Casting defects: causes, detection and prevention

01Main defect families

• Gas porosity: rounded smooth cavities from gas in the melt or from moulds and cores. Causes include moisture, poor venting, turbulence.
• Shrinkage: irregular cavities in sections that solidify last, from inadequate feeding.
• Inclusions: sand, slag or oxide entrapped in the metal.
• Cold shut and misrun: incomplete fusion of metal streams or incomplete filling, from low temperature or slow pouring.
• Hot tears: cracks during solidification from restrained contraction.
• Dimensional defects: core shift, mismatch, distortion, insufficient machining allowance.

02Detection

Surface defects are found by visual inspection, PT on non-ferrous castings and MT on ferrous castings. Internal defects need RT or UT, or sectioning of samples during approval. Pressure tightness is verified by leak testing. Many defects are revealed only by machining, which is why first articles should include machined samples.

03Prevention at the foundry

Prevention lies in method design (gating and feeding, often simulated), melt quality (degassing, inoculation, temperature control), sand and core quality, pouring practice and process control. During foundry audits we look at these controls rather than only at finished castings.

04What buyers should specify

• Material standard and grade, including microstructure where relevant.
• Casting quality class or acceptance level for surface and volumetric defects.
• Weld repair policy.
• First article requirements including sectioning or RT.
• Leak test requirements for pressure parts.