wire flame spraying, spray process in which the feed stock is
in wire or rod form.(1)
In about 1912 Schoop developed the first device for spraying metal
wires. The apparatus consisted of a nozzle in which a fuel, probably
acetylene or hydrogen, was mixed with oxygen and burned at the
nozzle's face(3). A stream of compressed air surrounding
the flame atomized and propelled the liquefied metal. Process
continuation depended on feeding the wire at a controllable rate
so it melted and was propelled in a continuous stream.
Schoop approached this problem by using a turbine
to actuated gears and drive rolls that pulled the wire into the
nozzle. This apparatus appeared to him to be similar to a pistol
or gun, and because of this, he and we, refer to thermal spray
devices as "guns" or "pistols" and never "torches".
A typical wire spray gun is shown in the graphic above. Schoop'
concepts of spraying solid metals has given rise to the thermal
spray industry and for this reason it is sometimes referred to
as the "Schoop Process". Regardless, the wire flame
spray gun has not radically changed since the days of Schoop.
While there have been changes in nozzle and air cap design, replacement
of the air turbine with an electrical motor and even the use of
barrel valves the basic principal, however, remains the same "push
or pull a wire into a flame, melt and atomize it and deposit the
molten droplets to form an adherent coating".
