Trouble with new 3MB gun
06-23-2008, 01:43 PM,
#1
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 workSad
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,
#2
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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06-23-2008, 06:54 PM,
#3
RE: Trouble with new 3MB gun
Hi Gordon,

It's a 3MB with a GH nozzle.

Jim
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06-24-2008, 12:58 AM,
#4
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 Big Grin
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06-24-2008, 04:45 PM,
#5
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 Sad

We will fire it up in the morning and see what happens.

Jim
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06-24-2008, 05:02 PM,
#6
RE: Trouble with new 3MB gun
Hi Jim

Don't worry, it happens to most at some time Happy0193 Why do think I suspect the distribution ring? Ashamed0002 Do it the other way round; a argon distribution ring running on nitrogen and the gun will refuse to ignite (just incase Happy0193)

I'm sure it will be fine now.
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06-24-2008, 05:39 PM,
#7
RE: Trouble with new 3MB gun
TurbineRepair Wrote: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 Sad

We will fire it up in the morning and see what happens.

Jim

The Ar ring is for the GH nozzle and has one hole in it. It positioned at 12 o'clock. The G nozzle uses the N2 ring. The N2 ring has two holes in it and is positioned at the 9 and 3 o'clock positions. The rings I have are always white, even if they are for N2 or Ar.

The GH nozzle has a tighter spray pattern and velocity than the G. The cones of the nozzle are the difference. The G has a short cone and the GH has a longer cone.
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06-25-2008, 09:15 AM,
#8
RE: Trouble with new 3MB gun
Hi guys,

I've changed the ring and managed to get the correct voltage with the test parameters... even though we still have a G nozzle.... GH nozzles on order!

Jim
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06-26-2008, 05:19 AM,
#9
RE: Trouble with new 3MB gun
TurbineRepair Wrote:Hi guys,

I've changed the ring and managed to get the correct voltage with the test parameters... even though we still have a G nozzle.... GH nozzles on order!

Jim
The G nozzle should work, but the velocity will be a lil slower and the spray pattern will be a lil bigger. Just depends on what you are looking for.
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06-27-2008, 03:53 PM,
#10
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 Rolleyes 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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06-30-2008, 10:21 AM,
#11
RE: Trouble with new 3MB gun
I did wonder about the differences but I didn't like to ask, just happy that it works for now Smile

Jim
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06-30-2008, 05:30 PM,
#12
RE: Trouble with new 3MB gun
Gordon Wrote: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 Rolleyes 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.

Thanks for that Smile
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