Principle of operation
The combustion wire process involves driving a wire (usually metallic) through the gun by means of a compressed air-driven turbine or motor. An oxy-fuel gas flame then melts the wire as it passes through the nozzle at the front of the gun. As the wire is melting, compressed air then atomises the molten wire and accelerates it onto a prepared surface.
It can been seen therefore that the thermal energy (heat) is supplied by the oxy-fuel gas flame and that the kinetic energy is supplied by the compressed air as it atomises the particles from the wire.
For hard wires such as steels, bronzes, molybdenum etc. acetylene (C2H2) is the usual fuel gas of choice as it can generate a heat source temperature of up to 3,100°C. These higher melting point materials are usually used for machine element reclamation (worn shafts, journal areas, seal areas etc.).
These types of gun and their ancillary equipment are widely used within the anti-corrosion industry. By preparing the steel or iron surface (by grit-blasting) and applying a coating of between 0.100mm – 0.300mm (100µm - 300µm) of zinc or aluminium, corrosion protection can be offered for up to 30 years in some cases.
Zinc and Aluminium have relatively low melting temperatures compared to the harder materials used in machine element work. For this reason, the favoured gas for the anti-corrosion industry is propane (C3H8) which gives a heat source temperature of up to around 2,600°C. Propane is generally cheaper than acetylene so combining this with the low melting points of zinc and aluminium, propane becomes very attractive in this very completive market.
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