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Spray Tips: Cold spray equipment and process parameters
February 06, 2019
Source: ASM International
The schematic shows a typical cold-gas spray system: The process gas is introduced through a gas control module to a manifold system containing a gas heater and powder-metering device. The pressurized gas is heated to a preset temperature, often by a coil of an electrical resistance-heated tube.
The gas is heated not to heat or soften spray particles, but instead to achieve higher sonic flow velocities, which ultimately result in higher particle impact velocities. The high-pressure gas is introduced into the converging section of a de Laval-type nozzle (i.e., a converging/diverging nozzle). Then the gas is accelerated to sonic velocity in the throat region of the nozzle, and the flow then becomes supersonic (Mach numbers ranging from 2 to 4) as it expands in the diverging section of the nozzle.
The powder feedstock is delivered by a precision metering device and typically is introduced into the high-pressure side of the nozzle in alignment with the throat orifice.
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