I am a welding instructor at a comunity college. We have 18 booths that are all connected and the machines are all grounded to the booth frames. We are experiencing arc blow in all booths. We are also a certification facility, and this arc blow is very frustrating for the students. We have tried several things from tacking different places, to direct ground from the machine to the work piece, with no good results.
One proposed solution is to have ground cables connected to the booths and run them outside away from the building to ground rods, however this is a costly endeavor for an experiment.
If anyone has had simular problems and resolved them or if you have an idea for solving the problem please feel free to give me your suggestions. Thanks Andy
I had a similar problem but it was on a single booth. Found that my fixture had become magnitized. Maybe this is the case for you. I bought a cheapy gauss meter and proved it. Problem was solved by changing the location of the ground on the welding table and demaging the fixture.
I would have thought a dirrect ground would have taken care of it.
Will be interesting to see what others have to say.
Best of luck to you.
kam
Throw a few loops of Stinger or Ground cable around the fixture and pull the magnetizem out of it while you weld, or if you have a Magna-Flux machine you can use that for demag-ing.
Try making multiple work connections from the output terminal of the welding machine. Try two or more cable connections. Use heavy cable that will carry the maximum amperage output of the machine. Bundle or tape them together to the point where the connection is made on the table or fixture. Make one connection to the fixture base or table leg. Make a second connection to the table surface (if you are welding left to right, make the connection at the start or left side). Third connection to the end of the position arm or top of positioner post. You may want to make connections with jumper cables between these points. Make the connections to the fixture/table with 1/2" bolts.
Another radical work connection is to wrap the cable around the table/fixture leg. Begin by taping the cable parallel with the leg (about 6-9") then wrap the cable tight around the pipe an uneven (not an even number of 360 degree wraps) number of times over nine (11,13,15)-(I don't know why). Tape a parallel lead to the pipe and make the connection to the table surface. Try these as a low cost fix.
Use squarewave AC for the open root pass is another option. Good luck.
gump,
You've been given some good advice by these people. I would definately try the cable wrapping.
You didn't say if you have the problem with plate tests, pipe tests, or both. My thought was you may not have enough steel in your holding fixtures at the ends of your test plates. That would allow the magnetic flux to concentrate and cause arc blow in plates. You can find out by welding on plates across the ends, similar to adding a large run-off tab, to provide a magnetic shunt. It doesn't have to be welded to the test plate, just to the fixture near the plates.
For pipe, you might look at providing an electrical path from each half to ground, maybe with a jumper added to your ground.
I think we all would appreciate a post on how you did it when you finally solve the problem. Nice to know how others solve common problems.
Good luck
CHGuilford
Dear Gump
Isolate each welding booth ( work station tables ) from each other, no connection between any should exist. do not use a building structure incase there are under ground connections. Go through the floor at each station with a copper rod (earth ground).
You have a ground trying to find its way to earth and is having trouble finding a path. Make the escap path as simple and uncomplicated as possible. Sounds like you have somethng close to a big motor winding.
Best of luck
sp09206
Just how much magnatism can be present with effecting the arc? I checked one of my fixtures with a gauss meter and get a reading of about 9. Could this affect and arc 5 inches away? I wasnt to worred about it because of the distance but was just curious as to how much magnitism affects the arc. Any formulas??
thanks
kam
I know a few schools that have changee from DC to AC on square wave tig machines with the balance control turned to maximum penetration. It has a great arc and no arc blow. I have seen them use to on state welding test with great results.
Kam,
The answer depends on several variables. I doubt I can identify them all.
Electrode characteristics (size) and arc energy are, I think, the most important. Beyond that there is as I recall something to do with the ionization characterists of the shielding gas... beyond where it effects the arc energy. I think penetration profiles will serve as a window to the characteristic of the arc; finger penetration = narrow arc.
It's internal arc parameters as well as external influence that contribute to arc blow. At least, thats how my understanding works.
I am unaware of any tables to show this data. I never needed any, but I hope this helps a bit.
Regards
d
Andy,
I recall within the past 2 years but longer than the past 6months a similar problem in welding booths (probably built on the same blueprint or by the same architect?) posted on the AWS "technical" or "shop talk" which finally found resolution. I am sorry I cannot point to it directly, nor can I certify it discussed the identical problem, but I do think the archive research will be worth the effort. I do recall at least two institutional cases; one with mains wiring issues which may be applicable as well as another discussing arc blow. Both may apply.
On the positive side, I have perhaps a controversial opinion. It might be constructive to have some peculiar or variable "booby-trap" in a training facility once the faculty itself devises and teaches means of identifying and manageing it. The real world does not maintain ideal circumstances. It is good training if your students become more competent welders, able to handle realistic, unusual eventualities... it becomes a better value to the student for his tuition and should reflect favorably upon respect the institution receives from local industry and the public.
Good luck with the problem; hope I helped.
d
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