Oxyfuel Cutting And Welding

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Oxyfuel Cutting And Welding
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Introduction
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• Oxyfuel the process of combining pure oxygen
  with a combustible fuel gas to produce a flame
• Can be used for welding, brazing, cutting, and
  heating metals
• Oxygen fuel gases are stored under pressure in
  cylinders and are released as individual gases
  through valves, regulators, and hoses.
• Mixed as they flow through torch assemblies
• Burn as they are discharged through special tips

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• Fuel gases
• Propane, natural gas, propylene acetylene
• Vary in their chemical composition
• React with the metal in different ways
• Factors to consider in selecting a gas
• Availability cost
• Welding process or operation to be performed
• Thickness of metal type of welded joint to be
  produced
• Physical properties of metals
• Chemical properties of metals

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Propane (C3H)
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• Supplied in a liquid form under positive
  pressure, which varies with temperature
• Most oxyfuel cutting torches can use LP gas, but
  special hoses and cutting tips are required.
• Readily available in most areas
• Due to cost, propane cutting is heavily used in
  the metal recycling industry.

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Propylene (C3H6)
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• Has been used for approximately 30 years
• Stable in both liquid and gas states
• Economical
• Produces little slag
• Has a high heat value
• Does not have the withdrawal pressure limitations
  that are necessary with acetylene
• Approximately 5 propylene, 87 propane traces
  of other gases

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Acetylene (C2H2)
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• Most widely used fuel gas for welding and cutting
  applications
• Produces a clean weld and a controllable flame
• Less stable and more expensive than other fuel
  gases
• Performs most functions well and is widely
  available

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Compressed Natural Gas (CH4)
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• Adaptable for cutting, soldering, brazing, and
  preheating
• A water seal or blowback valve to prevent
  backfiring into the gas supply line must protect
  the natural gas source.

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Facts About Oxygen (O2)
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• Odorless, colorless, tasteless heavier than air
• Makes up about 20 of the atmosphere
• Will not burn by itself
• Produced commercially by causing air to liquefy
• Compressed into steel cylinders at 1,800 to 2,400
  pounds per in2 (psi)
• Supports combustion and is explosive if handled
  improperly
• Cylinder sizes 80 to 244 ft3

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Facts About Acetylene (C2H2)
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• Colorless, but has a very distinct odor
• Highly combustible
• Cylinder sizes 60 to 300 ft3
• Cylinder contains a porous substance saturated
  with liquid acetone
• Acetylene is pumped into the cylinder, displacing
  some of the acetone
• Not under extremely high pressure
• Full cylinder is pressurized to approximately 250
  psi
• May not be withdrawn at a rate higher than 15 psi

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Functions of Oxyfuel Heat
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• Oxyfuel cutting of mild carbon steel heats the
  metal to rekindling temperature (1,400oF to
  1,800oF), then oxidizes and blows the slag from
  the cut with a stream of pure oxygen.
• Oxyfuel welding fuses two pieces of metal by
  heating them to the melting point with a
  combustible mixture of oxygen and fuel gas.
• Can be done with or without the use of a welding
  rod
• Brazing the joining of metals by adding bronze
  filler
• Soft and hard solders (lead silver alloys) are
  the filler materials used in soldering.
• The oxyfuel flame is also used to bend, shape,
  preheat, stress relieve, post-heat temper metal.