In this guide 6 sections
Silicone, EPDM and nitrile differ in cure temperature, post cure need, shelf life and the approvals customers hold. Keep one compound master that carries each rule, and have every job pull its material from it, so the wrong rubber cannot be loaded against a drawing.
Why the three compounds behave differently on the shop floor
Nitrile resists oils and fuels. EPDM resists water, steam and weather but swells in mineral oil. Silicone handles wide temperature swings and food or medical use but tears more easily. A seal in the wrong one fails fast.
They also look alike. Black nitrile and black EPDM sit on the same rack. Without clear codes, a loader trusts the label on the bag, and one mislabelled batch becomes a lot of scrap or a field failure.
Ask your technical sales team which two compounds get confused most often. The answer is usually obvious within a minute, and it tells you where to start the codes.
Cure and post cure rules differ
Each compound has its own cure time and temperature. Silicone parts often need post cure in an oven to drive off volatiles and reach final properties. EPDM and nitrile are frequently peroxide or sulphur cured, with different post cure habits.
Record these on the compound, not on the job card by hand. When the oven step is a field on the master, the router can add it automatically and nobody skips it.
Oven loading also matters. Parts stacked tightly in the post cure oven cure unevenly, so record trays and load size. A missed oven step is invisible until the seal takes a compression set test.
- Cure temperature and time per compound
- Post cure oven step, if required
- Cooling or deflashing step after cure
- Cure system, such as peroxide or sulphur
Storage life and handling are not the same
Uncured compound ages. Storage life depends on the type, and scorch risk rises with warm stores. Record the mix date, the expiry or retest date and the storage condition on every batch.
Use oldest first. If a planner can see that a nitrile batch is near expiry, the job can run while it is still within limits. Silicone gum and fillers carry their own rules, so keep colour and hardness on the same record.
Customer approvals attach to a compound, not a part
Many buyers approve a specific compound grade for a part. Food contact, potable water, fuel or medical approvals each name the formulation and sometimes the supplier of the base polymer. Change the base and the approval no longer applies.
Hold the approval name, number and expiry against the compound master. Then a quote or job for that customer can warn when the chosen compound is not approved for the end use.
- Approval type and certificate number
- Customer and part numbers covered
- Compound grade and hardness
- Expiry or review date
One compound master stops wrong material reaching a job
The fix is plain. Create one record per compound with code, polymer, hardness, colour, cure rules, post cure, shelf life and approvals. Every part and job points to it, and nobody types material by hand.
Start with the compounds behind your five most complained-about parts. Write those records first and check them against the drawings.
Nothing here is complicated. The discipline lies in keeping a single source for the rules and refusing to let anyone retype them onto a job card.
Compound master sheet
Printed on one page, with a single row for every compound. Columns hold compound code, polymer type, hardness, colour, cure temperature and time, post cure step, shelf life, storage condition, approvals and the parts that use it. A final column marks drawings checked and the date.
Open a blank worksheet to printQuestions owners ask
Which of the three needs post cure most often?
Silicone commonly does, especially for food or medical parts. Check the compound datasheet, since EPDM and nitrile post cure depends on the cure system.
How do we stop a loader picking the wrong rubber?
Use colour-coded bins, scan or enter the batch code against the job, and let the system reject a compound not listed for that part.
Does a hardness change need a new approval?
Often yes, because approvals usually name the exact grade. Ask the customer before substituting even a close match.
Where should the compound rules live?
In one shared master, not in job cards. That way a change to cure time or an approval updates every future job at once.