Hey guys,
Looking for any theories and observations you all may have about arc blow, especially with E7018. I work for a school that runs 30-40 welding booths all day, every day and some days just seem to be much worse with arc blow than others. For 20 years I've tried to pattern it and think that I have noticed some tendencies. Do you think changing weather patterns affect arc blow and/or the moon phase? Prior to working here I had never seen arc blow in the field. Now I have seen it so bad there are days that the rod toenails to the point that the arc is uncontrollable. The booths, base metal, filler metal and ground configuration do not change from day to day so why the difference in arc blow from day to day? Obviously we have all heard the things we can do to counter act it, rod angle, direction of travel, weld towards a ground/weld away from a ground etc..,but I'm looking for reasons as to why it changes from day to day. I'd love to hear some of your thoughts
Sometimes steel develops a residual magnetic charge that affects arc blow.
This can happen in different ways, such as exposure to the electromagnetic field creates by electrical wiring, equipment, power lines, etc. Do you store steel around an electrical transformer?
It can also strangely occur due to a sharp blow against another piece of steel. For instance, it is possible to magnetize a steel screwdriver simply by whacking it against a vise, or other steel object.
Magnetic lifting devices may also leave behind a residual field.
Used oil field drill pipe is so magnetic it's damn difficult to weld on.
Pipe is especially susceptible to retaining or developing a magnetic charge. I know of some pipe yards that are very careful about aligning their pipe during storage and fabrication with the magnetic earth poles to reduce arc blow issues, but I don't remember if they align north - south, or east-west.
Anyway, some of these reasons may help explain why your arc blow issues are sporadic.
Tim Gary
Perhaps the tables in the welding booths are getting magnetized.
I would suggest rotating them (after a quick test for arc blow) and see if that changes things.
My fertile imagination sees the layout of the facility as having turned into a superconducting supercollider like the CERN Hadron Collider.
Another thought is the right or left hand students are reversing the polarity. If a station is demonstrating a bad wandering arc, see if swapping a "lefty" for a "righty" helps or changes it.
What is the history of you materials? I worked in one fab shop where the bulk of our steel had been handled by lifting magnets. Complex weldments were also rotated at welding stations with magnets and so heavily magnetized that 1/16" FCAW-G would send off 00 Buckshot adhered to the pieces. We had dedicated cleaning crews with custom built scrapers and chisels that did little else other than spatter removal.
Finally, if nothing else resolves this problem...
Express your concerns with department head and tell them from now on this is a Stainless Steel training facility with all new 304 tables and 300 series filler and materials.
I do like that last suggestion!!!
Generally what we see is when one booth has it so do the rest. Not always but I'd say more often than not. Our material is typically 1/4" A36 for fillet practice or 1" A36 for grooves. We buy them sheared to length. We do not store them near anything electrical but I can't say about the steel supplier. I have wondered about the fact that we have put so much DC current through the building for 20 years. But there are some days when it is non existent. That's the weird part. That's why I was thinking about some external reason such as weather or moon phase? I don't know, I could be crazy.
Hello jsdwelder, we have similar issues at our school and it doesn't matter how well you track where it's happening etc. Some days it's worse than others and other days no one has any issues with it.
I believe that part of our problem stems from all of the booths being constructed of a steel framework that is common to one another. Originally we had 8-paks that were commonly grounded to these booth frames. Then we tried running individual grounds from each power source and separating the grounds, yet they were still common via the booth construction lay-out. It did help some to provide individual grounds for each power source, but definitely not the definitive answer.
So for us we observe and show/note these happenings for the students and then we explore options to deal with it, ie.: welding away from the ground, wrapping the ground first one direction and if that doesn't help, wrapping the ground the other direction and varying numbers of turns when we do this. We will also have students move to different booths, as the varying skills and processes that students are using in the various booths changes.
We have a main cluster of booths where we see this the most, there are two rows of booths of 12 each that have 6 booths up one side and another 6 directly opposite of those. So, 24 booths total for this grouping of machines. Each one of these booths has the power source to support SMAW, GMAW, FCAW, and lift-arc tig. We can have quite a mixture of different types of welding going on in an endless combination and locations of welding.
