Arc Wander and Magnetic Fields

This is a great thread!!! The theoretical discussion is even interesting as well. In welding however the arc wander is just a source of irritation that must be minimized to prevent slag inclussions and imperfect weld zone. A wandering arc causes localized heat affected zones that cause Martensite formation and Helium inclusion in the base metal. These two formations negatively afeect the quality and strength of the weld at a molecular level. If you are welding and notice that the arc is wandering (and you will notice), you need to either move your ground or move your magnetic squares further away from the weld. Once you have experienced the arc wandering you will begin to notice about how close you can get before it begins happening again. Best practices dictate that once jigged and properly tacked mechanical means of retaining the joints designed angularity is better than a magnetic means every time. That is why I frequently weld my jigging fixture to the surface of the welding table and only remove the jig after the completed weldment has been allowed to cool and been removed. It makes setting a repeatable and uniform spacing in a quick and easy no hassle way. This will increase through put and fatten the wallet. The result that we are all looking for ultimately. Great discussion!!!
Bob
 
so far you're referring to AC or DC welding. Using OxyAcy won't cause arc wander b/c there's no arc, correct? And heat itself won't destroy the magnet, right? For instance I think the sun has a magnetic field and that gets pretty hot.

The only thing that would cause a magnet to lose its magnetic field is dropping it or slamming it hard with something.

I'm not sure how a demagnetizer does the work of demagnetizing things.
 
Even if i cut up a little here i really like this thread usually at work ironworker/welder im the one trying to bring in welding theory to the discussion and i just get just weld it. Trying to understand what's really happening helps inform me as to the possible solutions and that makes this thread very useful.

Welding programs often teach to the test in the booth and the theory is just a forgotten power point or video. That reminds me one of my last supers ran off with my Lincoln Procedure Handbook of Arc Welding:angry: i brought into settle the old deeper or better polarity and penetration relationship argument, great book but nobody conceded.

Bob
 
SE18 said:
so far you're referring to AC or DC welding. Using OxyAcy won't cause arc wander b/c there's no arc, correct? And heat itself won't destroy the magnet, right? For instance I think the sun has a magnetic field and that gets pretty hot.

The only thing that would cause a magnet to lose its magnetic field is dropping it or slamming it hard with something.

I'm not sure how a demagnetizer does the work of demagnetizing things.
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Actually heat can effect a magnet but you have to get them quite hot. In a magnet the grains or crystals are aligned in the same magnetic direction. If you heat them up enough they can reorganize and then when they cool they will either be weaker or potentially loose their collective magnetism. For example nickel becomes, non-magnetic at 631K (676F) if a lump of nickel was heated to 676F or higher and then allowed to cool in a strong magnetic field it would gain some permanent magnetism, we did it to 1600F because that is the temp our muffle furnace was set to, bored geeks at work. Maintenance was ****** we use all their copper wire for the electromagnet. We used the 50 gram nickel balls for the GM-Quenchometer tester. To demagnetize them all we did was run them through the furnace again and cooled the outside the magnetic field. http://en.wikipedia.org/wiki/Curie_temperature
 
The temperature at which a metal becomes non-magnetic is called the Curie point and very closely aligns with the "critical temperature" which, in heat treating is the temperature when the metal becomes Austentite (i.e. fully considered a solution). Most old-fashioned heat treating techniques called for heating until a magnet wouldn't stick -then give it a little more heat (crude and sometimes effective).

The formula for Kelvin to Fahrenheit is: F = 1.8 x (K - 273.15 ) + 32.


Typical temperature for steel is around 1475 to 1550 F. Pure elements such as nickle have much lower Curie points.

BTW: The Curie we're talking about is Pierre Curie -not Marie Curie.

Ray

EDIT: And by the way, Austentite is named after William Roberts Austen (late 1800's). Curie and Austen were contemporaries. And by the way, I will bore everoyone with these history lessons of "who and when" as I feel it's fundamental knowledge -just as important as the techniques we employ because of their genius contributions.
 
magnetic fields in the sun seem to violate that curie principle

http://en.wikipedia.org/wiki/Stellar_magnetic_field

this seems to be another one of those mysteries.

(not related to this but the biggest science mystery I could never find the answer to is they say pollution causes the greenhouse effect and global warming. Yet, if a massive volcano spews pollution on a global scale, that causes global cooling)
 
SE18 said:
magnetic fields in the sun seem to violate that curie principle

http://en.wikipedia.org/wiki/Stellar_magnetic_field

this seems to be another one of those mysteries.
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No mystery, no violation. The Curie point is where ferromagnetic metals lose their magnetism. The Sun is not metal.

The Sun is plasma ( http://en.wikipedia.org/wiki/Plasma_(physics) ), like the welding arc that started this discussion. Plasmas conduct currents really really well, because plasmas are made of charged particles. When charged particles move (more precisely, when the positives move differently from the negatives) that is a current.
 
the earth's core is hot iron (supposedly), but earth has magnetic field?
 
Yep... Now don't quote or nitpick me here but, the Earth is something like 85% metal. Indeed, much of the core is beyond the Curie temperature but molten metals can still carry electrical currents. As magnetic waves fluctuate from the Sun and go past the Earth, it induces currents in the molten underlayers and those currents in-turn, produce a magnetic field of their own.


SE18 said:
the earth's core is hot iron (supposedly), but earth has magnetic field?
Click to expand...
 
General Curiosity *[was: Arc Wander and Magnetic Fields]

I'm going to respond to SE18's (great) question about the Earth's magnetic field, but first I wanted to say something more general.

I'm really really delighted that people are asking these kind of questions. It strikes me that quite a few of these questions would be covered in an introductory materials science course.
When I did my engineering degree (cough, choke, almost 40 years ago), every engineer (no matter what specialty - mechanical to chemical to electrical) had to do a "Materials Science for Engineers"
course, and that was one of the most enjoyable courses I took. Judging from a quickie search, many, if not most, programs have a similar requirement today.

My suggestion for many people is: go find what text book your local college uses for this course. Don't buy it new (new textbook prices are insane), but grab up a used copy. Or get an old edition.
Or find someplace doing a MOOC ( http://en.wikipedia.org/wiki/Massive_open_online_course ) and find out their course materials.
Look through some Amazon suggestions like http://www.amazon.com/Materials-Science-Engineering-An-Introduction/dp/0470419970/ . (Disclaimer, I haven't read that one, it just popped up first on my search.)
Get curious!



 
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