Metal ARC-spray materials and methods

Metal ARC-spray materials and methods

Metal ARC-spray materials and methods

Keywords Arc-spraying, Coatings

The US Army Corps of Engineers Construction Engineering Research Laboratories (CERL) is testing metal arc-spray materials and applications to determine the best ways of protecting a variety of structures from electromagnetic effects.

Arc spray is a thermal spray method that involves heating metal to a liquid state with an electric arc. An air blast is used to break down this molten metal into fine droplets that cool and solidify when they strike the substrate. The bonding of the sprayed metal is primarily mechanical, with hardened metal droplets macroscopically meshing with the sprayed surface irregularities.

Metal arc-spraying applications range from coatings for corrosion control, built-up bearing surfaces, and decorative coatings. While metal arc-sprayed coatings have primarily been used on metal substrates, they also adhere well to a variety of other substrate materials. Recent industrial uses of the technology include spraying the interior of electrical equipment cases to recover some of the inherent electromagnetic shielding that is lost when using plastic instead of metal.

CERL has conducted a series of experiments to test the application of various metals on common construction materials used for walls in shielded rooms. These include: an experimental zinc-on-drywall room; a zinc-on-cinder-block-sprayed laboratory room for processing sensitive data; a North Atlantic Treaty Organization (NATO) classroom constructed with copper-arc-sprayed fibreglass panels; a room with copper-on-fibreglass cloth glued to poured concrete walls; and a room using zinc sprayed onto fibreglasspanels. The studies have indicated that zinc and copper are useful materials for metal arc-spraying based on cost, workability, and performance. The researchers have found that a uniform coat of zinc 12 mil to 15 mil thick will satisfactorily provide an attenuation of 40 dB to 80 dB at frequencies of 200 kHz and up. In addition, a room assembled from zinc-sprayed fibreglass panels costs about 60 per cent less than conventional bolt-together shielded rooms.

Future studies will experiment with applying fibreglass cloth to walls or panels before spraying. This effort will also include developing an adhesive for attaching the fibreglass cloth to the wall. The adhesive will allow the completed composite-sprayed shield to move when wall panel materials crack or shift.