Lec 17 Gas Flame and Arc Welding Processes
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Questions and Answers

What is oxyfuel-gas welding?

  • A thermal cutting process
  • A type of flame straightening process
  • A type of arc welding process
  • A group of welding processes that use the flame produced by the combustion of a fuel gas and oxygen as the source of heat (correct)

    • Oxyacetylene welding is a type of arc welding process.

    False

    What is the purpose of preheating the metal in oxyacetylene welding?

    To provide shielding from oxidation

    The maximum temperature is at the _______________________.

    <p>inner cone</p> Signup and view all the answers

    Match the following welding processes with their descriptions:

    <p>Oxyfuel-gas welding = Uses the flame produced by the combustion of a fuel gas and oxygen as the source of heat Arc welding = Uses an electric arc to melt and join metals Flame straightening = Uses a flame to straighten bent or warped metal Thermal cutting = Uses a high-temperature flame to cut metals</p> Signup and view all the answers

    What is the name of the device used to control the flame in oxyacetylene welding?

    <p>Oxyacetylene torch</p> Signup and view all the answers

    Oxyfuel-gas welding is a type of thermal cutting process.

    <p>False</p> Signup and view all the answers

    What is the purpose of the oxyacetylene flame in welding?

    <p>To provide heat to melt and join metals</p> Signup and view all the answers

    What is the primary advantage of plasma arc welding?

    <p>Narrow welds with deep penetration</p> Signup and view all the answers

    Plasma arc cutting is a slower process compared to other thermal cutting methods.

    <p>False</p> Signup and view all the answers

    What is the name of the gas flow that transfers heat to the workpiece and melts the metal in plasma arc torches?

    <p>Orifice gas</p> Signup and view all the answers

    What is the temperature of an oxidizing flame?

    <p>3600°C</p> Signup and view all the answers

    Plasma arc cutting produces the highest temperatures available from any practical _______________.

    <p>source</p> Signup and view all the answers

    Oxyhydrogen-gas welding can be used to weld ferrous metals.

    <p>False</p> Signup and view all the answers

    What is the main difference between GTAW and plasma arc welding?

    <p>Constricted arc</p> Signup and view all the answers

    Plasma arc welding can be used to weld all metals and alloys.

    <p>True</p> Signup and view all the answers

    Flame straightening uses controlled, localized _______________ as a means of straightening warped or buckled material.

    <p>upsetting</p> Signup and view all the answers

    What is the most common thermal cutting process?

    <p>Oxy-fuel gas cutting</p> Signup and view all the answers

    What is the advantage of plasma arc welding in terms of distortion?

    <p>Reduced distortion</p> Signup and view all the answers

    Arc welding uses an oxyfuel-gas torch.

    <p>False</p> Signup and view all the answers

    What is the name of the process that uses an oxyfuel-gas torch to cut materials underwater?

    <p>Underwater cutting torch</p> Signup and view all the answers

    Which of the following welding processes is best used for welding ferrous metals?

    <p>Shielded Metal Arc Welding (SMAW)</p> Signup and view all the answers

    Flux-Cored Arc Welding (FCAW) equipment costs less than SMAW.

    <p>False</p> Signup and view all the answers

    What is the purpose of the flux in Shielded Metal Arc Welding (SMAW)?

    <p>To provide a gas shield around the arc, remove impurities, add alloying elements, and provide additional filler metal.</p> Signup and view all the answers

    In Gas Metal Arc Welding (GMAW), the supplemental shielding gas flows through the _______________________.

    <p>torch</p> Signup and view all the answers

    Match the welding processes with their characteristics:

    <p>SMAW = Best used for welding ferrous metals FCAW = Equipment cost greater than SMAW GMAW = Supplemental shielding gas flows through the torch SAW = Granular flux is deposited just ahead of the consumable electrode</p> Signup and view all the answers

    Submerged Arc Welding (SAW) uses a shielding gas.

    <p>False</p> Signup and view all the answers

    What is the primary purpose of Stud Welding?

    <p>To attach studs, screw, pins or other fasteners to a metal surface.</p> Signup and view all the answers

    Which welding process is best suited for making butt or fillet welds in low-carbon steels?

    <p>SAW</p> Signup and view all the answers

    What is the primary function of helium in Gas Tungsten Arc Welding (GTAW)?

    <p>To increase heat input for higher welding speeds and deeper penetration</p> Signup and view all the answers

    GTAW welded materials are always thicker than ¼ in.

    <p>False</p> Signup and view all the answers

    What is the most widely used gas in Gas Tungsten Arc Welding (GTAW)?

    <p>Argon</p> Signup and view all the answers

    In GTAW, the weld nugget begins to form at the surface where the _______________ makes contact.

    <p>gun</p> Signup and view all the answers

    Match the following components with their functions in GTAW:

    <p>Argon = Produces a smoother arc Helium = Increases heat input for higher welding speeds and deeper penetration Nozzle = Pressed firmly against the material Tungsten = Electrode that produces the arc</p> Signup and view all the answers

    What is the primary advantage of using helium in GTAW?

