ARC MAGAZINE

What’s the best way to fabricate a box for a back purge? I’m currently welding stainless, and the back side of the work piece always looks sloppy because I don’t have a back purge.
John Mucha, Chicago, IL

There are a couple different options. As long as you’re getting gas on the back side of the weld, you’re fine.

Before you can do anything, you’ll need two lines to purge. So you’ll have a Y connection – one that connects to the torch and the other for the purge. Once you have the Y connection, you can hook the torch up to a back-purge trail cup. Or if you don’t have a trail cup, you can cover the joint with aluminum foil and then tape the hose to the joint to enable a steady gas flow along the back of the weld. Make sure to poke exit holes at the opposite end of the gas purge hose (you can use your tungsten to do this) so you have continuous flow of gas on the back side. Make sure the gas hose is taped tightly to one end and there’s sufficient room to allow the gas to push the air out of the opposite end.

You can also use a simple cardboard box as a purge box. Be sure to cut away the side of the box that will be resting on the table. Sit the cardboard box over the table, which enables you to maintain your ground, and then mount your hose at the lower end of the box so the argon gas – which is heavier than air – can push the air upward and away from your work. While the TIG welding arc is very focused, use care to avoid igniting any of the surrounding cardboard panels. 

I have the Lincoln Electric POWER MIG^® 210 MP. I like using the TIG process with the foot pedal. Are there any good lift arc or scratch techniques that will help me reduce contamination of my tungsten and sticking during the start?
J.S. Fletcher, Old Pueblo, AZ

If you’re using the foot pedal, in order to make the arc start, you need to put the tungsten down with no power, push the pedal down with the tungsten touching the material, and then lift the tungsten. If you do it any other way, the tungsten is going to be hot, and it’s either going to scratch or it’s going to stick.

When TIG welding aluminum, what causes pin holes to keep appearing?
Will Barnett II, Sarepta, LA

Pin holes can result from either the presence of hydrogen or insufficient gas protection.

Any buildup of lubricants, grease, oil, paint, primer or other contaminants can be a source of hydrogen, so the aluminum needs to be extremely clean before welding. When cleaning the weld surface, use a de-chlorinated brake cleaner. Do not use alcohol. Alcohol will smear grease around without actually removing it. A dechlorinated brake cleaner will ensure that you don’t get phosgene gas when you strike the arc. You can get it in any auto store. It’s the best option because it evaporates very quickly.

If everything is clean and hydrogen free, the other possibility is insufficient gas protection. This can be the result of a number of different factors. First, check to make sure your flow rate setting on the gas bottle is correct. Also, avoid welding in conditions where winds or even mild drafts can affect your shielding gas setup. Finally, check your tungsten to make sure your stickout isn’t too far.

I run an older generator welder with a high-frequency converter. I only have scratch start. Any tips on not contaminating the tungsten?
John McCarty, Toutle, WA

The answer is as simple as a piece of copper.

If you’re scratch-starting, you should have a TIG torch with a valve on it so you can manually control the gas. This is where a two-line TIG torch usually comes in handy – one line connects to the bottle and the other connects to the machine. Turn the valve on and scratch off a piece of copper.

Wherever you’re going to weld, place the copper nearby, pop it quickly, and you’re ready to go.

I have a 19-year-old Lincoln SP 100 115- volt welder set up for flux-cored welding because I weld outside a lot. It makes great welds, but it welds “ugly” compared to a conventional MIG welder. Is that just the nature of the beast, or is there a way to make flux-cored welds look better?
Dan Anderson, Bouton, IA

The SP 100 is an older machine, but there’s no reason why you can’t produce good looking welds with it, as long as you set it up properly and recognize its limitations in relation to heavier gauge material. First, make sure the flux-cored wire is on the correct polarity. MIG runs positive. Flux-cored wire runs negative. So the torch end should be on the negative terminal.

You could be running too heavy of a material for the SP 100 output. The SP 100 is considered a light-duty machine, and you’re not going to get much power with 110 volts. Figure on a limit of 1/8 inch to no more than 3/16 inch for flux-cored. If you try welding anything heavier than that, you won’t have enough heat. It’s going to roll and bead up. But you can really put down some nice beads if you use 1/8-inch, 10-gauge material.

From the welding experts at
Lincoln Electric