Why Add HVAF to HVOF Equipment?
The Kermetico AK systems deposit the same specification coatings with a spray rate that is 5-6 times higher and at a 20-30% higher deposition efficiency, which leads to ½ of the HVOF cost and can provide a coating of higher quality when needed.
Choosing Kermetico AK, a manufacturing shop gains a 50% cost advantage over HVOF competitors and additional coating quality superiority as a bonus.
The Thermal Spray Industry uses the HVAF process infrequently because it is not consistent with most HVOF standards. (AF systems work best on fine powders, while some specifications require 15-45 or 20-53 μm powder sizes).
The Kermetico C (C for Convertible) equipment family operates in either mode.
Kermetico C uses gas fuel, oxygen and air to spray HVOF powders consistent with HVOF standards, and it works in pure HVAF mode to deposit ductile, high-hardness (1400-1600+ HV300, 6% deviation), non-permeable, smooth as-sprayed tungsten carbide coatings.
The HVOF mode Convertible is compliant with HVOF specifications and still lets you halve operating costs. The HVAF mode offers you greater savings or allows you to create coatings with properties superior to any HVOF spec – the choice is yours.
Coating Quality
The quality and efficiency of the Convertible equipment is the result of the relatively low combustion temperature of air-fuel or oxy-fuel mixtures combined with the axial injection of the feedstock through the long combustion chamber, where the low gas velocity provides sufficient time for the powder particles gradual heating.
The material’s acceleration occurs in the nozzle that has a large diameter.
The large diameter of the nozzle is needed to ensure that the nozzle walls do not interact with the powder particles, allowing the use of a nozzle that is as long as needed for feedstock acceleration, typically from 800 to over 1,000 m/s (2,600 – 3,300+ ft./sec.).
The Catalytic Insert is used in the combustion chamber to provide a broad range of stable combustion parameters.
Heating Efficiency
The 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.
Heating efficiency is a primary reason for the lower cost of Kermetico coatings.
Acceleration Efficiency
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.
Uniformity of Coating Quality
The diameter of the spray particle jet is several times smaller than the nozzle diameter. The influence of the nozzle walls on the spray particle velocity is negligible, providing even acceleration of the powder particles and improved consistency of the coating structure.