    <p>Higher welding speeds and deeper penetration</p> Signup and view all the answers

    Oxyfuel-gas welding is a type of arc welding process.

    <p>False</p> Signup and view all the answers

    What is the purpose of the vented nozzle on the modified TIG gun in GTAW?

    <p>improved gas coverage, reduced turbulence, and potentially better visibility</p> Signup and view all the answers

    Oxyacetylene welding uses a combination of oxygen and ______ gases to produce a high-temperature flame for welding and cutting metals.

    <p>acetylene</p> Signup and view all the answers

    The ______ contains valves for oxygen and acetylene flow control.

    <p>torch handle (oxygen control unit, fuel gas control valve)</p> Signup and view all the answers

    The ______ is where oxygen and acetylene gases mix.

    <p>mixing chamber</p> Signup and view all the answers

    A ______ flame is a balanced mixture of oxygen and acetylene; ideal for welding.

    <p>neutral</p> Signup and view all the answers

    To light the torch, open the ______ valve slightly.

    <p>oxygen</p> Signup and view all the answers

    Increasing oxygen flow increases ______ temperature and velocity.

    <p>flame</p> Signup and view all the answers

    Study Notes

    Plasma Arc Torches

    • Emerging gas transfers its heat to the workpiece and melts the metal, called the orifice gas flow.
    • Characteristics of plasma arc welding: fast welding speed, narrow welds with deep penetration, narrow heat affected zone, reduced distortion, and can be used to weld all metals and alloys.

    Arc Cutting

    • Types of arc cutting: carbon arc and shielded metal arc cutting, air carbon arc cutting, oxygen arc cutting, gas metal arc cutting, and plasma arc cutting.
    • Plasma arc cutting produces the highest temperatures available, is more economical, more versatile, and much faster.

    Oxyfuel-Gas Welding Process

    • Uses oxyfuel gas flame as the source of heat.
    • Types of flames: neutral flame, oxidizing flame, and carburizing flame.
    • Alternative fuel gases: propane, propylene, butane, natural gas, and hydrogen.

    Oxyfuel-Gas Cutting

    • Oxy-fuel gas cutting (flame cutting) is the most common thermal cutting process.
    • Metal is melted by the flame of the oxyfuel gas torch.

    Arc Welding

    • Types of arc welding: shielded metal arc welding (SMAW), flux-cored arc welding (FCAW), gas metal arc welding (GMAW), and submerged arc welding (SAW).
    • Shielded metal arc welding (SMAW):
      • Most widely used process due to versatility and low-cost equipment.
      • Best used for welding ferrous metals (carbon steels, alloy steels, stainless steels, and cast iron).
    • Flux-cored arc welding (FCAW):
      • Best used for welding steels.
      • Equipment cost greater than SMAW.
      • Needs good ventilation to remove fumes generated by the vaporizing flux.
    • Gas metal arc welding (GMAW):
      • Formerly known as metal inert-gas welding or MIG.
      • Supplemental shielding gas flows through the torch.
      • Consumable electrode: continuous, solid, uncoated wire or a continuous hollow tube with powdered alloy additions as consumable electrode.
    • Submerged arc welding (SAW):
      • Granular flux is deposited just ahead of bare-wire consumable electrode, and the arc is maintained beneath the blanket of flux.
      • No shielding gas used.
      • Most suitable for making butt or fillet welds in low-carbon steels.

    Other Processes

    • Stud welding: used to attach studs, screw, pins or other fasteners to a metal surface.
    • Flame straightening: uses controlled, localized upsetting as a means of straightening warped or buckled material.

    Oxyacetylene Welding Torch

    Principle

    • Oxyacetylene welding uses a combination of oxygen and acetylene gases to produce a high-temperature flame for welding and cutting metals.

    Components

    • Torch Handle: contains valves for oxygen and acetylene flow control
    • Mixing Chamber: where oxygen and acetylene gases mix
    • Nozzle: where the flame is produced
    • Hoses: supply oxygen and acetylene gases to the torch

    Operation

    • Lighting the Torch: open oxygen valve slightly, light the torch with a spark or flame, and adjust oxygen flow to achieve a neutral flame (feather-edged, blue-colored)
    • Adjusting the Flame:
      • Increasing oxygen flow increases flame temperature and velocity
      • Increasing acetylene flow increases flame size and reduces temperature

    Types of Flames

    • Neutral Flame: balanced mixture of oxygen and acetylene; ideal for welding
    • Oxidizing Flame: excess oxygen; used for cutting and heavy welding
    • Carburizing Flame: excess acetylene; used for bronze welding and brazing

    Safety Precautions

    • Wear protective gear (gloves, goggles, apron)
    • Ensure good ventilation
    • Keep the torch and hoses away from heat sources and sparks

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