Courtesy of Weldcraft
Unlike its welding counterparts—stick, MIG and flux-cored welding— TIG welding is a slow business.
You are viewing: Which Of The Following Is True Of Tungsten Contamination
Not surprisingly, experiencing excessive downtime for troubleshooting problems can make the process even slower. It can also cost unnecessary time, money and frustration.
In addition to common weld discontinuities, such as porosity, undercutting or lack of fusion that are associated with most all welding process, TIG welding is prone to two other pitfalls: tungsten and arc troubles. Having the know-how to identify and solve these problems quickly is important. It’s also relatively easy.
Keep to the point
In order to create an arc and transfer the welding current to the base material being welded, TIG welding requires the use of a tungsten electrode. Tungsten is a non-consumable electrode that has the highest melting point of any metal (3,410 degrees Celsius or 6,170 degrees Fahrenheit). So in theory it can’t melt, right? Wrong.
One of the most common tungsten troubles is excessive consumption. On AC (alternating current) applications, such as TIG welding aluminum, setting the balance control toward the electrode positive (EP) provides good cleaning action (removal of oxides) around the weld. However, it can also cause the tungsten electrode to melt. The best remedy is to set the balance control toward the electrode negative (EN), as this increases the amount of heat going into the work piece as opposed to the tungsten. Seventy to eighty percent toward the electrode negative is a good range. When TIG welding materials like steel, stainless steel, inconel or other ferrous materials using DC (direct current), also set the power source to the electrode negative mode.
Another cause of excessive tungsten electrode consumption is using too high of amperage for a given diameter of tungsten, regardless of whether it is on an AC or DC application. Always follow the tungsten electrode manufacturer’s recommended operating parameters for the diameter being used.
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Finally, incorrect or contaminated shielding gas and loose or cracked hose fittings can all cause excessive tungsten electrode consumption. Take care to use clean, pure argon and be certain all hoses are intact and fittings are tightened prior to welding.
Tungsten electrode contamination is another common pitfall that can occur during TIG welding. Indications that tungsten electrode contamination has occurred are: one, the weld puddle appears dirty; two, the filler rod does not join or melt smoothly into the weld puddle; and three, the arc becomes erratic.
Touching the tungsten electrode to the work piece and/or weld puddle is often the cause of tungsten electrode contamination. The easiest solution is to adjust the angle of the torch and/or move it further away from the work piece. If the power source requires a scratch-start method to initiate the arc, and tungsten electrode contamination continues to be a problem, consider using a machine with high frequency or LiftArc starting capabilities.
Touching the filler rod to the tungsten electrode can cause contamination as well. The only real solution to this problem is to practice feeding the rod into the weld puddle.
In certain cases, inadequate shielding gas flow, including lack of post-flow, can cause tungsten electrode contamination. An accepted rule of thumb: maintain a shielding gas flow rate of 10 to 20 cubic feet per hour (CFH), along with a post-flow of around one second for every 10 amps of weld current used. If the tungsten electrode turns from its normal color of light gray to a shade of purple or black, that is an indication to increase post-flow time even more.
Stay focused and stable
In addition to causing various weld puddle troubles, contaminated tungsten electrode is also the leading cause of an unstable arc. It doesn’t matter the original cause of the contamination—poor shielding gas flow, touching the base material or leaky hoses—but what does matter is how it’s remedied.
First, remove the tungsten electrode from the torch, clip the end and regrind it. An important rule to remember: always grind the tungsten lengthwise. Do not grind around it, as this causes ridges on the tungsten electrode and will also lead to an erratic or wandering arc. Also, grind a taper on the tungsten electrode that spans the distance of no more than two and a half times the electrode diameter. As an example, a 1/8-in. tungsten electrode would have a taper 1/4 to 5/16-in. long. Remember to use a grinding wheel especially designated for the purpose of grinding tungsten electrodes. Doing so helps avoid further contamination that can adversely affect arc (and weld) quality.
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Having too long of an arc can also cause it to become unstable and/or wander on both AC and DC applications. In both instances, shorten the arc by moving the torch and tungsten electrode closer to the work piece, taking care not to touch it.
Dirty base materials and shielding gas are other potential causes of an unstable TIG welding arc. Remember to wipe the material free of oil, dirt or debris and to wire brush materials like aluminum before welding. Be certain to use clean, pure argon for TIG welding (or reduce helium percentages if using a mixture) and keep the flow rate between 10 and 20 CFH.
When TIG welding using either AC or DC, select the appropriate size and type of tungsten electrode for the given amperage to avoid arc-starting problems. Too large of tungsten for the given amperage can cause the arc to rotate around the tip, while too small of tungsten can melt and cause the arc to become unstable. Always follow the manufacturer’s recommended welding parameters for each tungsten electrode diameter.
2% ceriated tungsten electrodes provide good arc starting at low amperages and can be used on both AC and DC applications when welding carbon or stainless steel, nickel alloys, aluminum or titanium. The same is true for 1.5 per cent lanthanated tungsten electrodes. For higher current applications or low-amperage AC applications, 2 per cent thoriated tungsten electrodes provide good arc starting. Note: Thorium is radioactive; therefore, you must always follow manufacturer’s warnings, instructions and the MSDS (Material Safety Data Sheet) for its use.
A final means to remedy arc-starting trouble is to be sure the ground clamp is secure and check that there are no loose or damaged cables leading to it. Keep the torch cables and work cables as short as possible, while still being able to reach the work area, and place them close together. Check that all power cables have been installed according to the power source manufacturer’s recommendations.
Get rid of trouble
Because there is no single cause for the tungsten electrode and arc troubles that commonly occur when TIG welding, there is no single way to solve them. A little knowledge, proper training and a lot of practice, however, can ease the troubleshooting process. It can also help avoid unnecessary, not to mention costly, downtime.
Weldcraft
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