Co-Extruded Rubber Seals Factory | OEM Supplier
By Zhouxin Sealing Engineering Team · · 6 views
For the overseas B2B specifier requiring a dual-durometer or multi-material seal in a single extrusion, the co-extruded rubber seals factory must demonstrate control over polymer compatibility, bond-line integrity, and post-vulcanization dimensional stability. Below are the engineering constraints and test data that define our production capability at Hunan Zhouxin Sealing Technology Co., Ltd.
Material Pairing & Bond Strength
Co-extrusion demands that two elastomers—often with different Shore A hardness values—form a permanent chemical bond during vulcanization without a mechanical interlock. The bond-line shear strength must exceed 80% of the weaker base material's tensile strength.
Common Co-Extruded Combinations
| Primary Material | Secondary Material | Typical Application | Bond Shear (MPa) |
|---|---|---|---|
| EPDM 70 Shore A | EPDM 40 Shore A | Soft lip + rigid base for door seals | 6.2 |
| Silicone 60 Shore A | Silicone 80 Shore A | Dual-durometer cabinet gaskets | 5.8 |
| EPDM 80 Shore A | Thermoplastic Vulcanizate (TPV) | Structural frame + flexible flap | 7.1 |
| NBR 70 Shore A | PVC 65 Shore A | Oil-resistant core + decorative cover | 4.9 |
Bond tests per ASTM D1876 (T-peel) at 23°C, 50 mm/min crosshead speed.
Mechanical Properties by Compound
All data from our internal QC lab, verified against third-party audits for ISO 9001:2015 certification.
| Property | EPDM (70 Shore A) | Silicone (60 Shore A) | NBR (70 Shore A) | Test Method |
|---|---|---|---|---|
| Tensile Strength (MPa) | 9.5 | 7.2 | 11.8 | ASTM D412 |
| Elongation at Break (%) | 420 | 350 | 380 | ASTM D412 |
| Compression Set (22 hr @ 70°C, %) | 18 | 12 | 22 | ASTM D395 Method B |
| Tear Resistance (kN/m) | 32 | 18 | 40 | ASTM D624 |
| Density (g/cm³) | 1.25 | 1.18 | 1.30 | ISO 1183 |
In our Hunan factory experience, a 2023 project for European railway door seals required a co-extruded EPDM profile with a Shore A differential of 35 points. The initial trials delaminated at the bond line after 500 hours of thermal aging. We adjusted the peroxide cure system and increased the co-extrusion head temperature by 12°C, achieving zero delamination through 1,200 hours of ASTM D573 aging at 100°C.
Environmental & Chemical Resistance
Thermal Aging & Ozone Resistance
| Material | Aging Temp (°C) | Tensile Retention After 1000 hr (%) | Ozone Resistance (50 pphm, 40°C, 200 hr) |
|---|---|---|---|
| EPDM | 125 | 92 | No cracks |
| Silicone | 200 | 95 | No cracks |
| NBR | 100 | 78 | Cracks after 72 hr |
Ozone test per ASTM D1149.
Fluid Immersion (ISO 1817, 7 days @ 23°C)
| Fluid | EPDM Volume Swell (%) | NBR Volume Swell (%) | Silicone Volume Swell (%) |
|---|---|---|---|
| ASTM Oil No. 1 | +8 | +2 | +15 |
| ASTM Oil No. 3 | +35 | +5 | +55 |
| 10% H₂SO₄ | +1 | +3 | +0.5 |
| 10% NaOH | +1 | +2 | +0.3 |
| Deionized Water | +2 | +1 | +0.8 |
Dimensional Tolerance for Co-Extruded Profiles
Extrusion tolerance is a function of cross-section size and material shrinkage anisotropy. Our co-extruded rubber seals factory holds the following limits on a 25 mm × 10 mm profile:
| Dimension Range (mm) | Tolerance (±mm) |
|---|---|
| 0 – 5 | 0.15 |
| 5 – 15 | 0.25 |
| 15 – 30 | 0.35 |
| 30 – 50 | 0.50 |
| > 50 | 0.75 |
Measured after 24 hr relaxation at 23°C, per ISO 3302-1 class E2.
Flame Retardancy Options
For applications requiring UL 94 compliance, we offer co-extruded compounds with the following ratings:
- EPDM + Halogen-free FR additive: V-0 at 3.0 mm thickness, LOI 32%
- Silicone + Ceramic-forming FR: V-0 at 1.5 mm, zero dripping
- NBR + PVC blend: V-1 at 2.5 mm (standard), V-0 with antimony trioxide
Compression Set Performance Over Service Life
Compression set is the primary failure mode for static seals. Data from accelerated aging at 70°C (ASTM D395 Method B, 25% deflection):
| Material | 22 hr (%) | 168 hr (%) | 500 hr (%) | 1000 hr (%) |
|---|---|---|---|---|
| EPDM | 18 | 22 | 28 | 35 |
| Silicone | 12 | 15 | 18 | 22 |
| NBR | 22 | 30 | 42 | 55 |
Silicone is preferred for long-term static sealing above 120°C.
Frequently Asked Questions
What is the minimum order quantity (MOQ) for custom co-extruded profiles?
MOQ is 500 meters per profile for standard EPDM or silicone compounds. For NBR or halogen-free FR grades, MOQ increases to 1,000 meters due to compound batch minimums. Prototype runs of 50 meters are available at 3× unit cost.
What is your typical lead time from CAD approval?
Tooling fabrication requires 10–15 working days for simple profiles (under 6 cavities), 20–25 days for complex multi-cavity dies. Production lead time is 15 working days for orders up to 5,000 meters; larger orders add 5–10 days depending on cure cycle length.
What dimensional tolerance can you guarantee on co-extruded profiles?
We hold ±0.25 mm for dimensions 5–15 mm, ±0.35 mm for 15–30 mm, and ±0.50 mm for 30–50 mm per ISO 3302-1 class E2. Tighter tolerances (±0.15 mm) are achievable on critical sealing lips with additional QC sampling.
How do you pack co-extruded rubber seals for export?
Standard packing: each profile coiled on plastic cores (250–500 mm inner diameter), wrapped in VCI paper, then polypropylene woven bags, and finally plywood crates for container loading. Anti-telescoping bands are applied every 200 mm. MOQ packing: 50 kg per coil, 4 coils per crate.
Can I get samples before placing a production order?
Yes. We provide 300 mm free samples of existing co-extruded profiles (you pay shipping). For custom profiles, sample tooling costs $150–$400 depending on complexity, refundable with first production order. Samples are shipped within 5 working days of tool completion.
Material Selection Guide: Co-Extruded vs. Single Extrusion
| Requirement | Recommended Co-Extruded Pair | Single Extrusion Alternative |
|---|---|---|
| Rigid base + soft sealing lip | EPDM 80A + EPDM 40A | Not possible with single durometer |
| UV-resistant cover + oil-resistant core | EPDM 70A + NBR 70A | NBR alone fails UV |
| Flame-retardant exterior + low-temp flexibility | Silicone V-0 + Silicone 50A | Single FR silicone lacks flexibility |
| Decorative color + technical performance | EPDM 70A (black) + TPV (colored) | Painting fails after 500 hr UV |
For your specific application, send your CAD drawing to our engineering team for a 24-hour quote on co-extruded tooling and material recommendations.
Need a Custom Quote?
Send your CAD drawing or specs (material, hardness, profile, temperature range, MOQ) — our engineering team will respond within 24 hours.