I want to deposit a nano-material which starts to degrade at 1000 deg. cel. and completely melts at 1600 deg. cel. I want to use HVOF process for coating, so which torch/gun is suitable ? What should be the process parameters so that particles must not be heated more than 1000 deg. cel. ?
As per my knowledge, you can use an online diagnosis monitoring system to visualize the temperature distribution of the particles. In that respect, you might know how much of the spraying powders are being fully melted and how much haven't. You'll have to play around with the process parameters to achieve the desired coating. A DOE might be handy somehow,
You can also inhibit fully melting by using a larger particle size distribution.
Hope it helps..
All the best.
Yes, these techniques are the last options, but these are costly ones, also powder will be consumed more which I have in small amount. I have worked with accuraspray, spraywatch but I have asked this question hoping that someone might have worked on similar type of material. I also know to reduce particle temperature higher velocity is required but it will result in coating with small porosity. In my case I am interested in high porosity (>5%).
Would you use plasma spray, my answer were: reduce electric power input and/or reduce the flow rate of secondary working gas (hydrogen). In HVOF torch, the burning of combustion gas in oxygen gives the temperature of 3400°C or so. The variable here were combustion gas/oxygen ratio. But you newer lower down the gas temperature to 1000°C. One thing you can reach is the slight modification of gas temperature and velocity.
Then we touch the second point, which the heat transfer. The particles remain in the flame less than 1 milisecond and, moreover, the heat conduction in agglomerated particles as yours, is weak. Consequently, the shortening of time of contact between flame and particle would reduce the temperature of particles.
Still, when we speak about temperature of particles depends on its thermal conductivity. Low conductivity particles (Biot number=
Dear Mr. Pawlowski,
Thanks for your valuable answer, I know that you are a practical man of plasma spraying but I have never worked on plasma torches. Can you tell me what is the lower limit of plasma temperature that can be achieved without affecting the arc stability ?
regards
Here again, no easy answer is possible. At thermal spraying what counts is rather heat and momentum transfer from gaz to particles. Consequently, such gaz coefficients as heat conductivity and viscosity of gazes are of importance. To increase these coefficients, the molecular gases as hydrogen and nitrogen are added to argon.
Using pure Ar plasma and relatively low power input you will reach lower temperature than 10 000 K. But you can hardly melt any material because plasma has low heat transfer capacity.
- Badges
- Science topic
- Similar topics
- Engineering
- Materials Engineering