Most seal failures traced to rubber are not caused by a bad recipe. They are caused by variation: a new lot of polymer, a different filler source, a mixer that ran hot, a cure that was shortened. A supplier that controls variation can show it with data.
What consistency needs
- A defined specification. Limits for each release test, based on measured data for that compound and not copied from a general datasheet.
- A fixed recipe and procedure. The recipe, mixing order, temperatures, times and equipment are written down, and changes go through a record.
- Raw-material control. Incoming lots are identified and tested where it matters, and a change of source triggers re-qualification. Polymer, black and curatives are the main drivers.
- Batch testing. Each lot is tested for at least cure rheometer data, hardness and density, with slower tests such as compression set run on every lot or at a planned frequency.
- Traceability. Each lot ID links to the raw-material lots, the mixing record, the test results and the shipment.
- Change control. Customers are told before any change of polymer grade, supplier, plant or process.
- Retained samples. A sample from each lot is kept for investigation.
Why trends beat pass or fail
Limits catch a failing batch, but they do not show drift. If compression set creeps up across six lots and every one is inside the limit, an alarm is justified, because the process has moved. Plotting each test against lot date, with limits, shows this early. The batch passport on the Pascalor site does exactly this for every public lot: the current lot's results against the limits, and the history of the last several lots of the same compound.
What to ask a supplier
- Can you show me the certificate of analysis for a recent lot, including the test methods?
- Which tests are run on every lot, and which on a schedule?
- How do you trace a lot back to raw-material lots?
- What happens when a polymer or filler source changes?
- Do you hold retained samples, and for how long?
- Can I see lot-to-lot data for the last ten lots?
Regional supply
A compound mixed in more than one region must be controlled as one compound. That means one recipe, one specification and the same release tests at each site, with a reference sample compared across sites. It is possible, but it requires planning and records. Ask any supplier who offers multi-site supply how they control it.
Sources and further reading
- ISO 9001 for the structure of a quality system. ISO/IEC 17025 for laboratories. ASTM D5289 and D1646 for the main process tests.