Magnets, how do they work?

This is probably what you were expecting, given the title – but too bad because this post is about science and, therefore, way cooler.

Welding is a science on its own. Some see it as a mechanical way to connect two existing steel members together while others see it as an art form – and, in many respects, it’s more the latter than the former. Nonetheless, welding steel also means hitting guaranteed roadblocks that can make the process cumbersome and tiring.

(If you’re new to welding, or don’t quite know what it is or how it works, watch this great 8-minute video about the basics of SMAW or “stick welding.”)

While there are many different types of welding techniques, this post concerns SAW, or Submerged Arc Welding. A submerged arc welding machine (commonly known as the “tractor”) wouldn’t weld on a joint connecting two steel plates together. But before we delve into the problem, let’s take a closer look at these complicated little devices.

This is what these machines sometimes look like:

Lincoln-Electric-LT-7-Tractor-3

They literally run on motorized tracks that move the weld along a linear path. And this is what it actually does:

fig78_01

This welding method relies on something called welding flux which looks like a combination of kitty litter and sand. Here’s what flux looks like while the sub arc machine welds a joint:

IMG_20160517_140929

The material is actually a composite of oxides, sodium silicate, and a variety of chemical binding agents. This flux shields the molten pool of hot steel as it fuses between the two pieces of existing metal being welded together. The process is explained in greater detail in this 20-minute video:

Since welding is essentially a hot, electrical current transferring steel from a positive current (electrode) to a negative one, these electrical currents can magnetize (similar to this drawing below).

FIGURE M-2

The magnetization of the welding process can result in something called a magnetic arc blow which happens when the magnetic field surrounding the arc is unbalanced. Other magnetic factors can affect the quality of the weld, such as coiled up (or “rolled up”) welding leads. In layman’s terms, rolled up welding wires create a strong magnetic field due to the high voltage of electricity passing through them – or, an electromagnetic field.

7007-02The welder applied a coating of galvanizing spray to the joint and the submerged arc welding machine worked. Why? Galvanizing sprays contain zinc – yes, the same chemical element found in food and medicine that helps metabolic function in cells and strengthens immune systems. Zinc, however, also has the capability to shield a magnetic field; in this case, the zinc in the galvanized paint acted as a balancing element between the magnetized, rolled up welding leads and the steel being welded, giving the sub arc machine the capacity to weld the joint effectively without significant magnetic interference.

So, problem solved.