06-23-2008, 01:43 PM,
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TurbineRepair
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Trouble with new 3MB gun
Hi all,
We have just bought a brand new 3MB gun to replace the hybrid thing the guys were using. To our disappointment it doesn't seem to work
We ran a test with the test parameters, Ag 40l/m, H6.6l/m, 500A but we can't get near the 60-70V it should be, a mere 45V was the best. We reconnected the 3MB/3MB-II, entered the above and got 65V, very annoying.
We stripped the gun and everything looks good. Can anyone suggest what may be going wrong (A3000 system)? Incidentally the test pieces we have tried with the new gun have been really bad.
Thanks
Jim
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06-23-2008, 04:59 PM,
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Gordon
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RE: Trouble with new 3MB gun
Hi Jim
When you say a brand new 3MB, is that a 3MB-II or the old style 3MB? Which nozzles are used in the comparison?
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06-24-2008, 12:58 AM,
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Gordon
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RE: Trouble with new 3MB gun
Hi Jim
With your indicated flows I would expect ~ 65-70V measured at console with 15' hoses (~ 3V lower at gun) at around 400-500A with the GH nozzle. Something is very wrong, as you are not getting alot above the natural voltage of pure Ar. One thought, are you sure you are not using a nitogen insulator/distribution ring instead of the one for argon. That would certainly lower voltage
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06-24-2008, 04:45 PM,
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TurbineRepair
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RE: Trouble with new 3MB gun
Hi Gordon
Again thank you for pointing me in the right direction. After reviewing the manual it would seem we have the wrong nozzle (G rather and GH) fitted and the wrong distribution ring.
Unfortunately our guys did not spot this when they "checked" it was ok. The distribution rings for argon and nitrogen are difference colours and have different hole configurations right? humm
We will fire it up in the morning and see what happens.
Jim
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06-24-2008, 05:02 PM,
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Gordon
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RE: Trouble with new 3MB gun
Hi Jim
Don't worry, it happens to most at some time Why do think I suspect the distribution ring? Do it the other way round; a argon distribution ring running on nitrogen and the gun will refuse to ignite (just incase )
I'm sure it will be fine now.
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06-27-2008, 03:53 PM,
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Gordon
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RE: Trouble with new 3MB gun
Out of interest, the reason many of the Metco guns use different plasma gas distribution rings/insulators, is to make the guns compatible to run with both argon and nitrogen plasma gases. Argon being relatively easy to ionise and generates low energy plasma. Nitrogen on the other hand is more difficult and requires more energy, this is mainly due to nitrogen being diatomic and requiring dissociation before ionisation. Argon distribution rings/insulators produce a non-laminar swirling flow, that effectively increases radial gas velocity and increases the electrical resistance of the plasma giving higher energy (voltage). Nitrogen is injected in a less turbulent laminar manner to try an lower the electrical resistance, voltage and energy of the plasma so that the gun becomes compatible to use with both plasma gases (without using excessive argon flows anyway). Hope that makes sense Argon will all too easily form a plasma using the (wrong) nitrogen distribution ring, producing a much lower voltage plasma. Nitrogen through an argon distribution ring though would probably be impossible to start due to the excessive voltage required.
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