EPDM, NBR and FKM are material families rather than single formulations. Cure system, fillers, plasticisers and production conditions can change hardness, recovery and fluid response. A useful incoming record therefore links test method and condition to the exact compound batch and supplied clamp insert.
Do not release an insert batch from polymer family and Shore hardness alone. Freeze the compound and revision, define specimen preparation, hardness method, compression-set condition and relevant service-liquid ageing, then compare results with project acceptance limits. A test on a different compound, cure, specimen or liquid does not qualify the supplied insert automatically.
- Best for
- Supplier approval, first-article release, compound or moulding-source changes and risk-based incoming inspection for hydraulic, cooling and offshore clamp inserts.
- Not suitable for
- A universal material-property specification, prediction of service life, approval of an unidentified compound, or proof that a Weique insert meets an unreported project limit.
- Decision checks
- compound code and revision, batch and cure record, specimen source, conditioning, Shore scale, compression strain/time/temperature/recovery, service liquid, immersion condition, property change and acceptance authority
- RFQ inputs
- fluid identity and temperature, service and standby temperatures, required hardness method, compression-set condition, immersion test plan, drawings, compound specification, CoA, batch sample and change history
§ 01 Freeze the compound before comparing results
Record elastomer family, supplier, compound code, colour, cure system where controlled, revision, moulding site and batch. Two black EPDM inserts or two nominal 70 Shore A compounds are not necessarily interchangeable because family name and nominal hardness do not define the full formulation.
§ 02 Specify the hardness method and specimen
ISO 48-4 defines Shore durometer methods and different scales for normal, high, low and thin rubber test pieces. State scale, specimen thickness and preparation, conditioning, measurement locations and acceptance range. A reading on a finished curved or thin insert may not be directly comparable with a standard plaque.
§ 03 Use compression set to check recovery, not service life
ISO 815-1 defines compression-set methods at specified strain, time, temperature and recovery conditions. These variables must accompany every result. A short laboratory test can support compound classification or batch control, but it does not by itself predict years of clamp force retention in a turbine.
§ 04 Age in the liquid that matters
ISO 1817 evaluates changes before and after immersion in service or reference liquids. Select actual hydraulic oil, glycol mixture, cleaning agent or other justified liquid, together with concentration, temperature and duration. Water, standard oil and project fluid results are not automatically interchangeable.
§ 05 Control preparation and conditioning
ISO 23529 covers preparation, storage, conditioning and the interval between forming and testing. Define whether specimens come from a moulded plaque, the same production batch or the finished insert. Mixing specimen sources can create apparent supplier differences that are actually test-preparation differences.
§ 06 Choose release tests by failure risk
Hardness is a practical identity and consistency check. Compression set addresses recovery after sustained deformation. Liquid ageing addresses mass, volume or property change in a defined exposure. Use only the tests connected to the service risk, and define project limits from design validation or approved material specifications.
§ 07 Escalate changes instead of silently averaging them
Quarantine lots with wrong compound identity, missing traceability or failed critical limits. A borderline result needs the pre-agreed retest and disposition rule. Supplier, formulation, cure, colourant or moulding-process changes should trigger documented engineering review rather than being hidden inside historical averages.
§ 08 Evidence levels
| Evidence level | Use | Boundary |
|---|---|---|
| TESTED | Result matches the tested configuration. | Does not cover changed components or installation. |
| BATCH-TRACEABLE | Record links to the delivered lot. | Does not prove unrecorded system performance. |
| STANDARD-BASED | Official scope defines a method or decision system. | Does not select project criteria or prove this product passed. |
| PROJECT-SPECIFIC | Customer risk and drawings close the decision. | Cannot be generalized to another project. |
| INDICATIVE | Example or early screening logic. | Not an acceptance plan or guaranteed value. |
§ 09 Decision matrix
| Release situation | Minimum evidence | Boundary |
|---|---|---|
| Routine approved batch | Compound/batch identity plus agreed CoA tests. | CoA values only support listed methods and limits. |
| New compound or supplier | Full qualification against service exposures. | Family equivalence is not formulation equivalence. |
| Finished insert hardness check | Defined geometry, thickness and locations. | May not equal a standard plaque result. |
| Compression-set result | Strain, time, temperature and recovery stated. | Not a direct service-life prediction. |
| Liquid-ageing result | Exact liquid, concentration, temperature and duration. | Cannot transfer automatically to another fluid. |
| Failed or missing critical evidence | Hold lot and apply documented disposition. | Retesting cannot erase wrong identity or traceability. |
§ 10 Official sources and evidence boundary
The ISO pages directly define the scope of hardness, compression-set, liquid-effect and specimen-conditioning methods. They do not prescribe a universal acceptance value for wind-turbine clamp inserts or demonstrate equivalence between compounds. Limits and test frequency remain project-specific and must come from design validation, approved specifications and the actual service environment.
- ISO 48-4:2018 — Shore hardness by durometer method
- ISO 815-1:2019 — Compression set at ambient or elevated temperatures
- ISO 1817:2024 — Effect of liquids on vulcanized or thermoplastic rubber
- ISO 23529:2016 — Preparation and conditioning of rubber test pieces
EPDM vs FKM inserts · EPDM vs NBR selection · Insert degradation signs · Hydraulic pipe clamps