Welding trim holes in bed

[ItWillBeSlow]

Originally Posted by HO455

By its nature the electrical arc is an electromagnetic force. External magnetic fields affect the arc by pushing it or pulling it. Thus the arc doesn't do what you want it to. The molten metal in the puddle almost always takes a polarity and will flow towards or away from the external magnetic field depending on the polarities.

Say you are butt welding 2 pieces of steel together along the long sides. One piece has become magnetized so it will have a north and south pole.

And for this discussion we will say the arc and the puddle are negatively charged. We all know that magnetic opposites attract.

So we will start on the south end of the steel piece with our weld. The arc will be pushed away from the magnetic piece of steel into the non-magnetic piece. Naturally you will start to bias the arc to the magnetic side in order to get that piece to turn molten. Once the puddle is established the molten material will be pushed away from the magnetic piece like the arc did. The resulting weld is likely to be poor weld. The non-magnetic side will have spotty arc pentration and the molten material will be pushed over cold spots and not fuse. As your bead travels from the south end to the north end the affect will move towards the magnetic piece and away from the non-magnetic piece.

Now this being said your piece of steel has to be pretty well magnetized to cause real problems. This is most likely to happen when using used steel. Especially pipe that has had heavy products flowing through it for long periods. Years ago at work we had a new 20 foot stick of 3/8" x 4" flat bar that was so magnetized that it ended up being unusable for the project it was originally purchased for.

It is also common when building small boxes that require welding on both the outside and the inside. Where the pieces meet in the inside corners can become a magnetic mess that will blow the puddle away making it very difficult to weld without degausing the project. Sometimes a couple good smacks with a hammer may reduce the magnetism enough to allow proper welding. (By the same token hammering iron can also make it magnetic.) Starting the assembly at the inside corners can help reduce the problem.

So if you feel the need to mess with someone when they're welding just put a rare earth magnet on the back side near the weld joint. Just make sure they have a sense of humor and are smaller or at least slower than you are.

Hope this explains my comments.

Very interesting, thanks for the info.