Not all pores have the same parents.
Gas porosity vs shrinkage porosity
Gas porosity comes from air or gases entrained in the melt and trapped during fill — often rounded, distributed pores linked to shot speed, venting and melt handling. Shrinkage porosity forms where solidifying metal cannot be fed — typically near hot spots and thick sections, with irregular internal voids.
The distinction guides the fix: gas problems point at process and venting; shrinkage points at design and feeding.
A practical sorting method
Start from location and appearance: section suspect castings, map where pores sit relative to thick sections and parting lines, and correlate with shot curves.
Fixes then follow the diagnosis — venting and melt practice for gas, section changes and local feeding for shrinkage.
FAQ
Is some porosity always present?
High-pressure castings commonly contain some porosity; what matters is whether it is within the acceptance level the application requires.
Does machining expose porosity?
Often yes — machining cuts into sections where pores were hidden, which is why machining stock and pore location are reviewed together.
Can impregnation solve leaks?
Sealants can block leak paths for pressure-tightness, but they are a remedy, not a substitute for controlling the casting process.
All figures above refer to standard product data sheets; final confirmation is subject to written quotation.