SM 3MB Gun with GP Nozzle

[ykang]

Dear All:

I am facing a serious problem with my 3MB gun with GP nozzle. It gave inconsistent ignition, which the pilot Argon gas took slightly longer time to ramp up, or worse case, the flame could cut-off itself, or it couldn't sustain the plasma flame. Sometime it couldn't ignite at all. Even if it was succeeded in ignition, we observed the displayed voltage readings were fluctuating quite a lot.

Same gun with GH nozzle was perfect. System had been checked without significant leakage or faulty. SM commented that the voltage fluctuation was due to the inconsistent ionization of argon gas, but my question is "WHY" if the system has no faulty. Hence, I would like to know if anyone experienced similar problem before.

I wish to know, if such problem could be caused by long cycle spraying (>20mins)?

Thank You very much

Regards

[Gordon]

Hi Ykang

Your problems tend to suggest you have a problem with your equipment or set-up.

System had been checked without significant leakage or faulty

Does that mean you can't detect any leaks, as any leakage is significant. Water or air getting into the system will certainly cause problems even in tiny amounts.

The fact that GH nozzle parameters appear to work ok, may not be a good guide as plasma forming conditions are much easier.

I wish to know, if such problem could be caused by long cycle spraying (>20mins)?

This should not be a factor unless you are damaging/wearing out nozzle/electrode hardware. I assume from this that you are managing to get the plasma running. If so, does it appear to run ok at final parameter settings - is voltage stable and correct for your specific plasma gas flows.

[TurbineRepair]

Hi Ykang,

I don't use a GP very often but we always start our 3MB as if it were a F4 gun. Your system may not let you to this but our old A3000 lets us change the gun type quiet easily. As I understand it the F4 needs a bit more juice to get it going so by fooling the system into thinkings its running the F4 gun it allows more argon to flow and gun lights better.
I'f you try this just make sure you don't exceed the 40KWatt rating as 3MB has a lower power limit compared to some other guns.

Jim

[ykang]

To Gordon:

Would you please elaborate a bit more about your statement "

The fact that GH nozzle parameters appear to work ok, may not be a good guide as plasma forming conditions are much easier.

"... I was told that GP was more 'sensitive' to voltage fluctuation due to its nozzle configuration is more 'restricted' to gas flow than GH, do you read that?

We detected a very minor gas leakage at the insulator body, hope this would be the causes, now awaiting for the spare part to be delivered...Thanks

To Jim:
Thanks for your advices as well...

Regards;
YKang

[LEN WOOD]

Hi Ykang,

Not sure that your "minor gas leakage" will be the "Eureka" but it may be contributory and certainly needs to be sorted.

I am assuming that you're spraying 450NS with the GH and then 601NS with the GP nozzle?

Here the major parameter differences are low Primary Ar gas with High Secondary COMPARED to High Primary Ar and low secondary Hydrogen. Add to this the different inner geometries of the nozzles. The GP is smaller and without going into the Plasma dynamics and relative Physics; these factors make (as was already touched on) the '450NS' Plasma much easier to create, sustain and stabilise. You will notice when using the GP set-up that as you increase the Secondry gas and bring up the Amps the instability lessens and settles. Obviousy both these different Plasmas and their injection arrangements are created relative to the powder they are melting and conveying in their respective streams.

Look at the aft (rear) of the GP nozzle where it tapers in. Are there arc strikes quite close to the back. If so then you have an gas purity problem. This could arise from a bad gas supply (or the latest delivery) or a contaminated line either from a leak or from another type of gas that shares a section of the line for another process? The fact that your voltage is erratic and spiking suggests that Argon (which spirals and elongates the ignition strike) is not doing what it should because it is not pure enough.

While there are many possible reasons and contributing factors for this issue. I would start with the looking at the GP nozzle aft.

Also worth double checking is the Argon pressure setting.

Has the system been sufficiently serviced recently?

Let me know how you get on. I could drop by if you pay my ticket!

Cheers
GlenB

[Gordon]

Hi Ykang

To Gordon:

Would you please elaborate a bit more about your statement "

The fact that GH nozzle parameters appear to work ok, may not be a good guide as plasma forming conditions are much easier.

"... I was told that GP was more 'sensitive' to voltage fluctuation due to its nozzle configuration is more 'restricted' to gas flow than GH, do you read that?

We detected a very minor gas leakage at the insulator body, hope this would be the causes, now awaiting for the spare part to be delivered...Thanks

To Jim:
Thanks for your advices as well...

Regards;
YKang

GlenB has gone some way in answering your question .

As to my statement regarding plasma forming conditions are much easier with the GH, I should really have said controlling (ramping up to operating conditions) the plasma in the GH nozzle is easier. A bit like the difference in flying a aerodynamic stable aircraft compared to a unstable one (so I'm told ) which needs computer aided control. The GP nozzle having a smaller bore and much higher gas velocities just makes for a less stable plasma or one that is more sensitive to conditions. A rough ramp-up in power with the GP nozzle will easily blow out the plasma, while the GH nozzle will be more tolerant to instabilities and self-correct to some extent.

[ykang]

Hi GlenB:

Please see the attached photos, if you think that there were caused by the 'Argon purity'? Try to take a better angle but just wasn't easy to do that..

   
   


Just one more question, did you experience the voltage drop gradually (i.e. 72V -> 68V) within a cycle run of maybe 20 cycle-passes? I am not sure if this is common for GP nozzle as the voltage dropped so much within a cycle run, which it was not common in GH nozzle.

Regards;
Ykang

[LEN WOOD]

Hi Ykang,

Not sure about your sentences, especially the latter. Are you saying that you couldn't take a picture at a better angle?

Please see the attached photos, if you think that there were caused by the 'Argon purity'? Try to take a better angle but just wasn't easy to do that..

Even from the front I can see the gouging. Please try to get a picture from the back of the nozzle (rear) and also the electrode. When you take close up pictures you should utilise the macro function for better clarity. Make sure that your light and/or shadow doesn't obscure the shot. Also try not to use the flash.

I can see that you do have issues and they look like they are gas or cooling related. Does the electrode white spark continuously from new to life-end or failure?

Depends on how big the component being processed is - a whole IP Case assembly takes a long time! How long (hours or mins) has this particular GP nozzle been run?

Please can you list the parameters (including powder port) for GP? Are you spraying 601NS? What are your system cooling set points (min & max). Is condensation a factor in your environment?

Would you say that the GH nozzles last, sustain voltage and perform normally? How long have you been spraying with GP nozzles - have you ever achieved normal results?

I know I've asked a lot of questions. You can paste this post and put your replies after the question marks for ease. You could PM me if you find it easier. I could then let you know our Dark Knight assistance rates

Cheers