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8.1 State THREE welding aspects that must be focused on during the arc welding procedure - NSC Mechanical Technology Welding and Metalwork - Question 8 - 2021 - Paper 1
Question 8
8.1 State THREE welding aspects that must be focused on during the arc welding procedure. 8.2 How can centre-line cracks in welding joints be reduced? 8.3 State TW... show full transcript
Worked Solution & Example Answer:8.1 State THREE welding aspects that must be focused on during the arc welding procedure - NSC Mechanical Technology Welding and Metalwork - Question 8 - 2021 - Paper 1
Step 1
State THREE welding aspects that must be focused on during the arc welding procedure.
Answer
- Rate of rod burning: Ensuring that the rod is burning at an optimal rate to maintain weld consistency.
- Amount of penetration and fusion: Monitoring to ensure the weld penetrates properly into the base material without excessive penetration.
- Observing for welding defects while welding: Continuously checking for defects such as cracks, porosity, or lack of fusion to take corrective actions immediately.
Step 2
How can centre-line cracks in welding joints be reduced?
Answer
- Adjust travel speed: Decrease the travel speed to allow for proper melting and cooling of the weld metal.
- Decrease current: Lowering the welding current can help reduce penetration and minimize stress, which can lead to cracks.
Step 3
State TWO causes of EACH of the following arc-welding defects:
Answer
8.3.1 Lack of fusion:
- Travel speed is too slow: This prevents proper fusion between the weld and base metal.
- Weld metal not permitted to roll in front of the arc: This can lead to incomplete fusion at the joint.
8.3.2 Porosity:
- Contaminated weld surface: Impurities can lead to gas entrapment during solidification.
- Wet or dirty electrodes: Moisture or contamination can introduce gases into the weld pool.
8.3.3 Incomplete penetration:
- Welding current too low: Inappropriate current levels can hinder the ability to achieve proper penetration.
- Improper electrode angle: An incorrect angle can lead to insufficient heat application.
Step 4
Describe the process of setting an oxy-acetylene torch flame to a neutral flame.
Answer
- Open the acetylene torch valve: Start with the acetylene valve open about ½ turn and ignite.
- Adjust the oxygen valve: Slowly increase the oxygen valve until the flame reaches a neutral state, where the inner cone is no longer burning yellow.
- Observe the flame characteristics: A neutral flame will have a clear inner cone and a defined outer envelope, indicating optimal balance.
Step 5
Explain how to conduct a guided bend test on a welded joint.
Answer
- Prepare the specimen: Position the welded joint specimen horizontally across the supports of the bending die.
- Apply force: Use a hydraulic press to apply force to bend the specimen into the shape of the die.
- Measure results: After the test, determine and record the percentage of elongation of the weld metal to assess ductility.
Step 6
State TWO aspects that are tested when conducting a free-bend test on a welded joint.
Answer
- Ductility of the weld: Evaluate how the welded joint deforms before fracture occurs.
- Percentage elongation: Measure how much the weld metal stretches in relation to its original length during the test.
Step 7
Name TWO different types of dye used to conduct a liquid dye penetration test.
Answer
- Fluorescent dye: This type emits visible light when viewed under a black light, aiding in defect identification.
- Brightly colored liquid dyes: These can be inspected under regular light for visible indications of surface defects.
Step 8
Explain why a nick-break test is conducted on a welded joint.
Answer
A nick-break test is carried out to evaluate:
- Internal quality of the weld metal: This test examines the weld's internal soundness and integrity.
- Presence of defects: It reveals internal defects such as slag inclusions, porosity, and lack of fusion that might compromise the weld's performance.