FKM Compound Design Fundamentals
FKM fluoroelastomer compounding differs significantly from general-purpose rubbers (NR, SBR, NBR). The two primary cure systems — bisphenol and peroxide — produce different crosslink structures with distinct performance profiles.
Cure System Comparison
| Property | Bisphenol Cure | Peroxide Cure |
|---|---|---|
| Compression Set | Better (15–20%) | Moderate (25–35%) |
| Chemical Resistance | Good | Excellent |
| Steam Resistance | Poor | Better |
| Processing Safety | Good scorch safety | Requires careful control |
| Post-Cure Required | Yes (24h at 230°C) | Optional |
| Typical Curative | Bisphenol AF + BPP accelerator | Peroxide + TAIC coagent |
Typical Bisphenol-Cured Compound
| Ingredient | phr |
|---|---|
| FKM-26 bipolymer | 100 |
| MT Black (N990) | 20–30 |
| Ca(OH)₂ | 6 |
| MgO | 3 |
| Bisphenol AF | 2.0 |
| BPP (onium salt accelerator) | 0.5 |
Processing Parameters
- Mill mixing: 2-roll mill at 50–60°C, band on slow roll
- Internal mixer: 80–100°C, 3–5 min total cycle
- Press cure: 170–180°C × 10–15 min
- Post-cure: 230°C × 24h (bisphenol cure); 200°C × 4–8h (peroxide cure)
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