TWI Frequently asked questions
by Suman Shrestha
The disadvantages associated with HVOF spraying include:
- HVOF sprayed coatings can be extremely complex, with their properties and microstructure depending upon numerous processing variables.
- Powder sizes are restricted to a range of about 5 - 60µm, with a need for narrow size distributions.
- HVOF spraying requires experienced, qualified personnel to ensure safe operation and to achieve consistent coating quality.
- As with all the thermal spraying processes, particular health and safety issues should be addressed. HVOF spraying usually needs to be undertaken in a specialised thermal spray booth, with suitable sound attenuation and dustextraction facilities.
- HVOF equipment requires more investment than other thermal spraying processes, for example flame and arc spraying.
- Manual operation of an HVOF spray gun is not recommended and automated manipulation of the gun is usually needed.
- Deposition of coatings is difficult or impossible to achieve on to internal surfaces of small cylindrical components, or other restricted access surfaces, because HVOF spraying needs line of sight to the surface and a spraydistance of 150-300 mm.
