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High Velocity Oxy-Fuel (HVOF) thermal spray technology is a dry process that produces a dense metal coating. HVOF is a technique where a very high velocity is used to propel the particles at near supersonic speeds before impact onto the substrate. One of the key benefits of this system’s high velocity is the extremely high coating density and low oxide content. Properties include also good wear resistance, corrosion resistance, low stress, low porosity, and high bonding strength to the base metal.
How does HVOF work?
HVOF is a supersonic process and can exceed bond strengths of 8.4 kg/mm2. It is an extremely versatile system that offers an unlimited range of possibilities to industries with extreme corrosion and wear environments. The thermal spray uses a fuel (i.e., propylene, hydrogen, propane, kerosene) oxygen mixture in a combustion chamber. Combustion temperature is between 2760°C to 3320°C depending on fuel (we use propane, 3’160°C).
This combustion process melts a metal powder that is continually fed into a gun using a carrier gas (argon) and propels it at high speeds 550m/sec towards the surface of the part to be coated. The high speed of the spray produces a coating upon impact that can be used as an alternative to the hard chrome plating (HCP) process.
The metal powder is available in many compositions, including: nickel, nichrome, inconel, chrome carbide, and tungsten carbide. With both thermal and kinetic energy, the high velocity particles are practically embedded into the substrate to form a superior coating with the following characteristics.
- High Density The coatings produced though HVOF develop very high densities
- High Bond Strengths (in excess of 8.4 kg/mm2)
- Zero Porosity (with no interconnecting porosity)
- Good Metal Working Capabilities
- Essentially Stress Free
- Greater Hardness
- Greater Thickness
- Low Thermal Input (substrate temperature less than 150 degrees Celsius which insures original mechanical properties, no stress relieving required)
The properties of HVOF coatings are highly dependent on a number of parameters including the preparation of the part surface, composition, morphology, size distribution and feed rate of the powder, and the precise control of gas flows, relative torch/part motions, stand-off angle of deposition and part temperature. We will gladly take that part for you.
Typical coating thicknesses range from about 50 to 500 µm, but both thicker and thinner coatings are used on occasion depending on the specific application.
- Multiple choice of coating materials.
- Surface coating physical properties are at least equal to those of HCP, and often exceed HCP in corrosion protection, abrasive wear resistance, and adhesive wear resistance.
- A major attribute of this technology is the ability to apply coatings with high melting points to substrates (workpiece or part) without significantly heating the substrate.
- Standard production coatings include pure metals and metallic alloys such as nickel or nichrome, cermets such as tungsten carbide-cobalt, and many ceramics.
- These coatings are used in many industries
If you need to maximize the life of your present or future equipment, than HVOF maybe the answer to your particular problems.
The only waste stream produced by HVOF is from the capture of the overspray. Current systems use a dry cartridge filter system with an optional high efficiency particulate air (HEPA) filter.
Since the overspray contains only the pure metal or alloy, it is feasible to recycle or reclaim this waste stream. Traditional plating operations such as hard chrome plating (HCP) generate a large volume of hazardous waste from contaminated plating bath solutions and rinse waters.
We use inhalation protective equipment when working with fine particulate matter that consists of various compositions of different metals.