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What is Thermal Spray
Methods Molten Metal FlameSpray Powder Flame Spraying Wire Flame Spraying Ceramic Rod Flame Spraying Detonation Flame Spraying High Velocity Oxy/Fuel Spraying (HVOF) Cold Spray Nontransferred Plasma Arc Spraying Electric Arc Spraying RF Plasma Spraying References Acknowledgements		Thermal spray raw materials by end-use Identification Underlayments and bond coats Build-up and reclamation Wear resistance Clearance control coatings Thermal barrier coatings Environmental proteching coatings Electrical conductivity and resistivity Biomedical coatings Metal and ceramic matrix composites Thermal Spray Processes used by Various Industrial Segments Chart Thermal Spray Coating Applications According to Industry Served Chart Industrial use of Gas Metallic Materials Chart

Powder Flame Spraying
Powder flame spraying, a thermal spray process in which the material to be sprayed is in powder form. ⁽¹⁾
Powder flame spraying is probably the simplest of all the spray processes to describe - feed a powder through the center bore of a nozzle where it melts and is carried by the escaping oxy-fuel gases to the work piece. Unfortunately, this approach yields coatings high in oxides and with void contents approaching 20 volume percent (v/o). However, coating quality can be improved by feeding air to the nozzle through a small jet, which reduces the pressure in a chamber behind the nozzle. This chamber is connected to the powder feed hopper. In this way a gentle stream of gas is sucked into the gun and carries powder with it. A typical gun is illustrated below.

This concept was developed by Fritz Schori⁽²⁾ in the early 1930's. However, the amount of powder that can be supported by a gas stream depends on many factors including powder characteristics. If air is not used then the density of the supporting gas influences the feed rate and, for any particular powder there is an optimum amount that can be carried in a gaseous stream. It depends upon the velocity and volume of the gases used. The usefulness and criticality of flowmeters and pressure gauges are governing factors.

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	International Thermal Spray Association - Headquarters Office - 208 Third Street - Fairport Harbor, Ohio 44077 USA Voice: 440.357.5400 - Fax: 440.357.5430 - Email: kathydusa@thermalspray.org