HVOF tungsten carbide coatings became an industry standard to protect corrugating rolls from wear. Many industry experts have tried to improve the quality/cost ratio of the manufacturing process.
Our HVAF and HVOF equipment provide a way to apply corrugating roll coatings on site and in-house with higher hardness and ductility and deposits those coatings 5 times faster than conventional HVOF.
Ultra-quality ductile 1,350 – 1,600+ HV300 Kermetico HVAF WC-10Co-4Cr coatings provide a new level of wear protection resulting in consistent coating quality and longer overall life of a corrugated roll.
Mobile Kermetico HVAF equipment offers even greater benefits for on-site spraying.
HVAF Coating Features
Kermetico HVAF tungsten carbide coatings are superior to HVOF WCCoCr rivals regarding both wear protection and production cost.
The high velocity of the in-flight particles (greater than 1,000 m/s| 3,300 ft./sec.) in the Kermetico HVAF process enables the production of very dense coatings with high bond strength.
Moreover, the low combustion spraying temperature (1,960-2,010°C | 3,560-3,650°F depending on fuel gas) and gentle particle heating result in minimal feedstock phase transformation and almost nonexistent elemental depletion or decomposition of the in-flight particles.
A Phase Analysis of a WCCoCr Coating (Red) and a Feedstock (Black)
Furthermore, the replacement of HVOF-specific pure oxygen with air in the Kermetico HVAF process significantly reduces the oxide content in the deposited material, which is desirable for high-performance coatings.
The Key Features of HVAF and HVOF Tungsten Carbide Coatings
| WCCoCr 86/10/4 Coating Feature | Typical HVOF | Kermetico HVAF Modes | ||
| Economy | Balanced | Ultra | ||
| Deposition efficiency, % | 40-55 | 60-70 | 48-58 | 36-42 |
| Hardness, HV300 | 1,050-1,250 | 1,050-1,250 | 1,250-1,350 | 1,350-1,600+ |
| Young’s Modulus E, GPa | 300 | 400 | 450 | 450 |
| Apparent metallographic porosity | <0.8 | <0.8 | <0.5 | <0.3 |
| Bond strength, MPa (PSI) | 80+ (12,000+) | |||
| Range of as-sprayed roughness, µm (µ in.) | 3.5-4.5 (150-180) | 1-3.2 (40-130) | ||
Higher deposition efficiency, herewith spray rates that are 5-fold faster than HVOF offers a substantial cost advantage for a company using Kermetico equipment. In other words, HVAF technology provides the best surface hardening at the lowest cost.
Notes on Kermetico HVAF Equipment
The traditional thermal spray approach is to melt and atomize the feedstock, propel it to the surface of the target part whereupon contact ‘splat cooling’ builds up a coating.
The Kermetico HVAF process operates differently.
We heat the feedstock material to near its’ liquid phase temperature without exceeding it.
Then we accelerate the particles to an optimized high velocity, and when the particles impact the substrate, there is a rapid conversion of kinetic to thermal energy that allows for the plastic deformation of the particle and a bond which we cannot accurately measure.
A 60μm (0.002”) Thick Kermetico HVAF Coating of a Corrugating Roll with a Thickness Deviation of <10%
In the ASTM 633C bond test, the only result we get is broken glue at 12 KSI, even with 0.040“ (1 mm) of WCCo 88/12.
What if you have to use HVOF for some jobs because of old-fashioned specifications? You can use our Convertible system spraying HVAF or HVOF mode with the same gun after a simple and quick hardware setup change.
On-site thermal spray coating of Corrugating Rolls
Kermetico HVAF and HVOF systems are ideal for on-site coating application.
- It sprays fast:
- Our HVAF AK7 and HVAF/HVOF C7 spray 550 gram of tungsten carbide per minute (73 lbs./hr.), allowing a reduction of spraying time for a corrugating roll five-fold
- It is mobile-friendly:
- No water chiller – we cool guns with the same air we use for combustion
- No oxygen in HVAF mode – we spray with air and gaseous hydrocarbons
- Reliable and robust equipment designed for on-site jobs
- It is safe and easy
- Technologically efficient system accepts various fuels and forgives operators’ mistakes
- The absence of fumes of sprayed powders makes the coating process less hazardous
- We developed some valuable options for on-site jobs:
- Blast-and-spray grit feeders
- Manual Kermetico AK-HH gun for hand-held coating
- Instant gas permeability tester to check coating through porosity on-site
Safety of On-Site Coatings
Safety of on-site tungsten carbide coating deposition depends on the equipment.
The HVOF combustion temperature is usually higher than the boiling point of a metal material, which can result in possible hazardous metal evaporation. It is especially dangerous during on-site operation, where ventilation systems could be insufficient.
The Kermetico HVAF AK combustion temperature is near most materials melting point, which preheats metals and carbides but does not evaporate them. It prevents oxidation and decomposition of the feedstock material and also keeps the air clean.
On Site HVAF Blasting And Coating
Typically, we apply corrugating roll 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 needs much less grit than manual blasting.
HVAF grit blasting also produces even surface preparation and induces less stress into the base metal.
Kermetico HVAF & HVOF Thermal Spray Coating Equipment
Kermetico designs and manufactures HVAF and HVOF 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 – recommended for corrugating rolls
- AK6 – a gun to spray tungsten and chromium carbide onto 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
- Additional equipment:
- A Grit Feeder for the grit blast preparation of parts to reduce coating cost
- A Gas Permeability Tester for an instant check of a coating’s through porosity
- A Powder De-Duster to screen fine particles from a metallic powder
Kermetico, Inc. – HVAF and HVOF Material Science Excellence, Equipment Manufacturing and Thermal Spray Coating Since 2006
We create equipment that helps material scientists, engineers and business managers achieve their goals.
We have installed more than 60 Kermetico 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 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 and HVOF equipment in action.
We also deposit HVAF and HVOF thermal spray coatings for customers in North America – ourselves and through our network of partners.
