Patent of the Month – extreme heat

Materials World magazine
28 Nov 2018

A new patent can help aircraft carriers withstand extreme temperatures, by Patent Attorney, Gemma McGeough from Withers & Rogers.

Steels are widely used in a variety of metal fabrication applications worldwide. One of the most common, particularly for plate steel, is in shipbuilding. While both civilian and military ships present a number of challenges for designers or manufacturers of plate steel, military applications can be especially demanding for modern materials. Deck surfaces of modern aircraft carriers must be able to withstand the considerable forces exerted upon them during aircraft take-off and landing. They must also be able to withstand temperatures of up to 2,000˚C due to an effect known as ‘gas wash’.

Gas wash is caused by jet engine exhausts, such as those used on aircraft capable of vertical take-off and/or landing (VTOL). It can be a particular problem when taking off from or landing on aircraft carriers, due to the limited space available on-board. During VTOL, the jet engines of these aircraft are directed downward onto the deck surface of the aircraft carrier, causing the surface temperature of the deck material to increase rapidly from ambient, typically between -50˚C to 50˚C depending on location, to temperatures at or exceeding 2,000˚C. This can cause areas of paintwork to be burnt away, which subsequently leaves deck surfaces vulnerable to corrosion. This effect is exacerbated by the marine working conditions in which aircraft carriers are deployed.

However, Monitor Coatings, a UK-based surface engineering company, has recently patented a method of coating a sheet of steel to enable it to better cope with such harsh working conditions, detailed in the patent GB 2529608 B.

The method describes a multi-stage process. The first step involves performing a surface preparation, typically done via sand blasting a steel sheet material with a grit made up of brown-fused alumina. This ensures that the surface of the steel sheet material is oxide-free and suitably rough to enable a strong bond for the first coating.

Once the steel sheet material has been prepared in this way, a first coating is applied, which is made up of aluminium and an optional dopant, consisting of a combination of zinc, molybdenum, gallium, tin or indium. A second coating is then applied, which comprises aluminium doped with at least one of titanium, chromium, manganese, boron or any compounds derived from these materials. The first and second coatings are typically applied via arc spraying.

Notably, the second coating is applied in a number of stages. During the first stage, the particles experience higher levels of acceleration towards the surface of the steel sheet material. During the second stage, the particles are accelerated at a slower rate. The faster movement of the particles in the first stage ensures that a strong bond is provided between the first and second coatings. The lower speed of movement during the second stage ensures a rougher surface finish is achieved, meaning that the coating is non-slip. Finally, a barrier coating is applied, typically made up of potassium silicate, which helps to prevent any oxidisation of the aluminium first and second layers.

Monitor Coatings has found that by using this fabrication method, the coating applied is resistant to rapid changes in temperature, which ensures that the underlying steel sheet material is protected from the effects of gas wash. Furthermore, the surface provided by the coating is non-slip, which means it is safer for operational staff to walk on, whilst its friction resistant properties also ensure its suitability for use during the take-off and landing of a variety of aircraft.