High-velocity oxygen Fuel, abbreviated as HVOF, is a thermal spray coating process that is quite common nowadays. HVOF is the same process as the combustion spray process/LVOF only that it has been developed to give out a high spray velocity. It is used for the manufacture of high grade and dense layers of carbides. It is a distinct thermal spray covering process where the powder particles are transported to a workpiece at high velocity using a gas or oxygen flame. This process generates a layer that is attached to the surface at a molecular level. The result is a dense homogeneous layer that has a very high bond strength.
The gas and oxygen flame with a temperature of almost 3000 degree Celsius hits the workpiece with powder flecks like tungsten carbide. The flame travels at a speed of over 1000 meters per second, a speed nearly five times the rate of a conventional thermal spray. High velocity oxygen fuel thermal spraying makes the production of very dense and homogeneous coverings that have low internal stresses, high adhesion value and high bond strength possible, which is ideal for a linear.
Well, there are several types of HVOF guns that employ various methods to achieve the high velocity spraying. The first method is high-pressure water-cooled (high-velocity oxygen-fuel) combustion chamber with a long nozzle. In this process, oxygen and fuel are fed into a chamber, and the combustion produces a high-pressure flame that is then forced down the nozzle. Another method employs a simpler system of an air cap and a high-pressure combustion nozzle. Oxygen and the fuel gas are supplied at high pressure, and combustion happens outside the nozzle. However, this happens within an air cap fed with compressed air. This compressed air accelerates the flame and ideally works as a coolant for the gun.
As you can already guess, there are two obvious differences between conventional thermal spraying and HVOF coating. HVOF employs confined heating along with a longer nozzle to heat and speed up the covering material that is in the form of a powder. The conventional thermal spray devices work at Hypersonic gas acceleration. Extreme velocities give higher energy, and this leads to HVOF coating sprays being more dense and long lasting.
The technology seen in High-Velocity Oxygen Fuel thermal spraying is among the most important processes employed in applying carbide based coating. High velocity oxygen fuel(HVOF) has been changing from gas-fueled towards liquid fueled systems.
So, What Are The Benefits HVOF Coating?
First and foremost, it gives a stronger bond of 10,000 psi or more.
The particle velocity of this process achieves less porosity and fewer oxides.
The quality and the mass of the coatings gives the ability to obtain Ra finishes of 8 or even less.
Depending on the type of High-Velocity Oxygen Fuel spray that is being applied, an RC-quality of above 60 can be obtained through this process.
Tungsten Carbide spray coatings through HVOF thermal process have the best resistance to wear and distress.