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Thermal spraying is a cost-effective method for applying coatings that enhance surface properties. In the simplest terms, thermal spray involves heating a feedstock material, generally in powder or wire form, to a molten or semi-molten state. The feedstock is propelled using a stream of gas or compressed air to deposit it, creating a surface structure on a given substrate.

The coating feedstock material may consist of a single metallic element, but more often it is an alloy, composite, ceramic, carbide or blend that will give rise to a surface having physical properties that are only achievable through the thermal spray process. Thermal spray is a family of processes, with each member of the process family providing unique opportunities for engineered surfaces.

Oerlikon Metco actively supports all common thermal spray methods, with options to suit your surfacing and applications requirements — such as the size of your production run, geometry of your part, environmental concerns and portability. Through thermal spray, Oerlikon Metco has developed and marketed application technologies to apply coatings that solve our customers’ toughest surface challenges since 1933.

Wear- and corrosion-resistant surfaces are needed to protect critical components in various industries. The High Velocity Oxygen Fuel (HVOF) process supplies this protection by producing very dense, hard coatings with fine microstructures.

Key benefits of this process
  • Produces coatings that are very clean, very hard and dense with fine, homogeneous structures
  • Coatings are tenaciously bonded to the substrate
  • Using liquid fuel allows compressive coating stress, using gas fuel generally allows spraying of thicker coatings
Typical applications 
  • Oil & gas gate valves and seats
  • Hydroturbine components
  • Paper manufaturing rolls
  • Aircraft landing gears
Process description

High Velocity Oxygen Fuel (HVOF) spraying uses oxygen and fuel to form a combustible mixture. Liquid-fuel HVOF (HVOF-LF) generally uses liquid kerosene as the fuel. Gas-fuel HVOF (HVOF-GF) employs fuel gases such as propylene, propane, hydrogen, or natural gas (methane). The fuel is thoroughly mixed with oxygen within the gun and the mixture, combusted and then ejected through a nozzle at supersonic velocities. The feedstock material, in powdered form, is fed through the gun, generally using nitrogen as a carrier gas. The ignited gases surround and uniformly heat the powder material as it exits the gun and is propelled onto the workpiece surface. 

As a result of the high kinetic energy transferred to the powder particles the feedstock powder material generally does not need to be fully melted. The resulting coating has a very predictable chemistry that is homogeneous and has a fine granular structure. 

Process basics
  • Heat source: combustion 
  • Feedstock: powder (metals, alloys, carbides) 
  • Flame temperature: approx. 2 800 °C (5 000 °F) 
  • Particle velocity: 400 to 800 m/s (1 300 to 2 600 ft/s) 
  • Approximate application rate: 40 to 200 g/min (5 to 26 lb/h) 

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