Our other booths are separated by cinder block walls and do not share common grounds and we see much less issues of arc-blow in these areas/booths.
We always discuss magnetics associated with welding(a lot of what Tim shared) and explain that when you are using DC current that it will inherently set-up and cause varying degrees of magnetic flux/fields in and around the area of welding. We also discuss how certain mechanized GTAW processes will utilize electro-magnetics to direct and control the welding arc(this visually gives them something to grasp as arc-blow is discussed). Additionally, we discuss the effects of set-up magnets and how they can cause you grief if you forget to remove one or more of them as you progress with your various weld-outs. Yet another, is tandem welding of parts where fillets are being applied on opposite sides of a part by 2 operators and how it is beneficial to allow for one of these welders to be slightly ahead of the other one and not directly in line or straight across from the other one.
This is a situation where you can interject that AC current can sometimes be beneficial for certain welding challenges if it is qualified or allowed by the applicable code. There used to be an aluminum smelter in our area and a lot of the maintenance welding that occurred on their millsite in or around the smelting pots was done with AC for that very reason. There is also a method that incorporates an AC welding machine and provides for setting it to a low output(so that it does not over-heat while it is dead-shorted) and passing that current through the piece being welded by hooking the work lead up at one end of the part and the stinger at the other end(or at least having one hooked up on one side of where you are welding and the other hooked up on the other side of where the work is being performed), this will allow for some of the magnetic fields to be disrupted enough to allow for less chance of arc-blow.
Well I am sure that others will have additional items to include here for you, good luck and regards, Allan
Not at all sure this would even be relevant but I wondered whether in a common grounded situation as Allen describes whether having multiple processes going on simultaneously using both reverse polarity for stick electrode and straight polarity for tig welding might not cause some kind of magnetic turbulence. I'm pretty sure someone here can refute or confirm this speculation either from observation and experience or a better understanding of basic electrical currents than I possess.
Hello yojimbo, I definitely agree with that, but as you somewhat said, I'm in the same "electrical boat" as you so I don't have a very good handle on what exact things could be going on nor whether it has a lot or a little to do with the severity or issues of arc-blow. Best regards, Allan
Interesting,
I wonder if the magnetic fields affecting other booths would be eliminated if all booths were cinder block walls.
Tyrone
No,
The harsh voice of experience here... Cinder block walls are awesome but will not eliminate arc blow :)
When you have many, many, many power supplies, each with energized coiled leads hanging from them... When the power infrastructure is typically circular through the shop... When you have AC, DC, CC, and CV power delivered at various current flow rates ....
You are going to generate electromagnetic fields. It's just unavoidable.
Training fixtures often become magnetized.... Running AC current through each part of the fixture will help break that up... A dead short with a 5/32 electrode and 100 amps (until it melts) is a very quick way to break up magnetism in a fixture... But it will not deal with *All* the different flux fields generated day in and day out in a weld lab.
There are times when being completely counter intuitive is the only remedy.... Example... Most SMAW and Self-Shielded FCAW operations work best when welding away from the work lead... But sometimes in a wildly misfunctioning lab, the exact opposite of what normally works makes the best *countermeasure*.
Hello again Tyrone, here's the sketch that I couldn't attach to the private message. Best regards, Allan
Perfect!
Thanks Allan.
It will be fun and interesting to see if it works on large, complex geometries.
Tyrone
If everything else is exactly the same (rod diameter, current level, direction of travel, joint type, material thickness, method and location of clamping, location of work piece on the table, work clamp location, etc) my first guess would be that the leads are laying on the ground in a different place - unless you have looked at this variable as well. Or perhaps they are even over the table top.
Having taught for 17+ years in 3 different school shops, this is something I am well familiar with. One of the worst cases of arc blow I ever saw, about 15 years ago, after trying the normal methods to minimize, was solved immediately and completely by pulling one welding lead about a foot away from the base plate of the pole (for a sliding table) in the booth.
While I feel I am very effective at magnetic arc blow minimization, I don't understand how leads on the ground effecting matters works. I do know it is not uncommon to have table legs or base plates Hilti bolted to the floor with one or more of the boots hitting rebar. Perhaps the orientation of the lead to the rebar can be a contributor?
