Porosity, Voids and Blisters in Cured Rubber

Voids have four main sources, and each needs a different fix. Guessing costs tooling time.

Moisture and volatiles

The most common cause. Sources include hygroscopic fillers stored in humid conditions, wet process aids, and insufficient drying before moulding. Look for voids distributed fairly evenly through the section, with a slightly rough internal surface.

Trapped air

Air folded in during mixing, or trapped during mould filling. Typical when the mould closes too fast, when venting is inadequate, or when the preform shape does not suit the cavity. Voids tend to concentrate at flow-front meeting points and in thick sections.

Under-cure combined with gas evolution

Some accelerators and blowing-agent residues generate gas at cure temperature. If the compound is under-cured or the pressure is released too early, that gas expands into visible voids.

Insufficient pressure or early pressure release

Voids forming near the surface often point to this. Check that the press is holding the stated pressure for the full cure and that the mould is closing fully.

Diagnostic order

Dry the compound and re-run a trial before changing anything else — it is the lowest-cost test and moisture is the most frequent cause. Then review mould venting and closing speed. Then look at cure state and pressure profile. ## Need the documents or today's price? Send us the grade, quantity and destination port — we return a quotation with COA and MSDS attached. Email manager@fipolymer.com or use the inquiry form on this site.