Gordon England Surface Engineering Forum



Re: thermal spray variables


Posted by Gordon England on January 08, 2004 at 02:03:25:

In Reply to: Re: thermal spray variables posted by Leo on December 17, 2003 at 10:14:22:

: : : Hi gordon, I'm finding the factors that could affect the spray flame temperature. I found there is a pic in your page : the nature of thermal spray coating. But the resolution is too low, is it possible for me to got a better one?

: : : And one more thing, my project is facing a problem that the flame may be too hot in flame spray process and change the phase of the powder, do you have suggestions?

: :
: : Hi Leo

: : Thank you for pointing out the poor quality image, I did intend to update this image ages ago!
: : Please revist the page to see a new image.

: :
: : What equipment and set-up are you using?

: Terodyn 2000
: oxygen 60psi acetylene 15 psi
: substrate is steel plate (polished) sprayed with silicon oxide by high gas pressure

Hi Leo

Try altering the gas flow rate while maintaining the ratio e.g. 52 psi oxy 13 psi acetylene, then try changing gas mix ratio or combination. I find it best to do this when the gun is spraying the powder. Watch the colour/brightness of the particles in the flame, you should be able to see if you are spraying hotter or colder.

If you still need to reduce the heat input, you could try using oxygen/propane. You will probably need some hardware changes for this though.

Not sure if this accessory/technique is used on this gun, but I would recommend trying it: Compressed air jets mounted either side of the nozzle crossed so that the air jets intersect the flame at around 50 mm and use a spray distance of 50 + 12 mm. If memory serves me right, the air jet nozzle diameters are about 3mm and air pressure about 70 psi. This set-up is primarily design as an accelerator and produces much denser and higher quality ceramic coatings. In your case, with some playing around it may give you more scope for controlling temperature while also increasing particle velocity.

Hope this helps

PS Are you producing a pure TiO2 coating or are you employing a lower melting point matrix phase for binding?


Regards Gordon




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