1. Addition Order — Get This Wrong and the Batch Dies
The single most common platinum-cure failure we see is not the additive — it is the order it goes in.
Extrusion grade (G50A + G25B)
Compound base until smooth
Raw gum + silica, milled until the surface is smooth.
Add Part B (G25B) first
Mix to uniformity.
Then add Part A (G50A)
Mix to uniformity, then sheet out 2–3 times.
⚠ Never reverse the order. Adding Part A before Part B can cause premature cure (scorch) in the mixer. For 30–50 Shore A fumed gum, letting the compound stand 3–24 h after Part B and before Part A improves results further.
Molding grade (A3 + H350B)
Compound base until smooth
Same preparation.
Add A and B together
The two parts may be added at the same time. Mix to uniformity.
Sheet out three times
Three passes through the mill before molding.
Pro tip — schedule freely. Molding-grade compound keeps for 10+ days at room temperature after A/B incorporation. No refrigeration needed. Extrusion-grade compound must be processed within 4 hours.
2. Catalyst Poisoning — The Five Rules
Platinum is deactivated by sulfur, amines, phosphorus and tin compounds. A poisoned catalyst means under-cured parts — the entire batch. These rules are absolute:
Rule 1 — Isolate your equipmentDo not run platinum compounds on equipment, lines or tools that were just used for peroxide-cure (or sulfur-vulcanized rubber) without thorough cleaning. Residues poison the catalyst.
Rule 2 — Separate storageCompound containing A/B parts must never be stored together with peroxides, raw rubber, or sulfur-, amine- or tin-containing materials.
Rule 3 — Mind the mixer temperatureDo not add the agent while the mixer (including rolls) is above 45 °C. Cool down first — hot addition can kill the catalyst.
Rule 4 — One system per workshop zoneAvoid producing peroxide-cure rubber products simultaneously in the same workshop area as platinum products — cross-contamination travels through the air and tools.
Rule 5 — Adjust for dark colorsBlack and deep-color pigments inhibit the cure — increase the platinum (Part A) dosage accordingly. Contact us for a starting point.
Why we publish these rulesMost suppliers print half of this on a label and leave the rest for you to discover in production. Every rule above was learned from real batch losses — and every one is preventable.
3. Troubleshooting Table
Symptom → likely cause → fix. If your symptom is not here, send it to us — we will diagnose it with you.
| Symptom | Likely causes | Corrective action |
|---|---|---|
| Under-cure (sticky parts) | Catalyst poisoning · A/B dosage too low · temperature too low · pot life exceeded | Check equipment contamination · recalculate dosage for hardness · verify oven temperature · process within pot life |
| Scorch / premature cure | Over-standing beyond pot life (extrusion grade) · mixer too hot · addition order reversed | Shorten standing time · cool the mixer · strictly observe “B first, then A” |
| Whitening / blooming | Under-cure · incompatible or mixed internal release agents · anti-blooming dosage low | Raise cure level · never mix internal release agents · increase FD-A6 dosage |
| Yellowing | Cure temperature too high · insufficient anti-yellowing performance | Reduce temperature · use high anti-yellowing grade |
| Mold sticking | Release agent dilution wrong or spray uneven | Dilute W-8630 at 20:1 · spray uniformly · increase concentration for difficult molds |
| Roller sticking (milling) | Internal release agent missing or under-dosed | Add / increase FD-68 |
| Sticking to steel belt (extrusion) | Formulation not suited for steel-belt lines | Use extrusion-grade G50A / G25B system |
| Poor clarity | Wrong cure system for the application | Switch to high-clarity platinum grade · confirm no peroxide contamination |
4. Frequently Asked Questions
No. Addition cure leaves no volatile by-products, so the secondary bake used to remove peroxide residues is not needed with our platinum systems.
Molding grade: 10+ days at room temperature, no refrigeration. Extrusion grade: 4 hours — plan your extrusion runs accordingly.
Yes — both fumed and precipitated HTV silicone gum, provided the compound does not contain decomposed low-molecular gum.
Usually insufficient mixing after adding Parts A and B. Sheet the compound out 2–3 times before feeding the extruder.
This is blooming. Add FD-A6 anti-blooming agent at 0.3–0.5% during compounding, and do not mix internal release agents. If it persists, the cure level may be insufficient — verify temperature and dosage.
Our additives are manufactured to meet EU REACH / RoHS / PAHs requirements, with food-contact applications in scope. Compliance documentation is available on request — we will always tell you plainly which reports exist today and which are in progress, and for food-contact markets we support testing routes such as FDA 21 CFR 177.2600 and LFGB.
Sealed, cool and dark, strictly separated from peroxides and raw rubber. Molding grade platinum agent: 2 years below 28 °C. Internal release agent: 12 months. External release agent: 18 months.
Significantly faster than peroxide systems, with lower energy consumption — and unlike peroxide, no post-cure oven stage at all. For the exact differential in your process, run our free sample side by side with your current recipe.
Problem Not on the Table?
Describe the symptom, your compound and your process. Our engineers will work the diagnosis with you — usually within 24 hours.
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