Photo AI
9.1 Describe the meaning of shrinkage in a welded joint - NSC Mechanical Technology Welding and Metalwork - Question 9 - 2019 - Paper 1
Question 9
9.1 Describe the meaning of shrinkage in a welded joint. 9.2 State FOUR factors that affect distortion and residual stress during welding. 9.3 Explain back-step we... show full transcript
Worked Solution & Example Answer:9.1 Describe the meaning of shrinkage in a welded joint - NSC Mechanical Technology Welding and Metalwork - Question 9 - 2019 - Paper 1
Step 1
Describe the meaning of shrinkage in a welded joint.
Answer
Shrinkage in welding refers to a form of plastic deformation where the metal has deformed due to contraction as it cools. As the molten metal cools and solidifies, it results in a reduction in volume, leading to shrinkage. This can cause internal stresses and influence the integrity of the welded joint.
Step 2
State FOUR factors that affect distortion and residual stress during welding.
Answer
- Expansion during Heating: When metal is heated, it expands. If this expansion is not allowed, it leads to deformation.
- Contraction during Cooling: As the weld cools, if contraction is resisted, residual stresses will arise in the material.
- Applied Stresses: If the applied stresses during welding cause movement, this can lead to distortions in the final structure.
- Movement Resistance: Residual stresses will remain in the weld joint if the applied stress does not result in movement.
Step 3
Explain back-step welding as a method to reduce distortion by using a neatly labelled sketch.
Answer
Back-step welding is a technique where each segment of the weld is completed before moving to the next, effectively ‘back-stepping’ each segment towards the rear of the weld. This approach helps in controlling thermal expansion and minimizes distortion. The sketch would typically show the direction of welding, with segments labeled accordingly to illustrate the order of operations and the heat progression.
Step 4
State FOUR factors that affect the temperature at which cold-worked steel will recrystallise when heated.
Answer
- Prior Amount of Cold Work: The greater the cold work done on the steel, the lower the recrystallization temperature.
- Temperature and Time of Annealing Process: Higher temperatures and longer times can affect the recrystallization process.
- Composition of the Metal: Alloying elements can alter the recrystallization temperature by affecting the material's properties.
- Melting Point: The inherent melting point of the steel can provide a baseline for understanding its behavior during the heating process.