Porosity describes voids, but it does not identify a single mechanism. Gas-related porosity and shrinkage-related porosity call for different investigations. The appearance of an indication is useful evidence, yet its position and relationship to the manufacturing route are equally important.

Shape provides a clue, not a final diagnosis

Gas-related voids can appear rounded, while shrinkage can show irregular or interconnected features associated with solidification. Real castings can contain mixed conditions, and the examination method influences what is visible. A two-dimensional image may not reveal the complete shape of an internal feature.

Record the observation without overstating certainty. Additional examination or sectioning, where approved, may be needed to establish what the indication represents.

Map the voids onto the component geometry

An indication associated with a heavy junction suggests different questions from dispersed small voids across multiple regions. Review the location relative to feed paths, section changes and the expected solidification sequence.

For a shrinkage investigation, ask whether the region could receive adequate feeding as it solidified. For a gas investigation, examine relevant melt, mold and filling conditions. These are directions for controlled investigation, not reasons to apply an unverified shop-floor remedy.

Consider what machining has revealed

Porosity may first become visible when a bore or sealing face is cut. That does not mean machining created the internal void. The affected depth and its relationship to the rough casting should be recorded so the foundry can connect it to the production geometry.

If the part must contain pressure, dimensional acceptance alone may not address the consequence of connected porosity. The purchase specification should define the required examinations and functional tests for the delivered condition.

Choose corrective action after the mechanism is supported

Changing the feed arrangement, melt practice or mold conditions addresses different potential causes. Compare production evidence before and after an approved change and check that other requirements remain satisfied.

Northeast Castings can review porosity-related acceptance needs with the drawing and examination results. A useful report distinguishes the observed void from the inferred mechanism, allowing disposition and process improvement to proceed on evidence rather than a label alone.