Magnetic Particle Inspection Level 2 Practice Exam

Which defect is caused by non-uniform cooling resulting in stresses that rupture the surface of the metal?

1. Shrink

2. Hot tears

3. Porosity

4. Dross

The correct answer is: Hot tears

Hot tears are surface ruptures that occur in a metal due to non-uniform cooling, which creates internal stresses during the solidification process. As the metal cools, different areas may contract at different rates, leading to tensile stress that exceeds the material's strength. When these stresses become too great, they cause cracks along the surface, manifesting as hot tears. This phenomenon is particularly prevalent in cast metals, where the cooling process can vary significantly due to factors like section thickness and mold material properties. On the other hand, the other defects do not specifically relate to surface ruptures caused by non-uniform cooling. Shrink defects, while related to cooling, typically refer to overall dimensional changes rather than surface cracks. Porosity involves trapped gas bubbles during solidification rather than cracks formed through stress. Dross consists of impurities that form on the surface of molten metal and is not a result of cooling stresses but rather of contamination or oxidation. Understanding the distinct nature of these defects is crucial for effective inspection and material evaluation in magnetic particle inspection processes.