High Velocity Oxy-Fuel (HVOF) Thermal Spray Coating Services

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High Velocity Oxy-Fuel (HVOF) Spray Coating Info & Benefits

HVOF Thermal Spray

HVOF is similar in theory to combustion flame spraying, but uses a different torch design that enables the flame to expand when the spray nozzle is activated. This causes a surge in acceleration, which in turn accelerates the mixture particles. When the mixture is released from the nozzle, the velocity of the mixture leads to a very thin and evenly applied coat. The final coating is well-adhered, strong, and dense. In fact, its hardness, corrosion resistance, and overall wear resistance is often superior to plasma spraying. Because of the low temperature of the torch flame, which both melts the powder and propels the coating's deposition, the mixture is not suited to withstanding high temperatures.

In the early 1980's Browning and Witfield, using rocket engine technologies, introduced a unique method of spraying metal powders. The technique was referred to as High Velocity Oxy-Fuel (HVOF). The process utilizes a combination of oxygen with various fuel gases including hydrogen, propane, propylene, hydrogen and even kerosene. In the combustion chamber, burning by-products are expanded and expelled outward through an orifice where at very high velocities.

Powders to be sprayed via HVOF are injected axially into the expanding hot gases where they are propelled forward, heated and accelerated onto a surface to form a coating. Gas velocities exceeding Mach 1 have been reported with temperatures approaching 2,300°C (4,172°F). The coupling of inertially driven/highly plasticized particles can achieve coatings approaching that of theoretical density. Disadvantages include low deposition rates and in-flight the oxidation of particles. Future efforts will focus on applying thick coatings and improvements in processes control including in-flight transit time and exposure to atmospheric oxygen.

Our HVOF coating method uses tightly controlled processing to apply an array of coatings, such as tungsten or chromium carbide, in place of hard chrome.

HVOF Thermal Spray Coating benefits are:

  • Reduced oxide content
  • Reduced solutioning of carbides
  • Neutral or compressive stress
  • Smoother sprayed surface
  • True coating uniformity
  • Tensile band strength >10,000 psi.
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