High-Velocity Oxy-Fuel

High-Velocity Oxy-Fuel (HVOF)

Coatings applied by the HVOF process exhibit density, hardness, and bond strength characteristics that can significantly outperform other methods of application.

Common Applications

  • Hard Chrome Replacement
  • Roll Surfacing
  • Cutting Edges
  • Wear Surfaces

Method

Every thermal spray process requires a method of propelling the sprayed material onto the work surface.

The essential feature of a thermal sprayed coating is that the particles sprayed, upon impact with the work, must deform enough to mechanically lock into the profile of the surface they impact. Initially, thermal spray technology seemed to center around techniques of heating the particles into plasticity before impact to guarantee adequate deformation. HVOF introduced a new method.

By using a small combustion chamber to generate extreme (essentially supersonic) exhaust velocities, powdered material injected into this focused exhaust stream is imparted with enough velocity that the force of the impact alone is virtually enough to achieve adequate bonding. The kinetic energy of the particles is so great, in fact, that most porosity typical in a traditionally applied coating is essentially hammered out. Low-porosity, denser coatings wear better and can provide more protection per thousandth of an inch applied.

Practice

Hayden’s facilities allow spray automation for most components, and most workstations include flexible six-axis ABB robots.

The HVOF process uses high volumes of gas flow and tends to be used for the application of high-value, high performance coatings such as tungsten carbide and cobalt superalloys. For this reason, an HVOF-applied coating will typically cost more than a plasma application of the same material. Additionally, the higher velocities of the HVOF stream tend to remove typical masking materials, and customized hard masking is often required.

Work setup and operation parameters are key in optimizing the performance of an HVOF coating. Hayden’s role as a service and support facility for several industries requires our staff to have exceptional abilities in creating effective procedures for a wide variety of materials on parts of all geometries. ISO 9002-certified process control guarantees that a procedure will be monitored for quality and will be infinitely repeatable from batch to batch.

HVOF coatings are capable of producing deposits with less than one percent porosity, as demonstrated by the photomicrograph above.