HVOF applied Tungsten Carbide coatings are applied at supersonic velocity. This gives a very dense surface that can be machined afterwards. This is extremely useful for the coating of wire drawing pulleys and drums, valve balls, drilling tools and offshore downhole tools and control valves. HVOF can also be used to repair equipment such as shafts, pulleys, rolls and gears.
With the HVOF process, the gas stream is heated and accelerated by mixing and igniting oxygen and fuel (gas or liquid) in a combustion chamber and allowing the high pressure gas to accelerate through a nozzle. Powder is introduced into this stream where it is heated and accelerated towards the component’s surface. The resulting coating consists of thin overlapping platelets.
The coating thickness can be varied depending upon the application but is usually in the 200 to 300 microns range.
HVOF coatings are used for abrasion, wear and erosion resistance all of which are excellent at temperatures up to 760 °C, even in high load situations.
A polymer coat is not normally applied to an HVOF coated surface as it tends not to bond very well. Post coating machining or grinding can be carried out to achieve a smoother finish and to finish within tolerances.