.’ The chemical process creates an electrically insulating layer over the exposed wire. The leftover solution is washed away.

Kauffman adds, ‘Cracks require a mist, while one centimetre-length insulation damage would require a couple of drops’.

The second PATCH solution is a water-soluble solid that can be built into the wiring during manufacture. It is housed in between the copper wire and its insulation. If the insulation is cracked, water caused by condensation in the aircraft will enter the damaged area and, through a chemical reaction, transform the PATCH coating into a permanent seal. ‘Small amounts of the solid layer dissolve within seconds, and these are sufficient to form the required insulating layers,’ notes Kauffman.

The solid coating is incorporated into the wire’s manufacture by simply passing the conductor through the PATCH solution before air or oven drying it, followed by the traditional insulation procedure. And the cost of the solution is very economical, he adds, ‘along the same order as school glue’.

Keith Harrison, Chairman of the IOM3 Surface Engineering Division Board, says the PATCH system is a good idea, though he has some reservations. ‘The spray sounds like a line-of-sight process. But with the amount of wires in an aeroplane, there are going to be inaccessible areas with covered up wires that are impossible to reach,’ he says.

‘The second system relies on water always being there. I will have to take [Kauffman’s] word that is actually the case in aircraft.’

Working with a grant from the US Federal Aviation Administration, Kauffman and colleagues have successfully tested wires six to 12 inches in length. They aim to produce several hundred feet coated with the permanent solution for trialling in aircraft equipment.

The team is also investigating ways to improve the lifespan of these materials. The coatings are intended to be a temporary fix, says Kauffman. ‘The higher the molecular weight [of the PVAL], the tougher the formed polymer, but also the less flexible the repair. We are looking at making the repair strong enough to withstand surface interactions while remaining flexible enough not to crack with vibration/bending.’