I have heard of welders using a jumper ground to defeat Magnetic Arc Blow. One end was clamped near the start of the arc blow, and the other near the end of the weld joint. I haven't tried this myself; all the tricks I have used seem to have a voodoo aspect to them and do not work consistently (except changing to AC current). Does anyone have a solution to Magnetic Arc Blow they are willing to share?
Look around garage/estate sales for an AC buzz box. Put two work clamps on the weld cables. Clamp one on each end of the weldment and turn the machine on and run a low amperage so it has a 100% duty cycle output. Check the voltage from work clamp to work clamp when clamped on (dead short) and running, should be about 1 (more/less) volt.
Let's say the machines rating is 20% (2 minutes out of 10) at 180 amps at 25 volts. That is about 4500 watts. 90 amps at 25 volts would be 2250 watts and the duty cycle would be 40%. 45 amps at 25 volts would be 1125 watts and the duty cycle would be 80%.
Now with the amperage at 180 and the voltage at only 1 volt that would only be 180 watts with a dead short. So it would easily be a 100% duty cycle machine output with 180 amps. Making certain the length of weld cable can carry 180 amps. 100 feet of #2 would be good for 200 amps.
Most buzz boxes will work with the 230 volt from the shop wall and also engine drives when making corrals out of magnetized oil field tubing and sucker rod.
If this is too high tech solution; cable wrapping is another technique. Increase the size and length of the work cable. Tape the start of the wrap (about a foot or two) parrallel with the pipe (as an example) and wrap an odd number of complete wraps around the pipe. Now two voodoo parts; the complete number of wraps must be an odd number over nine, not ten not 12 but any odd number greater than nine complete wraps. Clamp the work clamp and try it. Now, the second voodoo is wrapping clockwise or counter clockwise?? Try it one way may increase the magnetism the other way will decrease it.
If the welding machine has an AC weld output that is the simplest, weld the root with AC SMAW and then weld out with DC or use GMAW or FCAW. The buzz box has been for me the simplest demagnetizing tool. It works with GMAW, FCAW and SMAW.
Hey 357max:
Just wanted to explain the "voodoo that you do."
Voodoo 1) "Odd wraps, over 9." This makes sure you remember to wrap the cable around the magnetized material several times. By saying "ODD" and "OVER 9," the person who uses this technique is sure to go around the magnetised material enough to create a magnetic field from the welding cable. Now can you create a magnetic field with the welder set to AC, or should it be set to DC?
Voodoo 2) "Wrapping clockwise or counter clockwise." Wrapping one direction sets up a magnetic field in one direction; wrapping the other direction does the opposite. If you knew what direction your magetized material was set, you could determine how to wrap your cabling around it. Of course, you could always just flip the polarity settings of your welding machine!
Note also that more wraps produces a stronger magnetic field. Too many wraps, and you will start magnetizing the material in the opposite direction.
Just food for thought, I guess.
Good thoughts. Changing polarities wouldn't help much to change the magnetic field. Electrode would need to maintain a certain polarity. Back to basic electricity, around every current carrying conductor is a magnetic field. (we see this when steel grindings form a pattern around weld cable)This is the basis for a transformer. Current carrying conductor wrapped around the steel laminations. Alternating current causes a building and collapsing inducing or causing voltage/pressure/force to push electricity (electrons/those little microbee things) from the primary side to the secondary side without an electrical connection. I believe (its been awhile since it was tried) for an example if you connect a 12 volt battery directly to a coil, It would short out. Put AC to the coil and no worries.
BTW, wrapping cable around a piece of pipe is a poor boy engineering method of adding inductance for SCMT GMAW to flatten out stainless welds.
