Plastics, rubber and composites
Rubber moulding and vulcanising: what goes wrong and where to inspect
Seals, gaskets, anti-vibration mounts and rubber to metal bonded parts are moulded and vulcanised from compounded elastomers.
01How the process works
A compound of polymer, fillers and curatives is mixed, preformed and moulded by compression, transfer or injection in heated moulds, where it vulcanises. Bonded parts use metal inserts coated with adhesive systems. Parts are deflashed and sometimes post cured.
Compound consistency (hardness, cure curve) and cure state decide the properties. Flash, non-fills, bubbles and poor bonding are typical defects; hardness and compression set confirm the material.
- Compound mixing. Batches mixed and tested by rheometer.
- Preform. Blanks cut or extruded.
- Moulding. Cured in heated mould.
- Deflashing. Flash removed mechanically or cryogenically.
- Testing. Hardness, dimensions, bond tests.
02What typically goes wrong
| Defect | Typical cause | How it is found |
|---|---|---|
| Non-fill | Insufficient compound, flow | Visual |
| Bubbles and porosity | Trapped air, moisture | Visual, section |
| Flash | Mould wear, excess material | Visual |
| Undercure | Time or temperature | Hardness, rheometer |
| Bond failure | Insert preparation, adhesive | Peel or pull test |
| Hardness out of range | Compound variation | Shore durometer |
03Where an inspector should look
Before production
- Compound specification and batch tests
- Mould approval
During production
- Cure time and temperature
- Batch traceability
After production
- Hardness and dimensions
- Bond tests for bonded parts
- Visual against limit samples
04Standards and references
ISO 3302 (rubber tolerances), ISO 48 (hardness), ISO 815 (compression set), ISO 813 (adhesion to rigid substrates).
Standards are named for orientation. The applicable edition and acceptance criteria are those in your contract and specification.