The spray-and-fuse process
is a two-step process in which powdered coating material is deposited by using either a combustion gun or plasma spray
gun, and subsequently fused using either a heating torch or a furnace. The coatings are usually made of nickel or cobalt
self-fluxing alloys to which hard particles, such as tungsten carbide, may be added for increased wear resistance.
Coatings ranging from 0.020 to 0.080 in. thick can be made by building up several layers at a rate of 0.005 to 0.030 in. per
pass. Typical deposition rates are 9 to 12 lb/hr.
Most workpiece substrate metals can be hardfaced using the spray-and-fuse process without special precautions, while
others require special pre-heating or cooling procedures to prevent cracking of the hardfacing. Most plain carbon, manganese,
molybdenum, chromium, chromium-vanadium, and nickel-chromium-molybdenum steels can be hardfaced by the spray-and-fuse
process without special precautions, provided the carbon content is below approximately 0.25%. When the carbon content of-the
steel is above 0.25% the workpiece requires a 500 to 700 of preheat prior to fusing the
sprayed coating and slow cooling after fusion.
Irons
(such as gray cast, meehanite, malleable, ingot, and wrought) and nonferrous metals and alloys (such as copper, nickel, Mone1
400, Inconel 600, Nichrome, and most high temperature alloys) are also amenable to hardfacing by the spray-and-fuse process
without special precautions.
There
are many formnulations of tungsten carbide powders, and Lund engineers rely on many years of experience to select the optimal
formula for a specific application.
