07-15-2010, 06:12 PM,
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desMoira
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obstruction during deposition of amorphous powders
Dear "surfacers",
I am new to amorphous materials and have little experience with hvof thermal spray. I wonder if you could help me with spraying problems.
I'm using a tafa jp 5000 to do an amorphous iron based coating with a nanosteel powder, but only the first deposition runs ok while following coatings are impossible to obtain even changing thermodynamics by parameters such as oxigen and fuel flow and ratio.
No problems with other powders but when I try again with this again I can do only one coating, as at the second deposition obstruction of injectors happens and need to stop.
What can I do?
I worked with fuel enriched flow to preserve particles from oxidation.
Thanks,
Moira
"Progress of science requires opportunity for share with no restriction all results and all point of views: this freedom of communication is indispensable for the development and extension of scientific knowledge". [A. Einstein]
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07-16-2010, 10:07 AM,
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desMoira
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RE: obstruction during deposition of amorphous powders
Hi Simon,
thank you very much for your answer.
I do have high amorphous fraction also in the second coatings, but I have to stop the process perhaps the temperature is higher (don't know why as I stop the equiment between depositions) or some other problems occur in the powder flow before combustion chamber: at the second deposition the flexibles burn on the injectors and also the barrel has some internal deposits!
Then I change barrel, injectors and flexibles but still I can't get a good process. The only way is to spray some others powders for a while (that you know is not so easy with only one distributor available) and then spray the amorphous one to have the first good coating.
Can't go on in this way. How can I do?
Thanks a lot,
Moira
"Progress of science requires opportunity for share with no restriction all results and all point of views: this freedom of communication is indispensable for the development and extension of scientific knowledge". [A. Einstein]
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07-20-2010, 04:34 PM,
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desMoira
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RE: obstruction during deposition of amorphous powders
Hi Simon,
I'm spraying a gas atomized powder -53μm/+15μm. The particles are near-spherical with satellites attached. That's why I got problems. I already worked with high pressure (up to 110psi) and with the 4" barrel that is the shorter one, with no results. Now I arrive to have two deposition done before internal deposition in the barrel occur with an enlargement of the barrel ending. Next trial will be at lower powder feed rate with increasing of the flow of the carrier gas.
Thanks again for your interest,
Moira
"Progress of science requires opportunity for share with no restriction all results and all point of views: this freedom of communication is indispensable for the development and extension of scientific knowledge". [A. Einstein]
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07-21-2010, 03:20 PM,
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loriolo
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RE: obstruction during deposition of amorphous powders
Hi desMoira
One of my customers, had the same problem with Hastelloy C 276 powder, the fines in powder produce this kind of problem, I solved the problem, just pouring off from a can to another in front of a vane of an exhaust fan, in order to eliminate fines, I tried with different powder productors but the result was the same, finally I decided to change to HVOF wire system, and finally I had a good result, with satisfation of my customer, for all the other answers Simon was right.
Regards
Luigi
Best regards
Luigi
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07-22-2010, 01:18 PM,
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desMoira
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RE: obstruction during deposition of amorphous powders
Wire system... very interesting. I'll look for information and soon I'll keep you up to date.
Thanks a lot Loriolo.
"Progress of science requires opportunity for share with no restriction all results and all point of views: this freedom of communication is indispensable for the development and extension of scientific knowledge". [A. Einstein]
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