Since I started routinely pulling excess leads away from the weld area, table legs, poles, etc to the extent possible, combined with the usual moving of the work clamp, changing direction of travel, and so on, I have not seen a case of arc blow that couldn't be reduced to quite manageable since.
Arc blow can have so many variables contributing to the situation even with a single machine that in the cases mentioned it can be one major can of worms.
Having the work stations all grounded and/or fastened together will add to that factor even with separate grounding for each machine in use. In fact, considering all the factors mentioned, is it possible there is a conflicting current if one has some operating on DCEN and others on DCEP while even others are on AC? That may be more of a problem than a cure.
Even with each machine individually grounded if the booths are tied together you are getting mixed currents, so much so that I don't even know how to describe it. I'm bad enough keeping 'series' and 'parallel' straight but thinking about this has me totally confused (I know, that's not hard to do).
Depending on which machines are running and on what you could be creating the problem as you are working. And, then with the right combination, leave quite a residual charge in the work stations.
I think I see a need for total isolation of units here or there will always be potential for problems.
He Is In Control, Have a Great Day, Brent
Darn it! I had this written and hit the wrong key and erased the whole thing. Here we go again!
If you have all the benches in a line and they are interconnected, the condition is similar to a beam where several welders are trying to weld simultaneously. There is a fix.
Assume there are six welding machines in a row identified as A through F. Each of the benches are connected to a common "ground". Typically, all the work piece connections are to a common lug. The result is the bench closest to the common connection is seriously magnetized when all six welders are welding simultaneously. The current flowing through the end connection is the sum of the welding currents used by each person (assuming everyone is welding with the same polarity). The bench furthest from the common connection will experience the least influence of the magnetic field produced.
The fix is to place half the work piece connections to bench A and half the work piece connections to bench F. Connect benches D, E, and F to bench A. Connect the work piece connections for benches A, B, and C to bench F. The resulting welding currents are said to be "bucking" each other. The counter flowing current negate each other and the resulting magnetic fields are zeroed.
The attached sketch depicts how the work piece connections should be connected to the benches.
I use this approach when I have several welders working on the same girder.
Regarding the subject of long materials being magnetized during transportation, it is not unusual. Long bars, pipe, angles, etc. typically become magnetized as a result of being transported in a northerly/southerly direction as a result of the influence of Earth's magnetic field. The problem is amplified as one approaches the North and South Poles. In many cases, the parts must be demagnetized before they can be welded. Once demagnetized, they are stockpiled with the long axis in the East/West direction to minimize the influence of the Earth's magnetic field.
Demagnetization can be accomplished by wrapping several loops of welding lead around the piece and energizing with alternating current. The system is energized with the current at a maximum setting. The circuit is de-energized, the current reduced by say ten amps. The circuit is re-energized and then de-energized. The current is reduced by another ten amps and the process repeated in a series of 20 steps, each with reduced amperage. Then, with the welding machine at its lowest setting, the loops are removed from the part, one loop at a time.
The demagnetization can be done using direct current, but the process is complicated by the need to reverse the polarity each time the current is reduced by ten amps.
Do not attempt to demagnetize the component by reducing the current by greater amperages (say 50 for example). Every time the circuit is energized, the magnetic field is at a maximum. When the current is shut off, the magnetic field collapses, but the part has a retained magnetic field, call a residual field, that is less than when the current is flowing. The next application of current, at a reduced current, re-magnetizes the component, but at a reduced strength. Again the magnetic field collapses when the current is turned off. This time the residual field is at a reduced level because the magnetizing current was at a reduced level. The secret is that the magnetizing field strength must be greater that the residual field strength of the component. Thus with DC, there is a need to reverse the polarity of the magnetizing current each time the current is reduced by 10 amps. The graph depicting the relationship between the magnetizing current and the magnetic field strength is a hysteresis curve. Once the welding machine is at the lowest amperage setting, the field strength is further reduced by removing the loops of cable one by one.
The mathematical equation for an approximation of the magnetic field strength can be shown as: B = Am, where B is the field strength, A is the magnetizing current, and m is the magnetic permeability of the ferromagnetic material.
Best regards - Al
