Foundry defects — identification by visual symptom In sand casting practice, which named defect describes a general enlargement or bulging of the entire casting shape due to pressure of molten metal acting on a weak mould face (i.e., the casting comes out slightly over-size everywhere)?

Introduction / Context:
Recognising common casting defects is essential for process troubleshooting in foundry engineering. “Swell” is a defect that causes the whole casting or a region of it to appear enlarged compared to the pattern. This question checks your ability to match the correct technical term to the observed symptom and link it to its root causes in moulding practice.

Given Data / Assumptions:

• Sand moulding with metallic pattern or wooden pattern is assumed.
• The final casting is consistently larger in some area than intended, without a simple relative displacement between cope and drag.
• Molten metal exerts hydrostatic and ferrostatic pressure on the mould wall.

Concept / Approach:
A “swell” occurs when weakly rammed or low-strength sand yields under metal pressure, allowing the mould face to move outward. The result is a uniformly “fatter” profile in the affected zone. This is different from “shift”, which is a mismatch caused by misalignment of the cope and drag; “scab”, which is a raised, scaly patch due to sand lifting; and “sand wash”, which is erosion or washing of sand into the cavity causing rough surfaces. Correct identification suggests corrective actions such as improving ramming uniformity, increasing mould hardness, or adding reinforcements like gaggers.

Step-by-Step Solution:
Observe the symptom: overall enlargement/bulging rather than a discrete patch or a clean mismatch line.Relate symptom to cause: inadequate mould hardness/strength allows wall movement under metal head.Map to terminology: this behaviour matches the defect known as “swell”.Confirm by prevention strategy: better ramming, correct moisture, and stronger facing sand reduce swell.

Verification / Alternative check:
If the defect were a “shift”, measurement would show two halves of the casting offset across the parting plane; if it were a “scab”, you would see a flaky, sand-laden patch. Absence of these confirms “swell”.

Why Other Options Are Wrong:

• Shift: misalignment at the parting line, not uniform enlargement.
• Sand wash: erosion produces rough, sand-embedded surfaces, not bulging.
• Scab: localized raised blister with sand inclusion, not overall growth.
• Misrun: incomplete filling, giving undersize/rounded edges, opposite of enlargement.

Common Pitfalls:
Confusing “swell” with machining allowance; swell is unplanned and irregular, machining allowance is deliberate and uniform.

Final Answer:
swell