Question and Answer Tig

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    1. Should I use an air-cooled or water-cooled torch?

    For low-amperage applications, an air-cooled torch cooled by shielding gas works well. These

    torches are simple to operate and require minimal setup. For high-amperage applications, youcan still use an air-cooled torch, but the cable and torch must be much heavier and may be

    cumbersome to manipulate.

    A water-cooled torch, which circulates water through the torch and cable, works equally well,

    but requires additional equipment and maintenance. These torches use clean, de-ionized waterwith filters that prevent contaminants from entering the cooling supply or the inner-diameter tube

    of the torch. You also may need to use additives to prevent algae growth.

    Whether you choose a water-cooled system depends on your willingness to invest in additional

    equipment, as well as additional time and money for maintenance. Many welders, however,prefer these systems because the smaller torch configuration provides better maneuverability and

    reduces operator fatigue.

    2. When should I use a gas lens?

    A gas lens should be used when your application requires increased shielding gas coverage. Thegas lens reduces turbulence and provides lengthier, undisturbed gas flow and allows you to move

    the nozzle farther away from the workpiece while still keeping the arc or weld puddle in view.

    Using a larger nozzle with a gas lenswhich consequently produces a larger blanket of shieldinggascan help when welding on materials such as stainless steel and titanium.

    A gas lens allows more direct and broader gas coverage on tight joints, such as an inside corner,

    where access is limited. In critical applications that have potential for atmosphericcontamination, a gas lens can help to reduce the likelihood of weld discontinuities.

    3. What are the causes of an unstable arc, and how can I

    remedy them?

    Using the wrong size tungsten, whether in AC or DC applications, is one of the more commoncauses of an unstable arc. If the tungsten is too large for the amperage, the arc may rotate around

    the end of the tungsten. Conversely, if the tungsten is too small for the amperage, the current can

    melt the electrode and cause an erratic arc. To remedy either of these conditions, match your

    welding current to the tungsten size recommended by the manufacturer.

    Contaminated tungstencaused by debris on the base metal, oxidation from inadequate

    shielding gas, or gas impurities from a leakalso can cause an unstable arc in both AC and DC

    applications. To resolve this problem, replace or regrind the tungsten, make sure the base metalis clean, or increase the shielding gas flow after making sure all your hoses are intact and leak-

    free.

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    4. How do I prevent tungsten contamination and

    discoloration?

    Allowing the tungsten to touch the weld pool is one of the most common causes of

    contamination. This problem can be resolved by moving your torch farther away from theworkpiece, which in turn lengthens the arc. Touching the filler metal to the tungsten also can be

    a source of contamination, but there is no clear solution to this problem other than practice; trialand error will determine your best technique.

    If you feel your technique is not the culprit of tungsten contamination or discoloration, check to

    see that you have adequate gas flow, and allow adequate postflow time as well. Allow several

    seconds of postflowabout 1 second for every 10 amps of weld current.

    Finally, you may want to consider using a power supply that offers high-frequency starts if you

    think using the scratch-start method is causing the contamination.

    5. What are the causes and solutions for excessive electrode

    consumption?

    Using too much current on a given application is a major cause of excessive electrode

    consumption and is most easily solved by increasing the tungsten size, changing the type of

    tungsten you are using, or decreasing the amperage.

    Using the wrong polarity also can result in excessive tungsten consumption. During AC welding,

    for example, using more electrode-positive current may provide more cleaning action, but it also

    subjects the tungsten to more current and thus consumption. Instead, it is best to set the powersource more toward electrode negative on the balance control to minimize the amount of currentand time spent on the electrode.

    Using an incorrect or contaminated shielding gas can lead to high electrode consumption. Be

    sure to use pure argon, and check for leaks in the hoses, either from cracks or loose fittings.

    6. What causes porosity in a GTAW bead, and how can I

    prevent it?

    A loose hose or torch component is a primary cause of porosity. It is remedied by tightening thefittings. If you cannot find loose hose connections by doing a visual check, you might want toplace the hose in soapy water until you find the leak and tighten the fittings accordingly.

    Using the wrong shielding gas or one that has impurities also can lead to porosity. This is

    remedied by using pure argon after using nitrogen to purge the line of air and any condensation

    that may have accumulated. Drafts from fans or open doors also can lead to porosity, so be sure

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    that your working environment is well-isolated from drafts or use a gas lens to provide better gas

    coverage.

    To prevent porosity caused by inadequate shielding gas flow, follow the recommended flow rate,which is approximately 10 to 20 cubic feet per minute (CFM), depending on the application.

    Doing so helps ensure quality welds.

    7. What type of tungsten should I use?

    The four main tungsten choices for GTAW are 2 percent thoriated tungsten, pure tungsten, 2percent ceriated tungsten, and 1.5 percent lanthanum tungsten.

    Two percent thoriated tungsten is a good choice when using a DC power source because it

    maintains a pointed shape, resists melting, and has a high current-carrying capacity. When

    welding thin aluminum0.09 in. or lessthoriated tungsten is also a good alternative to puretungsten because it creates a more focused arc. It is recommended that thoriated tungsten be used

    in a ventilated area and measures be taken during preparation to capture dust from grindings.

    Pure tungsten performs well when welding aluminum using a conventional AC power source.

    Two percent ceriated tungsten is a good alternative to thoriated tungsten and provides good arc

    starts at low currents, along with greater arc stability. This type of tungsten is recommended foraluminum AC welding with an inverter-based power source.

    Last, a 1.5 percent lanthanum tungsten is most commonly used for applications in which long

    weld times and multiple arc restarts are necessary.

    8. What is the proper procedure for cleaning base metals?

    The base metal should be free of all contaminants, including dirt, paint, and oil. Wipe the base

    metal with a cloth or scrape it with a wire brush dedicated for use on a particular material. Before

    welding on aluminum, in particular, you need to remove oxides with a stainless steel brushmanually; using a power brush is not recommended as it can re-embed contaminants into the

    metal. You can also use a caustic solution to clean aluminum. If you are considering using this

    method, your local welding distributor is the best resource to provide you with product options.

    You can also discuss several scraping methods with your distributor if you do not want to usechemicals.

    9. How do I solve high-frequency-interference problems?

    Malfunctioning electrical equipment, such as computers, telephones, and radios, is often a sign

    that you are experiencing high-frequency interference from your welding power source.

    To remedy such high-frequency interference, start by verifying that the power source is grounded

    according to the installation instructions provided in the operator's manual. Keep your torch

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    cables and work cables as short as possible, and place them close together. Physically separating

    your welding equipment from devices that may experience interference is also an option, but

    doing so can be time-consuming and space-prohibitive.

    If all else fails, you could switch to an inverter-based power source that provides a high

    frequency for arc starting only.

    10. What are the cause and solution for arc rectification?

    Arc rectification occurs when the surface oxide of a nonferrous metal acts as a barrier, making itmore difficult for electrons to flow from the workpiece to the tungsten than from the tungsten to

    the workpiece. Excessive arc noise, unstable weld pools, or a weld pool that appears to dry up

    are all signs of arc rectification.

    You can either increase your travel speed or decrease the amperage for the application. Anotheroption is to adjust the balance control on your power source toward electrode negative, which

    provides more penetration.

    As a last resort, switch to an inverter power source that offers advanced square wave technology.