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The AK-ID Rotating Gun to HVAF HVOF Spray Metals and Carbides onto Bores and Internal Diameters

High Velocity Air-Fuel Spraying (HVAF)  and HVOF High Velocity oxygen fuel is an advanced thermal spray process for the deposition of quality carbide and metallic alloy coatings to protect internal surfaces of industrial equipment against severe wear and corrosion.

The Kermetico AK-IDR Rotating HVAF Spray Gun

The ID rotating HVAF and HVOF thermal spray gun is a recent development of Kermetico Inc., and it is a perfect tool for the application of HVCOF coatings inside sophisticated shapes, such as elbows, square-to-round shape transition nozzles as well as for internal spraying of parts where the rotation of such parts is difficult or impossible.

  • They include vessels with long protruding nozzles, massive blocks of cylinders, pump housings, etc.
  • The ID rotating gun fits internal diameters from 100 mm (4″) and larger, up to 600 mm (2′) deep.
  • We use high-torque motors in the Kermetico rotators with the entire rotating assembly mounted on the robot or linear traverse device.
  • [Kermetico ID Rotating Torch to Spray Carbides onto Internal Diameters 100 mm+ (4"+)]
  • Kermetico ID Rotating Torch to Spray Carbides onto Internal Diameters 100 mm+ (4″+)
  • High-pressure air flow provides sufficient cooling of both the torch and the part.
  • [The Kermetico HVAF AK-ID-Rotating Spraying a WC-10Co-4Cr Coating Inside an Elbow with a 150 mm (6”) Internal Diameter]
  • The Kermetico AK-IDR Spraying a WC-10Co-4Cr Coating Inside an Elbow with a 150 mm (6”) Internal Diameter

As you can see from numerous photographs of actual work, we have completed extensive testing of our internal diameter guns. Here in California, we are surrounded not only by Silicon Valley IT companies (which help us in our research) but by five oil refineries and numerous marine and power repair job shops. All the parts presented were HVAF thermally sprayed for our customers in the USA.

The Kermetico HVAF ID rotating burners have three main differences from any other equipment:

Axial powder injection through the combustion chamber provides enough time to heat the powder in size-restricted areas of small ID parts
We spray very fine powder particles that are easier to heat and accelerate
The lower HVAF process temperature prevents overheating of such fine particles and the sprayed coating layer

Those features allowed us to create the smallest internal diameter guns in the world, working inside pipes as long as needed to deposit high-quality tungsten carbide and metal alloy coatings.

The Kermetico HVAF Process vs. HVOF Process for Spraying Internal Surfaces

Usually, reducing the size of HVOF ID guns leads to low particle velocity and poor coating quality.

Kermetico HVAF gun design leads to a different result.

The Kermetico HVAF AK-IDR gun is “a small rocket engine,” generating a jet of spray particles with a velocity of more than 800 m/sec even with a short nozzle, the length of which is restricted by the ID size. Such particles form dense and tough coatings.

Our internal diameter tungsten carbide coatings (WC-12Co, WC-10Co-4Cr, etc.) are non-permeable to gas and have hardness 1,050-1,250 HV300.

Regardless of the high hardness, these coatings are not brittle since neither decarburization nor oxidation occurs in our low-temperature HVAF process.

The combustion temperature of HVAF air-fuel mixtures (1,800-2,100o C / 3,272-3,812°F) is ideal for gradual and precise heating of the spray particles of metals and cemented carbides to or slightly above the metal’s melting tempera­ture. This prevents material oxidation, carbide decomposition, and formation of other coating defects. Our equipment applies many alloys without particle melting.

Key advantages of the HVAF Equipment over standard HVOF

Heating efficiency: Heating of the spray particles in the combustion chamber occurs at high pressure, where heat tran­sfer is the most efficient. The size of the chamber provides a long residence time for spray particles to heat. Thus, the energy transfer efficiency increases noticeably compared to other high-velocity spraying methods. This results in much higher spray rates with HVAF guns produced by Kermetico.

Acceleration efficiency: Kermetico HVAF guns have a large nozzle diameter that eliminates the nozzle length limitations of HVOF guns. The spray particles can be accelerated up to the gas velocity. The spray particle velocity is often purposely limited to reach the target deposit efficiency (cost) and decrease residual stresses in the coating.

Uniform coating quality: The diameter of the spray particle jet is several times smaller than the nozzle diameter. The influence of the nozzle wall on the spray particle velocity is negligible, providing even acceleration of the feedstock and improved consistency of the coating structure.

Kermetico, Inc. – Material Science Excellence, HVAF and HVOF Equipment Manufacturing and Thermal Spray Coating Services Since 2006

Kermetico is not just ID thermal spray gun developer. We produce complete high velocity air fuel systems working on propane, propylene, natural gas and MAPP gas.

Since our incorporation in 2006, we have installed more than 60 HVAF and HVOF systems in the USA, Europe, Japan, and China.

Some of the systems are at work in Universities and National Labs, but most of them are used in production thermal spray shops.

We can equip our systems with different guns; they are robust and technologically efficient.

We proudly design and produce our HVOF and HVAF thermal spray equipment in California and install it all over the world. You can visit our R&D center in Benicia to meet our designers and see our HVAF equipment in action.

Bexxon Global in Singapore is the partner of Kermetico in Asia and provides training and thermal spray support on the HVAF and HVOF systems

HVAF Controller
Heavy Duty ID HVOF torch

Internal Diameter Tungsten Carbide Coating

Internal diameter torches down to 80 mm

AK-ID Internal Diameter Gun

  • ​HVAF internal diameters as small as 80 mm
  • Up  to 1,5 meters deep.
  • ID HVAF spraying and blasting
  • Spray Rate up to 5 kg / hour
  • Elegant design, axial powder feed + air cooling provide long spraying times and good process stability.
  • Spray metals, alloys, and carbides.

 AK-IDR Internal Diameter Gun

  • HVAF Rotating head, as small as ID 100 mm
  • Up to 600 mm depth
  • Spray Rate up to 5 kg / hour
  • Air cooling and axial powder injection provides hours of continuous ID operation.  
  • Spray angle 90°.


  • Manual on-site HVAF spraying and blasting
  • Spray Rate up to 15 kg / hour
  • This compact dual-use hand-held or robot-mount equipment
  • Excellent for field and on-site
  • Spray metals, alloys, and carbides.
  • Gun weight: 2.5 kg