Mumbai University > Mechanical Engineering > Sem 3 > Production Process 1

Marks: 5M

Year: May 2016

There are three basic flame types: neutral (balanced), excess acetylene (carburizing), and excess oxygen (oxidizing).

• Neutral Flame:

  • The neutral flame has a one-to-one ratio of acetylene and oxygen.
  • It obtains additional oxygen from the air and provides complete combustion.
  • It is generally preferred for welding.
  • The neutral flame has a clear, well-defined, or luminous cone indicating that combustion is complete.

  Neutural welding flames are commonly used to weld:

  • Mild steel
  • Stainless steel
  • Cast Iron
  • Copper
  • Aluminum

• There are two clearly defined zones in the neutral flame. The inner zone consists of a luminous cone that is bluish-white. Surrounding this is a light blue flame envelope or sheath.
• The neutral or balanced flame is obtained when the mixed torch gas consists of approximately one volume of oxygen and one volume of acetylene.

• In the neutral flame, the temperature at the inner cone tip is approximately 5850ºF (3232ºC), while at the end of the outer sheath or envelope the temperature drops to approximately 2300ºF (1260ºC).

• Carburizing Flame:

  • The carburizing flame has excess acetylene, the inner cone has a feathery edge extending beyond it.
  • Reducing or carburizing welding flames are obtained when slightly less than one volume of oxygen is mixed with one volume of acetylene.
  • The reducing or carburizing flame can always be recognized by the presence of three distinct flame zones. There is a clearly defined bluish-white inner cone, white intermediate cone indicating the amount of excess acetylene, and a light blue outer flare envelope.
  • This type of flare burns with a coarse rushing sound. It has a temperature of approximately 5700ºF (3149ºC) at the inner cone tips.

• Oxidizing Flame:

  • Oxidizing welding flames are produced when slightly more than one volume of oxygen is mixed with one volume of acetylene.
  • When the flame is properly adjusted, the inner cone is pointed and slightly purple.
  • An oxidizing flame can also be recognized by its distinct hissing sound.
  • The temperature of this flame is approximately 6300ºF (3482ºC) at the inner cone tip.
  • Oxidizing welding flames are commonly used to weld these metals:
    • zinc
    • copper
    • maganese steel
    • cast iron