Al-GMAW - restarts without burnback

Hi all
Burn-back to contactor tip on pulling trigger is my big problem at the moment.
Wire feed is smooth. I clean out the contactor-tip frequently with an oxy-acetylene nozzle
cleaner - the set of serated wires.
Yet - often - very quickly - burns back in fraction of a second so arc'ing off a blob on the contactor tip.
I'm trying things like holding a greater stand-off on start-up.
Will try snipping off wire at shroud so wire-feed has time to come up to speed (?) before wire touches job.
Etc.
Hints?
Best wishes, Rich Smith
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"Richard Smith" wrote in message
Hi all
Burn-back to contactor tip on pulling trigger is my big problem at the moment.
Wire feed is smooth. I clean out the contactor-tip frequently with an oxy-acetylene nozzle cleaner - the set of serated wires.
Yet - often - very quickly - burns back in fraction of a second so arc'ing off a blob on the contactor tip.
I'm trying things like holding a greater stand-off on start-up.
Will try snipping off wire at shroud so wire-feed has time to come up to speed (?) before wire touches job.
Etc.
Hints?
Best wishes, Rich Smith
---------------------
https://americantorchtip.com/blog/5-causes-of-contact-tip-burnback/
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On 7/22/2021 10:48 PM, Richard Smith wrote: > Hi all > > Burn-back to contactor tip on pulling trigger is my big problem at the > moment. > > Wire feed is smooth. > I clean out the contactor-tip frequently with an oxy-acetylene nozzle > cleaner - the set of serated wires. > > Yet - often - very quickly - burns back in fraction of a second so > arc'ing off a blob on the contactor tip. > > I'm trying things like holding a greater stand-off on start-up. > > Will try snipping off wire at shroud so wire-feed has time to come up > to speed (?) before wire touches job. > > Etc. > > Hints? > > Best wishes, > Rich Smith >
I'm absolutely not an expert or even a good apprentice at any kind of welding, however your experience mirrors mine in the few dozen feet of aluminum bead I have laid down with a spool gun. There are a couple little tricks that helped.
* 3/4 inch stickout. Yes, really. That much.
* Shorten the inner tube the contact tip screws into. I shortened the inner tube about 3/16 inch and threaded it deeper for the tips. This helps you maintain stick out.
* Clip the bead off the end of the wire every single time I stop. I found if I had a ball on the end of the wire burn back was much worse than if I clipped it off every single time.
* Some sort of gas lens inside the nozzle to better unify the gas flow. One youtube welder (I don't recall who) used some sort of very porous scrubber material. I use a piece of screen.
* Don't trust the table on the flip card on the welder. (On my 212 I almost universally needed slightly higher wire feed rate.) The flip card values are only good for a starting point before making some practice welds.
* Buy bulk tips off of your domestic import seller platform like Ebay, and don't be afraid to swap them out and throw them away many times in a modest large job.
* Don't be afraid to adjust the gas flow away from that suggested on the tables. I haven't really needed to do this, but your mileage may vary.
* Look up information on line for travel speed and try to do a couple cold runs at what you think is that travel speed for practice.
* if possible always make a hot practice weld or two on the same size material as the job you will be doing. If you can make the practice weld push it to the point of failure (usually drop out) so you know when to stop, and always stop in half that time or bead length in your real weld.
* Tack and fill switch areas allowing heat dissapation between short welds if needed.
* Start and finish on a previous weld or tack.
* It might be possible to weld larger than 1/4 inch (6.35mm), but it takes lots of preheat and maybe some non approved wallowing around with the gun.
* Remember that while aluminum dissipates heat fast (problem with thick stuff) it doesn't necessarily dissipate it as fast as you are putting it in to a local area (problem with thinner stuff).
These things allow me to almost (but not always) make barely ok aluminum welds even with my low hours on the gun. An experienced welder such as yourself should be able to do better.
I have welded upto 3/8, but it was bad and took lots of work and preheat. I found 1/8-1/4 was pretty easy to accomplish with down to .08 being within the capability of the machine if not necessarily within my skill level. I did actually make one (1) very very short weld on .043 wall tube that was ok, but I had to whip the gun around the joint almost as fast as I could move it.
These are ignorant beginner suggestions based on my limited experience. Nearly all of them were learned from other welders on this group.
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Thanks for suggestions, respondents.
On topic of avoiding burn-back to contactor tip when trying to start weld on Ali GMAW / MIG.
Stand-off - there is a spray shroud for the common industrial GMAW guns. On steel it makes a significant difference in the favourable direction. On steel it also works well when using Pulse to get spray-like characteristics on average Amps less than spray (as you might do positionally welding on thinner material) Must try one on Ali GMAW. So that's * keeping close in for good shielding * having plenty of electrical stick-out (workpiece to contactor tip)
Contactor tips - even with regular cleaning, you get through a lot, yes.
In all other ways, with being a commercial welder, and with having good kit - all Miller industrial grade running off 3-phase supply - when arc is running, get the welds I want, now. It seems instinctive. I suspect I may be able to make smaller faster welds in future - don't need much fillet-size for joining a stiffener rib to a plate it is stiffening - but don't want to try to run before can walk...
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