With reference to manual metal arc welding, answer any three of the following: (i) Name the components A, B and C in the welding circuit shown above - Leaving Cert Engineering - Question a - 2014

1. Transformer: The transformer steps down the mains voltage (220V) to a suitable level (80-100V) for welding. It does this by transforming voltage using turns on the primary coil, creating a lower voltage alternating current (AC).

2. Rectifier: The rectifier converts the alternating current (AC) from the transformer to direct current (DC). It typically consists of four diodes that allow current to pass in only one direction, providing a consistent flow of DC.

3. Capacitor: The capacitor smooths out the voltage fluctuations, providing a stable low voltage DC supply to the welding circuit.

1. Equipment Maintenance: Ensure welding equipment is well-maintained, with cables secure and properly insulated to prevent electric shock.

2. Ventilation: Adequate ventilation should be in place to avoid the build-up of harmful fumes.

3. Protective Clothing: Wear appropriate protective gear, including darkened face plates to protect against UV light and gloves to avoid burns.

1. Structural Integrity: Multi-run welds allow several welds to be layered. This enhances the structural integrity of the weld joint, making it stronger and more durable than a single run.

2. Heat Distribution: Each weld in a multi-run process has a smaller heat effect on the previous weld. This reduces the risk of warping and overall distortion of the workpiece.

A suitable welding process for an exhaust pipe is Tungsten Inert Gas (TIG) welding.

In TIG welding:

• An arc is formed between a non-consumable tungsten electrode and the metal being welded.
• An inert gas, typically argon, is used to prevent oxidation during the welding process.
• A filler material may be added if necessary, and a high frequency generator provides the spark for welding. This process allows for excellent control and is well-suited for thin materials.

1. Neutral Flame:

   • Composition: Balanced proportions of oxygen and acetylene.
   • Use: Most common flame for welding steel.

2. Oxidising Flame:

   • Composition: Excess oxygen.
   • Use: Useful for welding brass and achieves higher temperatures.

3. Carburising Flame:

   • Composition: Excess acetylene.
   • Use: Suitable for welding aluminum and protects against oxidation.

1. Welding Curtains: Use of curtains or barriers to protect others from UV light.

2. Slag Inclusion: Maintain a layer of slag on the weld to protect it while cooling.

3. Inert Gas Shielding: Applying inert gas during the welding process to prevent contamination.