On Site Coating of Corrugating Rolls: HVAF & HVOF Tungsten Carbide Thermal Spray Equipment
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.
Kermetico's 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.
Kermetico HVAF Process
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.
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.
For information on the differences between HVOF and HVAF, Click Here.
