Why Liquid fuel is better than Gas fuel in HVOF?
04-30-2008, 12:35 PM,
#1
Why Liquid fuel is better than Gas fuel in HVOF?
Dear Forum

Why liquid fuel system is better than gas fuel for HVOF coating??

It is said that Luquid fuel sistem gives better porosity, bond strength, and density. why?
Again liquid fuel produce higher heat which mey produce undesirable metastable phase and oxide for Wc coating. It's little bit confusing.

Please help me.
Can any one send me any literature(link)?

Thanks & With worm regards.

Dibyendu Dhara*

Question
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05-02-2008, 07:24 PM,
#2
RE: Why Liquid fuel is better than Gas fuel in HVOF?
Hi Dibyendu Dhara

Quote:Why liquid fuel system is better than gas fuel for HVOF coating??
Don't think liquid fuel necessarily is better than gas fuel.

Quote:It is said that Luquid fuel sistem gives better porosity, bond strength, and density. why?
Again liquid fuel produce higher heat which mey produce undesirable metastable phase and oxide for Wc coating. It's little bit confusing.
If we consider say the two extremes kerosene/oxygen and hydrogen/oxygen. H2/O2 will be capable of much higher flame velocity, but on the other hand kerosene/O2 will be capable of much higher gas density. Gas velocity and density both have major effect on particle acceleration and ultimate speed (assuming relatively equal gun design technology like barrel or Laval nozzle, nozzle length, combustion chamber pressures etc.). At the moment I think with the various HVOF equipment available the liquid fuel systems possible have a slight particle velocity advantage. So the answer to why? is particle velocity. But, parameter tuning and powder selection will have a major effect as well on coating properties.

Quote:liquid fuel produce higher heat
Not sure what you mean to say here. If it that say a JP5000 throws out a lot more BTU's or Joules than a Diamond jet then fair enough, but this in itself will not necessarily effect particle temperature/velocity and coating quality. If you mean maximum flame temperature then really all the common HVOF fuels are roughly in the same ball park (also need to consider pressure - higher pressure - higher temperature). Move to air/fuel systems (HVAF) then that is significantly cooler or oxyacrtylene at the top end of combustion temperatures. Production of undesirable metastable phase and oxide really is mainly down to parameter and powder size tuning.

Starting to ramble on, sorry. Complex subject, swings and roundabouts etc. Some interesting reading here, some way through the text there is discussion of HVOF design and fuels. Very good, even though there are a few questionable items Big Grin
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05-06-2008, 11:14 AM,
#3
RE: Why Liquid fuel is better than Gas fuel in HVOF?
Thank you very much Mr. Gordon for your valuable information. You are right it is a very complex subject; we have to choose appropriate system depending on the application and requirement.

Thank you once again.

Dibyendu*
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12-30-2013, 02:36 PM,
#4
RE: Why Liquid fuel is better than Gas fuel in HVOF?
I have the experience to use both system, coating quality is almost same, however liquid fuel system can put more powder on part (powder feeder rate higher) at same time will put more heat on part during process, it may lead coating problem on complicated geometry part, such as blistering. If the process can be controlled well, liquid fuel system is more efficiency system. Smile
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