Loose Particle of Flame Coat

[operator]

Hi all,

I using Sulzer Metco 14E gun with 1/8in aluminum wire and powered by Oxygen and Acetylene.
The problem is it has a lot of white colour loose particles,. The more layer I sprayed, the more loose particles. But if I sprayed less layer, I couldn't achieve required Ra.
Is there any parameter that playing big role here?
What if I wait for the work piece to cool down before I proceed for 2nd layer?

[Gordon]

Hi operator

to the Surface Engineering Forum.

I can't really visualise your problem unless your doing something totally away from the norm. Could you provide us with photo of the coating.

Quote:Is there any parameter that playing big role here?

Are you a beginner at thermal spray? To be honest and no offence intended, it sounds like you need some decent training and instruction on the process.

[operator]

I'm totally new in surface engineering stuff, just came into contact with this weeks ago. This is a very informative forum and Im glad I found this.

My Ra requirement is 600-800uin. So I need to spray 3 times to achieve this Ra. But the more layer I sprayed on substrate (aluminium) it seem to have more white colour loose particle coming off from substrate.

So now I have drafted a few experiment to get better result in term of Ra and in term of loose particle.
1. Ra value before coating on substrate. (Higher Ra after grit blasting better for coating to take place)?
2. After first layer coating do I need to wait for the substrate to cool down before proceed for 2nd layer?
3. Im using pure Aluminum wire 1/8" currently, is there other wire suitable for this process, how bout Ni-Al?

Basically, my workpieces consist of sputtering parts which need to be coated and stripped on bi-weekly basis.

[Gordon]

Hi operator

Quote:1. Ra value before coating on substrate. (Higher Ra after grit blasting better for coating to take place)?

Well you could use a slightly finer grit blast. As long as it is clean and sharp and your coating is not excessively thick, there should be no problem.

What coating thickness do you require?, I guess you only need a covering so tune your grit blasting to give the final roughness required with the minimum coating thickness required say around 0.004".

Quote:2. After first layer coating do I need to wait for the substrate to cool down before proceed for 2nd layer?

That depends on how hot the coating/substrate gets. Most metal substrates will benefit from a preheat of around 80 - 100C, though not aluminium or magnesium substrates which are best not directly preheated with flame at all. During spraying try and keep temperature as constant as possible and try and keep lower than a maximum of round about 180C. You can use a air blast cooler to assist in temperature control.

Quote:3. Im using pure Aluminum wire 1/8" currently, is there other wire suitable for this process, how bout Ni-Al?

Not sure what the exact function of your coating is, can you give more detail.

I can only think that the white particles are aluminium oxide. What hardware and parameters are you using? What is the length of the wire tip in the flame (protruding from air cap)?

[plasmajet1990]

(12-16-2011 10:50 AM)operator Wrote:  Hi all,

I using Sulzer Metco 14E gun with 1/8in aluminum wire and powered by Oxygen and Acetylene.
The problem is it has a lot of white colour loose particles,. The more layer I sprayed, the more loose particles. But if I sprayed less layer, I couldn't achieve required Ra.
Is there any parameter that playing big role here?
What if I wait for the work piece to cool down before I proceed for 2nd layer?

Hi,

Try to lower the oxygen / acetylene ratio.

Ion

[operator]

Ion,
I'm using 80-90scfh Oxy and 30-40scfh Acetylene as recommended in the manual. For a complate combustion for Oxy and Acetylene is Oxy/Acetylene is 2.5. So should I increase acetylene or lower oxy flowrate? How about air flowrate.
Sometimes, i think is the environment factor, the spray booth is quite dusty.

Gordon,
The EDX for the white loose particle is purely Al. What does it tell? Does it come from the wire which not melted and deposited on substrate?
How about wire speed? how to take wire speed measurement.

Merry Christmas to all.

[plasmajet1990]

(12-25-2011 05:15 AM)operator Wrote:  Ion,
I'm using 80-90scfh Oxy and 30-40scfh Acetylene as recommended in the manual. For a complate combustion for Oxy and Acetylene is Oxy/Acetylene is 2.5. So should I increase acetylene or lower oxy flowrate? How about air flowrate.
Sometimes, i think is the environment factor, the spray booth is quite dusty.

Gordon,
The EDX for the white loose particle is purely Al. What does it tell? Does it come from the wire which not melted and deposited on substrate?
How about wire speed? how to take wire speed measurement.

Merry Christmas to all.

Hi,

You can try O2/C2H2 = 2 (80/40) and decrease the wire speed.

Ion