Process Gasses Purity Impact towards Plasma Spray Process, equipment or outcome
09-07-2007, 06:20 AM,
#1
Process Gasses Purity Impact towards Plasma Spray Process, equipment or outcome
Gordon,

Why is purity utmost important in process gas (1st gas or 2nd gas).

for argon used as 1st gas, the grade used is normally pre-purified grade 5 9s and above 99.9995% etc, can we use anything lower than 4 9s? what is the impact to the equipment, process or coating outcome?

Thanks.

Regards,
Alex
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09-07-2007, 01:30 PM,
#2
RE: Process Gasses Purity Impact towards Plasma Spray Process, equipment or outcome
Hi Alex

Quote:Why is purity utmost important in process gas (1st gas or 2nd gas).
Contaminants such as oxygen and water will effect the plasma's properties and will be detrimental to nozzle and electrode.

Quote:for argon used as 1st gas, the grade used is normally pre-purified grade 5 9s and above 99.9995% etc, can we use anything lower than 4 9s? what is the impact to the equipment, process or coating outcome?
Not sure on the percentage purity, but I would be inclined to follow the equipment manufacturers recommendations on this one. If you want to try out the lower purity grade for economic reasons, then knowing you I'm sure you will do extensive trials to establish pros and cons.

I know where nitrogen is concerned, you should always specify oxygen free Wink Reminds me of a phone call I got from someone complaining that he was getting 90V from his parameters, when he normally only gets 65V. He rang up shortly after saying he had sorted the problem Happy0193 They had been using an argon base weld shielding gas instead of normal argon Happy0193
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09-10-2007, 02:09 AM, (This post was last modified: 09-10-2007, 03:10 AM by Alexangel1226.)
#3
RE: Process Gasses Purity Impact towards Plasma Spray Process, equipment or outcome
Gordon,

I am thinking in the same direction on the impurities that causes potential impact to the process e.g u said O2 & stuffs.

Not really to try a lower grade ones.. but given a cylinder source with 99.9998% purity and the feasibility to used piped-in from central source with 99.9995% ..am thinking what would be the difference.. I guess not much.. but just a second thought on if a lower purity grade to be used, what would be the impact. I remembered one of my seniors expereince on the Argon purity prob. but do not know the exact story, something did not work but found out they had been using Argon with 3 9s, not the prepurified one, then changed to 5 9s grade..the thing worked...etc something like that.

Anyway, we have been using the piped-in from central supply (as it was a shared usage for some other process which use argon) for the ignition, before the process gasses (N2/H2) kick in. So I am quite sure it is alright for the ignition gas type to be used as process gas in our application.

Regards,
Alexangel1226
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09-10-2007, 08:00 PM,
#4
Exclamation  RE: Process Gasses Purity Impact towards Plasma Spray Process, equipment or outcome
Hi all,

Concerning Ar purity, i just want to give you a recent example:

A gas supplier( i won't say the name :p) change normal argon for one with a nice "commercial name"... in the fact i took a closer look and discovered that o? tolerance pass from 5 ppm to 50 ppm Sad (and of course for the same price)

you can imagine the effect with a ar/h? parameter...

The same supplier change o? in the same way but this time it was H?O that pass from 5 to 50 ppm....

We had problem this time with kerosene hvof...

My advice is to be very careful with purity.

Hope it help

Diucky
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09-11-2007, 01:47 AM, (This post was last modified: 02-29-2008, 03:41 AM by Alexangel1226.)
#5
RE: Process Gasses Purity Impact towards Plasma Spray Process, equipment or outcome
Gordon,

Quote:I know where nitrogen is concerned, you should always specify oxygen free Reminds me of a phone call I got from someone complaining that he was getting 90V from his parameters, when he normally only gets 65V. He rang up shortly after saying he had sorted the problem They had been using an argon base weld shielding gas instead of normal argon

When O2 get ionized, how would O2+ react with the Ar+ or other element? do you mean it will react with the nozzle bore which is Cu to form CuO or something? I still do not understand how existance of O2 will be detrimental? still cant corelate with the nozzle wear mechanism...=). or it happens when it releases the nozzle with the amount of o2 in the jet, it promotes the oxidation rate of the particle?


Duicky,

Quote:A gas supplier( i won't say the name :p) change normal argon for one with a nice "commercial name"... in the fact i took a closer look and discovered that o? tolerance pass from 5 ppm to 50 ppm (and of course for the same price)
you can imagine the effect with a ar/h? parameter...
The same supplier change o? in the same way but this time it was H?O that pass from 5 to 50 ppm....

Just out of curiosity, what is the effect you observe? Could you describe in more details? like gun can't start, parameter gone out of range, nozzle wear, gun burn...etc..?

Thanks
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09-11-2007, 01:28 PM,
#6
RE: Process Gasses Purity Impact towards Plasma Spray Process, equipment or outcome
Hi Alex

Oxygen and contaminants like cabon dioxide, water and to a much lesser extent nitrogen will show increasing nozzle/electrode erosion with increasing contamination. At some point of increasing contamination, the natural voltage you get for a pure argon plasma will rise (as in the effect of adding secondary plasma gas). Basically, low level contamination will mainly just effect hardware life, at higher levels plasma characteristics may change drastically. I would like to think most of us know how detrimental water can be in the plasma (talking gas stabilised plasma not water stabilised plasma here). The old test of seeing whether a cold glass surface/mirror "mists" prior to starting the plasma should always be done particularly when changing hardware. A small amount of water in the plasma will at best destroy your nozzle and electrode and at worst take out the whole gun.
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09-14-2007, 09:46 PM,
#7
RE: Process Gasses Purity Impact towards Plasma Spray Process, equipment or outcome
Hi Alex,

Gordon said almost everything on oxygen and contaminants effect.
Just to give you a tip to recognise a contamination on Ar/H? parameters: you can observe a blue ring at the base of the cathode (1 or 2 mm), the second point is a very bright silver colour on the top of the cathode.

You should note that you will have the same effect if you've got water or gas leaks on your gun, this time o? is coming from air or water...

Diucky
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09-15-2007, 05:01 PM,
#8
RE: Process Gasses Purity Impact towards Plasma Spray Process, equipment or outcome
Hi Alex and Diucky

Good tip there from Diucky Cool you may also notice an increase in tungsten and copper inclusions within your coatings.
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06-12-2012, 02:46 PM,
#9
RE: Process Gasses Purity Impact towards Plasma Spray Process, equipment or outcome
Looking for the Spec that calls out gas purity fro metal spray processes and having some trouble. Can anyone help?
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