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 configuration is crucial for ensuring proper arc stability during the cutting operation.

Two important personal safety items include fireproof gloves and safety goggles. These items are essential to protect the hands and eyes from sparks and heat generated during plasma cutting.

The metals that can be cut using an oxyacetylene cutting set include mild steel, cast iron, and stainless steel. These materials are commonly used in various welding and fabrication applications.

To successfully weld in the overhead position:

1. Ensure a proper gas mixture is present to achieve the desired flame characteristics.
2. Maintain the flame at an appropriate distance from the workpiece for optimal penetration.
3. Adjust the angle of the welding rod to maintain consistent movement and prevent overheating.
4. Utilize a steady hand to control the welding motion while supporting the weight of the apparatus.

At A, the type of distortion is lateral shrinking, while at B, it is angular shrinking. These distortions often occur due to uneven heating and cooling during the welding process.

Three factors impacting the shrinking in a welding joint include:

1. The welding procedure utilized, which affects heat distribution.
2. The number of weld runs, as more runs can lead to increased cumulative heat.
3. The material's resistance to deformation, influenced by its composition and treatment.

To prevent distortion, one can:

1. Employ pre-setting techniques to align parts correctly before welding.
2. Use clamping methods to secure the components in place, reducing movement during the welding process.

The vertical up arc welding process involves:

• Welding in an upward direction to counteract the pull of molten metal.
• A specially designed electrode that minimizes the motion of the weld pool.
• Maintaining a short arc length to control heat and achieve penetration without excessive pooling of molten metal.

When preparing cast iron for welding, one should:

1. Use a nickel welding rod to accommodate the cast iron's composition.
2. Set the amperage on the machine to its lowest level to prevent cracking.
3. Clean the surfaces to be welded of all grease, rust, and old paint, ensuring good fusion.
4. Remove the surface layer of metal where the join is to be formed.

Three disadvantages of MIG welding include:

1. Higher initial setup costs compared to other welding methods.
2. Limitations on operations due to the necessity for stable atmospheric conditions.
3. Additional maintenance costs attributed to the electronic components in MIG machines.

The causes of porosity in MIG welding can be:

1. Improper gas flow, either too high or too low.
2. Blocked or malfunctioning nozzles affecting shielding.
3. Contaminants on the base metal, such as dust or oil, which can lead to trapped gas bubbles.