HVOF Thermal Spray

The High Velocity Oxy-Fuel (HVOF) process is a high-velocity, low-temperature thermal spray coating method. It relies on the combustion of gases such as hydrogen or liquid fuels like kerosene. This combustion generates extremely high velocities, propelling coating particles to near supersonic speeds before they impact the substrate. A fundamental principle of thermal spraying is that higher combustion pressure produces higher gas velocity, which results in greater particle velocity and, ultimately, superior coating quality.

Originally developed and proven successful in the aerospace industry, HVOF coatings have since expanded into a wide range of industrial markets, including textiles, steel, plastics, paper and pulp, chemicals, and power generation. Today, its applications are virtually limitless.

How does it work

The HVOF process uses supersonic acceleration to propel coating material at several times the speed of sound. The enormous impact energy bonds the particles to the surface, creating a coating of exceptional strength. The system effectively combines kinetic and thermal energy for optimal performance.

Fuel and oxygen are introduced into the spray gun and ignited in an internal combustion chamber, providing the energy source for this unique coating method. The chosen coating material, in powder form, is fed into the combustion stream through a controlled feeder. As it passes through the nozzle, the powder is heated and accelerated, exiting at supersonic velocities. When these high-energy particles strike the surface, they form a solid, homogenous, and extremely dense coating. Characteristic “shock diamonds” in the spray plume can often be observed at the nozzle exit, indicating the supersonic velocity of the process.

HVOF advantage

What sets HVOF apart is its ability to achieve extremely high particle velocities, creating a phenomenon known as Impact Fusion. This process effectively “forge welds” particles to the substrate and to each other, producing dense, well-bonded coatings with outstanding durability.

Unlike conventional thermal spray methods, HVOF coatings feature compressive stresses within the material, ensuring superior adhesion— even in thicker coatings. This eliminates issues commonly seen in coatings with residual tensile stresses, such as cracking, and results in:

Better coating integrity
Enhanced corrosion resistance
Improved thermal fatigue properties

At TSS, our HVOF technology delivers carbide and metallic coatings with unmatched wear life, adhesion strength, and quality. The HVOF gun functions much like a high-pressure, liquid-fueled rocket, propelling molten coating particles at velocities far exceeding those of other application methods. The result is coatings of exceptional quality, offering superior bond strength, wear resistance, and corrosion protection.

Typical HVOF surface applications / industry

Aviation: Aviation Turbine engine fan blade mid-spans, compressor blades, turbine blade roots, bearing journals, stator and rotor disk snap diameters, landing gears, actuator pins, flap tracks, helicopter rotor joints and gears, actuators, flap tracks, helicopter rotor joints and sleeves
Power Generation: Industrial gas turbines, hydroelectric Pelton buckets, nozzles and blades, exhaust fans
Transportation / Heavy Equipment: Hydraulic rods, pistons, ship steering rams
Paper and Printing Machinery: Print roll covers, inking rolls, calendar and press roll covers
Petrochemical: Pump components, gate valves, ball valves, valve seats, exhaust stacks, sucker rods, hydraulic rods, conveyor screws
Glass Manufacture: Glass-mould plungers
Metal Processing: Steel mill guides and rolls, wire-drawing capstans, forming dies, sheet metal cutters
Textile Machinery: Thread guides, crimping rolls
General Industry: Pump housings, impellors and shafts, plastic extruders, cam followers, wear rings, machine bedways, press fits, restoration of machinery components

Compared to other processes

HVOF wear resistant coatings typically out-perform the wear life of hard chrome plating, hardening, anodizing and other hard facing techniques most of the time by a great deal.