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Casting defects: types, causes and prevention
Most casting rejections fall into a handful of families. Name the defect correctly and the cause - and the fix - usually follows. This guide maps the common defects and links to a focused page for each.
The defect families
A wrong label is worse than no label, because it sends you chasing the wrong cause. Nearly every casting reject fits one of these families, and each family has its own tell and its own fix.
| Family | Typical defects | Usually points to |
|---|---|---|
| Gas | Blowholes, pinholes, gas porosity | Mould/core gas, permeability, dissolved gas in the melt |
| Shrinkage | Shrinkage porosity, shrinkage cavity, sink | Feeding and gating, thermal hot spots |
| Sand & mould | Sand inclusion, scab, penetration, drop, veining | Sand properties, mould strength, ramming |
| Pouring & metal | Cold shut, misrun, cold shot | Pouring temperature, speed and gating |
| Inclusions & cracks | Slag, dross, hot tear, cold crack | Melt cleanliness, contraction and stress |
Gas defects
Smooth-walled, rounded cavities. Gas from the mould, a core or the melt is trapped as the metal freezes. The smooth wall is the tell that separates gas from shrinkage. Start with the blowhole guide.
Shrinkage defects
Rough, jagged, dendritic cavities at thermal centres and under feeders, where the metal pulled away as it solidified and was not fed. The fix is feeding and gating, not dryness. See shrinkage porosity.
Sand & mould defects
The mould loses material into the casting or fails under heat: sand inclusions, scabs, and metal penetration. These trace back to sand strength, moisture and ramming - numbers that only mean something if the sand lab instruments are calibrated.
Pouring & metal defects
The metal is too cold or too slow to fill and fuse: cold shuts and misruns. Pouring temperature, speed and gating are the levers.
Inclusions & cracks
Non-metallic matter carried into the mould (slag, dross, refractory), and cracks from contraction stress (hot tears while solidifying, cold cracks after). Melt handling, filtration and mould give govern these.
Why naming and tracking matters
The same photograph, labelled "blowhole" one day and "porosity" the next, hides the pattern that would fix the process. A consistent, photo-backed register - which defect, on which part, at which stage - turns scattered rejections into a Pareto you can act on, and into the evidence a customer or auditor will accept.
Frequently asked questions
What are the main types of casting defects?
How do I tell a gas defect from a shrinkage defect?
Log defects on the floor, free
CaRe 101 is a free shop-floor app from Versatile: your team photographs the casting, marks the defect and taps its name - no typing, works offline. The rejection register builds itself, so you can see which defects hit which parts and act on the pattern.
Open CaRe 101 - free See how it works