Manual Metal Arc welding (MMA) – Engineering

Manual Metal Arc welding (MMA) – Engineering

1. Circuit

Step-down Transformer

Converts high voltage AC to a lower voltage (220V to 80V-100V). This means the
output current is greater than the input current. This is due to the primary coil having
more windings than the secondary coil.

Smoothing Capacitor

Produces a more uniform direct current by smoothing the surges produced by the
rectifier.

Rectifier

  • Allows current to flow in one direction only.
  • Converts AC to DC.
  • Consists of four diodes arranged so to allow current to flow in one direction only.

 

 

Circuit for Manual Metal Arc Welding

2. Safety

  • Ensure equipment is well maintained.
  • Wear protective clothing.
  • Weld curtain/cubicle.
  • Ventilation

3. Hazards

  • Electric shock: Ensure conditions are dry, equipment is earthed and and insulated.
  • UV Light radiation: Suitable weld shield/goggles. Use of welding curtain.
  • Inhalation of fumes: Ventilation system.

4. Function of Electrode Coating

  • Generates Carbon Dioxide shield to protect from oxidation by nitrogen and oxygen.
  • Forms a slag.
  • Facilitates striking of Arc.

5. Functions of Slag

  • Fluxing action prevents contamination/oxidation of the weld by atmospheric gases.
  • Allows the weld to cool slower, producing a better weld.
  • Prevents cracks and brittleness in the weld.

Multi Run Welds

  • Produces a finished weld that is more refined in structure than single run welds.
  • Each run of welds has a post heating effect on the previous.
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