What Is High Velocity Oxygen Fuel (HVOF) And How Does It Work?
Metallisation | 21st October 2020
High Velocity Oxygen Fuel (HVOF)
HVOF uses a Fuel (commonly Kerosene or Hydrogen) and Oxygen mix which are ignited in a combustion chamber under precisely controlled conditions. The combustion gases accelerate through a converging and diverging nozzle at very high speeds (up to Mach 7). Powders, such as Tungsten Carbide, Nickel Chrome alloys, and Chrome Carbides are injected into the high-temperature gas stream where they soften in the heat and impact the substrate at very high velocities (circa Mach 2) and with a large amount of kinetic energy.
HVOF: What is it used for?
HVOF is widely accepted in many demanding industries where applications are in quite extreme environments such as in the oil and gas industries, steel mills, power generation, valves and pumps and in hard chrome replacement. HVOF produces very dense, hard-wearing coatings which can then be traditionally silicon carbide ground, or in some cases need to be diamond ground or polished, to produce a high level of surface finish.
What Are the Advantages?
The denser coatings applied by the HVOF process typically allow for better performance in the protection of both corrosion and erosion in highly demanding environments. For example, in ball valves for the oil and gas industry, HVOF coatings can last up to 10x longer than traditionally hard chrome plated valves, protecting against corrosive crude oil/water and the erosion of mud and sand mixed with the oils.
The structure of the coating commonly allows for very hard-wearing Tungsten Carbide particles to be very firmly embedded/retained in the coating and this is what offers the exceptional wear characteristics of the coatings.
A high coating quality could be extremely hard (up to 1400 HV), very dense coating with low porosity levels <1% and a very high bond strength >80MPa and despite all this, the component/substate temperature is minimalised so that the process remains metallurgically cold (it does not heat the substrate to such a level that it changes it’s metallurgical structure.
High performing, specialised materials can be applied to lower quality materials to possibly reclaim and improve existing components, provide better wear resistance to surfaces to improve the life of the component, or to combat corrosion, high temperatures, erosion and cavitation.
One such common use of the HVOF process is the replacement for chrome plating where environmental legislation in respect of hexavalent chrome in the chrome plating process has meant that many plating companies have sought alternatives to the traditional chrome plating process. The HVOF spraying of Tungsten Carbide based alloys to achieve excellent hardness and performance for sliding wear applications as well as resistance to corrosion, can in some cases lead to wear characteristics up to 10 times that of a chrome-plated surface. Tungsten Carbide coatings are so hard that they require grinding but more on a par with hard chrome plating, coatings of NiCrB type are commonly ground with conventional SiC grinding wheels.
The Final Finish
Metallisation has been working in the metal coating industry since 1922 and in that time, we have become the UK's leading developer, manufacturer and worldwide supplier in a full range of metal spraying equipment and consumables including HVOF.
Interested in finding out more about HVOF and whether it’s the right choice for you? Then Get in touch and speak to a member of the Metallisation team today on 01384 252 464 or send us an email on firstname.lastname@example.org. We look forward to hearing from you.