Welding Flame Types

Resistance Welding

• Employs the principle of both pressure and fusion welding methods
• Heating is accomplished by the passage of a heavy localized electric current
• Temperature at the joint increases due to high resistance
• External pressure is applied at the joint to result in a forge weld
• Used for fastening thin metal sheets and wires

Gas Welding

• Combustion is obtained by mixing oxygen with a fuel gas (e.g. acetylene)
• Oxyacetylene weld is produced by heating with a flame obtained from combustion
• Filler metal is used to supply additional material to the weld zone
• Fluxes are used to clean the surfaces to be joined and promote a better bond

Types of Flames

• Oxidising flame: desirable for fusion welding of brass and bronze, obtained by adding more oxygen
• Carburising or Reducing flame: used to weld Monel metal, nickel, and nonferrous materials, obtained by turning on oxygen

Advantages and Disadvantages of Oxyacetylene Welding

• Advantages:
  • Portable and inexpensive equipment
  • Can be used for cutting
  • Can weld practically all metals
• Disadvantages:
  • Slower than electric arc welding
  • Not suitable for heavy sections
  • Gas cylinders are highly explosive and require careful handling
  • Prolonged heating of the joint results in distortion and loss of corrosion resistance

Soldering

• Process of joining two metal pieces by adding filler metal with a melting temperature below 450°C
• Filler metal is usually solder, an alloy of tin and lead
• Fluxes used include resin, zinc chloride, and ammonium chloride
• Strength of the soldered joint is relatively low

Gas Welding Equipment

• Gas cylinders: oxygen (125 kgf/cm2) and acetylene (16 kgf/cm2)
• Regulators: reduce cylinder pressure to working pressure and produce a steady flow of gas
• Pressure gauges: monitor pressure
• Hoses: connect regulators to welding torch
• Welding torch: mixes oxygen and acetylene and ignites the mixture
• Check valve and non-return valve: used in gas welding equipment