ceramic rod flame spraying, a spraying process in which material
to be sprayed is in ceramic rod form.(1)
The spraying of ceramic rods dates back to the early 1950's when
a demand arose for heat resistant refractory coatings. Plasma
had not come into its own and flame sprayed powder coatings, due
to their porous nature, lacked the integrity and protection required.
The solution was rather simple - Coors Ceramic and Norton developed
ceramic rods, referred to as Rokide, while the Metallizing Engineering
Company (Mogul), modified a wire gun to spray rods. What differentiated
the guns were the drive rolls. A wire gun had serrated steel rolls
to grip and feed the wire while the Rokide gun employed "V"
slotted fiber rolls that pinched the rods and fed them forward.
The principle of operation in either gun is similar - the nozzle's
flame is concentric to the wire or rod in order to maximize uniform
heating. In the graphic below, a coaxial sheath of compressed
gas around the flame atomizes the molten material and accelerates
it to the workpiece. Particle velocities in both the wire and
rod process are approximately the same - 185 m/sec (600 ft/sec)
while coating densities have been measured at approximately 95
v/o.
Ceramic rods are 61 cm (24 in.) in length and offered in three
diameters 1/8, 3/16 and 1/4 in. Compositions include several stabilized
zirconias, white and gray alumina, and a spinel.
