The Kermetico HVAF process provides higher quality coatings more consistently than any HVOF process does.
It means not only higher hardness, higher ductility and higher density of our coatings, but also the lower deviation of these parameters.
What is the science behind our high-quality HVAF coatings?
The Combustion Temperature of Kermetico HVAF
The combustion temperature in air-fuel mixtures is typically 1,000°C | 1832°F lower than in oxygen-fuel combustion.
This lower temperature is ideal for the gradual heating of the feedstock particles of metals and cemented carbides to or slightly above the metals’ melting temperature.
The initial oxygen content in the combustion gas mixture is 5-fold lower in our HVAF process compared to a conventional HVOF process.
Both factors prevent the oxidation of metals and the decomposition of carbides and their dissolution into the metal binder.
These factors allow the retention of the original ductility of the powder feedstock material in the applied coating, even when the hardness of the cemented carbide coating exceeds 1,600 HV300.
The Heating Efficiency of Kermetico HVAF
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 the spray particles to heat.
Thus the energy transfer efficiency is increased noticeably compared to other high-velocity spraying methods, resulting in much higher spray rates.
The Acceleration Efficiency of Kermetico HVAF
The large diameter of the nozzle eliminates its length limitations, known to other guns.
The spray particles can be accelerated up to the gas velocity both in the Kermetico HVAF and Kermetico HVOF processes.
The Uniformity of Kermetico Coating Quality
The influence of the nozzle walls on the spray particle velocity is negligible, providing even acceleration of the particles which results in the improved consistency of the coating structure and its quality. This is essential for depositing dense and well-bonded coatings.
Precise temperature control of the spray powder near its melting point and high impact velocities are the distinguishing characteristics of the Kermetico coating deposition process.
How Low is “Low Oxygen Content” in a Coating?
Here is an example of chemical analysis data for oxygen content in the Ni-45Cr-1Ti coatings, applied by different thermal spray processes.
In each coating, oxygen is present in the form of an oxide scale and as dissolved oxygen in the metal matrix.
Due to high chromium content, the chosen material is sensitive to oxidation in a spray jet, thus, ideal for comparison purposes. All data about the oxygen content are in wt.%.
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- Plasma » stock: 0.05% coating: 3.8%
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- Electric Arc » stock: 0.02% coating: 7.0%
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- HVOF » stock: 0.06% coating: 1.9%
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- Kermetico HVAF » stock: 0.06% coating: 0.28%
A Comparison of Abrasive Wear and Erosion Protection Properties of HVOF and Kermetico HVAF Coatings
A slurry erosion test, courtesy of Schlumberger.
This trial compares an Economy mode Kermetico HVAF WCCoCr coating to the layers of the same material deposited by industry-leading HVOF and detonation systems.
The following chart is courtesy of the Central Power Research Institute of India.
Could the reason for this result be that we were compared to less than the best available coating equipment?
You may also be interested in a comparison of Kermetico HVAF WCCoCr coatings with one of the most advanced HVOF systems on the market.
A Comparison of HVAF WCCoCr Coatings with HVOF and Ultra-HVOF Specimens
Are you interested in how our HVAF Balanced and Ultra modes provide such excellent results?
“Wear and corrosion performance of WC-10Co-4Cr coatings deposited by different HVOF and HVAF spraying processes.”
As Prof. Wang has shown in his article:
“Three WC-10Co-4Cr coatings were deposited by HVOF and HVAF processes, and their microstructure and properties were investigated in this study. The following conclusions were drawn as a result.
(1) The WC-10Co-4Cr coating deposited by the HVAF spraying process exhibited nearly the same phase composition as its initial feedstock powder, which included mainly the WC and some Co3W3C and crystal Co phases with nearly no decarburization. The JK coating sprayed with Jet Kote III-HVOF equipment exhibited the most severe decarburization with high-intensity W2C and even metallic W phase. The phase composition of the JP coating deposited by the JP8000-HVOF system was composed of main WC and minor W2C peaks and exhibited a light degree of decarburization.
(2) The wear resistance and mechanism of the HVOF/HVAF-sprayed coatings were influenced not only by their hardness but also by their fracture toughness. The high hardness of carbide coating could effectively hinder the cuts caused by the abrasives, and their high toughness could make the binder absorb some of the energy caused by abrasive attacks with some degree of plastic deformation.
(3) The WC-10Co-4Cr coatings, which had different degrees of decarburization, exhibited different dominant wear mechanisms.
(4) The electrochemical corrosion resistances and mechanisms of HVAF- and HVOF-sprayed WC-10Co-4Cr coatings were influenced by their phase compositions and microstructures.”
Scientists tell us that HVAF provides better wear and erosion resistance than HVOF. But a lot of companies still use HVOF to protect their equipment.
Why is that?
Maybe HVAF is too expensive?
The Economic Aspects of Kermetico HVAF Coatings
The list price of our HVAF equipment is lower than the price of good HVOF equipment.
HVOF vs HVAF Tungsten Carbide Coating Quality-Cost Analysis
A Comparison of HVAF and HVOF cost per kilogram of deposited WC-10Co-4Cr (prices in Texas, USA).
With Kermetico HVAF thermal spray systems we are not limited to the “best coating possible.”
We can choose how to spray a tungsten carbide coating:
- save money spraying in HVAF economy mode, getting HVOF quality with lower costs;
- apply the highest coating quality in HVAF U-mode to achieve high hardness, ductile, non-porous, abrasion and cavitation resistant coatings;
- or choose HVAF Balanced mode to gain a competitive edge in both cost and quality.
But it’s not the end of the story.
Blasting and Spraying with Kermetico High Velocity Equipment
Usually, we deposit coatings using robotic blast and spray operations.
We blast a surface with a Kermetico HVAF gun (it is extremely fast and uniform) and spray with the same gun after switching the powder feed hose and perhaps changing the nozzle
It is much faster, more accurate and consumes much less grit than manual blasting.
Hot grit blasting provides very even surface preparation and induces less stress into the base metal.
Kermetico HVAF Thermal Spray Coating Equipment
Kermetico designs and manufactures three families of HVAF thermal spray equipment.
- Convertible HVOF and HVAF equipment:
- Multi-purpose HVAF AK systems, with a variety of spray guns:
- AK7 – a high-power gun for the thermal spray of large parts
- AK6 – a carbide gun to spray a balanced mix of parts
- AK5 – a compact gun to spray smaller parts, thin walls and complex surfaces
- AK-ID – an 80 mm (3.15”) and larger internal diameter spray gun
- AK-IDR – a rotating ID gun to spray 4” (100 mm) and larger bores
- AK-HH – a handheld gun for on-site coating
- Specialized HVAF S equipment:
- Additional equipment:
- An HVAF grit feeder for the grit blast preparation of parts to reduce coating costs
- A Gas Permeability Tester for an instant check of a coating’s through porosity
Kermetico Inc. – the Specialist in Material Science and HVAF Equipment Manufacturing
Since our incorporation in 2006, we have installed more than 60 HVAF systems worldwide. Some of these systems are at work in Universities and National Labs, but most of them are used in production thermal spray shops.
We proudly design and produce our 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 person.
We provide HVAF thermal spray coating services in California, USA.
