The High Velocity Oxygen Fuel (HVOF) process is principally different from other thermal spraying processes, because the powder particles are transported to the workpiece at a very high speed and a low temperature.
It forms a coating on the substrate with a high density and a particularly high bonding value. The HVOF flamespray principle is based on a transfer of thermal and, in particular, kinetic energy from the spray particles of the substrate.
The HVOF "High Velocity Oxygen Flamespray" spraying principle
With HVOF spraying (High Velocity Oxygen Fuel) a mixture of gas and oxygen is ignited. The gas flow expands and reaches a speed of up to 1500 m/sec. The powder injected into this gas stream gets a very high speed (up to 800 m/sec). The cover layers that are thus created are characterized by their low porosity and high adhesive strength.
In the newly developed high pressure high speed process (HP-HVOF High Pressure High Velocity Oxygen Fuel), a mixture of kerosene or gas and oxygen ignites. The gas flow expands and reaches a speed of up to 2200 m/sec. The powder injected into this gas stream reaches a very high speed (up to 1100 m/sec). The cover layers that are created in this way are characterized by their even lower porosity and higher adhesive strength compared to the previous generations of HVOF systems.
Features HVOF coating
- Fine microstructure
- Very dense and low porous layers
- High adhesive strength
- Very smooth to finish
- Optimal micro hardness
- Good corrosion properties
- Excellent for hard metal (carbide coatings)
- Low degree of oxidation
HVOF spraying materials
Commonly used HVOF spraying materials for coatings are:
- Tungsten carbides
- Chromium carbides
- Cobalt alloys
- Nickel/chrome alloys
- Inconel 625
- Stainless steel alloys
- Cermets, carbides (carbides, tungsten carbides, chromium carbides)
- Super alloys based on iron, nickel and cobalt (Stellite, Triballoy, Inconel, etc.)
- HCR - Hard Chrome Replacement
- MCrAlY's adhesive under-corrosion coatings under TBC's (Thermal Barrier Coatings)
Applications of HVOF flamespray
Against running into the seals.
To improve abrasion resistance and chemical protection.
Hydraulic piston rods
In the offshore to protect seawater environment.
Repairs or size corrections
From run-in journal or bearing seats.
For Thermal Barrier Coatings (TBC).
At hydropower plants.
Pump housings and impellers
Against chemical degradation.
What is flame spraying
Flame spray is a unique and practical technique to apply a coating to almost any kind of metal and non-metal surfaces. This coating improves the basic material properties such as hardness, abrasion, scratch and corrosion resistance.
The high heat level and conductivity of the plasma flame, in combination with the very high gas- and transport velocity of the molten particles result in optimal condtions for very strong adhesion, uniformity and purity of the sprayed layer.
Electric wire spraying is a form of thermal spraying where two consumable metal wires are fed independently into the spray gun. With electrical wire spraying, coatings can be applied quickly and at low cost.
With autogenous powderspray, coatings have a homogeneous structure. These hot sprayed layers are well resistant to line, point and impact loads.
Autogenous wire spray
For corrosion protection, repairs or size corrections. The spray layers applied in this way are more or less impact or shock resistant. The structure of the layer is always micro-porous. This gives the ability to hold oil and thus self-lubricating properties are obtained.