Piston rods of reciprocating compressors suffer wear in packaging seal areas. Kermetico HVAF technology and equipment provide a way to replace an old compressor rod coating with hard and ductile tungsten carbide coatings that are easy to apply. Numerous researchers have pointed out that HVAF WCCoCr coatings work several times longer than electrolytic hard chrome and HVOF carbide overlays.
Kermetico HVAF allows spraying of highly wear resistant rod coatings, impermeable and chemically resistant to corrosive gases.
The high ductility of our coatings reduces the risk of cracking if flexed and provides loading stress resistance.
The optimal surface structure provides good frictional characteristics between a rod and a seal.
We repair compressor rods in California, USA, and spray coatings onto OEM piston rods.
HVAF Spraying a Tungsten Carbide Coating onto a Compressor Piston Rod
Compared to traditional electrolytic hard chromium plating, our compressor rod coatings provide significantly higher wear resistance and the absence of hydrogen embrittlement of high-strength steels.
The Features of our HVAF Coating Technology
Kermetico High Velocity Air Fuel (HVAF) technology has been shown to be very competitive as an environmentally friendly alternative to electrolytic hard chromium (EHC).
The ecological aspect and shorter processing time reduce processing costs.
The option to apply thicker layers provides a way to repair heavily worn compressor rods.
Kermetico HVAF carbide coatings are also superior to conventional HVOF counterparts regarding wear resistance, corrosion protection and production cost.
The high velocity of the Kermetico HVAF in-flight particles (over 1,000 m/s | 3,300 ft./sec.) enables the production of very dense and high-bond coatings.
Moreover, the low combustion spraying temperature (1,960-2,010°C | 3,560-3,650°F) and gentle particle heating lead to minimal feedstock phase transformation and almost nonexistent elemental depletion/decomposition of the in-flight particles.
Furthermore, the replacement of pure oxygen necessary for HVOF with air in our HVAF process significantly reduces the oxide content of the coatings, which is desirable for high-performance coatings.
Key Features of Kermetico HVAF and HVOF WCCoCr Coatings
| WC-10Co-Cr Coating | Typical HVOF | Kermetico HVAF Mode | ||
| 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 | 1,450-1,600+ |
| Young’s Modulus E, GPa | 300 | 400 | 450 | 450 |
| Apparent metallographic porosity | <0.8 | <0.8 | <0.5 | <0.1 |
| 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) | ||
The Kermetico HVAF Coating Method
The traditional thermal spray approach is to melt and atomize the feedstock, propel it to the surface of the target part whereupon contact a coating is built up by what is called ‘splat cooling.’
The Kermetico HVAF process operates on a different principle “heat slowly, spray faster.“
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 plastic deformation of the particle and a bond that we cannot accurately measure.
In the ASTM 633C bond test, the only result we get is broken glue, even with 0.040“ (1 mm) of WCCo 88/12.
A Polished Compressor Piston Rod with a Kermetico HVAF Tungsten Carbide Coating
A Polished Compressor Rod with a Kermetico HVAF Coating
Blasting and Spraying Compressor Rod Coatingss with Kermetico High Velocity Equipment
Usually, we deposit compressor rod coatings using robotic blast and spray operations.
We blast a surface with a Kermetico HVAF gun (it is extremely fast and uniform).
After switching the powder feed hose and perhaps changing the nozzle, we spray it with the same gun.
It is much faster, more accurate and uses much less grit than the conventional compressed air blasting.
Hot blasting provides very even surface preparation and induces less stress into the base metal.
Kermetico HVAF & HVOF Thermal Spray Coating Equipment
Kermetico designs and manufactures three families of HVAF and HVOF thermal spray equipment.
- Convertible HVOF and HVAF equipment:
- Multi-purpose HVAF AK systems, with a range 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 in a job shop – recommended for compressor rod coating
- AK5 – a compact gun to spray smaller parts and thin walls
- 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. – Material Science Excellence, HVAF and HVOF Equipment Manufacturing and Thermal Spray Coating Services 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
