detonation flame spraying,a thermal spray process variation in
which the controlled explosion of a mixture of fuel gas, oxygen
and powdered coating material is utilized to melt and propel the
material to the workpiece.(1)
In the early 1950's Gfeller and Baiker (2),
employees of Union Carbide Corporation, Linde Division, developed
concepts of using explosions in a unique manner. Their concept
was to introduce powdered materials into detonation or shock waves.
The "waves" are produced by igniting a mixture of acetylene
and oxygen into the detonation chamber which is opened to a one
meter long tube two and one-half centimeters in diameter as in
the graphic below.
The system is complex. In operation, a mixture of spray material,
acetylene and oxygen is injected into the detonation chamber.
Combustion gases can be neutral, reducing or oxidizing and can
have their temperature controlled by the addition of an inert
gas, for cooling, or hydrogen to heat it. The procedure is initiated
by a gas/powder metering system that measures and delivers the
mixture to the chamber where it is ignited. The resulting shock
wave accelerates the powder particles to over 731 m/sec (2,400
ft/sec) and produces temperatures in excess of 4,000°C (7,232°F).
Pressures from the detonation close the controlling valves until
the chamber pressure is equalized. When this occurs the cycle
may be repeated either 4 or 8 times per second. There is a nitrogen
purge between cycles. Each detonation deposits a dense and adherent
layer several microns thick and about 2.54 centimeters (1 in.)
in diameter. Repeating the cycle produces thicker coatings. Detonation
coatings are designed for applying hard materials, especially
carbides, on surfaces subject to aggressive wear. The Linde Division,
Union Carbide Corporation (now Praxair Surface Technologies),
referred to the process as "Flame Plating", this is
no longer used. The term “D-gun” is currently used
by Praxair Surface Technologies for this process. Also, the equipment
generates noise in excess of 150 dBA and must be acoustically
housed confining noise emissions.
