What is the main factor for affecting the efficiency of melting the powder?
06-21-2011, 12:41 PM, (This post was last modified: 06-21-2011, 02:57 PM by Justin.)
#1
Shy  What is the main factor for affecting the efficiency of melting the powder?
Hello...everyone!

I'm a newbie.Big Grin

I have a question about melting the powder. I heard a special view point from someone. He said "The powder would be melted better if the gun have higher energy density, although the power of this gun is smaller than the other gun." Is it possible?

I feel confused very much. The energy desity becomes higher and higher with increasing the power, doesn't it?

Please share your experience and opinion.Shy

Thanks.
Justin
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06-21-2011, 02:47 PM,
#2
RE: What is the main factor for affecting the efficiency of melting the powder?
What types of gun ? and what types of fuel du you use in your system...?
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06-21-2011, 03:19 PM,
#3
RE: What is the main factor for affecting the efficiency of melting the powder?
(06-21-2011, 02:47 PM)Metallurgy_eng Wrote: What types of gun ? and what types of fuel du you use in your system...?


First, thanks for your reply.Smile

Herein, we discuss plasma guns. Two used gases are argon and hydrogen.

Generally, we can know how the power of a plasma gun is. But we may rarely hear about what the energy density of the gun is.

Regards,
Justin
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06-22-2011, 02:22 AM,
#4
RE: What is the main factor for affecting the efficiency of melting the powder?
Hi Justin

Sign0016 to the Surface Engineering Forum.

Quote:I have a question about melting the powder. I heard a special view point from someone. He said "The powder would be melted better if the gun have higher energy density, although the power of this gun is smaller than the other gun." Is it possible?

Yes

Quote:I feel confused very much. The energy desity becomes higher and higher with increasing the power, doesn't it?

Yes to some extent, when considering the same plasma system and nozzle.

But plasma spraying a powder to form a good coating is reliant on many other factors. A lot of my experience with the higher energy plasma spraying has been with carbide based coatings. These do not actually require that much heating, but very high velocity.

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06-23-2011, 06:31 AM,
#5
RE: What is the main factor for affecting the efficiency of melting the powder?
Hi Gordon

Thanks for your reply.Smile

How about NiAl coating?

Velocity is also a reason of affecting the quality of coating.

Herein, Energy density that we discuss is related closely to the concentration of heating (power) for a plasma gun.
I don't know whether the statement exists or not.Shy

Regards,
Justin
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07-14-2011, 07:10 AM,
#6
RE: What is the main factor for affecting the efficiency of melting the powder?
Justin,
Just to complicate the issue for you there are other factors affecting the melting of powders:
1. Plasma flicker. I have seen cases with an F4 where there was no plasma 10% of the time due to arc strike. It was very clear during the times when there was no plasma that the particles were not melted.
2. Plasma Shape. Different torch manufactures claim their plasmas have various shapes which help particle melting. For example, the Sulzer Metco Triplex torch has a three lobed plasma. They inject the powder inbetween the lobes and are able to get a very consistent powder injection and energy transfer to the particles.

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07-15-2011, 03:31 AM, (This post was last modified: 08-15-2011, 01:14 AM by ServiceTech.)
#7
RE: What is the main factor for affecting the efficiency of melting the powder?
When dealing with plasma guns, powder injection parameters are extremely important factors to consider. Injector angle, carrier gas flow, injector to nozzle distance and diameter are all factors to consider. Guns rated at higher KW levels are not always the most efficient at coating production. Low power, lip feed injection guns that inject powder at close proximity to the plasma arc can produce coatings at similar or greater efficiencies and feed rates as higher KW guns with traditional injection schemes. Your friend may have this in mind with his statement.
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08-13-2011, 10:00 AM,
#8
RE: What is the main factor for affecting the efficiency of melting the powder?
Justin,

The term energy density is not known to me but I can imagine that when something has a higher desnity it contains more energy. Although it is not so simple to say that higher density, asuming energy, results in higger efficiency and/or better coatings (can you still follow me?)

It depends on many, many factors, for example if the density of the plasma increases it is more difficult to inject the powder (especially smaller grain sizes) they cannot penetrate the surface tension. Also every powder has its own melting behavior so sometimes (as Gordon stated with carbides) material does not require high energy. This in contrast to Zirconium materials who do. So this special viewpoint from someone, as you mention in your question, is not very well discribed and from my opinion a wrong statement.
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09-26-2011, 06:03 PM,
#9
RE: What is the main factor for affecting the efficiency of melting the powder?
Hi justin,

i agree with comments of gordon & joris Kraak

I think it is better to carry coating at optimum parameters related to powder & Thermal Spray Gun.

if heat input is more than required, then there is always chances to occur unwanted reactions like decomposition, oxidation and phase changes etc in more extend than normally occurred at optimum heat input and intensity of internal stresses also more and all these reactions leads to reduce coating performance.

Please note that High Power density leads to high heat input only. Hence, it is better to maintain it at optimum conditions only.
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