By aevald 
Date 08-24-2006 05:08
Edited 08-24-2006 05:34
Hello sdcwi, you mentioned the word "voodoo" regarding arc blow. I would say that fairly well sums up the way that you have to deal with arc blow sometimes. The main rule of thumb that I was always told, was to always weld away from the ground, easier said than done in many instances. You also mentioned using AC current, obviously not always possible to do either. Another suggestion is to simply try shifting the ground to some other spot, sometimes this will work and other times not. I have also heard and tried wrapping the ground around the part to be welded on a few times and then reconnecting it, similar results, sometimes yes and other times no. Certainly a major consideration is the condition of the ground clamp and other connections, need to make sure they are in good condition and the point of grounding is clean and not causing any arcing. I have noticed that any external magnetic fields in the vicinity of the welding will have an effect as well. Magnetic drills being used on the part while welding is going on would be a no-no, those handy little magnetic right-angle holders will also cause arc blow effects, the proximity of two welding arcs happening simultaneously on both sides of a tee weld can cause the dreaded arc blow to have a noticeable effect. In some instances the number of welders and their position relative to one another has caused some pretty severe arc blow conditions, using a common ground such as the ones that are found on the Miller 8 paks, 4 paks and similar machines can also promote this condition. Arc length and rod angle have helped or made worse the effect for me at times. I too have always tried to keep an open mind and open ears for ways of defeating the effects of arc blow. There was a post on the forum here quite a while back where the poster made mention of using an old welder in line with the ground lead, I don't remember all of the specifics but that is one that I haven't tried yet (didn't have an old welder to try it with). Thanks for bringing the question up for consideration sdcwi, I hope there are some other responses and suggestions for dealing with ARC BLOW. Regards, aevald
The few casses Ive encountered we just degaused the part to be welded. establish the direction of the magnetic field. wrap the welding cable around the part sothat the resluting magnetic field will counter the existing one and send DC current through it, reduce the current, change polarity and repeat, and repeat and repeat.Its all about energy input and enough of it to randomize the the domains that was alligned. It is trial and error. but ive been fairly sucsesfull. it is a bit more technical if you look at the theoretics, i have an articel of a experiment some guys did to degaus plates of considerable size. I can mail it to you.
hope it helps
I weld alot of pipe and being that it is code work, I cannot tolerate arc blow, so...................I take th ground cable and wrap it around the opposite way to where I am welding and this usually takes care of it. Four or five wraps is enough.
As previously stated, if DC is being used with SMAW, especially when operating above 250 amps, changing to AC may eliminate the problem. In general, other options are: (a) holding as short an arc as possible to help the arc force counteract the arc blow. (b) reduce the welding currect which may also require a reduction in arc speed. (c) angle the electrode with the work opposite the direction of arc blow. (d) make heavy tack welds on both ends of the seam and apply frequent tack welds along the seam, especially if the fitup is not tight. (e) weld toward a heavy tack or toward a weld already made. (f) use a back step technique. (g) weld away from the ground to reduce back blow, weld toward the ground to reduce forward blow. (h) with processes where heavy slag is involved, a small amount of back blow may be desirable, and can be achieved by welding toward the ground. (i) wrap the ground cable around the workpiece and pass ground current through it in such a direction that the magnetic field set up will tend to neutralize the magnetic field causing the arc blow.
Fixturing can interfere with the magnetic field and also have an effect on arc blow. Some points to consider are: (a) fixtures for welding the longitudal seam of cylinders should be designed for a minimum of 1" clearance between the supporting beam and the work. The clamping fingers or bars that hold the work should be nonmagnetic. Do not attach the ground cable to the copper backup bar, ground directly to the work if possible. (b) fabricate the fixture from low carbon steel. This will prevent the buildup of permanent magnetism in the fixture. (c) welding towards the end of horn type fixtures reduces back blow. (d) design the fixture long enough so that end tabs can be used if necessary. (e) the backup bar should be all copper, but relieved under the joint. If the bar is placed in a support, the support should be of nonmagnetic material. (f) provide for continuous or close clamping of parts to be seam welded. Wide, intermittent clamping may cause seams to gap between clamping points, resulting in arc blow over the gaps. (g) do not build into the fixture large masses of steel on one side of the seam only. Counterbalance with a similar mass on the other side.
I just saw a question in the Technical section on arc blow / magnetized parts. I spent several minutes answering it. I should have looked here first. You already answered the gentleman's questions.
Silly me!
Best regards - Al
