MIG Gun Overheating

[FlashBlind]

I practiced spray transfer last night with my Miller Vintage 250 at Tap #6 of the High range (Max Setting) and .035 wire set at about 550 IPM on 1/2" fillets and T joints. I guess I had the gun too close to the work, when I had finshed a 6" pass, the nozzle was cherry red and had burned back on the side closest to the work. I realize that this is working the limits of my setup, and I had the nozzle too close, but if I keep the gun back a bit, can I expect to be able to use spray transfer on 1/2" without burning up my gun completely?

[Scott V]

I don't know what gun you have,but maybe there is a heavyduty front end for it?Did you have the tip inside the nozzle also?It does take a decent sized gun to do very much spray arc,also maybe back your voltage down to where it kind of just spraying.That make a big difference in heat.It will be popping every now,and again.I find the back side of my off hand over heats before my guns.Find one of those shields with the foil type covering for your off hand makes a big difference.It does sound like your too close.

[cope]

spray transfer

I haven't done much spray, just ran a few beads so far, but my Tweco gun gets warm. Haven't gotten it red. Rock should be along in a couple of hours and he may have some Vintage specific answers. Another thought would be what gas setting you were running. As Scott said, mine crackles at the beginning of the weld and sometimes I get a mini-crackle during the weld. I have never set mine wide open and I have buried .035 wire in a 4" pipe flange cover, so you should be able to back off and still get good welds. Check theis site for some help on settings:

http://www.weldreality.com/spray_transfer_above100.htm

This is a set of suggested parameters for both short arc and spray transfer:

http://www.weldreality.com/short_circuit_under100.htm

[FlashBlind]

Gun is a Tweco #2, tip recessed about 3/8" within the nozzle. Now, after thinking about it, I had the nozzle edge within 1/4"-1/2" or so from the work. That probably explains the overheat issue. How far back should the nozzle be from the work with spray transfer?
In edit after seeing Dan's post:
I estimated my wirespeed based upon the manufacturers' manual that shows a range of 150-1030 IPM in the high speed mode. I did the beer math and at a setting of 45 (Out of a range of 0 [150 IPM] to 100 [1030 IPM] I should be at about 550 IPM. Realistically, I need to pick low and high settings, and do the time/ wire measurement exercise to verify speed. I might be way off..
The gas mix is a "Tri Mix" recommended by the weldors at Chickasha Industrial and Welding for both pulsed and spray transfer: 90% Argon, 8% CO2, 2%Oxygen.

[cope]

I think you were running too hot, but I'm not the spray transfer expert. Gun is surely big enough and tip recess seems OK also.

[d.paulson]

I think that gun is rated for 200A. You'll find yourself spending alot of money on tips if you don't upgrade to a bigger gun. The tips and cones are not heavy enough to take that kind of heat. I would suggest 300A min.

[Doug]

Mig gun overheating

Hi Flashblind, what is probably happening is you are keeping too close of a work to tip distance. When in spray tranfer you need to keep a 5/8" to 3/4" distance from tip of your gun to the metal that you are welding. Also the tip may be even with the nozzle of the gun. When in short circuit transfer the work to tip distance is about a 1/4" away. This is usually the hardest thing for first time welders to get used to on spray transfer. You may also want to try to set the flow on the regulator up to 30 cfh. This will keep the gun cooler. Good luck. Doug

[Franz]

This oughta cause smoke

Use straight Co2 instead of C25.
Definitely increases the cooling, and works well on steel.

[d.paulson]

You need under 15% co2 in order to spray with good results. I prefer 90-8-2 mix. You should hear a bit of crackle when welding. If you do not hear any noise, turn up wire feed until you do. Too low of wire feed will give you undercut and excess smoke in the air

[Guest]

Dr. Flash...your tip is recessed too much...it should only be 1/8" inside the nozzle that also accounts for your overheating. Your 90-8-2 gas sound real good...now just find the "sweet spot" in you parameters.