HVOF

(High Velocity Oxy-Fuel)

The HVOF process is a high velocity, low temperature coating process used for the production of hard facing coatings. MBI is a well equipped facility for all types of coatings including high end HVOF. We help you protect your components against wear and corrosion.

The success of HVOF coatings in the aircraft industry paved the way to the industrial markets including textile, steel, plastic, paper/pulp, chemical and power generation. Now, HVOF applications are nearly endless.

HOW DOES IT WORK?

HVOF (High Velocity Oxy-Fuel) is a process that utilizes supersonic acceleration of coating material to several times the speed of sound (See the shock diamonds in the picture). The tremendous impact energy fuses the coating particles to the part surface to form an extremely strong coating. Both, kinetic and thermal energies are combined in a very effective fashion.

Fuel and oxygen are fed into the spray gun where they’re ignited in the internal combustion chamber providing the energy source for this unique coating system. The desired material in powder form is injected into the stream from a controlled feeder, where it gets heated and accelerated as it’s exiting the nozzle. The material stream reaches velocities of several times the speed of sound as it impacts the work surface to form a solid homogenous coating. Shock diamonds in the spray stream can be observed in front of the spray gun nozzle.

THE MBI HVOF ADVANTAGE

We apply HVOF coatings using a unique system that has even faster material particle velocities, resulting in what is called “Impact Fusion”. The particles are practically forge welded onto the surface and onto each other to form the coating. Higher particle velocities and Impact Fusion result in denser, better bonded coatings. Compressive stresses within the coating ensure very high adhesion (even at thicker coatings). Conventional or competitve HVOF coatings have higher residual stresses which are in tension. This condition can cause cracking or dis-bonding. MBI’s HVOF coatings will not dis-bond because they are in compression. This condition results in better coating integrity, enhanced corrosion properties and improved thermal fatigue properties.

MBI’s HVOF process provides carbide & metal coatings unsurpassed quality and wear life. The HVOF gun is essentially a liquid fuelled rocket running at high pressure. It imparts extremely high velocity molten coating particles. This velocity is much higher than other application methods. Higher Velocity means higher quality coatings in terms of bond, wear and corrosion.

MATERIALS APPLIED VIA HVOF TYPICAL CHARACTERISTICS TYPICAL APPLICATIONS
Tungsten Carbide Smooth as-sprayed surface Texture: 90 – 450 (Ra), due to the impact fusion of the particles. High strength Tungsten carbide coatings where needed.
Tungsten carbide – chrome alloy Mirror-like finish: After grinding, super-finishing will result low 0-1 Ra smooth finish. Coatings on Roll faces (various types, Doctoring, Chill, Laminator, Idler, Feed, etc.)
Chrome carbide alloys High hardness, Macro: 1300 (DPH300). This is basically the result of the material choice. Release properties coatings on Rolls, MBI’s Carbide – TRACLON (Extreme non-stick)
Nickel – Chrome alloys Better wear resistance: 74 Rc hard tungsten carbide coatings make this possible. Release properties coatings on Rolls, MBI’s Carbide – TRACLON (Extreme non-stick)
Stainless steel materials Superior bond strength at over 12,000 psi, due the impact fusion of our process. Protection against extreme wear areas
Hastalloy Versatile thickness: from .001” – .100″ due to better cohesion and reduced stress levels Hard-facing Granulator Rotors
Inconel Low stress: The process thermal energy reduces the compressive tension. Pump housings & Impellers
And more Low porosity: virtually none, due to the high velocity involved in the process. Mandrels
Shredding components
Extruders
Tracks
Screw shafts & augers
Conveyors
Blowers & Fan blades
Mixer parts
Turbine shaft surfaces
And many more!

COMPARE 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.

MBI’s HVOF coatings are very dense, extremely well bonded and free of all oxides and tensile stresses inherent in coatings provided by other thermal spray coating processes. Consequently, HVOF coatings perform better in service.

HVOF Carbide coatings contain higher carbide percentage than Clad-carbide methods, which makes them more wear resistant at lower thickness; thus, the process avoids excess waste and the higher cost associated with cladding.

COST EFFECTIVE

Thin HVOF coatings on production equipment provide increased service life. This allows engineers to choose inexpensive and lighter materials for part’s manufacturing, then specify coatings to achieve the desired properties and performance.

Experience shows that in practically every case, the right choice of coating material can lower cost while improving performance. HVOF coatings have demonstrated that the carbide containg metal coatings are extremely effective against wear and corrosion.

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