Casting defects — identifying sand wash In foundry practice, the defect termed “sand wash” refers to which observable condition on a casting?

Introduction / Context:
Quality control in casting requires recognizing surface and internal defects and linking them to their causes. “Sand wash” is a typical surface defect that reveals issues with gating design, metal velocity, or mould strength near the ingates.

Given Data / Assumptions:

• Sand mould casting with gravity gating.
• Defect is visible on the external surface after shakeout and cleaning.
• Observed particularly close to ingates or regions of high metal velocity/turbulence.

Concept / Approach:
Sand wash occurs when the incoming metal stream erodes the mould face. The entrained sand is then swept onto the fresh metal surface and freezes there as rough, scabby deposits. It is distinguished from mismatch (alignment error), enlargement (pattern/allowance error), and gas-related defects (smooth cavities). Understanding flow patterns and protecting mould surfaces eliminates sand wash.

Step-by-Step Solution:
Link defect location to ingates and high-velocity streams.Identify texture: rough, scabby, adhering sand/metal mixture.Associate cause: erosion due to excessive turbulence or weak mould.Therefore, select the description of rough lumps near ingates caused by sand erosion.

Verification / Alternative check:
Trial casting with reduced gating velocity or with splash/core prints often shows reduction of sand wash, confirming mechanism.Use stronger sand, correct moisture, and well-designed sprue/runner/gate to minimise turbulence.

Why Other Options Are Wrong:
Mismatch is a parting-line alignment issue and appears as a stepped offset, not scabby lumps.

General enlargement is a dimensional error, not a local surface defect.

Sand patches on upper surfaces are more typical of scabs or rat-tails, not classic sand wash concentrated at ingates.

Gas blows present as smooth cavities/bubbles, unlike the gritty texture of sand wash.

Common Pitfalls:
Confusing sand wash with scabbing; ignoring sprue well and gate orientation; underestimating the role of sprue taper to avoid aspiration and erosion.

Final Answer:
Rough, scabby lumps near ingates where eroded sand is deposited on the surface