Holy Slag Batman.
Slag is the arch nemesis of a welder. It’s as much of a struggle as the joker was for batman. Just when you think it’s gone for good, and you have it mastered, it can always pop back up anytime it pleases. If you don’t know what welding slag is, then you probably are just getting your feet wet in the welding world, or you’ve been welding MIG all your life. But honestly in MIG, you have light surface slag from time to time that should be removed before you make your next pass. Slag is the leftover remains of the weld process that is a result of the flux having done its job. Slag is formed from the flux, decomposing into either a shielding gas, or deoxidizers, which form molten compounds that cover the weld while it cools to prevent oxidation of the freshly formed weld. welding slag is usually gray, brown, or a charcoal black in color. It can be composed of several different oxides and it varies according to manufacturer. It can be thick or it can be paper thin. Some will release easily, and others will cling to the weld until it is etched with chemical or driven off by harsh mechanical means. Slag is great for protecting the weld while it cools, but once it has done it’s job, it has to be removed before the next pass. So, there are many ways to remove welding slag, but the most common method in years past was with a chipping hammer. A chipping hammer is a pencil like hammer that uses a flat blade on one end and on the other end, it forms a point. The chipping hammer is great for general purpose welding, and when combined with a wire brush, results are generally good. But certain fluxes can leave a hard to remove scale, or a flux that will not release cleanly. The problem that using a chipping hammer presents is that it can damage the weld face leaving tiny marks where the weld can fail. In this scenario, the next pass would not necessarily remove the marks creating a weak point or even a void in the weld. So many places have banned the use of a chipping hammer, and gone in favor of a needle scaler. Needle scalers are usually pneumatic driven, and have several dozen, hardened needles that dance and vibrate when the trigger is pulled. This vibration is literally composed of small, but harmless (to the weld that is) impacts several times a second of each free floating needle on the weld face. This vibration pulverizes the welding slag away, and a smooth clean surface is the result. Another way to remove slag, is with the use of a wire wheel, but that is typically employed after all the slag has been removed manually. Different welding rods may require other forms of slag removal but when it comes down to it, chipping hammers are the most economical. One final form of welding slag removal that works exceptionally well, but is tedious and slow is a file. Any old time welder carries a file in their tool box. The file can get right into the small corners and toes of the weld that a dull chipping hammer, or wire brush cannot. It removes a small amount of metal as well, but that is of no concern. A file does the job and does it well, so don’t forget about that as a tool that works when nothing else will.