Casting
Sand casting: what goes wrong and where to inspect
The most widely used casting process, from small iron housings to steel castings of several tonnes. Flexible and economical, but quality depends heavily on method design and process discipline.
01How the process works
A pattern is moulded in sand bonded with clay and water (green sand) or with chemical binders (no-bake). Cores form internal passages. Molten metal is poured through a gating system and fed by risers while it solidifies. After shake-out the casting is fettled, heat treated where required and often machined by the foundry or the buyer.
Most sand casting defects originate in the method (gating and feeding design), the moulding sand, the melt and the pouring practice. Many of them are internal and only appear after machining, which is why first article sectioning, NDT and process audits matter more than a final visual check.
- Pattern and cores. Pattern, core boxes and gating are made to the method design.
- Moulding. Sand is compacted around the pattern; cores are set.
- Melting and pouring. Melt chemistry and temperature are controlled; metal is poured.
- Shake-out and fettling. Sand, gates and risers are removed; surfaces are ground.
- Heat treatment and finishing. Annealing, normalising or quench and temper; then inspection.
02What typically goes wrong
| Defect | Typical cause | How it is found |
|---|---|---|
| Shrinkage porosity | Insufficient feeding of thick sections | RT, UT, sectioning of first articles |
| Gas porosity and blowholes | Moist sand, low permeability, gassy melt | Visual, RT, machined surface check |
| Sand and slag inclusions | Weak mould, turbulent pouring, poor skimming | Visual, MT/PT, machining |
| Core shift and mismatch | Core setting, worn pattern, flask alignment | Dimensional layout, wall thickness by UT |
| Cold shut and misrun | Low pour temperature, slow pouring | Visual, PT |
| Hot tears and cracks | Restrained contraction, hot spots | MT/PT after cleaning |
03Where an inspector should look
Before production
- Method design and simulation if available
- Pattern identification and condition
- Material grade, test bar plan and NDT class agreed
During production
- Melt chemistry and inoculation records
- Pouring temperature and time
- Sand properties (moisture, compactability, permeability)
After production
- Visual surface to agreed standard
- Dimensional layout and machining allowance
- NDT, test bars, heat treatment chart, weld repair records
04Standards and references
EN 1561 and EN 1563 (grey and ductile iron), EN 10293 and EN 10213 (steel castings), EN 1369 and EN 1371 (MT and PT of castings), EN 12680 (UT of steel castings), ASTM E446 and E186 reference radiographs.
Standards are named for orientation. The applicable edition and acceptance criteria are those in your contract and specification.
05How we support buyers of sand casting parts
Frequently asked questions
Can porosity be found before machining?
Volumetric defects can be found by radiography or ultrasonic testing before machining, at a cost. A common approach is full NDT and sectioning on first articles, then sampling in series production based on results.
Are weld repairs on castings acceptable?
Often yes, if the material standard and the buyer allow it, using a qualified repair procedure and with records. Unreported repairs are a frequent finding in foundry audits.