4.1 Plasma cutting is an advanced method used to cut metal - NSC Agricultural Technology - Question 4 - 2017 - Paper 1

The polarity of the earth clamp on the plasma-cutting machine is positive. This is important for ensuring the proper operation of the machine and achieving desired cutting results.

Two important personal safety items include fireproof gloves and safety goggles. These items protect the user from burns and harmful light emitted during the cutting process.

Three types of metal that can be cut with an oxyacetylene cutting set are mild steel, cast iron, and stainless steel. These materials are commonly processed using this technique due to their weldability and cutting characteristics.

The procedures include:

1. Lighting the torch to create a reduced melting pool that is large enough to penetrate the metal.
2. Regulating the size of the flame to ensure optimal welding conditions.
3. Using a slightly thicker welding rod for strength.
4. Ensuring the flame is directed to keep the molten metal in the correct position during the process.

The type of distortion that occurs at A is lateral shrinking, while at B it is angular shrinking. These distortions occur due to the stresses and heat variations during the welding process.

Three factors that influence shrinking are:

1. The welding procedure adopted.
2. The amount of welding done, including the number of weld runs.
3. The original state or condition of the materials being welded, including their thickness and type.

Two measures to prevent distortion are:

1. Pre-setting the components before welding.
2. Using clamping techniques to hold the pieces in place during the welding process.

The vertical up arc welding process involves:

1. Welding in a vertical position, which helps in controlling the molten puddle.
2. Using a special electrode that helps the weld pool cool slower, preventing sagging.
3. Keeping the arc short while ensuring sufficient heat is applied to fuse the metals effectively.

To prepare cast iron for welding:

1. Use a nickel welding rod suitable for cast iron.
2. Set the machine amperage to the lowest possible setting to prevent burn-through.
3. Clean the surfaces thoroughly, removing all grease, dirt, and rust before welding.
4. Mark the welding line and avoid overheating to prevent cracking.

Three disadvantages of MIG welding are:

1. Higher initial setup costs due to specialized equipment.
2. The process requires a stable atmosphere, making it less effective in drafty environments.
3. Higher maintenance costs attributed to the electronic components used.

Three possible causes of porosity include:

1. Inconsistent gas flow, either too high or too low.
2. Blockages in the nozzle or hoses leading to improper shielding.
3. Contaminants such as oil or rust on the welding surfaces.