**7.4 High velocity oxy-fuel spraying**

High velocity powder flame spraying was developed about 1981 and comprises a continuous combustion procedure that produces exit gas velocities estimated to be 4000–5000 feet per second. This is accomplished by burning a fuel gas (usually propylene) with oxygen under high pressure (60–90 psi) in an internal combustion chamber. Hot exhaust gases are discharged from the combustion chamber through exhaust ports and thereafter expanded into an extending nozzle. Powder is fed axially into this nozzle and confined by the exhaust gas stream until it exits in a thin high speed jet to produce coatings which are much denser than those produced with conventional or standard powder flame spraying techniques (**Figure 21**).

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**Figure 22.**

*Wire arc spray technology.*

*Wear: A Serious Problem in Industry*

*Detonation flame spray technology.*

**7.5 Wire arc spraying**

*HVOF spray technology.*

**7.6 Plasma spraying process**

content.

**Figure 20.**

**Figure 21.**

Twin wire arc spraying is the most economical thermal spraying process. In this type of spraying process the heating and melting occur when two oppositely charged wires are fed together in a way that arc is generated at their intersection (**Figure 22**). Once struck, the arc continuously melts the wires, and compressed air blown directly behind the point of contact, atomizes and projects the molten droplets, which sticks to the substrate to form a coating. Arc fluctuations due to periodic removal of molten droplets from the electrode tips have strong effects on melting and coating properties such as porosity, microstructure and oxide

Plasma spraying is a flexible and low-cost method to manufacture coating and bulk materials. The first idea of a plasma spray process was patented in 1909 in Germany, and the first structural plasma installation appeared in the 1960's, as the product of two American companies Plasmadyne and Union Carbide. A gas, usually argon, but occasionally including nitrogen, hydrogen, or helium, is allowed to flow between a tungsten cathode and a water-cooled copper anode. The cathode is placed in the cylindrical nozzle and the cylindrical nozzle is the anode. An electric arc is initiated between the two electrodes using a high frequency discharge and then

*DOI: http://dx.doi.org/10.5772/intechopen.94211*

**Figure 19.** *Flame wire spray technology.*

*Wear: A Serious Problem in Industry DOI: http://dx.doi.org/10.5772/intechopen.94211*

*Tribology in Materials and Manufacturing - Wear, Friction and Lubrication*

In rod type flame spray, the rod or wire is allowed to the heating zone where it melts and propagated by the plume towards the substrate to form coating

(**Figure 19**). The feedstock rod may be a conventional rod or wire or manufactured by powder metallurgy process (sintering or binding). The melted particles are propelled towards the substrate, strike the surface at high velocity and flatten and form coating with a high adhesion strength with previously formed splat and substrate.

By the term "detonation" is meant a very rapid combustion in which the flame front moves at velocities higher than the velocity of sound in the unburned gases, and therefore characterized as supersonic velocities. A precisely measured quantity of the combustion mixture consisting of oxygen and acetylene is fed through a tubular barrel closed at one end. In order to prevent the possible back firing a blanket of nitrogen gas is allowed to cover the gas inlets. Simultaneously, a predetermined quantity of the coating powder is injected into the combustion chamber. The gas mixture inside the chamber is ignited by a simple spark plug. The gas mixture combustion generates plume which melt the particles to form coating

High velocity powder flame spraying was developed about 1981 and comprises a continuous combustion procedure that produces exit gas velocities estimated to be 4000–5000 feet per second. This is accomplished by burning a fuel gas (usually propylene) with oxygen under high pressure (60–90 psi) in an internal combustion chamber. Hot exhaust gases are discharged from the combustion chamber through exhaust ports and thereafter expanded into an extending nozzle. Powder is fed axially into this nozzle and confined by the exhaust gas stream until it exits in a thin high speed jet to produce coatings which are much denser than those produced with

conventional or standard powder flame spraying techniques (**Figure 21**).

**7.2 Wire or rod flame spraying**

*Powder flame spray technology.*

**Figure 18.**

**7.3 Detonation flame spraying**

**7.4 High velocity oxy-fuel spraying**

(**Figure 20**).

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**Figure 19.**

*Flame wire spray technology.*
